LITERATURE CITED
Adler, I., Aixelrod, J. ~ h t t ld . c t a 7 , 91 (1955).
Spectio-
C‘auchois, Y., Hulubei, H., “Tables de constantes et donnkes numeriques. Constantes sklectionkes longuers cl onde des &missions S et des tliscontinuitks d’ahsorption S,” Hermann & Cie., Paris, 1947. Claisse, F., .Yorelco IZeptr. 3 , 3 (January-February 1957). Clark, G. I,,, \Vagner, \V. F., Carley, 11. \\-,, University of Illinois,
Chemistry Task Force, NGori 71 (Aug. 18, 1947). ( 5 ) Uunn. H. \T.. Oak Ridee Sntional Laboratory,’ Rept. ORNL-19 17 (Aug. 4, 1955). Fassel, V. A , , J . Opt. SOC.Atjier. 39, 187 (1949). Hevesey, G. yon, “Chemical Analysis b y S - R a y and Its Application,” p . , 126, S e w York, l1cGraw-Hill, 193%. Hillebrand, \T. F., Lundell, G. E. F., Bright, 11. S., Hoffman, J. I., “.%pplied Inorganic .inalJ-sis,“ 2nd
ed., pp. 550 ff., \ \ l e y , S e w York, 1953. (9) Sorris, J. A , , Pq>per, C. E , ) .is.u,. CHEJI.24, 1399 (195%). (10) Sttlmon, 11. L.,Blackledge, J. P., Sorelco Keptr. 3 , 68 (llarch-
September 195Bj. RECEIVEDfor review January 11, 1957. Accepted October 16, 1957. Contrihution 590. \Vork perf‘ornied in the Amrs Laboratory, U S. Atomic ICiiergy Commission. Presented i n part at the Pittsburg Conference on ?inalytiral Chemistry and Applied Spertro,5cwpy, JIarch 1057.
Emission Spectrometric Determination of Oxygen in Titanium and Titanium Alloys VELMER A. FASSEL and WILLIAM A. GORDON lnsfifufe for Afomic Research and Deparfment of Chemistry, Iowa Stafe College, Ames, lowa
b An emission spectrometric method for the determination of oxygen in titanium and titanium alloys is based on the direct current carbon arc excitation of a special electrode assembly which provides a molten platinum bath after the arc is initiated. The oxygen in the titanium sample is rapidly liberated from this bath into an argon atmosphere which supports the arc discharge. The intensity ratio of the line pair, 0 7771 A./A 7891 A., is related to the oxygen content of the titanium sample. This procedure provides oxygen determinations with a precision comparable to the vacuum fusion or bromination-reduction techniques, but has the advantage of greatly reduced time requirements.
T
of oxygen in t,itaniuni metal and titanium alloys has a niarkrd offcct on the physical and m e rhanical properties of these metals (9). Consequently, the dcterniination of oxygrn i n these mctals has bcrn PXtensivc,ly invcstigabed (3). Among the proccdurrs which have bern employed, thc various niodifications of the vaciiuni fusion tcchniqur (1, +!+, 8, 12, 1417) and t,hr bromination-carbon reduction nic,t81iod(3) have been found most satisfact’ory. H o w r r r , tlie pcrforniance of thc anal!-sc,s with these tcc-liiiiqucs is :I difficult task, and procedural subtleties must bc strictly followd, to obtain accurate rcsults. If the total time requircd for changing crucibles, outgassing, and rcducing the operating blank is takvn into caonsitleratioii, from 1 to 4 hours in:~y Ix, rrquircd per dct,crniination. Fassc.1 and Tnbclling ( 6 ) rrcently dmcrib(d 2 twhiiique for tlic rnii&on HE PRCSEXCE
spectrometric determination of oxygen in plain carbon steels. A modification of this basic procedurr has now been applied succcssfully to tlie determination of oxygen in titanium and titanium alloys. The prowdure provides oxygrn drterminations 11ith a precision comparable to the vacuum fuqion or bromination-reduction techniques. but greatly reduces the time requirrmc,nts. APPARATUS
With the exception of the excitation chamber, all the equipment used in this investigation has been described ( 6 ) . The excitation chamber wa5 redesigned (Figure 1) in order to improve operating efficiency and reduce the chamber blank (6) to a negligible value. T h e size and general construction of the chamber nere not altered, but the structural metal was changed from brass to stainless steel to improve the outgassing process. B y providing accommodations for 13 electrodes in the rotating platform, only one chamber outgassing is required for 11 sample excitations. T h e nests for accommodating electrodes are located on the rotating table so t h a t the solid angle of radiation rollected by the optical system of the spectrograph is unobstructed. The spectrographic facilities used are summarized in Table 111. PRELIMINARY EXPERIMENTS
