Combustion of Tungsten Carbide by High Frequency Induced Radiant Heating EDWARD L. SIMONS, JOHN E. FAGEL, JR., and EARL W. BALK Research Laboratory, General Electric Co., Schensctady,
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use tin alone or auxiliary fluxes such as vanadium oxides proved equally unsuccessful. The use of fluxes was abandoned, and the Lindberg crucible was wrapped in platinum foil to permit the sample container to couple directly with the high frequency field. The coupling of the field with the foil w m so strong that the platinurn was fused almost instantly. By trial and error, satidactory combustion without damage to the platinum was achieved b y abandoning the regular Lindberg crucible and using a Coors 5/0 porcelain crucible sandwiched between two disks of 40-mil platinum ('a/,&neh diameter), the upper one having a 0.25-inch hale in its center. (These crucibles were cleaned before use b y boiling for 5 t o 10 minutes in Concentrated nitric acid and then igniting for 2 hours in a muffle furnace a t 900" C.) By means of optical pyrometry the temperature of the upper platinum disk during operation of the unit w m estimated to b e 1600" C. Under the conditions it was possible to fuse a sample of calcium fluoride (melting oint 1386" C.) but not z sample of nickel (melting point 1453" in the crucible. The temperature achieved by radiation inside the crucible is therefore about 1400'C. The geometry of the platinum radiators proved to be critical, and a number of test specimens of radiators were melted before the design described above was developed.
Tungsten carbide can he burned rapidly and completely at about 1400' C. in a stream of oxygen without the use of flux. This temperature is attained hy suhjeoting the sample, contained in a small porcelain crucible, to the radiation from a surrounding platinum cage which is heated to about 1600' C. by the high frequency field of a modiiied Lindherg induction furnace. The resulting earbon dioxide is measured in the Lindberg volumetric apparatus. The standard deviation for the determination of the carbon in a tungsten carbide sample is 0.033% carbon.
T .
HE carbon content of tungsten carbide is determined by
6)
meesunng the carbon dioxide produced when a sample of the material is burned in oxygen. At the temperatures readily attainable in the conventional laboboratory furnaces (1000" t o 1100' C.) complete combustion is effected only in the presence of a flux, and aiter an oxidation period of 10 to 15 minutes (8). The authors have been able to burn tungsten carbide rapidly and completely a t about 1400".C. in a stream of oxygen without the use of flux by subjecting the sample, contained in a small porcelain crucible, t o the radiation from a surrounding platinurn cage which was heated to about 1600" C. by the high frequency field of a modified Lindherg induction furnace. The resulting carbon dioxide w a s measured in the Lindberg v o l u m e t r i c a p 115 V 60 fl paratus. The standard deviation for the determination of the carbon in a tungsten carbide s a m p l e w a s 0.033% carbon. EXPERIMENTAL
An P
I
Figure 1. Modified portion of electrical circuit of Lindberg high frequency induetion furnace
The apparatus used in this investigation was the high frequencycomb u s t i o n f u r n a c e (LI500-A) and volumetric attachment, m a n u f a c tured b y the Lindberg E n g i n e e r i n g Ca. and modified as described in this paper: , The initial comhustion experiments were carried out with about 100 mg. of carbide mixed with about 1 gram of known low-carbon steel and 0.25 gram of tin to movide a matrix which would couple with the h i g h f r e q u e n c y field. The scatter of the analytical results was great, and moat oi the 111"~ led to carbon values lower t h a n t h e s t o i c h i o m e t r i c v a l u e of 6.13%. A t t e m p t s t o
Figure 2.
Modified Lindherg high frec induction furnace
I n order to achieve greater flexibility in the use of the apparatus, the electrical circuit was modified to permit the operator to control the power output of the oscillator. This was done hv intro-
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ANALYTICAL CHEMISTRY
1124
radiittor,~t i regulaTe the power-supply 'as necessary to acrhieve the desired temperature. The proper setting for the variable transformer mu& be determined in a trial experiment in which the platinum temperature is measured with an optical pyrometer 8t various voltage settings. The maximum temperature is, of course limited by the melting paint of the radiator material (1769' C. in the ease of platinum). For any given voltage setting aud radiator design, the temperature in the crucible can be Patimated from the meltine behavior of various substances of known melting point. The radiator design currently in use in this laboratory is shown in Figure 3. It consists of two 40-mil platinum disks la/&oh diameter) connected by three channel-type posts built ram 20-mil Dhtinum sheet and spot welded a t top and bottom. ~~~~
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~~~~
volumetric apparatus, using the modifications and precautions described elsewhere ( 6 ) . The data from 26 determinations are listed in Table I. The average value obtained was 6.24% carbon, with a standard deviation of 0.033% carbon. Following the practice of this laboratory, the result of a single determination can be guaranteed within 3s limits, or i O . l O % carbon; the average of n determinations can be guaranteed within = t O . l O / d G % carbon
(4). DISCUSSION
In the absence of an ahsolute value for the carbon content of this sample, the evidence that the method described in this report hss resulted in complete combustion can only he indirect. The standard deviation obtained in this series of determinations may be compared with t h a t which would have been expected for the determination of the same amount of carbon in a steel sample for which combustion is complete. As reported previously ( 6 ) , the standard deviation for the carbon determination on a 1-gram steel sample is 0.00570 carbon. The standard deviation in per cent carbon for B sample of any other weight is 8 % ~ =
(0.0°5)
(con. factor for T and p ) (grams of sample)
The average sample weight for the 26 determinations listed in Table I was 0.1474 gram and the average correction factor wa8 0.95325. The expected standard deviation, therefore, is 0.032% carbon, which is in good agreement with the experimentally determined value of 0.033% carhou.
