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V O L U M E 28, NO, 2, F E B R U A R Y 1 9 5 6 Only insignificant differences have been found in samples taken from mill runs. In small scale laboratory runs, however, in order to obtain significant results, samples for analysis must be taken from the same position on each piece of fabric. DISCUSSION
Analyses made by this method agreed within 0.02% with those made in another laboratory by a colorimetric method in which the sodium silicate from the peroxide bomb is made t o react with ammonium molybdate, and the intensity of the resulting blue color is measured a t 715 mM. The agreement was very poor with analyses made in still another laboratory by dry oxidation in crucibles, as would be expected from the partial volatility of silicone oils a t high temperatures. The average difference between duplicate samples is 0.007%. Silica is a normal constituent of soil. If the textile fabric is not clean, or if silicon-containing compositions such as clay, talc, or colloidal silica have been used in processing, all the silicon present will be reported as silicone when determined by this method. The usual silica content of textile materials finished without the use of silicon-containing baths, and subsequently protected from
soil, is 0.00 t o 0.01%; occasionally amounts up t o 0.03% are found. The silicon content of textile materials which have been processed with silicon-containing compositions will be much higher than where silicon compounds are accidentally present. In any case, it is always well t o run an analysis for silica on a sample of the fabric before it has been treated with a silicone waterrepellent, if such untreated material is available. ACKNOWLEDGMENT
The author wishes to express his appreciation for the substantial encouragement and advice given by Alton A . Cook, technical director of The Arkansas Co., Inc. LITERATURE CITED
(1) Cook, A. A, and Shane, N. C., Teztile Research J . 25, 105-10 (1955). (2) hIcHard, J. A . , Servais, P. C., and Clark, H. A., ANAL.CHEW
20, 3 2 5 8 (1948). RECEIVED for review April 8, 1955. Accepted November 5, 1955. Presented in part before the Analytical Group, North Jersey Section, ACS, Meeting-hMiniature, January 1955, Newark, N. J.
Titrimetric Determination of Zirconium in Magnesium Alloys PHILIP J. ELVING University
of Michigan,
Ann Arbor, M i c h .
EDWARD C. OLSON The Upjohn Co., Kalamazoo, Mich.
The addition of zirconium to magnesium alloys intended for use at high temperatures requires rapid methods for determining zirconium in such alloys. The titrimetric measurement of zirconium by standard cupferron solution, employing amperometric detection of the equivalence point, has been applied to the direct determination of zirconium in commercial magnesium alloys following acid dissolution. The method is rapid, simple, and accurate, and should supplement the colorimetric alizarin S and gravimetric p-halomandelic acid procedures.
T
HE need for accurate and rapid methods for the determina-
tion of small amounts of zirconium in magnesium and magnesium alloys was cited by Wengert ( 5 ) in describing the colorimetric determination of zirconium in magnesium alloys by the alizarin red S method, and Papucci and Iclingenberg (4)in describing a similar gravimetric procedure using p-bromo- or pchloroniandelic acid. The addition of zirconium t o such alloys improves the operating temperatures and grain structure without adversely affecting the machinability and creep resistance when used for high temperature purposes as in jet engines. As zirconium can be rapidly and accurately determined gravimetrically and titrimetrically, employing cupferron as precipitant in 10% (ca. 2M) sulfuric acid solution ( S ) , it seemed that the titrimetric method employing amperometric equivalence-point detection might be advantageous as a supplement t o the colorimetric ( 5 )and gravimetric ( 4 ) methods. The present study describes the application of a titrimetric zirconium procedure to two magnesium alloys which were being used in a cooperative evaluation of the colorimetric alizarin red S procedure. Commercial magnesium alloys containing zirconium fall into two groups; one contains up to 6% of zinc and 0.8% zirconium; the other about 3y0 of rare earths and 0.4% of zirconium. The
zirconium occurs in both acid-soluble and acid-insoluble forms; the amount of the latter is usually small in comparison with the acid-soluble zirconium, and in currently available alloys is usually kept to within 0.02 t o 0.05%, since large percentages may be harmful. The dissolution procedures used in the present study are based on those proposed by Wengert ( 6 ) , which separate acidsoluble and acid-insoluble zirconium by treating the sample with dilute (1 to 4)hydrochloric acid; the insoluble fraction is changed to a soluble form by fusion with potassium hydrogen sulfate. Essentially the same dissolution procedure was used by Papucci and Klingenberg (4). EXPERIMENTAL
Reagent grade sulfuric acid (specific gravity 1.84) was diluted 1 to 10 by volume with distilled water. Cupferron was purified and stored as previously described ( 3 ) ; an approximately 0.01 to 0.02X standard solution was prepared daily by dissolving a carefully weighed portion in air-free water. Commercial waterpumped nitrogen was used for deoxygenating without further purification; other chemicals used were of reagent or C.P. grade, Titration was performed in a 150-ml. beaker fitted with a fourhole rubber stopper to accommodate the electrodes, buret (5or 10-ml. capacity, graduated t o 0.02 or 0.05 ml.) and nitrogen inlet; the beaker lip served as gas outlet. A Sargent ModelXXI polarograph or Fisher Electropode was used in conjunction with a dropping mercury electrode and a reference saturated calomel electrode (S.C.E.). PROCEDURES
Dissolution (Soluble and Insoluble Zirconium). Weigh 3.0 grams (0.370 Zr) or 2.0 grams (0.6y0Zr) of sample into a 400-ml.
