METHOD FOR THE PRODUCTION OF A CHEMICALLY BOUNDED CERAMIC PRODUCT AND A PRODUCT MANUFACTURED ACCORDING TO THE METHOD

Abstract: The present invention relates to a method for the production of a chemically bonded ceramic product by a reaction between one or several pulverulent binding agents as well as a liquid reacting with said binding agents. The ceramic product can also include one or several aggregate materials, which essentially do not participate in the chemical hardening reactions. According to the invention a powder body is compacted, which comprises said binding agent(s) and possibly aggregate materials without an addition of said liquid, by subjecting, before said raw compact is impregnated with said liquid, said powder body to such a high external pressure that a thoroughly integrated raw compact is obtained, in which the filling density has increased to at least 1.3 times the initial filling density, which is defined as that filling density, which is obtained by shaking, vibrating and/or carefully packing the loose powder in a container.

Description: METHOD FOR THE PRODUCTION OF A CHEMICALLY BONDED CERAMIC PRODUCT AND A PRODUCT MANUFACTURED ACCORDING TO THE METHOD TECHNICAL FIELD The present invention relates to Chemically Bonded Cera¬ mics (CBC) , i.e. chemically bonded materials as compared to other advanced ceramics, which usually are made by a si tering process at elevated temperatures. More specifically the invention relates to a method for the production of a chemically bonded ceramic product by a reaction between on or several pulverulent binding agents and a liquid which r acts with these binding agents. The ceramic product can al include one or several aggregates, which essentially do n react chemically with the other components. The invention also relates to the product manufactured according to the method. BACKGROUND ART The CBC-materials are a very large and heterogenous group of materials, which include anything from concrete, based on a conventional Portland cement, to advanced ceramics i the dental field as well as in the orthopaedics, to name few of the fields of application of the CBC-materials. In the dental field mainly only materials, which cannot b called CBC-materials, have been used as permanent tooth f lings. Amalgams have been used primarily, which do not me the high non-toxicity requirements for human use, which mu be increasingly satisfied . Also, other materials for pe manent tooth fillings, e.g. methyl ethacrylate-based com posites, which have a tendency to produce hypersensitivit reactions, are considered less suitable. Also, these plas tic materials have substantial drawbacks due to the fact thet they shrink after being applied and furthermore they display an unsatisfactory resistance to wear. Hydraulic cements have also been used as dental filling mat rials. Thus, US-A-4 689 080 relates to the use of calcium aluminate as a binding agent for dental applications. Another example of a material which can be called a CBC-ma- terial is the cement, which is used in the dental field and which is based primarily on zinc oxide and orthophospho ric acid. This cement has been used for temporary filling fastening of crowns etc., but its strength has so far been unsatisfactory and it can not be used as permanent fillings Another type of material used for dental applications are the so called glass polyalkenoate cements and similar mate¬ rials. SE-B-381 808, EP-A-0024056 and EP-A-0115058 exempli¬ fy this type of material. Generally, stiffening substances for dental or general or¬ thopedic applications (implants) must meet several require¬ ments in order to be rated as satisfactory and accepted sub stances, e.g. having hygienic and in the dental field also aesthetic properties. Also, these materials must not contai components, which are toxic or which in their environment can give rise to toxic substances. Furthermore, they must b functional, have mechnical properties designed for their field of use, be corrosion resistant, comfortable to use, be biological compatible, have an acceptable appearance as well as not be too expensive to use. An important property of a stiffening substance for dental applications on human beings is also that it stiffens slowly in order to make it possible to perform the desired application without great speed. On the other hand, such a stiffening material must comparatively quickly become sufficiently tough and suffi¬ ciently fastened in order to allow the treated person to eat a reasonably short time after the application. The abov mentioned hydration materials, zinc oxide-based materials, glasspolyalkeonate cement materials etc. satisfy these re¬ quirements for dental materials as regards i.a. hygienic and aesthetic properties, toxicity etc. However, the stren of these materials is not considered sufficient in contras to amalgams. As is well known, the strength properties of the CBC-mate¬ rials can be improved by various treatments of the compo¬ nents of the material or through additives of various typ Reinforcement of concrete by means of reinforcement bars one example of this technique on a macroscale. Also, it i well known how to reinforce advanced CBC-materials by mea of reinforcing fibers, which e.g. can be steel fibers, ca bon fibers, glass fibers, organic fibers etc. However, fe sible dimensions and treatment limitations constitute phy sical limits when choosing reinforcement materials and met ods designed to be used in the dental care and surgery fields. Also, the requirements as