Improvements in the Manufacture or Production Electrolytically of Coatings Composed of Oxides of the Earth Metals.
Year: 1895

page_text: This Print is in accordance with the Original Specification as it stands after
Amendment (under Section 18 of the Patents, &c. Act, 1883), as allowed
by the decision of the Comptroller General of the 16th day of February 1898.
Improvements in the Manufacture or Production Electrolytically of
Coatings Composed of Oxides of the Earth Metals.
I, RUDOLF LANGHANS, of 12 B, Elisabeth Strasse, Berlin, in the German Empire,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
The present invention relates to the production on electro-conductive bodies or
foundations of any shape of coatings composed of one or more of the oxides of the
earth metals, this term including the earth metals proper as well as the alkaline
earth metals.
I have succeeded in forming, by the electrolytic method with subsequent calcina-
tion, coatings composed of one or more earthy oxides and which are not only.
uniform but are perfectly cohesive and adhesive of themselves and which can be
made of any desired thickness, however irregular the shape of the body to be
coated may be.
If pure solutions of salts of the earths or alkaline earths be electrolysed, the
electrodes bring composed of some insoluble material, such as platinum, gold,
carbon, etc., no deposit is formed, either from dilute or concentrated solution. If to
such a solution alkaline salts are added and a current of weak density be employed,
then basic salts separate out: if, on the contrary, a current of high density be
employed, a deposit of hydroxides is obtained which closely surrounds the electrodes
but which is of so loose and voluminous a character as to readily slip off when the.
electrode is removed from the solution.
I have discovered that these difficulties can be overcome by the use of a solution
of "basic" earth salts.
Neutral earth salts, i.e. earth salts of normal composition, as for instance:-
Th(SO), Th(NO3), Zr(SO4)2,
Zr(NO), Al(SO), Al(NO3), Y2(SO4)37
Y(NO3), Ce2(SO4)3, Cе2(NO3), MgSO4, &c.,
-
are capable of dissolving the hydroxides of the particular earth of which they are
composed, as well as the hydroxides of other earth metals and alkaline earth metals.
Compounds so prepared are what I term "basic" earth salts.
Solutions of those "basic" earth salts behave on electrolysis in a manner
essentially different from that manifested by any other earth salts.
If in a nearly concentrated aqueous solution of a neutral earth salt as much
earthy hydroxide is dissolved as the solution is capable of taking up, eventually
with the aid of heat, (the said hydroxide having been produced by precipitation in
I

page_text: the cold and carefully deprived of the last traces of alkali by washing with cold
water) and if the solution so prepared be electrolysed by a current of high density,
hydroxide deposit is formed upon the negative electrode, covering it, whatever
its shape, with a regular and perfectly adhesive and cohesive layer, which, when
dried, presents a horn-like appearance, and can be roughly manipulated without
injury.
In carrying out the process, the body to be coated (for instance a cone shaped
body intended for use as an incandescent mantle for gas burners, and constructed of
wire gauze, or a fabric carbonized after being parchmentized, and eventually
covered with a metallic coating by galvanizing) is placed in a bath prepared
as described and connected with the negative pole of a powerful source of
electricity.
The positive pole is connected with an insoluble electrode contained inside a
diaphragm casing charged with hydrated oxides or carbonates of earth metals of
the same nature as those with which the solution is prepared; so that the acid split
off from the basic salts by the action of the current is at once fixed at the positive
pole, and thus the bath is regenerated.
When the evolution of hydrogen at the negative pole has fallen to a minimum,
the current is cut off and the electrode is disconnected, removed from the bath and
washed with water. Having been dried in an atmosphere of air free from carbonic
acid, it is calcined by gradually raising the temperature, the constitutional water
being thereby expelled, leaving the coating in the form of pure oxide without
injuring its cohesive and adhesive properties.
The solution of the "basic" salt can also be prepared in the following
way:
To an aqueous solution of the neutral salt, ammonia is added in such proportion
that the hydroxide which separates out is re-dissolved, and this is repeated so long
as there is re-solution, eventually with the aid of heat.
Instead of ammonia, basic organic derivation of same, for instance amines and
the like, as also sodium and potassium hydroxides, may be used. This mode of
preparing the bath has the advantage of causing the hydroxide to be deposited in
somewhat less dense condition, so that the current can pass more freely, whereby
the coating is allowed to form of such thickness as will be consistent with the
special shape of the body; and this result is obtained without affecting either the
cohesive and adhesive properties of the coating or its uniformity.
