TELLURIUM ALLOYS BY LOTTIE ELLA MUNN A. B. Baldwin Wallace College, 1917 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN CHEMISTRY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS, 1922 ( URBANA, ILLINOIS UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL May 22, 192-2 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY LOT-TIE- ELLA41UU3I ENTITLED TELLURIUM ALLOYS „ BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science Recommendation concurred in* Committee on Final Examination* 499uf *Required for doctor’s degree but not for master’s .... . Table of Contents. I. Introduction II. Experimental Work III. Results IV. Attempt to Analyze Lead- Tellurium Mixtures V. Summary VI. Bibliography VII. Acknowledgment 1 . o. 9 . 14 . 16 . 17 . 13 . Digitized by the Internet Archive in 2015 https://archive.org/details/telluriumalloysOOmunn 1 I. INTRODUCTION. The element tellurium is not so rare as is general - (D ly supposed. A recent estimate of the amount of tellurium that the United States can produce, without making any material addi- ( 2 , 3 , 4 ) tions to present plants, is 125,000 lbs. annually. There is little market for tellurium and a corresponding small produc- tion, only one or two refineries reporting production or sale of the element. Tellurium, like selenium, is a by-product of the e- lectrolytic refining of copper. The domestic production is capa- ble of large expansion if market conditions should warrant, as almost all blister copper contains recoverable quantities of tel- lurium. Much of this would be saved, if a demand existed, at prices of §1.50 to §2,50 per lb. In 1917, prices at the refin- ery averaged §3*00 per lb., but a very small additional output would probably have flooded the market. The chemical characteristics of tellurium are much like those of sulfur, but as would be expected in an element of higher atomic weight, it is more metallic. Tellurium looks much like antimony. It is silver-white and so crystalline that it is quite brittle and can be powdered. Toward acids it is as refrac- tory as antimony; toward alkaline solutions it is strongly re- sistant, while in water or moist air it does not rust or corrode appreciably. A consideration of these properties led to the idea that tellurium might be used as an alloying material to make met- als more resistive to corrosion. Although the literature on the subject reveals the preparation of several tellurium alloys, no studies have been 2 made as to their corrosion resisting power. Pushin prepared several alloys by fusing together weighed amounts of the pure met- als under a layer of potassium chloride and lithium chloride (to prevent oxidation) , and pouring the melt into molds of chalk or magnesium oxide. The alloys of silver and tellurium were black, crystalline, harder than either component, but very brittle. The properties of the copper- tellurium alloys varied greatly with composition. When rich in copper, they were dark gray, crystal- tellurium line, and brittle; with 30 to 33 %/[ they became much darker and more brittle; with more than 33 % tellurium, they were violet in color, and with more than 50 $, they were golden brown. Two com- pounds, Cu 2 Te and CuTe, formed solid solutions with each other. Alloys with lead, containing 50$ tellurium, were gray, granular, and brittle; PbTe formed solid solutions with lead but not with tellurium. Brittleness and a coarse grained structure also char- acterized the tin-tellurium alloys. The investigator proved the existence of the compounds Ag 2 Te, Cu 2 Te, PbTe, and SnTe. Two Japanese scientists, Chikashige and Nose, give give reports of work done on aluminium- tellurium alloys. Since tellurium and aluminium unite with explosive violencewhen neated together, the tellurium was first fused in a porcelain tube and the aluminium gradually added. Two compounds were formed, Te-jAl 2 , and Te^Al 5 * Te^Alg* which melted at 895 C , formed solid solutions with tellurium up to 4.4$ tellurium. The two compounds were rap- idly decomposed by water, and evolved a disagreeable poisonous gas H 0 Te, which rapidly decomposed into tellurium and hydrogen. (7) Henry Pay found that tin and tellurium united to form a compound SnTe, which melted at 769°* This compound formed f • 1 . t 3 with tellurium a eutectic which melted at 399°, and consisted of 85$ tellurium and 15$ tin. With tin the compound also formed a eutectic, but the solution of SnTe in tin was so low that it was impossible to locate the concentration. The melting point of the eutectic of low concentration appeared to be