to the surface smooth¬ ness of the stiffening material, its flow when prepared a applied and - when it is used as a cementum mass, i.e. as an adhesive - its joint thickness of less than 50 um , con titute an upper limit for the physical size of the reinfo cing particles in connection with dental and surgical app cations. Also, conventional reinforcing fibers might func tion, as to dental applications, as a footing for bacteri provided they protrude from the surrounding matrix materi and/or are not worn off concurrently with the matrix mate ial. It is known that the strength of at least some cement mat rials can be improved by compacting the paste of the pulv rulent binding agent and the reacting liquid, which can b attained by means of a dispersant, more specifically a so called plasticizer (Science, Feb. 1987, pages 235-236 as well as US-4 363 667 ) . When preparing the paste, which i done in connection with the application, the mass is homo nized and flaws are expelled through a repeated kneading. The method is statistical and isolated strength-impairing air pores may remain. Also, the homogenization in connect Also, the degree of close packing and consequently the strength can be improved, provided the powder is composed of well-balanced grain-size fractions; US-4 353 746 and US-4 353 747. It is true that this technique per se can be a part of the technique according to the present invention, but it is not sufficient for obtaining the required results Thus, merely inconsiderable strength improvements are ob¬ tained. BRIEF DESCRIPTION OF THE INVENTION The general object of the invention is to suggest a method for the improvement of the strength of chemically bonded ce ramic products, so called CBC-products or CBC-materials. A special object of the invention is to prepare the binding agent or binding agents as well as optional aggregates, of v/hich the CBC-product will be composed, in such a way, that the user can have the use of a binding agent product, which is prepared to obtain the required strength and which the user finishes by impregnating the finished binding agent with the liquid either before the application or in situ. According to one aspect of the invention one object is to suggest a material, which is suitable for dental applica¬ tions, particularly for permanent fillings. According to another aspect of the invention, one object is to suggest a material, which is suitable as a prosthesis ma terial (implant) for general orthopedic applications. According to another aspect of the invention one object is to facilitate an in situ addition of the hydration liquid (e.g. in the form of sea water) for underwater construction These and additional objects can be attained by compacting a pulverulent body, composed of said binding agent (s) and optional aggregates, by exerting the pulverulent body to such a high external pressure and at such a high tempera¬ ture, that, without sintering reactions, during the compac tion a well integrated raw compact is obtained, in which the filling density increases to at least 1.3 times the initial filling density, which is defined as that filling density, which is obtained by shaking, vibrating and/or carefully packing of the loose powder in a container, be¬ fore the raw compact is impregnated with the liquid. The pulverulent body is preferably exerted to such a high pres sure, that the filling density increases to at least 1.5 and suitably at least 1.7 times the initial filling densit According to a first preferred embodiment of the invention said binding agent consists of one or several hydraulic bin ding agents, the hydration phases of which belong to the group of compounds, which consists of aluminates, silicate phosphates and sulphates, the liquid being a hydration li¬ quid, consisting of water and possibly substances dissolve in the water. The preferred aluminate is calcium aluminate which can be present in various proportions between CaO and A1 2 0 3 . The preferred silicate is calcium silicate wit varying proportions between CaO and Si0 2 , which is the mai component of Portland cement, which however contains also other components, e.g. A1 2 0 3 . Other phases are e.g. 3 CaOx A1„0 3 and 4Ca0xAl 2 0 3 and 4CaOxAl 2 0 3 xFe 2 0 3 . Combinations of silicates and aluminates having a higher portion of alumin than in an ordinary Portland cement are also useful. Phos phates, which are useful as binding agents in this connec¬ tion, are e.g. calcium phosphate and zinc phosphate and a useful sulphate is the essentially non-hydrated gypsum, The above-mentioned substances may exist as natural minera or be produced synthetically. Irrespective of their origin they must be preliminarily treated according to conventio nal technique, which however does not constitute any part of the present invention. As a result of this treatment a powder is obtained, in which the pulverulent grains have a size ranging from a submicron-size up to a maximum size of 100 urn in the largest extension of the grains. An ordinary medium grain size can be as high as about 15 urn , i.e. 50 percent by weight of the grains have a size larger than abo 15 urn. The shape is very irregular. Also, the pulverulent grains generally form large porous agglomerates. For these reasons and due to an electro-static interaction between the powder grains, a very low filling density in the loose powder is obtained with this type of powder. A normal so called TAP-density, also called Bulk-density or Loose-dens ty for a calcium aluminate cement, e.g. of grade