Honey comb assembly

Abstract

The present invention relates to a composition comprising a non-oxide silicon containing component, a water soluble phosphate component, a metal oxide ceramic component, a polysaccharide component and water to 100% w/w. This composition can be transformed into a cement that holds individual honey comb filter segments of a honey comb filter together.

Claims

1. A hardened cement composition consisting of a non-oxide inorganic silicon containing component and metaphosphates, wherein the non-oxide inorganic silicon containing component comprises an inorganic powder having a bimodal particle size distribution consisting of coarse particles and fine particles, the coarse particles having a mean particle diameter size in the range from 20-150 m and the fine particles having a mean particle diameter size in the range from 1-20 m; and wherein the metaphosphates bind the coarse particles and the fine particles together to form the hardened cement composition.

2. An article of manufacture comprising: a first porous ceramic honey comb filter segment; a second porous ceramic honey comb filter segment; and a layer of the hardened cement composition of claim 1 between the first and second porous ceramic honey comb filter segments, wherein the cement holds together the first and second porous ceramic honey comb filter segments.

3. The hardened cement composition of claim 1, wherein the cement is hardened at a temperature sufficiently high to transform substantially all phosphate components into the metaphosphates.

4. The hardened cement composition of claim 1, wherein the cement is hardened at the temperature of about 800 C.-1000 C.

5. The article of manufacture of claim 2, wherein the hardened cement composition has a thermal conductivity equal to or greater than a thermal conductivity of the first and second honey comb filter segments.

6. The article of manufacture of claim 2, wherein the hardened cement composition has a specific heat capacity per unit volume equal to or greater than a specific heat capacity per unit volume of the first and second honey comb filter segments.

7. The article of manufacture of claim 2, wherein the hardened cement composition has a coefficient of thermal expansion substantially similar to a coefficient of thermal expansion of the first and second honey comb filter segments.

8. The hardened cement composition of claim 1, wherein the inorganic power is silicon carbide or silicon nitride or mixtures thereof.

9. The hardened cement composition of claim 8, wherein the silicon carbide is alpha-silicon carbide.

10. The hardened cement composition of claim 1, wherein the metaphosphates are aluminum metaphosphates.

Description

FIGURE LEGENDS

(1) FIG. 1 shows the coefficient of thermal expansion for a honey comb filter segment, a cement according to the present invention and a cement according to the prior art as a function of temperature.

(2) FIG. 2 shows the assembling layer of example 1 after 1050 C.

(3) FIG. 3 shows the assembling layer of example 2 after 1050 C.

(4) FIG. 4 shows the assembling layer of comparative example 4 after 1050 C.

(5) FIG. 5 shows the measuring positions of a thermal gradient.

DEFINITIONS

(6) In the present context, the term a porous honey comb filter as used herein means a filter for purifying exhaust gasses in which a plurality of porous ceramic honey comb filter segments are combined with one another through adhesive layers. Each of the porous ceramic honey comb filter segments comprises a number of through-holes that typically, are placed in parallel with one another in the length direction with partition wall interposed therebetween and wherein the partition walls functions as a filter for collecting particulates. The porous honey comb filter has its usual meaning as understood by the person skilled in the art, and suitable examples of such filters and how to make such filters are i.a. described in EP0816065, EP1382445, EP1382442, EP1306358, EP1270202, EP1142619, EP1479881, EP1719881, and EP1726796, reference is made in particular to the drawings and description of the drawings.

(7) In the present context, the term a non-oxide inorganic silicon containing component as used herein means a component not containing any oxide and containing silicon which builds up the main skeleton of the cement, such as silicon carbide or silicon nitride or mixtures thereof. This component determinates mainly the heat capacity and thermal conductivity of the cement. The reason to choose silicon containing non-oxide ceramic materials as the main component for the composition is their high thermal conductivity and their high specific heat capacity.

(8) In the present context, the term a water soluble phosphate component as used herein means a phosphate containing precursor material which is souble in water and able to form itself or in the presence of an oxide ceramic material by a condensation process phosphates and under subsequent heating is able to form metaphosphates, and examples of such components are potassium phosphate, monoaluminium phosphate, acid aluminium phosphate and phosphoric acid or mixtures thereof.

(9) In the present context, the term a metal oxide ceramic component as used herein means a metal oxide or mixed metal oxide powder for use as a reaction partner with the water soluble phosphate component to form phosphates and under subsequent heating metaphosphates, and examples of such components are Na.sub.2O, MgO, ZnO, CaO, SiO.sub.2, Al.sub.2O.sub.3or Mullite (Al.sub.6Si.sub.2O.sub.13).

