U.S. patent application number 12/153758 was filed with the patent office on 2008-09-18 for production of ceramic, glass ceramic and other mineral materials and composite materials.
This patent application is currently assigned to ITN NANOVATION AG. Invention is credited to Olaf Binkle, Ralph Nonninger.
Application Number | 20080223254 12/153758 |
Document ID | / |
Family ID | 29225059 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080223254 |
Kind Code |
A1 |
Binkle; Olaf ; et
al. |
September 18, 2008 |
Production of ceramic, glass ceramic and other mineral materials
and composite materials
Abstract
An inorganic binder for the production of ceramic, glass ceramic
and other mineral materials and composite materials comprises at
least one inorganic compound having a mean particle size of <100
nm and at least one solvent. The inorganic compounds are preferably
compounds selected from the group consisting of the chalcogenides,
the carbides and/or the nitrides. Further preference is given to
the mean particle size being <50 nm, in particular <25 nm.
The solvent is, in particular, a polar solvent, especially
water.
Inventors: |
Binkle; Olaf; (Kirkel,
DE) ; Nonninger; Ralph; (Saarbruecken, DE) |
Correspondence
Address: |
NATH & ASSOCIATES
112 South West Street
Alexandria
VA
22314
US
|
Assignee: |
ITN NANOVATION AG
Saarbruecken
DE
|
Family ID: |
29225059 |
Appl. No.: |
12/153758 |
Filed: |
May 23, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10513307 |
Feb 15, 2005 |
7384470 |
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PCT/EP03/04676 |
May 5, 2003 |
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12153758 |
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Current U.S.
Class: |
106/286.3 ;
106/286.5; 106/286.8; 427/372.2 |
Current CPC
Class: |
B01J 37/0246 20130101;
C04B 2235/5454 20130101; B01J 2229/42 20130101; C04B 2235/3272
20130101; C04B 2235/3218 20130101; C04B 35/6303 20130101; C04B
33/30 20130101; C04B 2235/3217 20130101; C04B 35/6263 20130101;
C04B 35/119 20130101; C04B 2235/3463 20130101; C04B 35/6264
20130101; C04B 33/28 20130101; C04B 33/14 20130101; B01J 29/06
20130101; C04B 35/62655 20130101; C04B 35/111 20130101; B82Y 30/00
20130101; C04B 2235/3244 20130101; C04B 2235/5445 20130101; C04B
2235/402 20130101; C04B 2235/6027 20130101 |
Class at
Publication: |
106/286.3 ;
106/286.8; 106/286.5; 427/372.2 |
International
Class: |
B05D 3/00 20060101
B05D003/00; C09K 3/00 20060101 C09K003/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 5, 2002 |
DE |
102 20 086.6 |
Claims
1-22. (canceled)
23. Method for the production of inorganic shaped bodies and
coatings, wherein a composition is prepared by mixing a binder
comprising at least one inorganic compound having a mean particle
size <100 nm and at least one suspension medium with coarser
particles or fibers having a size larger than the particles in the
binder, the composition is applied onto a substrate or transferred
into a form to obtain a green (unsintered) layer or body, the green
layer or the green body is sintered.
24. Method according to claim 23, wherein the binder is present in
the composition in an amount, based on the total weight of the
composition, of from 1% by weight to 40% by weight.
25. Method according to claim 23, wherein the binder is present in
the composition in an amount, based on the total weight of the
composition, of from 5% by weight to 20% by weight.
26. Method according to claim 23, wherein the at least one
suspension medium is present in the binder in an amount, based on
the total weight of the binder, of from 40% by weight to 95% by
weight.
27. Method according to claim 23, wherein the at least one
suspension medium is present in the binder in an amount, based on
the total weight of the binder, of from 50% by weight to 80% by
weight.
28. Method according to claim 23, wherein the at least one
inorganic compound having a mean particle size <100 nm is
present in the composition in an amount, based on the total weight
of the composition, of from 1,5% by weight to 15% by weight.
29. Method according to claim 23, wherein the at least one
inorganic compound having a mean particle size <100 nm is
present in the composition in an amount, based on the total weight
of the composition, of from 5% by weight to 10% by weight.