the same as that of pure tin. ( 3 ) J. K. Rose has established a complete freezing point curve for varying concentrations of gold and tellurium. The curve showed one compound AuTe 2 , with a melting point of 452°. This compound formed a eutectic with tellurium, containing 20$ gold and melting at 397°; with gold it formed a eutectic contain- ing 60$ gold, melting at 432°. (9) Kimata states that only one compound of antimony and tellurium exists, the formula being Sb 2 Te^ and the melting point 620°. This compound formed with antimony a eutectic melting at 540^ and containing 27"28$ tellurium; and with tellurium a eu- tectic melting at 420^, containing a little under 90$ tellurium. (10) The melting point curves worked out by H. Pela- bon showed the existence of Sb2Te-3(m.p.600 ( '') , SnTe (m.p. 780°) , Bi 2 Te^(m. p. 583°) , PbTe(m. p.860^) , AgTe(m.p.955°) , and Au 2 Te 4 (m.p. 472°). ( 11 ) Ransom and Thieme conceived the idea that tellur- ium might be used as a hardener for lead and other metals. When pure lead was melted and tellurium sprinkled on it, the tellurium glowed, and large lumps were formed, mixed with a coarse powder which floated as a dross. Upon separating the lumps from the powder the former were found to be hard, somewhat malleable, and to con- tain bo tn lead and tellurium. Tellurium could not be found in the 4 yellow powder and its nature has not been established. Some pure tin bars were melted and poured, and after removing from the heat tellurium was added in powder form and stirred in. No glowing was observed but a dross appeared on the surface. The alloy contained 1.12 % tellurium, was slightly harder than pure tin, and the ten- sile strength had increased from 3800 to 4265 lbs. per sq. in. Similar experiments we re performed with zinc and aluminium, but only traces of tellurium were found in the treated metal, most of it being in the dross; however the tensile strength was increased ' from 4955 to 5510 lbs. per sq. in. in the case of zinc, and from 13840 to 14810 lbs. per sq. in. for aluminium. The hardness was not changed. ( 12 ) Fay and G-illson have also made investigations with regard to lead- tellurium alloys. The composition of the al- loy of maximum freezing point corresponds with the proportions of the metals in PbTe. Lead easily became supersaturated witn PbTe, which separated out at the higher freezing point, and the lower freezing point then corresponded to the solidification of lead. When still more tellurium was present, PbTe again separated at the higher temperature, but the lower freezing point corres- ponded with the complete solidification of the alloy, which was a eutectic of PbTe and tellurium. 7/hen examined microscopically the eutectic could be seen interspersed between the crystals of lead or tellurium, according to which was present in excess. Al- loys containing more than 50 % tellurium were very brittle. This sums up very briefly the greater part of the work which has been done along this line. The resistance of tellurium to the action °f acids and alkalies led to the present 5 investigation as to the corrosion of lead- tellurium alloys, with a small the hope that the addition of^percentage of tellurium would make the lead more resistive to corrosion, without making it too brit- tle for its ordinary uses. 6 II. Experimental Work. Since the brittleness of the lead- tellurium alloy increases rapidly with increase in the percentage of tellurium, no attempt was made to use more than 10$ of the latter, a 10$ alloy being too brittle to serve the purposes for which lead is ordinarily used. The amounts of lead and tellurium, correspond- ing to the various percentages of tellurium desired, were care- fully weighed out, into clay crucibles ana morougnly mixed, un account of the ease with whi ch tellurium volatilizes and oxi- dizes, the mixture was then covered with a layer of charcoal be- fore fusion. A gas furnace furnished a sufficiently high temper- ature for the fusion, since the melting points of lead and tel- lurium are respectively 327 ( " > and 4-5 1*“*. After fusion for twenty minutes, the mixture was allowed to cool and the charcoal was removed from the top; sufficient heat was then applied to melt the alloy, so that it could be poured into a graphite mold, form ing strips of fairly uniform surface. The mold consisted of two plates of graphite, clamped tightly together; on the inner sur- face of one of them a rectangular depression about two and one half inches long, three -fourths of an inch wide, and one-eigth of an inch deep had been cut by a