Ah-AL Y TICAL EDI T I O S
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Vol. 2, KO.1
Determination of Carbon in High-Melting Alloys Using the High-Frequency Induction Furnace' G . Frederick Smith and G . L. Hockenyos UKIVERSITY OF ILLINOIS, U R B A N A , ILL.
HE determination of carbon in steel b y direct combus- induction furnace to prevent the difficulties described. The tion in oxygen a t 900-1 100" C. gives satisfactory results only objection to the proposed scheme is the cost of equiponly if the sample completely fuses during oxidation. ment. The use of high-frequency units in the preparation Failure to obtain fusion results in incomplete remora1 of of such alloys as those proposed for analysis provides access carbon as carbon dioxide. I n the customary combustion to the equipment required where most in demand. The train using a nichrome-mound electric furnace and silica smallest type of high-frequency induction furnace in common combustion tube, 1000" C. is the maximum practical tem- use serves the purpose, and costs but three or four times as perature for continuous use. with 1100" C. as the actual much as the good types of low-voltage, high-amperage, wirelimit for intermittent use. Such wound combustion furnaces with transformer and rheononferrous alloys as illium, stel- stat. B y principle there is no trouble from burned-out units lite metal, and their substitutes or need for expensive silica combustion tubes, and in addition cannot be fused during oxida- the process provides for the use of other than very finely dition a t 1100" C. Similarly, vided samples, The old process frequently requires the us? high-speed tungsten tool steels, of the diamond mortar for crushing the sample, whereas the stainless steels of high chromium new process permits very coarse cuttings or chips to be emcontent, etc., often do not fuse ployed. This fact is a distinct advantage, since the materiduring oxidation a t this tempera- als under consideration are difficult to sample. Other advantages will become apparent from the description of the ture. The properties of these alloys process. depend materially upon their Apparatus carbon content. The accurate determination of carbon is mad? Differing from the usual carbon combustion tube of silica following a modification of the used in a horizontal position, the induction-furnace combususual procedure. I n brief, this tion tube is made of Pyrex tubing and is held in a vertical modification consists in burning position. The combustion tube (a, Figure 1) is 15 by 15 a 5- or 6-gram sample of low- inches (38 by 38 cm.) with wall thickness of approximately carbon iron, such as American 0.04 inch (1.02 mm.). It is rounded a t the bottom and ingot iron, as if for the deter- flanged at the top to receive a two-hole rubber stopper mination of its carbon content, fitting well down into the tube and carrying a l/d-inch (6-mm.) but adding a 0.5- to I-gram sam- gas intake and exit tube, the former reaching to within 2 ple of the high-melting alloy. inches (5 em.) of the bottom. The bottom of the combustion Otherwise the usual procedure tube is filled 1 inch (2.5 em.) deep with RR alundum sand is followed exactly. The heat a n d t h e r e a c t i o n of combustion of the finely thimble placed on this I Figure 1-Combustion Tube divided turnings of ingot iron sand. More sand is a n d Thimble brings about fusion of the entire t h e n i n t r o d u c e d sample. The temperature thu; obtained locally, starting around the reaction with 1000° C., probably exceeds 1600-1800° C., depending thimble by means of upon the rate a t which the oxygen is supplied. A similar a small long-stemmed process was described by ?clam ( 1 ) . funnel, to keep the This procedure has many practical disadvantages. There thimble from tilting is a tendency to push the heating of the combustion furnace against the combusto its upper limit to offset the cooling effect due to the intro- tion tube. duction of the comparatively large sample of materials being T h e combustion burned. Heating units consequently require more frequent thimble (b, Figure 1) changing. The excessive spattering of the burning sample, is 1 inch (2.5 cm.) even when the various common protecting measures are high and 1 inch (2.5 used, frequently results in destruction of the expensim cm.) in outside disilica combustion tube. The fusion of the large sample ameter with a flat employed often overflows the alundum boats. even if alun- bottom and inch dum sand is employed as a protectire lining, in which case (3 mm.) wall thickthe combustion tube is perforated. The use of nickel boats ness. To make these of heavy gage with sand does not solve this difficulty, and thimbles equal proFigure 2-Ajax-Northrup 3 kv-a. the process inyariably proves troublesome from all these portions of alundunl Converter causes except in the hands of an unusually skilled manipula- cement a n d T e n tor, and even under the best conditions accidents are fre- nessee ball clay were mixed to a gumlike paste and molded quent. over the end of a properly proportioned rod of iron or flatThe present paper describes the use of the high-frequency tened glass test tube. After a preliminary drying in the electric oven, the thimbles were removed from the mold and 1 Received August 8, 1929.