(10) In the present context, the term a polysaccharide component as used herein means natural polysaccharides such as starch or cellulose as well as modified polysaccharides such as methylated cellulose (cellulose ether). Such a polysaccharide or modified polysaccharide component acts as a temporary binder after drying of the composition for preparing the cement of the present invention. In addition, the polysaccharide component is used to adjust the plasticity of the composition of the present invention. It has furthermore the ability to keep the water in the composition. High porous ceramics have a tendency to absorb a huge amount of water. This leads to the effect that a cement, which is based on a water containing composition, will dry out very fast if it gets in contact with such a high porous ceramic. The water is sucked out of the cement and the cement itself loses its paste like character. To ensure, that the water is kept in the composition of the present invention, the polysaccharide component is used, which is typically a cellulose or cellulose ether. The cellulose or cellulose ether is swelling by absorbing water and keeps the water inside the mixture. At the same time, this swelled cellulose creates a paste like characteristic of the composition, i.e. it can be easily deformed by applying a force and it keeps its shape when no force is applied. This tixotropic behavior is important for the assembling process. The composition needs to flow under pressure when two segments are pressed toward each other and it should stay in between the segments, when the final thickness of the composition layer is reached. This characteristic feature is also called plasticity. The optimal plasticity can be achieved by adding a cellulose or cellulose ether to the composition. The best results in respect to a good plastification can be achieved, if a cellulose ether is added. Cellulose ether can be any type of a methyl cellulose, ethylhydroxyethyl cellulose, hydroxybutylmethyl cellulose, hydroxyethyl cellulose, hydoxymethyl cellulose or hydroxypropyl cellulose or mixtures thereof. After the drying, the cellulose ether acts as a temporary binder and has a significant contribution to the mechanical stability of the cement. Subsequent heating to higher temperatures leads to the formation of the metaphosphates, which are then responsible for the mechanical strength and stability of the cement. At temperatures above 350 C. the cellulose ether decomposes and disappears.

DESCRIPTION OF THE INVENTION

(11) The present invention provides a composition comprising a non-oxide silicon containing component, a water soluble phosphate component, a metal oxide ceramic component, a polysaccharide component and water to 100% w/w. This composition can be used to create a cement with the advantages as explained above.

(12) Preferably the composition consists essentially of a non-oxide silicon containing component, a water soluble phosphate component, a metal oxide ceramic component, a polysaccharide component and water to 100% w/w. In an embodiment composition consists of a non-oxide silicon containing component, a water soluble phosphate component, a metal oxide ceramic component, a polysaccharide component and water to 100% w/w. In one embodiment no silica sol is present in the composition of the present invention.

(13) In a further embodiment of the composition of the present invention the non-oxide silicon containing component is selected from an inorganic powder. The non-oxide silicon containing component is typically selected from silicon carbide or silicon nitride or mixtures thereof. In a particular embodiment the non-oxide silicon containing component is selected from alfa-SiC and beta-SiC or a mixture thereof, preferably alfa-SiC. In another embodiment the non-oxide silicon containing component is selected from Si.sub.3N.sub.4. In a further embodiment the non-oxide silicon containing component is selected from a mixture of alfa-SiC and Si.sub.3N.sub.4.

(14) In a still further embodiment of the composition of the present invention the non-oxide silicon containing component is selected from an inorganic powder having a bimodal particle size distribution consisting of coarse particles and fine particles. Typically, the inorganic coarse particles have a mean particle diameter size in the range from 20-150 m and the fine particles have a mean particle diameter size in the range from 1-20 m. In one embodiment the inorganic coarse particles have a mean particle diameter size in the range from 20-100 m.

(15) The particle size distributions may be determined using the laser diffraction method as described in the ISO 13320. As used herein the mean particle diameter size is intended to means the D.sub.50 value of the particle size distribution. The D.sub.50 value specifies the particle diameter, for which 50% of all measured particles are equal or smaller in diameter.

(16) In a further embodiment of the composition of the present invention the water soluble phosphate component is selected from a powder and a liquid solution. In one embodiment the water soluble phosphate component is selected from a powder. In another embodiment the water soluble phosphate component is selected from a liquid solution. Typically, the water soluble phosphate component is selected from monoaluminium phosphate, acid aluminium phosphate and phosphoric acid or mixtures thereof. In a particular embodiment the water soluble phosphate component is selected from monoaluminium phosphate. In a further embodiment the water soluble phosphate component is selected from acid aluminium phosphate. In a still further embodiment the water soluble phosphate component is selected from phosphoric acid. In a further embodiment the water soluble phosphate component is selected from potassium phosphate.