beaker. Cover with a watch-glass, cool in an ice bath, then add cautiously 150 ml. of cold ( I 1 ) hydrochloric acid. After dissolution is complete as indicated by the cessation of gas bubbles, filter through KO.42 Whatman paper into a 250-ml. volumetric flask, wash the beaker and residue with hot water which is transferred to the flask via the filter paper, transfer the residue to the filter paper, and dilute the flask contents to volume; this solution contains the acid-soluble zirconium.
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ANALYTICAL CHEMISTRY
Place the filter paper and residue in a porcelain crucible, Table I. Determination of Zirconiurii in Magnesium Allo>-s, Emploj ing Amperonietric c h a r slowly, a n d h e a t a t 'Titration with Cupferron 950' C. for 30 minutes. Add Sulfuric Acid 1 gram of potassium hydrogen Sample Hydrochloric Acid Dissolution -_ Dissolutiou -__ sulfate and fuse. Cool and disInsolublea Solublea Run Insoluble Solubleb SolubleC Total Total' soltie the melt in a 150-ml. SO. Zr, % Zr. % So. Z r , b% Zr, % Zr, % Zr. 70 Zr. beaker with about 50 ml. of ZK 60 0 05 0.59 1 0.034 0.564 0.574 0.608 10% sulfuric acid; this solu2 0.025 0.571 0,580 0.605 tion contains the acid-insoluble 3 0 floc E K 30 0.06 0 33 4 0.029 0.311 0.317 0 346 zirconium. 5 0.031 0.308 0.313 0 34-1 Dissolution (Total Zirco6 0.349 nium). Weigh about 0.5 gram a Based on 1 : 4 hydrochloric acid dissolution for separation and colorimetric alizarin red S method for measof sample into a 150-ml. beaker. urement. 6 Dissolved in 1 : 1 hydrochloric acid and aliquot of cloudv solution titrated. Cover the beaker and dissolve c Aliquot of solution mentioned in b evaporated with sulfuric acid t o sulfur trioxide fumes and then diluted t o the alloy at room temperature 10% sulfuric acid before titration. with the minimum amount of d Sum of insoluble and soluble Zr (first and third columns). e Sulfuric acid dissolution of original sample. 10% sulfuric acid ( a b o u t 10 m1.j. .4dd 5 ml. of conc e n t r a t e d sulfuric acid and evaporate to the appearance of sulfur trioxide fumes. Cool, dilute to 50 ml. with distilled water, and proceed with the titration. The final zirconium solution prepared by dilution to volume of Amperometric Titration. Transfer a 50-ml. aliquot from the the hydrochloric acid solution apparently is unstable in reference acid-soluble zirconium solution to a 150-ml. beaker or use all of to precipitation of zirconium salts, since a haze appeared in the the acid-insoluble or total zirconium solution. Cover the beaker volumetric flask shortly after dilution. Titration with cupferron with the four-hole stopper. Remove oxygen by flushing with nitrogen (about 10 minutes). ,4dd standard cupferron solution would probably not pick up all of the zirconium in such a susin 1-ml, increments (if the titration is expected to consume less pension. The prewnce of minute amounts of ziiconicim in the than 5 ml. of standard solution, 0.5-ml. increments are advisab!ej suspensions was confirmed by taking an aliquot of each solution with nitrogen bubbling after each addition until the end point after shaking to render the suspension homogeneous, evaporating is reached; then add smaller increments. Read the current 1 to with 5 ml of concentrated sulfuric acid to sulfur trioxide fumes, 1.5 minutes after each addition a t a potential between -0.84 and - 1.OO volt 2's. S.C.E. (no gelatin need be added to the sample diluting with 50 ml. of water, and titrating. solution for this potential range). Plot the points so obtained As a further check, the total zirconium content was directly in the conventional manner; read the equivalence point volume determined by sulfuric acid dissolution of single samples and from the intersection of the two straight lines; calculat'e per cent titration (Table I). The agreement betxeen the results obtained zirconium in each fraction by the following expression and report as soluble, insoluble, or t o t d zirconium: by the latter procediire