SECAR 71, is 32 %. This can be elevated to about 39 % by shaking the powder, vibrating it or exerting it to a careful packing i the container, used to store the powder . The filling dens ty in the latter condition, i.e. subsequently to a vibrati a shaking or a careful compaction, which is seen as the in tial filling density as regards the method according to th invention. However, the same can be additionally increased somewhat by impregnating the powder with a non-reacting li quid, which subsequently is removed previous to the very heavy compaction according to the invention. It is true that the invention has been developed for hyd¬ ration materials, e.g. aluminates, silicates, phosphates and sulphates, but the invention's principal features pro¬ bably can be utilized also in other systems. In the dental field, and also in other fields, the invention can e.g. be utilized in case the binding agents mainly are one or seve ral oxides, e.g. zinc oxide, while said liquid is one or several acids, e.g. a phosphorus-based acid, preferably and mainly orthophosphoric acid. An additional feasible application field among several others is the production of a so called glass polyalkeonat cement, the binding agent possibly consisting of a mixture of a glass powder and a freeze-dehydrated acid according t a technique known per se, while the liquid can be water. Besides the binding agent and the liquid, which subsequent to the reaction with the binding agent forms a solid phase it is possible, as is generally known, to add an aggregate material, i.e. a material which does not participate in th chemical reactions between the binding agent and the liqui but v/hich is present as a solid phase in the finished, so¬ lid final product. For certain application fields such agg regate materials can be reinforcements of various types, e.g. fibers of metals, carbon, glass or organic materials etc. The reinforcement advantageously can be obtained by introducing long crystals, so called whiskers, e.g. of SiC Si 3 N. and/or A1 2 0 3 . Also, for dental applications or as a prosthesis material for general surgical applications the CBC-material accordi to the invention can include aggregate materials, provided they meet certain requirements. Thus, they must not be tox ic, they must be biocompatible, must not cause irritations in the oral cavity in the case of dental applications, mus not corrode etc. A small amount of boron nitride can e.g. added to be used as a solid lubricant in connection with the compaction of the dry pulverulent material, preferably an amount of 5-15 percent by volume of the dry substance previous to the compaction and the impregnation with said liquid. In case the binding agent is one or several hydration mate rials, the aggregate material can also be e.g. hydroxylapa tite or solid solutions thereof and/or oxides of one or se veral of titanium, zirconium, zinc and aluminum and/or som prehydrated phase of the binding agent or binding agents. It is particularly advantageous " to use as aggregates out¬ wardly projecting, needle-shaped crystals, preferably of titanium dioxide, which are biocompatible and chemically inert in all the systems considered here, i.e. also to 8 such hydration liquids as phosphoric acid etc. Said titaniu dioxide aggregate suitably comprises three-dimensionally oriented and star-shaped, needle-shaped crystals, the thick ness of which can be a few tenths of a micrometer but the length of which normally is several times larger. These cry tals are agglomerated to larger particles or agglomerates having a size of several micrometers. The reinforcement ef¬ fect of the agglomerates in the hardened product is due to the nature of the agglomerates. Thus, the bond between the setting phase and the agglomerates of titanium dioxide crys tals is improved and strengthened when the agglomerates are etched, e.g. in 0.5-10 M, particularly 1-3 M, sodium hydrox ide or in another etch solution, e.g. a mineral acid such a phosphoric acid. According to the invention a superplasticizer can also be admixed in a dry condition or by means of a water-free solu tion, subsequent to which the raw compact is produced. A su table superplasticizer is e.g. 79 % hydrolysed polyvinyl ac tate. When the raw compact is impregnated with a liquid, it is im portant that not only a high but also a regular filling den sity has been obtained to avoid large pockets, which would be filled with the liquid, when the impregnation takes plac Thus, the mean value of the liquid content in the moistened raw compact has to be low, but also within every small sub- volume the liquid content has to be low. Nevertheless, the liquid content has to be sufficient in order to dissolve th binding agent to such a high degree, that it will not be pr sent in large continuous bands throughout the finished CBC- material. In case the binding agent is an aluminate or ano¬ ther hydration material and in case the material is used as tooth fillings, then long continuous bands of non-reacted ca cium aluminate would result in, when the filling gradually is v/orn off, a reaction between the aluminates and the wate in the oral cavity in a not desirable way. However, the agg regates can be used as not only mainly reinforcement materi¬ als but also as agents conducive to an optimal distribution, a sufficient but not too high liquid content being available in every sub-volume for reaction with the binding agent, and consequently long continuous bands of non-reacted binding agent substance mainly being avoided. The