Patent Publication Number: US-2007108672-A1

Title: Method for producing molybdenum metal and molybdenum metal

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This is a divisional of co-pending U.S. patent application Ser. No. 10/719,234, filed Nov. 20, 2003, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/464,324, filed on Jun. 18, 2003, which is a divisional application of U.S. Pat. No. 6,626,976, issued Sep. 30, 2003, which are hereby incorporated herein by reference for all that they disclose. 
    
    
     FIELD OF THE INVENTION  
      The invention generally pertains to molybdenum, and more specifically, to molybdenum metal and production thereof.  
     BACKGROUND OF THE INVENTION  
      Molybdenum (Mo) is a silvery or platinum colored metallic chemical element that is hard, malleable, ductile, and has a high melting point, among other desirable properties. Thus, molybdenum is commonly used as an additive for metal alloys to impart various properties thereto, and hence to enhance the properties of the metal alloy. For example, molybdenum may be used as a hardening agent, especially for high-temperature applications. However, molybdenum does not naturally occur in pure form. Instead, molybdenum occurs in a combined state. For example, molybdenum ore typically exists as molybdenite (molybdenum disulfide, MoS 2 ). The molybdenum ore may then be processed by roasting it to form molybdic oxide, MoO 3 .  
      Molybdic oxide may be directly combined with other metals, such as steel and iron, to form alloys thereof, or molybdic oxide may be further processed to form pure molybdenum. In its pure state, molybdenum metal is tough and ductile and is characterized by moderate hardness, high thermal conductivity, high resistance to corrosion, and a low expansion coefficient. Therefore, molybdenum metal may be used for electrodes in electrically heated glass furnaces, nuclear energy applications, and for casting parts used in missiles, rockets, and aircraft. Molybdenum metal may also be used as a filament material in various electrical applications that are subject to high temperatures, such as X-ray tubes, electronic tubes and electric furnaces. In addition, molybdenum metal is often used as a catalyst (e.g., in petroleum refining), among other uses or applications.  
      Processes have been developed for producing molybdenum metal in its pure state. Such a process involves a two-step process. In the first step, a mixture of molybdenum tri-oxide and ammonium di-molybdate is introduced to a first furnace (e.g., a rotary kiln or fluidized bed furnace) to yield molybdenum dioxide, as expressed by the following formula: 
 
2(NH 4 )MoO 4 +2MoO 3 →3MoO 2 +4H 2 O+N 2 (g)   (1) 
 
 In the second step, the molybdenum dioxide is transferred to a second furnace (e.g., a pusher furnace) and reacted with hydrogen to form molybdenum powder, for example, as expressed by the following formula: 
 