T
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ISDCSTRIAL A4SD ENGINEE&IIZ'G CHEJIISTRY
January 15, 1930
baked in a muffle furnace a t 1100-1200" C., after which they were ready for use. The high-frequency induction equipment is a 3 kv-a. mercury arc conrerter. (Figure 2) The reaction chamber (Figure 3) consists of a water-cooled coil of flattened comer tubing wound to form a cylinder 15/s inches (4.1 &)-in diameter and approximately 6 inches (15 cm.) long. The coil is mounted in a small block in a vertical position and lined with a thin mica insulation. The combustion tube (a, Figure 1) is mounted in a vertical position within the inductor coil (Figure 3).
Figure 3-Inductor
sions from the same stock material. The sample for analysis may be very coarse turnings or chips. A 1-gram sample provides a sufficient weight of evolved carbon dioxide, since such materials as those under investigation are not low in carbon content. Combustion Operation
The charged combustion tube is connected with the combustion train as illustrated in Figure 4. and, with the by-pass of the flowmeter open, the whole train is flushed out with oxygen during 1 minute a t a rapid rate of flow without the weighed absorption tube in the train. With the purification train connected in, the power is then applied for 20-30 seconds. The current induced within the coil of ingot iron causes arcing a t the tn-o ends, which starts the combustion. The rapid application of oxygen supplied to the system with
Coil WlLll
aUbUIULlUI1
I-
LUUt:
for weighing the carbon dioxide reaction timebf less than 1 minute, attains a rate of appioxiFigure 5-Combustion Thimbles Showing Melt a t End Combustion Operation mately 2 liters per minute. This rate of flow demands the use of solid reagents exclusively, and these must be selected especially for their speed of reaction. The reagents suggested the flowmeter by-pass open instantly brings the metal to the condition* During this stage the Oxygen be may be obtained from all chemical supply houses. Phosphorus pentoxide or Dehydrite (granular &fg(C104)2.3Hz0) introduced just enough to cause a flow at the may be substituted for Anhydrone (granular anhydrous mag- exit end of the train. nesium perchlorate). Table I-Carbon Content of High-Melting Alloys Using t h e Combustion Materials NO.
The charging of the combustion thimble must be carried out according to a definite scheme. A strip of American ingot iron, or other soft iron of approximately 0.01 per cent carbon content, 4 by 6 / 8 inches (10 by 1.6 em.) cut from 16gage material is placed inside a coil of 2 to 2'/2 turns haring an outside diameter equal to the inside measurement of the combustion thimble. After pinching the two overlapping ends into a superficial contact with the pressure from pliers,
Induction Furnace and t h e Resistance Furnace INDUCTIONRESISTANCE SAMPLE FURKACE FURNACE Per cent Per cent Tungsten steel (w, 1,,85; Cr, 4 , 5 0 ; 0 74 v, 1 00)
{E
Tungsten steel 3
Illium (sample g - 7 2 ) (sample g-29)
5
Blank (8rmco iron)
I M
Figure 4-Combustion
Train
the coil is inserted within the combustion thimble (b, Figure 1) and the weighed sample to be analyzed placed within the coil of ingot-iron as shown. The coil should weigh 5 to 6 grams and the sample approximately 1 gram. The coil need not be weighed if it is always cut to the same dimen-
(w, 15
L
76, Cr, 2 4 , 6 )
{;:! {E:
{
{;:mi
.. .. .. 0.28 ..
.... ...
0.011
At the end of the first 20 seconds the power is cut off and the exothermal reaction of oxidation allowed to advance for approximately 15 seconds without application of power. Power is applied for a second 15-second period, or until the rapid rate of oxygen consumption is complete. The rate of flow of oxygen is then reduced to 20 liters per hour, the flowmeter by-pass closed, the whole train flushed out, and the carbon dioxide absorbed ready for weighing. A blank determination is made using no sample but with other conditions duplicated. The resulting melt is shown in Figure 5 . The combustion thimble is seen to be uncracked and unperforated. Alundum extraction thimbles may be substituted for those described, but are too expensive for this purpose. Experimental Results
The type of results obtained using the induction furnace is s h o m jri 'Cable J. Check. analjTses are also reported using the old method cf -?ctcrinin;,tion.
A S A L Y TICAL EDI T I O X
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It will be noted that the agreement between the figures for the tungsten steel sample 1 using the old and new methods is satisfactory. The results for illium using the old method are low, indicating incomplete burning of nonferrous alloys of this type unless the induction furnace method is applied. The analysis of the blank suggests the determination of
Vol. 2, s o . 1
carbon in sheet steel without the use of drillings as sample and indicates the comparative accuracy of the two methods. Literature Cited (1) Marr,Iron SteelInd , a, 184 (1929).
