EP2454214A1

EP2454214A1 - Aluminium magnesium titanate composite ceramics

Info

Publication number: EP2454214A1
Application number: EP10734423A
Authority: EP
Inventors: Satoko Iwato; Rina YAMANAKA
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2009-07-15
Filing date: 2010-07-15
Publication date: 2012-05-23
Also published as: AU2010273362A1; WO2011008938A1; CN102471170A

Abstract

An aluminium magnesium titanate composite ceramic which comprising the firing raw materials, as expressed on a weight percent oxide basis, 36.0-57.0 % of TiO₂; 41.5-62.0 % of Al₂O₃; and 0-2.2 % of MgO, with the sum total of the three components adding up to 100 %, and 0-10 % of SiO₂, for forming particulate filters, with a relatively high porosity, low thermal expansion efficiency (CTE), and high mechanical strength.

Description

TITLE ALUMINIUM MAGNESIUM TITANATE COMPOSITE CERAMICS FIELD OF THE INVENTION

The present invention relates to aluminium magnesium titanate composite ceramics for forming particulate filters, which are characterized by a relatively high porosity, low thermal expansion efficiency (CTE), and high mechanical strength of which measurement are used a flexural strength, and to a process for its production.

BACKGROUND ART

Particulate filters are used to remove particulate matter (PM) such as soot and ash in exhaust gas produced by compression ignition internal combustion engines, i.e., diesel engines. In general, particles that collect on an exemplary honeycomb structure filter that traps the particles in its pores and along its walls can be removed from the filter through

regeneration, which is essentially carried out by heating or burning the PM that has been collected in the filter (by measuring a different pressure between upstream and downstream of the filter and determining if more than the predetermined amount of PM has been accumulated on the filter.)

It has long been desirable to achieve diesel particulate filter (DPF) that possess sufficient resistance to decomposition at temperature of higher than 1 ,300 ⁰C , high thermal shock resistance and high porosity.

The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:

WO2004/039747 discloses aluminium magnesium titanate having excellent mechanical strength represented by a flexural strength and having an elemental composition ratio of Al, Mg and Ti represented by a formula (T):

AI₂(I -X)Mg_xTi(I +x)Oδ (1¹)

wherein coefficient x satisfies 0.1≤ x < 1. Alkali feldspar ((Na_yKi_-y)AISi3θ8, wherein y satisfies 0≤ y < 1 ) is added to enhance sintering of aluminum magnesium titatane because of its low melting point.

Such ceramics are desired to have a low CTE as well as more excellent mechanical strength represented by a flexural strength.

U.S. Patent 5,153, 153 discloses sintered ceramic material which comprises doped aluminum titanate and mullite having the composition: 50-61.5 % AI₂O₃,36-47.5 % titanate oxide,2.5-5 % SiO₂, with the sum total of the three components adding up to 100%, and which further comprises 0.3-1 % MgO 0.015 to 0.5% iron oxide and up to 1 % impurities, being useful as particle filters in diesel engine. However, such ceramic material are time consuming and expensive to produce, and it is not possible to attain the required properties such as the porosity and thermal shock resistance through the particulate filter formation. This is because iron oxide component influences strength of aluminum magnesium titanate ceramics at high temperature. Further, it would be desirable to provide an aluminium magnesium titanate ceramic which is produced by firing at a temperature of from 1 ,400 to 1 ,700⁰C a raw material mixture comprising Al-containing compound, Ti-containing compound and Mg-containing compound, subsequently pulverizing the raw material mixture (it is typically understood that the smaller the average particle size, the better) and which achieve the desired porosity of at least 30% and thermal shock resistance (which is calculated by R(thermal shock resistance) = σ(the strength of the ceramic )(1 - V)/Eα - is proportional to the strength of the ceramic and is inversely proportional to CTE; where V is Poisson ratio, E is Young's modulus, and α is the linear CTE given by (1/ ⁰C.) for DPF application while avoiding the conventional limitations of known aluminium magnesium titanate ceramic. SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to an aluminium magnesium titanate composite ceramic of which the main component is represented by the empirical formula Mg_xAl2(i-_x) Ti(-|_+X)θ5

(wherein coefficient x satisfies 0≤ x < 0.1 ),comprising the firing raw materials, as expressed on a weight percent oxide basis, 36.0 - 57.0 % of TiO₂; 41.5 - 62.0% Of AI₂O₃; and 0 - 2.2 % of MgO, with the sum total of the three components adding up to 100%, and 0 - 10% of SiO₂ .

