Patent Publication Number: US-3877999-A

Title: Hydration-disintegration of cobalt-rare earth alloy containing material

Description:
Lerman et a1.  
 [ Apr. 15, 1975 HYDRATION-DISINTEGRATIQN OF COBALT-RARE EARTH ALLOY CONTAINING MATERIAL Inventors: Theodore B. Lerman; Charles M.  
 McFarland, both of Schenectady, NY.  
 Assignee: General Electric Company,  
 Schenectady, NY.  
 Filed: June 3, 1974 Appl. No.: 475,900  
 US. Cl. 148/105; 148/3157; 148/101;  
 Int. Cl C2ld l/04 Field of Search 148/105, 101, 31.57; 75/0.5 BA; 23/267, 270, 309, 310, 312; 209/138, 158, 174, 176, 39  
 References Cited UNITED STATES PATENTS Bean 209/39 2,683,685 7/1954 Matheson 209/138 3,625,779 12/1971 Cech 148/101 3,687,284 8/1972 Leeman et a1.. 209/39 3,748,193 7/1973 C6611 148/101 Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm.lane M. Binkowski; Joseph T. Cohen; Jerome C. Squillaro [57] ABSTRACT A self-regulating process for disintegrating reaction product cake to recover rare earth alloy particles contained therein. A support screen is selected having holes through which material of desired size will pass and placed within a hydration zone. The cake is placed on the screen and a water vapor-carrying gas is passed through the zone to react with calcium and/or calcium compounds in the cake to produce calcium hydroxide. The resulting volume expansion disintegrates the cake which, upon disintegrating to the desired size, falls through the holes in the screen away from substantial contact with the incoming water vapor-carrying gas.  
 4 Claims, 1 Drawing Figure HYDRATlON-DISINTEGRATION OF COBALT-RARE EARTH ALLOY CONTAINING MATERIAL The present invention relates to the treatment of an alloy containing material useful in the production of magnets produced by a reduction-diffusion process and particularly to the hydration-disintegration of such material without significantly deteriorating the potential magnetic properties of the rare earth alloy particles contained therein.  
  U.S. Pat. No. 3,748,193, which is assigned to the assignee hereof and which by reference is made part of the disclosure of the present application, relates to a reduction-diffusion process for producing rare earth intermetallic compounds or alloys. Briefly stated, one embodiment of the disclosed process comprises providing a particulate mixture of a rare earth metal oxide, calcium hydride and a metal such as cobalt or iron, or alloys or mixtures thereof which can also include manganese, heating the particulate mixture in a nonreactive atmosphere to decomposethe calcium hydride and thereby effect reduction of the rare earth metal constituent. then heating the resulting mixture in a nonreactive atmosphere to diffuse the resulting rare earth metal into the aforementioned metal particles to form the desired rare earth intermetallic alloy particles which are then recovered from the product.  
  It is actually calcium resulting from the decomposition of the calcium hydride which acts to reduce the rare earth oxide to form the rare earth metal. If desired, the calcium hydride can be formed in situ by a number of methods. One particular advantage of the use of calcium hydride is that calcium does not alloy in any significant amount with the cobalt-rare earth alloy or other magnetic rare earth alloys formed herein.  
  The oxides of the rare earth metals useful in the disclosed patented process are those of the rare earth metals which are the 15 elements of the lanthanide series having atomic numbers 57 to 71 inclusive. The element yttrium (atomic number 39) is commonly found with and included in this group of metals and, in this disclosure, is considered a rare earth metal. Mixtures of rare earth metal oxides can also be used. Representative of the oxides useful in the present invention are samarium oxide (Sm O yttrium oxide (Y- O and mischmetal oxides (M mischmetal being the most common alloy of the rare earth metals which contains the metals in the approximate ratio in which they occur in their most common naturally occurring ores.  
  A number of rare earth intermetallic alloys can be formed merely by using the proper amounts of the active constituents. The following equation represents the stroichiometric reaction for forming Co R, where R is a rare earth metal, by the reduction of the rare earth from the oxide to a constituent of the cobalt intermetal- -lic alloy using samarium as an example:  
 5 C0 1/2 Sm O 3/2 Cal-M52 Co Sm 3/2 Ca0 U.S. Pat. No. 3,748,193 discloses that preferably, an amount of calcium hydride in excess of the stoichiometric amount necessary to reduce the rare earth metal oxide is used so that the excess calcium hydride is converted to metallic calcium which precipitates at the boundaries of the particles of the resulting cobalt-rare earth intermetallic compound, and that the resulting product mass can then be placed in air or other oxygen and moisture-containing atmosphere to allow the precipitated calcium to oxidize whereupon it undergoes a change in volume sufficient to disintegrate the mass and release the particles of the cobalt-rare earth intermetallic compound.  
