TANTALUM CARBIDE ITS RELATION
TOOTHERHARD REFRACTORY COMPOUNDS PHILIP M. McKENNA Vanadium-Alloys Steel Company, Latrobe, Pa.
I
N RECENT years tool materials harder than any tool steel have been increasingly used in metal-working industries. Examples are tungsten carbide cemented with cobalt, compositions of tantalum carbide with tungsten and nickel, and the same compositions with titanium carbide. These compositions have comprised as major ingredients certain refractory elements or their compounds with metalloids, together with minor percentages of a metal of the iron group. T h e commercial success of these new tool materials has stimulated study of these high-melting metals and compounds. This article discloses new observations of the compounds of tantalum and of columbium with the metalloids carbon and boron, including new figures for densities and crystalline form as disclosed by x-ray methods and pycnometric measurements. For purposes of comparison, it is enlightening to compare this new information with other data in the group of compounds of titanium, vanadium, chromium, zirconium, columbium, molybdenum, hafnium, tantalum, and tungsten, with the m e t a l l o i d s boron, carbon, and nitrogen. Table I shows this information (including new o b s e r v a t i o n s marked with asterisks). Important information is still lacking, and the author is not responsible for the data in cases not marked with asterisks. However, t h e best available information has been given. A MACHINING OPERATION ON 13 PERCENTMANGANESE
STEEL WITH TANTALUM CARBIDE TOOLS
A high melting point seems to be the requisite for the chief ingredient of a successful hard tool material. Substances at present commercially useful include the following: tungsten carbide (melting point approximately 2867” C.), tantalum carbide (melting point approximately 3875” C.),columbium carbide (melting point approximately 3500” C.), and titanium carbide (melting point approximately 3140 ” c.). This requisite is not of itself so important a factor, for these cutting tools rarely attain a temperature above 850” C., but resistance to wear, or what is commonly called “hardness,” seems to be a concomitant of high melting point. The word “hardness” requires special definition to be useful to physicochemical reasoning, for crystalline form or arrangement of the atoms in the lattices as disclosed by x-ray crystallographic analysis affectsthe ease with which solids may be dislocated by shearing forces. The well-known differencebetween graphite and the diamond is a case in point. For present purposes, hardness will be considered as a function of chemical attraction between atoms, specifically in the sodium chloride type lattice as the square of the valence divided by the atomic volume to the two-thirds power. A second requisite is a simple crystalline structure which will permit slippage without breaking-in common words, to avoid brittleness. Crystalline structures with a high order of symmetry are more ductile than crystalline bodies of unequal or inclined axes of symmetry. A third requisite is that connoted by the term “metal” -namely, high thermal and electrical conductivity-and other properties such as are associated with metallic luster. A forth requisite is chemical stability under conditions of use. Referring to the first requisite of high melting point and its associated properties of hardness, Friederich attempted
INDUSTRIAL AND ENGINEERING CHEMISTRY
768
to correlate the physical properties of solid bodies as a consequence of chemical bond. Table I1 gives the calculations with new data on tantalum carbide and columbium carbide following Friederich (11). Included for comparison purposes are the figures for some other well-known compounds crystallizing in the sodium chloride type system. The true densities and lattice dimensions of titanium carbide and vanadium carbide are not known with sufficient accuracy to compare with tantalum carbide and columbium carbide.
