ANALYTICAL CHEMISTRY
1040 For best accuracy the temperature being measured must be observed with the stage in a reproducible equilibrium state and rising in temperature a t a uniform controlled rate. To achieve this most readily requires t h a t the cooling gas be passing through the stage at a controlled rate sufficient, if used without heating, to lower the temperature to some low figure below the desired range of melting points. Heating is then begun, so that the heating Elide on which the preparation is placed is simultaneously heated and cooled. Under these conditions, i t is possible to heat or cool quickly by use of the variable transformer alone. The new stage has been very useful in the study of Taxes. These applications are illustrated by Figure 7 , which presents photomicrographs of n-ax crystals from lubricating oil a t -20' C. Use of the new stage is not, however, restricted to studies
on waxes. It should prove valuable for studies of any system where positive temperature control near room temperature is necessary or in which cont,rast is very loiv when the crystals are studied under ordinary light. LITERATURE CITED
(1) Gavlin, G., Swire, E., Jones, S.P., Jr., Ind. Eng. Chem. 45, 2327 (1953). (2) Kofler, L., Xlikrochemie 38, 218-31 (1951). RECEIVED for review October 6, 19.55, Accepted March 8, 1956. Division of Physical and Inorganic Chemistry, 123rd Meeting, ACS, Los Angeles, Calif., March 1953. Research conducted under Contract S o . .IF 33(616)-7 with the United States Air Force, the sponsoring agency being the Aeronautical Research Laboratory of the Wright Air Deixelopment Center, Air Research and Development Command.
Simultaneous Determination of Carbon and Hydrogen in Titanium and Titanium Alloys R. B. NUNEMAKER and S. A. SHRADER M a i n laboratory, The Dow Chemical Co., Midland, Mich. The determination of carbon and hydrogen in titanium and its alloys has been investigated using a microcombustion technique. The titanium is burned in oxygen, using a iron-copper-tin flux at 1200" C. The carbon and hydrogen are converted to carbon dioxide and w-ater. The precision for carbon is within =k0.005%, and for hydrogen = k O . O O l O ~ . Results agree with those obtained by the macrocombustion method for carbon and the vacuuni extraction method for hydrogen.
R
ESEhRCH on the metallurgical significance of impurities in
titanium alloys has focused attention on analytical methods for determining the nonmetallic impurities in these alloys. The most widely used techniques for determining hydrogen in titanium are the vacuum extraction method (6, 8 ) and its modifications. Hydrogen is quantitatively removed from the specimen by evacuation a t high temperature with subsequent analysis of the gases, usually in an integrated closed system. Although such methods are capable of adequate precision, the apparatus is rather elaborate and considerable time is required to outgas the furnace assembly to obtain either a reproducible or a negligible blank. Moreover, if gases other than hydrogen are rvolved for the specimen, they must be separated and analyzed. A recent rapid and precise method for hydrogen (5) is based upon measuring the equilibrium pressure of hydrogen over the metal in a closed system under predetermined conditions. Another method (3) involves macrocombustion of the metal in dry oxygen, followed by gravimetric determination of the hydrogen as water. The method requires a relatively large sample weight and hydrogen is the only element determined. Carbon in titanium metal is usually determined by procedures used for carbon in steels (1, 7'). The metal is burned in oxygen at a temperature of 1200" to 1400" C., and the carbon dioxide is determined gravimetrically or measured volumetrically (4). Previous experience of one of the authors in determining carbon and hydrogen in magnesium alloys by a microcombustion procedure ( 2 ) indicated that the method might be applied, with modification, for determining carbon and hydrogen in titanium and its alloys. The xater and carbon dioxide are absorbed in micro absorption tubes filled with magnesium perchlorate and Ascarite, respectively. The carbon and hydrogen are calculated
from the increase in weight of the tubes. Titanium and its alloys containing 0.005 to 1.0% carbon and 0.001 to 0.5% hydrogen can be analyzed by this method (Table I and 11). REAGENTS
Ascarite (asbestos impregnated with sodium hydroxide). hlagnesium perchlorate, granular, anhydrous. Cupric oxide, wire form. 1 silver vire screen. Silver ~ 0 0 or Asbestos, fibrous. Sodium hrdroxide, pellets. Aluminum foil. Iron chir, accelerator (Plastics Metale. 191 Bridge - St.. Johnston-n, Pa.): Tinned copper strips (Dualaccelerator, K. JV. Dietert Co., 9330 R o s e l a m Ave., Detroit 4, M c h . ) . Sulfuric acid, concentrated. Platinized asbestos. APPARATUS
