Improvements in Processes of Obtaining Chromium and Chromium Alloys.
Year: 1890

page_text: COMPLETE SPECIFICATION.
Improvements in Processes of Obtaining Chromium and Chromium
Alloys.
We, ASAHEL KNOWLTON EATON, Chemist of 79 Washington Street and KEZIA ANN
VANDERBILT, of 120 Liberty Street both in the City of Brooklyn in the County of
Kings and State of New York, United States of America, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
The metal chromium, as is well known, possesses many valuable qualities or
properties, but it has hitherto been produced in such small quantities and at such
great expense, that its use in the arts has been extremely limited.
We have discovered a process or way of obtaining this mineral both in a pure state
and in alloy with other metals at an expense which is insignificant compared with that
which its production has heretofore involved.
Our present invention is based upon or involves a discovery made by us of certain
chromites, and the process of producing them, the complete process consisting in
general terms, in first producing a chromite of a desired metallic base, then reducing
the chromite to an alloy and then dissolving out the metal with which the chromium
is combined.
This process we will describe in detail and then indicate the parts which we regard
as the essential and important features therein.
As the first step-which is the production of a chromite-we combine in equivalent
proportions bichromate of potash and the sulphate of the desired base, the best of
which for practical purposes we have found to be iron, copper, tin or zinc.
The bichromate of potash and one of the sulphates above named in a finely divided
condition, are mixed in equivalent proportions and placed in a fire clay crucible or
other suitable receptacle, and exposed to a temperature gradually increasing until they
reach a white heat.
By this means a reaction is caused to take place resulting in a mutual decomposition
of the two substances. The results lead us to believe that the sulphuric acid of the
sulphate combines with the potash of the bichromate, forming. sulphate of potash, while
the chromic acid, released by this reaction and losing a portion of its oxygen, is
immediately reduced to chromous acid, which combines with the base and forms a
chromite of that base. The sulphate of potash is readily removed by subsequent
washing.
The second step-the reduction of the chromite is effected as follows: A quantity
of the chromite is mixed with any suitable reducing agent to take up the oxygen, such
as charcoal, or substances like sugar, which will become charcoal, and placed in a
suitable retort or crucible. The compound is then exposed to a temperature sufficiently
high to let down the two metals of the chromite as an alloy.
The third step the separation of the metallic chromium-is effected in any well
known way as by dissolving out the baser metal.
As some examples of this process we may cite the following: We have produced
chromite of zinc by combining sulphate of zinc and bichromate of potash in the
manner above stated. This chromite mixed with charcoal or equivalent reducing
agent, we have heated until the zinc and chromium were run down in a metallic state
as an alloy. We have then dissolved out the zinc with nitric acid leaving the metallic
chromium. In the same way we have produced alloys of chromium and copper,
chromium and iron, chromium and tin, and others.
The difficulty of separating the chromium from the alloys will be greater or less
according to the metal with which it is alloyed. To obtain pure chromium. We
prefer to produce the alloy of zinc and chromium, as this is very easily reduced..
Moreover, the other alloys named are products of great value themselves. For example,.

page_text: by adding to the alloy of chromium and tin a further proportion of tin, an alloy
resembling silver is produced, but which in every respect is superior to silver.
Chromium and copper make a chromium bronze of great value. Chromium and
iron make an exceedingly hard metal which takes a high polish.
In making the chromites, we may employ the chlorates of the metals instead of the
sulphates, but we prefer the latter.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is:
First. The process herein described of obaining metallic alloys of chromium, which
consists in first producing a chromite of the base of the desired metal, and then
reducing such chromite to an alloy, as set forth.
Second. The process, herein described, of obtaining chromium, which consists in
producing a chromite of a given metallic base, then reducing said chromite to an
alloy, and then separating the baser metal from the chromium.
Third. The process, herein described, which consists in heating a mixture of
bichromate of potash and the sulphate of zinc or its equivalent, to form a chromite,
then heating the chromite and a reducing agent to obtain an alloy.
Fourth. The process, herein described, which consists in heating a mixture of
bichromate of potash and the sulphate of zinc or its equivalent, to form a chromite,
then reducing the chromite with carbon to an alloy, and then dissolving out the baser
metal from the alloy to leave the chromium.
Fifth. The method or process of obtaining chromium alloys by reducing the
chromite of a metallic base by heat and a reducing agent, as set forth.
Sixth. The method or process of obtaining chromium by reducing the chromite of a
metallic base by heat and a reducing agent to obtain an alloy, and then separating the
chromium from the other metal of the alloy, as set forth.
Dated this 31st day of March 1890.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.