Abstract:
A porous tantalum used for medical implantation is provided, which includes a foam structure with three-dimensional interconnecting pores and produced by: mixing a solution made by organic binder and dispersant and tantalum powder to form tantalum slurry, casting the tantalum slurry into a organic foam body through impregnation until the pores of the organic foam body are filled, drying the impregnated organic foam body with the tantalum slurry to remove the dispersant, degreasing the dried organic foam body to separate the organic binder and the organic foam body from the dried tantalum slurry in a protective environment of inert gas, vacuum sintering the dried tantalum slurry to obtain a porous sintered body, and vacuum annealing then treating the porous sintered body with normal post-treatments to obtain the porous tantalum. Accordingly, the porous tantalum has well-distributed interconnecting pores and sintering neck structures resulting in good mechanical properties, and especially good ductility.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a porous metal material used for medical implantation, especially to a porous tantalum used for medical implantation and a method for preparing the same. 
         [0003]    2. Description of the Related Art 
         [0004]    A porous metal material used for medical implantation is important for specific application of treating traumatic osseous tissues, necrotic femoral tissues or the like. Such metal materials are normally porous stainless steel, porous titanium, and so on. As a porous implant material for the treatment of traumatic osseous tissues and necrotic femoral tissues, the porosity thereof should reach to 30-80%, and the pores should be all interconnected and well-distributed or partially interconnected depending on requirement. Thus, the porous implant material can make the growth phase of the osseous tissue uniform and have lower weight to fit the use of medical implantation. 
         [0005]    Due to good biocompatibility and mechanical properties of the insoluble tantalum, the porous form thereof is potential in place of the traditional metal biomaterials mentioned above in order to be used as a medical implant material for the application of treating necrotic femoral tissues. Also, due to the harmlessness, non-toxicity, few of side effects, the rapid development of the medicine, and the further knowledge of tantalum as an implant material, the requirement of porous tantalum for medical implantation is getting more urgent than before, and the criterion of the quality of porous tantalum is getting much higher. As a porous tantalum for medical implantation, having a lot of well-distributed interconnecting pores and mechanical properties adaptable to human body are of great importance for being a connecting component to keep the newborn tissues growing well at the positions of traumatic osseous tissues or ossature defects. 
         [0006]    The porous metal materials for medical implantation are manufactured mainly by powder sintering, like the preparation of general porous metal materials, especially by impregnating an organic foam body with metal powder and then sintering to obtain a porous metal having a foam structure with well-distributed interconnecting pores (also called “foam impregnation”). However, the porous metal materials with well-distributed interconnecting pores usually do not have sufficient mechanical properties because of the problems of the structural itself, as well as the collapse of the metal powder during sintering process. For now, such problems have not been solved according to any know research reports. 
         [0007]    There are not many research subjects about the powder sintering process for making porous tantalum, especially few of papers has mentioned about the preparation of porous tantalum for medical implantation. CN Patent Publication No. 200510032174 discloses “Three-dimensional through-hole or part-hole interconnecting porous metal foam and its preparing method”, and CN Patent Publication No. 200710152394 discloses “Porous foam tungsten and preparation method thereof”. Nevertheless, the porous metal is prepared for the applications of filtering materials, or for aerospace and other applications in high temperature environments. Furthermore, the porous metal processed in such application is not porous tantalum. 
         [0008]    Regarding porous tantalum, U.S. Pat. No. 5,282,861 discloses “Open cell tantalum structures for cancellous bone implants and cell and tissue receptors”. The porous tantalum is manufactured by commercial tantalum and a supporter such as a carbon skeleton obtained from heat degradation of polyurethane precursors. The carbon skeleton has multiple dodecahedrons with mesh structures inside and wholly distributed pores, and the porosity thereof reaches to 98%. Next, the commercial tantalum is bound to the carbon skeleton to form porous metal microstructure through chemical vapor deposition (CVD) (also called “chemical deposition”). The porous tantalum material obtained by such processes has a tantalum layer having 40-60 μm of thickness, and has about 99 wt % of tantalum and about 1 wt % based on the weight of whole porous tantalum materials. The patent further discloses that the porous tantalum has 50-70 MPa of compressive strength, 2.5-3.5 GPa of elastic modulus, 63 MPa of tensile strength and 15% of the amount of plastic deformation. However, the ductility of the porous tantalum described above is obviously insufficient causing subsequent processing of the porous tantalum, such as cutting the formed material. Similarly, the porous tantalum prepared by such methods mentioned above like foam impregnation has the same problems. Due to the limitation of the manufacturing methods, the obtained products usually are not pure enough and have remaining residues of the carbon skeleton such that the biosafety is much decreased.” 
       SUMMARY OF THE INVENTION 
       [0009]    The primary objective of the present invention is to provide a porous tantalum used for medical implantation with good biocompatibility and biosafety. 
         [0010]    The secondary objective of the present invention is to provide a method for preparing the porous tantalum used for medical implantation. The porous tantalum made by such method has good biocompatibility and biosafety, and more importantly has good mechanical properties. 
         [0011]    To achieve the primary objective, a porous tantalum used for medical implantation in accordance with the present invention is produced by foam impregnation and having a foam structure with three-dimensional interconnecting pores, wherein the foam structure has a foam skeleton and sintered tantalum particles located on the foam skeleton, and multiple sintering neck structures formed between the tantalum particles. 
         [0012]    The porous tantalum used for medical implantation having such structural characteristics can completely meet the requirement of biocompatibility and biosafety, especially the foam skeleton is accumulated by sintered tantalum powder, and the sintered neck structure formed between the tantalum particles greatly improves the mechanical properties of such material like ductility and anti-bending strength. Additionally, the porous tantalum has lower than 0.5% of impurities through testing. The porous tantalum has well-distributed interconnecting pores, and has 2.0-11 g/cm 3  of density, 40-80% of porosity, 150-500 μm of pore diameter, 2.0-4.6GPa of elastic modulus, 35-120 MPa of yield strength, 40-170 MPa of compressive strength, 150-300 MPa of hardness, 9.4%-17.3% of the amount of plastic deformation, 65-72 MPa of tensile strength 9.3-14.7% of percentage elongation. Accordingly, the mechanical properties of the porous tantalum, like the elastic modulus and the yield strength are also improved. According to the test of anti-bending, the fracture rate of the sintered neck structure formed between tantalum particles is less than 45%, the fracture rate of the interior of tantalum particles is larger than 55%, indicated that the structural reliability of the porous tantalum of the invention is good. 
         [0013]    The foam structure substantially has three-dimensional interconnecting pores, in other words, a limited amount of three-dimensional disconnecting pores are allowed to exist therein, for example, about 1% of the three-dimensional disconnecting pores are allowed to exist therein and can be ignored. 
         [0014]    As used herein, the term of “sintered neck structure” means that the structure formed by the powder heated and then binding together under high temperature, also usually called “sintering phenomenon”. 
         [0015]    As used herein, the term “sintering” means that the process of metallurgical binding of powder or particles under high temperature, usually performed at the melting point of the major ingredient through atomic mobilization. 
         [0016]    Through microscopic observation, it is found that the sintering neck structure (or named “attachable neck”) is growing during sintering, and causing changes of its properties. With the increasing sintering temperature, longer sintering time or appropriate control of the temperature and time during sintering, the sintering neck structure can grow gradually, the proportion of the sintering neck structure and the strength of the sintered body are both increase as well. That is, the sintering neck structure formed by partial tantalum particles also can achieve the objective of the present invention. 
         [0017]    In one aspect, the porous tantalum of the present invention is produced by sintering the tantalum powder having less than 43 μm of average diameter and less than 0.1% of oxygen content therein, wherein it has 40-80% of porosity and 150-500 μm of pore diameter, and the sintering neck structures formed between at least 50% of the tantalum particles. Preferably, the sintering neck structures are formed between at least 80% of the tantalum particles. In one aspect, besides the appropriate tantalum powder, the foam impregnation is using polyurethane foam having 0.48-0.89 mm (preferably 0.56-0.72 mm) of pore diameter, 0.015-0.035 g/cm 3  (preferably 0.025 g/cm 3 ) of density and larger than 50° (preferably 50°-80°) of hardness as an organic foam body. Accordingly, using such materials described above is beneficial to the formation and processing of the structure of the porous tantalum of the present invention, and also makes the process efficient and maintains sufficient mechanic properties 