MoO 2 +2H 2 (g)→Mo+2H 2 O 
 
      However, this process for producing molybdenum metal requires multiple batch steps, which is labor intensive, slows production, and increases production costs in addition, this process requires separate processing equipment (e.g., furnaces) for each step, which increases capital costs and maintenance costs. Furthermore, these processes only produce molybdenum metal having a surface area of about 0.8 square meters per gram (m 2 /g), or less, and may vary widely in size.  
     SUMMARY OF THE INVENTION  
      An apparatus for producing molybdenum metal according to the present invention may comprise a furnace, the furnace defining at least two heating zones of substantially equal length, the furnace maintaining each of the two heating zones at temperatures not greater than about 1200° C.; a supply of precursor material; a process tube extending through each of the two heating zones of the furnace, wherein the precursor material is introduced into the process tube and moved through each of the two heating zones of the furnace; a pressure regulator operatively associated with the process tube, the pressure regulator maintaining an interior region of the process tube at a substantially constant pressure greater than an ambient pressure; and a supply of process gas operatively associated with the process tube, whereby the process gas is introduced into the process tube such that the process gas reacts with the precursor material within the furnace to form the molybdenum metal.  
      In another embodiment, the furnace may comprise three heating zones of substantially equal length, the furnace maintaining the three heating zones at temperatures no greater than about 1200° C., and the process tube extending through each of the three heating zones.  
      In an additional embodiment, the apparatus may comprise a feed system linked to the process tube for introducing the precursor material into the process tube at a substantially constant rate.  
      In still another embodiment, the apparatus may comprise a scrubber operatively associated with the process tube. The scrubber may also comprise a dry pot fluidically connected to the process tube and a wet pot fluidically connected to the dry pot, the wet pot containing water therein.  
      In yet another embodiment apparatus for producing molybdenum metal may comprise a furnace defining a first heating zone and a second heating zone, the heating zones being of substantially equal length, the furnace maintaining the first heating zone at a temperature in a range of about about 540° C. to about 600° C., and the furnace maintaining the second heating zone at a temperature in a range of about 980° C. to about 1050° C.; a process tube having a proximal end and a distal end, the process tube extending through the first and second heating zones defined by the furnace, the distal end of the process tube extending beyond the second heating zone and comprising a cooling zone; a supply of precursor material operatively associated with the process tube; a supply of reducing gas operatively associated with the distal end of the process tube; and a pressure regulator operatively associated with the process tube, the pressure regulator maintaining an interior region of the process tube at a substantially constant pressure, the substantially constant pressure being greater than an ambient pressure.  
      Another embodiment may comprise a discharge hopper operatively associated with the distal end of the process tube, the discharge hopper collecting the molybdenum metal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Illustrative and presently preferred embodiments of the invention are illustrated in the drawings, in which:  
       FIG. 1  is a cross-sectional schematic representation of one embodiment of apparatus for producing molybdenum metal according to the invention;  
       FIG. 2  is a cross-sectional view of three sections of a process tube illustrating molybdenum metal production;  
       FIG. 3  is a flow chart illustrating an embodiment of a method for producing molybdenum metal according to the invention;  
       FIG. 4  is a scanning electron microscope image of molybdenum metal, such as may be produced according to prior art processes; and  
       FIG. 5  is a scanning electron microscope image of novel forms of molybdenum metal such as may be produced according to one embodiment of the invention 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Apparatus  10  ( FIG. 1 ) is shown and described herein as it may be used to produce molybdenum metal  12 . Briefly molybdenum metal does not occur naturally, but rather it occurs in a combined state, such as in an ore. Molybdenum ore may be processed to form molybdic oxide (MoO 3 ), which may be further processed in the presence of ammonium di-molybdate and hydrogen to form pure molybdenum metal. Conventional batch processes for producing molybdenum metal may be time consuming and relatively costly. Instead, it may be desirable to produce molybdenum metal on a continuous basis, particularly for industrial or commercial applications. For various applications it may also be desirable to produce molybdenum metal having a relatively uniform size and/or having a larger surface area to mass ratio than molybdenum metal that may be conventionally produced.  
      According to the teachings of the invention, novel forms of molybdenum metal  12  may be characterized as having a surface area to mass ratio of substantially 2.5 m 2 /g according to BET analysis. Also according to the teachings of the invention, novel forms of molybdenum metal  12  may be characterized as substantially uniform in size (see  FIG. 5 ).  
      Novel forms of molybdenum metal characterized according to embodiments of the invention are advantageous in and of themselves for various uses or applications. For example, molybdenum metal that is characterized by a relatively high surface area to mass ratio is particularly advantageous when used as a catalyst. That is, less molybdenum metal is required on a mass basis when used as a catalyst to achieve similar or even better results than when molybdenum metal characterized by a smaller surface area to mass ratio is used as a catalyst in the same reactions. Also for example, molybdenum metal characterized by a relatively large surface area to mass ratio and/or a relatively uniform size may be advantageous for use as a sintering agent. That is, the molybdenum-sintering agent has a higher bonding area than conventional molybdenum sintering agents, thereby enhancing the resulting sinter. These novel forms of molybdenum metal may also be particularly advantageous for other uses or applications not specifically called out herein.  
      Also according to the teachings of the invention, embodiments of apparatus  10  for producing molybdenum metal  12  are disclosed. Apparatus  10  may comprise a furnace  16  having at least two, and preferably three heating zones  20 ,  21 , and  22 . A process tube  34  preferably extends through the furnace  16  so that a precursor material  14  (e.g., MoO 3 ) may be introduced into the process tube  34  and moved through the heating zones of the furnace  16 , such as is illustrated by arrow  26  shown in  FIG. 1 . Also preferably, a process gas  62  may be introduced into the process tube  34 , such as is illustrated by arrow  28  shown in  FIG. 1 . Accordingly, the precursor material  14  is reduced to form or produce molybdenum metal  12 .  
      Apparatus  10  may be operated as follows for producing molybdenum metal  12  from a precursor material  14  (e.g., molybdic oxide (MoO 3 )). As one step in the process, the precursor material is heated to a first temperature (e.g., in Heating Zone  1  of furnace  16 ) in the presence of a reducing gas  64 . The first temperature is increased at least once (e.g., in Heating Zone  3 , and also preferably in Heating Zone  2 ) to reduce the precursor material  14  and form the molybdenum metal  12 .  
      Accordingly, molybdenum metal  12  may be produced in a continuous manner. Preferably, no intermediate handling is required during production of the molybdenum metal product  12 . That is, the precursor material  14  is preferably fed into a product inlet end  15  of furnace  16 , and the molybdenum metal product  12  is removed from a product discharge end  17  of furnace  16 . Thus, for example, the intermediate product  30  ( FIG. 2 ) need not be removed from one furnace or batch process and transferred to another furnace or batch process. As such, production of molybdenum metal  12  according to embodiments of the invention is less labor intensive and production costs may be lower than conventional processes for producing molybdenum metal. In addition, large-scale production plants may be more efficiently designed. For example, less equipment may be required for producing molybdenum metal  12  according to embodiments of the invention than may be required for conventional batch processes. Also for example, intermediate staging areas are not required according to embodiments of the invention.  
      Having generally described novel forms of molybdenum metal and apparatus and methods for production thereof, as well as some of the more significant features and advantages of the invention the various embodiments of the invention will now be described in further detail.  
     Apparatus for Producing Molybdenum Metal  
       FIG. 1  is a schematic representation of an embodiment of apparatus  10  for producing molybdenum metal  12  according to embodiments of the invention. As an overview, the apparatus  10  may generally comprise a furnace  16 , a transfer system  32 , and a process gas  62 , each of which will be explained in further detail below. The transfer system  32  may be used to introduce a precursor material  14  into the furnace  16  and move it through the furnace  16 , for example, in the direction illustrated by arrow  26 . In addition, the process gas  62  may be introduced into the furnace  16 , for example, in the direction illustrated by arrow  28 . Accordingly, the process gas  62  reacts with the precursor material  14  in the furnace  16  to form molybdenum metal product  12 , as explained in more detail below with respect to embodiments of the method of the invention.  
      A preferred embodiment of apparatus  10  is shown in  FIG. 1  and described with respect thereto. Apparatus  10  preferably comprises a rotating tube furnace  16 . Accordingly, the transfer system  32  may comprise at least a process tube  34  extending through three heating zones  20 ,  21 , and  22  of the furnace  16 , and through a cooling zone  23 . In addition, the transfer system  32  may also comprise a feed system  36  for feeding the precursor material  14  into the process tube  34 , and a discharge hopper  38  at the far end of the process tube  34  for collecting the molybdenum metal product  12  that is produced in the process tube  34 .  
      Before beginning a more detailed description of preferred embodiments of apparatus  10 , however, it should be clear that other embodiments of the furnace  16  and the transfer system  32  are contemplated as being within tie scope of the invention. The furnace may comprise any suitable furnace or design thereof, and is not limited to the rotating tube furnace  16 , shown in  FIG. 1  and described in more detail below. For example, according to other embodiments of the invention, the furnace  16  may also comprise, but is not limited to, more than one distinct furnace (e.g., instead of the single furnace  16  having separate heating zones  20 ,  21 ,  22  that are defined by refractory dams  46  and  47 ). Likewise, the transfer system  32 , shown in  FIG. 1  and described in more detail below, may comprise a variety of other means for introducing the precursor material  14  into the furnace  16 , for moving the precursor material  14  through the furnace  16 , and/or for collecting the molybdenum metal product  12  from the furnace  16 . For example, in other embodiments the transfer system  32  may comprise manual introduction (not shown) of the precursor material  14  into the furnace  16 , a conveyor belt (not shown) for moving the precursor material  14  through the furnace  16 , and/or a mechanical collection arm (not shown) for removing the molybdenum metal product  12  from the furnace  16 . Other embodiments of the furnace  16 , and the transfer system  32 , now known or later developed, are also contemplated as being within the scope of the invention, as will become readily apparent from the following detailed description of preferred embodiments of apparatus  10 .  
      Turning now to a detailed description of preferred embodiments of apparatus  10 , a feed system  36  may be operatively associated with the process tube  34 . The feed system  36  may continuously introduce the precursor material  14  into the furnace  16 . In addition, the feed system  36  may also introduce the precursor material  14  into the furnace  16  at a constant rate. For example, the feed system  36  may comprise a loss-in-weight feed system for continuously introducing the precursor material  14  into one end of the process tube  34  at a constant rate.  
      It is understood that according to other embodiments of the invention, the precursor material  14  may be otherwise introduced into the furnace  16 . For example, the feed system  36  may feed the precursor material  14  into the furnace  16  on an intermittent basis or in batch. Other designs for the feed system  36  are also contemplated as being within the scope of the invention and may differ depending upon design considerations and process parameters, such as the desired rate of production of the molybdenum metal product  12 .  