Instead of employing an aqueous solution of the basic earth salts, I may also
make use, in those cases where the salts are soluble in alcohol (ethyl, methyl,
propyl, butyl, amyl, &c.) of such alcohol solutions; as, for instance, by dissolving
nitrate of thorium in an alcohol; and in such a case, I prefer to cause the
separation and subsequent re-solution of hydroxide by means of an alcoholic
solution of ammonia.
Where a thin coating is desired, I prefer the first mode of preparing the
bath; while, for thicker coatings, the ammonia process is more advantageous.
It is obvious that a similar result will be obtained whether the bath be prepared
with one or several carth or alkaline earth salts; or whether, in the first method,
the hydroxide added to the solution be of the same or a different base.
The ordinary earths are preferably employed in the form of sulphates with the
addition of a small proportion of nitrate: for instance, I may employ a solution
of sulphate of aluminium to which has been added solutions of calcium and
magnesium nitrates, in which case I get a mixed deposit of the hydroxides of
aluminium, calcium and magnesium.
In the case of the so-called rare earths," I prefer to use the nitrates, or more
advantageously their ethylic sulphates and analogous compounds.
As regards the current density, the following should be observed; ND 100 meaning
normal density of current for 100 square centimetres:.
-
In the case of solutions containing 20 per cent. of zirconium or thorium salt, a
minimum current density of ND 166 amperes or 1'66 amperes per square
100
1

page_text: 100
-
centimetre; with solutions containing 20 per cent. of yttrium salt, a minimum
current density of ND 125 amperes or 125 amperes per square centimetre;
and with solutions containing 20 per cent. of aluminium or magnesium salts, one of
=
100 75 amperes or 075 ampere per square centimetre. In general practice,
I prefer to use a current of double the density in every case.
ND
In the act of drying and calcining, it may happen that the coating contracts
irregularly and forms cracks; or it may become so dense as to be unfit for certain
purposes, such for instance as for incandescent burners.
This may be prevented in the following way:-One mode consists in forming on
the foundations a reticulated cover composed of combustible fibres, such as cotton,
silk, etc., so as to present large interstices, whereby the deposition is prevented on
those parts where the fibres are in contact with the foundation. When the deposit
is calcined, the coating becomes porous by the destruction of the combustible fibres
and the shrinkage takes place uniformly.
Another method consists in converting the hydroxide deposit previous to calcining
into insoluble organic or inorganic salts capable of being converted into oxides by
means of heat. Such salts are, for example, tartrates, oxalates, formates, tannates
and carbonates on the one hand, and selenites on the other. I prefer the latter,
as on calcination they leave the oxides in a more porous or spongy condition than
is the case with the former.
This conversion can be carried out either by chemical or electrolytic means.
In the first place, the body coated with the hydroxide or hydroxides is dipped
into an aqueous solution of the said acids or their ammonia salts. Carbonic acid
can be applied as a gas. In the case of selenious acid, I prefer to use it as a
moderately concentrated solution.
According to the electrolytic method, I proceed as follows:-The body, coated
with the hydroxide or hydroxides, is connected with the positive pole of a weak
source of electricity and is placed in an aqueous solution of the selected acid or
salt. When the current is passed, the deposit is converted into the corresponding
salt or salts.
The electrolytic method is more advantageous as the transformation is brought
about more rapidly and perfectly.
For conversion into tannates, I employ a current the density of which is
00005 ampere per square centimetre, and for conversion into oxalates,
a current density of ND, 0'0002 ampere per square centimetre.
ND 100
=
100
=
A modified method of preparing the electrolytic bath, which method has the
advantage of avoiding the necessity of converting the hydroxide deposit into such
salts as specified previous to calcination, is as follows:-
In the solution of the basic earth salt or salts to be electrolysed, is dissolved an
organic base (alkaloid) in the form of one of the salts into which it combines with
an acid, for instance with sulphuric acid, or a mixture of such alkaloid salts.
Such organic bases are, for instance, opium, morphine, quinine, cinchonine, bases
of the veratrine class, strychnine, brucine, piperine, bases of the pyridine class &c.