         [0018]    To achieve the secondary objective, a method for preparing the porous tantalum used for medical implantation in accordance with the present invention comprises steps of: 
         [0019]    (a) providing an organic binder, dispersant and tantalum powder; 
         [0020]    (b) mixing the organic binder and the dispersant to form a solution and then mixing the solution and the tantalum powder to form tantalum slurry; 
         [0021]    (c) providing an organic foam body, wherein the organic foam body has multiple pores; 
         [0022]    (d) casting the tantalum slurry into the organic foam body and impregnating the casted organic foam body with the tantalum slurry until the pores of the organic foam body are filled with the tantalum slurry; 
         [0023]    (e) drying the impregnated organic foam body with the tantalum slurry to remove the dispersant; 
         [0024]    (f) degreasing the dried organic foam body to separating the dried tantalum slurry from the organic binder and the organic foam body in a protective environment of inert gas; 
         [0025]    (g) vacuum sintering the dried tantalum slurry to obtain a porous sintered body, wherein the porous sintered body has a foam skeleton, sintered tantalum particles located on the foam skeleton, and multiple sintering neck structures formed between the tantalum particles; and 
         [0026]    (h) vacuum annealing and treating the porous sintered body with normal post-treatments to obtain the porous tantalum. 
         [0027]    The method for preparing the porous tantalum of present invention is practicable, overcomes the technical bias about sintering process of porous metal powder (metallurgy sintering), and maintains the mechanical properties of the porous tantalum with such sintered neck structure, as well as the improved ductility thereof. Also, the porous tantalum prepared by such method can be conveniently and effectively used for the application of surgery implantation of medical metal material, especially as a component for connecting the tissue at positions of traumatic osseous tissues or ossature defects. Furthermore, the organic binder, dispersant and the organic foam body are resolvable such that the porous tantalum has great biocompatibility and biosafety when being used for medical implantation. 
         [0028]    The organic binder can be, but not limited to, polyvinyl alcohol (PVA), starch, ethyl cellulose, or other alternative substances, and preferably is polyvinyl alcohol. The dispersant can be, but not limited to, water, ethanol or the like, and preferably is water. The organic foam body can be, but not limited to, polyurethane foam body, polyether ester foam body, or other alternative substances. 
         [0029]    In one aspect, the tantalum powder has the tantalum powder has less than 43 μm of average diameter and than 0.1% of oxygen content, the organic binder is polyvinyl alcohol, the dispersant is water, the organic foam body is a polyurethane foam body, and the impregnated organic foam body with the tantalum slurry is dried by vacuum drying to remove water, and the obtained porous tantalum has 40-80% of porosity and 150-500 μm of pore diameter and the sintering neck structures formed between at least 50% of the tantalum particles. 
         [0030]    In one aspect, the solution is a 2-8 wt % (preferably 4-5 wt %) polyvinyl alcohol solution made by dissolving polyvinyl alcohol in distilled water under heat. In one aspect, 6-9 weight parts (preferably 7 weight parts) of tantalum powder and 1 weight part of the 2-8 wt % polyvinyl alcohol solution are mixed homogeneously and agitated to form a pasty substance (i.e. tantalum slurry), the pasty substance is casted into the polyurethane foam body having 0.48-0.89 mm (preferably 0.56-0.72 mm) of pore diameter, 0.015-0.035 g/cm 3  (preferably 0.025 g/cm 3 ) of density and larger than 50° (preferably 50°-80°) of hardness. 
         [0031]    It is beneficial to lowering the impurities and keeping good mechanical properties of the porous tantalum of the present invention by using the tantalum powder having less than 43 μm of average diameter and less than 0.1% of oxygen content. Also, it is beneficial to keeping required porosity and pore diameter of the porous tantalum of the present invention by using the polyurethane foam body having 0.48-0.89 mm of pore diameter, 0.015-0.035 g/cm 3  of density and larger than 50° of hardness. The technical features of the present invention optimize the conditions during processing, make the obtained porous tantalum have biocompatibility and biosafety, and benefit the formation of the sintered neck structures. 
         [0032]    In one aspect, the impregnated organic foam body with tantalum slurry is dried by vacuum drying under 10 −2 -1 Pa of vacuity, and the dried organic foam body with tantalum slurry is degreased at 400-800° C. in a protective environment (such as under 10 −4 -10 −3  Pa of vacuity) and the dried organic foam body and the organic binder are separated from the dried tantalum slurry, and the dried tantalum slurry is sintered by vacuum sintering at 2000-2200° C. under 10 −4 -10 −3  Pa of vacuity and keeping the temperature for 1-5 hours to obtain the porous sintered body. Alternatively, the protective environment can be supplied by employing inert gas in place of the vacuum environment. Then, the porous sintered body is annealed by vacuum annealing through keeping the temperature at 1000-1250° C. for 1-4 hours under less than 10 −4 -10 −3  Pa of vacuity. 
         [0033]    In one aspect, the dried organic foam body with tantalum slurry is degreased to separate the dried organic foam body and the organic binder from the dried tantalum slurry by increasing the temperature to 400-800° C. at a rate of 0.5-5° C./min in a protective environment of argon and keeping the temperature for 30-120 min of time, and then the dried tantalum slurry is sintered to form a porous sintered body under less than 10 −3  Pa of vacuity by increasing the temperature from room temperature to 1200-1500° C. at a rate of 10-20° C./min and keeping the temperature for 1-2 hours, and then increasing the temperature to 2000-2200° C. at a rate of less than 20° C./min and keeping the temperature for at least 2-4 hours; after sintered, the porous sintered body is cooled down by decreasing the temperature to 800° C. at a rate of 10-25° C./min by stages of which is for 30-90 minutes per stage, and then natural cooling; the porous sintered body is annealed under less than 10 −4  Pa of vacuity by increasing the temperature to 1000-1250° C. at a rate of less than 30° C./min and keeping the temperature for 4-6 hours, then decreasing the temperature slowly then rapidly to room temperature at a rate of 5-30° C./min by stages of which is less than 1.5-3 hours per stages. 
         [0034]    Furthermore, in another aspect, the impregnated organic foam body with tantalum slurry is dried by vacuum drying at 60-100° C. for 4-8 hours. The dried organic foam body with tantalum slurry is degreased by increasing the temperature to 600-800° C. by stages in a protective environment of argon (purity: 99.9999%), The temperature during degreasing is increased from room temperature to 400° C. at a rate of 1-5° C./min and kept for 30-60 minutes, and then increased from 400° C. to 600-800° C. at a rate of 0.5-1.5° C./min and kept for 60-120 minutes. The dried tantalum slurry is sintered to form a porous sintered body by vacuum sintering. The temperature during vacuum sintering is increased to 1200-1250° C. at a rate of 10-15° C./min and kept for 30-60 minutes under 10 −4 -10 −3  Pa of vacuity, and increased to 1500° C. at a rate of 10-20° C./min and kept for 30-60 minutes under 10 −4 -10 −3  Pa of vacuity, and then increased to 2000-2200° C. at a rate of 6-20° C./min and kept for 120-240 minutes under 10 −4 -10 −3  Pa of vacuity. After sintered, under 10 −4 -10 −3  Pa of vacuity, the temperature is decreased to 1500-1600° C. at a rate of 10-20° C./min and kept for 30-60 minute, and then decreased to 1200-1250° C. at a rate of 12-20° C./min and kept for 60-90 minute, and decreased to 800° C. at a rate of 10-20° C./min. Then, the porous sintered body is cooled naturally. After cooled, the porous sintered body was annealed by vacuum annealing. The temperature during vacuum annealing is increased to 1000-1250° C. at a rate of 15-30° C./min and kept for 240-480 minute under 10 −4 -z 10   −3  Pa of vacuity, and then decreased to 1000° C. at a rate of 5-10° C./min and kept for 90-180 minute under 10 4 -10 −3  Pa of vacuity, and decreased to 800° C. at a rate of 10-20° C./min and kept for 60-120 minute under lower than 10 −4  Pa of vacuity, and decreased to room temperature at a rate of 20-30° C./min under 10 −4 -10 −3  Pa of vacuity. 
         [0035]    As such, the treatments, like vacuum drying and degreasing, are beneficial to lowering the impurities and improving biocompatibility, biosafety and mechanical properties of the porous tantalum of the present invention. The optimization of the organic foam body overcomes the difficulty of collapse of the foam skeleton during sintering. The optimization of the conditions of the sintering and annealing processes is favorable to making more the sintered neck structures formed between the tantalum particles located on the foam skeleton accumulated by sintered tantalum powder, and further bettering the mechanical properties of the porous tantalum such as ductility, and lowering the fracture rate of the sintered neck structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a powder x-ray diffraction (XRD) pattern of a porous tantalum used for medical implantation in accordance with the present invention. 
           [0037]      FIG. 2  is a scanning electron microscopic (SEM) macrograph of a porous tantalum used for medical implantation in accordance with the present invention. 
           [0038]      FIG. 3  is a scanning electron microscopic (SEM) micrograph of a porous tantalum used for medical implantation in accordance with the present invention. 
       
