ANALYTICAL CHEMISTRY
106 accuracy, a Beckman Model G p H meter was used to locate the equivalence point of the titration. Meanwhile a 25-ml. aliquot of the solution was diluted to 250 ml. with 1 M hydrochloric acid in another volumetric flask, and two 25-ml. aliquots of this were analyzed coulometrically. When a 1.5052-gram sample of reagent grade picric acid (containing, according to ita manufacturer, 10.7% water) was analyzed by this procedure, it was found that 5.866 & 0.004 meq. of base would have been required to neutralize the entire saniple, and that 105.42 f 0.09 niillifaraday would have been required to reduce it. Assuming that the sample contained x millimoles of picric acid, for which n = 18, and y millimoles of dinitrophenol, for which n = 12, these values give
+ y = 5.866
2
and
18z
+ 12y = 105.42
whence the weight of picric acid in the sample is 1.338 grams (88.9%), and that of dinitrophenol is 5.2 mg. (0.38%). If water is the only other constituent of the sample, it would therefore be present to the extent of 10.75%, in good agreement with the direct determination. -4 sample of technical grade picric acid analyzed in the same way was found to contain 83.4% picric acid and 3.1% dinitro-
phenols. I t is evident that a simple alkalimetric titration of this material would give a seriously erroneous estimate of its picric arid content. ACKYOWLEDGMEYT
It is a pleasure to express thanks to Analytical Instruments, Inc., Bristol, Conn., for the generous grant-in-aid which made this work possible. LITERATIJRE CITED
(1) Bergman, I., and James, J . C., Trans. Faraday Soc. 50, GO
(1954). (2) Kolthoff, I. M., and Lingane, J . J., "Polarography" vol 2, p. 627, Interscience, New York, 1952 (3) Lingane, J. J., "Electroanalytical Chemistry," p 369, Interscience, New York, 1953. (4) Lingane, J. J , J . Am. Chern. SOC.67, 1916 (1945). (5) Meites, L., ANAL.CHEW27, 1116 (1955). (ti) Muller, 0. H., in "Physical Methods of Organic Chemistry" (A Weissberger, editor), vol. 2, pp. 1845-6, Interscience, New York, 1949. (7) Neiman, M. B., Kuznetsov, L. I., Rabinovitch, I. B., and Ryabov, A. V., Zavodskaya Lab. 15, 1280 (1949). (S) Pearson. J., Trans. Faraday Soc. 44, 683 (1948). RECEIVED for review J u n e 6, 1955. Accepted October 17, 1955. Division of Analytical Chemistry, 128th Meeting, ACS, Minneapolis, Minn , September 1955. Contribution No. 1306 froni the Department of Chemistry of Tale LTniversity.
Determination of Hydrogen in Titanium and Titanium Alloys MAURICE CODELL and GEORGE NORWITZ Pitman-Dunn Laboratories, Frankford Arsenal, Philadelphia 37, Pa.
As hydrogen in titanium and titanium alloys is considered an undesirable impurity, its determination is a matter of importance. In this paper an ignition method is proposed. The sample is ignited in oxygen in the presence of lead as a flux, the gases are passed through hot copper oxide to ensure complete oxidation of the hydrogen to water, and the water is collected in an Anhydrone collection tube. An important probleni in developing the method was to find means for preventing the large amount of heat generated by the reaction between the titanium and oxygen from cracking the reaction tube. This problem was solved by weighing the sample in a piece of 96% silica tubing and resting this tubing in the reaction tirhe on clay supports.