~~~
The densities, crystalline form, and lattice dimensions of tantalum and columbium carbides were determined (for TaC, d = 14.48, a = 4.445 A.; for CbC, d = 7.82, u = 4.4578 'ii.); both crystallize in the sodium chloride type. The results are in good agreement with the calculated densities using these lattice dimensions and the new (1936) atomic weights for tantalum and columbium of 180.89 and 92.91. The heat of formation of tantalum carbide is 38 * 5 kilocalories; tungsten carbide (WC) has no perceptible heat of formation. The melting points of carbides of chromium, molybdenum, and tungsten are lower than those of
Tantalum and Columbium Carbides DENSITIES.A new physical form of both tantalum carbide and of columbium carbide was prepared, and the purities were checked by chemical and spectrographic tests. The densities of these substances were determined by pycnometric methods. The density of different samples of this tantalum carbide was observed t o be 14.51, 14.46, 14.49, and 14.47 grams per cc. compared to water a t 20" C. The average is 14.48 at 20" C. This figure is considerably higher than the result of 14.05 reported by others (8). The new form of tantalum carbide has a typical golden metallic luster. The density of the new form of columbium carbide, with a lavender-gray luster, was found to be 7.82, compared to water a t 20" C. This value compares with previous reports of 7.56 for the density of columbium carbide (6). LATTICEDIMENSIONB. The lattice dimension of tantalum
VOL. 28, NO. 7
carbide was determined by back-reflection precision methods, and was found to be a = 4.445 * 0.0005 A., compared to previous reports of figures varying from a = 4.427
~
TABLEI. COMPILATION OF DATAON Titanium Ti boride 9 (6) Electrical resistance, 0.152 X 10-4 (6); temp. liquid air, 0.037 X (6)
H
+
Vanadium boride 9 (1% Elec. res., 0.16 X 10-4 (room temp.), temp. liquid air, 0.035 X 10-4 TT
H
Zirconium
Chromium Borides
+
CraBz (9) d = 6.7 (9)
(6)
CrB (9) d = 5.4, 5.5, 6.1 (9) H 8 (9)
Columbium
Zr boride H 9 (6) M. p. 2990' C. 50' (6) Elec. res., 0.092 X 10-4
+
f
(6)
ZrBz* d = 5.64 approx. Hex. a = 3.15 c = 3.53 - = 1.12 a
*
0.02
Carbides
TIC H 8 ( + 9 ) (6) NaCl type, a = 4.60 (6) d = 4.25 (6) M. p, 3140' C. * 90" ( 6 )
+ ?
vc
H 9-10
(6)
d = 5.36 (6) NaCl type, a = 4.30 (6) Elec. res., 1.56 10-6 (?) M. p. 2830' C. (?) ( 1 6 )
Cr4C d = 6.97 (18) cfc a = 10.638 (18)
CraC2 d = 6.683 (18) Rhombic (18) a = 2.821 b = 5.52 c = 11.46
ZrC H 8-9 ( 6 ) d = 6.90 ( 6 ) NaCl type a = 4.76 (6) M. p. 3530' C. (1) Elec. res.. 0.634 X 10-4 (5): temp. liquid air, 0.378 X 10-4 ( 5 )
CbC d = 7.82* (d = 7.56) (6) M.p. 36OO0C. 125' (1) Color, lavender-gray* NaCl type f
a = 4.46* (a = 4.40) (6. 13)
> quarts M. p. 1890' C. (15)
H
C r G (18) Hex. a = 13.98 c = 4.523 - =
a
TiN H 8-9 ( 6 ) NaCl type ( 6 ) a = 4.40 (6) M. p. 2950" C. * 50' (6) d = 5.18 (5)
VN d = 5.63 ( 1 5 ) M. p. 2050' C. ( 1 5 ) NaCl type a = 4.28 (18)
0.324
Nitrides CrN Decomposes a t 1400' C. NaCl type a = 4.140 (18)
ZrN H + 8 d = 6.93 (5) NaCl type a = 4.63 (14) Elec. res., 0.136 X 10-4 (6'); temp. liquid air, 0&%7 X 10-4 (6) M. p. 2983' C. * 50 (6)
CbN d = 8.40 (6) NaCl type a = 4.41 (5) H 8 (5)
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
JULY, 1936
RECONCILIATION OF DENSITYAND LATTICE DIMENSIONS. According to Becker (6) columbium carbide has a calculated density (from a = 4.40) of 8.20 against his observation of 7.56. Likewise tantalum carbide is recalculated (from a = 4.49) to have a density of 13.95 against his observation of 14.05. With the new data, much closer checks are obtained between densities calculated from the x-ray observations and the pycnometric determinations. Calculating the density of tantalum carbide from the figure obtained in this laboratory as the average of four determinations ( a = 4.445), we obtain
either carbon or the metal; carbides of tantalum, columbium, vanadium, haf nium, zirconium, and titanium have higher melting points than the respective metals. ZrBz,TaBz,CbBz were subjected to x-ray crystallographic examination and yielded definite patterns, but no evidence of a compound TaB was found. Uses of hard carbides of tungsten and tantalum as constituents of tool materials are discussed. Compositions containing 80 per cent tantalum carbide are little affected by acids such as sulfuric and hydrochloric; they are harder than steel, and have a strength of 275,000 pounds per square inch on cross rupture tests.