    
    
       [0039]    It has been illustrated that: 
         [0040]    1. The porous tantalum of the present invention has high porosity and the pores are well-distributed and interconnecting. Such three-dimensional interconnecting pores are advantageous to adhesion, differentiation and growth of osteocytes as well as ingrowths of bones, and also strengthen the connections between implants and bones to perform the biocompatibility well. 
         [0041]    2. The porous tantalum of the present invention has excellent mechanical properties and microstructures with uniform particles and obvious sintered neck structures. The porous tantalum with such characteristics maintains good mechanical properties and ductility. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0042]    The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of examples. 
         [0043]    The present invention provides a porous tantalum used for medical implantation which is produced by foam impregnation. As shown in figures, the porous tantalum has a foam structure with three-dimensional interconnecting pores. The foam structure has a foam skeleton, and tantalum particles located on the foam skeleton, and multiple sintering neck structures formed between the tantalum particles. 
         [0044]    In one preferred embodiment, the present invention provides a porous tantalum used for medical implantation which is produced by sintering the tantalum powder having less than 43 μm of average diameter and less than 0.1% of oxygen content, wherein it has 40-80% of porosity and 150-500 μm of pore diameter, and the sintering neck structures formed between at least 50% of the tantalum particles. 
         [0045]    In one preferred embodiment, the porous tantalum is produced by dissolving polyvinyl alcohol in distilled water under heat to form a polyvinyl alcohol solution with proper weight percentages of polyvinyl alcohol, mixing 1 weight part of the polyvinyl alcohol solution and adequate weight parts of tantalum powder to form tantalum slurry. The tantalum slurry is casted under pressure into a polyurethane foam body having multiple pores with adequate pore diameter, density and hardness, and then impregnated the casted polyurethane foam body with the tantalum slurry repeatedly until the pores of the polyurethane foam are filled with the tantalum slurry. The impregnated organic foam body with the tantalum slurry is dried at adequate temperature for an adequate time under adequate vacuity to remove water. The dried organic foam body is put into a tungsten device in an atmosphere furnace with increasing to adequate temperature. The dried organic foam body is degreased under constant temperature to separate the organic binder and the organic foam body from the dried tantalum slurry in a protective environment of inert gas and a degreased sample is formed (preferably of argon having at least 99.999% of purity). The inert gas is employed before increasing temperature to exclude the air in the atmosphere furnace before increasing the temperature. Then, the degreased sample is cooled naturally. The degreased sample in the tungsten device is heated in a sintering furnace and sintered under proper vacuity to form a sintered sample by increasing the temperature to 2000-2200° C. by stages and keeping the temperature for 1-5 hours. The vacuity reaches to an adequate level before increasing the temperature in the sintering furnace. Then, the sintered sample is cooled naturally. The sintered sample is cooled down under constant vacuity, or by stages at a suitable rate of decreasing the temperature to keep the temperatures for proper periods of time. The inert gas can be employed as protective atmosphere during keeping the temperature. After cooled, the sintered sample is put in a corundum container in an annealing furnace with proper vacuity. The sintered sample is annealed by increasing the temperature by stages and keeping the temperatures for proper periods of time. The vacuity reaches to an adequate level before increasing the temperature in the annealing furnace. Then, the annealed sample is cooled naturally. The annealed sample is cooled down under constant vacuity, or by stages at a suitable rate of decreasing the temperature to keep the temperatures for proper periods of time. The inert gas can be employed as protective atmosphere during keeping the temperatures. The annealed sample is treated with normal post-treatments to obtain a porous tantalum. 
         [0046]    The dried polyurethane foam body is put into a tungsten device in an atmosphere furnace and degreased by increasing to adequate temperature at a proper rate. The inert gas is employed before increasing temperature to exclude the air in the atmosphere furnace before increasing the temperature. The process of controlling temperature is increasing the temperature from room temperature to adequate temperature, keeping the temperature for a proper period of time, increasing the temperature again, and keeping the temperature for a proper period of time again. The degreased sample in the tungsten device is heated in a sintering furnace and sintered by increasing to the highest sintering temperature of tantalum at a proper rate in the sintering furnace under proper vacuity. The vacuity reaches to an adequate level before increasing the temperature in the sintering furnace. The temperature in the sintered furnace is increased to adequate temperature (such as 1200-1250° C.) at a proper rate and kept for a proper period of time under constant vacuity, and then increased to adequate temperature (such as 1250-1500° C.) at a proper rate and kept for a proper period of time under constant vacuity, and then increased to the highest sintering temperature of tantalum at a proper rate and kept for a proper period of time under constant vacuity. After sintered, the temperature is decreased to adequate temperature (such as 1500-1600° C.) at a proper rate and kept for a proper period of time under constant vacuity, and then decreased to 800° C. at a proper rate. Then, the sintered sample is cooled naturally. After cooled, the sintered sample is put into a corundum container in a annealing furnace under proper vacuity and annealed by increasing to adequate temperature (such as 1000-1250° C.) at a proper rate. The vacuity reaches to an adequate level before increasing the temperature in the annealing furnace. The temperature in the sintered furnace is increased from room temperature to adequate temperature (such as 1000-1250° C.) at a proper rate and kept for a proper period of time under constant vacuity, and then decreased to 1000° C. at a proper rate and kept for a proper period of time, and then decreased to 800° C. at a proper rate and kept for a proper period of time, and then decreased to room temperature. The annealed sample is treated with normal post-treatments to obtain a porous tantalum. 
         [0047]    The sintering process used in the present invention is mainly the foam impregnation. It is analyzed and verified on a basis of lots of theories and experiments that the porous tantalum obtained by the sintering process has a foam structure with three-dimensional interconnecting pores (as shown in figures). The foam structure has a foam skeleton accumulated by the tantalum powder, and tantalum particles located in the foam skeleton, and sintered neck structures formed between the tantalum particles. 
       Example 1 
       [0048]    12.5 g of polyvinyl alcohol was put in a container filled in 240 ml of water, and then the container was put on a hotplate. The polyvinyl alcohol and water are heated and agitated to form a polyvinyl alcohol solution. 60 g of tantalum powder with less than 43 μm of diameter and less than 0.1% of oxygen content was scaled by a 200 g balance an added to 50 ml of the polyvinyl alcohol solution (the polyvinyl alcohol solution was cooled). The tantalum powder and the polyvinyl alcohol solution were mix and agitated homogeneously to form tantalum slurry. The tantalum slurry was casted into a 10×10×30 mm porous polyurethane foam body (0.48 mm of pore diameter, 0.025 g/cm 3  of density and 50° of hardness) until the pores of the polyurethane foam body were filled with the tantalum slurry. Then, the polyurethane foam body filled with the tantalum slurry was put into a porcelain dish placed in a vacuum drier. The polyurethane foam body filled with the tantalum slurry was dried in the vacuum drier at 60° C. for 8 hours under 1 Pa of vacuity. The dried polyurethane foam body filled with the tantalum slurry was degreased at 600° C. for 120 minutes under lower than 10 −4  Pa of vacuity. The dried polyurethane foam and the dried tantalum slurry were separated after the process of degreasing. Then, the dried tantalum slurry are sintered in a vacuum sintering furnace at 2000° C. for 2 hours under 10 −4  Pa of vacuity to form a porous sintered body. The argon is employed as a protective gas during sintering. The porous sintered body was cleaned out of the dust and dirt and then treated with normal post-treatments to obtain a porous tantalum. 
         [0049]    With reference to the figures, it is shown that the porous tantalum made in Example 1 has a foam structure with three-dimensional interconnecting pores. The foam structure has a foam skeleton accumulated by the tantalum powder, and tantalum particles located in the foam skeleton, and multiple sintered neck structures formed between more than 50% of the tantalum particles. 