A second embodiment of the present invention is directed to a process for producing an aluminium magnesium titanate composite ceramic of which the main component is represented by the empirical formula Mg_xAl2(i-χ) Ti(i+_X)θ5 (wherein coefficient x satisfies 0 < x≤ 1 ), comprising the following raw materials, as expressed on a weight percent oxide basis, 36.0 - 57.0 % of TiO₂; 41.5 - 62.0% of AI₂O₃; and 0 - 2.2 % of MgO, with the sum total of the three components adding up to 100%, and 0 - 10% of SiO₂ , which comprising the firing said raw materials at a temperature not lower than 1 ,300 ⁰C.

Another embodiment of the present invention is a ceramic comprising a first component represented by the empirical formula

Mg_xAl2(i-_x) Ti(i_+X)θ5 (wherein coefficient x satisfies 0≤ x < 0.1 ) as a result of firing a mixture comprising TiO₂, AI₂O₃, MgO, and SiO₂ , as expressed on a weight percent oxide basis of 36.0 - 57.0 % of TiO₂; 41.5 - 62.0% of AI₂O₃; and 0 - 2.2 % of MgO with the sum total of the TiO₂, AI₂O₃, MgO adding up to 100%, and the addition of 0 - 10% Of SiO₂ . This ceramic has been shown to have a coefficient of thermal expansion (30- 1000 ⁰C) of less than 3x10^"6(1/K) and a porosity of at least 28% by volume of the pore space of the ceramic body. In addition, the ceramic of the present inventions has also been shown by Applicants to have a flexural strength of greater than about 8MPa according to JIS R1601. It is preferred that the ceramic of the present invention is fired at a temperature in a range from 1200⁰C to 1700⁰C.

Another embodiment of the present invention is a process for producing a ceramic comprising the following steps: a) combining TiO₂, AI₂O₃, MgO, and SiO₂ to form a mixture, as expressed on a weight percent oxide basis of 36.0 - 57.0 % Of TiO₂; 41.5 - 62.0% Of AI₂O₃; and 0 - 2.2 % of MgO with the sum total of the TiO₂, AI₂O₃, MgO adding up to 100%, and the addition of 0 - 10% of SiO₂; b) mixing the mixture; b) drying the mixture, c) firing the mixture at a temperature in a range from 1200⁰C to 1700⁰C. It is preferred that the drying step is at a temperature from 110°C to 130⁰C and the mixing occurs by a wet process in a ball mill. In addition, the mixture may include a grinding aid, a dispersant, an anti-foaming agent, or a combination of one or more thereof. The process of the present invention also may include the steps of grinding the ceramic after firing, placing the ground ceramic in a mold, and then firing the ground ceramic in the mold to create a shaped ceramic.

DETAILED DESCRIPTION OF THE INVENTION

Composition:

The aluminium magnesium titanate composite ceramic of the present invention primarily comprises, on an oxide basis, 36-57.0% Ti- containing compound, 41.5-62.0% Al-containing compound, 0-2.2% Mg- containing compound, with the sum total of the three components adding up to 100%, and 0- 10% Si-containing compound, which are formed by mixing and firing the mixture of the compounds.

The aluminium magnesium titanate composite ceramic of the present invention may optionally comprise other additives such as titanate oxide; alumina; Magnesium oxide; silica; MgAI₂O₄; mullite; and the like, provided that their presence does not appreciably or deleteriously increase the CTE of the composite ceramic.