These salts are split up by the action of the electric current, the organic base
being caused to deposit upon the negative electrode. Now if the compound
solution containing one or more alkaloid salts besides the basic earth salt or salts,
for instance a mixed solution of the sulphates of thorium and cinchonine, is
bjected to electrolysis, thorium hydroxide and cinchonine are simultaneously
leposited on the negative electrode in the form of an intimate mixture, so that the
calcination of this deposit, in destroying the cinchonine or other organic base,
eaves the earth oxide in a perfectly porous condition. The coatings thus pro-
Juced are as adhesive and cohesive as those brought about with the aid of the
other methods described. Moreover, the addition of alkaloid salts enables
solutions of "neutral" earth salts to be employed with advantage for the electro-
ytical production of earth oxide coatings that are likewise uniform and dense as
vell as cohesive and adhesive. But I prefer to use the described compound
olutions prepared with "basic" earth salts for the reason that in this case the

page_text: yellowish or brownish colouration of the bath resulting from decomposition of the
alkaloid salt, occurring to some extent at the positive pole, is by far slighter than
when neutral earth salts are employed.
Improvements in the Manufacture or Production Electrolytically of
Coatings Composed of Oxides of the Earth Metals.
I, RUDOLF LANGHIANS, of 12 B, Elisabeth Strasse, Berlin, in the German Empire,
Electrical Engineer, do hereby declare the nature of this invention and in what
manner the same to be performed, to be particularly described and ascertained in
and by the following statement:-
The present invention relates to the production on electro-conductive bodies or
foundations of any shape of coatings composed of one or more of the oxides of the
earth metals; this term including with the earth metals proper the alkaline earth
metals.
If pure solutions of salts of the earths or alkaline earths be electrolysed, the
electrodes being composed of some insoluble material, such as platinum, gold,
carbon, etc., no deposit is formed, either from dilute or concentrated solutions. If
to such a solution, alkaline salts be added, and a current of low density be
employed, basic salts separate out. If, on the other hand, a current of high
density be employed, a deposit of hydroxides is obtained which closely surrounds
the electrodes but which is so diffuse in character as to readily slip off when the
electrode is removed from the solution.
I have discovered that, by the use of basic earth salts, the difficulties hitherto
encountered in the production by electro-deposition, upon electro-conductive
foundations, of firmly adhesive coatings which can subsequently be converted into
oxides, are overcome.
Neutral earth salts i.e., earth salts of normal composition-as, for example,
Improvements in the Manufacture or Production Electrolytically of
Coatings Composed of Oxides of the Earth Metals.
I, RUDOLF LANGHIANS, of 12 B, Elisabeth Strasse, Berlin, in the German Empire,
Electrical Engineer, 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 present invention relates to the production on electro-conductive bodies or
foundations of any shape of coatings composed of one or more of the oxides of the
earth metals; this term including with the earth metals proper the alkaline earth
metals.
If pure solutions of salts of the earths or alkaline earths be electrolysed, the
electrodes being composed of some insoluble material, such as platinum, gold,
carbon, etc., no deposit is formed, either from dilute or concentrated solutions. If
to such a solution, alkaline salts be added, and a current of low density be
employed, basic salts separate out. If, on the other hand, a current of high
density be employed, a deposit of hydroxides is obtained which closely surrounds
the electrodes but which is so diffuse in character as to readily slip off when the
electrode is removed from the solution.
I have discovered that, by the use of basic earth salts, the difficulties hitherto
encountered in the production by electro-deposition, upon electro-conductive
foundations, of firmly adhesive coatings which can subsequently be converted into
oxides, are overcome.
Neutral earth salts i.e., earth salts of normal composition-as, for example,
Th(SO), TH(NO3)4, Zr(SO4)2
Zr(NO), Al2(SO4)3, Al2(NO3), Y2(SO4)39
Y₂(NO), Ce(SO), Cе₂(NO), MgSO4,
are capable of dissolving the hydroxides of the particular earth metals of which
they are composed, as well as the hydroxides of other earth metals and alkaline
46 basic" earth salts.
earth metals. Compounds so prepared are what I term
Solutions of these basic earth salts behave when electrolysed in a manner
essentially different from that manifested by any other earth salts.
up
no
In preparing the bath, I take earthy hydroxide, produced by precipitation in
the cold and carefully deprived of every trace of alkali by washing with cold water.
I dissolve the same in an approximately concentrated solution of a neutral earth
salt, continuing the operation by the aid of heat until the solution will take
more of the hydroxide. This solution of the basic salt, constituting the electrolytic
bath, is contained in a diaphragm casing placed in a vessel the latter being by
preference cylindrical and forming or being lined with an indissoluble electrode.
Between the diaphragm casing and the wall of the vessel or positive electrode is
placed hydrated oxide or carbonate of the same earth metal with which the basic
earth salt constituting the bath is prepared.