-
4 X 192.88 X 1.6489 X (4.445 x 10-)a
4 X 104.91 X 1.6489 X lowz4= 7.81 (4.4578X
HIGH-MELTING COMPOUKDS" Hafnium
Tantalum
Tungsten
Borides M03& (30) d = 7.1 (90) H 9 (30)
+
MoBz
Mo& H 7-9 (6) d = 8.9 (6) M. p. 2687' C. * 50' (1) Hex. close-packed a = 2.99 (6) c = 4.72 (6) - = 1.68 (6)
Hf boride M. p. 3062' C. Elec. res., 0.10 X 10-4 (room temp.)
TaBz (3) H 9 (3) d = 11.0 (9)
+
Carbides TaC H + Q M. p. 3887'C. * 150' (5) d = 14.49* Elec. res., 1.09 X (5) M. p. 3875'C. * 150' (1) Elec. res., 0.17 X 10-4 (8) [i x 10-4 (1,611 NaCl type a = 4.446* Color, golden metallic HfC ~~. d = 12.20 (5)
WBz d = 10.77 (81) H + Q
MoC H 7-8 (6) d = 8.40 (6) M. p. 2692' C. * 50' (1) Hex. close-packed (8)
w.c H9-10 (6) d = 17.20 (6) Hex close-packed ( 6 ) a = 2.99 c = 4.72 - = 1.578 a M. p. 2867' C.
(1)
WC H 9 (6) d = 15.50 (6) Hex. close-packed (6) a = 2.94 c = 2.86
+
a = 4.88 c = 6.64
- =
'
a
- = 1.34
0.973
M. p. 2867' C. * 50'
Nitrides TaN H 8 (6) d = 14.1 (calcd., 6) M. p. 3090' C. * 50' (6) Hex. a = 3.05 c = 4.95
+
- = 1.62 a =
This compares with the observed density of 7.82 f o r t h e n e w f o r m of columbium carbide. The old atomic weight for c o l u m b i u m (93.1) would yield a h i g h e r density than when the n e w (1936) a t o m i c weight of 92.91 is employed in the calculat,ion (16).
*50°
* Hardness (H) is given on Mohs' scale (diamond A n asterisk indicates that the datum is new.
= 14.47
which is in excellent agreement with the average pycnometric density figure, 14.48. The old atomic weight of tantalum accepted prior to 1936 was 181.4, which gives a molecular weight of 193.4 instead of 192.88, and would give a calculated density of 14.525. Hence, the new atomic weight for tantalum is more consistent with observations made here. Recalculating the density of columbium carbide from the new observed lattice dimension of a = 4.4578, we find
(19) to a = 4.49 (6). The lattice dimension of columbium carbide was found to be a = 4.4578 * 0.0003 8.,compared to a previous report of 4.40 (6).
Molybdenum
769
10); electrical resistance is given in ohms per cm.
Table I11 s h o w s the observations reported to date on the density and lattice p a r a m e t e r s of columbium and tantalum carbides.
Zirconium Boride h c o m p o u n d of zirc o n i u m , boron, a n d a small amount of carbon: was prepared by heating zirconium dioxide and carbon with an excess oE boron o x i d e a t about 2000" c.: ZrOp
+ BzOs+ tic----+ ZrBz + 5C0
Three t i m e s a s m u c h b o r o n o x i d e a s indicated in the above equation w a s e m p l o y e d . The heating was done in an Acheson g r a p h i t e crucible with 492 grams zirconium dioxide, 840 grams boron oxide, and
.
770
INDUSTRIAL AKD ENGINEERING CHEMISTRY
VOL. 28, IVO. 7
OBTAINED BY CONSIDERING THE VALENCE SQUARED DIVIDED BY THE ATOMICVOLUME TO THE TWO-THIRDS TABLE 11. FIGURES POWER IN A SERIES OF COMPOUNDS OF SODIUM CHLORIDE TYPECRYSTALLINE ARRANGEMENT Compound"
NaCl
Valence Density Lattice a htomic vol.