(17) In a further embodiment of the composition of the present invention the metal oxide ceramic component is selected from an oxide ceramic powder and an oxide ceramic fiber or mixtures thereof. In one embodiment the metal oxide ceramic component comprises Na.sub.2O, MgO, ZnO, CaO, SiO.sub.2, Al.sub.2O.sub.3 or Mullite (Al.sub.6Si.sub.2O.sub.13). In another embodiment the metal oxide ceramic component comprises Al.sub.2O.sub.3. In a further embodiment the metal oxide ceramic component comprises mullite. In a further embodiment the metal oxide ceramic component comprises Na.sub.2O. In a further embodiment the metal oxide ceramic component comprises MgO. In a further embodiment the metal oxide ceramic component comprises ZnO. In a further embodiment the metal oxide ceramic component comprises CaO. In a further embodiment the metal oxide ceramic component comprises SiO.sub.2.

(18) In a still further embodiment of the composition of the present invention the polysaccharide component is selected from a polyvinyl alcohol and a cellulose ether, preferably a cellulose ether. In one embodiment the polysaccharide component is selected from cellulose. In another embodiment the polysaccharide component is selected from methyl cellulose, ethylhydroxyethyl cellulose, hydroxybutylmethyl cellulose, hydroxyethyl cellulose, hydoxymethyl cellulose and hydroxypropyl cellulose or mixtures thereof.

(19) Typically, the composition of the present invention contains a high amount of the non-oxide silicon containing component to ensure a high thermal conductivity. In one embodiment the non-oxide silicon containing component is present in an amount of 30 to 90% w/w, typically at least 50% w/w, such as from 50 to 80% w/w, e.g. 50 to 70% w/w.

(20) In a further embodiment of the composition of the present invention the water soluble phosphate component is present in an amount of 1 to 25% w/w, typically at least 2% w/w, such as 2 to 20% w/w, e.g. 2 to 15% w/w.

(21) In a still further embodiment of the composition of the present invention the metal oxide ceramic component is present in an amount of 1 to 30% w/w, typically at least 3% w/w, such as 3 to 25% w/w, e.g. 3 to 20% w/w.

(22) In a further embodiment of the composition of the present invention the polysaccharide component is present in an amount of 0.2 to 1% w/w, typically at least 0.5% w/w, such as 0.5 to 0.8% w/w.

(23) The new type of cement of the present invention is obtainable by drying a composition of the present invention (and as specified in any one of the embodiments described above) at 100 C. and subsequently hardening at a temperature sufficiently high to transform substantially all phosphate components into metaphosphates, preferably the temperature is sufficiently high to transform all phosphate components into metaphosphates.

(24) In a further aspect the cement of the present invention consist of a non-oxide inorganic silicon containing component and metaphosphates.

(25) This cement of the present invention has several purposes and is typically useful for a) plugging open ends of channels of a porous ceramic honey comb filter segment and/or a porous ceramic honey comb filter to form a wall flow filter; b) applying on a lateral outer surface of a porous ceramic honey comb filter; and c) an assempling layer for assempling at least two porous ceramic honey comb filter segments into a porous ceramic honey comb filter.

(26) In a further embodiment of the cement of the present invention the temperature of hardening is at least 200 C., such as from 200 C. to 800 C., such as from 200 C. to 700 C. Typically, invention the temperature of hardening is at least 350 C., such as from 500 C. to 800 C., such as from 500 C. to 700 C.

(27) After drying and hardening a cement consisting essentially of a non-oxide silicon containing component and metaphosphates is obtained. At temperatures of hardening above 350 C., the polysaccharide component has disappeared, and the water soluble phosphate component has reacted with the metal oxide ceramic component to form the metaphosphates.

(28) In particular with a high content of silicon carbide a high thermal conductivity is realized. The thermal conductivity is further optimized by a bimodal mixture of a coarse grain and a fine grain powder, which reduces the porosity of the cement layer. The coarse silicon carbide builds up the main structure and dominates the thermal conductivity by its big grains. The fine grains fill up the space between the large particles and reduce therefore the porosity. The phosphate and the metal oxide ceramic component reaction partner together build up a binder system, which reacts preferably by heating up to a specific temperature and which shows a low shrinkage during drying and subsequent hardening. The inventor found out, that cements based on the composition of the present invention can be used to create assembling layers, for instance Diesel particle filters, which have a higher elasticity than the filter material and which have an excellent adhesive strength to the filter material. The mechanical strength itself is high and even higher than that of the filter. The thermal conductivity and the coefficient of thermal expansion are similar to that of the filter, and the specific heat capacity is slightly higher than that of the filter. This type of cement does not change his properties under thermal stress. Especially the adhesion to the filter material and its mechanical properties do not change after thermo shock regeneration. For applications with very high thermal gradients in the filter or especially between assembled filter segments, one of the metal oxide ceramic components can be oxide ceramic fibers. In that case the elasticity and crack deflection inside the assembling layer is increased.

