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M. R. N A D L E R .kND CHARLES P. KEMPTER
Vol. 64
SOME SOLIDUS TEMPERATURES I N SEVERAL METAL-CARBON SYSTEMS BY M. R. KADLER AND CHARLES P. KEMPTER Los Alamos Scientific Laboratory, University of California, Los Alamos, New Mexico Received April 4, 1960
Minimum eutectic temperatures were determined for systems involving carbon and some refractory metals. These solidus temperatures for the systems C-, Ta, Os, W, Re, Nh, Ir: Mo, Ru, 50Ir-50Rh, Pt, Rh and Pd are 2902, 2732, 2732, 2486 2328, 2296,2210, 1942, 1932, 1736, 1694 and 1504", respectively. For the Nb-C system, the Nb& peritectic and the N b d C eutectic are located at 3080 and 3220", respectively. For the Ta-C system, the Ta2C peritectic and the TaC-C eutectic are located a t 3500 and 3710", respectively. The melting points of Mo2C, WC and NbC are 2410,2720 and 3480", respectively.
Introduction Measurement of temperatures above 1500" in carbon atmospheres is very difficult in situations where optiral methods cannot be employed. Thermocouples using combinations of refractory metal wires, carbides and graphite have been most recently reviewed by Thielke and Shepard,' and are being further developed. The absolute maximum operating limits of such thermocouples are fixed by certain eutectic, peritectic and compound melting temperatures of the thermoelements in combination with carbon. Another method has been used in this Laboratory for determination of the maximum temperature which was obtained in short-time high-temperature situations. In this method, small pieces of refractory metals are placed in contact with graphite at the point of desired measurement. Indications that a liquid phase had formed with a particular metal is evidence that the lowest eutectic temperature had been exceeded in that metal-carbon system. This investigation involved the determination of minimum (eutectic) solidus temperatures in various metal-graphite systems, and of some eutectic, peritectic, and compound melting temperatures in carbide systems. Alaterials of interest included all of the platinum group metals, molybdenum, tungsten, niobium, tantalum, rhenium and the carbides of molybdenum tungsten, niobium and tantalum. These include all metals melting in excess of 2000". Of the six Group T'III noble metals, zl carbonmetal solidus has been determined only for platinum. Using rigorous experimental techniques, Collier, Harrison and Taylor2 found a platinumcarbon eutectic a t 2007 f 3°K. (1731 i 3") corresponding to approximately 1.2% carbon. (In this article, all carbon percentages are given in weight per cent.) Hughes3 has reported an M-C solidus temperature of 2480" (at 1.3% carbon) for rhenium (Group VII). For the Mo-C system, Takei4 reported a Mo-Mo& eutectic at approximately 2200" and 4% carbon. Sykes, Van Horn and Tucker5 found this solidus point at 2200 i 25" and approximately 1.8% carbon. For the (1) N. R. Thielhe and R. L. Shepard, "High Temperature Thermocouples Baqed on Carbon and its Llodifications," High Temperature Thermometrv Seminar, Oak Ridge National Laboratory, Octohei, 1959. (2) L. J . Collier. T. H. Harrison and W. G. A. Taylor, Trans. Faraday Soc., 30, 581 (1954). (3) J. E . Hughes, J . Lesa-Common Metals, 1, 377 (1959). (4) T. Takei, Science Repts. Tohoku r n t v . , 17, 939 (1928). ( 5 ) W. P. Sykes. K. R. Van Horn and C If. Tucker, Trans. A I M E , 117, 17.3 (193;).