Determination of Cobalt in Driers, Japans, and Alloys’ Oscar Heim 119-01 NEW
YORK
BLVD.,J A M A I C A , LOSC
T
HE method here described is generally useful and
time-saving in determining cobalt in the presence of a large number of other metals, as is often necessary with the inorganic constituents of varnishes and japans, especially those that have been extracted by organic solvents from the pigment. Sometimes appreciable quantities of metals are extracted in the form of their soaps which originally belonged t o the pigment. The results obtained by the nitroso-/?-naphthol method are as unsatisfactory as those obtained by Carnot’s method (precipitation by means of ammonium molybdate as ammonium cobaltic molybdate). T o isolate cobalt quantitatively, the writer has macle quantitative the well-known qualitative cobalt test devised by T’ogel ( 2 ) . The solution used contained cobalt, nickel, iron, aluminum, chromium, manganese, zinc, tin, lead, copper, titanium, and vanadium. Procedure
HYDROCHLORIC ACID SOLUTIOXOF hIETaLs-Treat the ash of the japan with hydrochloric acid, preferably by oxidizing 10 grams of the material, in a tall beaker or an Erlenmeyer, with about 40 cc. of sulfuric acid (concentrated) and 20 cc. of hydrogen peroxide (30 per cent). After the violent reaction has ceased drive off the excess of water by boiling until white sulfuric acid fumes begin to form. Cool somewhat, again add 20 cc. of hydrogen peroxide, and treat as before. When the dark liquid has finally become light, indicating the absence of organic matter, drive off the bulk of the sulfuric acid (hood). Cool, dilute, and add ammonium hydroxide and then hydrochloric acid, each in slight excess. If metals other than cobalt are to be determined also, make u p the solution in a volumetric flask. To the dilute hydrochloric acid solution a t 50” C. add pure zinc oxide in very small quantities, until only a trace of the oxide remains undissolved. If no iron is present, add a few drops of 10 per cent ferric chloride solution. (Even a small excess of zinc oxide will precipitate a little cobalt.) DETERMINATION OF COBALT-Filter the precipitate and wash it with warm water. (It may contain iron, aluminum, chromium, copper, vanadium, titanium, and some lead.) If properly treated with zinc oxide the precipitate should give a negative “Vogel” reaction for cobalt, which is sensitive t o 0.02 mg. The filtrate may contain cobalt, nickel, manganese, and some lead. Reduce the volume t o about 20 cc. and transfer it, with several portions of water, quantitatively to a separatory funnel so that the total volume is not more than 50 cc. Add and dissolve about 30 grams of ammonium thiocyanate. Shake out the solution with a mixture of ether and amyl alcohol, 9 : 1, until exhausted, which is indicated by the disappearance of the blue color of the ammonium cobaltous thiocyanate. (A Rothe estraccor serves 1
Received March 26, 1929.
IsLaND,
h-,Y .
best.) Shake the ether solution with 15 to 20 cc. of sulfuric acid (10 per cent) and wash several times with water. Evaporate the excess water from the aqueous solution, neutralize the remainder with ammonium hydroxide, and electrolyze it. Or make the solution while hot alkaline with sodium hydroxide, filter the precipitate, wash thoroughly with boiling water, ash, and weigh as cobalt oxide. It is possible also to determine the cobalt, as it is the only metal in solution, by means of its 3,5-dimethylpyrasole compound, according to the following method devised by the Siemens Laboratory in Berlin. Pour a 2 per cent solution of the specific cobalt reagent (cold) into the previously nearly neutralized (KaOH) cobalt solution. It should still be faintly acid. Then add about 5 cc. of 0.5 N sodium hydroxide, whereupon all the cobalt settles out as a beautiful purple precipitate, which is analogous t o nickel dimethylglyoxime. Filter this precipitate, wash with cold water, and dry in a Gooch crucible a t as low a temperature as possible. 3,5-Dimethylpyrazole, SH N H3C.C
C.CHa
CH which is a derivative of pyrazole, CK
ecH
CH reveaIed, when its reactions were studied by Fischer (f), a very characteristic affinity toward cobalt. It may be conveniently prepared (after Knorr and Rosengarten) by condensation of acetylacetone with hydrazine hydrate. It may be obtained from the Chemische Werke Schubert in Goerlitz, Germany. It is advisable to recrystallize it before using if it does not show a melting point of 107”. The purple cobalt compound CH C.CH3 C.CH3 CH \SCoN( \ I I / C.CHI N N C.CHs obtained, multiplied by 0.23483, gives the quantity of cobalt. By the foregoing method cobalt contents u p to about 20 per cent (based on the sum of the inorganic constituents of driers) have been satisfactorily determined. The maximum percentage of cobalt that can accurately be determined by i t has not been ascertained, but cobalt can be removed quantitatively from a solution containing a pure cobalt salt when properly treated in this manner. Literature Cited
I
(1) Fischer, Ti’iss. T’eroflegentlzch. Siemens-Konzern, Bd. IV, Heft I1 (1925). ( 2 ) Treadwell and Hall, “Analytical Chemistry,” Vol. I, p. 192, Wiley, 1927.
