ified Tin-Flux Technique CH. VENKATESWARLU'
and MANLEY W. MALLETT
Battelle Memorial Institute, Columbus 7, Ohio
b The standard Walter method of determination of oxygen in titanium was reinvestigated and a modified tin-flwx procedwre was developed. The extraction of oxygen was carried out at 1950" C. without the use of graphite chips or crucible lid, which were considered essential by early workers. Also, conditions for rapid degassing of t h e crucible assembly were established.
3.0 inches; and wall thickness, d / l e inch) was used without a lid. Materials. For preliminary experiments, samples of alloyed and unalloyed titanium were used, the alloying elements being aluminum, vanadium, and molybdenum. Standards were prepared by allowing iodide-titanium to react with measured amounts of oxygen in a Sieverts apparatus and then arc melting to homogenize. ANALYTICAL PROCEDURES
s 1950, Walter reported a method (6) for the determination of oxygen in titanium, which is still considered the standard or umpire method. Later, Albrecht and Mallett (1) critically studied this method and emphasized certain details of the technique which should be rather closely adhered to for its successful utilization. NcDonald et al. (4) explained some of the difficulties in applying the iron-bath technique. Recently. Hansen et al. ( 3 ) revieited briefly the present status of the analysis and described a platinum-flux technique. One of the authors (Ch. V.), while working with the Walter technique for the determination of oxygen in titanium, found it difficult to retain graphite chips inside the crucible. Occasionally during a run, the chips blew up to the lid and blocked the passage from the crucible. Sometimes degassing the crucible was not satisfactory, even after 6 hours of heating a t 2300" C. Also, it was difficult to open the lid for checking the operating temperature after the addition of tin without loss of contents of the crucible. The only alternative was to rely on the often unsteady power output of the conrerter. 4 critical study of the literature and close examination of the contents of the crucible after each of a number of experiments led to a systematic reinvestigation of the Walter method. This resulted in the establishment of a rapid method of degassing the furnace setup and the development of a modified tinflux technique. EXPERIMENTAL
Apparatus. The vacuum fusioii apparatus was described earlier (6). In the furnace assembly, a single crucible (inside diameter, 1.0 inch; height, 1888
ANALYTICAL CHEMISTRY
Degassing the Furnace Assembly. A critical look a t the general blank rates experienced in different vacuum fusion techniques revealed that the presence of graphite chips in the crucible is generally associated with high blank rates. To test the effect of chips, a blank was taken after degassing as for the Walter method. The furnace assembly containing chips was degassed a t 2300" C. for about 3 hours and then for another hour a t 2000" C. after the addition of tin. The blank was started a t 1200" C. and the temperature raised to 2000" C. in about 4 minutes. The total blank for 30 minutes was of the order of 0.100 mm. of mercury in a volume of 500 ml. In contrast, an empty crucible degassed at 2300" C. for 3 hours, as for the hot extraction method for oxygen in niobium (S), yielded a 30-minute blank of about 0.050 nun. of mercury a t 2000" C. Similar tests were made with and without -200 mesh graphite powder in the crucible. The furnace assemblies were degassed a t 2150" C. for 2 hours, and 30-minute blanks were taken starting at 1200" 6.and completing a t 1950' C. The results are recorded in Table I. It is evident from runs 3, 4, and 5 (column 3) that the graphite powder in the crucible is the culprit responsible for higher blank rates. Also, comparison of run 2 uith runs 1, 3, and 4 (column 3) shows that the higher blank rates in the Walter method might be due to the graphite chips in the crucible, There are different views regarding the role of tin in the analysis of metals by vacuum fusion techniques. However, it is universally agreed that tin aids in a rapid and quantitative extraction of oxygen from metals. To test the effect of tin on degassing, a gram of tin was