chisel. Some difficulty was experienced in getting a smooth surface on the strips contain- ing the higher percentages of tellurium. This was overcome by sandpapering. For the corrosion tests, the alloys were first weighed and then placed in nitric acid (.01 and .1 molal), also in hydrochloric acid (.1 molal), and in sulfuric acid (.1 molal) 7 for successive periods of five days each. After each period the strips were removed, cleaned, dried, and weighed before replacing in the acids on the shaking machine. The shaking machine served to agitate the solutions sufficiently so that they should not form saturated layers around the alloys. From the loss in weight, the per cent of corrosion was calculated. The greatest difficul- ty encountered in these tests was to remove the corrosion com- pletely or at least equally from the strips, especially in the case of the .01 molal nitric acid, where a yellowish-white pre- cipitate always formed and clung tenaciously to the surface. This precipitate upon analysis seemed to contain no tellurium, and was probably a basic nitrate of lead, which formed due to the great dilution of the nitric acid. Best results were obtained by sim- ply removing the corrosion by means of a brush, except in the case of the sulfuric acid, where it was necessary to place the strips in sodium acetate solution for equal lengths of time in order to remove the lead sulfate. In all probability this diffi- culty in removal of corroded material caused the discrepancies which will be seen in the results. However, since in general the relationships were the same between successive five day periods, fairly representative results were obtained by averaging the per- centages of corrosion, and plotting these averages against the composition. No curve is shown for the results with sulfuric acid because the values obtained were very irregular. This is due no doubt, as said before, to the very slight action of sulfuric acid on lead and to the unequal removal of corrosion. The curve •• for .01 molal nitric worked out well and showed an increased re- 8 sistance with increase of tellurium present. Some irregularities are seen in the curves for . 1 molal nitric acid and . 1 molal hy- drochloric acid, especially in the case of the former, where there is a very marked increase in corrosion for alloys containing , 07 % and . 09 % of tellurium. This is probably due to experimental error but it is possible that another compound of lead and tellurium is formed. In general, the presence of tellurium seems to lessen the corrosion to a slight extent. ■ 9 III. RESULTS. Per cent of Corrosion in .01 Molal HNO3. 1 . 2. 3- 4. 5. 6 7. 8 . Av. Pb 1.0376 1.0000 1 .1880 1. 0397 0 . 9999 0.9895 0.9995 1.0395 1.0367 1$Te 0.7794 0.6648 0 .7760 0. 6322 0 . 7118 0.9137 0.8984 0.9566 0.7919 2$Te 0.8102 0.5828 0 .7751 0 . 6513 0 . 7443 0.8239 0.8953 0.9550 0.7798 3/aTe 0.5965 0.4365 0 .5702 0 . 5923 0 . 7313 0.6875 0.7040 0.6317 0.6250 Per cent of corrosion in . 1 Molal HNO 3 . 1 . 2. 3. 4. 5. 6. Av. Pb 1.3220 2.0549 1.6117 1 .6363 1 .6944 2.3291 1 .7744 . 06^Te 1.0400 1 .9161 1.4355 1.5804 1-7842 2.2569 1 .6683 . 07;^Te 2.4290 2.9415 3.277 6 3 . 1 406 3*2975 3.5313 3.1112 . 09/^Te 2.5000 2. 6105 2.9663 3.0241 3.2492 3.2956 2.9409 . lO^Te 1.2790 2.5608 1.41 1 1 1 . 2947 1.7881 2.0616 1.7325 . 30;^Te 1.3000 2.6532 1 . 5334 1.5620 1.6139 1.9704 1 .7708 . 50^Te 1.2110 2.6463 1.5200 1.6163 1 . 5488 2.0132 1.7592 .SO^Te 1.6920 1.3639 1.5950 1 .6337 2.5569 1.7783 1$Te 1 .6629 1.3398 1.3528 1 .3245 2.2585 1.6877 2/^Te 1.651 1 1.3943 1 .4443 1.9058 2. 1360 1 .7063 5/o Te 1.7840 2,2813 1 .8191 1.7641 2.3293 2 . 7045 2. 1 137 8;^Te 2.1550 2.9483 2.0399 2 . 1373 2.7031 3.2356 2.5382 lO^Te 3. 1780 3.2662 2.3101 2.0669 2.9671 3.8926 2.7775 10 Per cent of corrosion 1. 2. 3- in .1 Molal HG1 . 4. 3 . Av. Pb 0. 1001 0.5924 0.5381 0.7277 0.5633 0.5144 . 06$Te 0.0931 0.4024 0.5613 0.5764 0.5254 0.4317 .07foTe 0.0993 0.4107 0.5397 0.5478 0.6255 0.4466 . 2QfoTe 0. 1342 0.4937 0.6030 0.6067 0.7006 0.5076 .40$Te 0.0621 0.3497 0.4901 0.5894 0.5302 0.4043 .80%Te 0.0982 0.4302 0.5062 0.5814 0.6010 0.4434 1 .OO^Te 0.0992 0.3932 0.5165 0.5241 0.5141 0.4094 2. 20%Te 0. 1225 0.4126 0.5457 O.6166 0.6231 0.4641 6.70/oTe 0. 1301 0.4525 0.6354 0.3438 0.7039 0.5531 Per cent of corrosion ill . 1 Molal H2S04. 1 . 2. 3. 4. Av. Pb 0.01 16 0.0156 0.0058 0 . 0097 0.0107 ,07^Te 0.0083 0.0264 0.0059 0.0177 0.0146 . 2Q^Te 0.0069 0.0108 0.0000 0.0079 0.0064 .40^Te 0.0000 0.0099 0.0000 0.0119 0.0055 • SO.