Dec. 27, 1938. _ R. R. RIDG‘WAY 2,141,617 > BORON CARBIDE ALLOY AND METHOD OF MAKING THE SAME Filed June 10, 1936

/r G_ ,2 RHYMu/vu RR/DEWHY Patented Dec. 27, 1938 2,141,617

UNITE :IJ- STATES TENT .FFI 2,141,617 BORON CARBIDE ALLOY AND METHOD OF MAKING THE SAME Raymond R. Ridgway, Niagara Falls, N. Y., as signor to Norton Company, Worcester, Mass., in. corporation of Massachusetts Application June 10, 1936, Serial No. 84,474 7 Claims. (Cl. 75-136) This invention relates to a boron carbide alloy In accordance with this invention, I propose and to a method of making the same, and par to make the desired alloy by the electrical heating ticularly a boron rich boron carbide of controlled of reagent materials in a. resistance furnace and composition which is adapted for various indus by so controlling the composition of the charge trial uses. and the power input as to produce the desired In accordance with my prior Patent 1,897,214, product. This invention is based on the dis boron carbide having a continuous crystalline covery that if the boron oxide content of the structure free from parting planes of graphite furnace charge is increased over the stoichio and conforming substantially to the formula B40 metric requirements for making a composition - ' has been made in an electric resistance furnace corresponding with the formula 34C as set forth 10 by heating a properly proportioned mixture of in my prior patent, and if the power input is held boron trioxide and carbon to a temperature in the below a de?nite rate, then the product will con vicinity of 2400" C. at which the materials of the tain an excess of boron which. may be as high as . charge react to form boron carbide and carbon 85 or 90% of boron with the remainder carbon. monoxide. The pure material has approximately Since the optimum power input varies with the 15 the composition of 78.3% of boron and 21.7% of furnace construction and size, de?nite ?gures carbon. A product called boron carbide has also for the power input are necessarily specified with been marketed which has a carbon content great relation to the surface area of the resistor, as ly in excess of the theoretical requirements for noted below.' However, it may be generally stated B40 and which is considered to consist of a mix that the higher the power input, the richer will ture of boron carbide of unknown formula con be the carbon content and conversely, the lower taining a large excess of free graphite intimately the rate of energy input, the richer the boron con associated with the crystals of boron carbide. An tent of the boron carbide composition. analysis of one composition thus made heretofore The alloy may be made in a furnace of the type has approximated 50% of boron and 40% of car covered by my previous patent and which may bon as well as small amounts of impurities. be structurally arranged as shown in my prior Owing, however, to the presence of the free application Serial No. 50,932, filed November 1, graphite, this material has been wholly unsatis 1935. This preferred type of furnace is shown in factory far various industrial uses. For ex the accompanying drawing, wherein: ample, the presence of the ?akes of graphite Fig. l is a vertical central section of the fur 80 interspersed with the crystals of boron carbide nace; and has prevented the mixture from being molded Fig. 2 is a vertical section on the line 2-2 of into a shape of any utility such as is feasible with Fig. 1. the boron carbide made in accordance with my As illustrated, the furnace comprises a metal prior patent. ‘ casing having a cylindrical or peripheral wall ill In the metallurgical field, there is a demand of iron, aluminum or other suitable metal and for a material comprising boron which may be the two end walls 12 of similar material, which suitably employed in the deoxidation of molten are shaped and arranged to form a cylindrical metals, such as copper, and in the manufacture reaction chamber within which an electrical re of boron alloys; but the high content of free sistor is mounted substantially centrally or axial 40 graphite in the boron carbide and carbon mixture ly of the peripheral wall. For the purpose of heretofore made or the low content of boron in fastening the peripheral wall to the end walls, the the boron carbide of commerce formerly sold for former is provided with outstanding annular metallurgical purposes has made it diflicult to ?anges M at its two ends, thus forming a spool use such materials metallurgically. It is, there shaped structure. The end walls l2 are each fore, highly desirable to provide a boron carbide annular in shape and coextensive with the ?anges, alloy which is richer in boron than the products so that they may be readily fastened together. heretofore obtained. In order that the end walls l2 may be electri It is, accordingly, the primary object of this cally insulated from the peripheral portion 10 of invention to make a boron carbide alloy of a the casing, a gas tight insulation iii of asbestos or 50 high boron content and which has a controlled other suitable material is placed between the composition and to provide an economical and ?anges and the end walls. This insulation is efficient method of making the same. Further made annular in shape and located only adjacent objects will be apparent in the following disclo to the ?anges l4, since it is not needed at the sure. central portion of the furnace and particularly 55 2 2,141,617 because it is fusible at the high temperature of resistor rod 22 and be clamped tightly there the resistor. To facilitate assembly and loading against by means of suitable bolts and nuts. of the furnace charge, the end walls are made The electrode terminals are suitably fastened readily removable. They are fastened to