30. Method according to claim 23, wherein the green layer or the
green body is sintered at a temperature lower than the
sintering-temperature of the coarser particles or fibers.
31. Method according to claim 23, wherein the green layer or the
green body is sintered at a temperature at which essentially no
shrinkage occurs.
32. Method according to claim 23, wherein inorganic shaped bodies
and coatings with an open-pored structure are obtained after
sintering.
33. Method according to claim 23, wherein the at least one
inorganic compound has a mean particle size <50 nm.
34. Method according to claim 23, wherein the coarser particles or
fibers in the composition are micron scaled particles or
fibres.
35. Method according to claim 23, wherein the coarser particles or
fibers in the composition have sizes in the range from 500 nm and
500 .mu.m.
36. Method according to claim 23, wherein the at least one
inorganic compound is chemically neutral with respect to the
coarser particles.
37. Method according to claim 23, wherein the at least one
inorganic compound is chemically neutral with respect to water.
38. Method according to claim 23, wherein the at least one
inorganic compound contained in the binder is selected from the
group consisting of chalcogenides, carbides and/or nitrides.
39. Method according to claim 23, wherein the coarser particles or
fibers are chalcogenide particles or fibres, carbide particles or
fibres, nitride particles or fibres or mixtures thereof.
40. Method according to claim 23, wherein the at least one
suspension medium is a polar suspension medium.
41. Method according to claim 23, wherein the at least one
suspension medium is water.
42. Method according to claim 23, wherein the coarser particles
comprise at least one zeolite.
43. Inorganic shaped body or coating, obtained by a method
according to claim 23.
44. Body or coating according to claim 42, wherein it has an
open-pored structure.
Description
[0001] The invention relates to the production of ceramic, glass
ceramic and other mineral materials and composite materials, in
particular an inorganic binder suitable for such production. In
this context, the invention also provides a composition in which
this binder is present and the articles and coatings produced using
this composition.
[0002] In the prior art, both organic binders (e.g. phenolic
resins) and inorganic binders (e.g. cement) are utilized for
binding a variety of substances in the production of materials. The
use of hybrid materials produced on the basis of the sol-gel
process as binders is also known.
[0003] Organic binders or hybrid materials are used to hold
together a desired structure. However, materials which have been
bound in this way cannot be used at high temperatures since both
the organic binders and the hybrid materials burn and thus lose
their strength. In addition, the pyrrolysis products formed when
such binders are used are in most cases toxic. If materials are to
be bound together so that the resulting composite materials are
thermally stable, inorganic binders are therefore used.
[0004] Among inorganic binders, a distinction is made between two
types, namely binders which require water for setting (e.g. cement,
lime and plaster of Paris) and those which require further
additives in addition to water for setting (e.g. water glass,
magnesia binders, phosphate binders).
[0005] The best-known inorganic binders must be cement, lime and
plaster of Paris. Mixed with water, these serve as inorganic
binding building materials in mortar and concrete production, as
fillers and hardening agents. They make it possible to achieve
virtually any moldability, which is however maintained for only a
limited time, and solidify or cure at low temperatures.
[0006] Cement, lime and plaster of Paris are all reactive toward
water. After these inorganic materials have been mixed with water,
chemical transformations occur and lead to products which are more
or less crystalline. Among the setting processes, a distinction is
made between three types: setting by hydration, hydraulic setting
and setting by carbonate formation. In setting by hydration, the
water added is bound and incorporated in molecular form (e.g.
CaSO.sub.4 is converted into CaSO.sub.4*H.sub.2O); in hydraulic
setting, hydrolysis of the starting material occurs (e.g. CaO is
converted into Ca(OH).sub.2); and in the case of setting by
carbonate formation, carbon dioxide is taken up and chemically
bound (e.g. CaO is converted into Ca(OH).sub.2 and in the second
step into CaCO.sub.3). Pure types of setting are rare in practice
and a combination of two or all three types of setting is usually
present. It also needs to be stated that the setting of these
inorganic binders is always exothermic.