placed in the crucible during assembly and blank rates at 1950" C. (starting a t 1200" C.) were determined. Also, about 0.5 gram of tin was analyzed, as if it were a sample. The data are included in Table I. Tin had no significant effect in lowering the blank (runs 6, 7, 8, 9; column 3), but formed a thin film on the walls of the furnace which probably obstructed gettering by other deposits formed during degassing. The film also facilitated cleaning of the furnace. The addition, during a blank determination, of a quantity of tin equal to that dropped with each sample provides a means of compensating for the gas content of the tin flux (see data in column 4 of Table I). Modified Tin-Flux Method. A careful examination of the contents of the crucible a t the end of each run b y the Walter method showed t h a t only part of the graphite chips were clustered, the sample probably acting as a binder. This indicated that successful analyses were achieved with relatively small areas of contact between sample and graphite. Hence, to avoid the blowing around of chips, a graphite disk, about '/8 inch thick and 1s/18 inch in diameter, was made with 1/16inch-deep grooves cut a t right angles on the top surface. This increases the surface area by forming a number of miniature pyramids. A few samples were analyzed a t 1950" C., replacing chips with this disk and otherwise following Walter's procedure. The extraction of oxygen was quantitative. However, even the disk moved about inside the crucible during the run of samples. Whether the samples came in contact m-ith the disk or the crucible itseIf, the extraction of oxygen mas good. Consequently, analyses were tried, dropping the samples into the empty crucible. ilgain the results were satisfactory. To speed up the analyses, samples were dropped a t 1950" C. instead of 1200" C. The complete extraction of oxygen was achieved in 20 minutes. However, the samples sometimes stuck 1 Present address, Analytical Division, Atomic Energy Establishment Trombay, Government of India, Bombay, India.
to the funnel during dropping or blew back and stuck t o the lid or the walls of the crucible and did not react. When the lid was omitted to alleviate this problem, samples occasionally blew out of the crucible because of the high vapor pressure of tin. The boiling was less violent a t 1900" C., provided the amount of tin was not excessive. Different ratios of tin flux to sample were tried at 1900" 6. A minimum of 2 to 1 was found essential for quantitative recovery of oxygen. The results of a few samples, extracted a t 1900" C. and using this ratio, are recorded in Table
11. This procedure was satisfactory provided the tin required was less than about 0.5 gram. This meant that sample weight could not be increased to increase precision, as may be desirable in the case of samples of low oxygen content. Spattering would become intolerable also for samples of high hydrogen content. Hence, it was decided to drop the sample at 1200' C., as in the Walter method, extracting gases for 30 minutes.
Procedure. T h e graphite crucible was packed with -200 mesh graphite powder in a Vycor thimble. The funnel was placed in position and any graphite powder spilling inside the crucible was removed. One gram of tin was added to the crucible and then the assembly was inserted in the apparatus, The samples were prepared in the usual way, surface abraded, weighed, wrapped in twice their weights of tin, and kept immersed in acetone (c.P.) until they were loaded in the apparatus. A 0.5gram piece of tin, followed by samples, was loaded in the sample arm. The apparatus was pumped down and degassed at 2150' C. for 2 hours. The initial heating was done slowly to form a film of tin on the walls of the furnace tube without spattering. $fter degassing, a &minute outgassing rate of about 0.04ml. (standard temperature and pressure) a t 2150" C. was generally obtained. The converter was set to heat the crucible at 1950' C. and then was switched off. When the temperature
Table 1.
Run NO.
Comparison of Furnace Blanks
Initial Contents of Crucible Empty Chips Empty Empty -200 mesh graphite powder, 0.1 gram Tin conditioner, 1gram Tin conditioner, 1gram Tin conditioner, 1gram Tin conditioner, 1gram
30-Minute Blanks" a t 1950' C. Without With tin 8am le, tin Sam le, mm. d'g mm. d'g ... 0 . O5Ob ... 0 1OOb ... 0.045 ... 0.032 0.110 0.030 0.043 0.060
0.026
Wt. of Tin Sample, Gram
0:oso 0.053 0.090 0.045
...
*..
...
...
...