         [0050]    The density, porosity, pore diameter and other mechanical properties of the obtained porous tantalum were tested by standard test methods such as GB/T5163-2006, GB/T5249-1985, GB/T6886-2001 and the like. The porous tantalum has three-dimensional interconnecting pores and less than 0.5% of impurities. The interconnecting pores are well-distributed. The tested porous tantalum has 3.5 g/cm 3  of density, higher than 40% of porosity, 100μm of average pore diameter, 2.0 GPa of elastic modulus, 35 MPa of yield strength, 40 MPa of compressive strength, 150 MPa of hardness, 17.3% of the amount of plastic deformation, 65 MPa of tensile strength and 14.7% of percentage elongation. According to the anti-bending test on a basis of metal bending strength, the microstructure of the porous tantalum has less than 45% of fracture rate of the sintered neck structure, and larger than 55% of fracture rate of the interior of the tantalum particles. 
       Example 2 
       [0051]    10 g of polyvinyl alcohol was put in a container filled in 200 ml of water, and then the container was put on a hotplate. The polyvinyl alcohol and water are heated and agitated to form a polyvinyl alcohol solution. 40 g of tantalum powder with less than 43 μm of diameter and less than 0.1% of oxygen content was scaled by a 200 g balance an added to 32 ml of the polyvinyl alcohol solution (the polyvinyl alcohol solution was cooled). The tantalum powder and the polyvinyl alcohol solution were mix and agitated homogeneously to form tantalum slurry. The tantalum slurry was casted into a 10×10×25 mm porous polyurethane foam body (0.56 mm of pore diameter, 0.030 g/cm 3  of density and 60° of hardness) until the pores of the polyurethane foam body were filled with the tantalum slurry. Then, the polyurethane foam body filled with the tantalum slurry was put into a porcelain dish placed in a vacuum drier. The polyurethane foam body filled with the tantalum slurry was dried in the vacuum drier at 100° C. for 4 hours under 10 −2  Pa of vacuity. The dried polyurethane foam body filled with the tantalum slurry was degreased at 800° C. for 120 minutes under 10 −4  Pa of vacuity. The dried polyurethane foam body and the dried tantalum slurry were separated after the process of degreasing. Then, the dried tantalum slurry are sintered in a vacuum sintering furnace at 2100° C. for 4 hours under 10 −4  Pa of vacuity and formed in a porous sintered body. The argon is employed as a protective gas during sintering. The porous sintered body was cleaned out of the dust and dirt and then treated with normal post-treatments to obtain a porous tantalum. 
         [0052]    With reference to the figures, it is shown that the porous tantalum made in Example 2 has a foam structure with three-dimensional interconnecting pores. The foam structure has a foam skeleton accumulated by the tantalum powder, and tantalum particles located in the foam skeleton, and multiple sintered neck structures formed between more than 50% of the tantalum particles. 
         [0053]    The density, porosity, pore diameter and other mechanical properties of the obtained porous tantalum were tested by standard test methods such as GB/T5163-2006, GB/T5249-1985, GB/T6886-2001 and the like. The porous tantalum has three-dimensional interconnecting pores and less than 0.5% of impurities. The interconnecting pores are well-distributed. The tested porous tantalum has 5 g/cm 3  of density, higher than 70% of porosity, 200 μm of average pore diameter, 3.0 GPa of elastic modulus, 70 MPa of yield strength, 80 MPa of compressive strength, 200 MPa of hardness, 17% of the amount of plastic deformation, 70 MPa of tensile strength and 14% of percentage elongation. According to the anti-bending test on a basis of metal bending strength, the microstructure of the porous tantalum has less than 40% of fracture rate of the sintered neck structure, and larger than 60% of fracture rate of the interior of the tantalum particles. 
       Example 3 
       [0054]    11 g of polyvinyl alcohol was put in a container filled in 220 ml of water, and then the container was put on the hotplate. The polyvinyl alcohol and water are heated and agitated to form a polyvinyl alcohol solution. 45 g of tantalum powder with less than 43 μm of diameter and less than 0.1% of oxygen content was scaled by a 200 g balance an added to 36 ml of the polyvinyl alcohol solution (the polyvinyl alcohol solution was cooled). The tantalum powder and the polyvinyl alcohol solution were mix and agitated homogeneously to form tantalum slurry. The tantalum slurry was casted into a 8×8×25 mm porous polyurethane foam body (0.70 mm of pore diameter, 0.035 g/cm 3  of density and 70° of hardness) until the pores of the polyurethane foam body were filled with the tantalum slurry. Then, the polyurethane foam body filled with the tantalum slurry was put into a porcelain dish placed in a vacuum drier. The polyurethane foam body filled with the tantalum slurry was dried in the vacuum drier at 80° C. for 6 hours under 10 −1  Pa of vacuity. The dried polyurethane foam filled with the tantalum slurry was degreased at 700° C. for 90 minutes under 10 −3  Pa of vacuity. The dried polyurethane foam body and the dried tantalum slurry were separated after the process of degreasing. Then, the dried tantalum slurry are sintered in a vacuum sintering furnace at 2200° C. for 2.5 hours under 10 −3  Pa of vacuity and formed in a porous sintered body. The argon is employed as a protective gas during sintering. The porous sintered body was cleaned out of the dust and dirt and then treated with normal post-treatments to obtain a porous tantalum. 
         [0055]    With reference to the figures, it is shown that the porous tantalum made in Example 3 has a foam structure with three-dimensional interconnecting pores. The foam structure has a foam skeleton accumulated by the tantalum powder, and tantalum particles located in the foam skeleton, and multiple sintered neck structures formed between more than 50% of the tantalum particles. 
         [0056]    The density, porosity, pore diameter and other mechanical properties of the obtained porous tantalum were tested by standard test methods such as GB/T5163-2006, GB/T5249-1985, GB/T6886-2001 and the like. The porous tantalum has three-dimensional interconnecting pores and less than 0.5% of impurities. The interconnecting pores are well-distributed. The tested porous tantalum has 8 g/cm 3  of density, higher than 60% of porosity, 300 μm of average pore diameter, 4.0 GPa of elastic modulus, 90 MPa of yield strength, 100 MPa of compressive strength, 250 MPa of hardness, 17.2% of the amount of plastic deformation, 71 MPa of tensile strength and 14.5% of percentage elongation. According to the anti-bending test on a basis of metal bending strength, the microstructure of the porous tantalum has less than 35% of fracture rate of the sintered neck structure, and larger than 65% of fracture rate of the interior of the tantalum particles. 
       Example 4 
       [0057]    12 g of polyvinyl alcohol was put in a container filled in 230 ml of water, and then the container was put on a hotplate. The polyvinyl alcohol and water are heated and agitated to form a polyvinyl alcohol solution. 50 g of tantalum powder with less than 43 μm of diameter and less than 0.1% of oxygen content was scaled by a 200 g balance an added to 40 ml of the polyvinyl alcohol solution (the polyvinyl alcohol solution was cooled). The tantalum powder and the polyvinyl alcohol solution were mix and agitated homogeneously to form tantalum slurry. The tantalum slurry was casted into a 12×12×30 mm porous polyurethane foam body (0.60 mm of pore diameter, 0.027 g/cm 3  of density and 80° of hardness) until the pores of the polyurethane foam body were filled with the tantalum slurry. Then, the polyurethane foam body filled with the tantalum slurry was put into a porcelain dish placed in a vacuum drier. The polyurethane foam body filled with the tantalum slurry was dried in the vacuum drier at 90° C. for 5 hours under 1 Pa of vacuity. The dried polyurethane foam body filled with the tantalum slurry was degreased at 500° C. for 120 minutes under 10 −4 -10 −3  Pa of vacuity. The dried polyurethane foam body and the dried tantalum slurry were separated after the process of degreasing. Then, the dried tantalum slurry are sintered in a vacuum sintering furnace at 2150° C. for 2 hours under 10 −4  Pa of vacuity and formed in a porous sintered body. The argon is employed as a protective gas during sintering. The porous sintered body was cleaned out of the dust and dirt and then treated by normal post-treatments to obtain a porous tantalum. 
         [0058]    With reference to the figures, it is shown that the porous tantalum made in Example 4 has a foam structure with three-dimensional interconnecting pores. The foam structure has a foam skeleton accumulated by the tantalum powder, and tantalum particles located in the foam skeleton, and multiple sintered neck structure formed between more than 50% of the tantalum particles. 
         [0059]    The density, porosity, pore diameter and other mechanical properties of the obtained porous tantalum were tested by standard test methods such as GB/T5163-2006, GB/T5249-1985, GB/T6886-2001 and the like. The porous tantalum has three-dimensional interconnecting pores and less than 0.5% of impurities. The interconnecting pores are well-distributed. The tested porous tantalum has 2.1-5.1 g/cm 3  of density, higher than 50% of porosity, 400 μm of average pore diameter, 3.5 GPa of elastic modulus, 120 MPa of yield strength, 170 MPa of compressive strength, 300 MPa of hardness, 17.3% of the amount of plastic deformation, 72 MPa of tensile strength and 14.6% of percentage elongation. According to the anti-bending test on a basis of metal bending strength, the microstructure of the porous tantalum has less than 43% of fracture rate of the sintered neck structure, and larger than 57% of fracture rate of the interior of the tantalum particles. 