the to these clamping members as by welding metal ?anges by the bolts i8 passing through aligned strips 46 thereon, so that the electric current openings in the metal parts and the asbestos may be readily transmitted from an outside ring therebetween and secured in place by the source of power to the resistor rod. It will be nuts IS. The various parts of the clamping bolts understood that various electrical apparatus well and nuts are also insulated from the metal parts known to those skilled in the art is to be em 10 by means of the insulating washers as well as ployed in connection with this furnace structure sleeves surrounding the bolts which may be made for transmitting the required electrical power to of any suitable material, such as asbestos. the furnace and regulating the same. Also, the The resistor 22 is mounted axially of the pe dimensions of the furnace chamber and the ripheral wall In and arranged to extend through length and cross sectional area of the resistor 15 the charge and project outwardly from each end rod will be so proportioned as to obtain the de of the casing. In order to support the resistor, sired electrical results. It is desirable in this each of the annular end walls i2 is provided with type of furnace that the graphite resistor be a cylindrical extension or hub 24 which has an su?lciently large relative to the size of the ingot outwardly extending ?ange 26. These parts form to be made that it will not be wholly consumed an annular trough within which cooling water or broken until the reaction has gone on for 20 may ?ow. Mounted within these cylindrical hubs a su?icient time. It may be observed that in 24 are graphite sleeves 30 which have been shaped making boron carbide the rod is protected to to ?t snugly therein and prevent the passage of a large extent by the moron carbide formed gases as well as to conduct heat to the water around it so that the boron oxide cannot con cooled trough wall 24. The graphite sleeves 30 in tact and react therewith. turn support the resistor rod 22 which is adapted The exposed ends of the resistor rod and the to carry the electrical current for heating the end walls l2 are kept cool by circulating water charge of material within the casing. This re through the hollow clamps and in the trough 24 sistor is preferably made of graphite, although it surrounding the sleeve 30. This may be readily 30 may be made of other suitable electrically con accomplished by means of the valved water pipes 30 ductive material depending upon the nature of 50 which communicate from a suitable source of the charge being treated. This graphite rod 22 water supply to the lower members of the clamps. is also shaped for accurate sliding ?t within the A pipe 5| connects the upper clamp with the sleeves 30 so as to' provide a gas tight joint and lower member, and from each of the upper clamps a heat conducting path. Thus the sleeve 30 a further pipe 52 carries water to the branch arm 35 serves as an enlargement on the end of the high 53 where the water escapes through perforations temperature rod 22 which may be water cooled into the upper portion of the trough 24. Like su?iciently at its outer surface so that it may wis'e an extension of the pipe 52 communicates be supported on the metal wall of the hub 24 with the pipes 55 which extend longitudinally of and in turn cool the exposed end of the resistor the cylindrical wall ill and near the top thereof. rod. Being made of the same materials, the rod These pipes 55 are perforated so that water may and the sleeve have the same coei?cients of ex issue therefrom and ?ow downwardly over the pansion and the joint therebetween cannot open outer casing wall ill for the purpose of keeping to permit passage of gas to or from the furnace the wall cooled to a required temperature. Suit 45 chamber. able valves may be provided for regulating the Egress of the gases generated during the oper flow of water to these various parts. By using the ation of the furnace is permitted through the sleeve 30, it is possible to cool the resistor rod pipes 34, which have open upper ends and are 22 closely adjacent to the hot zone and thus fur welded to the casing l0 around suitably shaped ther protect the end walls and the insulation 50 holes therein. Plugs 38 of graphite or other suit within the chamber. able material are arranged to close the passages Located within the upper portion of the cas during the cooling stage. When the furnace is ing is a perforated wall 54 made of a coarse running, two of the plugs may be left loosely in meshed screen of iron or other suitable metal place to prevent any circulation of air into the which is arranged beneath the pipes 34 and 55 casing as the generated carbon monoxide gas spaced from the top of the casing wall In to pro escapes through the third opening. These plugs vide a space 56 for the accumulation of’. gases are left somewhat loose however so that they generated within the charge and to prevent the may be blown out by the gas pressure and pro charge from contacting with and closing the vide an emergency exit for the-gas, in case the openings of the pipes 34. These screens may be 60 third passage becomes plugged through a building welded in place if desired, or slidably secured by up of deposited material adjacent to the opening means of the metal strips 51 welded to and pro thereof. During the cooling step, all of the plugs jecting downwardly from the wall ID. This may be ?tted in place, or one may be allowed to space 55 thus provides a passage for the accumu remain open while kerosene is injected to pro lation and escape of the large volume of carbon 65 vide a neutral to reducing atmosphere. monoxide gas which is liberated during the fur The electrical connections are made at the