and those based on the corrected sum of V X T X D acid-soluble and -insoluble zirconium, when considered on the %Zr = 10 x basis of the known precision of the cupferron procedure for zirconium, may mean that the present results are more accurate where V equals milliliters of cupferron solution used; T is the cupferron solution titer-i.e., milligrams of zirconium equivalent than those obtained by the colorimetric procedure as given for the to each milliliter of cu ferron solution; D is the dilution factorsample analysis in Table I. The actual discrepancy is in the Le., reciprocal of the &action of the prepared solution taken for data for insoluble zirconium, where results by the present protitration; and S is the number of grams of sample taken. cedure differ from the given values by 0.02 or 0.03% Based on previous studies ( 1 , 3)> iron(III), vanadium(%'), RESULTS AND DISCUSSION niobium(V), uranium(IV), and large amounts of tin(1V) are the The basis for the amperometric titration of zirconium with only commonly interfering metals in the amperonietric titration ; cupferron in 10% sulfuric acid solution has been discussed (3); hafnium and titanium sholy behavior similar t o zirconium ( 1 ) . the following reaction is moderately rapid as well as essentiallv Iron is usually extremely low in magnesium alloys containing complete and stoichiometric zirconium and will tend to concentrate in the acid-insoluble fraction since iron and zirconium form an acid-insoluble intermetalZr(S04)p-4 Cup- = ZrCup, 3904-lic compound. The procedures described were applied to two representative As compared with the colorimetric alizarin red S procedure, magnesium alloys (Table I). Sample ZK 60 contained 6% of anions such as fluoride, phosphate, and sulfate do not interfere in zinc and Sample E K 30, 3% of rare earths [these are the same the cupferron titration. as samples 67333 and 67365 in Wengert's Table I1 (6)];the Obviously, the zirconium cupferrate precipitate could be zirconium percentages, furnished by the sample supplier, were filtered, washed, and ignited to the oxide for a gravimetric measobtained by the alizarin red colorimetric method. urement if it were so desired. The hydrochloric acid ( l f l ) dissolution used to separate acidsoluble and -insoluble zirconium results in sufficient heat to warm ACKNOWLEDGMENT the solution to near the boiling point; this is believed t o be the The authors wish to thank M. F. Loucks of The Dow Chemical cause of the somewhat discordant results for insoluble zirconium. Co. for furnishing the analyzed magnesium samples and much The use of 1 to 4 hydrochloric acid results in rapid dissolution but helpful information concerning the determination of zirconium in some zirconium may hydrolyze and be found in the insoluble magnesium alloys, and the atomic Energy Commission for supfraction; perhaps hydrochlolic acid ( l f 2 ) would be a more port of an investigation of the polarography of organic compounds suitable concentration for separating the two forms of zirconium of which the work described is an application. (8). The behavior of the alloys on treatment with sulfuric acid LITERATURE CITED indicated that it might be possible to separate acid-soluble and -insoluble zirconium using dilute sulfuric acid-e.g., 1 to 57&as (1) Elving, P. J., and Olson, E. C., ANAL.CHEM.27, 1817 (1955). (2) Loucks, M . F., private communication. dissolution agent. I t has been the authors' experience that sul(3) Olson, E. C . , and Elving, P. J., ANAL.CHEM.26, 1747 (1954). furic acid and perchloric acid solutions of zirconium do not show (4) Papucci, R. A., and Klingenberg, J. J., Ihid.. 27, 835 (1955). the hydrolytic behavior observed in hydrochloric acid solution. I n (5) Wengert, G. B., Ihid., 24, 1449 (1952). addition, the dissolution of magnesium alloy is a smoother process RECEIVED for review August 25, 1955. Accepted October 26, 1955. in sulfuric acid as compared with that in hydrochloric acid. ~
t.;
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