T
HE effect of hydrogen
011 titanium is not as marked as the effect of oxygen and nitrogen on titanium, in so far as such properties as hardness, ductility, and electrical conductivity are concerned (22, 28). Hydrogen, however, can change the grain structure of titanium ( 5 , 12, 29) and has a profound effect on notch bar toughness (SO, 54). The effect of hydrogen that might be picked up during welding, forging, or pickling operations is controversial (26, 35, 69). K O beneficial effect of hydrogen on titanium has been noted; therefore hydrogen must be classified as a contaminant and closely controlled (34). For proper understanding of the problems involved in the determination of hydrogen iri a metal it is essential to consider the metallurgical relationships between hydrogen and the metal. For no other element is there such a close tie-in between metallurgy and analysis. Titanium belongs to a group of metals, which includes zirconium, cerium, tantalum, and niobium, that is capable of absorbing considerable hydrogen in the solid state (15, 21, 53, 5 4 ) . The solution of hydrogen in titanium is
exothermic, and the solubility decreases as the temperature increases, the decrease becoming rapid a t about 600" C. I t is not possible to absorb much hydrogen in titanium a t room temperature. However, if titanium is heated to about 300" to 400" C. and cooled to room temperature, the hydrogen that has been absorbed is retained. When hydrogen dissolves in titanium there is eo film formation, as with oxygen or nitrogen (24, 25). Hydrogen in titanium, when present in moderate amounts, is stable under a vacuum of 10-6 mm. of mercury to approximatel) 275" C. ( 2 5 ) . The properties of titanium saturated with hydrogen (titanium hydride, TiH,) (1-3, 20) have bearing on the determination of hydrogen in titanium. Titanium hydride contains about 4% hydrogen, is metallic in appearance, and is indefinitely stable a t room temperature. l17hen titanium hydride is heated in air, no change takes place until its temperature of dissociation is reached. The hydrogen is gradually expelled and burns with a quiet flame, and when most of the hydrogen has been expelled, the titanium starts to burn with considerable heat. It is important to contrast the behavior of hydrogen in titanium with its behavior in iron, nickel, copper, aluminum, silver, molybdenum, and tungsten (16, 55, 54) in considering application of published methods for the determination of hydrogen in these metals to its determination in titanium. These metals ran absorb only small amounts of hydrogen, and the hydride formed is not stable under ordinary conditions of temperatuIcx and pressure. The hydrogen is absorbed interstitially as atoms without specific interaction with the metal atoms. The process of solution is endothermic, and the solubility increases as the temperature is raised. When iron is cooled from a high tempernture, the hydrogen is slowly evolved over a period of weeks and finally approaches the solubility of hydrogen in iron a t room temperature. I n determining the hydrogen content of freshly cast iron and steel specimens, such treatments as covering with
V O L U M E 28, NO. 1, J A N U A R Y 1 9 5 6 mercury, coating with metallic tin, or cooling in solid carbon dioxide or liquid air are necessary to prevent escape of the hydrogen (66, 64). Such treatments are not necessary for titanium or titanium alloys. I n studying the hydrogen-titanium system, the hydrogen content of the material was determined by the pressure of the hydrogen or by means of a miciobalance in a vacuum system. The vacuum fusion method has been the only available published method for the actual determination of hydrogen in titanium and titanium allols. Several investigators have indicated that hydrogeri in titanium and titanium alloys can he determined by vacuum fusion a t the same time that oxygen is determined (32, S9, 58, 61, 67). .is the vacuum fusion method is costly and time-consuming, an investigation was undertaken to develop an inexpensive rapid method. Hydrogen has been determined in steels, bronzes, and nickel silver by drilling the specimen under water and collecting the hvdiogen evolved ( 7 , 58,Ql), or by subjecting the specimens to cold worh and collecting the hydrogen evolved ( 6 , 8, 57). Such methods are not applicable to titanium, because the hydrogen in the metal is held too strongly. Ionic bombardment methods have bcen used for the determination of hydrogen in aluminum (37, 48),iron ( S T ) , magnesium ( 4 , 9 ) , tantalum (@), and palladium (43'). The specimen is made the cathode in a vacuum discharge tube. Bombardment of the cathode with mercurj ions induces an ionization of the gas atoms within the metal, and the ionized gases are then drann from the metal by the high potential between the electrodes. The discharge tube is evacuated continuously, and the gases are collected for analysis. The equipment was not available in this laboratory to test the applicability of the ionic bombardment method to the determination of hydrogen in titanium. Chemical solution methods, whereby the hydrogen in the metal is set free after solution of the sample, have been proposed. Hydrogen in aluminum was determined by dissolving the metal in bromine under carbon disulfide (10). The liberated hydrogen bromide was estimated gravimetrically as silver bromide, and the residual hydrogen was collected and oxidized with copper okide. Hydrogen in steels has been deteimined after dissolving the sample in potassium cuprochloride solution ( 2 3 ) . Solvents such as bromine and potassium cuprochloride will not dissolve titanium. A method has been proposed for determining hydrogen in titanium hydride by dissolving the material in 10% hydrochloric acid in the presence of dio\ane and collecting the hydrogen evolved ( 3 ) . This method would be inaccurate for small amounts of hydrogen in titanium. Hydrogen has been determined in aluminum by fusion of the