When the TiO₂ content is below 36.0 wt%, the CTE becomes high because of the excess amount of AI₂O3. When the TiO₂ content is above 57.0 wt%, the CTE becomes high because of the excess amount Of TiO₂. In a similar way, when the AI₂O₃ content is below 41.5 wt%, the CTE becomes high because of the excess amount of TiO₂, and when the AI₂O₃ content is above 62.0 wt%, the CTE becomes high because of the excess amount Of AI₂O₃. As for MgO, when the amount of MgO is above 2.2 wt%, enough high porosity cannot be obtained. Furthermore, as for SiO₂, when the SiO₂ content is above 10 wt%, CTE becomes high.

More preferably, the aluminium magnesium titanate composite ceramic of the present invention primarily comprises, on an oxide basis, 37.5-49.0% Ti-containing compound, 50.0-61.5% Al-containing compound, 0-2.2% Mg-containing compound, with the sum total of the three

components adding up to 100%, and 0- 10% Si-containing compound.

When the lower CTE is needed in order to focus on thermal shock resistance, the aluminum magnesium titanate composite ceramic may not comprise other component such as titanate oxide; alumina; Magnesium oxide; silica; MgAI₂O₄; mullite; and the like as much as possible except for aluminum magnesium titanate itself which is represented by the empirical formula Mg_xAl2(i-χ) Ti(i+_x)Os (wherein coefficient x satisfies 0<x<0.1 ).

The amount of Si-containing compound in the ceramic material is preferably in the range of 0-7% on an oxide basis.

And when the high porosity is needed in order to focus on lower pressure loss, the aluminum magnesium titanate composite ceramic of the present invention primary comprises, on an oxide basis, 38.3-43.9% Of TiO₂, 55.5- 61.5% of AI₂O₃, 0-1.0% of MgO, with the sum total of the three

components adding up to 100%, and 0-10% SiO₂.

The titania source is a compound to be a titanium ingredient to constitute aluminium magnesium titanate, and for example, includes titanium oxide. Titanium oxide includes, for example, titanium(IV) oxide, titanium(lll) oxide, titanium(ll) oxide, etc. Preferred is titanium(IV) oxide. The crystal type of titanium(IV) oxide includes an anatase type, a rutile type, a brookite type, etc., and may be amorphous. More preferred are an anatase type and a rutile type.

The titania source includes a powder of a compound to be led to titania (titanium oxide) by firing alone in air. The compound includes, for example, titanium salt, titanium alkoxide, titanium hydroxide, titanium nitride, titanium sulfide, titanium metal, etc.

The titanium salt concretely includes titanium trichloride, titanium tetrachloride, titanium(IV) sulfide, titanium(VI) sulfide, titanium(IV) sulfate, etc. The titanium alkoxide concretely includes titanium(IV) ethoxide, titanium(IV) methoxide, titanium(IV) t-butoxide, titanium(IV) isobutoxide, titanium(IV) n-propoxide, titanium(IV) tetraisopropoxide, and their chelate compounds, etc.

The titania source is preferably titanium oxide.

The alumina source in the mixture is a compound to be the aluminium ingredient constituting aluminium magnesium titanate, and, for example, includes a powder of alumina (aluminium oxide). The crystal type of alumina includes a γ-type, a δ-type, a θ-type, an α-type and others, and may be amorphous. As the alumina, preferred is an α-type alumina.

The alumina source also includes a compound capable of being led into alumina by firing alone in air. The compound includes, for example, aluminium salt, aluminium alkoxide, aluminium hydroxide, metal aluminium, etc.

The aluminium salt may be an inorganic salt with an inorganic acid, or an organic salt with an organic acid. Concretely, the aluminium inorganic salt includes, for example, aluminium nitrate salts such as aluminium nitrate, ammonium aluminium nitrate, etc.; aluminium carbonate salts such as ammonium aluminium carbonate, etc. The aluminium organic salt includes, for example, aluminium oxalate, aluminium acetate, aluminium stearate, aluminium lactate, aluminium laurate, etc.

