Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a light ceramic material
usable, for example, for building purposes, particularly as a
thermal and/or noise insulating material or as an aggregate for
high temperature building materials, furnace buildiny materials
and/or refactory building materials and to a method for
producing the said material.
Light structural materials, based upon lime and cement,
are already known as so-called "porous concrete or "foam
concreten. To this end, mixtures of calcium-oxide,
silicon-dioxide and water, with the addition of foaming agents,
or in the oamed condition, are hardened in an autoclave.
Although existing porous light structural materials, as
known, for example, from European Patent 0 007 585, have
satisfactory strength and other properties important for
building purposes, they may be too costly to produce for many
applications.
It is the purpose of the invention to provide a new
light ceramic material which can be used as a light-weight
aggregate and also for producing moulded objects, such as
bricks, for heat and/or sound-insulating purposes in particular,
and also for refractory building purposes, in the form of light
compression-proof mouldings, made from simple initial
substances, by an economical method.
According to the invention, is provl~ed a process
for producing a lightweight ceramic material for use in building
purposes, particularly as a thermal and/or noise insulating
material or as an aggregate for high temperature building
materials, furnace building materials and/or refractory building
materials, having a bull density of 300 to 700 g/liter, which
comprises forming a starting mixture containing 45 to 80 parts
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by weight of clay, 0 to 50 parts by weight of an aggregate, 15
to 30 parts by weight of water, 0 9 01 to 0,03 parts by weight of
a deflocculant and 0,001 to 0,01 parts by weight of a
surfactant; foaming the starting mixture at a pressure of 1 to
10 bar by compressed air at a temperature between ambient
temperature and 95C to form a foam; molding and drying the
foam to give a dried clay blank; and firing the dried clay blank
at a product temperature between 600 and 1400C.
In this connection it is particularly desirable to use,
as aggregate, calcite, quartz sand, dolomite, feldspar,
chamotte, sawdust and coal.
If, for production reasons, a product is required with
particularly high green strength, as may be the case with
products larger than bricks, a hydraulic binder, such as cement,
may be added. One special advantage of the method according to
the invention is that the clay used may be simple brick-clay,
but Westerwalder stoneware clay, fine stoneware clay, kaolin,
montmorlllonite, bentonite or marl may also be used.
It is of special interest, from an economical point of
view, that, according to the invention, any mouldings that are
unsatisfactory after drying or, where granules are used, any
fine granular material separated by screening, can be returned,
without further treatment, directly to the initial mixture,
since they have merely been dried, not fired, and are therefore
still fully reactive.
The method according to the invention usually proceeds
in such a manner that the cla~v is stirred up with water and the
deflocculating agent to form a thixotrophic suspension
containing little moisture. To produce a foam-suspension from
the clay suspension, surfactant is added and foaming is carried
out in a dispersing unit with the addition of compressed air.
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It is possible to make use of conventional dispersing units, as
sold by Messrs. Hansa-Mixer, Bremen, under the trade mark
~ansa-~ixer~ which add specific amounts of compressed air under
pressure (1 to 10 bars). The dispersing unit has an additional
precision-metering pump by means of which fluid may be added
before and, if necessary, during the foaming operation. During
the execution of the method according to the invention, it is
desirable to use a suhstance opposing the action of the
deflocculating agent, a deflocculant-counteracting agent, for
example dilute hydrochloric acid, this makes it possible to
produce highly viscous, thixotropic, inherently stable
foam-suspensions.
The inherently stable, thixotropic foam-suspension is
then dried, the water-vapour emerglng readily through the pores
because of the high porosity of the material. In this
connection it is particularly beneficlal if the mixture of
initial materials contains a relatively small amount of water.
The dried material is usually obtained in lengths of about 1 cm.
in diameter, the drying times being not more than 5 minutes at
temperatures of 200C This dried material is crushed into
granules prior to firing.
Due to the porosity of the material, and above all in
the case of objects of small dimensions, very favourable
processing is possible, such as drying. With a furnace-
temperature of between 1000C and 1400C, corresponding to amaterial-temperature of between 800 and 1000C, it is possible
to produce light ceramic materials for building purposes with a
firing time of less than 5 minutes, including heating-up and
cooling-down times. Treatment at an elevated temperature is
particularly desirable if the product is to be used for building
purposes, since this mazes it possible to obtain particularly
satisfactory strength propertles.
The invention also relates to the use of the light
ceramic material in the form of a solid and/or granules as a
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heat and/or sound-insulating material for building purposes,
also as an aggregate for high-temperature building materials
such as structural materials for furnaces, refractory building
materials, and the like.
The aggregates normally used for refractory building
materials for example are, of course, also used accordingly,
i.e. additions of clay, maynesite, quartz and the like, as
required by the particular application.