nace run. The exit pipe 34 may be connected to two ends of the graphite resistor 22 by means further piping to conduct the gas away from the of clamps, which comprise two hollow casings furnace for such use as may be desired and par through which water may be passed to keep them ticularly to prevent its escape into the room. 70 cool. vEach of these casings is made of two Or, the gas may be allowed to burn quietly at the semicylindrical concentric walls 40 and 4| con end of the exit tube 34. It will be appreciated nected by the diametrically positioned walls that because of the generation of the large vol 42 and the end walls 43 to form a. closed cham ume of gas during the furnace run, no air can ber. The central wall 4| of each of these clamps enter the exit passage 34. Because of the large 75 is shaped to ?t against the outer surface of the space 56 provided in the upper portion of the 2,141,617 3 reaction chamber, there is also little danger of result in decreasing the boron content, hence a the boron metal vapor escaping through a small primary condition is that of having the tempera blow hole in the charge. and the temperature of ture low enough to prevent that excessive vola the chamber 56 is su?iciently low so that the tilization and to permit the boron metal which vapors are condensed therein and are retained in is freed from its oxide to remain in the central the charge. zone of the charge. It is desirable that the granular furnace charge In accordance with the preferred procedure, itself serve as the container within which the the boron carbide alloy may be made from a ingot of metal carbide may be formed. Conse mixture of granular anhydrous boron oxide and 10 quently, the furnace chamber is made su?i carbon in the required stoichiometric amounts 10 ciently large so as to provide room for an outer according to the principles set forth in my prior zone of the cooled charge which in turn supports patent and applcation. For example, a furnace the inner hot zone within which the ingot is charge of 1000 pounds of anhydrous boron oxide made. Thus, the charge itself serves as a pro mixed with 610 pounds of petroleum coke and 15 tection for the inner cooled wall of iron and heated as herein de?ned will produce, when com 15 neither the boron oxide nor any reaction product pletely converted, about 360 pounds of alloy hav will attack this wall. nor will the wall material ing approximately the composition of 85% boron react with the charge to detrimentally affect the and 15% of carbon. properties of. the desired abrasive metal com By carrying on these various reactions in an pound. As a further insulation,'\the furnace is enclosed furnace, as shown in the drawing, ni 20 lined with an insulative material which keeps the trogen, oxygen and water vapor are excluded and charge from contacting directly with the metal the only gas present is the carbon monoxide walls. A suitable insulation for this purpose com evolved from the charge. Kerosene or other prises ordinary wooden boards which carbonize hydrocarbons may be included in the furnace during the run of the furnace but are not con charge for the purpose of providing a volatile 25 sumed and so remain in a protective capacity. carbonaceous gas which will aid in excluding air The arrangment illustrated comprises a set of and other undesired gases. Hence, the alloy is boards 58 arranged parallel with the resistor not affected by the atmosphere during either the rod and lining the inner furnace wall in except heating or the cooling stages. 30 adjacent to the screen, as shown in Fig. 2. Like If desired, this process may be carried on in 30 wise, the end walls are covered by the boards 59. two stages in which a boron rich material de The furnace walls and the charge located adja rived from an initial furnace run may be re cent thereto must be kept su?iciently cool so that cycled in a second furnace run under the condi their conductivity is low and the danger of cur tions above described so as to still further in 35 rent leakage is small. This is accomplished by crease its boron content. The proportions of the 35 pouring water into the trough 24. and thus cool ingredients of the charge for both the initial and ing the wall l2 by conduction. If desired, a fur the ?nal furnacing step will. of course, be calcu ther water spray may be thrown directly upon the lated to provide the necessary carbon to remove end walls at any suitable point. all oxygen present in the charge and to produce In accordance with the present invention, the by reduction additional boron which will serve to 40 power input to the resistor of graphite or other enrich the ingot. It is also desirable to incor suitable material should be below 22 kilowatts porate the reduced boron rich material from the per square foot of surface area of the resistor preceding run in a zone immediately surrounding employed for the purpose. It is preferred that the resistor. The additional boron oxide and car the energy density range from 18 to 20 kilowatts bon needed for the reaction are placed around the per square foot of resistor surface area. Then zone containing the boron rich material. With by maintaining this particular power input and this practice the electrically conductive nature of by controlling the composition of the charge so the pre-reduced material causes the current to as to provide the required amount of boron for the particular composition of product desired distribute in this zone and, therefore, serves to further lower and distribute the temperature. 