1

page_text: The accompanying drawing shows diagrammatically the form of apparatus
I prefer to use. a is the outer vessel, preferably of glass, 6 the positive electrode
consisting of a thin sheet of platinum formed into a cylindrical vessel and provided
with a terminal and the diaphragm casing formed of vegetable parchment.
g is a stand having an adjustable arm f from the extremity of which is suspended
by means of a platinum wire e, the electro-conductive foundation d consisting, for
example, of a cone-shaped hood composed of thin platinum wire. The arm f, is
insulated from the stand g and serves as the negative terminal.
In this bath, I place the body to be coated-for instance, a cone-shaped hood,
adapted for use as an incandescing mantle, and composed of wire gauze or made of
vegetable fibre, parchmentized, carbonised and then electroplated-and I connect
the same with the negative pole of a powerful source of electricity, whilst the
vessel forming the insoluble electrode is connected with the positive pole of the
said source of electricity. Upon the current being turned on the following action
results: The acid split off from the basic salt is immediately fixed at the positive
pole and a hydroxide deposit is formed upon the negative electrode or body to be
coated, its surface, however irregular, being covered with a regular and perfectly
adhesive and cohesive layer, which, when dried, presents a horn-like appearance,
and can be roughly handled without injury.
As the electrolytic action proceeds, the evolution of hydrogen at the negative
electrode must be closely observed; and when this has fallen to a minimum, the
current is cut off, the electrode removed from the bath and washed with water.
It is then dried in an atmosphere of air, free from carbonic acid, and calcined by
gradually raising the temperature. By this operation, the constitutional water is
driven off and a firmly adhesive coating of pure oxide is left.
"
The solution of the "basic salt can also be prepared in the following manner.
To an aqueous solution of the neutral salt, ammonia is added in such proportion
that the hydroxide which separates out is re-dissolved, and this is repeated so
long as there is re-solution, eventually with the aid of heat.
Instead of ammonia, basic organic derivatives of same, for instance amines and
the like, as also sodium and potassium hydroxides, may be used. This mode of
preparing the bath has the advantage of causing the hydroxide to be deposited in
a somewhat less dense condition, so that the current can pass more freely, whereby
the coating is allowed to form of such thickness as will be consistent with the
special shape of the body; this result being obtained without affecting either the
cohesive and adhesive properties of the coating or its uniformity.
Instead of employing an aqueous solution of the basic earth salts, I may also
make use, in those cases where the salts are soluble in alcohol (aethyl, methyl,
propyl, butyl, amyl, &c.) of such alcoholic solutions; as, for instance, by dissolving
nitrate of thorium in alcohol. In such a case I prefer to cause the separation
and subsequent re-solution of hydroxide by means of an alcoholic solution of
ammonia.
Where a thin coating is desired, I prefer the first mode of preparing the bath;
while, for thicker coatings, the ammonia process is more advantageous.
It is obvious that a similar result will be obtained whether the bath be prepared
with one or several earth or alkaline earth salts; or whether, in the first method, the
hydroxide added to the solution has the same or a different base.
The ordinary earth metals are preferably employed in the form of sulphates
with the addition of a small proportion of nitrate. For instance, I may employ a
solution of sulphate of aluminium to which has been added solutions of calcium
and magnesium nitrates, in which case, get a mixed deposit of the hydroxides of
aluminium, calcium and magnesium.
In the case of the so-called" rare earths," I prefer to use the nitrates, or more
advantageously their ethylic sulphates and analogous compounds.
The minimum current density required in the case of solutions containing
20 per cent. of zirconium or thorium salt is 1'66 amperes per square centimetre ;
with solutions containing 20 per cent. of yttrium salt, 125 amperes per square

page_text: centimetre; and with solutions containing 20 per cent. of aluminium or magnesium
salts, 075 ampere per square centimetre. In general practice, I prefer to use a
current of double the density in every case.
In the act of drying and calcining, it may happen that the coating contracts
irregularly and forms cracks; or it may become so dense as to be unfit for certain
purposes, such, for instance, as for incandescent mantles for gas-burners. One
mode of preventing this consists in forming on the foundations a reticulated cover
or winding composed of combustible fibres, such as cotton, silk, etc., so as to present
large interstices, whereby the deposition is prevented on those parts where the
fibres are in contact with the foundation. When the deposit is calcined, the coating
becomes porous by the destruction of the combustible fibres and the shrinkage
takes place uniformly.