The method for the emission spectrometric determination of oxygen in metals is based on the evolution of the osjgen in the sample into a n argon atmosphere ( 6 ) . For stec.1 samples this is achieved by simply arcing tlie metal sample in a supporting carbon electrode. The nioltrn metal dissolves carbon from the retaining wall of the receptac*le,bringing tlic c-nrhon into inti-
niate contact with the dissolved osidvs in the fluid metal. This causw cheniirnl reduction of t,he oxides to carbon nionoxide, d i i c h is evolved into a static argon atmosphere. The formation and evolution of the carbon monoxide require lrss than 1 minute. The high tciiipcmiture of the anode spot on the niolten nictal globule and the high temptmture gradients mithin the globule appear t,o lie cssmtial factors in the rapid cvolution of the carbon monoxide. In a direct current arc discharge in argon the carbon nionoside is readily dissorirtted, and thc osygc’n tripkt a t 7 7 i l A. is rscited with sucficient’ sensitivity to make oxygen tititermiiiations possible. A 4 r ( h gmrtallic spcxcimtm of titanium in cm+mn electrodrs docs not cause evolution of the os!*grn content from the sample, crcn though calculations show that a t tenippraturt)s grcatcr t,lian 1600” C., the reduction of titaniuni oxide to the carbide is thcriiiodynamically favorable (15 ) . Investigators n.ho have eniploycd vacuum fusion trchiiiqurs also h a w observed that fusing titanium saniplcs in caarbon cwcihlcs docs not produce quantitativr r.volution of carlion monosiilc,, c v n in a vacuum. The inconiplctr evolutmionof carlion monoxide appcws to br assocaiated with tlir n-ctting of thc carbon ivalls of the cmcil)le by the titanium t o form a titanium carhide cinder or strurturc. \vhirh traps thc evolved carbon monoxidr (15. 16). T h c problem, therefore, is resolvrd into finding thc proper environmental renditions ~vliich will allorr quantitative trolution of tlir oxygen a t the tcnipcraturcs produccd liy the arc discliargc. Under vacuum fusion conditions, quantitative evolution of carbon nioiioxide ran h achieved by adding anVOL. 30, NO. 2, FEBRUARY 1958
* 179
othrr metal t o the reaction system. I n the iron bath modification ( I , 4, 8,12, 15') t,he sample is dropped into a molten iron-t'in bath in a graphit'e crucible. Trader optimum expcriniental condit'ions, the bath providcs a rmctioii medium or solvmt t o bring the sample into intimate contact n-ith carbon dissolved in the bath. Certain prwaut'ions must be obsrwed t o obtain quantitative evolution of carbon nionoxidf. The addition of thc titanium to the bath must result in a dilute solution of titanium ( I ) ; consequcntly, bath-sample w i g h t ratios of 40 to 1 are generally eniplo>-ed. Care must also be exercised that the iron bath is not saturated with carbon, lest prccipitation of carbon near the top of the melt cause entrapment of the el-olved carbon monoxide (I-$). K a l t e r ( 1 6 ) has shon-ii that t'he carbon monoxide can be quantitatively extractcd under vacuum fusion conditions if tlie titanium saniplt., accompanied by sufficient tin for fluxing. is dropped into graphite shavings a t 1900" C. Sniiley ( I S ) has shown t,hat the oxygen content of soiiie metals is quantitatively evolved as carbon nioiioxide against argon a t atmospheric pressure when metal samples are dropped into a molten platinum bath in a carbon crucible. According to Sniiley the addition of t'itaniuni specimens to the platinum bath resulted in a brilliant flash, but quantitat,ive recovery of the oxygen could not be obtained. JJ-liile the present