  When an excess amount of calcium hydride is used, a reaction product cake is produced wherein particles of rare earth intermetallic alloy, for example, cobaltrare earth alloy, are substantially or completely surrounded by calcium and/or calcium oxide. Also, depending on the particular reaction conditions and atmospheres with which the product cake is contacted, calcium hydride and calcium nitride may also be present, usually in minor amounts, at or between the boundaries of the alloy particles. Placing such a cake or lumps thereof in a moisture containing atmosphere to hydrate calcium and its compounds to produce calcium hydroxide and disintegrate the cake by the accompanying volume expansion is a slow process which tends to be partially blocked off by the disintegrating powder and is not practical on a commercial scale. The problem is that the disintegration does not proceed at the same rate uniformly throughout the cake but proceeds in stages since not all of the calcium or calcium compounds can be contacted with the moisture containing atmosphere at the same time. Specifically, with each disintegration additional calcium or calcium compound is exposed and only then becomes available for reaction with the moisture. The disadvantage inherent in the use of water or an oxidizing atmosphere is that they react with the alloy particles and cause them to oxidize and lose their potential magnetic properties.  
  The present inyention provides a significantly faster, substantially self-regulating uniform hydration technique for disintegrating the cake or lumps thereof to a desired size for purposes such as storage or to disintegrate it to completion to free the particles of rare earth alloy contained therein without significant deterioration. The disintegration proceeds between and along the boundaries of the particles and the final disintegrated product is usually a free-flowing powder comprised of calcium hydroxide and particles of the rare earth alloy.  
  Briefly stated, in the present process the reaction product cake is comprised of alloy particles substantially or completely surrounded by calcium and/or a calcium compound selected from the group consisting of calcium oxide, calcium hydride and calcium nitride. The alloy particles consist essentially of rare earth metal and a metal selected from the group consisting of cobalt, iron, manganese and alloys thereof. The process comprises providing a hydration zone having a gas inlet at one end portion and a reacted gas outlet at substantially the opposite end portion. A support screen is selected having holes through which material of a desired size or smaller passes and placed within the hydration zone substantially between the gas inlet and the reacted gas outlet. The reaction product cake is placed on the support screen and a water vapor-carrying gas is flowed through the gas inlet through the hydration zone at a rate which at least envelops the reaction product cake reacting with the calcium and/or calcium compounds therein to form substantially calcium hydroxide causing a significant volume increase which disintegrates the cake. The water vapor-carrying gas initially has a temperature ranging from about 0C to about C and a relative humidity ranging from about 5% up to 100%. The reaction product cake material is substantially inert to the gas component of the water vapor-carrying gas. The resulting reacted gas passes through the reacted gas outlet. The disintegrated cake falls through the holes in the support screen upon disintegrating to the desired size or smaller to a collection zone associated with the hydration zone and away from substantial contact with the incoming water vapor-carrying gas.  
  The form of the support screen can vary. For example, it can be planar and placed horizontally across a cross-section of the hydration zone, or it can be vertical tube closed at its lower end portion and placed within a hydration zone as shown. The support screen selected has holes through which material of a desired size or smaller passes. When the cake disintegrates to the size of the holes, it passes through the screen substantially upon forming or shortly thereafter to a collection zone provided in association with the hydration zone beneath the screen support. Preferably, the screen support is vibrated to accelerate passage of the disintegrated material through it. Upon passing into the collection zone, the disintegrated cake is removed from effective contact with the incoming water vaporcarrying gas. If desired, a number of support screens can be used in the same hydration zone, one below the other, with each screen having holes progressively smaller so that thedesired disintegration is carried out progressively in a series.  
  The water vapor-carrying gas consists essentially of water vapor and a gas to which the alloy particles are substantially inert such as nitrogen or argon. Before it is introduced into the hydration zone, the water vaporcarrying gas has a relative humidity ranging from about 5% to and a temperature ranging from about 0C to 70C, and preferably, it is close to room temperature, i.e., 20C to 30C. At a relative humidity below the water vapor-carrying gas produces a hydration reaction too slow to be commercially useful. With increasing relative humidity, the rate of reaction in the hydration zone increases resulting in a faster disintegration of the cake. At a temperature below 0C, the water vapor-carrying gas cannot provide the minimum necessary relative humidity, and as a practical matter, temperatures higher than 70C cannot be used since the hydration reaction to form calcium hydroxide is exothermic, and the product may overheat and begin to oxidize.  
  The water vapor-carrying gas can be passed through the hydration zone upwardly, sideways or downwardly to envelop the reaction product cake material therein. The particular rate at which the water vapor-carrying gas passes through the hydration zone depends largely on its initial relative humidity and temperature and the rate at which the reaction product cake disintegrates. As the incoming water vapor-carrying gas passes in contact with the reaction product cake, its water vapor component reacts with the calcium or calcium compound of the cake leaving, in most instances, no significant amount of water vapor in the resulting reacted gas passing through the outlet. In the present process, water does not condense on the reaction product cake during disintegration since its hydration is exothermic keeping its temperature higher than that of the water vapor with which it is contacted. However, once the reaction product cake is completely disintegrated, i.e., there is no more calcium or calcium compound available for hydration, the temperature of the disintegrated mass cools and such final product should be kept from contact with water vapor to prevent condensation of water thereon and its accompanying deterioration of potential magnetic properties.  