0.4
0.6 0.5 0.5
Values in columns 3 and 4 indicate pressure in a volume of 500 ml. 30-minute blank at 2000' C.
fell to 1200' C. (in about 5 minutes), the tin was dropped, the converter was switched on, and a 30-minute blank was collected and analyzed for carbon monoxide by the usual fractional freezing method. Following this, the sample was dropped and analyzed in the same manner. RESULTS
The results of analysis of a number of samples are given in Table I11 along with check analysis by the platinumflux technqiue. Statistical analysis of the fourteen results for arc melted iodide-titanium indicated a standard deviation of 0.0044 weight % and a variance of 14.2% at the level of 0.031 weight % of oxygen in titanium. Comparison of these results and those for standards 1 and 2, a t 0.112 and 0.206 weight % oxygen, by the tin-flux method with results b y the platinumflux method, showed reasonable agreement. The average deviations of tinflux data, 10.0035 to 50.008 weight yo, are comparable to those reported for the platinum-flux methods (3). It was shown that the sample weight could be increased up to 0.50 gram to
Table II. Analysis of Samples Extracted at 1900' C. for 20 Minutes (Tin flux t o sample ratio, 2 to 1) Oxygen, Wt. yo -
Sample Tin flux Standard 1 0.106
Platinum flux at 1850' C. 0.104
0.119
0.106 Av. 0.110 f0.006
Av. 0,211 i0.008 Table 111. Analysis of Samples by Modified Tin-Flux Method
Oxygen, Wt. % PlatinumTin-flux flux method method
Samples Arc-melted iodidetitanium 0.025 0 028
0.028 0.022 0.029
I
0.037 0.036
0.036 0.031 0.027 0.024 0.035 0.031 0.030 0.032 0.029O 0 . 026b Av. 0.031 i0.0035 Standard 1 0.123
0.104
0.106 0.106
Figure 1. A. E. C.
Crucible bottoms after various treatments Degassed with tin After run of samples not wrapped in tin After run of six samples with tin
Av. 0.112rt0.008 Standard 2 0.207 0.210 0.212 0.198 0.198 Av. 0.206 f0.005 b These samples weighed 0.35 and 0.50 gram, respectively, and the rest weighed about 0.20 gram each.
VOL. 32, NO. 13, DECEMBER 1960
a
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improve the precision of analysis of samples of low oxygen content. DISCUSSION
This study, primarily aimed a t the reinvestigation of the Walter method, resulted in the successful elimination of the difficulties therein encountered. The troublesome use of graphite chips was completely avoided. Eliniination of the chips permitted better control of the contents of the crucible during analysis and facilitated degassing. Also, i t was shown that if graphite powder, used for thermal insulation, enters the crucible, satisfactory degassing becomes difficult. Up t o six samples were analyzed in a single run withno signs of incomplete extraction of gases. Reconditioning of the furnace between analyses was not required. A better understanding of the reaction conditions was gained. Figure 1 shows the bottom parts of the crucibles
TMinati on
subjected to different treatments. During degassing, the tin appears to have volatilized completely. The escaping vapor bombarded and conditioned the walls of the crucible. In the absence of tin flux, the titanium melted and spread but retained its metallic luster, showing practically no carbide formation. On the other hand, when tin flux was used, the sample residue appeared black and showed little or no metallic luster. Contrary to common belief, a sample fluxed with tin spread over less area than a sample without flux. The presence of tin mas evidently more essential than a large area of sample-graphite contact for completing the reaction. From this it was concluded that the graphite chips of the Walter method are superfluous, ACKNOWLEDGMENT
The authors are grateful to the many members of the Battelle staff who showed interest in the progress of the
work, and particularly to M. A. Van Camp and D. F. Kohler, whose cooperation contributed considerably to the success of this work. One of the authors (Ch. V.) gratefully acknowledges the fellowship granted by the International Cooperation Administration, Washington, D. C., and the deputation by the Atomic Energy Establishnient Trombay, Government of India, Bombay, India. LITERATURE CITED
(1) Albreoht, W. AI., hlallett, M. W., ANAL. CHEW26,401 (1954). ( 2 ) Hansen, W. R.,Mallett, 31.R., Ibid., 29,1868 (1957).