107 sample with a mixture of lead dioxide aiid ferrous oxide and measurement of the water formed (68). I t is riot known whether the method would be applicable to titanium. The hydrogen content of copper and aluminum has been determined by measuring the relative number and size of pinholes or blisters, or the density of the specimens (13, 16, 17, 56). None of the methods depending upon blister or pinhole coiint or density are applicable to titanium because of the mode of combination of hydrogen in titanium. The method for determining hydrogen in aluminum by supersonic waves ( 4 6 ) or x-rays ( 1 6 ) is not applicable to the determination of hydrogen in titanium for the same remon. Hydrogen has been determined in steels ( 1 4 , 27, 40, 44,47, 58, 68),magnesium (9, SS), and zirconium (31) by hot vacuum extraction. I n this procedure the sample is heated (hut not ineltcd) under a vacuum and the resultant gases are analyzed. Pepkowitz and Proud (46)have proposed a procedure for hydrogen in metals in which the eample is heated in an iron tube, the hydrogen is diffbsed through the tube under a vacuum, and the gases are analyzed. The hot varuum extraction method and the method of Pepkowitz and Proud are applicable to titanium and titanium alloys. Hydrogen has been determined in steel by heating in an inert atmosphere and measuring the hydrogen released (45). This method does not seem applicable to titanium, since when a sample of titanium ivaa melted in helium the hydrogen content of the material decreased only from 0.010 to 0.004% (34). Hydrogen has been determined in aluminum (55) and magnesium (9) by passing a stream of inert gas through the molten metal and analyzing the gases released. Whether these methods could be applied to titanium is not known. Hydrogen haa been determined in steels by measuring the thermal conductivity (61). The sample is fused under a vacuum, and the thermal conductivity of the released gases is measured. The method depends upon the fact that the thermal conductivity of hydrogen is seven times that of carbon monoxide or nitrogen. This method might be applicable to titanium or titanium alloys. Hydrogen has been determined in steels (18, 19, 56,49, 60, 60, 65, 6 6 ) and magnesium alloy€! (9) by burning the sample in oxygen and collecting the water formed in a weighed bulb containing Anhydrone. Sometimes copper oxide (9, 36), platinum gauze (50), or palladiumized asbestos (60) is used to ensure complete oxidation of the hydrogen to water. The ignition method was found to be applicable to the determination of hydrogen in titanium and titanium alloys. However, it was necessary to use lead as a flux to ensure complete recovery of the hydrogen. APPARATUS AND M A T E R I A L S
Figure 1. Apparatus for determination of hydrogen in titanium and titanium alloys 1. 2. 3.
4. a. A.
i. 8.
0. 10. 1I .
12. 13. 14.
Tank of oxygen Needle valve Tygon tubing Sulfuric acid Small gas-washing bottle Ground-glass joint (24/40) hleker burner Crumpled ball of fine copper wire Copper oxide Small glass tube inserted t o separate copper oxide from Ascarite G!ass wool Aecarite Purification tube (Vycor, 25 mm. in diameter) Anh,-drone
15.
16.
17. 18. 14. 20.
21. 22. 23. 24. 25. 26.
Ground-glass joint (29/42) Clay supports Electric furnace (hinge type) Sample t u b e (Vycor, 15 mm. in diameter, 7 inches long) Reaction tube (Vycor, 25 mm. in diameter) Copper oxide tube (Vycor. 25 mm. in diameter) Ground glass joint (10/30) Collection tube (boroslllcate glass, 15 mm. i n diameter) Calcium chloride tower (10 inches high) Rubber stopper Microstopcock Ground glass joint (12/18)
The apparatus used, together with its important dimensions, is shown in Figure 1. All the ground-glass joints shown in Figure 1 are held together by springs. A considerable problem in applying the ignition method to titanium and its alloys was t o find means for preventing the large amount of heat generated by the reaction between titanium and oxygen from cracking the reaction tube. This problem was solved by weighing the sample in a piece of 96% silica tubing, 15 mm. in diameter and 7 inches long, and resting the tubing in the reaction tube on clay support8 (three rounded clay covers for combustion boats, Leco). Probably an equally effective and cheaper method for preventing the cracking of the reaction tube would be to weigh the sample in a clay boat and insert this boat into a hollow cylinder made of clay or magnesia. The cylinder would then be inserted into the reaction tube
ANALYTICAL CHEMISTRY
108 Table I. Sample
Results of Hydrogen in Standard Samples of Titanium and Titanium Alloys
WA2
Type of Alloy Cr-A1-Ti alloy
Alloying Elements 5 % Cr, 3% .U, 0.7%, C
WA9
RC-130B
4% Al, 4% Mn
W910
Comm. pure T i
W-412
Ti-150.4
No.