  The reaction of calcium or its compounds in the present process is exothermic, and if desired, a cooling jacket may be used to prevent the hydration zone from overheating. The hydration zone can be equipped with conventional equipment such as a humidity sensor, preferably at its upper end portion, to determine the amount of water vapor left in the reacted gas. Preferably, it is provided with thermocouples which are.  
 equipped to maintain the disintegrating mass below a certain desirable maximum temperature, for example 50C, by stopping the introduction of the water vaporcarrying gas into the hydration zone, and once the disintegrating mass cools below the set desired maximum temperature, starting up the reaction again by allowing the water vapor-carrying gas to be passed into the hydration zone.  
  Those skilled in the art will gain a further and better understanding of the present invention from the detailed description set forth below, considered in conjunction with the sole FIGURE accompanying and forming a part of the specification which illustrates the present hydration-disintegration process and shows a vertical cross-section taken through a typical apparatus constructed in accordance with the invention.  
  A run was made using the apparatus shown in the FIGURE. A vertical tubular screen 1 made of conventional aluminum window screen 16 mesh in size supported by A inch hardware cloth which would allow passage therethrough of disintegrated material less than 1 millimeter in size was placed within hydration zone 2 as shown in the accompanying FIGURE. The hydration zone was purged with dry nitrogen gas. A charge 7 consisting of lumps of reaction product cake having an average diameter size of about 1 inch was placed in the support screen 1 through charge port 3. The reaction product cake was comprised of cobaltsamarium alloy particles substantially of the formula Co Sm surrounded substantially by calcium and calcium oxide. The alloy particles had an average particle size less than 40 microns. The incoming water vaporcarrying gas, which consisted essentially of water vapor and nitrogen and which had a relative humidity of about 98% and a temperature of about 25C, was pro vided through a conventional home humidifier 4 and passed through a squirrel cage blower 5 through gas inlet 6 and flowed upwardly at a rate which substantially enveloped charge 7 causing it to disintegrate at a rate of up to about 7 lbs. per hour. Humidity sensor 8 was placed at the upper portion of the hydration chamber 2 to determine the water vapor content of the resulting reacted gas which passed through the reacted gas outlet 9 and which was recycled back to the humidifier 4. The humidity sensor 8 showed the resulting reacted gas to have less water vapor than the incoming gas. The disintegrated powder fell through the support screen 1 into the collection zone 10 and then into transfer cannister 11. The disintegrated powder in transfer cannister 11 was free-flowing. Standard chemical analysis of this powder showed it to be comprised substantially of calcium hydroxide and particles of alloy of substantially the formula Co Sm and a minor amount of calcium oxide.  
  When the disintegration is carried out to completion, the final product is generally comprised of the rare earth alloy particles and calcium hydroxide. For certain of these alloys the particles are preferably separated from the calcium hydroxide magnetically, and particularly as disclosed in copending application Ser. No. 475,969 filed of even date herewith and assigned to the assignee hereof where a separation technique of the particles of rare earth alloy using a rotating multi-pole radially magnetized magnet is disclosed and which, by reference, is made part of the disclosure of the present application.  
 What is claimed is:  
  1. A substantially self-regulating process for hydrating and disintegrating a reaction product cake comprised of alloy particles substantially or completely surrounded by calcium and/or a calcium compound selected from the group consisting of calcium oxide, calcium hydride, and calcium nitride, said alloy particles consisting essentially of rare earth metal and a metal selected from the group consisting of cobalt, iron, manganese and alloys thereof, which comprises providing a hydration zone having a gas inlet at one end portion and a reacted gas outlet at substantially the opposite end portion, providing a collection zone in association with said hydration zone, selecting a support screen having holes through which material of a desired size or smaller passes, placing said support screen within said hydration zone substantially between said gas inlet and said reacted gas outlet, placing said reaction product cake on said support screen, passing an incoming water vapor-carrying gas through said gas inlet at a rate which at least envelops said reaction product cake reacting with said calcium or said calcium compound therein to form substantially calcium hydroxide causing a significant volume increase which disintegrates said reaction product cake. said incoming water vaporcarrying gas initially having a temperature ranging from about 0C to about C and a relative humidity ranging from about 5% to said reaction product cake being substantially inert to the gas component of said water vapor-carrying gas, passing the resulting reacted gas through said reacted gas outlet, said disintegrated cake falling through said holes in said support screen substantially upon disintegrating to said desired size or smaller to said collection zone away from substantial contact with said incoming water vapor-carrying gas.  
  2. A process according to claim 1 wherein said incoming water vapor-carrying gas is at room temperature.  
  3. A process according to claim 1 wherein said support screen is vibrated.  
  4. A process according to claim 1 wherein said reaction product cake is disintegrated to produce a freeflowing powder comprised substantially of calcium hydroxide and said alloy particles.