      In any event, the precursor material  14  is preferably introduced into the furnace  16  by feeding it into the process tube  34 . The process tube  34  preferably extends through a chamber  44  that is formed within the furnace  16 . The process tube  34  may be positioned within the chamber  44  so as to extend substantially through each of the heating zones  20 ,  21 , and  22  of the furnace  16 . Preferably, the process tube  34  extends in approximately equal portions through each of the heating zones  20 , although this is not required. In addition, the process tube  34  may further extend beyond the heating zones  20 ,  21 , and  22  of the furnace  16  and through a cooling zone  23 .  
      According to preferred embodiments of the invention, the process tube  34  is a gas-tight, high temperature (HT) alloy process tube. The process tube  34  also preferably has a nominal external diameter of about 16.5 centimeters (cm) (about 6.5 inches (in)), a nominal internal diameter of about 15.2 cm (about 6 in), and is about 305 cm (about 120 in) long. Preferably, about 50.8 cm (about 20 in) segments of the process tube  34  each extend through each of the three heating zones  20 ,  21 , and  22  of the furnace  16 , and the remaining approximately 152.4 cm (60 in) of the process tube  34  extend through the cooling zone  23 .  
      In other embodiments of the invention, however, the process tube  34  may be manufactured from any suitable material. In addition, the process tube  34  need not extend equally through each of the heating zones  20 ,  21 , and  22  and/or the cooling zone  23 . Likewise, the process tube  34  may be any suitable length and diameter. The precise design of the process tube  34  will depend instead on design considerations, such as the feed rate of the precursor material  14 , the desired production rate of the molybdenum metal product  12 , the temperature for each heating zone  20 ,  21 , and  22 , among other design considerations readily apparent to one skilled in the art based on the teachings of the invention.  
      The process tube  34  is preferably rotated within the chamber  44  of the furnace  16 . For example, the transfer system  32  may comprise a suitable drive assembly operatively associated with the process tube  34 . The drive assembly may be operated to rotate the process tube  34  in either a clockwise or counter-clockwise direction, as illustrated by arrow  42  in  FIG. 1  Preferably, the process tube  34  is rotated at a constant rate. The rate is preferably selected from the range of approximately 18 to 100 seconds per revolution. For example, the process tube  34  may be rotated at a constant rate of 18 seconds per revolution. However, the process tube  34  may be rotated faster, slower and/or at variable rotational speeds, as required depending on design considerations, desired product size and the set points of other process variables as would be apparent to persons having ordinary skill in the art after having become familiar with the teachings of the invention.  
      The rotation  42  of the process tube  34  may facilitate movement of the precursor material  14  and the intermediate material  30  ( FIG. 2 ) through the heating zones  20 ,  21 , and  22  of the furnace  16 , and through the cooling zone  23 . In addition, the rotation  42  of the process tube  34  may facilitate mixing of the precursor material  14  and the intermediate material  30 . As such, the unreacted portion of the precursor material  14  and the intermediate material  30  is continuously exposed for contact with the process gas  62 . Thus, the mixing may further enhance the reaction between the precursor material  14  and the intermediate material  30  and the process gas  62 .  
      In addition, the process tube  34  is preferably positioned at an incline  40  within the chamber  44  of the furnace  16 . One embodiment for inclining the process tube  34  is illustrated in  FIG. 1 . According to this embodiment of the invention, the process tube  34  may be assembled on a platform  55 , and the platform  55  may be hinged to a base  56  so that the platform  55  may pivot about an axis  54 . A lift assembly  58  may also engage the platform  55 . The lift assembly  58  may be operated to raise or lower one end of the platform  55  with respect to the base  56 . As the platform  55  is raised or lowered, the platform  55  rotates or pivots about the axis  54 . Accordingly, the platform  55 , and hence the process tube  34 , may be adjusted to the desired incline  40  with respect to the grade  60 .  
      Although preferred embodiments for adjusting the incline  40  of the process tube  34  are shown and described herein with respect to apparatus  10  in  FIG. 1 , it is understood that the process tube  34  may be adjusted to the desired incline  40  according to any suitable manner. For example, the process tube  34  may be fixed at the desired incline  40  and thus need not be adjustably inclined. As another example, the process tube  34  may be inclined independently of the furnace  16 , and/or the other components of apparatus  10  (e.g., feed system  36 ). Other embodiments for inclining the process tube  34  are also contemplated as being within the scope of the invention, and will become readily apparent to one skilled in the art based upon an understanding of the invention.  
      In any event, the incline  40  of the process tube  34  may also facilitate movement of the precursor material  14  and intermediate material  30  through the heating zones  20 ,  21 , and  22  of the furnace  16 , and through the cooling zone  23 . In addition, the incline  40  of the process tube  34  may facilitate mixing of the precursor material  14  and intermediate material  30  within the process tube  34 , and expose the same for contact with the process gas  62  to enhance the reactions between the precursor material  14  and/or the intermediate material  30  and the process gas  62 . Indeed, the combination of the rotation  42  and the incline  40  of the process tube  34  may further enhance the reactions for forming molybdenum metal product  12 .  
      As previously discussed, the furnace  16  preferably comprises a chamber  44  formed therein. The chamber  44  defines a number of controlled temperature zones surrounding the process tube  34  within the furnace  16 . In one embodiment, three temperature zones  20 ,  21 , and  22  are defined by refractory dams  46  and  47 . The refractory dams  46  and  47  are preferably closely spaced to the process tube  34  so as to discourage the formation of convection currents between the temperature zones. In one embodiment, for example, the refractory dams  46  and  47  come to within approximately 1.3 to 1.9 cm (0.5 to 0.75 in) from the process tube  34  to define three heating zones  20 ,  21 , and  22  in the furnace  16 . In any event, each of the three heating zones are preferably respectively maintained at the desired temperatures within the chamber  44  of the furnace  16 . And hence, each segment of the process tube  34  is also maintained at the desired temperature, as shown in more detail in  FIG. 2  discussed below.  
      Preferably, the chamber  44  of the furnace  16  defines the three heating zones  20 ,  21 , and  22  shown and described herein with respect to  FIG. 1 . Accordingly, the precursor material  14  may be subjected to different reaction temperatures as it is moved through each of the heating zones  20 ,  21 , and  22  in the process tube  34 . That is, as the precursor material  14  is moved through the process tube  34  and into the first heating zone  20 , the precursor material  14  is subjected to the temperature maintained within the first heating zone. Likewise, as the precursor material  14  is moved through the process tube  34  from the first heating zone  20  and into the second heating zone  21 , it is subjected to the temperature maintained within the second heating zone.  
      It is understood that the heating zones  20 ,  21 , and  22  may be defined in any suitable manner. For example, the heating zones  20 ,  21 , and  22  may be defined by baffles (not shown), by a number of separate chambers (not shown), etc. Indeed, the heating zones  20 ,  21 , and  22  need not necessarily be defined by refractory dams  46 ,  47 , or the like. As an example, the process tube  34  may extend through separate, consecutive furnaces (not shown). As another example, the chamber  44  of the furnace  16  may be open and a temperature gradient may be generated within the chamber  44  to extend from one end of the chamber  44  to the opposite end of the chamber  44  using separate heating elements spaced along the length thereof.  
      It is also understood that more than three heating zones (not shown) may be defined within the furnace  16 . According to yet other embodiments of the invention, fewer than three heating zones (also not shown) may be defined in the furnace  16 . Still other embodiments will occur to those skilled in the art based on the teachings of the invention and are also contemplated as being within the scope of the invention,  
      The furnace  16  may be maintained at the desired temperatures using suitable temperature control means. In preferred embodiments, each of the heating zones  20 ,  21 , and  22  of the furnace  16  are respectively maintained at the desired temperatures using suitable heat sources, temperature control, and over-temperature protection. For example, the heat source may comprise independently controlled heating elements  50 ,  51 , and  52  positioned within each of the heating zones  20 ,  21 , and  22  of the furnace  16 , and linked to suitable control circuitry.  
      In one preferred embodiment, the temperature is regulated within the three heating zones  20 ,  21 , and  22  of the furnace  16  by twenty-eight silicon-carbide, electrical-resistance heating elements. The heating elements are linked to three Honeywell UDC3000 Microprocessor Temperature Controllers (i.e., one controller for each of the three heating zones  20 ,  21 , and  22 ) for setting and controlling the temperature thereof. In addition, three Honeywell UDC2000 Microprocessor Temperature Limiters (i.e., also one controller for each of the three heating zones  20 ,  21 , and  22 ) are provided for over-temperature protection. It is understood, however, that any suitable temperature regulating means may be used to set and maintain the desired temperature within the furnace  16 . For example, the heating elements need not necessarily be electronically controlled and may instead be manually controlled.  
      Although each of the heating zones are preferably maintained at relatively uniform temperatures, respectively, it is apparent that conduction and convection of heat may cause a temperature gradient to be established within one or more of the heating zones  20 ,  21 , and  22 . For example, although the refractory dams  46 ,  47  are spaced approximately 1.3 to 1.9 cm (0.5 to 0.75 in) from the process tube  34  to reduce or minimize the transfer or exchange of heat between the heating zones  20 ,  21 , and  22 , some heat exchange may still occur therebetween. Also for example, the process tube  34  and/or the precursor material and/or intermediate material may also conduct heat between the heating zones  20 ,  21 , and  22 . Therefore, the temperature measured at various points within each of the heating zones  20 ,  21 , and  22  may be several degrees cooler or several degrees warmer (e.g., by about 50 to 100° C.) than the center of the heating zones  20 ,  21 , and  22 . Other designs are also contemplated to further reduce the occurrence of these temperature gradients, such as sealing the refractory dams  46 ,  47  about the process tube  34 . In any event, the temperature settings for each of the heating zones  20 ,  21 , and  22  are preferably measured in the center of each of the heating zones  20 ,  21 , and  22  to more accurately maintain the desired temperature therein.  
      Preferably, the cooling zone (illustrated by outline  23  in  FIG. 1 ) comprises a portion of the process tube  34  that is open to the atmosphere. Accordingly, the molybdenum metal product  12  is allowed to cool prior to being collected in the collection hopper  38 . However, according to other embodiments of the invention, the cooling zone  23  may be one or more enclosed portions of apparatus  10 . Likewise, suitable temperature regulating means may be used to set and maintain the desired temperature within the enclosed cooling zone  23 . For example, a radiator may circulate fluid about the process tube  34  in cooling zone  23 . Or for example, a fan or blower may circulate a cooling gas about the process tube  34  in cooling zone  23 .  
      The process gas  62  is preferably introduced into the furnace  16  for reaction with the precursor material  14  and the intermediate product  30 . According to preferred embodiments of the invention, the process gas  62  may comprise a reducing gas  64  and an inert carrier gas  65 . The reducing gas  64  and the inert carrier gas  65  may be stored in separate gas cylinders near the far end of the process tube  34 , as shown in  FIG. 1 . Individual gas lines, also shown in  FIG. 1 , may lead from the separate gas cylinders to a gas inlet  25  at the far end of the process tube  34 . A suitable gas regulator (not shown) may be provided to introduce the reducing gas  64  and the inert carrier gas  65  from the respective gas cylinders into the process tube  34  in the desired proportions and at the desired rate.  