investigation was in progress! Killiins and FleischPr (17') st,udied the application of platinum baths under 1-acuum conditions and showed that oxygen in titanium could be successfully determined. Quantitative evolution of carbon monoxitic was obtained if th? alloyed titanium in the bath did not' exceed 10%. The success of these bath techniques suggested that a n adaptation of this approach might prove successful under tlie direct current arc conditions. The type of electrode assembly used is shown in Figure 2 . Suitably shaped metal cups nere machined from the bath material and placed in the cavity of the undercut graphite electrodes. Specimens of titanium weighing about 0.1 gram were then placed inside the metal cup and arced a t various currents and time periods. The bath materials and ratios of bath to sample weight (Table I) approximated, in so far as possible, the environmental conditions which have been successfully used under vacuum fusion conditions for the determination of oxygen. Significant evolution of the oxygen content from titanium specimens was observed only for the experiments in which a platinum bath was used. The spectrometric approach imposes some liniitations on the bath technique n hich are not encountered under vacuum fusion conditions. First, in the aacuum fusion technique. carbon inonoxide is liberated into a vacuum
180
ANALYTICAL CHEMISTRY
COILED CALROD HEATER
1 4
U
L
M
L
T R A h S TE COVER
NEOPRENE
o
"
RING-
G L A S S CYLINDER ROTARY ELECTRODE HOLDER (13 POSITIONS) TOP AND BOTTOM PLATES OF STAINLESS STEEL
VAC
Figure 1 .
Table I.
-
Excitation chamber
€
Bath Materials Investigated
Ratio of Bath to Sample
Bath
Iron Tin Tin and iron Tin saturated with carbon Nickel (IO) Platinum
Weight 3 to 9
a
10 t o 40 2 to 9 10 to 40 3 to 40 1 to 10
4
and pumped from the reaction system. I n the spectrometric approach, the gas is liberated against a n argon pressure of 1 a t m . plus the partial pressure of carbon monoxide e\ olved from the sample during the preceding period of the arcing cycle. The degree of carbon monoxide evolution for these two cases may be greatly different. Second, the niaximuni ratio of bath to sample neight is limited by the bulk of the electrode assembl) and by the residual oxygen arising from the bath material. Prior outgassing of each electrode assembly to reduce the blank contribution destroys the time advantage of the spectrometric method. Third, for the sake of both speed and niinimuin chamber blanks (e),arcing periods of 1 minute or less are desirable. Consequently, bath materials nhich can be used successfully in T-acuuni fusion methods, where extraction periods of 15 to 30 minutes are commonly employed, may not be effective under the much shorter arc duration. Finally, the high temperatures attained in the direct current arc discharge may enhance the formation of solid or semisolid carbides in the melt. As a result, gas evolution from the viscous bath may be incomplete.
Figure 3. Effect of various ratios of platinum to sample weight on oxygen evolution
The evolution of the oxygen content of titanium samples from platinum baths under the arcing conditions \vas rapid. A factorial study on the optimum experiniental conditions for carrying out this excitation revealed other significant results. A violent reaction, which preceded the gas erolution, could be rcduced by pre-arcing the electrode assembly a t a lower current and then incrpasing thc current to the operating
level without' extinguishing the arc. The optinium rat,io of platinum to sample weight, consistent n-ith minimum consumption of platinum, was about 5 for 0.1-gram t,itanium samples (Figure 3). Incomplete evolution of the oxygen content \vas frequently. but not aln-ays, obseri-ed when the tit'anium sample iyas able to wet the graphite electrodes before alloying completely with
Figure 2. Electrode assembly for metal bath excitations Dimensions in inches
-
i
5.0.
d 4.0. c1
23.0, I-
-
C
0
2.0. 1.0.
