Патент USA US3091526код для вставки
_ tates in atet 3,9915 1 6 Patented May 28, 1963 2 1 contains large amounts of iron and other metals. It is 3,091,516 preferred to charge the tellurium in powdered form to TELLURIUM John B. Conn, West?eld, N.J., assignor to Merck & Co., Inc., Rahway, NJ., a corporation of New Jersey No Drawing. Filed Nov.'25, 1960, §er. No. 71,402, 6 Claims. (01. 23_z09). carrying out the process, tellurium and zinc are brought together in a solution of alkali metal hydroxide. It is PROCESS FOR THE PURIFICATION 0F This invention relates to elemental tellurium and more provide a large surface area for contact with the zinc. 1In preferable to employ an excess of zinc over that required by the s-toichiometry of the reaction for production of a solution of zinc and tellurium or required for reduction of tellurium by zinc according to Equation 1. This excess particularly to the preparation of tellurium of a high de 10 zinc reduces or converts to insoluble tellurides any con taminating heavy materials, such as iron. The amount gree of purity. of excess is not critical, and can be varied with good Many solid state materials which have application in results from 1% to 100% of theory. In a preferred em the electronics industry contain tellurium as an essential bodiment of the process a 40-60% excess of zinc is em constituent. For example, bismuth telluride is used in cooling and power generating devices. Cadmium and 15 ployed. The insoluble heavy metal impurities may be re moved by ?ltration before precipitation of puri?ed tellu zinc tellurides when properly activated have found wide rium. As in the case of tellurium, it is desirable that applicability in computers as electroluminescent and the zinc be in a ?ne state or subdivision; it is preferred photoconductor materials. to use granulated zinc as the reducing agent. As electronic chemicals, it is of importance that these tellurides be of a high degree of purity, that is free of 20 As the alkaline reaction medium, an aqueous solution of alkali metal hydroxide of su?icicnt strength to solu bilize the zinc telluride that is formed is ‘used. ‘In a preferred embodiment of the present invention, a a source of pure tellurium is required. For example, in 35-65% aqueous solution of alkali metal hydroxide is the preparation of bismuth tellurides the component ele ments are melted together at a high temperature. Sim~ 25 utilized as the reaction medium, with a concentration of about 40-50% being most satisfactory. Zinc telluride ilarly, tellurides may be prepared by direct combination has a solubility of about 1.05 moles per 1,000 grams of of the elements. In the process which involves precipita 11.7 molar alkali metal hydroxide. Thus, the ratio of tions of a metallic telluride from solution, elemental tellurium to base at the start of the process should not tellurium is also used as a starting material. Accordingly, it is an object of the present invention to 30 exceed 1.08 moles of tellurium per thousand grams of 11.7 molar alkali metal hydroxide, (e.g., 1.05 moles of provide a method whereby tellurium of a high degree of tellurium per 1,000 grams of 45% hydroxide). An alkali purity may be prepared from impure tellurium. concentration above 35% permits the reduction of rea A more de?nite object of the instant invention is to sonable amounts of tellurium without exceeding the solu provide a process wherein tellurium is reduced with zinc in a strongly alkaline medium to a’ soluble zinc telluride 35 bility ‘of zinc telluride. It will, of course, be appreciated by those skilled in the art that more dilute alkali could and thereafter tellurium in a high degree of purity is pre be used satisfactorily in the process, but it would then be cipitated from solution by the action of an oxidizing agent. necessary to reduce the amount of zinc telluride produced _ A still more speci?c object of this invention is to per unit volume. > provide a process of puri?cation of tellurium wherein Any of the alkali metal hydroxides, such as potassium, tellurium is reduced with zinc in‘ a strongly alkaline me— 40 sodium or lithium hydroxides, are suitable for practicing dium and thereafter precipitated in a highly puri?ed form metals other than those used as activators. ‘In a typical preparation of tellurium containing electronic chemicals by the oxidizing action of chlorine. These and other objects, features and advantages of the invention, will be apparent from the following more particular description of preferred embodiments of the 45 invention. _ What is provided herein is a process of preparing high ly puri?ed tellurium. It has been discovered that treat ment of tellurium with metallic zinc in a strongly alkaline reaction medium leads to a reduction of the tellurium to telluride and formation of a solution of zinc telluride this novel process. However, potassium hydroxide. is preferred since tellurium may then be readily recovered without risk of contamination of alkali metal salts. The alkaline reduction discussed above is preferably carried out at elevated temperatures of about 50—80° C. although a range of about 35—l00° C. may vbe utilized if desired. The reaction is exothermic so that the 'ap plication of external heat is not normally required. _ At the outset of the process polytelluride ions form as transient intermediates. These are very heavily coll which, when an excess of zinc is employed,‘ is formed ored, being inky purples This color is conveniently substantially free of any metallic impurities present in the used as a ready visual index to the course of the re tellurium. Impurities present in the original impure action. When the characteristic purple color substan tellurium either are deposited on the zinc or are pre tially ‘disappears from the solution, the reduction stage cipitated from solution as tellurides. of the process is ‘complete. The solution is then nor mally ?ltered to remove any insoluble materials, thus The solution is then subjected to the action ‘of an oxidizing agent, such as chlo rine, bromine, iodine or oxygen, and a precipitate of high ly puri?ed tellurium obtained thereby. The chemistry of insuring the recovery of tellurium of high purity. Pref erably