1 2.2 5.628 13.53 18
100
w* x -*VADJS
AgCl
NaF
1
1
5.56 5.54 12.8 19
2.83 4.62 7.42 26
PbS
CaO
MgO
TIN
ScN
VN
CbN
2 7.42 5.97 16.1 63
2 3.37 4.79 8.39 97
2 3.65 4.20 5.57 127
3 5.18 4.40 6.17 268
3
3
3
4.46 4.44 6.65 255
6.63 4.28 5.77 280
8.40 4.41 6.42 260
-
a These compound8 are all of the same crystalline form-NaC1 type cubic. W valence; V A = atomic volume = atomic weight/density.
*
111. LATTICEPARAMETERS AND D~NSITIES FOR TANTALUM AND COLUMBIUM CARBIDE Investigator ao, A. Calcd. Density Gramsjcc.
TaC
4.56 4.427 4.49 4.4460 4.445 4.4450 CbC
4.40 4.4578
ZrC
HfC
4 6.90 4.76 7.48 418
4 12.20 . 7.81 406
..
VC 4 5.36 4.30 5.87 491
CbC
TaC
4 7.82 4.46 6.708 450
4 14.47 4.445 6.67 452
The distance a is the number of AngstrBm units between similar kinds of atoms.
TABLE:
Becker and Ebert (7) McKenna, Smith, and Walters
TIC 4 4.25 4.60 7.05 435
8.20, 7.56 7.81, 7.82
the structure indicated by the two films. There were just the exact number of lines of the correct relative intensities to place the zirconium atoms on the lattice points of a simple hexagonal cell with an axial ratio of c/a 1.12 * 0.02. This leads to values of c and of a of 3.53 and 3.15, respectively. The zirconium atoms in the pure metal are on the lattice points of a close-packed structure with an axial ratio of c = 1.59. This seems to be a logical variation in arrangement inasmuch as there is 66.66 a for each per cent of boron present, which must be included somewhere. The more open simple hexagonal lattice would allow this.
Thermal Properties of Carbides and of Twoe Component Systems 120 grams carbon black. After cooling, a gray friable mass was obtained in the lower part of the crucible, weighing 446 grams. Boiling with hydrochloric or with nitric acid had no effect. Chemical analysis showed (in per cent) Birconium, 78.55; boron, 18.15; carbon, 1.89; silicon, 0.03; total, 98.62. Spectrum analysis showed the presence of some iron in this product. The density was 5.64 compared to water at 25" C. On the assumption that a compound ZrBz exists, it would contain about 19.2 per cent boron. Therefore this material is probably ZrB2, with impurities. A portion, 170 grams, was heated with 8.5 grams boron oxide in a vacuum electric furnace at 1530" C. and resulted in a carbon content of 1.09 per cent. Two x-ray spectrograms of the purified product were made. When the sin 8 values for the various lines of the two photograms were fitted on a series of Davey-Hull charts, an exact agreement was found between
MACHINING STEELWITH TANTALUM CARBIDE TOOLS (Note the interrupted cut.)
Of the materials used in modern hard-tool compositions, (1) tantalum carbide and (2) tungsten with carbon differ fundamentally. As to crystalline form, the tungsten-carbon system is of close-packed hexagonal form, whereas tantalum carbide, columbium carbide, and titanium carbide definitely crystallize in the sodium chloride type cubic system. It should be noted that according to the best available data the tungsten-carbon systems and the molybdenum-carbon systems melt at temperatures below the melting points of their respective metals; on the contrary, the melting points of the other carbides mentioned which are in the IV and V groups of the periodic table, have melting points higher than those of their respective metals. This is shown in Table IV. Since a definite and sudden increase in melting point of a two-component system is interpreted by physical metallurgists to mean the formation of a comDound, it was believed that the compounds of tantalum, columbium, vanadium, hafnium, zirconium, and titanium with carbon are of a more definite and stable nature than those of tungsten and molybdenum with carbon, if indeed these latter two systems may be said to be chemical compounds at all. Accordingly, determinations of the heats of combustion of tantalum carbide and tungsten carbide were made with a view to establishing the heats of formation of the alleged compounds. In confirmation of this, tantalum carbide was found to have a positive heat of formation of 38 kilocalories per gram molecular weight, while the tungsten-carbon system gave a zero heat of formation. The determination of the heat of formation of tantalum carbide was as follows: OBSERVATION.The value 1590 calories was obtained by burning 1.000 gram tantalum which contained 6.31 per cent carbon in a bomb calorimeter of the Berthelot type in oxygen of 25 atmospheres ressure. KNOWN %AT,. Tantalum plus oxygen gives 498.3 kilocalories per gram molecular weight of tantalum pentoxide (17). Carbon plus oxygen gives 94.4 kilocalories per gram molecular weight carbon dioxide.