(3) Hanseii, W. R., Mallett, M. W., Traeciak, X I . J., Zbid., 31, 1237 (1959). ( 4 ) McDonald, R. S., Fagel J. E., Balia, E. W., Ibzd., 27, 1632 (1955). (5) Mallett, X I . Vi7., Griffith, C. B., Trans. Am. SOC.Metals 46, 375 (1954). (6) Walter, Dean I., ANAL. CHEM. 22, 297 (1950). RECEIVEDfor review June 6, 1960. Accepted Bugust 26, 1960.
of Forima Ide hyd by Gas
atography SIR: Schepartz and McDowell (6) recently reported an elution time for formaldehyde. The elution was obtained from a Carbowax 2Ohf (Union Carbide Chemicals Go.) column at 90" C. Kyryacos, Menapace, and Boord (5),in an earlier publication, presented chromatograms showing the separation of formaldehyde on an iso-octyi decyl phthalate column at 105' 6. but were not able to effect a quantitative estimation. In addition, Yokley and Ferguson (6) reported that some formaldehyde passes through a bis [2-(2methoxyethoxy)ethyl] ether column but were not able to resolve it a t 50' C. The authors investigated a variety of substrates from which formaldehyde can be eluted. These were not useful for quantitative work for reasons of relatively high substrate volatility-e.g., his [2-(2-methoxyethoxy)ethyl]ether a t 10.5" C. and Carbom-ax 2GM a t 120' C. -or poor resolution of formaldehyde in the presence of other polar compounds that occurs on a sorbitol or erythritol column a t 135' @. Recently we found that the surfactants present in several of the commercia! detergents can act as substrates from which formaldehyde may be suc1
ANALYTFCAL CHEMISTRY
cessfully eluted and estimated quantitatively. Desty and Harbourn ( 2 ) used the detergent Tide in granular form directly as a column packing to effect a variety of separations, not including that of formaldehyde. On the other hand, Decora and Dhneen ( 1 ) used Tide support only, coated with other substrates, for the separation of pyridines, I n the present investigation, the surfactant \vas extracted from the detergent pom-der and coated on such standard supports as C 22 firebrick hnd Fluoropak 80. This was necessary to reduce substantially the tailing of the formaldehyde and vater peaks which was always obtained on the heattreated detergent powder packed columns, Data obtained from two different columns are given below. One column was used to show that formaldehyde could be separated and quantitatively determined from its solution in v-ater. The other was operated to demonstrate the qualitative analysis of some complex solutions containing f crmzldehyde. ~ X P ~ ~ I M ~ N ~ A ~
The detergent powder wm heated, first at 125' C.and then at 180" C.,
for 24-hour periods to remove volatiles. The surfactant present nas subsequently extracted with petroleum ether or benzene. I n the quantitative work a borosilicate glass column 4 feet long and with a 6/32-inch bore was used. This was packed with a mixture of 30to 60-mesh Fluoropak 80 coated with 10% by weight of Tide surfactant and 30- to 60-mesh sand coated with 1% by weight oE the same surfactant, in the proportion, two volumes of the former to one of the latter. The coated sand was required to prevent compaction of the Fluoropak with its resulting nonuniformity of packing and unreasonably high backpressures. For the qualitative analyses, a copper column 15 feet long and with a bore of l/4 inch was packed with 30- to 60mesh C 22 firebrick coated with 30% by weight of the surfactant obtained from Sail detergent powder (A & P Food Stores). The active material is a blend of sodium tridecyl- and dodecylbenzene sulfonates, manufactured by Ultra Chemical Works, Inc. Columns containing such a blend gave separations which were as good as those given by the extracted material. Hence, heating the detergent apparently does not substantially affect, the composition of the surfactants. Preliminary work indicates that the surfactants obtained from such commer-