50 the reaction may be carried on to produce a ma The optimum power input above de?ned applies terial which may analyze as high as 90% of boron, to standard resistance furnace constructions with the rest made up of carbon and such slight used in the industry and it should not be exceeded amount of impurities as may be present. if a high boron content is to be obtained. In any liVhile the theoretical principles underlying this case the primary condition to be observed is that 55 invention are not fully understood, it is presumed of preventing excessive volatilization of the boron that a higher power input with the attendant content of the charge and to insure that it re higher temperature will result in vaporizing more mains in the inner zone where it may enrich the of the boron from the charge and driving it out boron carbide there present. That is, the tem " wardly. into the outer layers and thus make the perature is so controlled in the reaction zone that ingot itself low in its boron content. If, on the it is held slightly below that point at which the other hand, a lower power input is employed, normal boron carbide or a carbon rich boron car this serves to decrease the temperature of the bide are obtained. Hence the claims which speci resistor nnd charge, and it apparently decreases fy the exact kilowattage are to be thus broadly the tendency for the boron to vaporize and pass interpreted. 85 outwardly as well as for the carbon of the charge By this procedure, I make an alloy or a com or of the resistor core to dissolve in the molten position of matter having a polyphase. polycry boron carbide at the center of the furnace. The stailine. heterogeneous or aggregate structure, decreased distillation of free boron metal outward comprising one phase of crystalline boron carbide ly from the central zone thus results in the boron of the formula 134C intimately associated with or 70 vapor being retained in this inner zone and en cemented together by one or more phases of a riching the B-iC material there present. The boron rich material which has boron for its pri higher temperature may also volatilize the boron mary constituent and is substantially free from oxide or the suboxide and thus drive further uncombined carbon in the form of graphite. LII boron outwardly. Such volatilizing effects all I claim: 76 4 l. The method of making boron rich boron heating a charge of boron oxide and carbon carbide comprising the steps of providing a around an electrical resistor and maintaining charge containing boron oxide and carbon and such an electrical power input that the tempera progressively heating the charge by an electrical ture conditions will insure the formation of resistor to a temperature at which said boron car boron carbide having a higher boron content bide is formed, while maintaining such an elec than is required for the formula 134C, and there trical power input below 22 kilowatts per square after re-furnacing said material intermixed with foot of surface area of the resistor that the tem further boron oxide and carbon proportioned to perature conditions will insure the formation of remove all of the oxygen as carbon monoxide and 10 boron carbide having a boron content higher than to provide additional boron, while maintaining a 10 is required for the formula B40. power input between 18 and 22 kilowatts per 2. The method of making boron rich boron car square foot of surface area of the resistor and ' bide comprising the steps of providing a charge controlling the temperature to insure the forma containing boron oxide and carbon proportioned tion of an alloy of high boron content. 5. A composition of matter comprising mixed 15 stoichiometrically for making boron carbide of 15 the formula B4C together with boron oxide and crystals of boron carbide of the formula 184C and carbon proportioned for forming an excessive of a boron rich material intimately united as an boron metal so as to give a boron content of at aggregate which is substantially free from un least 85%, progressively heating the charge combined carbon in the form of graphite, the 20 around an electrical resistor and maintaining boron content being as high as 85% by weight. 20 such an electrical power input that the tempera 6. An alloy comprising boron and carbon in ture will insure the formation of boron carbide of which all of the carbon is combined in the form the formula 134C and is low enough to form an of ‘B40 and in which additional boron is present alloy of boron therewith and provide a total in a second phase, the boron content being as high boron content of at least 85%. as 85% by weight. 3. The method of making a boron carbide alloy 7. The method of making boron rich boron car comprising the steps of making a boron rich boron bide comprising the steps of providing a charge carbide material by proportioning and electrically containing boron oxide and carbon proportioned heating a charge of boron oxide and carbon in stoichiometrically for making boron carbide of accordance with claim 2, and thereafter re-fur the formula B40 together with boron oxide and 30 nacing said material intermixed with further carbon proportioned for forming an excess of boron oxide and carbon proportioned to remove boron metal, progressively heating the charge all of the oxygen as carbon monoxide and to around an electrical resistor and maintaining provide additional boron, while maintaining a such an electrical power input between 18 and 22 power input below 22 kilowatts per square foot of kilowatts per square foot of surface area of the surface area of the resistor and controlling the resistor that the temperature conditions will in temperature to insure the formation of an alloy sure the formation of boron carbide having a of high boron content. higher boron content than is required for the 4. The method of making a boron carbide alloy formula B40. RAYMOND R. RIDGWAY. 40 40 comprising the steps of making a boron rich boron carbide material by proportioning and electrically