Year: 1898

page_text: I, CHARLES DENTON ABEL, of Birkbeck Bank Chambers, Southampton Buildings,
in the County of London, Consulting Engineer and Chartered Patent Agent, do
hereby declare the nature of this invention (as communicated to me from abroad
by Christian Westphal, of Berlin, in the Empire of Germany) to be as follows:-
This invention relates to a process for hardening artificial stone whose main
constituents are lime and sand, by means of carbon dioxide.
In the known processes of this kind the carbon dioxide is employed in the form
of a mixture thereof with air and other gases such as passes away from lime kilns
and the like. In that case the artificial stone to be treated is first dried before
being treated with the carbon dioxide gases, or the hot gases are led directly
from lime, cement or other kilns into chambers filled with the freshly formed
artificial stones, so as both to effect the drying of the latter and to effect the
hardening thereof.
The first named method yields hard stones of amorphous calcareous structure
which in cooling are liable to split; it also causes considerable expense for the
drying; by the second method on the other hand only a very slow hardening of
the stones is effected on account of the small percentage of carbon dioxide in the
waste gases.
According to the present invention, instead of employing waste gases containing
only a small percentage of carbon dioxide, the freshly formed wet stones are
subjected to an atmosphere consisting either of pure carbon dioxide or having
at most a small percentage, such as from 10 to 20 p.c. of other gases.
When treating artificial stone with very dilute carbon dioxide, the reaction of
the latter upon the hydrate of lime only causes a very slight increase of tempera-
ture, such as from 20° to 25° C.; on the other hand, when treating the stone
with more or less concentrated carbon dioxide according to this invention they
become heated to from 60° to 70° C.
This considerable heating of the stones is of the greatest importance both for
the hardening and the drying thereof. By the considerable development of
heat produced by the action of the carbon dioxide upon a certain layer of the
stone, the evaporation of the water from the contiguous layers is greatly facili-
tated at the same time the combining capacity between the lime and the carbon
dioxide is increased, so that the transformation of the hydrate of lime into the
carbonate progresses rapidly in the mass, crystals being at the same time formed,
as water is always present.
By this means stones formed of lime and sand will harden and dry in from
5 to 6 hours while with the known process of treatment with very dilute carbon
dioxide, such as comes from lime kilns, the drying and hardening takes several
days, as in this case the combining of the hydrate of lime with the carbon dioxide

page_text: does not give rise to the considerable increase of temperature which is necessary
for accelerating the hardening and drying.
The mode of producing the concentrated carbon dioxide is quite immaterial to
the present invention.
As a factory which produces the artificial stones will generally also effect the
burning of the requisite lime, it will generally be convenient to utilise the waste
gases from the lime kilns, in extracting from these the required carbon dioxide.
For this purpose any of the known methods for concentrating carbon dioxide can
be employed, in particular the so called "Potta" process in which waste gases
containing carbondioxide are led over carbonate of soda thereby producing
bicarbonate which is then reconverted into carbonate with liberation of concen-
trated carbon dioxide. As pure carbon dioxide is considerably heavier than air,
the hardening process may generally be carried on in open vessels without material
loss of carbon dioxide; or the vessels may be closed to such an extent as to pre-
vent any material loss of heat while allowing the steam produced to escape.
It may however in certain cases be of advantage to retain the steam in the
hardening vessels in order to assist the hardening by the solution of silicic acid
and re-deposition thereof. In this case the gaseous carbon dioxide introduced
into the vessel forms an aqueous solution with the steam in acting upon the stone,
causing a solution of silicic acid which is the greater, the greater is the percentage
of carbon dioxide in the steam; as the former is given off to the stone the solution
becomes proportionately weaker, and this alternate solution and separation con-
tinues until all the lime is converted into carbonate.
This method of utilising the steam for the hardening process can of course also be
carried on under considerable pressure in closed vessels, into which a separate
steam supply can be introduced at the commencement of the process.
That this eth
1000
ABEL & IMRAY,
Agents for the Applicant.
I, CHARLES DENTON ABEL, of Birkbeck Bank Chambers, Southampton Buildings,
in the County of London, Consulting Engineer and Chartered Patent Agent, do
hereby declare the nature of this invention (as communicated to me from abroad
by Christian Westphal, of Berlin, in the Empire of Germany) and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement:-
This invention relates to a process for hardening artificial stone whose main
constituents are lime and sand, by means of carbon dioxide.
In the known processes of this kind the carbon dioxide is employed in the form
of a mixture thereof with air and other gases such as passes away from lime kilns
and the like. In that case the artificial stone to be treated is first dried before
being treated with the carbon dioxide gases, or the hot gases are led directly
from lime, cement or other kilns into chambers filled with the freshly formed
artificial stones, so as both to effect the drying of the latter and to effect the
hardening thereof.
The first named method yields hard stones of amorphous calcareous structure
which in cooling are liable to split; it also causes considerable expense for the
drying by the second method on the other hand only a very slow hardening of