[0007] In addition to cement, lime and plaster of Paris, there is
also a group of inorganic binders which require additives in
addition to water for setting. The curing of magnesia binders (MgO)
is based on the formation of sparingly soluble basic magnesium salt
hydrates as a result of the addition of magnesium chloride or
magnesium sulfate solutions. Phosphate binders, on the other hand,
cure as a result of mixing of Al(OH).sub.3 with phosphoric acid
(H.sub.3PO.sub.4) or as a result of mixing of Al(OH).sub.3 with an
Al(H.sub.2PO.sub.4).sub.3 solution to form tertiary aluminum
phosphate. In the case of water glass (aqueous solution of
Na.sub.2O and SiO.sub.2), setting occurs as a result of the
addition of additives such as esters of organic acids, acids in
general or addition of oxides or hydroxides. In the case of setting
after addition of oxides (e.g. ZnO) or hydroxides, formation of
sparingly soluble silicate hydrates (e.g. ZnSiO.sub.3) occurs. In
the last three cases discussed, water does not lead directly to a
chemical reaction but the presence of water as reaction medium is a
basic requirement for the chemical reactions which take place.
[0008] The application of mineral layers, especially ceramic
layers, to metal, glass, enamel or ceramic substrates or the
production of ceramics usually requires the use of a binder, since
the mineral starting materials, in particular the ceramic starting
materials, are in powder form. Use is here made virtually
exclusively of organic binders which give the layer or the shaped
body sufficient strength prior to firing (sintering). During the
sintering process, the organic binders are decomposed pyrolytically
and leave the shaped ceramic body or the ceramic layer as gaseous
degradation products. The burning-out of the organic binders causes
shrinkage of the ceramic layer or the shaped body during the
sintering process, and this in turn leads to stresses and cracks in
the layer or in the shaped body.
[0009] It would therefore be ideal to carry out the production of a
shaped ceramic body using an inorganic binder which remains in the
layer or in the shaped body during the sintering process, so that
the shrinkage remains small and stresses do not result.
[0010] However, the inorganic binders discussed in the prior art do
not satisfy the requirements here. All inorganic binders discussed
display excessively fast and consequently insufficiently controlled
reaction rates, so that uniform application of a layer, e.g. in an
industrial spray process, or customary ceramic shaping methods such
as tape casting, extrusion or injection molding are virtually
impossible. Furthermore, problems are caused by the heat of
reaction evolved in the process and the fact that ceramic
layers/shaped bodies bound in this way would undergo
after-condensation under the action of heat, which would likewise
lead to stress cracks. There are also numerous applications which
do not allow water as solvent or as reactant.
[0011] It is accordingly an object of the invention to eliminate
the disadvantages known from the prior art or at least to avoid
them to a substantial extent. In particular, the invention should
provide an inorganic binder which has the most important advantages
of an organic binder. The inorganic binder should thus be
chemically neutral in the production of the ceramic, glass ceramic
or other mineral materials/composite materials. It should
nevertheless join or adhesively bond the particles/powder
particles/fibers and the like which are to be joined to one
another. The binder should function in this way independently of
external activation, for example not by addition of water as in the
setting of cement, but be an intrinsic property of the binder. The
inorganic binder should remain in the material during the
curing/strengthening of the material, in particular during a
sintering or firing process, and the shrinkage occurring during
sintering/firing should in this way be kept as small as possible so
that stresses and cracks are avoided.
[0012] This object is achieved by the inorganic binder having the
features of claim 1 and the composition as claimed in claim 10.
Preferred embodiments of the binder of the invention and the
composition of the invention are presented in the dependent claims
2 to 9 and 11 to 15, respectively. Claims 16 to 18 relate to the
materials produced in this way. Claims 19 to 22 claim the use of
particular inorganic compounds. The wording of all claims is hereby
incorporated by reference into the present description.
[0013] The inorganic binder according to the invention is intended
for the production of ceramic, glass ceramic and other mineral
materials and composite materials and comprises at least one
inorganic compound having a mean particle size of <100 nm and at
least one solvent.
[0014] To elaborate, the following may be said.
[0015] A feature critical to the function of the binder of the
invention is the presence of nanosize inorganic compounds. The term
nanosize particles or powders is usually applied to particles or
powders having a mean particle size well in the submicron range.