       Example 5 
       [0060]    Tantalum powder having less than 43 μm of diameter and less than 0.1% of the oxygen content as a raw material was mixed with a polyvinyl alcohol solution as a binder solution to form tantalum slurry. The tantalum slurry was casted into a polyurethane foam body. The polyurethane foam body with the tantalum slurry was dried, degreased, vacuum sintered, vacuum annealed and treated with normal post-treatments to obtain a porous tantalum. 
         [0061]    In the exemplary embodiment, the poly urethane foam body has 0.56-0.72 mm of pore diameter, 0.025 g/cm 3  of density and 50°-80° of hardness. The polyurethane foam body with the tantalum slurry was dried under 10 −2 -1 Pa of vacuity to remove water. The dried polyurethane foam body and polyvinyl alcohol are separated from the dried tantalum slurry at 400-800° C. of the temperature under 10 −4 -10 −3  Pa of vacuity or in a protective environment of inert gas with keeping the temperature for 30-120 minutes. The dried tantalum slurry was sintered at 2000-2200° C. under 10 −4 -10 −3  Pa of vacuity and keeping the temperature for 1-5 hours. The argon or other alternative inert gas was employed as a protective gas when keeping the temperature during sintering process, to obtain a porous sintered body. After sintered, the porous sintered body was annealed by keeping the temperature at 1000-1250° C. for 1-4 hours under 10 −4 -10 −3  Pa of vacuity, and then treated with normal post-treatments to obtain a porous tantalum. 
         [0062]    With reference to the figures, it is shown that the porous tantalum made in Example 5 has the foam structure with three-dimensional interconnecting pores. The foam structure has a foam skeleton accumulated by tantalum powder, and tantalum particles located in the foam skeleton, and multiple sintered neck structures formed between more than 50% of the tantalum particles. 
         [0063]    The density, porosity, pore diameter and other mechanical properties of the obtained porous tantalum were tested by standard test methods such as GB/T5163-2006, GB/T5249-1985, GB/T6886-2001 and the like. The porous tantalum has three-dimensional interconnecting pores and less than 0.5% of impurities. The interconnecting pores are well-distributed. The tested porous tantalum has 2.1-11 g/cm 3  of density, 40-80% of porosity, 150-500 μm of average pore diameter, 2.0-4.6 GPa of elastic modulus, 35-120 MPa of yield strength, 40-170 MPa of compressive strength, 150-300 MPa of hardness, 9.4-17.3% of the amount of plastic deformation, 65-72 MPa of tensile strength and 14.7% of percentage elongation. According to the anti-bending test on a basis of metal bending strength, the microstructure of the porous tantalum has less than 43% of fracture rate of the sintered neck structure, and larger than 57% of fracture rate of the interior of the tantalum particles. 
       Example 6 
       [0064]    Tantalum powder having less than 43 μm of diameter and less than 0.1% of the oxygen content as a raw material was mixed with a polyvinyl alcohol solution as a binder solution to form tantalum slurry. The tantalum slurry was casted into a polyurethane foam body having 0.48-0.89 mm of pore diameter, 0.015-0.035 g/cm 3  and 50°-80° of hardness. The polyurethane foam body with the tantalum slurry was dried, degreased, vacuum sintered, vacuum annealed and treated with normal post-treatments to obtain a porous tantalum. 
         [0065]    In the exemplary embodiment, polyvinyl alcohol was dissolved in the distilled water under heat to form a 5 wt % polyvinyl alcohol solution. 7 weight parts of tantalum powder and 1 weight part of the 5 wt % polyvinyl alcohol solution were mixed homogeneously and agitated to form pasty tantalum slurry. The polyurethane foam body was impregnated repeatedly until the pores of the polyurethane foam body were filled with the tantalum slurry. The polyurethane foam body with the tantalum slurry was dried at 60-100° C. for 4-8 hours under 1 Pa of vacuity to remove water. 
         [0066]    The dried polyurethane foam body was put into a tungsten device in a non-oxidizing atmosphere furnace with increasing to 800° C. at a proper rate. The dried organic foam body was degreased under argon having at least 99.999% of purity as a protective gas. The pure argon was employed as a protective gas for 30 minutes before increasing the temperature to exclude the air in the atmosphere furnace. The temperature was increased from room temperature to 400° C. at a rate of 1° C./min with argon flowing at a rate of 0.5 L/min and kept for 30 minutes, and then increased to 400-800° C. at a rate of 0.5° C./min with argon flowing at a rate of 1 L/min and kept for 120 minutes. Then, the power was closed and the degreased sample was cooled down with the temperature in the furnace while argon flowing at a rate of 1 L/min. The argon supplier was closed until the temperature of the degreased sample was decreased to the room temperature. 
         [0067]    The degreased sample in the tungsten device was heated in a sintering furnace and sintered by increasing to 2200° C. at a proper rate. The vacuity reached to 10 −4  Pa before increasing the temperature in the sintering furnace. The temperature in the sintered furnace was increased from room temperature to 1200° C. at a rate of 10-15° C./min and kept for 30 minutes under 10 −4  Pa of vacuity, and then increased to 1500° C. at a rate of 10° C./min and kept for 30 min under 10 −4 -10 −3  Pa of vacuity, and then increased to 2200° C. at a rate of 6° C./min and kept for 120 minutes under 10 −3  Pa of vacuity. After sintered, under 10 −3  Pa of vacuity, the temperature was decreased to 1600° C. at a rate of 10-15° C./min and kept for 30 minutes, and then decreased to 1200° C. at a rate of 12° C./min and kept for 60 min, and then decreased to 800° C. at a rate of 10° C./min. Then, the sintered sample was cooled naturally. 
         [0068]    After cooled, the sintered sample was put into the corundum container in an annealing furnace under proper vacuity and annealed by increasing to 1250° C. at a proper rate. The vacuity reached to 10 −4  Pa before increasing the temperature in the annealing furnace. The temperature in the sintered furnace was increased from room temperature to 1250° C. at a rate of 15° C./min and kept 240 minutes under 10 −4 -10 −3  Pa of vacuity, and then decreased to 1000° C. at a rate of 5° C./min and kept for 180 min under 10 −4 -10 −3  Pa of vacuity, and then decreased to 800° C. at a rate of 10° C./min and kept for 120 minutes under 10 −4  Pa of vacuity, and then decreased to room temperature at a rate of 20° C./min under 10 −4  Pa of vacuity. Then, the annealed sample was treated with normal post-treatments to obtain a porous tantalum. 
         [0069]    With reference to the figures, it is shown that the porous tantalum made in Example 6 has a foam structure with three-dimensional interconnecting pores. The foam structure has a foam skeleton accumulated by the tantalum powder, and tantalum particles located in the foam skeleton, and multiple sintered neck structures formed between more than 80% of the tantalum particles. 
         [0070]    The density, porosity, pore diameter and other mechanical properties of the obtained porous tantalum were tested by standard test methods such as GB/T5163-2006, GB/T5249-1985, GB/T6886-2001 and the like. The porous tantalum has three-dimensional interconnecting pores and less than 0.5% of impurities. The interconnecting pores are well-distributed. The tested porous tantalum has 4.52 g/cm 3  of density, 72.8% of porosity, 300 μm of average pore diameter, 3.5 GPa of elastic modulus, 108 MPa of yield strength, 69 MPa of compressive strength, 230 MPa of hardness, 11.4% of the amount of plastic deformation, 67 MPa of tensile strength and 14.7% of percentage elongation. According to the anti-bending test on a basis of metal bending strength, the microstructure of the porous tantalum has less than 40% of fracture rate of the sintered neck structure, and larger than 60% of fracture rate of the interior of the tantalum particles. 
         [0071]    Besides the examples illustrated above, the organic binder also can be starch, ethyl cellulose or other alternative substances, the dispersant also can be pure ethanol or other alternative substance, and the organic foam body also can be a polyether ester foam body. However, no matter what substances are used as the organic binder, the dispersant and the organic foam body, the purposes of their use are looking forward things that the dispersant can be easily removed and the metal powder during sintering process cannot collapse but easily eliminated to form the porous tantalum having a foam structure with three-dimensional interconnecting pores. 
         [0072]    Besides the processes mentioned above in Example 6, people skilled in the art can make changes and modifications of the conditions to obtain the porous tantalum of the present invention. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Diameter 
                   