Oxygen Purification Train (Figure 1). Oxygen reservoir bottle, 1-gallon, filled about two thirds full of concentrated sulfuric acid. Absorption tower containing a layer of glass wool, a layer of sodium hydroxide pellets, and another layer of glass n-001. TKOside-arm 1-ycor combustion tubes are packed by placing 7 c m of silver ~ o o or l Jrire screen in the far end of the tube, folloir-ed by 3 mm. of ignited asbestos, 7 . 3 cm. of copper oxide, 3 mm. of platinized asbestos, i . 5 em. of copper oxide, and then 3 mm. of platinized asbestos to hold the copper oxide in place. The tubes are placed in tn-o electric tube furnaces, so t h a t all of the copper oxide and 3.5 cni. of the silver are n-ithin the heated zone. Four U-tubes, tn-o filled J\-ith .4scarite and two filled with magnesium perchlorate. Combustion Tube. The combustion tube for burning the titanium metal is made of quartz tubing as follows: A 520-mm. lengt,h of 26-mm. inside diameter tubing is sealed to a 300-mm. lengt,h of 10-mm. inside diameter tubing. The latter should have a 30-mm. length of 3-mm. outside diameter t,ubing on the exit end. The large tube has two side arms of 3- to 5-mm. outside diameter tubing opposite one another and 25 mm. from the open end, through xhich oxygen is admitted. The combustion tube is filled (beginning a t t,he small end) with 100 mm. of silver wool or screen, 2 mm. of ignited asbestos plug, 90 mm. of copper oxide, 2 mm. of platinized asbestos plug, 90 mm. of copper oxide, and 2 mm. of platinized asbestos plug. This filling is different from the usual micro carbon-hydrogen filling, in that no lead dioxide is used. The copper oxide is heated to 650" C. in an electric tube furnace. The first 20 to 30 mm. of
1041
V O L U M E 28, N O . 6, J U N E 1 9 5 6 OXYGEN PURIFICATION T R A I N O T H E R S I D E A R M OF C O M B U S T I O N T U B E
TO FURNACE BELOW
G LA s'S WOOL/
\DOUBLE SIDE A R M COMBUSTION TUBE AND DUPLICATION O F T H E E N T I R E O X Y G E N PURIFICATION TRAIN
ASBESTOS PLUGS
ABOVE
II II
II
\IH
A S H,O
II 4
1 C AS CO:'\hAGNESIUM PERCHLORATE
+
A'Sc A R I T E
600° C
175OC
BOTTLE
Figure 1. Apparatus for the deterniination of carbon in titanium metal or alloys
silver is also located nithin the furnace and is heated t o 500" t o 600' C. T h e remainder of the silver is heated in a constant temperat'ure mortar a t l i s o C. A microstopcock is attached t,o t h e 3-mm. section of the combustion tube protruding from the constant temperature mortar. T h e standard micro carbon and hydrogen absorption tubes are used for collecting the water and carbon dioxide. These tubes are filled \\-it11 magnesium perchlorate and Ascarite in the usual manner. Aspirator System. -1U-tube filled with magnesium perchlorate and Xsc:trite is insert,edbetween t h e absorption tubes and the aspirator bottle. This prevents any Trater or n-ater vapor from backing u p into the absorption tubes. .4 4-liter aspirator bottle filled about tn-o thirds full of water. Alundum Shields, which should just fit inside the larger part of t,he conil)urtisn tube, can be purchased from the Fisher ScienS o . 7-685, Size 2 (5.5 inches long). These tubes are then cut along their length, so t h a t an arc of about 2 em. is cut out,. Il-ith the Phield inserted, cut side dorm, the combustion hoat can r w t directly on the quartz tube while the upper p a r t of the tutie is protec,ted from spattering of the sample. Furnace. The high temperature furnace (1200" C.), equipped with therniocwuple arid pyrometer, is a split furnace t h a t can he pulled over the combustion tube to fire the snniple. It Tras construcatetl i n the authors' lahoratorj-. Tw-o ox!-geii cylitidc~s\\.it11 reducing gages. R1icroli:il:iiicc~. Coml)iistion h i t s , Leco HF-B, 3 V 4 inches long, 5 / 8 inch wide, and ' / ? inrh high. For protection during coml)ust,ion, the ho:its sliould liiictl \vitli 60-mesh ~4lundnin. PROCEDURE
Conditioning of Combustion Tube a n d Absorption Tubes. With the entire train set u p as in the diagram, open the aspirator bottle :mi pass oxygen through the train a t a rate of approximately 30 t o 50 ml. per minute. Measure the water in a graduated cylinder and adjust the stopcoclc on the last U-t,ube t,o obtain the correct rate of f l o ~ . K h e n this adjustment is complete, use a 1500-ml. beaker to catch the water during a complete analysis. X i t h osygrn passing through the train, move the high temperature furiiacr, which has been brought u p t o 900" C., over the combustion tube (which contains the Alundum shield and boat), T u r n the pyrometer u p t o 1200" C. and heat for about 10 t o 15 minutes or until about 500 nil. of water has been collected. Turn the pyromet,er hack t o 1000" C. and continue heating until 750 t o 800 nil. of water has been collect,ed. Remove the furnace and alloiT- t h e combustion tuhe and contents to cool, meanT7hile continuing t h e sweeping until 1 liter of water has been collected.