Here, this particle size applies to the individual particles/powder
particles in the nonagglomerated state. Owing to their high surface
energies, nanosize particles frequently clump together and in this
way form agglomerates or aggregates which have a particle size
which is misleadingly larger than the actual size of the individual
particles. The sizes indicated in the description of the invention
accordingly relate, as far as possible, to the mean particle size
of an individual particle, which can in this context also be
referred to as a "primary particle".
[0016] For the advantages according to the invention to be present,
the particle size of the inorganic compounds used according to the
invention, which are usually used in powder form, should, as
mentioned, be far in the submicron range. Accordingly, the mean
particle size should usually be <200 nm, in particular <100
nm as defined in claim 1.
[0017] The terms "ceramic", "glass ceramic", "mineral" and
"materials" and "composite materials" used in claim 1 are known to
those skilled in the art and should be interpreted very broadly.
Inorganic binders according to the invention are suitable and
advantageous for the production of very many inorganic
materials/composite materials. Ceramics are, as is known,,
materials and products which are shaped from a powder using the
methods of ceramic technology and are subsequently converted into
their final form by means of a sintering process or firing process.
Glass ceramics are materials produced from glasses by controlled
crystallization, while the term mineral materials is the generic
term for such inorganic materials. This will be explained further
in the following with reference to the zeolites. In any case, the
invention is intended to extend to the production of all inorganic
materials which are formed from a raw composition with the aid of a
binder, in particular by strengthening/curing at temperatures above
200.degree. C.
[0018] In preferred embodiments of the inorganic binder, the mean
particle sizes of the inorganic compounds used are far below 100
nm. Emphasis is here placed on particle sizes of from 2 nm to 50
nm, with particle sizes of from 2 nm to 25 nm being more
preferred.
[0019] The nanosize powder particles used for the binder of the
invention are, in particular, nanosize chalcogenide, carbide or
nitride powders. The chalcogenides are, as is known, binary
compounds in which the elements oxygen, sulfur, selenium and
tellurium occur as electronegative component. The chalcogenide
powders can thus be oxide, sulfide, selenide or telluride powders.
Nanosize oxide powders are preferred. It is possible to use, in
particular, all powders which are customarily used for powder
sintering. Examples are (anhydrous or hydrated) oxides such as ZnO,
CeO.sub.2, SnO.sub.2, Al.sub.2O.sub.3, CdO, SiO.sub.2, TiO.sub.2,
In.sub.2O.sub.3, ZrO.sub.2, yttrium-stabilized ZrO.sub.2,
Al.sub.2O.sub.3, La.sub.2O.sub.3, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4,
Cu.sub.2O, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, V.sub.2O.sub.5,
MoO.sub.3 or WO.sub.3, and also phosphates, silicates, zirconates,
aluminates and stannates, sulfides such as CdS, ZnS, PbS and
Ag.sub.2S, selenides such as GaSe, CdSe and ZnSe, tellurides such
as ZnTe or CdTe, carbides such as WC, CdC.sub.2 or SiC, nitrides
such as BN, AlN, Si.sub.3N.sub.4 and Ti.sub.3N.sub.4, corresponding
mixed oxides such as metal-tin oxides, e.g. indium-tin oxide (ITO)
antimony-tin oxide, fluorine-doped tin oxide and Zn-doped
Al.sub.2O.sub.3, luminescent pigments comprising Y- or
Eu-containing compounds, and mixed oxides having a perovskite
structure, e.g. BaTiO.sub.3, PbTiO.sub.3 and lead zirconate
titanate (PZT). It is also possible to use mixtures of the powder
particles indicated.
[0020] The inorganic binder of the invention preferably comprises
nanosize particles which are composed of a chalcogenide, preferably
oxide, oxide hydrate, nitride or carbide of Zr, Al, B, Zn, Si, Cd,
Ti, Ce, Fe, Sn, In, La, Cu, Ta, Nb, V, Mo or W, particularly
preferably Zr, Al, Ti, Fe and Si. Particular preference is given to
using oxides. Preferred nanoparticles are particles of aluminum
oxide, boehmite, zirconium oxide, yttrium-stabilized zirconium
oxide, iron oxide and titanium dioxide or mixtures of such
nanoparticles.