771
I\-DUSTRIAI, AND ENGINEEHIXG CHECIISTIIY
JULY, 1936
CALCUWTIONS. A 1.000-gram sample of tantalum carbide containing 0.31 per cent carbon contains 0.9369 gram tantalum and 0.0631 gram carbon, whichgives0.005165moletantalum and 0.005258 mole carbon, using the atomic weights given in International Critical Tables (tantalum = 181.4, carbon = 12.00). (If the atomic weight of tsntalum is taken as equal to 180.89, the new d u e , then the amount of tantalum becomes 0.005179 mole.) K d ocu1. Hent from burning 0.005185 gram mol. r t . 01 T a Heat from burning 0.005165 gram mol. wt. oi c Heat from burning 0.000003 gram mol. wt. of c Total best if elamenta were uncombined Hest of oombvstian sotually observed Far 0.005165 TaC For 1 mole TaC
1.287 0.488
0.009 1.784
1.590 . 0.194
3s*5
*.!I
The uncertainty is about kilocalories. Therefore should write: Ta(c) + C(c) = TaC(c).Q = 88 * 5 kilooal.
we
Likewise the heat of formation of tungsten carbide was investigated by combustion in oxygen in a bomb calorimeter, obtaining a value of practically zero for the heat of formation of tungsten carbide. One gram of tungsten carbide gave 1461 calories or 286.3 kilocalories per gram molecular weight of 196 grams compared to the total heat of 286 kilocalories which would have been obtained from burning the equivalent amounts of tungsten and ca.rbon separately, using the data in International Critical Tables for the heats of formation of tungsten trioxide and carbon dioxide.
Group IV. Column .--I Element Atomio wt. M p. Carbide
c. Ti
zr
Hi
41.0 91.22
178.6
1800
1700 1700
M. p. 0
Tic BrC IIiC
3530 3887
Inner diffrsction circle Intermediate diffraction eirole Outer diffrsction e i ~ c i e
" c. V Cb
'rn
50.95 92.91
180.~9
The products of the corubustions were carefully examined, showing them to be pure oxides, and the carbon dioxide gas was weighed, checking the completeness of the reactions.
Borides of Tantalum and Columbium Of tho compounds of tantalum and of columbium with boron, TaBl and CbR2 were made corresponding to the formulas of Andrieux (3). These compounds yielded definite x-ray diffract,ion spectra but were not identifiable here BS any of the simpler forms. Some of the literature hesitates to supply a formula for tmtalum boride or colunrbium boride. Substances were also prepared here corresponding to the rough composition TaB, but x-ray diffraction patterns of these were not obtained, the rays being entirely scattered; this behavior indicates tliat they were not compounds but mixtures in a h e degree of dispersion. Ilence no corroboration of a compound TaB was obtained.
Cu Kg (028) Cu KO, 1044) Cu K,. (044)
found for these eompounris is a mixture of hydrofluoric and nitric acids. Technical uses of conlpositions of tantalum carbide in the chemical industry have inclnded spray nozzles for clieniicals. Here we lrave a hard met;tlic material with a hardness
__-Group v, column I Element Atomio w t . M. D, Carbide
c.