(29) The mechanism of phosphate bonding and the corresponding hardening processes are described in detail in the papers of Karpukhin et al in Refractories and Industrial Ceramics, Vol. 46, No. 3, 2005 and Vol. 46, No. 5, 2005. There are several possibilities to make a phosphate based binder material. One way is to use mullite type materials together with phosphoric acid to form a monoaluminumphosphate
3Al.sub.2O.sub.3.2SiO.sub.2+18H.sub.3PO.sub.4=6Al(H.sub.2PO.sub.4).sub.3+2SiO.sub.2+9H.sub.2O

(30) Under heating above 150 C. the monoaluminum phosphate dehydrates to build acid aluminium pyrophosphate. If a metal oxide ceramic component is present, phosphates are build at elevated temperatures. In case of an aluminium oxide, the aluminium ortho phosphate is build at elevated temperatures. One can also use direct a monoaluminium phosphate and combine it with a metal oxide ceramic component.

(31) These reactions under elevated temperatures, starting at 150 C. up to a temperature of about 300 C. can be summarized by the following equations (see again Refractories and Industrial Ceramics, Vol. 46, No. 3, 2005 and Vol. 46, No. 5, 2005):
2Al(H.sub.2PO.sub.4).sub.3.fwdarw.elevated temperatures>150 C..fwdarw.Al.sub.2(H.sub.2P.sub.2O.sub.7).sub.3+3H.sub.2O
Al(H.sub.2PO.sub.4).sub.3+Al.sub.2O.sub.3.fwdarw.elevated temperatures>150 C..fwdarw.3AlPO.sub.4+3H.sub.2O

(32) Under subsequent heating above 300 C. aluminium metaphosphate is produced. This is decribed by Karpukhin et al and also in an information sheet from Zschimmer & Schwarz, which can be downloaded from their website. Dehydration does not only occur in each individual molecule but even between them (intermolecular). This condensation brings about chain- and ringshaped compounds (Zschimmer & Schwarz).
nAl.sub.2(H.sub.2P.sub.2O.sub.7).sub.3=[Al(PO.sub.3).sub.3].sub.n+nH.sub.2O

(33) At 500 C. most of the phosphates will be converted into these metaphosphate structures. A fully conversion with an almost complete dehydration can be achieved at temperatures of 800-1000 C.

(34) In EP0032532A1 a monoaluminium phosphate is used in combination with a Magnesium oxide and a filler material, which can be aluminium oxide, mullite or a clay, to form a refractory material.

(35) In US6309994B1 is described a fiber reinforced refractory material, in which a fiber based preform is infiltrated with a mixture of alumina and an aluminium phosphate solution and subsequent heated to a temperature above 200 C.

(36) Examples for the usage of phosphate containing binders are given by Chung in JOURNAL OF MATERIALS SCIENCE 38 (2003) 2785-2791, by Fernando et al in JOURNAL OF MATERIALS SCIENCE 36 (2006) 5079-5085, and by Baranova in Refractories and Industrial Ceramics Vol. 45, No. 6, 2004. Chung describes a binder on the basis of an acid alumina phosphate derived from phosphoric acid and aluminium hydroxide and Fernando describes a filter materials based on oxide ceramic fibers bonded together with this type of binder. Baranova describes the production of refractory bricks on the basis of boron aluminium phosphate and chromium aluminium phosphate in combination with silicon nitride, silicon carbide and aluminium oxide.

(37) The big advantage of using a phosphate based cement in comparison to a silica sol based cement can be shown by a direct comparison of the characteristic features to an example taken from the state of the art. We made this comparison to the EP 1 479 881 A1, which is a relevant solution according to the state of the art. The main differences between the solution according to this invention to the EP 1 479 881 A1 are given by table 1.