                 Tantalum 
                   
                   
                   
               
               
                   
                 of 
                   
                 powder 
               
               
                   
                 tantalum 
                   
                 (weight 
                 Pore 
               
               
                   
                 powder 
                 PVA 
                 part)/ 
                 diameter 
                 Density 
                 Hardness 
               
               
                   
                 (m)/ 
                 (g)/ 
                 PVA 
                 of poly- 
                 of poly- 
                 of poly- 
               
               
                 Ex- 
                 Oxygen 
                 Wa- 
                 solution 
                 urethane 
                 urethane 
                 urethane 
               
               
                 am- 
                 content 
                 ter 
                 (weight 
                 foam body 
                 foam body 
                 foam body 
               
               
                 ple 
                 (%) 
                 (ml) 
                 part) 
                 (mm) 
                 (g/cm 3 ) 
                 (°) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 7 
                 &lt;43/&lt;0.1 
                 2/100 
                 1/7.5 
                 0.50 
                 0.025 
                 50 
               
               
                 8 
                 &lt;40/&lt;0.1 
                 3/100 
                 1/8.5 
                 0.88 
                 0.035 
                 55 
               
               
                 9 
                 &lt;42/&lt;0.1 
                 4/100 
                 1/7.7 
                 0.70 
                 0.030 
                 77 
               
               
                 10 
                 &lt;41/&lt;0.1 
                 5/100 
                 1/8.3 
                 0.60 
                 0.027 
                 66 
               
               
                 11 
                 &lt;39/&lt;0.1 
                 6/100 
                 1/6.0 
                 0.55 
                 0.033 
                 73 
               
               
                 12 
                 &lt;38/&lt;0.1 
                 7/100 
                 1/7.3 
                 0.56 
                 0.016 
                 63 
               
               
                 13 
                 &lt;35/&lt;0.1 
                 8/100 
                 1/8.1 
                 0.72 
                 0.018 
                 53 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Vacuity of 
                   
                   
                 The atmosphere of annealing (Pa)/ 
               
               
                   
                 drying (Pa)/ 
                 The atmosphere of 
                   
                 The rate of increasing or decreasing the 
               
               
                   
                 Temperature 
                 degreasing (Pa)/ 
                 The atmosphere of sintering (Pa)/ 
                 temperature (° C./min)/ 
               
               
                   