.I .2 .3 .4 GRAMS pt/o.i'CRA~ TI
.S
.6
TITANIUM PLATINUM-?.
TiTA N IUM
LJ U
45\16" Figure 4. Electrode assembly for determination of oxygen in titanium
current is increased lat,er in tlie arcing cycle: the anode spot rests on the molten globule. This ensures maximum bath teinperat'ure and temperature gradient. Imth of ivhich appear essential for rapid quantitat,ire erolutioii of the oxygen content. Spcct'rogranis photographctl (luring tlir earl)- phase of the arcing cycli~s l i o ~ that ncy$gible rrolution of tlic oxygcm content takcs place, duriiig tlic flash, Ho\\-clvc~,t lie oxygen c on t c > i it i- ~ ) i i i plvtc.ly lilicmtcd during the first 30 ontls of thc arcirig cj-i*lc. JIoviiig platc spc~rtrogramspliotogrnplicd tluriiig thr, c,oniplctc arriiig c ~ - ( * Iroycd r tliat inxitcd intcmitj- ratio; for tlip first 30 oiids arc' tl[~c.id(~tlly lw-: rqmitluiililt i n iiitcnity r:itiox intc'gmtcd oviir tlic ontls (Figure 5 ) . Tlii, lui v:ii,iation in th(s iiitcwsitj- r:itioP (Iiwiiig oiitls is prohalily i*ausotl 11)- v:iri:itions in tlic al)solut(~ r:itc, of g : ~ cw)lution x i t l cliff usioi 1
3
c 361 0
1
1
30
60
1 90
I 120
I I80
I J
ELAPSED TIME ( S E C )
Figure 5. Reproducibility of intensity ratios for various arcing periods
tlw p1:~tiiiumbath. This is roinini of tliv 1)ch:ivior of zirconium in iron 1)ntIis u i i t l c ~v:aciiuni fusion conditions (Id). The result? from these experiments led to the electrode design illustrated in Figure 4 , The titanium specimens :ire formed into n-afers approximately l,i inch thick and 3 , , 1 6 inch in diameter hy using water-cooled cutoff n-heels. The specimenx are then burnished by filing lightly. The platinurn is fornied into 1 4-inch diameter cuplike 11-afers by hriquetting npproxiniat~ely 0.3 grani of 12-gage platinum n-ire a t 8000 pounds per square inch in 3, hriquetting press (Applied Research Laboratories) ( ~ 7 ) . The 1, a-incah diameter plunger used in t'liis operation is tapered to 16-inch diameter on the t'ip so that a depression is formed in the platinum. The t'itaniurii specimen is then pressed lightljinto the depression of the platinum wafer to form a coliesire pellet (Figure 4). The samples are stored in a vacuum desicwtor until ready bo be exposed. The electinde receptacle has a shallonside \ r d l t o niininiize the possibility of contact betn-een the sample and the ret:iining wall before alloying can take place. These electrodes are arced first, at I3 :iinperes for 13 seconds: then the current i a inc>re:isetl to 30 amperes without extinqiishing the arc. The reduced current for the initial phase of t'he arcing cycle serves tn-o useful functions. dlmut 2 to 3 seconds after t h e arc is started a brilliant flash orcurs n-liich may eject molten globules of the s:iniple charge if the current is too high. Also the lo\\-er current prorides bet,ter control of t h e alloy formation and reduces the possibilit!- of the titanium specimen's contacting t,he retaining wall before alloying is complete. \Then the