aggregate particles or the agglomerates of aggregate particles preferably have a particle size of 0.5-10 urn. It is particularly advantageous to let such particles have a mean particle size, which is considered smaller than the mean grain size of the binding agent, because then a somewhat higher initial filling densi¬ ty can be obtained. The amount of aggregate material is pre¬ ferably 3-25 percent by weight of the finished CBC-material or 4-30 percent by volume of the mixture of the binding agen powder and the aggregate material in the raw compact. In a special embodiment of the invention a fine-grained binding agent phase and a somewhat coarser aggregate mate¬ rial phase in the powder body are used instead. According to this embodiment the main portion of the powder grains in the binding agent phase can have grain sizes of 1-20 um , v/hile the main portion of the grains of the aggregate materi al phase have a size distribution of 5-50 um. This choice of particle size distribution betv/een the binding agent phase and the aggregate material phase will facilitate an almost total "consumption", i.e. a reaction between the binding agent phase and said liquid during the impregnation. Conse¬ quently, the final CBC-product will be composed of compara¬ tively large aggregate material particles, surrounded by completely hydrated areas and areas reacted in a correspon¬ ding way respectively. Such a material can be particularly suitable for wear applications in wet and preferably in hydration-environments. In case non-hydrated areas are ex¬ posed to this wet, wearing environment, the wear may be ac¬ celerated due to the fact that a release from a non-hydrated phase is larger than for a thoroughly hydrated phase. A cor¬ responding situation may exist, v/hen the binding agent is a non-hydration binding agent and the final product is de¬ signed for an environment, wich contains a liquid of the same type as is used as a reaction-liquid for the hardenin of the product. The initial filling density, i.e. the filling density be¬ fore the compaction according to the invention in a dry condition, is normally not higher than 40 %. By special treatment methods, e.g. through centrifugation in a chemi¬ cally non-reacting liquid, the filling density can be in¬ creased to a maximum of 50-55 %. According to a preferred embodiment of the invention the compaction according to the invention is carried out by a cold isostatic compaction. A cold isostatic compaction is an isostatic compaction carried out at such a low tempera¬ ture, that no sintering reactions take place, normally at ambient temperatures. However, other types of mechanical pressing, e.g. cold-rolling or forging, preferably gradual forging, can also be used. During the compaction the agglomerates of binding agent grains and possibly or preferably also the agglomerates of the used aggregate materials are disintegrated or crushed and the fragments are redistributed, the porosity decrea¬ sing and the material being homogenized. The process is fa cilitated, if the used powders are treated in a non-polar liquid, e.g. petroleum ether (light petrol) , the binding force for the resulting agglomerates after the removal of the liquid being small, i.e. soft agglomerates being ob¬ tained. When a cold isostatic compaction is used, the powder body is placed in an impermeable shell, suitably a plastic shel subsequent to which the enclosed powder body is subjected to an external pressure in a liquid volume surrounding the shell, preferably a pressure higher than 200 MPa, preferab not less than 250 MPa. Another method of carrying out the cold compaction of the binding agent and the optional aggregates according to the invention is by means of injection molding or extrusion, t powder also containing a solid lubricant, i.e. a polymer i an amount, which roughly is equivalent to the pore volume o the raw compact. After the compaction the polymer lubrican is allowed to evaporate, suitably through evaporization by heating. Irrespective of the type of compaction method used, the co paction is carried out in such a way that raw compacts are obtained having a geometrical shape adapted to the intende field of application. The raw compact can e.g., when it is designed for dental applications, be a thin string, possib subdivided into easily separable sections, or small granul In case the compaction is carried out as a cold isostatic compaction in a plastic shell, the raw compact suitably is kept encased in this shell up to the moment of application particularly if the raw compact contains hydration-type bi ding agents, which compact otherwise would require a packi to prevent it from being unintentionally subjected to mois ture during its transport and storage. A few suitable pro¬ duct embodiments are shown in the accompanying drawings, i which: Fig. 1 shows a string of a raw compact in a plastic shell according to a first embodiment; Fig. 2 shows a series of granule-shaped raw compacts in a long continuous plastic shell; Fig. 3 shows a section III-III in Fig. 2; and Fig. 4 shows a longitudinal section through a third possib embodiment of a raw compact in a impermeable plastic shell As regards the embodiment shown in Fig. 1, raw compact 1 simply comprises a straight even rod, which can have a cir cular or another cross-section and a thickness of e.g. 3-7 mm, if the material is designed for dental applications. The shell comprises a folded plastic film 2, which is lon¬ gitudinally sealed along one of the sides of " the shell, at 3a, and at its