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Патент USA US3091526

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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.
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