RR3
....
RR4
, . . .
RR5
,...
.... 2.7% Cr, 1.3% Fe
Hydrogen, % Found, proposed method 0.013 0.017 0 006 0 007 0 007 0.007 0.013 0.011 0,012 0 013 0.012
Present, vacuuni fusion 0.016 0.005 0.006 0.013 0 013
RRS
...
RR12
....
0 0070
0,0120 0 0123
0,010 0.011 0,009 0.004 0,005 0.005 0.010 0.009 0.011 0.012 0.011 0.011
0.008
0.004
....
0 0066
0.0140
RR6 RR7
.iverage i o U i C proposed method 0.0150
.
...
0,009
0 011
0.0100
0.0047 0.0100 0 0113
0.0257
-(without clay supports). The authors were unable to obtain boats and cylinders of suitable dimensions. The reaction tube used in the apparatus can be made of either 96y0 silica or quartz. Following the reaction tube is a small tube containing copper oxide which is heated with a Meker burner (or a heater). The purpose of this tube is to ensure oxidation of the hydrogen to water. The water is collected in a small Anhydrone collection tube with stopcocks a t each end. A protective tower containing Anhydrone and Ascarite is placed after the collection tube. The oxygen used in the determinations is purified by passing it through a long column of copper oxide heated to 750" C. and then through Ascarite and A4nhpdrone. The two furnaces used in the method should be of the hinge type (multiple unit, Hevi Duty Electric Co., Milwaukee, Xis.) because they shou!d be removab!e. The furnace used for heating the copper oxide in the purification tube is regulated by a Potentiostat, while the furnace used for heating the reaction tube is kept a t the maximum temperature obtainable (about 900" C.). The blank for the method (using 8 grams of lead) was found to be insignificant (less than 0.1 m g ) . I n running a blank it was necessnrfto use a sample tube wi?h its ends turned up in order to prevent the molten lead from flowing down the reaction tube and cracking it. Drillings, chips, and pieces can be used. Pieces are preferable. The method was applied to the determination of hydrogen over the range of 0.005 to 1%. Commercial titanium and titanium alloys contain about 0.005 to 0.02% hydrogen. The time required for a single determination is about a half hour. The apparatus is inexpensive and is not subject to breakdowns.
Prepare the sample in the form of drillings, chips, and pieces, clean twice with carbon tetrachloride, and dry in an oven a t 70' C. Weigh the sample. Use 5 grams when the hydrogen content is less than 0.30/, and 1 gram when the hydrogen content is 0.3 to 1%. Mix the sample with granulated lead (Mallinckrodt or Merck, reagent grade). Use 8 grams of lead for 5 grams of titanium and 2 grams of lead for 1 gram of titanium. Pour the mixture of the sample and lead into a piece of the 15-mm. 9677, silica tubing and push the mixture to the middle 4 inches of the tubing by means of a rod. Brush the tubing with the flame of a Meker burner in order to drive off superficial moisture. Insert the tubing into the reaction tube, placing it firmly on the clay supports. Push the tubing and the clay supports t o the center of the reaction tube by means of a stout iron wire bent a t the end. ~
Table 11. Hydrogen in Specially Prepared HydrogenTitanium Alloy Containing 0 . 9 7 y ~Hydrogen" % 0 94 92 92 94 93 0 92 Av. 0 93 a Calculated from gain in ueight of specimen.