Another method consists in converting the hydroxide deposit, previous to
calcining, into insoluble organic or incrganic salts capable of being converted into
oxides by means of heat. Such salts are, for example, tartrates, oxalates, formates,
tannates and carbonates on the one hand, and selenites on the other. I prefer the
latter as on calcination they leave the oxides in a more porous or spongy condition
than is the case with the former.
This conversion can be carried out either by chemical or electrolytic means.
According to the first plan, the body coated with the hydroxide or hydroxides
is dipped in an aqueous solution of the said acids or their ammonia salts.
Carbonic acid can be applied as a gas. In the case of selenious acid, I prefer to
use it as a moderately concentrated solution.
According to the electrolytic method, I proceed as follows:-The body, coated
with the hydroxide or hydroxides, is connected with the positive pole of a weak
source of electricity, and is placed in an aqueous solution of the selected acid or
salt. When the current is passed, the deposit is converted into the corresponding
salt or salts. The electrolytic method is more advantageous as the transformation
is brought about more rapidly and perfectly.
For conversion into tannates, I employ a current having a density of
0'0005 ampere per square centimetre, and for conversion into oxalates, a current
density of 0'0002 ampere per square centimetre.
A modified method of preparing the electrolytic bath, which method has the
advantage of avoiding the necessity of converting the hydroxide deposit into such
salts as above referred to previous to calcination, is as follows:-In the solution of
the basic earth salt or salts to be electrolysed, is dissolved an organic base
(alkaloid) in the form of one of the salts into which it changes when combined
with an acid for instance, sulphuric acid-or a mixture of such alkaloid salts.
Such organic bases are, for example, opium, morphine, quinine, cinchonine, bases of
the veratrine class, strychnine, brucine, piperine, bases of the pyridine class &c.
These salts are split up by the action of the electric current, the organic base being
caused to deposit upon the negative electrode. Now if the compound solution
containing one or more alkaloid salts, besides the basic earth salt or salts,-for
instance, a mixed solution of the sulphates of thorium and cinchcnine-be subjected
to electrolysis, thorium hydroxide and cinchonine are simultaneously deposited on
the negative electrode in the form of an intimate mixture; so that the calcination
of this deposit, in destroying the cinchonine or other organic base, leaves the earth
oxide in a perfectly porous condition. The coatings thus produced are as adhesive
and cohesive as those brought about with the aid of the other methods described.
Moreover, the addition of alkaloid salts enables solutions of "neutral" earth salts
to be employed with advantage for the electrolytical production of earth oxide
coatings that are uniform and dense as well as cohesive and adhesive. I prefer
however to use the described compound solutions prepared with "basic" earth salts
for the reason that in this case the yellowish or brownish colouration of the bath,
resulting from decomposition of the alkaloid salt, occurring to some extent at the
positive pole, is by far slighter than when neutral earth salts are employed.

page_text: Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I claim:-
1. In the production, by electrolysis and subsequent calcination, upon an electro-
conductive foundation of coatings composed of oxides of the earth metals, the
employment of an aqueous solution of a basic" earth salt prepared by dissolving,
in a nearly concentrated solution of a neutral salt, the hydroxide of like or other
earth metal base, substantially as herein described.
2. In the preparation of a solution of a "basic" earth salt for use in the process
referred to in the preceding claiming clause, the employment substantially as
described and for the purpose of rendering the deposit less dense, of ammonia or
of the alternative agents specified.
66
3. In the production, by electrolysis and subsequent calcination, upon an electro-
conductive foundation of coatings composed of oxides of the earth metals, the
employment, of an alcoholic solution of basic" earth salt prepared by dissolv-
ing, in a nearly concentrated solution of a neutral salt, the hydroxide of like or
other earth metal base, preferably in conjunction with an alcoholic solution of
ammonia, substantially as herein described.
4. In the production, by electrolysis and subsequent calcination, upon an electro-
conductive foundation of coatings composed of oxides of the earth metals, the
improved method of rendering the coating porcus and of preventing cracking,
consisting in converting the hydroxide deposit, previous to calcination, into
insoluble organic or inorganic salts capable of being converted into oxides by
means of heat, specifically as herein described.
5. The manufacture of bodies adapted for use as incandescent mantles for gas-
burners and otherwise, substantially as herein described; the same consisting of a
platinum, gold, or other suitable electro-conductive and indestructible foundation
coated with an oxide of an earth metal, such coating being produced by
electrolytically depositing upon the foundation a hydroxide of an earth metal in
any one of the alternative modes herein set forth and then converting the coating
into an oxide by calcination.