(38) TABLE-US-00001 TABLE 1 Main differences of the new cement in accordance to this invention in comparison to the state of the art. EP 1 479 881 A1 The present invention Coefficient of thermal .sub.L >> .sub.F (preferred) .sub.L .sub.F expansion or .sub.L << .sub.F Heat conductivity Low .fwdarw. insulation Equal to filter Specific heat capacity C.sub.p, L << C.sub.p, F C.sub.p, L C.sub.p, F Young modulus E.sub.L << E.sub.F E.sub.L << E.sub.F Ceramic fibers Yes Not necessarily

(39) One or more of the following characteristic features of the cement of the present invention when in use as an assembling layer for building up an integral assembly of high porous honey comb filter segments are obtained: For a porosity level of the honey comb filters of 60% and higher the thermal conductivity is equal or higher than that of the porous ceramic honey comb filter material The specific heat capacity is higher or equal than that of the filter material the coefficient of thermal expansion shows a maximum deviation from that of the filter of 10% over the temperature range of 300 C.-900 C. the porosity is less than 50%, typically less than 40% the Young modulus is lower than that of the filter material

(40) All of these features are realized by a cement obtainable by drying a composition of the present invention at 100 C. and subsequently hardening at a temperature sufficiently high to transform substantially all phosphate components into metaphosphates, wherein the composition contains a bimodal mixture of inorganic particles, preferably silicon carbide or silicon nitride or mixtures thereof, a water soluble phosphate containing component, minimum one component based on a metal oxide ceramic component as the reaction partner of the phosphate, and a temporary organic component which acts as a binder. In particular this cement is obtainable from a wet mixture, comprising the inorganic powders, the phosphate containing component, water and a cellulose as the temporary binder dissolved into water, which is subsequent dried at 100 C. and then hardened at a temperature above 200 C., preferably above 350 C. In table 2, the different components of the wet mixture are listed and their functionalities are described. As described before the metal oxide ceramic powder can be replaced by oxide ceramic fibers. It is also possible, to use a mixture of oxide ceramic fibers and a metal oxide ceramic powder. The water soluble phosphate containing component can be applied by a powder (monoaluminium phosphate) or in form of a solution (acid aluminium phosphate or dissolved monoaluminium phosphate).

(41) TABLE-US-00002 TABLE 2 components and their functionality in the cement. Component Content Description non-oxide 25-35% These particles build up the main structure silicon and define the heat conductivity. It is containing preferred to use silicon carbide or silicon coarse nitride or mixtures thereof. Particles are particles in the range of 20-100 m non-oxide 25-35% These particles fill up the voids between silicon the large particles so that the porosity containing can be reduced to a minimum. It is fine preferred to use silicon carbide or silicon particles nitride or mixtures thereof. Particles are in the range of 1-20 m Water soluble 2-15% This phosphate is given in form of a powder phosphate (monoaluminium phosphate) or a liquid containing solution (acid aluminium phosphate or component dissolved monoaluminium phosphate). Together with the reaction partner and under temperature it builds a solid metaphosphate, which glues the inorganic particles together and is highly corrosion and temperature resistant. Metal oxide 3.5-20% This fine powder is the reaction partner ceramic for the phosphate containing component, powder which reacts above 200 C. to build the solid metaphosphate. It is also possible to use oxide ceramic fibers instead or in combination with the metal oxide ceramic powder. Water 20-25% Water is used to control the viscosity of the system polysaccharide 0.5-0.8% The polysaccharide component is used to component adjust the plasticity of the wet mixture and is the temporary binder after the drying step. It is preferred to use poly vinyl alcohol or a cellulose, most preferred a cellusoe ether.

(42) In a further aspect the present invention concerns a porous ceramic honey comb filter comprising at least two honey comb filter segments which segments are assembled by a cement obtainable by drying a composition of the present invention at 100 C. and subsequently hardening at a temperature sufficiently high to transform substantially all phosphate components into metaphosphates.

(43) In a still further aspect the present invention concerns a porous ceramic honey comb filter comprising at least two honey comb filter segments which segments are assembled by a cement consisting essentially of a non-oxide inorganic silicon containing component and metaphosphates and subsequently hardening at a temperature sufficiently high to transform substantially all phosphate components into metaphosphates.

(44) In a further embodiment of the porous ceramic honey comb filter, the filter consists from 4-32 filter segments, such as from 8-16 filter segments, e.g. from 16 filter segments for a round filter with 143 mm diameter as described in the examples.

(45) In a still further embodiment of the porous ceramic honey comb filter, the porosity of the filter is from 20 to 70%, such as 30 to 50%, or 55-65%.

(46) In a further embodiment of the porous ceramic honey comb filter, the filter is made of a material selected from silicon carbide and silicon nitride or mixtures thereof. Typically, the filter is made of silicon carbide, such as alpha-SiC.

(47) In a further aspect the porous ceramic honey comb filter is for use as a diesel particle filter.