ends displays end seals 3b. The length of rod 1 can be e.g. 30-200 mm. Granules 4 according to Fig. 2 and 3 have a more or less spherical shape and are placed in a plastic shell 5, which e.g. can be shrink-sealed around granules 4 before the cold isostatic compaction. According to Fig. 4 raw compact 6 is instead designed as a rod, subdivided into sections 7 and v/eakenings 8 between the sections. An impermeable plastic shell 9 is used. In¬ stead of shells 3a, 5 and 9 respectively made of a plastic material it is possible to use shells made of another po¬ lymer, e.g. rubber. Subsequently to the compaction the intermediate product, obtained in this way, has developed a considerable bending strength and compression strength. Consequently, it is not easy to smash or break loose pieces of the raw compact. Thus, it is important that its size corresponds to the vo¬ lume of the desired final product or that the individual raw compacts are sufficiently small or that the raw compact has been designed with indications of fracture, so that smal pieces can be broken loose and.so that the final product can be easily reconstructed from a plurality of small raw compacts subsequent to the admixture of said liquid. These possibilities are available by means of the shown embodi¬ ments , reference being made to Figs. 1-4. The impregnation with said liquid, which will react with the binding agent, is done precisely when the CBC-product is to be used. The raw compact is then impregnated with the chosen liquid by moistening the raw compact with the liquid or by immersing the raw compact in the liquid. The pores of the raw compact now will function as capillaries, which suck in a suitable amount of the liquid. Due to the partial disintegration of the binding agent the strength o the raw compact decreases drastically; from a compression strength of about 10 MPa to a compression strength of abou 3 MPa. Consequently, the wet raw compact can now be broken and shaped into smaller pieces, if that is desirable. Con¬ sequently,, due to its initial disintegration its workabili ty v/ill be acceptable and it can e.g. be used as a tooth filling material. In case larger constructions are to be erected, a pluralit of raw compacts can be impregnated and subsequent to the impregnation be joined together to large units. The inven¬ tion particularly facilitates an in situ-adding of the li¬ quid, particularly a hydration-liquid in case the binding agent is one or several hydration-binding agents. The li¬ quid can in this case be e.g. sea water or water from lake and streams for underwater constructions, the impregnation v/ith water being carried out directly on the site of appli cation. In case the powder in the raw compact entirely comprises a binding agent, e.g. a cement material, then 30-60 % of the binding agent is dissolved by said liquid and is hardened by known reactions . The total dissolved amount depends on several factors, e.g. the size of the pulverulent grains, their shape and distribution, but also on the degree of co paction and the size of the raw compact are important in this respect, since the hydrates which are slowly formed will constitute diffusion barriers against additional wa¬ ter. The used aggregates can in this regard be utilized ac tively in order to maximize the hydration and the correspo ding reaction respectively in case other binding agents than hydration-materials are used. If it is assumed that the filling density in the raw compact is e.g. 67 % or 2/3 1/3 being pores, and assuming that 1/3 of the binding agen is "consumed", i.e. is dissolved by the liquid during the impregnation, it would be theoretically feasible to obtain a complete hydration, provided half the binding agent was replaced with the same volume portion aggregate material. In case the invention is to be used for the production of materials designed as permanent tooth fillings, the aggre¬ gate material preferably comprises needle-shaped titanium dioxide crystals, agglomerated to large particles having a size of 1-5 um , which has been described above. This aggre gate material has a very high whiteness, opacity and albedo. Also, it is completely stable to light, chemically inert, biocompatible and does not cause irritations or other types of discomfort in the oral cavity as regards dental applica¬ tions. This material comprises particles of pure titanium dioxide, comprising three-dimensional needle-shaped crystal having a star-shaped orientation. This material can be bough from e.g. TIL Central Laboratories, Stockton-on-Tees in Great Britain, under the trade name "Tilcom" . The thickness of the crystals is a few hundredths of a nanometer, but their length is several times larger. They are agglomerated to particles having a grain size of 0.5-10 um. Additional aspects of the invention are set forth in the following examples. EXAMPLE 1 A calcium aluminate cement, grade Secar 71 (manufactured by Lafarge) was used as a binding agent phase. Secar 71 is a mixture of CaOxAl 2 0 3 and CaOx2Al 2 ς> 3 . The medium grain size was about 15 um. An amount of about 5 cm of said binding agent powder was isostaticly compacted in a cold condition at a pressure of 300 MPa in an impermeable plastic shell to obtain parallelepiped-shape. The filling density of the raw compact was measured to 67.5 % efter the cold isostatic com paction. The plastic shell was removed and distilled water was added and the specimen was subsequently kept at 35°C and a relative humidity (RH) of 100 % for 24 hours. The strength, determined