      According to embodiments of the invention, the reducing gas  64  may be hydrogen gas, and the inert carrier gas  65  may be nitrogen gas. However, it is understood that any suitable reducing gas  64 , or mixture thereof, may be used according to the teachings of the invention. Likewise, the inert carrier gas  65  may be any suitable inert gas or mixture of gases. The composition of the process gas  62  will depend on design considerations, such as the cost and availability of the gases, safety issues, and desired rate of production, among other considerations.  
      Preferably, the process gas  62  is introduced into the process tube  34  and directed through the cooling zone  23  and through each of the heating zones  20 ,  21 , and  22 , in a direction opposite (i.e., counter-current, as illustrated by arrow  28 ) to the direction  26  that the precursor material  14  is moved through each of the heating zones  20 ,  21 , and  22  of the furnace  16 , and through the cooling zone  23 . Directing the process gas  62  through the furnace  16  in a direction that is opposite or counter-current  28  to the direction  26  that the precursor material  14  is moving through the furnace  16  may increase the rate of the reaction of the precursor material  14  and the intermediate material  30  ( FIG. 2 ) with the reducing gas  64 . That is, the process gas  62  comprises higher concentrations of the reducing gas  64  when it is initially introduced to the process tube  34  and is thus likely to more readily react with the remaining or unreacted portion of the precursor material  14  and/or the intermediate material  30  at the far end of the process tube  34 .  
      The unreacted process gas  62  that flows upstream toward the entry of the process tube  34  thus comprises a lower concentration of the reducing gas  64 . However, presumably a larger surface area of unreacted precursor material  14  is available at or near the entry of the process tube  34 . As such, smaller concentrations of reducing gas  64  may be required to react with the precursor material  14  at or near the entry of the process tube  34 . In addition, introducing the process gas  62  in such a manner may enhance the efficiency with which the reducing gas  64  is consumed by the reaction therebetween, for reasons similar to those just explained.  
      It is understood that in other embodiments of the invention the process gas  62  may be introduced in any other suitable manner. For example, the process gas  62  may be introduced through multiple injection sites (not shown) along the length of the process tube  34 . Or for example, the process gas  62  may be premixed and stored in its combined state in one or more gas cylinders for introduction into the furnace  16 . These are merely exemplary embodiments, and still other embodiments are also contemplated as being within the scope of the invention.  
      The process gas  62  may also be used to maintain the internal or reaction portion of the process tube  34  at a substantially constant pressure, as is desired according to preferred embodiments of the invention. Indeed, according to one preferred embodiment of the invention, the process tube  34  is maintained at about 8.9 to 14 cm (about 3.5 to 5.5 in) of water pressure (gauge). The process tube  34  may be maintained at a constant pressure, according to one embodiment of the invention, by introducing the process gas  62  at a predetermined rate, or pressure, into the process tube  34 , and discharging the unreacted process gas  62  at a predetermined rate, or pressure, therefrom to establish the desired equilibrium pressure within the process tube  34 .  
      Preferably, the process gas  62  (i.e., the inert carrier gas  65  and the unreacted reducing gas  64 ) is discharged from the process tube  34  through a scrubber  66  at or near the entry of the process tube  34  to maintain the process tube  34  at a substantially constant pressure. The scrubber  66  may comprise a dry pot  67 , a wet pot  68 , and a flare  69 . The dry pot  67  is preferably provided upstream of the wet pot  68  for collecting any dry material that may be discharged from the process tube  34  to minimize contamination of the wet pot  68 . The process gas  62  is discharged through the dry pot  67  and into water contained in the wet pot  68 . The depth of the water that the process gas  62  is discharged into within the wet pot  68  controls the pressure of the process tube  34 . Any excess gas may be burned at the flare  69 .  
      Other embodiments for maintaining the process tube  34  at a substantially constant pressure are also contemplated as being within the scope of the invention. For example, a discharge aperture (not shown) may be formed within a wall  74  ( FIG. 2 ) of the process tube  34  for discharging the unreacted process gas  62  from the process tube  34  to maintain the desired pressure therein. Or for example, one or more valves (not shown) may be fitted into a wall  74  ( FIG. 2 ) of the process tube  34  for adjustably releasing or discharging the unreacted process gas  62  therefrom. Yet other embodiments for maintaining the pressure within the process tube  34  are also contemplated as being within the scope of the invention.  
      The various components of apparatus  10 , such as are shown in  FIG. 1  and described in the immediately preceding discussion, are commercially available. For example, a Harper Rotating Tube Furnace (Model No. HOU-6D60-RTA-28-F), is commercially available from Harper International Corporation (Lancaster, N.Y.), and may be used according to the teachings of the invention, at least in part, to produce molybdenum metal product  12 .  
      The Harper Rotating Tube Furnace features a high-heat chamber with a maximum temperature rating of 1450° C. A number of refractory dams divide the high-heat chamber into three independent temperature control zones. The three temperature control zones feature discrete temperature control using twenty-eight silicon-carbide electrical resistance heating elements. Thermocouplers are provided at the center of each control zone along the centerline of the roof of the furnace. The temperature control zones are regulated by three Honeywell UDC3000 Microprocessor Temperature Controllers, and by three Honeywell UDC2000 Microprocessor Temperature Limiters, each commercially available from Honeywell International, Inc. (Morristown, N.J.).  
      The Harper Rotating Tube Furnace also features a gas-tight, high temperature alloy process tube, having a maximum rating of 1100° C. The process tube has a nominal internal diameter of 15.2 cm (6.0 in), nominal external ends diameter of 16.5 cm (6.5 in), and an overall length of 305 cm (120 in). The process tube extends in equal segments (each having a length of 50.8 cm (20 in)) through each of the temperature control zones, leaving 152 cm (60 in) extending through the cooling zone.  
      The process tube provided with the Harper Rotating Tube Furnace may be inclined within a range of 0 to 5°. In addition, the Harper Rotating Tube Furnace may be provided with a variable direct current (DC) drive with digital speed control for rotating the process tube at rotational speeds of one to five revolutions per minute (rpm).  
      The Harper Rotating Tube Furnace also features a 316-liter, stainless steel, gas-tight with inert gas purge, discharge hopper. The Harper Rotating Tube Furnace also features an atmosphere process gas control system for maintaining a constant pressure within the process tube. In addition, a 45-kilowatt (kW) power supply may be provided, for heating the furnace and driving the process tube. In addition, the Harper Rotating Tube Furnace may be fitted with a Brabender Loss-In-Weight Feed System (Model No. H31-FW33/50), commercially available from C.W. Brabender Instruments, Inc. (South Hackensack, N.J.),  
      Although preferred embodiments of apparatus  10  are shown in  FIG. 1  and have been described above, it is understood that other embodiments of apparatus  10  are also contemplated as being within the scope of the invention. In addition, it is understood that apparatus  10  may comprise any suitable components from various manufacturers, and are not limited to those provided herein. Indeed, where apparatus  10  is designed for large or industrial-scale production, the various components may be specifically manufactured therefor, and the specifications will depend on various design considerations, such as but not limited to, the scale thereof.  
     Method for Producing Molybdenum Metal  
      Having described apparatus  10 , and preferred embodiments thereof, that may be used to produce molybdenum metal product  12  according to the invention, attention is now directed to embodiments of a method for producing molybdenum metal product  12 . As an overview, and still with reference to  FIG. 1 , the precursor material  14  is preferably introduced into the furnace  16  and moved through the heating zones  20 ,  21 , and  22 , and the cooling zone  23  thereof. The process gas  62  is preferably introduced into the furnace  16  for reaction with the precursor material  14  and the intermediate material  30 . The precursor material  14  and the intermediate material  30  react with the process gas  62  therein to produce molybdenum metal product  12 , as discussed in more detail below with respect to preferred embodiments of the method.  
      According to preferred embodiments, the precursor material  14  comprises nano-particles of molybdic oxide (MoO 3 ). The nano-particles of molybdic oxide preferably have a typical surface area to mass ratio of about 25 to 35 m 2 g. When these nano-particles of molybdic oxide are used as the precursor material  14 , the molybdenum metal product  12  produced according to embodiments of the method of the invention may be characterized as having a surface area to mass ratio of about 2.5 m 2 /g. In addition, the molybdenum metal product  12  may be characterized as being uniform in size.  
      The nano-particles of molybdic oxide described above may be produced according to embodiments of the invention disclosed in co-owned, U.S. Pat. No. 6,468,497 issued on Oct. 22, 2002 for “METHOD FOR PRODUCING NANO-PARTICLES OF MOLYBDENUM OXIDE” of Kilian, et al., which is incorporated herein for all that it discloses. The nano-particles of molybdic oxide are produced by, and are commercially available from the Climax Molybdenum Company (Fort Madison, Iowa).  
      According to other embodiments of the invention, however, it is understood that the precursor material  14  may comprise any suitable grade or form of molybdic oxide (MoO 3 ). For example, the precursor material  14  may range in size from 0.5 to 80 m 2 /g. Selection of the precursor material  14  may depend on various design considerations, including but not limited to, the desired characteristics of the molybdenum metal product  12  (e.g., surface area to mass ratio, size, purity, etc.). In general, the surface area to mass ratio of the molybdenum metal product  12  is proportionate to the surface area to mass ratio of the precursor material  14 , and typically ranges from 1.5 to 4.5 m 2 /g.  
      Turning now to  FIG. 2 , the process tube  34  (walls  74  thereof are shown) is illustrated in three cross-sectional portions of the process tube  34 . Each cross-sectional portion shown in  FIG. 2  is taken respectively from each of the three heating zones  20 ,  21 , and  22  of the furnace  16 . According to preferred embodiments of the method, the precursor material  14  is introduced into the process tube  34 , and moves through the each of the three heating zones  20 ,  21 , and  22  of the furnace  16  (i.e., Heating Zone  1 , Heating Zone  2 , and Heating Zone  3 , in  FIG. 2 ). The process tube  34  may be rotating and/or inclined to facilitate movement and mixing of the precursor material  14  therein, as described in more detail above with respect to embodiments of apparatus  10 . In addition, the process gas  62  is also introduced into the process tube  34 . Preferably, the process gas  62  flows through the process tube  34  in a direction  28  that is opposite or counter-current to the direction  26  that the precursor material  14  is moving through the process tube  34 , such as may be accomplished according to the embodiments of apparatus  10  discussed in more detail above.  
      As the precursor material  14  moves through the first heating zone  20 , it is mixed with the process gas  62  and reacts therewith to form the intermediate product  30 . The reaction is illustrated by arrows  70  in heating zone  20  (Heating Zone  1 ) of  FIG. 2 . More particularly, the reaction in the first heating zone  20  (Heating Zone  1 ) may be described as solid molybdic oxide (MoO 3 ) being reduced by the reducing gas  64  e.g., hydrogen gas) in the process gas  62  to form solid moly-dioxide (MoO 2 ) (i.e., intermediate product  30  in  FIG. 2 ) and, for example, water vapor when the reducing gas  64  is hydrogen gas. The reaction between the precursor material  14  and the reducing gas  64  may be expressed by the following chemical formula: 
 