^Te 0.0184 0.0160 0.0100 0.0020 0.0116 A » 0 0 1-3 CD 0.0000 0.0060 0.0040 0.0041 0.0035 1 1 3%TC- 3%Tc- /%T e- °fo Corrosion i. n .ot moLaL K NO^ 12 6.7 %Te^ l^cTe. - /‘VoTe. i 8 7oTe - ■7*re. - -?7oTe i >77 oTe.— » >6 7 oTe - Pb- "" 7o Co i~roS(.on l n .1 m o Ul 14 IV. Attempt to Analyze a Lead-Tellurium Mixture. The separation and quantitative determination of tellurium from a mixture of lead and tellurium presents several difficulties, such as the formation of lead tellurate, the vola- tility and oxidation of tellurium, occlusion of sulfur etc., de- pending upon the method used. The following methods were tried: 1 . A mixture of lead and tellurium was evaporated just to dryness with nitric acid, forming lead nitrate and tel- lurium dioxide, which upon treatment with sodium hydroxide dis- solved to form sodium plumbite and sodium tellurite. Hydrogen sulfide was then used to precipitate the lead as lead sulfide, the sodium tellurite remaining in solution. T/Then the latter was acidified and hydrogen sulfide again passed in, the tellurium was precipitated as metallic tellurium, which was filtered off, evaporated to dryness with nitric acid, and ignited gently to tellurium dioxide . Pb"\ Ph( 1103 ) 2 ^ Na 2 Pb0 2 \ PbS [ HNOdv l NaQIL HoS . HOl.HpSs HNQ ? Te f ~ ~Te0 2 [ ^Na 2 Te 03 | * ? Na 2 Te 03 1 Te~ *Teq The determination was not at all successful owing probably to the volatility of tellurium dioxide. 2. The procedure was carried out the same as in 1, as far as the separation and formation of tellurium dioxide. This was then dissolved in sodium hydroxide, forming sodium tellurite, oxidized to sodium tellurate by sodiun peroxide, and precipitated as barium tellurate by the addition of barium chloride. 15 Pb' Te NaOH v ' NapTeO-2 Na 2 Pb0c TeOp The barium tellurate was ignited and weighed, but in every case the weight was much too high. This might be accounted for by the fact that there must be a large amount of sulfur precipitated with the tellurium, and this sulfur would be oxidized to a sulfate and be precipitated as barium sulfate along with the barium tellurate. The possibility of occlusion is also great. The use of hydrogen perox- ide as an oxidizing agent gave the same results. 3. The method which promised to give the best re- sults was the standard method of precipitation by sulfur dioxide in hydrochloric acid solution. The mixture of lead and tellurium was evaporated to dryness with nitric acid and the products dis- solved in sodium hydroxide, forming sodium plumbite and sodium tel- lurite. Upon acidifying with hydrochloric acid, most of the lead precipitated as lead chloride and was filtered off. When sulfur di- oxide was then passed into the solution, the tellurium came down as the element, and was filtered, dried, and v/eighed. Pb) Pb(N03) s TeOo - - I 16 V. Summary. 1. When exposed to the action of .01 molal nitric acid, alloys of lead and tellurium seem to show an increase of resist- ance to corrosion with increase of tellurium present. 2. Alloys of lead and tellurium containing from .06$ to 5 % tellurium, with the exception of the .07$ and . 09 $ alloys, show a slightly greater resistance to the action of . 1 molal ni- tric acid than does lead. 3. Pure lead is corroded more by . 1 molal hydrochlor- ic acid than are its alloys with tellurium, containing up to 4.8$ of the latter. 4. The results indicate that in general tellurium in- creases the resistance of lead to . 1 molal sulfuric acid; however these results are very irregular and unreliable on account of un- equal removal of corroded material. 5. Tellurium is probably best determined quanti tative- ly by reduction to metallic tellurium by sulfur dioxide in hydro- chloric acid solution, after filtering off the lead chloride. The tellurium is then dried and weighed. 17 VI. Bibliography. 1. Lenher,V. J. Ind. and Eng. Chem. , 12.597-3 . 2. Umpleby, J.B. Min. Res. of U.S.,1917. 3. Hill, J.M. U.S.Geol. Survey, 1913. 4. Loughlin,G.F. and Clark, Martha B.^-* Min. Res. of U.S.,1919. 5. Pushin,N.A. J. Russ. Ph.vs. Ghem. Soc. .39. 13-54. 6. Chikashige,M. and Nose,J.--- Mem. Coll . Sci .Kyoto Imp. Univ. 2,227-32. 7. Fay, Henry------ J. Am. Chem. Soc . .29. 1265-8. 8. Rose, T. K. ------ Trans. Inst. Min. Metal . Brit. . 17. Pt. 1 , 285-9 • 9. Kimata,Y. -J. Soc ♦ Chem. Ind. .34.1211. 10. Pelabon,H. Ann. Chem. Phys. , JLZ» 526-66 . 11. Ransom, J.H. and Thieme, C.O. Chem. and Met. .25. 102. 12. Fay, Henry and Gill son, C . B. Arne r. Chem. -J. .27.81-95. 18 VII. Acknowledgment. The writer hereby wishes to acknowledge her indebted- ness and to extend her thanks to Dr. B.S. Hopkins, under whose direction this work was done.