8146
FIGURE 1. BACK-REFLECTION PHOTOQRAM mn DETERMINING LTTICE Pmmmsa OF COLUMRIVM CARBIDE
1710 1950 28511
-.
x.p. 0
YC CbC 'rat
~~~~
@"up 7'1. Colurmn I
Element Atomic wt.
c. ..
2830 3600 3875
.M. D . 0
Cr .\lo
w
52.01 96.0 184.0
Cerhide
c.
1615
2820 3370
-
. .... M . p. 0
CGr? XOC
wc
c.
1800
2892 2867
much greater than steel and .iTith noncorrosive properties which approach platinum. Tests in various corrosive substances of composition comprising 80 per cent tantalum Carbide and the balance tungsten metal and nickel are s h o m in Table V. This tantalum carbide alloy lias a strength of 275,000 pounds per square inch in transverse rupture t,est and a Rockwell hardness of 88.4A, which is much harder than the hardest steel. That a inetal composition possessing this combination of physical and chemical properties is destined to play a large part in chemical industry seems obvious. TABLEV. ConnosIoN RESISTANCE 'hsm (Lusser i n ins. from 24-hour immeiaion st room temperatme: pieces of aDDioaimatelri eaual srea 13.2 BO. om.) ueivhinr ~. .. . about 5 z r ~ m seaohl TypiiTaC ---Typiesl W C Ailo B .Alloy !?4.5dwc, Reagent 80% TaC. S776 WC 5.57 Ca (Asueoue Sulns2 207" Ni w la% co' Fe
z.8
Technical Uses The technical use of such bard compounds as are discussed in this article requires that compositions containing them BS ingredients be capable of resisting mechanical stresses. Therefore, compounds with unsymmetrical structuresthat is, other than cubic or hexagonal-are generally not so well adapted t o these uses, for it is a general rule that such solids are brittle in aggregates. The chemical properties of compounds given in Table I are iargely influenced by the character of the metal atom in each compound. Carbides and borides of tantaluni, for instance, may be boiled with nitric acid solutions, with hydrochloric acid, or with mixtures of the two without effect. The only acid solvent
Its influence as a tool material in the chemical industry has already been felt, for tantalum carbide compositions are used to tip lathe and boring tools with which we may cut such hard and corrosion-resistant materials as stainless steels (both in the annealed and in the hardened condition), stellites,
INDUSTRIAL A 3 D ENGINEERING CHEMISTRY
772
VOI,. 28, NO. 7
Literature Cited (1) Agte and .Uterthum, Z. tech. Physik. 11, 182-90 (1Y30) ( 2 ) Andrews, Mary. J . Am. Chem. Soc., 54, 1845 (1932). ( 3 ) Andrieux, M. L., Compt. lend., 186, 1299 e t seq. (1929). ( 4 ) Arkel, A. E. v ~ n , Physim, 4, 286-301 (1924).
(5) Reoker. K., "Hochsohmelucnde Hertstoffe und ihre teohnisohe Anwendung," Berlin. Verleg Chimie, G. m. b. H.. 1935. (6) Booker, IC.,Phyaik. 2.. 34,185-97 (1933). (7) Becker. K., and Ebert, F.. 2.Physik, 31,
- " .~ ,10')RI ~."_",. 9RPc711
(8) Beoker and Ewest, Z. tech. Physik. 11. Toor. of TANTALUM ALL~V 218 (1930). (9) Binet de J~ssoneix. Corn@. rend.. 143, 1149 (1886). and other corrosion-resistant (IO) Burgers, W. G., and Basart. J. C. M. alloys of high chromium conZ. anorg. allgem. Chcm.. 216, 209-22 (1924). tent, such as Durallov, 1, (11) Friederioh. Emst, "Die physikdischen S i l l i c h r o m e , Illium, and ' Eigensohaften des festen Zustandes als others. Hadfield's 12 per Wirkungen der chemischen Bindung: Ahhanrlhmo a i l s d a m Oavnm cent manganese steel used in ._I ll.l gonvem B. I.;' pp. 335-42. ne.lin. Julius abrasion-resisting g r i n d i n g PADDLES roti CL.LY-MIXINQ MACHINES, Wmca Springer. 1930. machinery in the cheniical MUST WITHSTAND CONSIDERAHLE AHRASI~E WEAR,ARIBMAD^; OF 13 Pm CENTM ~ N ~ ~ N E B(12) ~ Friedsrioh, Emst, hrtach7. C h a . Physik i n d uinable s t r i e s ,,,ith is commercially tantafuni ST'EEL, OtiDlNAtiILYCoNsIDEHED UNMACUINAtiLE pbysik. Chern., 18. 