[0021] The amount of solvent present in the binder of the invention
is in principle not critical and can be varied according to the use
to which the binder is put. However, preference is given to the
solvent component being present in the binder in an amount, based
on the total weight of the binder, of from 40% by weight to 95% by
weight. Within this range, amounts of from 50% by weight to 80% by
weight are preferred. It is in principle possible to use a variety
of solvents, including, for example, aliphatics and oils. However,
it is advantageous in many cases to use polar solvents, in
particular esters, alcohols, diols, glycols and the like. If
alcohols are used, preference is given to C.sub.1-C.sub.5-alkanols,
in particular ethanol. A particularly preferred solvent is water,
which may also be preferred in admixture with alcohols. Aqueous
binder systems are particularly simple to handle, especially
because of their low toxicity.
[0022] The binder of the invention may, if appropriate, further
comprise additional additives. These are, in particular, additives
which aid distribution of the inorganic compound in the binder
system and/or inhibit agglomeration of the individual
nanoparticles. Such additives can be, for example, anionic or
cationic surfactants.
[0023] The composition or starting substance of the invention for
the production of ceramic, glass ceramic and other mineral
materials and composite materials comprises at least one inorganic
binder according to the invention. It is this binder which
distinguishes the composition from the prior art.
[0024] The amount of binder present in the composition is in
principle not critical according to the invention. This amount is
selected so that the effect provided according to the invention is
obtained. For cost reasons, the amount of binder will usually be
kept as small as possible. Preferred amounts of binder in the
composition are from 1% by weight to 40% by weight, in particular
from 5% by weight to 20% by weight. If the amount is based on the
nanosize inorganic compound, this is preferably present in the
composition in amounts of from 1.5% by weight to 15% by weight,
more preferably from 5% by weight to 10% by weight.
[0025] Depending on the composition of the binder and depending on
the other components of the composition, the consistency of the
composition can be varied within wide limits. Thus, the composition
can be in the form of a low-viscosity suspension, in the form of a
relatively high-viscosity suspension or in the form of a slip
through to the form of a comparatively firm, paste-like mass. Thus,
when the composition is to be applied as a coating, a low-viscosity
suspension which can then be, for example, painted on, sprayed on
or even applied by dipping or flooding will frequently be selected.
When shaped bodies are to be produced from the composition, the
composition will tend to be in the form of a possibly paste-like
mass which can then be cast, extruded or the like.
[0026] Apart from the binder, the composition of the invention
comprises first and foremost those constituents (then bound by the
binder) of which the material or composite material to be produced
is to be composed. These constituents can advantageously be all
customary inorganic particles or fibers as are known for the
production of ceramics and glass ceramics. These customary "ceramic
powders" as further constituents of the composition then generally
preferably have a larger particle size than the nanosize particles
in the binder. These particles will frequently be in the micron
range, in particular in the range from 1 .mu.m to 500 .mu.m.
However, it is likewise preferred according to the invention for
submicron particles to be present in the composition in addition to
the nanosize particles of the binder (<100 nm), for example
powder particles having particle sizes in the range from 500 nm to
1000 nm (1 .mu.m).
[0027] The inorganic particles or fibers for the production of
ceramics and glass ceramics are preferably the abovementioned
chalcogenides, carbides and/or nitrides, with the use of oxides
also being preferred here. The corresponding information in the
previous description relating to these compounds is hereby
expressly incorporated by reference.
[0028] Furthermore, compositions in which zeolites are used in
addition to the binder of the invention also deserve particular
mention for the production of other mineral materials and composite
materials. Zeolites are, as is known, a group of water-containing
minerals based on aluminosilicates which are known to those skilled
in the art. Zeolites have voids in their interior, which
predestines them for various fields of use. Thus, zeolites are used
as molecular sieves or in ion exchangers. The advantages of
zeolite-based materials produced according to the invention will be
explained in more detail in the following.