0 0 0 0
PROCEDURE
Ignite several pieces of 96% silica tubing, 15 mm. in diameter and 7 inches long, and several clay supports in a muffle a t 1100' C. for 2 hours, remove, and store in a desiccator containing Anhydrone. Turn on the electric heaters and heat the copper oxide in the purification tube t o about 750' C. and the reaction tube containing three of the clay supports to about 900" C. while slowly passing oxygen through the system. Adjust the flow of oxygen t o a moderate rate, connect the copper oxide tube (20 in Figure I), and heat it with a Meker burner a t full heat. The Meker burner should be placed about 2 inches from the inlet end of the copper oxide tube. Connect the collection tube and allow the oxygen t o flow through it for a few minutes. Detach the collection tube, allow it t o stand 5 minutes in the balance case, open momentarily to the atmosphere to equalize the pressure, and weigh. While continuing the flow of oxygen, raise the reaction tube about an inch, and remove the furnace. Allow the reaction tube to cool to below 300' C. but keep the furnace a t about 900" C.
Attach the copper oxide tube, place the 1Ieker burner at full heat under it, and allow the oxygen to pass through for about 2 minutes. Attach the collection tube and the protective tower. Adjust the flow of oxygen to a rapid rate (about 400 ml. per minute), and place the furnace over the reaction tube. The sample will ignite in about 5 minutes. Fifteen minutes after the ignition, detach the collection tube, allow it to stand 5 minutes in the balance case, open momentarily to the atmosphere, and weigh. The gain in weight is water. Calculate the per cent hydrogen as follows: % ' hydrogen = 11 2 ( H - B )
W-
where H = weight of water (grams) obtained for run B = weight of water (grams) obtained for blank W = \veight of sample (grama)
V O L U M E 2 8 , NO. 1, J A N U A R Y 1 9 5 6 T o prepare for the next run remove the furnace for the reaction tube and allow the reaction tube t o cool while continuing the flow of oxygen a t a slow rate. When the reaction tube has cooled t o below 300' C., remove the 15-mm. 96% silica tubing and discard it. Weigh another saniple and proceed as before. T o shut down the apparatus detach the copper oxide tube and store it in a desiccator. ilttach t o the reaction tube a protective tube containing Anhydrone held in place by glass wool. The protective tube is made of a piece of borosilicate glass tubing about 6 inches in length xyith a male 29/42 ground-glass joint a t one end. NOTESOYPROCEDURE
The ground-glass joints are essential. If rubber stoppers are used, high and erratic blanks will be obtained. The temperature of the copper oxide in the purification tube must be about 750" C., and the length of the column a t least 10 inches. If the temperature is much less than 700' C. or a short column is used, high blanks will result. Glass wool should not be substituted for the crumpled copper wire t o hold the copper oxide in place in the purification tube because glass wool may melt. The reaction tube should be rotated 180" after every few runs t o prevent sagging. I t is essential t o have plugs of glass wool in the copper oxide tube in order t o remove particles of lead oxide produced in the reaction. The collection tube should be small t o increase the accuracy of the weighings. The collection tube should not be allowed t o become warm; otherwise erratic results will be obtained. The weight of the tube tends t o become less when the tube becomes warm. The Ascarite and hnhydrone used in the purification tube or the collection tube bhould be tramped down with a rod t o prevent the formation of an air space a t the top. The protective tower is necessary, as gas is drawn into the reaction tube from both ends of the system when the titanium starts t o burn. A sulfuric acid trap cannot be substituted for the protective tower. because the sulfuric acid would be sucked back into the apparatus. If necessary, the drillings should be pounded with