riocl thci o s y g c ~ icontc'iit of tliri :irgon :itmosplicrc. is 1)cting cxcitcvl. I t is not(,n-ortlij. that lirolongcd arcing doc,.;. not I)ring :ihout a significant cIi:ingc in intrnsitj- r:itio. This in sorption of tlic rvolvcd i z c d ianiplc. c:irl)on. or plat~inuni is nrgligililt~ and that tlic ljlank i-: not appi(~cia1)Iy incwasetl by prolonged :ming. T h r slight but tl(4iiiitc incrcm;c, of tlic intcnsity ratios aftw 1 minutr of arcing :ippcars to lit, tlic r(wilt, of slow outgassiiig of thi. excitation cIi:imlx~r. Th(, ['onstancy of thc intensity rntios aftw tlie initial evolution has sulJsidcd shows that sclcctctl argon lines achieve an cxccptionally liigli diyy-ec of iiitcrnal standartlization. Tlitsc rcsults arc similar to thos' oliserretl for stccl saniplcs (6). QUANTITATIVE CALIBRATIONS
OxygenBlank Contamination. d s i n dicatctl previously (6). oxy containing compoiinds or; sourrcs otlicr t,linn the. sample ma)c n i w apprc~ciahlec~ontaminationof the argon atmosphcw in t l i ~c*li:tnihclr during tlic (witation. This contaiiiiiiation or h1:irik may arise from osj-gi~ninipuritics in tlw platinum. graphitr clrctrodcs. : q o n atmoephcrc, or froin outmg of t,he cliamh(1r 11-:ills. A gas purification sJ-steni (6)is used for removing the oxygen m t l osygencontaining compounds from the argon before it is atlmittetl into the excitation chamber. The blank contributed by 0.5 grain of platinum used for each electrode is negligible in comparison to blie oxygen content of commercial t'itaiiiuni metals. The supporting electrodes are outgassed before use by pre-arciiig a t 35 aniperes under a n argon pressure of 160 nim. of mercury. After about 5 seconds of arcing, eT-acua-
t.ioii of the chamber is begun. \Iden the carbon volatilization becomes excessive, the arc is terniinat'ed. The elapsed tinie for this operation is about' 1 minute per electrode. V-ater is circulated through the outer cavity during these arcings. After elect'rode outgassing operations are completed, the chamlier is then opened and the samples are quickly transferred into the elertrotle receptacles. =il-r~ :it this tinie t,he glass separator i n q - be wiped free of carbon deposited on i t i inside sixface during the electrode outgassing. During the time the electrodes are exposed to air: readsorption of atniosplieric oy.gen and water vapor on tlie actir a t e d electrode surface nxiy i m u r . Apparently the aniouiit atlsorlied ic: negligible or tlie ulsorbetl gases are effectively renioi-et1 di~rin;; the sui,iiip of tlic exc,it:ition
:ill in-itle surfares of the cliarn1)er to stronger outg ' influcnc,er tli:in
tive i:. arliieyetl 1))- arciiig :in auxiliarj. 1)wir of elec'trodei :it high cuireiit> (33 :imperei) for :I i.el;itivel!. loiig time ( 3 nimutes) uiitler a reduced :irgon premire (200 mm.of iiieic>ury). Iluriiig these r1i:iiiil)er outg:r~singarciiigs. only the 0 ring cxritj- is w t e r cwoletl. A qirnple c,yliiitlricd :mode i-: useti in plncae of tlie underrut ynriation for the ing arringq i o t1i:rt the heat ed in the elertrode is contluc>tetl inore efKcientlj- to the rotary electrotlc platforin and to the clianiliei~. I t i b