Concretely, the aluminium alkoxide includes, for example, aluminium isopropoxide, aluminium ethoxide, aluminium sec-butoxide, aluminium tert-butoxide, etc.

The crystal type of aluminium hydroxide includes, for example, a gibbsite type, a bayerite type, a norstrandite type, a boehmite type, a pseudo-boehmite type, etc., and may be amorphous. Amorphous aluminium hydroxide includes, for example, an aluminium hydrolyzate to be obtained by hydrolysis of an aqueous solution of a water-soluble aluminium compound such as aluminium salt, aluminium alkoxide, etc.

The alumina source is preferably alumina. The magnesia source is a compound to be a magnesium ingredient to constitute aluminium magnesium titanate, and for example, includes a powder of magnesia (magnesium oxide).

The magnesia source also includes a compound capable of being led into magnesia by firing alone in air. The compound includes, for example, magnesium salt, magnesium alkoxide, magnesium hydroxide, magnesium nitride, metal magnesium, etc.

The magnesium salt concretely includes magnesium chloride, magnesium perchlorate, magnesium phosphate, magnesium

pyrophosphate, magnesium oxalate, magnesium nitrate, magnesium carbonate, magnesium acetate, magnesium sulfate, magnesium citrate, magnesium lactate, magnesium stearate, magnesium salicylate, magnesium myristate, magnesium gluconate, magnesium dimethacrylate, magnesium benzoate, etc.

The magnesium alkoxide concretely includes magnesium methoxide, magnesium ethoxide, etc.

As the magnesia source, usable is a compound serving both as a magnesia source and an alumina source. The compound includes, for example, magnesia spinel (MgAI₂O₄).

The silica source is a compound to give a silicon ingredient to be in the aluminium magnesium titanate composite ceramic, and for example, includes silicon oxide (silica) such as silicon dioxide, silicon monoxide, etc.

The silica source also includes a powder of a compound capable of being led into silica by firing alone in air. The compound includes, for example, silicic acid, silicon carbide, silicon nitride, silicon sulfide, silicon tetrachloride, silicon acetate, sodium silicate, sodium orthosilicate, glass frit, etc. Preferred are glass frit and the like, from the viewpoint of industrial availability.

As the silica source, also usable is a compound additionally serving as an alumina source. The compound includes, for example, an aluminosilicate containing at least one element selected from Na, K and Ca and containing Si and Al. When the elemental composition of the compound is represented by a compositional formula (2): (ci Na₂O₁Ch K₂O^iCaO) Y¹AI₂O₃ ZSiO₄ (2), wherein coefficient ci , di , and ei satisfy ci +di +ei = 1 , coefficient y' satisfies 0.4 < y'≤ 1 .2 (preferably 0.6≤ y'≤ 1 .1 ), and coefficient z satisfies 6≤ z≤ 12, preferably 7≤ z≤ 1 1 . The name of aluminosilicate is feldspar, and the feldspar may be a natural substance or a synthetic product, and the synthetic product is industrially available with ease.

Furthermore, as the silica source, also usable is a compound additionally serving as a titanate source, an alumina source, and magnesium source. Example of such compound includes any of titanate source, alumina source and/or Magnesium source, coated with silica source on a surface thereof.

Production Method

The alumina source, the magnesia source and the titania source are generally used as powder.

The mixture can be obtained, for example, by mixing an alumina source, a magnesia source and a titania source. The mixing may be attained by dry process or by wet process.

In mixing, for example, an alumina source, a magnesia source and a titania source may be mixed, preferably with stirring and grinding along with grinding media in a grinding container for producing an aluminium magnesium titanate composite ceramic having a uniform composition.

