Improvements in Porous Diaphragms for Electrolytic Apparatus
Year: 1897

page_text: Date of Application, 28th Sept., 1897-Accepted, 24th Dec., 1897
COMPLETE SPECIFICATION.
" Improvements in Porous Diaphragms for Electrolytic Apparatus."
We, JAMES DOUGLAS DARLING, of No. 4826 Greenway Avenue, in the City of
Philadelphia, State of Pennsylvania, United States of America, Electrical Chemist,
and CILARLES LELAND HARRISON, of 2028 Locust Street in the City of Philadelphia
aforesaid Manufacturer of Chemicles, 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:-
In the drawings lodged with this specification Figure 1 represents a vertical
longitudinal section through an apparatus embodying the invention in a preferred
form, Figure 2 being a top or plan view of the same.
In the electrolysis of many dissolved or fused salts there is usually a large loss
of efficiency, through the tendency of the liberated ions to recombine, either assum-
ing their former relation or forming some new compound. A common expedient
to avoid this difficulty is found in the use of porous diaphragms, which effect the
physical separation of the positive from the negative electrode, and consequently
prevent recombination, while at the same time affording no substantial impedi-
ment to the electrolytic travel in the desired direction.
Whilst in the case of aqueous solutions this method is quite practicable, it is
found that where the electrolyte is a fused mass, such as an hydroxide, or haloid
salt of an alkali metal, or an alkaline earth metal, or a nitrate or sulphate of such
metal, the action thereof is highly destructive of the porous diaphragm, so that the
utility of the apparatus is limited to a comparatively short duration.
The object of our invention is to provide a diaphragm which shall resist destruc-
tion as far as possible under the conditions of use, and which can be so arranged as
to afford any degree of resistance within the desired limits.
To these ends we combine with a suitable support, a filling, or mass of granular
material, whose chemical constitution is such that it is substantially not decompos-
ible or fluxible by the fused electrolyte, and whose physical properties enable it to
maintain with substantial permanence a definite granular form, without tendency
to break down into an impalpable powder and drift away. We have found that
material having the necessary chemical constitution may by exposure to a very
high heat attain a substantially vitrified condition, and that after such treatment
they may be reduced, to small granules, which can be used for the purpose
indicated, without fluxing or mechanical disintegration to such an extent as
prevents commercial economy.
.
We will now proceed to describe a typical and preferred embodiment of our
invention.
In the accompanying drawings, A represents a cylindrical shell of sheet iron or
steel, perforated with numerous small holes, as indicated at a, and firmly secured
to a solid base B. Within this shell is a smaller shell A', similarly perforated,
as partially indicated at a', and secured to a corresponding base B¹. The annular

page_text: inner space between the shells may be of such radial diameter as may be desired
to facilitate the insertion and removal of the filling which is about to be described,
or to provide for any desired thickness of such filling. So also a space may be left
between the bases B, B¹, as indicated.
Convenient dimensions are as follows:-The outer shell may be seventeen inches
in height, the inner one fifteen and one-half inches, the total diameter of the outer
shell nine and one-half inches, and the inner shell six inches, though we, of course,
do not limit ourselves to such dimensions; nor to the specific form above described.
The interspace between the shells contains the filling, which constitutes the
primary feature of our invention, and which is prepared as follows:-
We take preferably, magnesia, as nearly as possible chemically pure, and fuse it
in an electric furnace to a vitrified condition, approximating in appearance a
nearly clear glass. This is then crushed or granulated to a proper degree of fine-
ness, the particles being preferably of such size as to pass through a 20-mesh
sieve, but not through one of 30-mesh. The interspace between the cylinders A
and A', is then packed uniformly with this granular vitrified material, as indicated
at C, to a point near the top, above which a layer of cement D, may be applied to
hold the particles firmly in position. The perforations in the shells A and A',
are indicated conventionally in the drawings, but it must be understood, of course,
that they are not so large as to allow the material to readily, fall out under the con-
ditions of use. The porosity and resistance of the diaphragm thus formed may be
varied to suit any desired conditions, by increasing or diminishing the total thick-
ness of the mass of granular material, or by using finer or coarser granules.
A porous diaphragm can be thus obtained which resists in the highest degree
the destructive action of the fused salts, and which is at the same time properly
permeable for electrolytic travel.
We have indicated magnesia as the preferred material for the diaphragm, but
we do not limit ourselves thereto, since other earthy oxides, such for instance as
those of calcium, or barium, or mixtures of earthy oxides, may be employed, pro-
vided the material be such as resists in a high degree combination with, or fluxing
by, alkaline hydroxides, or the haloid salts of alkali metals, or the alkaline earth
metals, or the nitrates or sulphates of such metals.
The more nearly that the material employed for the filling is chemically pure,
the more highly resistant it will usually be found under given conditions, but in
commercial practice it is of course very difficult to obtain such chemically pure
material, and for commercial purposes absolute indestructibility of the material
is of course not essential, since the electrolytic process can be carried on with
economy and success, even though the filling should deteriorate, after a time,
under the intensely severe exposure to which it is subjected. Hence we do not
limit our invention to the use of chemically puie materials, nor to such as are
absolutely indestructible, but in our claims we employ the words substantially
resistant to combination and fluxing, as indicating the general characteristics of
the material, without rigid limitation to the possession of qualities beyond
practical needs.
We have described the invention as embodied in a cup, properly so called, but
obviously its use is not limited to this specific arrangement, since a diaphragm for
electrolytic purposes may be of any desired form, and we prefer to use the word
diaphragm as generally comprehending the structure without reference to.
shape.
its
So also we have specified perforated sheet metal as the preferred material for the
support used to retain the granulated filling, but we do not limit our claim thereto,
and use the term perforated support as comprehending broadly any retaining
device which is provided with openings, and which is otherwise suitable for the
indicated purpose.
We do not, however, claim broadly the use of such perforated supports, as we
are aware that they have heretofore been employed in electrolytic apparatus.

page_text: Having now particularly described and ascertained the nature of our said in-
vention and in what manner the same is to be performed, we declare that what we
claim is:
1. As an improvement in porous diaphragms for electrolytic apparatus, the com-
bination, with a support, of a granular filling consisting principally of a vitrified
oxide or oxides, substantially resistant to combination or fluxing by a fused
hydroxide or other above specified compound under the conditions of electrolysis,
substantially as set forth.
2. As an improvement in porous diaphragms for electrolytic apparatus, the com-
bination, with a support, of a granular filling consisting principally of vitrified
magnesia, substantially as set forth.
3. As an improvement in porous diaphragms for electrolytic apparatus, the com-
bination, of a pair of cylindrical, perforated supports, arranged with an interspace
between them; bases for said supports; an intermediate granular filling consist-
ing principally of vitrified magnesia arranged in the interspace between said
supports; and an annular top of cement above said filling, substantially as set
forth.
2
1007
CARPMAEL & Co.,
Agents for the Applicants.