(48) The porous honey comb filter of the present invention is in particular suitable for purifying exhaust gases discharged from internal combustion engines, such as diesel engines from buses and trucks, and construction machines. Such honey comb filter may be an integral part of a system for purifying exhaust gasses from internal combustion engines. Thus, in a further aspect the present invention relates to a system for purifying exhaust gasses selected from an exhaust and emission system comprising a porous ceramic honey comb filter, the filter comprising at least two honey comb filter segments which segments are assembled by a cement obtainable by drying a composition of the present invention at 100 C. and subsequently hardening at a temperature sufficiently high to transform substantially all phosphate components into metaphosphates. The above embodiments should be seen as referring to any one of the aspects (such as composition, cement, use of cement, or cement for use) described herein as well as any one of the embodiments described herein unless it is specified that an embodiment relates to a certain aspect or aspects of the present invention.

(49) All references, including publications, patent applications and patents, cited herein are hereby incorporated by reference to the same extent as if each reference was individually and specifically indicated to be incorporated by reference and was set forth in its entirety herein.

(50) All headings and sub-headings are used herein for convenience only and should not be construed as limiting the invention in any way.

(51) Any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

(52) The terms a and an and the and similar referents as used in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

(53) Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Unless otherwise stated, all exact values provided herein are representative of corresponding approximate values (e.g., all exact exemplary values provided with respect to a particular factor or measurement can be considered to also provide a corresponding approximate measurement, modified by about, where appropriate).

(54) All methods described herein can be performed in any suitable order unless other-wise indicated herein or otherwise clearly contradicted by context.

(55) The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise indicated. No language in the specification should be construed as indicating any element is essential to the practice of the invention unless as much is explicitly stated.

(56) The citation and incorporation of patent documents herein is done for convenience only and does not reflect any view of the validity, patentability and/or enforceability of such patent documents.

(57) The description herein of any aspect or embodiment of the invention using terms such as comprising, having, including or containing with reference to an element or elements is intended to provide support for a similar aspect or embodiment of the invention that consists of, consists essentially of, or substantially comprises that particular element or elements, unless otherwise stated or clearly contradicted by context (e.g., a composition described herein as comprising a particular element should be understood as also describing a composition consisting of that element, unless otherwise stated or clearly contradicted by context).

(58) This invention includes all modifications and equivalents of the subject matter recited in the aspects or claims presented herein to the maximum extent permitted by applicable law.

(59) The present invention is further illustrated by the following examples which, however, are not to be construed as limiting the scope of protection. The features disclosed in the foregoing description and in the following examples may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof.

EXAMPLES

(60) As described above a number of phosphate containing materials can be used to make a composition and cement according to this invention. The most preferable ones are phosphates, which form the pyrophosphates at temperatures above 150 C. In the following examples, a monoaluminium phosphate is used.

Example 1

(61) A wet mixture of the materials listed in table 3 has been made to make a cement for the assembling of porous ceramic honey comb filters

(62) TABLE-US-00003 TABLE 3 components and content for cement of example 1 component description content, weight-% SiC coarse grain SiC F240, ESK SiC 35% SiC fine grain SiC F800, ESK SiC 35% -Al.sub.2O.sub.3 99.9% alpha aeser 3.5% Monoaluminumphosphate Lithopix P15 from 3.0% Zschimmer & Schwarz Cellulose ether Zusoplast C 92 from 0.77% Zschimmer & Schwarz water 22.73%

(63) Using this cement highly porous honey comb filter segments made of silicon carbide have been assembled to form an assembly of 4 by 4 segments. The porosity of the filter segments was 60%, the size was for all 35 mm35 mm178 mm. All these different filter segments could be assembled without any problems, i.e. no voids or cracks occurred during drying and hardening. The wet thickness of the assembling layers was adjusted to 2 mm, the thickness varies over the whole assembly from 1.2 up to 2.5 mm. The thickness was measured at one position to monitor the changes during drying and hardening.

(64) The drying was performed at 100 C. for 1 hour and the hardening at 550 C. for 1 hour. To burn out any potential residual carbon the assembly was heated up once to 600 C. for half an hour.

(65) During drying and hardening the measured thickness in the specific point has been: Wet: 2.08 mm Dry: 1.78 mm Hardended: 1.75 mm

(66) Samples have been taken from the cement layer to measure porosity.fwdarw.result: 9.54% coefficient of thermal expansionwhich is plotted in FIG. 1 and at 700 C. the value is 4.74 10.sup.6 K.sup.1 thermal conductivity at 400 C. 4 result: 1.93 W/mK specific heat capacity at 400 C. 4 result: 1.12 J/gK

Example 2

(67) A wet mixture of the materials listed in table 4 has been made to make a cement for the assembling of porous ceramic honey comb filters

(68) TABLE-US-00004 TABLE 4 components and content for cement of example 2 component description content, weight-% SiC coarse grain F240 29.0% SiC fine grain F800 29.0% Alumo silicate fibers Unifrax FFXZ S24 10.31% -Al.sub.2O.sub.3 99.9% alpha aeser 3.42% Monoaluminumphosphate Lithopix P15 3.0% Cellulose ether Zusoplast C 92 0.68% Water 24.6%

(69) In the same way as in example 1 an assembly of 4 by 4 segments was built up.