Sam le Wt..
El*. 148.6 149.5 139.0 140.0 144.0 142.1 139.8
Sample Wt.,
Carbon. %
ME.
Carbon.
90
144.1 141.9
!?4.?
Figure 3.
Platiniim radiator
Procedure. The operation of the furnace is essentially the same as that described by the manufacturers (5). To start a combustion run the sample crucible and radiator cage &reraised into position in the combustion chamber, t h e filament switch is turned on, and the variable transformer 1s set, a t zero voltage. After the filament has warmed u , the plate switch is turned on, the variable transformer is t u r n e f u p until the voltmeter registers the desired OUtDut, and the oxygen flow is begun a t a rate of about
Blank runs made on empty crucibles produced no carbon dioxide. Five 200-mg. samples of a standard steel (NBC 160-1.015% carbon) were burned by exactly the same technique 88. that used in the comhustion of tungaten carbide. The 200-mg. samples of steel were too small to couple directly with the field in the Lindberg high frequency furnace. They were burned by radiant heating just as carbide is burned in ihis method. The results of the five runs show the absence of any hias in the method: %C 1.003 1.048 1.01: 0.990
is shout 270 ma. and &es during the combustion t o a value of about 310 ma. The grid current varies between 50 and 60 ma.
0.983
Av. 1.008 RESULTS ~~
This combustion method was tested on a tungsten carbide sample supplied by the Carbolay Department of the General Electric Go. The combustion was carried out as described above, and the carbon dioxide was measured in the Lindberg
temperatures lower than about 1400" C. (transformer output less than 118 volts), results as low as 4% carbon could be obtained. The tungsten oxide residues from these runs, when reburned a t 1400" C. r,ith about 50 mg. of vanadium pentoxide in the cruci-
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V O L U M E 2 7 , NO. 7, J U L Y 1 9 5 5 ble as a flux, produced carbon dioxide. The oxide residues from the 1400" C. combustions (6.24% carbon) produced no additional carbon dioxide when reburned in the presence of vanadium pentoxide. The gaseous combustion products from several runs, both complete and incomplete combustion, were examined n i t h a Mine Safety Appliances monoxide detector. S o carbon monoxide was noted in any cases. The stoichiometric value for tungsten carbide is 6.13% carbon; thi3 sample, therefore, contains an e w e s of 0.11% carbon. The principle of high frequency induced radiant heating is not new. I n this laboratory Horn and Neubauer ( 3 ) have used a quartz crucible whose hollow walls were filled a ith a low melting alloy as a container for melting silicon in a high frequency field. 11ore recently, Rennnet ( 1 ) has described a quartz-enclosed carbon crucible which he has used for the combustion of noncoupling samples in a Leco (Laboratory Equipment Co.) high frequency furnace. The authors believe that for routine combustion work the platinum cage coupler, developed independently here, has two advantages over the quartz-enclosed graphite crucible: It is less
fragile, and it provides a relatively large radiator surface directly over the mouth of the sample crucible. ACKNOWLEDGMENT
The authors wish to thank Marie D e Vito for her assistance in combustion work. LITERATURE CITED
(1) Bennet, E. L., Pittsburgh Conference on .knalytical Chemistry
and dpplied Spectroscopy, Pittsburgh, Pa., March 1 to 6 ,
1954. ( 2 ) Furey. J. J., and Cunninghani. T. It., ASAL. CHEM.,20, 563 (1948).
(3) Horn, F. H., and Seiibaiier, R . L., Rea. Sci. Instr., 24, 1154
(1953). (4) Liebhafsky, H. A , , Pfeiffer, H. G., and Balis, E. W., ANAL. C H E X . . 23. 1531 (l951). ~, (5) Lindberg Engineering Co., Chicago, Ill., "Lindberg Furnace
.