                 (° C.)/ 
                 Temperature (° C.)/ 
                 Temperature (° C.)/ 
                 Temperature (° C.)/ 
               
               
                 Example 
                 Time (h) 
                 Time (min) 
                 Time (min) 
                 Time of keeping temperature (min) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 7 
                 1/65/6.5 
                 increasing from room 
                 increasing from room temperature to 
                 10 −4  Pa/ 
               
               
                   
                   
                 temperature to 400° C. at a 
                 1200° C. at a rate of 10° C./min and 
                 increasing to 1030° C. at a rate of 15° C./min 
               
               
                   
                   
                 rate of 1° C./min and keeping 
                 keeping the temperature for 60 min 
                 and keeping the temperature for 480 min/ 
               
               
                   
                   
                 the temperature for 60 min; 
                 under 10 −4  Pa of vacuity; 
                 decreasing to 1000° C. at a rate of 5° C./min 
               
               
                   
                   
                 increasing from 400° C. to 
                 increasing to 1250° C. at a rate of 
                 and keeping the temperature for 180 min;/ 
               
               
                   
                   
                 600° C. at a rate of 0.5° C./min 
                 11° C./min and keeping the temperature 
                 decreasing to 800° C. at a rate of 11° C./min 
               
               
                   
                   
                 and keeping the temperature 
                 for 60 min; 
                 and keeping the temperature for 108 min;/ 
               
               
                   
                   
                 for 120 min. 
                 increasing to 2030° C. at a rate of 
                 decreasing to room temperature at a rate of 
               
               
                   
                   
                   
                 6° C./min and keeping the temperature 
                 21° C./min 
               
               
                   
                   
                   
                 for 240 min under 10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 increasing from room temperature to 
               
               
                   
                   
                   
                 1200° C. at a rate of 10° C./min and 
               
               
                   
                   
                   
                 keeping the temperature for 60 min 
               
               
                   
                   
                   
                 under 10 −4  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1520° C. at a rate of 
               
               
                   
                   
                   
                 11° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 60 min under 10 −4 -10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1200° C. at a rate of 
               
               
                   
                   
                   
                 13° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 90 min; 
               
               
                   
                   
                   
                 decreasing to 800° C. at a rate of 
               
               
                   
                   
                   
                 13° C./min, and natural cooling 
               
               
                 8 
                 1/75/5.5 
                 increasing from room 
                 increasing to 1210° C. at a rate of 
                 10 −4  Pa/ 
               
               
                   
                   
                 temperature to 400° C. at a 
                 11° C./min and keeping the temperature 
                 increasing to 1050° C. at a rate of 17° C./min 
               
               
                   
                   
                 rate of 1.5° C./min and 
                 for 58 min under 10 −4  Pa of vacuity; 
                 and keeping the temperature for 450 min/ 
               
               
                   
                   
                 keeping the temperature for 
                 increasing to 1270° C. at a rate of 
                 decreasing to 1000° C. at a rate of 6° C./min 
               
               
                   
                   
                 58 min; 
                 12° C./min and keeping the temperature 
                 and keeping the temperature for 150 min;/ 
               
               
                   
                   
                 increasing from 400° C. to 
                 for 55 min; 
                 decreasing to 800° C. at a rate of 12° C./min 
               
               
                   
                   
                 600° C. at a rate of 0.6° C./min 
                 increasing to 2050° C. at a rate of 
                 and keeping the temperature for 102 min;/ 
               
               
                   
                   
                 and keeping the temperature 
                 8° C./min and keeping the temperature 
                 decreasing to room temperature at a rate of 
               
               
                   
                   
                 for 110 min 
                 for 220 min under 10 −3  Pa of vacuity; 
                 22° C./min 
               
               
                   
                   
                   
                 decreasing to 1530° C. at a rate of 
               
               
                   
                   
                   
                 12° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 55 min under 10 −4 -10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1210° C. at a rate of 
               
               
                   
                   
                   
                 14° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 85 min; 
               
               
                   
                   
                   
                 decreasing to 800° C. at a rate of 
               
               
                   
                   
                   
                 14° C./min and natural cooling. 
               
               
                 9 
                 1/55/7 
                 increasing from room 
                 increasing to 1220° C. at a rate of 
                 10 −4  Pa/ 
               
               
                   
                   
                 temperature to 400° C. at a 
                 12° C./min and keeping the temperature 
                 increasing to 1100° C. at a rate of 20° C./min 
               
               
                   
                   
                 rate of 2° C./min and keeping 
                 for 55 min under 10 −4  Pa of vacuity; 
                 and keeping the temperature for 420 min/ 
               
               
                   
                   
                 the temperature for 56 min; 
                 increasing to 1300° C. at a rate of 
                 decreasing to 1000° C. at a rate of 7° C./min 
               
               
                   
                   
                 increasing from 400° C. to 
                 13° C./min and keeping the temperature 
                 and keeping the temperature for 130 min;/ 
               
               
                   
                   
                 680° C. at a rate of 0.7° C./min 
                 for 50 min; 
                 decreasing to 800° C. at a rate of 13° C./min 
               
               
                   
                   
                 and keeping the temperature 
                 increasing to 2100° C. at a rate of 
                 and keeping the temperature for 96 min;/ 
               
               
                   
                   
                 for 100 min; 
                 10° C./min and keeping the temperature 
                 decreasing to room temperature at a rate of 
               
               
                   
                   
                   
                 for 200 min under 10 −3  Pa of vacuity; 
                 23° C./min 
               
               
                   
                   
                   
                 decreasing to 1540° C. at a rate of 
               
               
                   
                   
                   
                 13° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 50 min under 10 −4 -10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1220° C. at a rate of 
               
               
                   
                   
                   
                 15° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 80 min; 
               
               
                   
                   
                   
                 decreasing to 800° C. at a rate of 
               
               
                   
                   
                   
                 15° C./min and natural cooling 
               
               
                 10 
                 1/45/7.5 
                 increasing from room 
                 increasing to 1230° C. at a rate of 
                 10 −4  Pa/ 
               
               
                   
                   
                 temperature to 400° C. at a 
                 13° C./min and keeping the temperature 
                 increasing to 1150° C. at a rate of 22° C./min 
               
               
                   
                   
                 rate of 2.5° C./min and 
                 for 50 min under 10 −4  Pa of vacuity; 
                 and keeping the temperature for 360 min/ 
               
               
                   
                   
                 keeping the temperature for 
                 increasing to 1350° C. at a rate of 
                 decreasing to 1000° C. at a rate of 8° C./min 
               
               
                   
                   
                 55 min; 
                 14° C./min and keeping the temperature 
                 and keeping the temperature for 120 min;/ 
               
               
                   
                   
                 increasing from 400° C. to 
                 for 45 min; 
                 decreasing to 800° C. at a rate of 14° C./min 
               
               
                   
                   
                 700° C. at a rate of 0.8° C./min 
                 increasing to 2150° C. at a rate of 
                 and keeping the temperature for 90 min;/ 
               
               
                   
                   
                 and keeping the temperature 
                 12° C./min and keeping the temperature 
                 decreasing to room temperature at a rate of 
               
               
                   
                   
                 for 90 min; 
                 for 180 min under 10 −3  Pa of vacuity; 
                 24° C./min 
               
               
                   
                   
                   
                 decreasing to 1550° C. at a rate of 
               
               
                   
                   
                   
                 14° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 45 min under 10 −4 -10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1230° C. at a rate of 
               
               
                   
                   
                   
                 16° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 75 min; 
               
               
                   
                   
                   
                 decreasing to 800° C. at a rate of 
               
               
                   