(70) The wet thickness of the assembling layers was adjusted again to 2 mm, the thickness varies over the whole assembly from 1.0 up to 2.0 mm. The thickness was measured at one position to monitor the changes during drying and hardening.

(71) During drying and hardening the measured thickness in the specific point has been: Wet: 1.28 mm Dry: 1.15 mm Hardended: 1.12 mm

(72) Samples have been taken from the cement layer to measure porosity.fwdarw.result: 23.84% coefficient of thermal expansionwhich is plotted in FIG. 1 and at 700 C. the value is 4.44 10.sup.6 K.sup.1

Example 3

(73) A wet mixture of the materials listed in table 5 has been made to make a cement for the plugging of porous ceramic honey comb filters

(74) TABLE-US-00005 TABLE 5 components and content for cement of example 3 Component Description content, weight-% SiC fine grain F800 70% -Al.sub.2O.sub.3 99.9% alpha aeser 3.5% Monoaluminumphosphate Lithopix P15 .sup.3% Cellulose ether Zusoplast C 92 0.8% Water 22.7%

(75) This cement was used to close the channels of high porous honey comb segments with a cell density of 200 cpsi and 300 cpsi. The channel opening of the 200 cpsi honey combs has been 1.41.4 mm and that of the 300cpsi has been 1.11.1 mm. In both cases the channels could be closed very well with a penetration of the wet cement into the channel of about 5-8 mm. The drying and hardening procedure was the same as for the assembling layers in example 1 and 2.

Comparative Example 4

(76) The commercial available fiber based cement Isofrax DPF-cement from Unifrax was used to assemble an assembly of 44 filter segments in the same way as described in example 1. This assembly was dried also at 100 C. for 1 hour and then subsequently heated up to 750 C. for 1 hour.

(77) The wet thickness of the assembling layers was adjusted again to 2 mm, the thickness varies over the whole assembly from 0.8 up to 1.8 mm. The thickness was measured at one position to monitor the changes during drying and hardening.

(78) During drying and hardening the measured thickness in the specific point has been: Wet: 1.09 mm Dry: 0.51 mm Hardended: 0.49 mm

(79) The same samples have been taken from the cement layer to measure the coefficient of thermal expansionwhich is plotted in FIG. 1 and the value at 700 C. is 5.56 10.sup.6 K.sup.1

(80) As described in the examples 1, 2, and 4 honey comb segments have been assembled to an integrate unit. The segments have been a high porous silicon carbide with 60% porosity. The coefficient of thermal expansion was also measured on these segments and the result is plotted over the temperature range from 200 C. to 700 C. in FIG. 1 together with the results for the cements of examples 1, 2 and 4. The value for the coefficient of thermal expansion for the honey comb segment was at 700 C. 4.72 10.sup.6 K.sup.1, its thermal conductivity at 400 C. was 2 W/mK and the specific heat capacity at 400 C. was 1.0 J/gK.

(81) Assembled units from examples 1, 2 and 4 have been taken and heated up to a temperature of 1050 C. with a holding time of 1 hour. The assembling layer was inspected under the microscope after the hardening and after the heating step at 1050 C. The result is summarized in table 6.

(82) TABLE-US-00006 TABLE 6 evaluation of the assembling layers if the examples 1, 2, and 4 after drying and heating up to 1050 C. Result after heating Result after drying up to 1050 C. Example 1 shrinkage of 14% no further change in no voids, no cracks, no dimensions delamination from honey no voids, no cracks, no comb surface delamination from honey comb surface Example 2 shrinkage of 10% no further change in no voids, no cracks, no dimensions delamination from honey no voids, no cracks, no comb surface delamination from honey comb surface Comparative shrinkage of 53% no further change in example 4 voids, cracks dimensions but increased number of cracks and the voids became larger

(83) Table 6 clearly show, that the silica sol based cement shows already problems during drying. The increased sintering behavior at 1050 C. lead to huge voids in the assembling layer. This type of cement will lead to problems in applications, where high temperatures can occur very often, i.e. active regenerated systems with fuel burners or passenger car systems with high soot load levels.

(84) The results of table 6 are also demonstrated by the FIGS. 2-4. Pictures with a light microscope at a magnification of 20 have been taken from the assembling layers of examples 1, 2, and 4. The presence of a number of huge voids can be clearly seen in the picture for comparative example 4 in FIG. 4. Examples 1 (FIGS. 2) and 2 (FIG. 3) did not show any voids.