In mixing the starting materials, additives such as a grinding aid, a deflocculant or a dispersant, an anti-foaming agent (defoamer which shali be understood to mean a substance that is used to reduce foaming) and the like may be added thereto. The term "dispersant" or "dispersing agent" as used herein connotes a surface-active agent that is added to

suspending media to promote uniform suspension or separation of typically extremely fine solid particles. Dispersanls suitable for purposes of the present invention may be selected from the group consisting of any anionic, cation sc or non-ionic dispersant, or combinations thereof. An example of a suitable dispersant is an isobutylene nialeic acid copolymer, Na salt, sold under the tradename Orotan™ 731 by Rohm and Haas, Examples of conventional "anti-foaming agents^" will be appreciated by those having skill in the field to which the invention pertains. A suitable antifoaming agent is a blend of modified fatty alcohols and polysiloxane sold under the tradenarne Dehydran^"™ 1620 by Cognis Corp.

The grinding aid includes, for example, alcohols such as methanol, ethanol, propanol, etc.; glycols such as propylene glycol, polypropylene glycol, ethylene glycol, etc.; amines such as triethanolamine, etc.; higher fatty acids such as palmitic acid, stearic acid, oleic acid, etc.; carbon materials such as carbon black, graphite, etc. One or more of these may be used either singly or as combined.

By firing the mixture, the aluminium magnesium titanate composite ceramic of the invention can be obtained.

For the firing, the mixture may be fired while powdery, or may be fired after shaped. The powdery mixture may be shaped, for example, according to a pressing method or the like.

The firing temperature may be generally from 1200⁰C to 1700⁰C from the viewpoint of easy production of aluminium magnesium titanate and from the practicability, preferably from 1400⁰C to 1600⁰C. The heating rate up to the firing temperature may be generally from 10°C/hr to 500°C/hr

The firing may be attained generally in air; but depending on the type and the blend ratio of the starting materials (the alumina source, the magnesia source, the titania source and optionally the silica source) to be used, the firing may be attained in an inert gas such as nitrogen gas, argon gas or the like, or may be attained in a reducing gas such as carbon monoxide gas, hydrogen gas or the like. During the firing, the water vapor pressure in the atmosphere may be reduced.

In general, the firing is attained using an ordinary firing furnace such as a tubular electric furnace, a boxy electric furnace, a tunnel furnace, a far-IR furnace, a microwave heating furnace, a shaft furnace, a

reverberating furnace, a rotary furnace, a roller hearth furnace, etc. The firing may be attained by batch process or by continuous process, and may be attained in a static mode or a fluidized mode. The time to be taken for the firing may be a time enough for production of aluminium magnesium titanate from the mixture, and may vary depending on the amount of the mixture used, the type of the firing furnace, the firing temperature, the firing atmosphere and others, but may be generally from 10 minutes to 24 hours. Generally, the firing temperature is at least 1 ,200⁰C.

The grinding and classification may be conducted by general methods such as a ball mill, a media mill, a roll mill, a hammer mill, a pin mill, a jet mill, a planetary mill, a vibrating mill, grinding by hands or by a mortar. The obtained grind aluminum magnesium titanium powders may be classified by general classification methods.

The average particle size (D50) of the powder of aluminum magnesium titanium composite ceramics is about 10 to 60 micron meters.

More preferably, 15 to 45 micron meters.

The composite ceramic can have a coefficient of thermal expansion (RT30-1000 ⁰C) of less than 3x10^"6(1 /K). The CTE (30 -

1000⁰C) can range from -3x10^"6 to 3x10^"6 (1/K).

The composite ceramic can have a porosity of at least 28%, specifically at least 30% by volume as a measure of the percent volume of pore space of the fired ceramic. The percent volume can range from 25 to 60% by volume.

The composite ceramic can have a flexural strength of greater than about 8 MPa according to JIS R1601. The flexural strength can range from 6 MPa to 40 MPa.

TEST METHODS

The testing methods and standards used to obtain the results in the Tables 1 to 3 comprise the following:

Porosity: Porosity (percent by volume) with respect to a rectangular shaped specimen of 3 mm x 4 mm x 40 mm, which was cut out from the second sintered shaped ceramic, was calculated by the following:

(volume of the specimens - (weight of the specimens/absolute specific gravity=3.8g/cm³)/volume of the specimens) x 100 %. Coefficient of Thermal Expansion (CTE): CTE with respect to a rectangular shaped specimen of 3 mm x 4 mm x about 20mm, which was cut out from the sintered shaped ceramic, was measured using thermal analysis measurement device such as Thermo Plus Evo commercially available from Rigaku Corporation. The specimens were heated from room temperature (22-25 deg.C) up to 1300 deg.C at 20 deg.C/min under air condition. From the inclination of the thermal expansion curve between 30 and 1000 deg.C, the CTE was calculated.