in a three-point bending test, was measured to 70 MPa. The open porosity of the specimen mea¬ sured according to an ASTM-method for porosity measurements was 1.7 %. EXAMPLE 2 Secar 71 according to Example 1 was isostaticly compacted in a cold condition as a block with the dimensions 4x4x8 cm at 320 MPa, and a raw compact having a density of 2.10 g/cm was obtained, which corresponds to a filling density of 70 . The block compacted isostaticly in a cold condition was cut up into a few test rods with the dimensions 40x3x3 mm. Distilled water was added, and substantially half of the specimens were kept in a moist environment (100% RH - relative humidity) and the rest in water at 37°C for vary¬ ing periods of time. Results as to the obtained medium ben¬ ding strength xn MPa, the open porosity (OP) and shrinkage (K) are given in the following table. TABLE 1 Specimen 1 day 7 days 120 days MPa OP % K % MPa OP % K % MPa OP % K % 100 % RH 66 1.4 <0.1 58 1.4 <0.1 64 1.0 <0.1 water 65 1.9 <0.1 58 1.3 <0.1 65 1.0 <0.1 EXAMPLE 3 In this example a cement material called OPC was used- (Ordi nary Portland Cement) .Consequentl , the cement material mainly comprised calcium silicates, CaOxSi0 2 and a small portion aluminum oxide, iron oxide etc. The cement powder had a medium grain size of about 10 um . The powder was isostaticly compacted in a cold condition at- MPa to a parallelepiped-shaped body having a volume of 30 3 cm . The raw compact was impregnated wxth ordinary tap wa- ter. The specimen was kept in water for 24 hours and subse¬ quently the density and the bending strength were measured, with the following results: TABLE 2 3 Specimen Density g/cm OP % Bending strength MPa OPC 2.63 0.9 40 + 4 EXAMPLE 4 In this example a calcium aluminate of a type which is calle Fondu (trade name) was used. The powder was isostaticly com¬ pacted in a cold condition in the same way as in Example 3. However, the storage time in water was 7 days. In this case the raw compact was impregnated with tap water, and subse¬ quently the specimen was treated in the same way as in Example 3, with the following results: TABLE 3 3 Specimen Density g/cm OP % Bending strength MPa Fondu 2.81 0.5 42 + 2 EXAMPLE 5 Cement powder of grade Secar 71., i.e. of the same type as i Example 1, was isostaticly compacted in a cold condition at 300 MPa to a cube v/ith the dimension 1 cm. Water was sucked into the specimen block, which subsequently could be disint grated into granules with the dimension 1-2 mm. The granule were pounded before 2 minutes had elapsed at a pressure of 5 MPa to a new cube, which was hydrated for 24 hours at 35° and 100 % RH, subsequent to which the compression strength was measured in a universal testing machi «ne, type Instron. The compression strength was measured to 270 MPa. EXAMPLE 6 Synthetic calcium aluminate cement, CaOxAl 2 0 3 , was ground in petroleum ether and was screened through a sieve having a mesh size of 100 u . About 40 g of the powder were isosta ticly compacted in a cold condition at 300 MPa. To water an a superplasticizer (grade Gohsenol; 79 % hydrolysed polyvi- nyl acetate) dissolved in the water a portion of the speci¬ men cube was added, while another portion of the specimen cube was centrifuged in the solution of water and superplas cizer at 6000 RPM. The specimen cube was not satisfactorily moistened v/ithout a centrifugation. The centrifuged specime was crushed to small granules and was treated subsequently in the same way as in Example 5. The resulting compressing strength of the final specimen cube was measured to 230 MPa EXAMPLE 7 A superplasticizer agent (grade Gohsenol) was added to an aluminate according to Example 6 and an admixture was carri out, partly in a dry condition and partly in a light petrol solution. Raw compacts were made of the powders by an isost tic compaction in a cold condition in a polymer tube. Water subsequently was forced through the tube. The tube was re¬ moved and the moinstened mass was pounded to a parallelepip with the dimensions 40x3x3 mm. The obtained bending strengt in the hardened specimens was measured to 49 + 7 MPa in the tv/o cases. EXAMPLE 8 To a cement raw material, grade Secar 71 (see Example 1) , boron nitride (of a type which is sold under the name HC Starck) , 5 percent by volume, was added. The boron nitride was a very fine pov/der, its grain fineness corresponding to 2 a specific surface of 3 m /g. The mixture was isostaticly compacted in a cold condition at 300 MPa. The obtained raw compact was impregnated with distilled water below 30°C. The moistened raw compact was subsequently crushed by sub¬ jecting it to a pressure of about 2 MPa. The granules ob- 18 tained in this way were pounded to a specimen block at a lo pressure. This pressure.was measured by a load sensor, con- nected.to the pounder, which comprised a cylinder having a diameter of 2.5 mm. The workability, i.e. the required pres sure to obtain en open porosity of not more than 2 % in a specimen, which has been hydrated for 24 hours at 35 C and 100 % RH, proved to be about 2 MPa lower than for the corre sponding specimen without any admixture of boron nitride. This example shows that boron nitride functions as a lubri cant v/hen the moistened raw compact is shaped. EXAMPLE 9 A cement raw material, grade Secar 71, according to Example 1, was mixed with 12 percent by volume fine-grained hydroxy apatite, which had a particle size less than 5 um , in a ba mill with petroleum ether and silicon nitride-cylpebs as a grinding agent (cylpebs = cylindrical pebbles; small cylind 3 rical grinding pebbles) . 