MoO 3 (s)+H 2 (g)→MoO 2 (s)+H 2 O(v) 
 
      The temperature in the first heating zone  20  is preferably maintained below the vaporization temperature of the precursor material  14 , and that of any intermediate material  30  that is formed in the first heating zone  20  (Heating Zone  1 ), relative to the pressure within the process tube  34 . Overheating the precursor material  14  and/or the intermediate material  30  may cause a reaction only on the surface thereof. The resulting surface reaction may cause beads of molybdenum metal to form, sealing unreacted precursor material  14  and/or intermediate material  30  therein. These beads may require longer processing times and/or higher processing temperatures to convert to pure molybdenum metal product  12 , thus reducing the efficiency and increasing the cost of production.  
      The temperature of the first heating zone  20  is preferably maintained at a lower temperature than the other two heating zones  21 , and  22  because the reaction between the precursor material  14  and the reducing gas  64  in the first heating zone  20  (Heating Zone  1 ) is an exothermic reaction. That is, heat is released during the reaction in the first heating zone  20 .  
      The second heating zone  21  (Heating Zone  2 ) is preferably provided as a transition zone between the first heating zone  20  (Heating Zone  1 ) and the third heating zone  22  (Heating Zone  3 ). That is, the temperature in the second heating zone  21  is maintained at a higher temperature than the first heating zone  20 , but preferably maintained at a lower temperature than the third heating zone  22 . As such, the temperature of the intermediate material  30  and the unreacted precursor material  14  is gradually ramped up for introduction into the third heating zone  22 . Without the second heating zone  22 , an immediate transfer of the intermediate material  30  and the unreacted precursor material  14  from the lower temperatures of the first heating zone  20  (Heating Zone  1 ) to the higher temperatures of the third heating zone  22  (Heating Zone  3 ) may cause beads of unreacted material to form. The disadvantages of these beads are discussed above. In addition, the molybdenum metal product  12  may agglomerate and produce undesirable product “chunks”.  
      As the intermediate material  30  moves into the third heating zone  22  (Heating Zone  3 ), it continues to be mixed with the process gas  62  and reacts therewith to form the molybdenum metal product  12 , as illustrated by arrows  72  in  FIG. 2 . More particularly, the reaction in the third heating zone  22  (Heating Zone  3 ) may be described as solid moly-dioxide (MoO 2 ) being reduced by the reducing gas  64  (e.g., hydrogen gas) in the process gas  62  to form solid molybdenum metal product  12  (Mo) and, for example, water vapor when the reducing gas  64  is hydrogen gas. The reaction between the intermediate material  30  and the process gas  62  may be expressed by the following chemical formula. 
 