(85) Test Filter due to Example 1 and Comparative Example 4

(86) Test Filter 1

(87) As described in example 1 and 2 a test filter was build up by Plugging each second channel complementary on both sides of porous silicon carbide honey comb segments with a porosity of 60%, a mean pore diameter of 20 m, a cell density of 300 cpsi with a channel opening of 1.11.1 mm, using the cement described in example 3. The edge length of the filter segments has been 35 mm at a total length of 178 mm. Assembling 16 of these filter segments to a square integral assembly of 44 segments using the cement described in example 1 with a thickness of the assembly layer of 2 mm0.25 mm Drying as described in example 1 Drilling out a round shaped filter with a diameter of 143 mm Coating of the lateral surface of the filter to close the open channels using the cement described in example 1 and drying it as described in example 1 Hardening of the filter at 550 C. and heating up to 600 C. for hour.
Test Filter 2

(88) As described in comparative example 4 a test filter was build up by Plugging each second channel complementary on both sides of porous silicon carbide honey comb segments with a porosity of 60%, a mean pore diameter of 20 m, a cell density of 300 cpsi with a channel opening of 1.11.1 mm, using a cement with the following composition: SiC F800 64.5 weigh-%, cellulose ether 1 weigh-%, silica sol (45% solid content) 23.5 weight-% and water 11 weight-%. The edge length of the filter segments has been 35 mm at a total length of 178 mm. Assembling 16 of these filter segments to a square integral assembly of 44 segments using the cement described in comparative example 4 with a thickness of the assembly layer of 2 mm0.25 mm Drying as described in comparative example 4 Drilling out a round shaped filter with a diameter of 143 mm Coating of the lateral surface of the filter to close the open channels using the cement described in comparative example 4 and drying it as described in comparative example 4 Hardening of the filter at 750 C. for 1 hour.
Test:

(89) Test with artificial soot generated by a diesel burner and simulation of a thermo shock regeneration at a loading level of 10 g/l.

(90) A DPG from Cambustion was used to load the filters. The temperature inside the filters was measured with thermo couples, positioned inside the channels in the middle and 13 mm from the out let of the filter. The thermal gradient was measured over the cement layer in the middle of two inner segments (position 1) and over the crossing point of assembling layers, connecting an inner segment with 3 outer segments (position 2). The positions are shown in FIG. 5.

(91) The thermo shock test was performed by heating up the gas flow through the filter from 400 C. up to 650 C. within 40 seconds. After another 50 seconds the temperature in the middle of the filter increased to 700 C. which indicates, that the soot has started to burn. At that time, the flow rate was dropped from 190 kg/h to 45 kg/h and the gas burner was shut off. This has led to the overheating effect with peak temperatures of about 1000 C. in the middle of the inner segments.

(92) TABLE-US-00007 TABLE 7 Result for maximum temperature and thermal gradients during the thermo shock test. Soot burn max. therm. gradient over therm. gradient over Filter rate Temperature cement layer, pos. 1 cement layer, pos. 2 Filter 1 50% 1001 C. 72 C./cm 142 C./cm Filter 2 47% 1015 C. 220 C./cm 267 C./cm

(93) The thermal gradients within the filter segments have been for both filters in the range of 120-180 C./cm. The soot burn rate and the maximum temperature in the filters have been within the repeatability for both filters also the same. The only difference between both filters can be seen in the thermal gradient measured over the cement layers. The values are given in table 7. It is significant higher for filter 2 with the Isofrax cement in comparison to filter 1. This is of course the effect of the higher thermal conductivity.

(94) The inspection of the assembling layers inside the filters has been done by cutting them into slices. In case of filter 1 no damages like cracks or defects like voids could be seen.

(95) In case of filter 2 a huge number of cracks and voids in the assembling layer could be observed. Near to the region which has been the warmest during the thermo shock test the cracks in filter 2 have been severe. The cut slice broke along these cracks in the assembling layer into several parts without applying any force. In contrast to that the slices cut from filter 1 have been still stable. This is a clear indication, that the cement used for filter 2 showed sintering effects at the high temperatures, resulting in additional shrinkage. This shrinkage is a result of the used silica sol. In case of the phosphate containing cement for filter 1 no shrinkage and therefore no cracks and voids inside the assembling layer could be observed. This result corresponds very well with the 1050 C. heat-up test of the assembled honey combs (see table 6). The voids in the assembling layer of filter 2 have the same appearance as shown for the example in FIG. 4.