8 cm of the powder mixture was is statically compacted in a cold condition at 300 MPa. The ob tained raw compact was impregnated with a hydration liquid comprising distilled v/ater, tap water or water admixed with 0.5 % of soluble chloride salts. The hydration was allowed to continue for 24 hours at 35 C and 100 % RH, subsequent t which a bending strength testing was done according to Exam 1. The mean strength of seven test rods was 61 MPa (the lo est value 42 MPa, the highest 93 MPa) , which shows that a substantial amount of a fine-grained aggregate phase can be added without a substantial decrease in the bending strengt (compare Example 1) and that the resulting strength mainly is not influenced by the degree of purity of the water, as far as this has been tested. EXAMPLE 10 To a calcium aluminate cement of the same grade as in Example 1, Secar 71, was added 35 percent by volume of a po lymer binding agent for injection molding, comprising a mix ture of polyethylene and ethyl vinyl acetate. The mixture o aluminate cement and polymer powder was homogenized in a mixer, type Brabender, and was injection molded at a pres¬ sure of 1200 bars to a parallelepiped. The polymer was sub¬ sequently vaporized by heating to 400 C. The filling densi ty was then 65.5 %. The porous raw compact obtained in thi way subsequently was impregnated with distilled water, ad¬ mixed v/ith 0.035 moles of a chloride salt and the moistene body was placed in water at ambient temperature. After a p riod of 24 hours its compression strength was 210 MPa. The rupture toughness of the material was measured by the i - L- pression method using a Vicker-diamond to 2.8 MPam 2 . EXAMPLE 11 A calcium aluminate cement of the same grade as in Example 1, Secar 71, was ground for 48 hours and was sieved throug a sieve having a mesh-size of 5 um. A portion of the fine- sieved powder was hydrated in water for 24 hours and the powder was completely hydrated. The slurry was evaporated and a hydrated powder fraction was obtained. Similar amoun of the fine-sieved powder and the hydrated powder were sub sequently admixed with the hydrated powder fraction. The mixture was isostaticly compacted in a cold condition at 300 MPa. In the body obtained in this way the prehydrated phase is an aggregate material, because it can not react further with water. The raw compact obtained in this way can be impregnated with a hydration liquid in the way de¬ scribed in the examples above.. The water which is sucked i to the body essentially corresponds to the volume of the po system and reacts with the non-hydrated calcium aluminate cement phase to the extent that after 24 hours essentially no non-reacted phase remains. In this way a volume increas due to a diffusion of additional water and consequently an additional hydration is prevented, which would mean a hyd¬ ration above the available pore volume. By the process de¬ scribed in the example it is possible to obtain a final pr duct having a bending strength of about 60 MPa. EXAMPLE 12 A gypsum powder - CaSO.x^H- j O - was compacted by an iso¬ static compaction in a cold condition at 300 MPa. The raw compact obtained a density corresponding to 66 % of the theoretical density. Water was subsequently added to it an it was hydrated for 24 hours. Ten specimen rods (35x3x3 mm were cut. The strength was measured by the three-point ben ding test to 34 MPa (mean value; the lowest value 28 MPa and the highest 39 MPa) . This strength exceeded the streng of ordinary gypsum more than five-fold. The density was 2. 3 g/cm , which is close to the theoretical maximum density, 3 which is 2.32 - 2.37 g/cm . This means that the porosity at least is less than 1 %. The present invention can of course be varied within the scope of protection defined by the following patent claims and other substances than those described in the preceding description can of course be added. Thus, it is possible to add to the mixture of binding agents, a liquid and pos¬ sibly aggregates also accelerators or retarders in order to speed up or suppress the hardening reaction.

Claims: CLAIMS 1. Method for the production of a chemically bonded ceramic product by a reaction between one or several pulverulent binding agents as well as a liquid reacting with these bin¬ ding agents, which ceramic product also can include one or several aggregate materials, which essentially do not par¬ ticipate in the chemical hardening reactions, c h a r a c t e r i z e d in that a powder body comprising said bin¬ ding agent (s) and possibly aggregate materials without the addition of said liquid is compacted by subjecting, before impregnating said rav/ compact with said liquid, said powder body to such a high external pressure and at such a low tem perature, that without sintering reactions when carrying out the compaction a thorougly integrated raw compact is obtained, in which the filling density has increased to at least 1.3 times the initial filling density, which is de¬ fined as the filling density v/hich is obtained by shaking, vibrating and/or carefully packing the loose powder in a container. 2. Method according to claim 1, c h a r a c t e r i z e d in that said pov/der body is compacted by mechanical pres¬ sing, preferably cold isostatic compaction. 3. Method according to claim 1, c h a r a c t e r i z e d in that said powder body also comprises an organic lubri¬ cant or binding agent, in that said powder body is shaped and compacted by injection molding or extrusion, in that said organic lubricant or binding agent is evaporized, a porous raw compact being obtained, and in that the raw com¬ pact obtained in this way is impregnated with said liquid. 