The light ceramic material may be characterized in that
the mixture preferably contains between 60 and 75 parts by
weight of clay, 15 to 20 parts by weight of water, 10 to 20
parts by weight of aggregate; 0.001 to 0.01 parts by weight of
surfactant, and 0.01 to 0.03 parts by weight of deflocculating
agent.
The invention may be further characterized in that the
clay blank is dried at a temperature between ambient temperature
and 200C.
Further characteristics and advantages of the `nvention
may be gathered from the following description, in which
examples embodying the invention are explained in detail in
conjunction with the diagrammatical drawing attached hereto,
which shows a flow-chart of a method according to the invention.
Thus, 45 to 80 parts by weight of clay, 15 to 30 parts
by weight of water, if necessary 0 to 50 parts by weight of an
aggregate, and 0.01 to 0.03 parts by weight of a deflocculating
agent, possibly with an appropriate amount of a hydraulic
bonding agent, are mixed together in a conventional mixer. The
following may be used as clay, for example: brick clay,
Westerwalder stoneware clay, fine stoneware clay, kaolin,
montmorillonite, bentonite or marl. Calcite, quartz sand,
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dolomite, feldspar, chamotte and/or organic materials such as
sawdust or coal may be used as the aggregate. Examples of
deflocculating agents are: water-glass, ca:Lcium polyphosphate,
sodium polyphosphate, phosphoric acid, chlorides or sulphates,
Preferably cement may be added as the hydraulic bonding agent in
order to achieve higher green strength
The mixture made out of the foregoing constituents, and
containing little water, is foamed so as to have a litre-weight
of between 30 and 80 g/l, and is dried in moulds or by means of
a moulding device. Drying may, if necessaryJ be accelerated by
establishing a vacuum or by the use of a drying oven. Drying is
extremely simple and rapid because of the high porosity of the
material to be dried. The dried products are then placed in a
furnace having a temperature of between 1000 and 1400C,
corresponding to a product temperature of between about ~00 and
1000C, and are fired. In producing light additives, as used in
building concrete and the like, it is desirable to use granular
material; this may be obtained by passing the dried products
through a crusher and a screening unit which retains the
preferred grain-size range and discards the fines; the latter
may then be returned to the mixer, as shown in the drawing.
500 kg of marl, 400 kg of crushed, dried foamed clay
(produced by crushing rejected, dried and not yet flred foamed
clay mouldings), 200 litres of water, 120 g of sodium
polyphosphate (deflocculating agent), and 100 g of sodium
dodecyl-sulphonate (dispersing agent), were foamed in a
dispersing unit made by Messrs. Hansa-Mixer, of Bremen, at a
pressure of 3 bars, with compressed air. The foamed product was
cast in moulds, passed to a drying oven, and dried at 200C for
10 minutes. The dried, foamed-clay mouldings were removed from
the moulds, and were fired for 7 minutes in a corlventional
furnace and in the usual way, at a furnace-temperature ox about
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1400C corresponding to a product temperature of about 1000C.
This produced yellowish-brown light ceramic panels having the
following characteristics:
pH value: 7 - 8
pore diameter: 1 mm.
bulk-density: about 0.6 g/cm3
Products made in this way have good heat- and sound-
insulating properties and low hygroscopicity. Panels or bricks
made in this way may replace glass-fibre wool, asbestos-fibre,
rock-wool or styropor for thermal insulation; they may also be
used for facing panels or for light partitions, if low weight
per unit of volume is necessary, because the sub-soil has
insufficient load-carrying capacity.
Example II
800 kg of kaolin, 200 kg of pumice-stone crushed to a
grain-size of between l and 2.5 mm, 200 litres of water and 100
g of 5% phosphoric acid were mixed and added to 300 g of sodium-
lauryl-sulphonate foam (lltre-weight 70 g/l). This was followed
by forming into lengths in a forming unit, then by crushing, in
a conventional roller-crusher, to a grain size of between and
5 mm diameter, followed by screening. The fines were separated,
all material below the said grain-size being discarded. The
crushed product was passed to a furnace having a furnace
temperature OL 1000C, was fired for 5 minutes, and the
resulting granular material was cooled and packaged. The
resulting material is particularly suitable for light additives,
for example for light concrete, gypsum-panels, and the like, and
possessed compressive strength, bulk-density, and heat-
conductivity coefficients which made it appear particularly
suitable for these applications. The pH value was between 7 and
8 and the bulk-density was in the vicinity ox 0.6 ~/cm3.
The addition ox hydraulic bonding agents, such as
cement, increased the strength values without impairing the
favourable properties, namely light weight and inexpensive
production.