MoO 2 (s)+2H 2 (g)→Mo(s)+2H 2 O(v) 
 
      The reaction between the intermediate material  30  and the reducing gas  64  in the third heating zone  22  (Heating Zone  3 ) is an endothermic reaction. That is, heat is consumed during this reaction. Therefore, the energy input of the third heating zone  22  is preferably adjusted accordingly to provide the additional heat required by the endothermic reaction in the third heating zone  22 .  
      When the molybdenum metal  12  produced by the reactions described above is immediately introduced to an atmospheric environment while still hot (e.g., upon exiting the third heating zone  22 ), it may react with one or more constituents of the atmosphere. For example, the hot molybdenum metal  12  may reoxidize when it is exposed to an oxygen environment. Therefore, the molybdenum metal product  12  is preferably moved through a cooling zone  23 . Also preferably, the process gas  62  flows through the cooling zone so that the hot molybdenum metal product  12  may be cooled in a reducing environment, thus lessening or eliminating the occurrence of reoxidation of the molybdenum metal product  12  (e.g., to form MoO 2 and/or MoO 3 ). The cooling zone  23  may also be provided to cool the molybdenum metal product  12  for handling purposes.  
      As explained above, the reactions in the first heating zone  20  (Heating Zone  1 ) are primarily the precursor material  14  being reduced to form intermediate material  30 . Also as explained above, the second heating zone  21  (Heating Zone  2 ) is primarily provided as a transition zone for the intermediate material  30  produced in the first heating zone  20  before it is introduced to the third heating zone  22  (Heating Zone  3 ). And also as explained above, the reactions in the third heating zone  22  are primarily the intermediate material  30  being further reduced to form the molybdenum metal product  12 . However, the preceding discussion of the reactions in each of the heating zones  20 ,  21 , and  22  shown in  FIG. 2  are merely illustrative of the process of the invention.  
      As will be readily apparent to one skilled in the art, it is understood that these reactions may occur in each of the three heating zones  20 ,  21 , and  22 , as illustrated by arrows  70 ,  71 , and  72 . That is, some molybdenum metal product  12  may be formed in the first heating zone  20  and/or the second heating zone  21 . Likewise, some unreacted precursor material  14  may be introduced into the second heating zone  21  and/or the third heating zone  22 . In addition, some reactions may still occur even in the cooling zone  23 .  
      Also as will be readily apparent to one skilled in the art, any unreacted reducing gas  64  and the inert gas  65  is also discharged in the effluent. Likewise, where a reducing gas  64  other than hydrogen is used, the reducing agent combined with oxygen stripped from the molybdic oxide, is also released in the effluent.  
      Having discussed the reactions in the various portions of the furnace  16  illustrated in  FIG. 2 , it should be noted that optimum conversion of the precursor material  14  to the molybdenum metal product  12  were observed to occur when the process parameters were set to values in the ranges shown in Table 1.  
                           TABLE 1                                   PARAMETER   SETTING                          Process Tube incline   0.5° to 1.2°           Process Tube Rotation Rate   18 to 100 seconds per revolution           Temperature           Zone 1   540° C. to 600° C.           Zone 2   760° C. to 820° C.           Zone 3   980° C. to 1050° C.           Process Gas Flow Rate   60 to 120 cubic feet per hour                      
 