                   
                   
                 16° C./min and natural cooling 
               
               
                 11 
                 1/85/6.0 
                 increasing from room 
                 increasing to 1240° C. at a rate of 
                 10 −3  Pa/ 
               
               
                   
                   
                 temperature to 400° C. at a 
                 14° C./min and keeping the temperature 
                 increasing to 1200° C. at a rate of 25° C./min 
               
               
                   
                   
                 rate of 3° C./min and keeping 
                 for 40 min under 10 −4  Pa of vacuity; 
                 and keeping the temperature for 300 min/ 
               
               
                   
                   
                 the temperature for 50 min; 
                 increasing to 1400° C. at a rate of 
                 decreasing to 1000° C. at a rate of 9° C./min 
               
               
                   
                   
                 increasing from 400° C. to 
                 15° C./min and keeping the temperature 
                 and keeping the temperature for 100 min;/ 
               
               
                   
                   
                 730° C. at a rate of 0.9° C./min 
                 for 40 min; 
                 decreasing to 800° C. at a rate of 15° C./min 
               
               
                   
                   
                 and keeping the temperature 
                 increasing to 2160° C. at a rate of 
                 and keeping the temperature for 84 min;/ 
               
               
                   
                   
                 for 80 min; 
                 14° C./min and keeping the temperature 
                 decreasing to room temperature at a rate of 
               
               
                   
                   
                   
                 for 160 min under 10 −3  Pa of vacuity; 
                 26° C./min 
               
               
                   
                   
                   
                 decreasing to 1560° C. at a rate of 
               
               
                   
                   
                   
                 15° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 40 min under 10 −4 -10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1240° C. at a rate of 
               
               
                   
                   
                   
                 17° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 70 min; 
               
               
                   
                   
                   
                 decreasing to 800° C. at a rate of 
               
               
                   
                   
                   
                 17° C./min and natural cooling 
               
               
                 12 
                 1/95/5.5 
                 increasing from room 
                 increasing to 1250° C. at a rate of 
                 10 −4  Pa/ 
               
               
                   
                   
                 temperature to 400° C. at a 
                 15° C./min and keeping the temperature 
                 increasing to 1230° C. at a rate of 27° C./min 
               
               
                   
                   
                 rate of 4° C./min and keeping 
                 for 30 min under 10 −4  Pa of vacuity; 
                 and keeping the temperature for 270 min/ 
               
               
                   
                   
                 the temperature for 40 min; 
                 increasing to 1450° C. at a rate of 
                 decreasing to 1000° C. at a rate of 10° C./min 
               
               
                   
                   
                 increasing from 400° C. to 
                 16° C./min and keeping the temperature 
                 and keeping the temperature for 90 min;/ 
               
               
                   
                   
                 750° C. at a rate of 1.0° C./min 
                 for 35 min; 
                 decreasing to 800° C. at a rate of 16° C./min 
               
               
                   
                   
                 and keeping the temperature 
                 increasing to 2170° C. at a rate of 
                 and keeping the temperature for 78 min;/ 
               
               
                   
                   
                 for 70 min; 
                 16° C./min and keeping the temperature 
                 decreasing to room temperature at a rate of 
               
               
                   
                   
                   
                 for 140 min under 10 −3  Pa of vacuity; 
                 27° C./min 
               
               
                   
                   
                   
                 decreasing to 1570° C. at a rate of 
               
               
                   
                   
                   
                 16° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 35 min under 10 −4 -10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1245° C. at a rate of 
               
               
                   
                   
                   
                 18° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 65 min; 
               
               
                   
                   
                   
                 decreasing to 800° C. at a rate of 
               
               
                   
                   
                   
                 18° C./min and natural cooling 
               
               
                 13 
                 1/100/4.5 
                 increasing from room 
                 increasing to 1225° C. at a rate of 
                 10 −4  Pa/ 
               
               
                   
                   
                 temperature to 400° C. at a 
                 13° C./min and keeping the temperature 
                 increasing to 1250° C. at a rate of 30° C./min 
               
               
                   
                   
                 rate of 2° C./min and keeping 
                 for 45 min under 10 −4  Pa of vacuity; 
                 and keeping the temperature for 240 min/ 
               
               
                   
                   
                 the temperature for 30 min; 
                 increasing to 1500° C. at a rate of 
                 decreasing to 1000° C. at a rate of 5.5° C./min 
               
               
                   
                   
                 increasing from 400° C. to 
                 17° C./min and keeping the temperature 
                 and keeping the temperature for 170 min;/ 
               
               
                   
                   
                 800° C. at a rate of 1.3° C./min 
                 for 30 min; 
                 decreasing to 800° C. at a rate of 17° C./min 
               
               
                   
                   
                 and keeping the temperature 
                 increasing to 2180° C. at a rate of 
                 and keeping the temperature for 72 min;/ 
               
               
                   
                   
                 for 60 min; 
                 18° C./min and keeping the temperature 
                 decreasing to room temperature at a rate of 
               
               
                   
                   
                   
                 for 120 min under 10 −3  Pa of vacuity; 
                 29° C./min 
               
               
                   
                   
                   
                 decreasing to 1580° C. at a rate of 
               
               
                   
                   
                   
                 18° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 30 min under 10 −4 -10 −3  Pa of vacuity; 
               
               
                   
                   
                   
                 decreasing to 1250° C. at a rate of 
               
               
                   
                   
                   
                 19° C./min and keeping the temperature 
               
               
                   
                   
                   
                 for 60 min; 
               
               
                   
                   
                   
                 decreasing to 800° C. at a rate of 
               
               
                   
                   
                   
                 19° C./min and 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 The mechanical properties of the porous tantalum prepared in Example 7-13 
               
             
          
           
               
                 Example 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
                 13 
               
               
                   
               
             
          
           
               
                 Density (g/cm 3 ) 
                 9.9 
                 7.5 
                 5.8 
                 4.2 
                 9.1 
                 3.5 
                 8.3 
               
               
                 Porosity (%) 
                 40 
                 55 
                 65 
                 75 
                 45 
                 80 
                 50 
               
               
                 Pore diameter (μm) 
                 170 
                 290 
                 480 
                 380 
                 330 
                 210 
                 430 
               
               
                 Elastic modulus (GPa) 
                 2.1 
                 2.5 
                 3.3 
                 3.9 
                 3.6 
                 4.3 
                 4.5 
               
               
                 Yield strength (MPa) 
                 110 
                 100 
                 90 
                 80 
                 70 
                 65 
                 40 
               
               
                 Compressive strength (MPa) 
                 50 
                 160 
                 150 
                 130 
                 100 
                 140 
                 110 
               
               
                 Hardness (MPa) 
                 160 
                 170 
                 210 
                 230 
                 280 
                 290 
                 270 
               
               
                 The amount of plastic deformation (%) 
                 17.30 
                 17.20 
                 17.25 
                 17.22 
                 17.28 
                 17.29 
                 17.30 
               
               
                 Tensile strength (MPa) 
                 65 
                 66 
                 67 
                 68 
                 69 
                 70 
                 71 
               
               
                 Percentage elongation (%) 
                 14.70 
                 14.60 
                 14.50 
                 14.65 
                 14.55 
                 14.75 
                 14.80 
               
               
                 Fracture rate of the sintering neck structures (%) 
                 45 
                 40 
                 35 
                 30 
                 43 
                 37 
                 32 
               
               
                 Fracture rate of the interior of tantalum particles (%) 
                 55 
                 60 
                 65 
                 70 
                 57 
                 63 
                 68