713-36 (1926). (13) Friederieh and Sittig, Z. anorg. allgem. carbide tools. These alloys Chem., 144, 169 (1925). (141 Goldsohmidt, Y. M., report in 'Stmkturberioht. 1913-28." hy are therefore made more available to use in chemical industry Ewnld, P. P.,slid Hsnnann, C., Leipzig, Akademisohe Ye*in finished machined forms. Isgsgesellsehaft. 1981. Tantalum carbide possesses tile Ilighest Inelting point of (~,i) International Critical Tables, v01. I. p. 135. ~ e w York. all substances (with the wssible excention of hafnium carMcGraw-Hili Bonk Co.. 1926. (16) International Uni& of Chemistry. Committee on Atomic bide). Since other valnagle pl~ysicaland chemical properties Weights. 3. Am. Chem. Soe., 57, 790, 791, 793. 794 (1935). are associated with it as required by physico-chemical theories, (17) Moose and Parr, J . A m . Chem. Soc., 46, 2656 (1924). the increasing technical use of tantalum carbide for high-duty N ~ , M. ~(;., ~e~ItSntgcnogrsphic ~ ~ ~ der ~ Motalle ~ , ihrs to he inevitable. services of all kinds appeam Leaieruncen." Stutt,mrt. Ferdinand Enke Verlae. 1929. .. (19) Sehwhre, "on, and Summa, O.,DPeldluirtscho~t,"fZ,No. 21. Acknowledgment 29R (1933). (20) Tucker and Moody, Proc. Chem. Sac.. 17, 129 (1901): J . Chem. Grateful acknowledgment is hereby made to F. M. Walters, Soc., 81, 14 (1902). Jr., €1. A. Smith, D. It. Harper, 3rd, C . W. Balke, and Vv'illiain (21) mdekind. R ~ ~46. . .1198 ( I ~ I : < ) .
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THE SOYBEAN A Plant Immigrant Makes Good W.L. BURLISON University of Illinois. Urbana, Ill
ILE soybean is one of the oldest c r o p grown. It was dewihcd in a Chinese book on materia medica, "Ben Tsao Cane Mu." witten hv Eirineror Shon-Knne about 4800 years ago.' In China "and japan the soybian has heen of prime importance since ancient times, and in value and variety of uses is still the outsdanding legume grown in those countries. Production of soybeans in Asia is concentrated in Japan, Korea, and two regions in the eastern part of China. Previous to 1908 the trade in soyheans was confined almost altogether to oriental countries, particularly China and Japan. Since then the usefulness of t.he soybean has been more generally appreciated in other countries, and an important international trade has developed. Soybeans were introduced into the United States in 1804, yet a hundred years later there Were very few grown outside the southern states. By 1919 t,he crop had reached a fairly uniform development in t,he area east of the Mississippi
River arid considerable prominence in New England and certain southern and western states. However, the total acreage of soybeans in the United States Boctnated noticeably, and by 1924 had decreased in the eastern part of the country, particularly in Kew England and New York. In 1924, twenty-two states produced the hulk of soybeans in the United States, the total crop of gathered beans being slightly above 5,000,000 bushels. From 1924 to 1935, inclusive, production increased rapidly, figures for 1935 indicating a total of nearly 39,637,000 bushels of gathered beans. The more rapid increase of production has occurred in the corn-l,elt states, particularly in Illinois, Missouri, Indiana, and Iowa. In 1933 Illinois produced about one-half of all the beans crushed in Amerien.
Description of the Bean The soybean (Soja mm) is a suniiner leguir~inousannual. Pods are from 1 to 2.5 inches long and contain from two to four seeds. The stems, leaves, and seed pods are covered with short reddish brown or gray hairs. The root tubercles are large and ahundent. There are many varieties of soy-