[0029] Finally, the compositions of the invention can in all cases
further comprise additional customary additives which, for example,
influence the properties of the composition itself (addition of
dispersants, surfactants and the like) or its processability (e.g.
adhesion promoters in the case of coating materials). If desired,
at least one further organic binder which is removed again from the
composition during the strengthening carried out at relatively high
temperatures, i.e. is burned out, can be added to the composition
of the invention in addition to the inorganic binder of the
invention.
[0030] The invention further provides the inorganic shaped bodies
and the inorganic coatings which are or can be produced with the
aid of the binder of the invention or from the composition of the
invention. In this context, the invention also encompasses all
those articles which are provided (in their entirety or partly)
with a novel coating of this type.
[0031] At this point, the function of the nanoparticles present in
the binder of the invention will be explained.
[0032] The nanoparticles used as inorganic binder have very large
specific surface areas which preferably bear reactive hydroxyl
groups. These surface groups are able, even at room temperature,
i.e. before the sintering or firing process, to crosslink with the
surface groups of the materials to be bound (e.g. ceramic powders,
fibers, etc.). In this way, strengthening of the unfired (green)
layers/shaped bodies analogous to that effected by organic binders
is possible. Owing to the high radii of curvature of nanoparticles,
nanoparticles also have extremely high surface energies. Even at
temperatures above 200.degree. C., preferably above 300.degree. C.,
it is found that these surface energies lead to material transport
(diffusion) from the nanoparticles to the points of contact of the
(usually coarser) materials to be bound. The bound, coarser powder
particles have significantly lower surface energies and therefore
do not yet sinter at this point in time, i.e. they also do not yet
shrink. The material transport triggered by the nanoparticles leads
to sintering of the bound particles without mass transfer occurring
in the bound coarser particles. This form of mass transfer is
completely new, since the nanoparticles used as binder dissolve in
a manner analogous to sacrificial materials, i.e. lose their
original shape and in the process join/sinter the coarser powder
particles to one another. This shrinkage-free sintering leads
firstly to a porous (frequently highly porous) layer having an
open-pored structure. For the present purposes, the term open-pored
structure means that the pores present in the layers/shaped bodies
are accessible from the outside, i.e. are not closed to the
outside. The open porosity thus extends at least partly over the
layers/shaped bodies, but does not necessarily extend right through
the entire layers/shaped bodies. If this were the case, the
corresponding shaped body would, for example, be able to be used as
a filter, in particular as a ceramic filter. However, the porous
layer can be sintered to close to the theoretical density or to the
theoretical density when the temperature is increased further.
Accordingly, the porosity can be set by selection of the
temperatures when performing the invention. As long as the firing
temperature employed is below that at which the coarser powder
particles sinter, viz. display mass transfer, the strengthening
occurs without shrinkage and stresses.
[0033] It can be seen from what has been said above that the
inorganic shaped bodies of the invention and the inorganic coatings
of the invention can as a matter of choice be made more or less
porous. If the materials/composite materials, in particular the
ceramic and glass ceramic materials/composite materials, are
strengthened or sintered at comparatively low temperatures and/or
for comparatively short times, shaped bodies and coatings having a
relatively high porosity are obtained. If strengthening or
sintering is carried out at higher temperatures and/or for longer
times, materials/composite materials having close to the
theoretical density or the theoretical density are obtained. Under
appropriate strengthening/sintering conditions, shrinkage-free and
stress-free shaped bodies and coatings which are consequently
largely free of cracks can be obtained. This clearly distinguishes
the shaped bodies and coatings of the invention from the prior art.
Such shaped bodies and coatings are also particularly stable to
high temperatures.
[0034] The ceramic and glass ceramic materials and composite
materials of the invention are particularly suitable for a wide
variety of applications. Particular mention may here be made of
their possible use as insulation materials, as filters for gas and
liquid filtration, as scratch-resistant layers, as diesel
particulate catalysts and as high-porosity support materials for
catalytically active substances.
[0035] When the materials and composite materials of the invention
are to be applied as coatings to articles, possible substrate
materials are, in particular, metals, ceramics, glass ceramics,
glass and enamel.
[0036] As stated above, the binders of the invention can also be
used for binding zeolites. It is in this way possible to produce
both zeolite layers or zeolite coatings and shaped zeolite
bodies.