Place a pinchclamp on t h e aspirator bottle and close the stopcock on t h e U-tube. Disconnect the absorption tubes. Wipe the tubes with a chamois, place them on the rack holder, and remove a n y static charges .4110~t h e tubes t o stand 15 minutes before x-eighing. Preparation of Sample. T h e titanium metal should preferably be in the form of turnings or shavings. It was found that approsimately 0.5 gram of iron chip accelerator plus 0.3 to 0.5 gram of tinned copper (Dualaccelerator) burns 0.5 gram of sample completely and forms a homogeneous melt. Weigh the sample in a boat, smaller than the one used for the combustion Insert the small boat containing the weighed sample into the conibustion tube a n d empty it into t h e large boat iiseti for combustion by means of it long pair of forceps. Spread 0.5 gram of iron chip accelerator on top of the sample. Plat-e one piece (approximate 0.15 gram) of the tinned copper strips (Dualaccelerator) in t h e large combustion boat before and after the addition of the sample a n d iron chips. Procedure for Combustion of Metal. Close the microstopcock and increase t h e flow of oxygen. Remove the large aluminum foil-covered rubber stopper from t,he large end of the combustion tube. The fast rate of o rgen coming out the side arms of the conibustion tuhe prevent an!- air from entering the tube. By rod with a platinum !!-ire attached pi111 the boat hield, but do not remove it from the combustion tube. IYith t h e long pair of forceps place one strip cf tinned copper in t h e boat. S e s t transfer t h e sample which contains the iron chip accelerator t o the boat. Finally place another etrip of tinned copper on top of the sample in t h e conibustion boat. Push the conibiustion boat bark into the midtile of t h e shield and r e p l x e tlic rubber stopper. Open the microstopcock a n d let the oxygen pass through the conibustion tube for 10 minutes. Connect the tared absorption t:tbes in the proper place in the train (between the microstopcock and the protective U-tuhe). Close the microstopcock. K i t h the oxygen turned on at a fast rate to maintain a constant pressure, move the high temperature furnace ( a t 900" C.) over thesample. Turn the pj-rometer up to 1200" C. When the combustion of t h e titanium has ceased (approximately 1 t o 2 minutes), open the microstopcock and the aspirator bottle. Reduce the oxygen rate so that just an excess is indicated in t h e reservoir bottles. Sv-eep a t 1200" C . until about 500 nil. of oxygen has been passed through, then turn t h e pyrometer back t o 1000" C. Hold this temperature for another 250 t o 300 ml. of \rater. Remove the furnace from the combustion tube and continue sweeping until 1 liter of water (total) has been collected. Shut off the aspirator bottle and t h e protective U-tube. Disconnect the absorption tubes. TYipe t h e tubes with a chamois, discharge them, and place on the rack holder for 15 minutes before
1
1042
ANALYTICAL CHEMISTRY
weighing. Weigh the tubes and reserve them for the next determination. Run a blank determination under identical conditions without the sample.
Table 11.
Carbon in Titanium and Titanium Alloys
Sample NO.