      It is understood that molybdenum metal product  12  may also be produced when the process parameters are adjusted outside of the ranges given above in Table 1, as may be readily determined by one skilled in the art based on the teachings of the invention.  
      According to preferred embodiments of the invention, it is not necessary to screen the molybdenum metal product  12  to remove precursor material  14 , intermediate material  30 , and/or other contaminating material (not shown) from the product. That is, preferably, 100% of the precursor material  14  is fully converted to pure molybdenum metal product  12 . However, according to embodiments of the invention, the molybdenum metal product  12  may be screened to remove oversize particles from the product that may have agglomerated during the process. Whether the molybdenum metal product  12  is screened will depend on design considerations such as, but not limited to, the ultimate use for the molybdenum metal product  12 , the purity and/or particle size of the precursor material  14 , etc.  
      An embodiment of a method for producing molybdenum metal  12  according to the teachings of the invention is illustrated as steps in the flow chart shown in  FIG. 3 . In step  80 , the precursor material  14  may be introduced into the furnace  16 . As discussed above, the precursor material  14  is preferably introduced into the furnace  16  by feeding it into a process tube  34  extending through the furnace  16 . In step  82 , the precursor material  14  is moved through the furnace  16 . As discussed above, the precursor material  14  is preferably moved (e.g., within the process tube  34 ) through three heating zones  20 ,  21 , and  22 , and through a cooling zone  23  of the furnace  16 . In step  84 , the reducing gas  64  may be introduced into the furnace  16 . Again, as discussed above, the reducing gas  64  is preferably introduced into the process tube  34  and preferably flows therethrough in a direction  28  that is opposite or counter-current to the direction  26  that the precursor material  14  is moving through the furnace  16 . Accordingly, the precursor material  14  is reduced and molybdenum metal  12  is produced, as illustrated by step  86  and described in more detail above with respect to  FIG. 2 .  
      It is understood that the steps shown and described with respect to  FIG. 3  are merely illustrative of an embodiment of the method for producing molybdenum metal  12 . Other embodiments of the method are also contemplated as being within the scope of the invention. Another embodiment of the method may also comprise the steps of inclining the process tube  34  for feeding the precursor material  14  into the furnace  16 . Likewise another embodiment of the method may also comprise rotating  42  the precursor material  14  to facilitate movement of the same through the process tube  34  and to enhance the reaction thereof, as described above in more detail with respect to apparatus  10 . Yet another embodiment of the method may comprise the step of maintaining the furnace  16  at a constant pressure. For example, such an embodiment of the method may comprise the step of discharging the process gas  62  from the furnace  16  through a scrubber  68  to maintain the furnace  16  at a constant pressure.  
      Still other embodiments are also contemplated as being within the scope of the invention. Indeed, it is expected that yet other embodiments of the method for producing molybdenum metal product will become readily apparent to one skilled in the art based on the teachings of the invention.  
     Characteristics of Molybdenum Metal  
      Having described methods and apparatus  10  for producing molybdenum metal according to the invention, characteristics of molybdenum metal will now be shown and described in further detail.  
     Prior Art  
       FIG. 4  shows molybdenum metal that may be produced according to prior art processes.  FIG. 4  is an image produced using a scanning electron microscope (SEM) in a process that is commonly referred to as scanning electron microscopy. As is readily seen in  FIG. 4 , the individual particles of molybdenum metal vary widely in size and shape from one another. While the size of the molybdenum metal can be expressed in terms of the mean length or the mean diameter of the particles (e.g., as detected by scanning electron microscopy), it is generally more useful to express the size of molybdenum metal in terms of surface area per unit mass due to the correlation between size and surface area.  
      Measurements of particle surface area per unit weight may be obtained by BET analysis. As is well known, BET analysis involves an extension of the Langmuir isotherm equation using multi-molecular layer absorption developed by Brunauer, Emmett, and Teller (hence, BET). BET analysis is an established analytical technique that provides highly accurate and definitive results.  
      The molybdenum metal, as shown in  FIG. 4  and produced according to prior art processes, may be characterized by a surface area of about 0.8 square meters/gram (m 2 /g), as measured in accordance with the BET analysis technique. Alternately, other types of measuring processes may be used to determine particle characteristics.  
     Novel Forms of Molybdenum Metal Product  
       FIG. 5  is a scanning electron microscope image of molybdenum metal product  12  produced according to an embodiment of the invention. As can be readily seen in  FIG. 5 , the individual particles of molybdenum metal  12  comprise a generally elongated or cylindrical configuration having a mean length that is greater than its mean diameter. In addition, the molybdenum metal product  12  is substantially uniform in size and shape. For example, 50% of the non-screened molybdenum metal product  12  shown in  FIG. 5  has a mean size of less than 24.8 micrometers (μm), and 99% of the non-screened molybdenum metal product  12  shown in  FIG. 5  has a mean size of less than 194 μm. After grinding to break up agglomerations of the product, the non-screened molybdenum metal product  12  has an overall mean size of 1.302 μm, with 50% of the non-screened molybdenum metal product  12  having a mean size of less than 1.214 μm, and 99% of the non-screened molybdenum metal product  12  having a mean size of less than 4.656 μm.  
      Again, although the size of the molybdenum metal product  12  can be expressed in terms of the mean length or the mean diameter of the particles (e.g., as detected by scanning electron microscopy), it is generally more useful to express the size of molybdenum metal in terms of surface area per unit mass due to the correlation between size and surface area.  
      The molybdenum metal product  12  shown and described with respect to  FIG. 5  was produced according to an embodiment of the method and apparatus of the invention. The molybdenum metal product  12  is characterized by a surface area of about 2.5 m 2 /g, as measured in accordance with the BET analysis technique. Again, other types of measuring processes may be used to determine particle characteristics.  
     EXAMPLE 1  
      In this Example 1, the precursor material comprised nano-particles of molybdic oxide (MoO 3 ) having a typical size of about 25 to 35 m 2 /g. Such nano-particles of molybdic oxide may be produced according to embodiments of the invention disclosed in co-owned, U.S. Pat. No. 6,468,497 issued on Oct. 22, 2002 for “METHOD FOR PRODUCING NANO-PARTICLES OF MOLYBDENUM OXIDE”. The nano-particles of molybdic oxide used as precursor material in this example are produced by and are commercially available from the Climax Molybdenum Company (Fort Madison, Iowa).  
      The following equipment was used for this example: a Brabender Loss-In-Weight Feed System (Model No. H31-FW33/50), commercially available from C.W. Brabender Instruments, Inc. (South Hackensack, N.J.); and a Harper Rotating Tube Furnace (Model No. HOU-6D60-RTA-28-F), commercially available from Harper International Corporation (Lancaster, N.Y.). The Harper Rotating Tube Furnace comprised three independently controlled 50.8 cm (20 in) long heating zones with a 305 cm (120 in) HT alloy tube extending through each of the heating zones thereof. Accordingly, a total of 152 cm (60 in) of heating and 152 cm (60 in) of cooling were provided in this example.  
      In this example, the precursor material was fed, using the Brabender Loss-In-Weight Feed System, into the HT alloy tube of the Harper Rotating Tube Furnace. The HT alloy tube was rotated and inclined (see Table 2, below) to facilitate movement of the precursor material through the Harper Rotating Tube Furnace, and to facilitate mixing of the precursor material with a process gas. The process gas was introduced through the HT alloy tube in a direction opposite or counter-current to the direction that the precursor material was moving through the HT alloy tube. In this example, the process gas comprised hydrogen gas as the reducing gas, and nitrogen gas as the inert carrier gas. The discharge gas was bubbled through a water scrubber to maintain the interior of the furnace at approximately 11.4 cm (4.5 in) of water pressure (gauge).  
      Optimum conversion of the precursor material to the molybdenum metal product occurred when the parameters were set to the values shown in Table 2.  
                           TABLE 2                                   PARAMETER   SETTING                          Precursor Feed Rate   5 to 7 grams per minute           Process Tube Incline   1°           Process Tube Rotation   20 seconds per revolution           Temperature Set Points           Zone 1   555° C.           Zone 2   800° C.           Zone 3   1000° C.           Process Gas Rate   80 cubic feet per hour                      
 
      Molybdenum metal  12  produced according to this example is shown in  FIG. 5 , and discussed above with respect thereto. Specifically, the molybdenum metal product  12  produced according to this example is characterized by a surface area to mass ratio of 2.5 m 2 /g. The molybdenum metal product  12  produced according to this example is also characterized by a uniform size. That is, 50% of the non-screened molybdenum metal product  12  shown in  FIG. 5  had a mean size of less than 24.8 μm, and 99% of the non-screened molybdenum metal product  12  shown in  FIG. 5  had a mean size of less than 194 μm.  
     EXAMPLE 2  
      In this Example 2, the precursor material comprised nano-particles of molybdic oxide (MoO 3 ) having a typical size of about 30-50 m 2 /g. Such nano-particles of molybdic oxide may be produced according to embodiments of the invention disclosed in co-owned, U.S. Pat. No. 6,468,497 issued on Oct. 22, 2002 for “METHOD FOR PRODUCING NANO-PARTICLES OF MOLYBDENUM OXIDE”. The nano-particles of molybdic oxide used as precursor material in this example are produced by and are commercially available from the Climax Molybdenum Company (Fort Madison, Iowa).  
      The following equipment was used for this example: a Brabender Loss-In-Weight Feed System (Model No. H31-FW33/50), commercially available from C.W. Brabender Instruments, Inc. (South Hackensack, N.J.); and a Harper Rotating Tube Furnace (Model No. HOU-6D60-RTA-28-F), commercially available from Harper International Corporation (Lancaster, N.Y.). The Harper Rotating Tube Furnace comprised three independently controlled 50.8 cm (20 in) long heating zones with a 305 cm (120 in) HT alloy tube extending through each of the heating zones thereof. Accordingly, a total of 152 cm (60 in) of heating and 152 cm (60 in) of cooling were provided in this example.  
      In this example, the precursor material was fed, using the Brabender Loss-In-Weight Feed System, into the HT alloy tube of the Harper Rotating Tube Furnace. The HT alloy tube was rotated at 20 seconds per revolution and inclined to 0.3°(see Table 3, below) to facilitate movement of the precursor material through the Harper Rotating Tube Furnace, and to facilitate mixing of the precursor material with a process gas. However, satisfactory results can be obtained with other tube inclinations (e.g., in a range of about 0.2° to about 0.4°). The process gas was introduced through the HT alloy tube in a direction opposite or counter-current to the direction that the precursor material was moving through the HT alloy tube. In this example, the process gas comprised hydrogen gas as the reducing gas, and nitrogen gas as the inert carrier gas. The discharge gas was bubbled through a water scrubber to maintain the interior of the furnace at approximately 11.4 cm (4.5 in) of water pressure (gauge).  
      Optimum conversion of the precursor material to the molybdenum metal product occurred when the parameters were set to the values shown in Table 3.  
                           TABLE 3                                   PARAMETER   SETTING                          Precursor Feed Rate   9.0 grams per minute           Process Tube Incline   0.3°           Process Tube Rotation Rate   20 seconds per revolution           Temperature           Zone 1   600° C.           Zone 2   800° C.           Zone 3   1000° C.           Process Gas Flow Rate   80 cubic feet per hour           Surface Area, BET, m 2 /g   2.0837           Horiba Data           Horiba mean, microns   1.598           D10, microns   0.858           D50, microns           D90, microns   2.598                      
 