a steel mortar and pestle t o enable them t o fit into the 15-mm. tubing. It is essential that the sample be thoroughly cleaned with carbon tetrachloride t o remove grease that is frequently present. The presence of grease xi11 cause high results for hydrogen. The carbon tetrachloride must be completely evaporated, otherwise high results will be obtained for hydrogen. Ether, alcohol, and acetone are not satisfactory solvents for grease. I t is important that the 15-mm. tubing be brushed viith a flame after the sample is put into it, in order to drive off any moisture that may be introduced in handling the tube. This treatment also drives off moisture from the surface of the titanium and the lead. It is essential that the sample ignite and burn completely, otherwise very low results will be obtained for hydrogen. A fast flow rate of oxygen is necessary for complete burning. The furnace must be heated to the operating temperature before it is put in place, as the proper ignition of the sample depends upon a high temperature being attained immediately. When a sample of commercially pure titanium is ignited in the method, the melt is usually j-ellow, owing t o the litharge (PbO) produced. When a sample of a titanium alloy is ignited, the melt is frequently brown or black. Occasionally some metallic lead is found a t the bottom of the melt. Experiments were carried out using many types of fluxes. Tin and iron were found t o be ineffective. The use of various lead oxides caused erratic results because they contained organic material. RESULTS
The rcsults obtained for the proposed method on 11 standard samples, whose hydrogen content has been determined by vacuum fusion, are shown in Table I. The first four samples were obtained from Watertown Arsenal and the remaining samples from Wright Air Development Center. The results for samples from Wright -4ir Development Center are tentative and unofficial pending further compilation of data and a statistical study by that establishment. As can be seen from Table I, the accuracx and precision of the proposed method are satisfactory. The results obtained on a special hydrogen-titanium alloy obtained by heating titanium metal in a stream of high purity hydrogen a t 500" C. are shown in Table IT. As judged by gain in weight of the specimen, the hydrogen content of the sample was 0.97%. However, this result was probably somewhat high
109 because of the absorption of small amounts of oxygen and nitrogen by the titanium. LITERATURE CITED
Alexander, P. P., Metals & AlZo~ls9, 45 (1938). Anderson, K., and Fleshman, W. S., I d . Eng. Chem. 42, 1381 (1950). Anderson, K., and Grunewald, -4.L., "Titanium Hydride," Fairchild Engine and Airplane Corp.. NEPA Division, Oak Ridge, Tenn., 1948. Arkel, A. E. van, "Reine JIetalle," p. 124, Julius Springer, Berlin, 1939. -4rmour Research Foundation, "Proceedings of the Symposium on Analysis and lletallography of Titanium," Chicago, Ill., June 1951, p. 26. Baker, T.. J . Iron Steel Inst., Carraegie Schol. Mems. 3, 249 (1911). Baker, W.A., Child, F.C., and Glaisher. W.H.. J . Inst. Metals 70, 373 (1944). Bardenheuer, P., and Ploum, H., Mitt. Kaiser Wilhelm Inst. Eisenforsch., Dusseldorf 16, KO.11. 129 (1934). Uobalek, E. G., and Shrader, S. A . , ISD. Esc;. CHEM.,AKAL. ED. 17, 544 (1945). Chretien, P. E., Nipper, H. A,, and Piwowarsky, E., AluminumArch. 33 ( S o . 23) (1939); J . Inst. Metals 66 (Pt. 4), M e t . Abstracts 7, 146 (1940). Chufarov, G. I., and Nosyreva, S. S.,Zavodskaya Lab. 13, 287 (1947). Craighead, C. AI., Lenning. G. d.,and Jaffee, R . I.. J . Metals 4, 1317 (1952). Caochralaki, J., 2.Metallkunde 14, 2 7 i (1922). Derge, G., Peifer. TV., and Alexander, A,. Trans. 4 m . I n s f . Mining Met. Engrs. 162, 361 (1945). Dushman, S., "Scientific Foundations of l-acuu~iiTechnique," chap. 9, p. 547, Wiley, New York, 1949. Eastwood, L. FV., "Gas in Light .4lloys," pp, 15-19, Wiley, Kew York, 1946. Eastwood, L. W.,and Kura, J. G., Foundry 75 (Xo. 7 ) , 70 (1947). Gerke, F. K., Zavodskaya Lab. 13, 298 (1947). Gerke, F. K . , and Zolotareva, X. Y., Ibid., 4, 19 (1935). Gibb, T. R. P., J . Electrochem. Soc. 93, 198 (1948). Gibb, T. R. P., and Kruuchwita, H. TT., J . Am. Chem. Soc. 72, 5365 11950). Ganser, H. TV,, I n d . Etig. Cheni. 