Operating Instruction," 1950. (6) Simons, E. L.. Fagel, J. E., Jr., Balis, E. W., and Pepkowitz, L. P., AXAL.CHEM.,27, 1119 (1955). RECEIVED f o r review January 7 , 1955. dccepted February 23, 1955. Presented before the Division of .4nalytical Chemistry a t the 126th Meeting of the AXERICAN C ~ ~ a r r c .SOCIETY, 4~ S e n York, N. Y . , 1954.
Determination of Magnesium in Alkali Products Photometric Method Using Thiazole Yellow OLLIE A. KENYON and GEORGE OPLINGER Solvay Process Division, Allied Chemical & D y e Corp., Syracuse,
A rapid and precise method for the determination of less than 0.1% magnesium in alkali products was required. The use of thiazole yellow to determine magnesium as a magnesium dye lake in a sodium chloride solution has been developed. Results are accurate to within 2 to 5% of the true value. The critical factors of magnesium dye lake stability, removal of interfering cations, and the control of sodium chloride concentration were studied thoroughly in respect to their effect on color development.
T
H E colorimetric determination of magnesium with thiazole yellow has been used principally in the analysis of plant tissue and soil extracts ( 2 , 5, 6). Mikkelsen and Toth (3)found thiazole yellow (sodium salt of 2,2-disulfonate of methyl benzothiazole) superior as a leagent for magnejium. The use of thiazole yelloTv for the determination of micro amounts of magnesium in alkali products has not been previously reported. il number of tests refer to thiazole yellow as being synonymous with Titan yellow, Clayton yellow, mimosa, etc. Thiazole yellow (1;astman P59i7) was used in this work. The proposed procedure was developed in three steps: ( l ) ,the removal of aluminum, copper, iron, manganese, and nickel through the cliloroform extraction of their oxinates; (2), the removal of ralcium and the decrease in sodium chloride concentration by treatment with sulfuric acid in a 98'3, methanol solution; aiid (3), the formation of a stabiljzed magnesium dye lake This paper describes the factors which infliience the development arid stability of the magnesium dye lake complex in a sodium chloride solution. The factors investigated were: reagent concentration, effect of light and heat, the stabilization of the thiazole yellorr reagent and magnesium dye lake, the effect of interfering rations and their removal, the effect of various concentrations of sodium chloride, the procedure for producing a
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nearly constant low concentration of sodium chloride, and the reproducibility of the method. APPARATUS AND REAGENTS
Beckman spectrophotometer, Model DU, with two 1-cm. matched cells. Beckman p H meter, Model H-2. Amber mixing cylinders, 50-ml. A water bath a t 60" to 70" C. consisting of a variable controlled electric hot plate and a 150-mm. borosilicate glass crystallizing dish partially filled with water. .4 water bath in the sink maintained a t 25" C. by proper regulation of the hot and cold water streams. Alcohol, Formula 30. Chloroform, reagent grade. Hydrochloric acid, 1O.Oh'. Hydroxylamine hydrochloride, 5% w./v. Methanol, 99.5%. reagent grade. Sodium chloride recrystallized twice. Sodium hydroxide, 1 . O N . Sodium hydroxide, lO.0K (prepared from mercury cell caustic sod3 .. 1
Sulfuric acid, 9.ON. 8-Hydroxyquinoline (oxine 1.2% n-/v.). Dissolve 2 grams of oxine (Eastman 794) in 6 ml. of glacial acetic acid and dilute to 100 mi. with water. Polp(viny1alcohol). 2% w./v. Dissolve 20 grams of poly(viny1 alcohol) ( D u Pont Elvanol Grade 71-24) in 400 ml. of water using heat up to 90" C., and stirring. Dilute the cool solution t o 1 liter with water and store in the refrigerator. Poly(viny1 alcohol), 0.5% w./v. Dilute 50 ml. of 2% poly(viny1 alcohol) to 200 ml. with water. Thiazole yellow, 0 5% w./v. Dissolve 0.5 gram of thiazole yellow (Eastman P5977) in 50 ml. of 95% ethyl alcohol and dilute to 100 ml. with water. This reagent will keep indefimtely when stored in a dark bottle. Thiazole yellow, 0.01% w./v. Add 2 ml. of 0.5% thiazole yellow and 5 ml. of 0.5% polv(viny1 alcohol) to water, and dilute with water to 100 ml. A fresh 0.01% thiazole yellow solution should be prepared a t least once every 2 weeks and stored in a dark bottle. Standard magnesium stock solution (1 nil. contains 5.0 mg. of I