uecei;:iry to tlirect a bla external surfiice of tlic nearest the arc rliirlia oyerhenting and rrarking of the qe1j:irator. Tn.o outgassing arcings are made, n-itli intervening evacwitioii :inti replenisliing IT-itli iinre argon. The exicuat'ioiis :ire nintle ac quick after the 33-ampere ni'c i The Calrod lieateis i(~utler-Hnmnier. Iiic., Xln-aukee. l\-is,). which heat tlie chamber to :tl)out 150" C.,maj- lie employed to furnish adc1it'ion:il heat during t'lie o u t g a s h g exposurpb. but this has not bepn necessary. \Vtien samples are exciietl, the use of Ion-er arc currents (-10amperes), the shorter arcing times (60 seconds). the reduced lieat f l o ~t o tlie cliamher, the higher argon pressures, and the xltlitionnl cooling provided by the flow of water tlirough the inner cayit!. make it possihle to reduce the charnljer tilank to =Is a prenegligible proportions. cautionary measure monitoring I h n k exposures are niade at, the lieginning and end of a series of exposures. h sample elect'rode not loatled nitli a saiiiple is used for this purpos;r. \\-lien operating conditions permit, the chaml~ermay he outgassed by el-acuating it 17-hile the C,'alrod heaters are supplying heat. This alternative method is effectire only if the heating and e~acu::tion are applied for 3- to 4-hour pmiotls. Standardization. Stantl:id samples of titanium and titanium alloys in which t h e oxygen content had hcen measurcd by racuuiii fusion methods VOL. 30, NO. 2, FEBRUARY 1958
181
were used, a description of these standards a n d their measured oxygen content is given in Table 11. T h e experimental conditions used for t h e calibration experiments are summarized in Table 111. Other details of operating procedures have been described previously ( 6 ) . Photography, microphotometry. and intensity ratio computations folloived standard practices ( 2 ) . The analytical curve obtained from these standards is Phon-n in Figure 6. The linearity of this curve down to 0.034% of oxygen provides verification of the negligible blank contribution a t this concentration. T h e fact that the points for unalloyed and alloyed titanium fall on a single curve suggests, b u t does not prove conclusively, that a single
curve is applicable for the analysis of both pure titanium and its alloys. PRECISION
Prrrision data \\-ere obtaincd from single exposures of saniplrs on individual plates, which ivere exposed over a prriod of several weeks. For analyses of t x o samplcs containing 0.13 and 0.19% ouygen, the corfficients of variation wrrc 3.8 and 4.6, respectively.
gr-a a
i
Table
II.
for
Standard Samples Oxygen in Titanium
\Yright of sample Argon pressure Anode Cathode dnalytical gap Exposure conditions Emiilsion \T-ave length Filter Slit I1cvelopmen t Emulsion calibration Microphotometer ~
ACKNOWLEDGMENT
0 H
0l 5o b
c o IL
0 0 0 0 0 0 0 0
Table 111.
Source unit
/‘
1 r-
272 13%
131 340 035 166 280 557
a Average of results obtained by cooperating laboratories of Task Force on C h r g e n , Panel on Methods of Analysis, RI&llurgical Advisory Committre on Titanium, 11atertown Arsenal.