Flexural strength: three point method on 3mm x 4mm x 40mm specimens of second sintered ceramic body made of the material according to the present invention using JIS R1601

Average Particle size (D₅₀) of each material: D₅₀ was measured using a laser diffraction technique such as LA-920 commercially available from Horiba Ltd.; is calculated using JIS R16222 and 1629

EXAMPLES

The invention is described in detail with reference to the following Examples; however, the invention should not be limited by these

Examples.

Application Example 1 , 2 & Comparative Examples 1 and 2:

The following titanium oxide powder, α-alumina powder and magnesium oxide, of which the components were as shown in Table 1 ,with the sum total of the three components adding up to 100%, and 5 parts by mass of silica powder, 1.5 parts by mass of Orotan 731 (sold by Rohm & Haas)(10% aq.) as dispersantjsobutylene maleic acid copolymer, Na salt, 0.2 parts by mass of a blend of modified fatty alcohols and polysiloxane sold under the tradename Dehydran™ sold by Cognis Corp (10% aq.) as antifoam agent and 100 parts by mass of water were put into a grinding container along with alumina balls (diameter 15 mm), and stirred and mixed by wet process in a ball mill for 5 hours. Then the mixture was dried at 120 deg.C for about 12 hours to get raw material mixture.

α-alumina powder: AI2O3, Sumitomo Chemical, "AES-12" Titanium oxide powder: TiO2, DuPont, "R-900".

Magnesium oxide: MgO, Konoshima Kagaku K.K.,

tradename "StarMagL".

Silica powder: Fukushima feldspar

Dispersing agent: Orotan (trade mark)731 ( (10% aq.),isobutyiene rnaleic acid copolymer, Na salt, commercially available from Rohm & Hass.

Anti-foaming agent: Dehydran TM 1620, a blend of modified fatty alcohols and a poiysiioxane from Cognis Corp., Ambler, PA.

The obtained raw material mixtures were put in aluminum saggers, and were fired in a boxy electric furnace under the below profiling in the air. After cooling the sintered materials to room temperature, aluminum magnesium titanate composite ceramics were obtained.

Room Temperature(RT) - 1450deg.C, where RT is room temperature (about 20 to 25°C) for 30 hours

Keeping at 1450deg. C 4 hours

1450deg.C - Room temperature Standing to cool

The obtained sintered material was ground and classified to get grind powder with average grain size of about 24 micron meter. 10 g of the obtained grind powder was taken out, and put into a rectangular mold with the size of 10 mm x 10 mm x 50 mm, and pressed under a shaping pressure of 120 kgf/cm², thereby giving a shaped ceramic. The shaped ceramic was again fired in air in a boxy electric furnace under the firing temperature and time as shown in the Table 1 , thereby giving a second sintered shaped ceramic.

By using the second sintered shaped ceramic obtained in the above, a rectangular shaped specimens of 3 mm x 4 mm x 40 mm and 3 mm x 4 mm x 20 mm was cut out. Porosity, CTE and flexural

measurement are carried out as described above. The results are summarized in Table 1.

As shown in the Table 1 , Application Example 1 and 2 which has MgO contents of 0 to 2 wt% achieved low CTE below 2 x 10^"6/K and high porosities around 30 % by volume. On the other hand, Comparative example 1 which has MgO contents of about 5 wt% showed high CTE around 4 x 10^"6/K while keeping 30% porosity. Furthermore, Comparative example 2 which is the same composition as Comparative example 1 , except that, the firing time was 10 hours showed low porosity around 19% by volume while it showed low CTE.

Thus, when the amount of MgO was high, high porosity and low CTE are incompatible. Consequently, MgO contents of 0 to about 2 wt% are preferred.