42, 222 (1950,~ Goutal, E., T-lIth l i l t . C o n p . .4ppiied ( ' h e m . . Lor~don 1 , 50 (1909). Gulbransen, E. -4.. and .indi,ew, K. I..,.J. Electrochem. SOC.96, 364 (1949). Gulbransen, E. h.,arid Andrew, K. F., Trans. A m , Inst. Jfirling M e t . Engrs. 185, 741 (1949). Hartbower, C. E., and Daley, D. AI., Welding J . S. Y ,33, ( S o . 7), 311s (1954). Holm, V. C. F., and Thompson, J. G., J . Research Natl. B u r . Standards 26, 245 (1941). Jaffee, K. I., and Campbell, I. E., Trans. Am, Inst. Mining N e t . Engrs. 185, 646 (1949). Lenning, G. A, Craighead, C. LI.,and Jaffee,R. I., J . Metals 4, 1317 (1952). Ibid., 6, 367 (1954). AIcGeary, R. K., "Zirconium and Zirconium Alloys," Symposium, Am. Soc. for Metals, p. 168, Cleveland, Ohio, 1953. Mallett, hl. W., Trans. A m . Soc. Metals, Preprint 41 (1948). Gerds, A . F., and Griffith, C. B., ASAL. CHEM. lIallett, 11. W.. 25, 116 (1953). lletallurgical Advisory Committee on Titanium, Watertown Arsenal, "Status Bulletin on Unclassified Titanium Research and Development of Army Ordnance Corps," No. PI2 (February 1954). Meyer, H. hI.,and Rostoker, W., Felding J . LV. Y . 33, 173s (1954). Moore, G. A., Trans. A m . Inst. Mining M e t . Engrs. 162, 404 (1945). Moreau. L., Chaudron, G., and Portevin, A . , Compt. rend. 201, 212 (1935). Muller, F. C G., B a . 12, 93 (1879). National Research Corp., Cambridge, Nass., "Operation Instructions for Vacuum Fusion Analysis," 1952. Naughton, J., Trans. A m . Inst. Mining Met. Engrs. 162, 385 (1945). Pearson, T.F., Baker, W. A., and Child, F. C., Proc. Inst. Brit. Foundrymen, Paper 904, 1948. Pepkowita, L. P., and Proud, E. R., AXAL. CHEY.21, 1000 (1949).
110
ANALYTICAL CHEMISTRY
(43) Portevin. h., Chaudron, G., and Aloreau, L., Compt. rend. 204, 1252 (1937). (44) Post, C. B., and Schoffstall, D. G., Trans. Am. Inst. Miniiig Met. Engrs. 162, 390 (1945). (45) Rooney, T. E., and Barr, G., J . Iron Steel Inst. London 119, 575 (1929). (46) Rummel, T., Esmarch, W., and Beuther, K., Metallwirtschaft 19. 1029 (1940). (47) Scafe. R. Ri., Tjans. Am. I n s f . Mining Met. Engrs. 162, 375 (1945). (48) Schmid, E., and Schweinita, H. D. von, Aluminium 21, 772 (1939). (49) Schwarte, H. rl., and Guiler, G. M., Trans. Am. Foundrymen’s Assoc. 47, 742 (1939-40). (50) Scott, W. W.. “Standard Methods of Chemical Analysis,” vol. I, p. 443, Van Nostrand, New York, 1939. (51) Shields, B. AI., Chipman, J., Grant, N. J., and Carney, D. J., Materials & Methods 40 (No. l ) ,220 (1954). (52) Sloman, H. A., Harvy, C. A , , and Kubaschewski, O., J . Inst. Metals 80. 391 (1951-2). (53) Smith, D. P., “Hydrogen’in Metals,” p. 160, University of Chicago Press, Chicago 1948. (54) Smithells, C. J., “Metals Reference Book,” p . 380, Interscience, Sew York, 1949.
Sterner-Rainer, R., Z. Metallkunde 23, 274 (1932). (50) Swain, ii. J., J . Inst. Metals 75, 863 (1949). 157) Tammann, G . , and Schneider, J., Z . Q?WQ. u. allgem. C‘hem. 172, 155)
43 (1928). (58) Thompson, J. G., Trans. A m . litst. Minino Met. Engrs. 162, 369
(1945:. (59) Titanium Metals Corp. of -Iinerica, New York, “Handbook on Titanium Metal,” pp. 66, 75, 89, 1952. (60) Veinberg, G. Ya., and Proshutinskii, 9. I., Zavodskaya Lab. 6, 422 (1937). 161) Walter, D. I., A x . 4 ~ CHEx . 22, 297 (1950). (62) Wells, J. E., and Barraclough, K. C., J . Iron Steel Inst. Loudon 155, 27 (1947). 163) Willems, F., Aluminium 23, 337 (1941). (64) Yao, Y . L., and hfilliken, K. S., ANAL. CHEY. 25, 363 (1953). (65) Yavoiskii, V. I., Zavodskaya Lab. 11, 406 (1945). (66) Ibid., 13, 262 (1947). (67) Yeaton, R. A., Vacuum 2, 115 (1952). (68) Yenson, T. D., and McGeary, R. K., Trans. Am. Inst. Mining Met. Engrs. 162, 355 (1945). R E C E I V E Dfor review June 4. 1955. Accepted September 21, 1955.