Calculations
YGcarbon
WA-IO
Composition Comin. pure Ti
=
0.2729 X wt. of carbon dioxide in milligrams X 100 wt. of sample in milligrams
Carbon, % hlacroMicrocombustion combustion 0.106" 0.100 0.102 0.104 0.099 0.105
WA-12
2 . 7 Cr, 1 . 3 2 Fe
0.054"
water in milligrams X 100 tz hydrogen = 0.1119 Xwt.wt.ofofsample in milligrams Operating Schedule. A complete determination can be run in spprosimately 1 hour according t o the following schedule: 5 minutes to ignite sample 30 minutes to heat and sweep entire train 15 minutes to wipe, discharge, and prepare absorption tubes for weighing 5 minutes to weigh absorption tubes 5 minutes to load sample and connect absorption tubes
NBS ferrotitaniuin No. (116a)
0.025
WA-57
0.046b
WA-67
0.1946
._
60 minutes total
0.102 i 0.003 0.052 0.050 0.052 0,049 0.051 i 0 . 0 0 2 0.024 0 021 0.022 0 022 L 0 002 0.037 0 041 0.041 0 045 0.041 jz 0 004 0.181 0.198 0.203 0.196 0.183 0.192 0.010
Seven determinations can be run in an %hour Jay according to the following schedule: Condition new boat and absorption tubes with a complete blank run. 9:00 A . M . Burn sample 1. 1o:oo A.?,f. Burn sample 2. 1 1 :00 A.M. Burn sample 3. 11:45 .4.51. Condition new boat and discard boat from first three combustions. 12:oo s o o n Connect absorption tubes on train over noon hour. 1:oo P.M. Burn sample 4. 2:oo P.41 Burn sample 5 . 3 : O O P.M. Burn sample 6. 4:OO P . h l . Burn sample 7 . 4:45 P.M. Discard boat from combustion tuhe. 8 : 00
A.M.
Table I. Sample NO.
Hydrogen in Titanium and Titanium Alloys Composition
Hydrogen, % Vacuum Microcombustion extraction method
-4ccording t o this schedule, tR-0 boats are used in one day. .4 new combustion tube should be conditioned b y actually firing three or four 0.5-gram samples of titanium according t o the procedure and also b y heating and cooling the combustion tube for 15-minute periods until on running a blank determination t h e hydrogen absorption tube nil1 show an increase of not over 0.2 mg. and the carbon tube not over 0.1 mg. Once a new combustion tube has been conditioned, i t is not necessary to run a blank every day unless different amounts of flu^ arc added. The blanks on 0.5 gram of iron chip accelerator plus two strips of tinned copper (0.3 gram) are usually consistent, T h e combustion boat is replaced with a new boat lined with -4lundum and placed in the combustion tube and the 1200" C. furnace is brought over the combustion tube for 10 minute.. T h e absorption tiibes are not connected during this conditioning period. ACKNOWLEDGMENT
FA-12
2 . 7 Cr, 1 . 3 F e
0.0130'
RR-2
5 Al, 2 . 5 Sn
0.0128 b 0.0139 0.0131 0.0133 f 0.0006
RR-7
2 Fe, 2 Cr, 2 &Io
0,00876 0.0078 0.0080 0.0082 f 0.0005
RR-13
3 hfn, 1 . 5 AI
0.01566 0.0157 0.0164 0.0159 i 0 0005
0.0060 i 0.0010 0.0130 0.0107 0.0123 0.0123 0 . 0 1 2 1 1 0.0014 0.0123 0.0135 0.0130 0.0130 f 0.0005 0.0086 0.0082 0.0072 0.0080
=t0.0010
0,0148 0.0148 0.0152 0.0149 i 0.0003
4 Average of results from 11 laboratories serving on Task Force on Vacuum Fusion Method of Analysis for Hydrogen in Titanium sponsored b y Watertown Arsenal. b Results obtained b y vacuum extraction technique (R. E. Brocklehurst and J. A. Winstead, Analytical Section, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio).
T h e authors are indebted t o Samuel Vigo of Watertown .hsenal for the WA samples and the results obtained by the macromethods, and to R. E. Brocklehurst of Wright Air Development Center, Wright-Patterson Air Force Base, Ohio, for the RII samples and results by the vacuum fusion method. LITERATURE CITED
(1) Am. SOC.Testing Materials, "ASTAT Methodsfor Chemical.4naly-
sis of Metals," Total Carbon by Direct-Combustion Method.
p. 147,1950. (2) Bobalek, E. G., Shrader, 544 (1945).
S.il., IND.ENO.CHEM.,4 x 4 ~ED. . 17,
(3) Codell, IT.,Frankford Arsenal, Philadelphia, Pa., private com-
munication.
(4) Laboratory Equipment Co., Carbon Determination, Central Scientific Co. Catalog J.150,p. 526. (5) McKinley, T.D., J . Electrochem. SOC.102, 117 (1956). (6) hIcMahon, J.,Foster, L. S.. J . Chem. Educ. 30, 609 (1953). (7) Pepkowitz, L. P., Rloak, W. D., ANAL.CHEM.26, 1022 (1954) (8) Yeaton, R. A., Vacuum 2, 115 (1952). RECEIVED for review September 30, 1955.
Accepted February 6, 1956.