      The molybdenum metal product  12  produced according to this Example 2 is characterized by a surface area to mass ratio of 2.0837 m 2 /g (BET), After grinding to break up agglomerations of the product 12, the non-screened molybdenum product  12  had an overall mean size of 1+598 μm, as measured by a Horiba laser scattering analyzer.  
     EXAMPLE 3  
      In this Example 3, the precursor material comprised nano-particles of molybdic oxide (MoO 3 ) having a typical size of about 30-50 m 2 /g. Such nano-particles of molybdic oxide may be produced according to embodiments of the invention disclosed in co-owned, U.S. Pat. No. 6,468,497 issued on Oct. 22, 2002 for “METHOD FOR PRODUCING NANO-PARTICLES OF MOLYBDENUM OXIDE”. The nano-particles of molybdic oxide used as precursor material in this example are produced by and are commercially available from the Climax Molybdenum Company (Fort Madison, Iowa).  
      The following equipment was used for this example: a Bra bender Loss-In-Weight Feed System (Model No, H31-FW33/50), commercially available from C.W. Brabender Instruments, Inc. (South Hackensack, N.J.); and a Harper Rotating Tube Furnace (Model No. HOU-6D60-RTA-28-F), commercially available from Harper International Corporation (Lancaster, N.Y.). The Harper Rotating Tube Furnace comprised three independently controlled 50.8 cm (20 in) long heating zones with a 305 cm (120 in) HT alloy tube extending through each of the heating zones thereof. Accordingly, a total of 152 cm (60 in) of heating and 152 cm (60 in) of cooling were provided in this example.  
      In this example, the precursor material was fed, using the Brabender Loss-In-Weight Feed System, into the HT alloy tube of the Harper Rotating Tube Furnace. The HT alloy tube was rotated at 20 seconds per revolution and inclined to 0.30 (see Table 4, below) to facilitate movement of the precursor material through the Harper Rotating Tube Furnace, and to facilitate mixing of the precursor material with a process gas. However, satisfactory results can be obtained with other tube inclinations (e.g., in a range of about 0.2° to about 0.4°). The process gas was introduced through the HT alloy tube in a direction opposite or counter-current to the direction that the precursor material was moving through the HT alloy tube. In this example, the process gas comprised hydrogen gas as the reducing gas, and nitrogen gas as the inert carrier gas. The discharge gas was bubbled through a water scrubber to maintain the interior of the furnace at approximately 11.4 cm (4.5 in) of water pressure (gauge).  
      Optimum conversion of the precursor material to the molybdenum metal product occurred when the parameters were set to the values shown in Table 4.  
                           TABLE 4                                   PARAMETER   SETTING                          Precursor Feed Rate   9.0 grams per minute           Process Tube Incline   0.3°           Process Tube Rotation Rate   20 seconds per revolution           Temperature           Zone 1   600° C.           Zone 2   790° C.           Zone 3   900° C.           Process Gas Flow Rate   80 cubic feet per hour           Surface Area, BET, m 2 /g   3.412           Horiba Data           Horiba mean, microns   1.019           D10, microns   0.681           D50, microns           D90, microns   1.422                      
 
      The molybdenum metal product  12  produced according to this example is characterized by a surface area to mass ratio of 3.412 m 2 /g (BET). After grinding to break up agglomerations of the product  12 , the non-screened molybdenum metal product  12  had an overall mean size of 1.019 μm, as measured by a Horiba laser scattering analyzer.  
     EXAMPLE 4  
      In this Example 4, the precursor material comprised nano-particles of molybdic oxide (MoO 3 ) having a typical size of about 30-50 m 2 /g. Such nano-particles of molybdic oxide may be produced according to embodiments of the invention disclosed in co-owned, U.S. Pat. No. 6,468,497 issued on Oct. 22, 2002 for “METHOD FOR PRODUCING NANO-PARTICLES OF MOLYBDENUM OXIDE”. The nano-particles of molybdic oxide used as precursor material in this example are produced by and are commercially available from the Climax Molybdenum Company (Fort Madison, Iowa).  
      The following equipment was used for this example: a Brabender Loss-In-Weight Feed System (Model No. H31-FW33/50), commercially available from C.W. Brabender Instruments, Inc. (South Hackensack, N.J.); and a Harper Rotating Tube Furnace (Model No. HOU-6D60-RTA-28-F), commercially available from Harper International Corporation (Lancaster, N.Y.). The Harper Rotating Tube Furnace comprised three independently controlled 50.8 cm (20 in) long heating zones with a 305 cm (120 in) HT alloy tube extending through each of the heating zones thereof. Accordingly, a total of 152 cm (60 in) of heating and 152 cm (60 in) of cooling were provided in this example.  
      In this example, the precursor material was fed, using the Brabender Loss-In-Weight Feed System, into the HT alloy tube of the Harper Rotating Tube Furnace. The HT alloy tube was rotated at 20 seconds per revolution and inclined to 0.3° (see Table 5, below) to facilitate movement of the precursor material through the Harper Rotating Tube Furnace, and to facilitate mixing of the precursor material with a process gas. However, satisfactory results can be obtained with other tube inclinations (e.g., in a range of about 0.2° to about 0.4°). The process gas was introduced through the HT alloy tube in a direction opposite or counter-current to the direction that the precursor material was moving through the HT alloy tube. In this example, the process gas comprised hydrogen gas as the reducing gas, and nitrogen gas as the inert carrier gas. The discharge gas was bubbled through a water scrubber to maintain the interior of the furnace at approximately 11.4 cm (4.5 in) of water pressure (gauge).  
      Optimum conversion of the precursor material to the molybdenum metal product occurred when the parameters were set to the values shown in Table 5.  
                           TABLE 5                                   PARAMETER   SETTING                          Precursor Feed Rate   5.0 grams per minute           Process Tube Incline   0.3°           Process Tube Rotation Rate   20 seconds per revolution           Temperature           Zone 1   600° C.           Zone 2   750° C.           Zone 3   850° C.           Process Gas Flow Rate   80 cubic feet per hour           Surface Area, BET, m 2 /gm   4.106           Horiba Data           Horiba mean, microns   1.005           D10, microns   0.618           D50, microns           D90, microns   1.468                      
 
      The molybdenum metal product  12  produced according to this example is characterized by a surface area to mass ratio of 4.106 m 2 /g (BET). After grinding to break up agglomerations of the product  12 , the non-screened molybdenum metal product  12  had an overall mean size of 1.005 μm, as measured by a Horiba laser scattering analyzer.  
      It is readily apparent that novel forms of molybdenum metal as discussed herein have a relatively larger surface area to mass ratio and are relatively uniform in size. Likewise, it is apparent that apparatus and methods for production of molybdenum metal discussed herein may be used to produce molybdenum metal in a continuous, single stage manner. Consequently, the claimed invention represents an important development in molybdenum metal technology. Having herein set forth various and preferred embodiments of the invention, it is expected that suitable modifications will be made thereto which will nonetheless remain within the scope of the invention. Accordingly, the invention should not be regarded as limited to the embodiments shown and described herein, and it is intended that the appended claims be construed to include yet other embodiments of the invention, except insofar as limited by the prior art.