liquid Scintillation Counter for Carbon-1 4 Employing Automatic Sample Alternation ARTHUR J. WEINBERGER, JACKSON B. DAVIDSON’,
and
GUS A. ROPP
Chemistry Division, O a k Ridge National Laboratory, O a k Ridge, Tenn.
A scintillation counter for carbon-14, which uses solution phosphors, has been described. This instrument has been used to measure the activity ratio of a pair of carbon-14-containing solutions with an average deviation of approximately0.5% from the mean and from the calculated value. It employs automatic alternate counting of three cells, one of which is usually a standard and one a background. The alternating feature was designed to reduce possible effects of instrument drift and changing background on the results from long counting periods. A series of experiments to test this feature is reported. The counter is simple, electronically. The mechanical parts are not difficult nor expensive to build where adequate shop facilities are available.
T
HE vibrating reed electrometer when used with a Borkowskitype ionization chamber is a standard instrument for the assay of carbon-14 compounds. The organic compound is burned to form carbon-14 dioxide, which, when introduced into the ionization chamber, produces a current which is measured by the electrometer (6, 6). Scintillation counting (8, 3) of carbon14 compounds dissolved in organic solvents containing scintillators such as terphenyl has the advantage that the compound need not be burned. Several instruments have been described for this type counting. The present paper discusses the design and testing of one such instrument. The principal objective was to obtain an instrument M hich would measure precisely and reproducibly the ratio of activities contained in two or more samples of the same compound, n ithout regard for whether or not the individual measurements of the activity of any sample varied from time to time. It is well known that for most tracer studies ratios of activities of several samples are needed, whereas the absolute activity of any one sample is not needed. For this reason an automatic sample changer was designed to allow three samples (one to measure the 1 Present address, Instrumentation and Controls Division, Oak Ridge Sational Laboratory, Oak Ridge, Tenn.
background which could be subtiacted from each of the other two before calculation of their ratio) to be counted alternately for short intervals with the integrated counts for each sample stored on a eeparate register. It was felt that such an alternating system could reduce the effect of instrument drift and probably permit ratios of activities of several samples t o be measured with greater precision than that obtained with instruments not employing sample alternation. The use of refrigerated systems employing two photomultipliers, two amplifiers, and a coincidence circuit to reduce background has been described by several writers (1, 4), and a commercially available unit has been recently introduced ( 7 ) . These dual channel systems are characterized by high efficiencies for carbon-14 (values as high as 75% have been reported) and by low backgrounds (100 to 200 counts per minute). However, they are bulky, since refrigerators and rack mounting are required, and the electronic circuitry is fairly complex. These systems also require that the counting cell and contents be refrigerated to 0” C. or belolT, which in general decreases the solubility of the scintillator and the sample in the solvent. Finally, they are expensive. For the present purpose it seemed that a counter using one refrigerated phototube and one amplifier would be more stable, easier to maintain, and, incidentally, less expensive than one using two such units and a coincidence circuit plus a large refrigerator. The amplifier and scaling unit employed in the counter described here are those of a commonly used proportional counter; thus it may appeal to those who already possess such equipment DESIGV
Detector. The detector is a lP21 photomultiplier which is operated a t liquid nitrogen temperature. The tube rests with its base u p on the bottom of a 500-ml. Deyar flask with its cathode facing a 1.25 x 2 inch unsilvered window in the side of the flask. The base of the phototube is partially removed by chucking the base end in a lathe and cutting away the upper part of the base until there is no mechanical connection with the glass envelope, except that of the wire leads. This is done in order t o eliminate the strains on the envelope and on the soldered connections to the prongs of the base, which are caused by the drastic cooling which occurs when liquid nitrogen is poured over the phototube.