IV-C system. Ruff and Wunsch6 found the first eutectic (W-WpC) at 2690" and approximately 1.4% carbon. S y k e ~ ,however, ~ reported this eutectic to be a t 2175" and approximately 1.5% carbon. A phase diagram for the Nb-C system was first published by Pochon, McKinsey. Perkins and Foreng,8 mho reported the Kb-NbeC eutectic a t 2335 f 20" and 1.5% carbon and the NbzC peritectic at 3265 f20". Elliottgreported the Nb-NblC eutectic a t 2230" and 1.50% carbon and the NbC-C eutectic at 3250°.2 Storms and ICrikorian'O located the Nb-Xb& eutectic a t 2335 & 20°, the SbzC peritectic at 3090 f 50°, and the melting point of NbCose a t 3500 f 75". A phase diagram for the Ta-C system was first published by Ellinger," who found the Ta-TapC eutectic a t 2800" and 0.6% carbon, the Ta2C peritectic a t 3400°, and the TaC-C eutectic at 3300" and -10% carbon. Pochon and co-tvorkers18 however, placed the Ta-TazC eutectic at 0.8% carbon. No solidus temperatures have been reported for an KbC-C eutectic . The melting points of RloL!, WC, NbC, TaC and Tad2 have been most recently reviewed by IIansen.12 The various reported values are &lo&: 2405, 2230-2330, 2690 f 50'; WC: 2650 f 50", 2780, 2880, 2870, 2600 and 2630"; NbC: 37003800°, 3500 f 125'; TaC: 3730-3830", 3880 f 150°, 3540"; and Ta&: -3400". The melting points of Nb2C, KbC and Ta,C reported too late for inclusion in Hansen's reviev are discussed above. The MzC type carbides listed do not exhibit true melting points since they first show the appearance of liquid a t a peritectic point. Experimental The experimental work was divided into two phases: (1) detrrmination of the minimum solidus temperatures in metal-graphite systems, and (2) determination of eutectic, peritectic and compound melting temperatures in carbide systems. For the metal-graphite systems, wires were obtained for a11 of the metals except ruthenium and osmium, which (6) 0. Ruff and R. Wunsch, Z . anorg. Chem.. 86, 292 (1914). (7) 3'. P. Sykes, Trans. A S S T , 18, 988 (1930). ( 8 ) Jf. L. Pochon, C. R. hIcKinsey, R.A. Perkins and W, D. Forgeng, "The Solubility of Carbon and Structure of Carbide Phase8 in Tantalum and Colunibium," Union Carbide Corporation Report, August 29, 1958. (9) R. P. Elliott, U. S. At. Energy Conim. Report A R F 2120-4, May 6, 1959. (IO) E. K. Storms and N. H. Krikorian, THISJOCRXAL,64, 1471 (1960). (11) F. H. Ellinger. Trans. A S M , 31, 89 (1943). (12) hl. Hansen, "Conetitution of Binary Alloys." McGraw-Hill Book Co., New York. N. Y., 1958.
SOLIDUS TEMPERATURES IN METAL-CARBON SYSTEMS
Oct., 1960
TABLE I SIZES AND SOURCES OF Wire
hfETALS USED
diameter,
inches
Source
Palladium 0 039 Johnson, Matthey and Co., Ltd. Rhodium ,020 Bram Metallurgical-Chemical Co. Platinum 025 Unknown Iridium-50 Rhodium .OlO Engelhard Industries, Inc. Ruthenium .062“ Varlacoid Chemical Go. Molybdenum .OS0 Unknown Iridium ,010 Engelhard Industries, Inc. Kiobium .062 Fansteel Metallurgical Corp. Rhenium .(I62 Chase Brass and Copper Co. Tungsten ,080 Unknown Osmium .062“ J. A. Samuel and Co., Inc. Tantalum .060 Unknown 5 0.062” diameter pellets pressed from metal powder. Wire not, available from ruthenium or osmium. were not commercially available in wire form. These two metals were obtained in powder form and cold-pressed into ’/16’’ diameter pellets in a steel die. Table I gives the
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sizes and sources of the metals used. Those metals known to carbide (Le., molybdenum, tungsten, niobium and tantalum) were used in large enough diameters to ensure a metal-rich system during the few minutes required to reach the testing temperatures. Results of spectrographic analysis of the metals are given in Table 11. The iridium-rhodium alloy wire analyzed 50.0 weight %rhodium. A piece approximately l / s t t long of a metal to be tested was placed in an axial off-center hole drilled in a cylinder of spectro grade graphite 6/16” in diameter by 8/8” high. The hole was 1/,” deep and not more than 0.002” larger in diameter than the particular piece of metal to be contained. The graphite cylinder fitted snugly into a graphite crucible with lid, which was positioned inside a cylindrical graphite susceptor. A split graphite radiation shield 3/4” 0.d. by 1-s/8”high with slotted lid separated the susceptor from a water-cooled copper concentrator. Temperatures were read optically through a 1/12’’ diameter hole in the crucible lid into a 1/18‘’ diameter hole drilled I/d’’ deep in the center of the spectro graphite cylinder. Temperature measurements were made with a Leeds and Northrup optical pyrometer which had been checked against an NBS-calibrated pyrometer. Corrections for the window and prism were made to 2000” using an NBScalibrated standard lamp, and to 2850” by simultaneously observing an induction-heated tantalum carbide target directly with the NBS-
TABLE I1 SPECTROGRAPHIC AXALYSIS RESULTS(IN P.P.M.BY WEIGHT“) Rli
Pd
Li Be
ND ND
B
KD XD
Ya bIg A1 Si I< Ca Ti
v
Cr RIn Fe Co Si Zn Sr Zr Xb Mo Ru Rh