the solution is passed through a glass line-?lter in the puri?cation process of the present invention may be 60 order to avoid contact of the alkaline solutions with or represented by the equations: ganic materials such as rubber or plastic. Recovery of puri?ed tellurium from the alkaline mix~ ture is brought about upon completion of the reduction. and 65 According to a preferred practice tellurium is precipi tated from solution by oxidation with chlorine. Clari? (2 ) Te= + Cl2—> Te+ 2Cl- (precipitation step ) cation is aocomplished ‘by admitting chlorine gas into The purity of the tellurium used as the starting mate the alkaline solution under vigorous stirring conditions. Finally the puri?ed tellurium is obtained ‘by ?ltering the rial in the process of the present invention may vary with in wide limits. In fact, one of the features of the inven 70 solution upon glass, washing with dilute alkali hydrox ide solution and deionized water and then with hot dilute tion is that it makes possible the production of high Zn (OH) 4=+Te= (reduction step) purity tellurium from commercial grade tellurium which acid solution to remove the last traces of alkali metal 3,091,516 3 4 salts. Finally the solid ‘tellurium is washed free ‘of acid What has been described herein is a noval process and dried ‘under an inert atmosphere. The following examples ‘are given ‘for purposes of il for the preparation of elemental tellurium of a high de lustration and not by way of limitation. a commercial scale to provide an economical source of gree of purity. 7 The process is readily carried out on high purity tellurium for the manufacture of improved solid state materials and devices containing tellurium. To a B-necked flask ?tted with agitator and gas inlet While the invention has been particularly shown and is added 8 liters of 45% potassium hydroxide solution. described with reference to preferred embodiments there Nitrogen is bubbled through the alkali solution which of, it will be understood by those skilled in the ‘art that is maintained at about 80° C. To this solution is added 10 various changes in form and details may be made therein the tellurium powder (1276 g.) (10 g.-atoms) followed Without departing from the spirit and scope of the in by an excess of granulated zinc (785 g.-20-30 mesh). vention. The mixture is stirred in ‘order to keep the zinc granules What is claimed is: in rapid motion. Within a few seconds the gray sus 1. A process of preparing elemental tellurium of a high pension changes into an inky purple solution; the heat 15 degree of purity ‘which comprises intimately contacting evolution from the reaction mixture is sufficient to main impure tellurium with an amount of zinc in excess of the tain the solution ‘at ‘about 80° C. The purple solution amount of zinc required to form soluble zinc telluride in fades and disappears after about 105 minutes to ‘give a a solution of alkali metal hydroxide of su?icient strength nearly colorless solution. This solution is then ?ltered to prevent precipitation of zinc telluride, oxidizing said with nitrogen pressure onto a sintered glass ?lter coated 20 telluride ion with an oxidizing agent selected from the with a lining of precipitated calcium carbonate into a group consisting of a halogen and oxygen to form crystals second ?ask equipped with an agitator and gas inlet. of tellurium and recovering the solid tellurium thus Example 1 Chlorine gas is then ‘admitted at 4 cubic feet per hour and mixed with nitrogen to avoid suck-back under con formed. 2. The process according to claim 1 wherein the alkali tinuous stirring. The solution becomes purple ‘again and 25 metal hydroxide is potassium hydroxide. evolves heat. Crystals of tellurium begin to separate 3. The process according to claim 1 wherein the oxi ‘in the ?ask and at the end ‘of about 3 hours there is dizing agent is chlorine. a rapid fading of color to pinkish purple at which time 4. The process of preparing elemental tellurium of a the solution is full of tiny glittering tellurium crystals.’ high degree of purity which comprises intimately contact 30 Chlorination is interrupted, the suspension is allowed ing impure tellurium with an amount of zinc in excess to cool and the tellurium is collected on a sintered glass of the amount required to form soluble zinc telluride in a solution ofalkali metal hydroxide, the ratio of tellurium rectly with 10% reagent potassium hydroxide in de to base being less than 1.05 moles of tellurium per 1,000 ionized water and then with deionized water. The wet g. of 11.7 molar alkali metal hydroxide, ?ltering the solu mass is transferred to ‘2 liters of a 4 N hydrochloric 35 ?lter. The solid tellurium ‘is pressed down, washed di tion, oxidizing said telluride ion with an oxidizing agent solution inla 5 liter ?ask and agitated under nitrogen on a steam bath for 2 hours. selected from the group consisting of a halogen and oxy After cooling solid tel gen to form crystals of tellurium and recovering the solid lurium is washed free from acid with deionized water, tellurium thus formed. . then with methanol and dried under nitrogen at 100° C. The yield of puri?ed tellurium is 1206 g. (94.5% 40' 5. The process according to claim 4 wherein the alkali metal hydroxide is potassium hydroxide. theoretical). A spectrographical analysis of the tellurium 6. The process according to claim 4 wherein the oxi prepared as above shows a virtually complete absence dizing agent is chlorine. of metallic impurities. Example 2 References Cited in the ?le of this patent The process described above was repeated using liquid bromine as the oxidizing agent to produce highly puri tied tellurium. ' FOREIGN PATENTS 786,310 . Example 3 The process described above was carried out in 'a sim 50 Great Britain _________ __ Nov. 13, 1957 OTHER REFERENCES Mellor, Comprehensive Treatise on Inorganic and Theo ilar manner using solid iodine as the oxidizing agent retical Chemistry, Longmans, Green & Co., New York, to provide ultra-pure tellurium. vol. XI, pages 29, 74 and 75 (1931). Example 4 Tsyb et al. in “Tsuetnye Metally,” 33 No. 7, pages 61 55 65 (1960). In a similar manner puri?ed tellurium was prepared .using oxygen as an oxidizing agent.