page_text: the stones is effected on account of the small percentage of carbon dioxide in the
waste gases.
According to the present invention, instead of employing waste gases containing
only a small percentage of carbon dioxide, the freshly formed wet stones are
subjected to an atmosphere consisting either of pure carbon dioxide or having
at most a small percentage, such as from 10 to 20 p.c. of other gases.
When treating artificial stone with very dilute carbon dioxide, the reaction of
the latter upon the hydrate of lime only causes a very slight increase of tempera-
ture such as from 20° to 25° C.; on the other hand, when treating the stone
with more or less concentrated carbon dioxide according to this invention they
become heated to from 60° to 70° C.
This considerable heating of the stones is of the greatest importance both for
the hardening and the drying thereof. By the considerable development of
heat produced by the action of the carbon dioxide upon a certain layer of the
stone, the evaporation of the water from the contiguous layers is greatly facili-
tated; at the same time the combining capacity between the lime and the carbon
dioxide is increased, so that the transformation of the hydrate of lime into the
carbonate progresses rapidly in the mass, crystals being at the same time formed,
as water is always present.
By this means stones formed of lime and sand will harden and dry in from
5 to 6 hours, while with the known process of treatment with very dilute carbon
dioxide such as comes from lime kilns, the drying and hardening takes several
days as in this case the combining of the hydrate of lime with the carbon dioxide
does not give rise to the considerable increase of temperature which is necessary
for accelerating the hardening and drying.
The mode of producing the concentrated carbon dioxide is quite immaterial to
the present invention.
"
As a factory which produces the artificial stones will generally also effect the
burning of the requisite lime, it will generally be convenient to utilise the waste
gases from the lime kilns, in extracting from these the required carbon dioxide.
For this purpose any of the known methods for concentrating carbon dioxide can
be employed, in particular the so called " "Potta process in which waste gases
containing carbon dioxide are led over carbonate of soda thereby producing
bicarbonate which is then reconverted into carbonate with liberation of concen-
trated carbon dioxide. As pure carbon dioxide is considerably heavier than air
the hardening process may generally be carried on in open vessels without material
loss of carbon dioxide; or the vessels may be closed to such an extent as to pre-
vent any material loss of heat while allowing the steam produced to escape.
It may however in certain cases be of advantage to retain the steam in the
hardening vessels, in order to assist the hardening by the solution of silicic acid
and re-deposition thereof. In this case the gaseous carbon dioxide introduced
into the vessel forms an aqueous solution with the steam in acting upon the stone,
causing a solution of silicic acid which is the greater, the greater is the percentage
of carbon dioxide in the steam.
This dissolved silica enters into combination with the lime forming silicate
of lime, and partially liberating the bound carbon dioxide. The latter passes
to the contiguous layer of lime, driving off the water of hydration which in pass-
ing out becomes saturated with carbon dioxide.
The aqueous carbon dioxide mixture thus formed will then be absorbed by
the uncombined hydrate of lime, and thus a progressive formation of carbonate
of lime in the inward direction will be effected.
The driving out of the water of hydration and the inward penetration of the
carbon dioxide in aqueous solution into the stones will continue until the whole
of the hydrate of lime has been converted.
This method of utilising the steam for the hardening process can of course also be
carried on under considerable pressure in closed vessels, into which a separate
steam supply can be introduced at the commencement of the process.

page_text: Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I declare that what I claim is :-
1. Process for hardening artificial stone consisting in treating freshly formed
moist blocks containing hydrate of lime with carbon dioxide of such a degree
of concentration that the heat produced by its combination with the lime is
sufficient to dry the stone, substantially as described.
2. Process for hardening artificial stone formed of lime and sand, consisting
in treating the stone blocks with carbon dioxide not containing more than from ten
to twenty per cent. of other gases whereby the heat generated by the combination
thereof with the lime is sufficient to effect the drying of the stone substantially
as described.
3. Process for hardening artificial stone formed of lime and sand, consisting in
first treating gases from lime kilns for the extraction of the carbon dioxide there-
from and then employing the concentrated carbon dioxide thus obtained for
treating the stone blocks, substantially as described.
4. Process for hardening artificial stone formed of lime and sand, consisting
in treating the stone blocks with carbon dioxide in closed vessels, substantially
as and for the purpose described.
1900
ABEL & IMRAY,
Agents for the Applicant.