4. Method according to any of claims 1-3, c h a r a c ¬ t e r i z e d in that said first binding agent is one or several hydraulic binding agents, the hydration phase be¬ longing to that group of compounds, which comprises alumi- nates, silicates, phosphates and sulphates, and in that sai liquid is a hydration liquid comprising water and substance dissolved in the water. 5. Method according to any of claims 1-3, c h a r a c ¬ t e r i z e d in that said first binding agent mainly is one or several oxides, preferably mainly zinc oxide, and in that said liquid is one or several acids, preferably mainly orthophosphoric acid. 6. Method according to claim 1, c h a r a c t e r i z e d in that said raw compact or a separate part of the same is impregnated with said liquid by allowing the liquid to be sucked into the body by capillary forces acting inside the body. 7. Method according to claim 1, c h a r a c t e r i z e d in that said rav/ compact or a part of the same is impregna¬ ted with said liquid partly by allowing the liquid to be sucked into the body by capillary forces acting inside the body and partly by centrifuging, shaking or vibrating said raw compact or said separate part or by subjecting said ra compact or said separate part to a similar treatment in the liquid. 8. Method according to claim 1, c h a r a c t e r i z e d in that when producing said raw compact the filling density is increased to at least 1.5 and preferably at least 1.8 times the initial filling density. 9. Method according to claim l, c h a r a c t e r i z e d in that said compaction is carried out at a temperature less than 100 C, preferably at ambient temperature. 10. Method according to any of the preceding claims, c h a r a c t e r i z e d in that said raw compact is de¬ signed as a narrow string or a thin disc, possibly provided with fractual impressions. 11. Method according to claims 1-9, c h a r a c t e r i z e in that said raw compact is shaped as granules. 12. Method according to any of claims 1-11, c h a r a c ¬ t e r i z e d in that said powder body is encased in a plas tic shell and in that it is subjected to a cold isostatic compaction in a liquid in said plastic shell. 13. Method according to claim 1, c h a r a c t e r i z e d in that the optimal amount and content of said liquid de¬ pends on the degree of compaction and the corresponding amount of liquid, which by capillary forces is sucked into said rav/ compact. 14. Method according to claim 1, c h a r a c t e r i z e d in that a plurality of impregnated raw compacts are joined in order to build larger constructions. 15. Method according to claim 2, c h a r a c t e r i z e d in that said raw compact is hydrated in situ in a v/ater en¬ vironment, preferably for underv/ater constructions. 16. Method according to claim 1, c h a r a c t e r i z e d in that said pov/der body includes up to 50 percent by volume aggregates. 17. Method according to claim 16, c h a r a c t e r i z e d in that said powder body includes 5-25 percent by volume aggregates. 18. Method according to claim 1, c h a r a c t e r i z e d in that said powder body includes 25-50 percent by volume aggregates. 19. Method according to any of claims 1-18, c h a r a c ¬ t e r i z e d in that said binding agent is a hydration- binding agent and in that said aggregates completely or part ly are hydroxylapatite or solid solutions thereof and/or oxides of preferably titanium, zirconium, zinc and alumi¬ num. 20. Method according to any of claims 1-19, c h a r a c ¬ t e r i z e d in that said powder body includes 5-15 per¬ cent by volume boron nitride. 21. Method according to any of claims 1-19, c h a r c ¬ t e r i z e d in that said aggregates completely or partly are shaped as whiskers or fibers. 22. Method according to any of claims 1-19, c h a r a c ¬ t e r i z e d in that said powder body includes 5-20 per¬ cent by volume of a granulate, consisting of outwardly pro¬ jecting , needle-shaped crystals of mainly titanium dioxide 23. Method according to claim 22, c h a r a c t e r i z e d in that said titanium dioxide is etched. 24. Method according to claims 1-23, c h a r a c t e ¬ r i z e d in that said aggregate material comprises a mate rial , which is more fine-grained than said binding agent phase and in that it preferably has a mean grain size of less than 10 um . 25. Method according to any of claims 1-23, c h a r a c ¬ t e r i z e d in that said aggregate material is coarser than said binding agent phase, more precisely in that said binding agent phase in said powder body mainly has a partic size of between 1 and 20 um, while said aggregate material comprises a powder having grain sizes mainly between 5 and 50 um. 26. Method according to any of the preceding claims, c h a r a c t e r i z e d in that a certain amount of a powder of the same type as said binding agent phase is hydrated and subsequently is admixed with a non-hydrated pulverulen binding agent, and in that the powder mixture subsequently possibly jointly with additional aggregate materials , is compacted, the prehydrated powder constituting an aggregat material in said raw compact.

Inventors: FORBERG SEVALD, HERMANSSON LEIF, JIANGUO LI, FORBERG, SEVALD, HERMANSSON, LEIF, JIANGUO, LI
Applicants: DOXA CERTEX AB, DOXA CERTEX AKTIEBOLAG
Application year: 1990
Main classification: A61K6
IPC codes: A61K6