Spectrograph
20
rIC
Oxygen, Content, Standard Description W.4-2 5 % Cr, 3 7 A1 ITA-9 4c; AI, 4c/c 1111 W.4-10 Unalloyed KA-12 2 i %Cr. 1 3c: Fe KA-49 Unalioyeh ITA-50 Unalloyed \Y-4-51 Unalloyed iY.4-52 Unalloyed
501 OXYGEN
CONCENTRATION (%)
Figure 6. Analytical curve for determinations of oxygen in titanium and titanium alloys
ANALYTICAL CHEMISTRY
The authors arc grateful to the Panrl on Methods of Analysip, Metallurgical Advisory Committee on Titanium, and to its rhairman, Sam Yigo, \T7atertowi Arsenal, for supplying the standard samples. The investigators n ere ass i s t d by helpful discussions with Frank Benner, Sational Itmearch Corp.; Ted D . llcKinley, D u Pont Co.; and Harry J. Srec and Richard S . Knisrley of ION a State Coll(,ge. LITERATURE CITED
DISCUSSION
The primary advantage of the cmission spectromctric mrthod is that oxy-
Experimental Conditions
Jarrell-Ash Co., 3.4-meter 1-bert mounting plane grating spectrograph, using 6-incl1, 15,000 lines per inch first order ( 7 ) grating blazed for 13,000 -4.) Kational Spectrographic Laboratories Spec PoFer; 250-volt, 35-ampere capacity ilpproxiinately 0.1 gram. 1Ieasiired oxygen concentration is corrected t,o 0. I-gram basis by dividing osygen value obtained by actual sample weight 200 nim. for outgassing elertrocics; 640 f 5 mm. initial pressure for exposurep Undercut type, as shown in Figiire 1,fabricated from United Carbon Co. Grade U-2 graphite 3.18-mm. diameter, 2.5 crn. long, mith 120’ point fabricated from Cnitcd Carbon Co. Grade C-2 graphite 6 mm. Prr-arc, 15 secsonds at 15 amperrs thrn 15 seconds at 30 amperes. Esporurr, 30 seconds at 30 amperes Eastman Type l K 7100-8400 A , , 1st order Corning 2-63 (transmits less than 0.57; a t radiation shorter than 5680 A , ) 0 , 0 5 mm. 4 minutes at 21’ C. i n Eastman Kodak D-19 with continuous agitation in Applied Research Laboratories developing machine ( 1 1 ) Two-step sector, preliminary ciirve method Jarrell-Ash console microphotometer, Model JA-2100 ~
182
gen determinations can be made in a fraction of the time required by othrr techniques. Approximately 1 hour is required to expose 11 samples. If t\vo operators are employed-one for the excitation and the other for plate nieasurenicnt and calculations-it is possihle to drtermiiie thc oxygen content of approximately 70 samplrs per day. The amount of platinum consunled is virtually nrgligiblt. The spent globulm are accuiiiulatfd and returned to commcrcial refinrrs for reclaiming. Prpliminary r e s i d s indicate that thc oxygen content of niobium. tantalum, zirconium, thorium, and the rare earth nirtals can be dctermiiied by this techn iq uc .
Albrecht, K. lI., hlal!ett, 11 W., ASAL. CHEM.26, 401 (1954). Churchill, J. R., IND.ENG.CHEV., AXAL.ED. 16, 653 (1914). Codell, M., Sorwitz, G , ANAL.CHEM. 27, 1083 (1955). Derre, G., J . JIetals 1 (Yo. lo), 31 (1949). Uietert. H. I\-.. J . Oat. Soc. A m e r . 31, 6b3 (1941j. Fassel, F’. A , , Tabeling, R. IT., Spectrochim. Acta 8 , 201 (1956). Jarrell, R. F., J . Opt. Soc. A l m e r . 45, 259 (1955). LIcIIonald, R . S., Fagrl, J E., Balis, E. \T*., A N A L . CHEM. 27, 163%(1955). McQuillan, A. D., llcQuillan, 11.K., “Titanium,” Chap. 10, .4cademic Press, Xm- York, i956. Peterson, D. T., Beerntsen, D. J., AVAL.CHEV.29, 254 (1957). Schuch, J., J . Opt. SOC.Anier. 32, 116 (1912). Sloman, H. il., Harvey, C. A , , J Inst. J l e t a l s 80, 391 (1951-2). Sniiley, W. G., ANAL. CHEX 27, 1098 (1955).
Smith, W.H., Ibid., 27, 1636 (1055). Stanley, J. K., von Hoene, J., Wiener, G., Zbzd., 23, 3 7 (1951). Walter, D. I., Zbzd., 22, 297 (1950). \T-ilkins, D. H., Fleischer, J. Is , Anal. C h i m . dcta 15, 334 (1956). RECEIVEDfor review June 12, 1957. Accepted A4ugust31, 1957. Contribution KO.589. JYork performed in the Ames Laboratory, U. S. Atomic Energy Commission.