Table 1

Application Examples 3 to 5 & Comparative Example 3:

Application Example 3 to 5 and Comparative Example 3 were carried out in the same manner as in Example 1 to 2, except that, the compositions and the firing temperature of shaped ceramics were as shown in Table 2.

As shown in the Table 2, Application Example 3, 4 and 5 which have an AI₂O₃ content below 62wt% achieved high porosity above 28% by volume, low CTE below 2 x 10^"6/K and high above 8 MPa simultaneously. On the other hand, Comparative Example 3 which has the AI₂O₃ content above 62 wt% resulted in high CTE of 3.5 x 10^"6/K.

Therefore, the composition range of 41.5 to 62.0 wt% Of AI₂O₃ and 36.0 to 57.0 wt% of TiO₂ is preferred. Especially, when the low CTE is important, Application Example 3 is preferred.

Table 2

Application Examples 6 to 8 & Comparative Example 4:

Application Example 6 and 7 and Comparative Example 4 were carried out in the same manner as in Example 1 and 2, except that, the compositions and firing temperatures of shaped ceramics were as shown in Table 3. Application Example 8 was carried out in the same manner as in Example 1 and 2, except that, TiO2 powder with SiO2 coating (about 5wt%) was used instead the silica powder and the composition and firing temperature of shaped ceramics were as shown in Table 3.

Application Example 7 of which component is 36.0-57.0 wt% of TiO₂, 41.5-62.0 wt% Of AI₂O₃, 0-2.2 wt% of MgO and 0-10 part by mass of SiO₂ on an oxide basis showed extremely high porosity. Furthermore, Application Example 8 which doesn't use silica powder but uses TiO2 powder with silica coating showed very low CTE of 1.3 x 10^"6/K and kept above 8 MPa.

Table 3

Claims

CLAIMS What is claimed is:

1. A ceramic comprising a first component represented by the empirical formula Mg_xAl2(i-χ) Ti(i+χ)Os (wherein coefficient x satisfies 0≤ x < 0.1 ) as a result of firing a mixture comprising TiO₂, AI2O3, MgO, and SiO2 , as expressed on a weight percent oxide basis of 36.0 - 57.0 % of TiO₂; 41.5 - 62.0% Of AI₂O₃; and 0 - 2.2 % of MgO with the sum total of the TiO₂, AI₂O₃, MgO adding up to 100%, and the addition of 0 - 10% of SiO₂ .

2. The ceramic according to claim 1 having a coefficient of thermal expansion (30-1000 ⁰C) of less than 3x10^"6(1/K).

3. The ceramic according to claim 1 having a porosity of at least 28% by volume of the pore space of the ceramic body.

4. The ceramic according to claim 1 having a flexural strength of greater than about 8MPa according to JIS R1601.

5. The ceramic according to claim 1 wherein the firing is at a temperature in a range from 1200⁰C to 1700⁰C.

6. A process for producing a ceramic comprising the following steps:

a) combining TiO₂, AI₂O₃, MgO, and SiO₂ to form a mixture, as expressed on a weight percent oxide basis of 36.0 - 57.0 % of TiO₂; 41.5 - 62.0% of AI₂O₃; and 0 - 2.2 % of MgO with the sum total of the TiO₂, AI₂O₃, MgO adding up to 100%, and the addition of 0 - 10% of SiO₂;

b) mixing the mixture;

b) drying the mixture,

c) firing the mixture at a temperature in a range from 1200°C to 1700⁰C.

7. The process of claim 6, wherein the drying occurred at a

temperature from 110°C to 130°C.

8. The process of claim 6, wherein the mixing occurs by a wet process in a ball mill.

9. The process of claim 6, wherein the mixture further comprises a grinding aid, a dispersant, an anti-foaming agent, or a combination of one or more thereof.

10. The process of claim 6, wherein the ceramic is ground after firing to produce a ground ceramic, placing the ground ceramic in a mold, and then firing the ground ceramic in the mold to create a shaped ceramic.