[0037] In such materials produced using zeolites, the pores of the
zeolites are surprisingly not filled. Thus, both the voids of the
zeolites and the large (internal) surface area of the zeolites are
retained. In the case of zeolite layers, strengthening of the
layers can be carried out even at comparatively low temperatures,
in particular in the range from 500.degree. C. to 600.degree. C.,
over short periods of time, e.g. within a few seconds. The layers
obtained have excellent thermal shock resistance and survive
repeated heating from room temperature to relatively high
temperatures, for example 600.degree. C., within short periods of
time, for example within only 3 seconds, without problems.
[0038] It is possible to obtain high layer thicknesses up to shaped
bodies having thick walls. Usually preferred layer thicknesses are
in the range from 1 .mu.m to 300 .mu.m. If such layers are applied
to flexible substrates, in particular metallic substrates, the
coated substrates can be bent/deformed without the applied zeolite
layers flaking off. Fine, open structures (e.g. thin wire meshes or
thin metal platelets) can readily be coated, too.
[0039] Preferred application areas for zeolite layers and shaped
zeolite bodies are, for example, catalyst layers or shaped catalyst
bodies for gas-phase reactions, as filters for the separation of
gases, the possible use as sensors, in particular gas sensors, the
possible use as adsorption layers (e.g. to remove pollutants or for
gas adsorption) and the possible use as ion exchangers.
[0040] Finally, the invention encompasses the use of inorganic
compounds having a mean particle size of <100 nm as binder
constituents for the production of ceramic, glass ceramic and other
mineral materials and composite materials. This use is disclosed by
the previous description. Accordingly, the corresponding
information given above is expressly incorporated by reference.
[0041] The stated advantages and further advantages of the
invention can be derived from the description of the following
examples in conjunction with the subordinate claims. The individual
features of the invention can be realized either alone or in
combination with one another.
EXAMPLES
Example 1
[0042] 40 g of an aluminum oxide powder (Ceralox APA 0.5
(corresponding to a particle size of 0.5 .mu.m) from Condea-Chemie
GmbH, Germany) are slurried with 10 g of water. 10 g of an
inorganic binder solution (45% by weight of nanosize zirconium
oxide (mean particle size <50 nm) in 55% by weight of water) are
added to the suspension obtained in this way. 0.9 g of commercially
available organic binder (PVA, polyvinyl alcohol) are then mixed
in. This gives a composition according to the invention in the form
of a suspension. The viscosity of this suspension can be adjusted
as desired by addition of preferably small amounts of water and/or
nitric acid or by alteration of the amount of organic binder added.
These suspensions can subsequently be applied to metal, ceramic,
glass ceramic, glass and enamel substrates by means of a spraying
process to produce ceramic layers. Strengthening is carried out by
sintering/firing at temperatures above 500.degree. C. The porosity
of the ceramic layers obtained can also be set by selection of the
final temperature and/or the duration of the sintering/firing
process.
Example 2
[0043] A further low-viscosity ceramic suspension is prepared as
described in example 1. Shaped ceramic bodies are obtained from
this suspension by slip casting. The green body obtained is firstly
dried at 70.degree. C. in a drying oven and subsequently
sintered/fired at above 500.degree. C. Here too, porosities of the
shaped body obtained can be varied in a comparable way by means of
the temperature level and time for which it is maintained.
Example 3
[0044] A sol is prepared from 1.63 g of a boehmite AIOOH (product
Disperal P3 from Sasol Ltd.) and 7.43 g of water by stirring. 1.64
g of Ceralox powder (see example 1) are added to this sol in a bead
mill and the mixture is milled for a period of 10 minutes. Finally,
4.5 g of a zeolite (product Fe-MSM-1S from Alsi-Pentha-Zeolith
GmbH, Germany) and 1.5 g of iron oxide (Fe.sub.2O.sub.3) from
Riedel-de Haen are added as filler and colorant.
[0045] The suspension obtained in this way is sprayed as a coating
on a ceramic support, dried at room temperature and subsequently
fired at 600.degree. C.
* * * * *