CN1063411C - Method of preparing (ALxOx+Tibx) foamed ceramic filter by self-overgrowth high-temp. synthesis control - Google Patents

Abstract

The present invention relates to a method for preparing a (AlxO2+TiB2) foamed ceramic filter by SHS control, which belongs to the field of material. The method is characterized in that the reacting material powder of Al, TiO2 and B2O3 which can carry out an SHS reaction is taken according to stoichiometry, 1 to 20% of additive is added, a body is directly formed by being pressed, the physical property of a product of the body is controlled b controlling the density of the body so that the product has good heat resistance (more than 1000 DEG C), the porosity is 50 to 80%, the pore diameter is from 0.1mm to 0.5mm, and the product has the required characteristics of electric conductivity and microwave absorbability. The product has the advantages of short sintering time, simple process, no need of high-temperature sintering furnaces, good high-temperature property, good refractoriness (more than 1800 DEG C) and low cost.

Description

Self-propagating high temperature synthesis controlled preparation (Al)2O3+TiB2) Method for manufacturing ceramic foam filter

The invention relates to a soot foamed ceramic filter for an internal combustion engine and a production method thereof, belonging to the field of preparation and application of filter products.

The diesel engine has better dynamic property and low oil consumption, so the diesel engine is widely applied to the modern society that energy is increasingly tense. But the exhaust gas contains a large amount of soot particles, and the mass concentration of the soot particles is dozens of times of that of the gasoline engine. With the increasing emphasis on environmental quality, countries in the world have established more and more strict emission regulations to limit the emission of soot particles in diesel engines, and technically, the removal of particles from diesel engine exhaust by using a ceramic foam filter or a wall-flow ceramic filter is one of the most representative methods, so that the research on ceramic filters and production methods thereof is an important content of research of technologists.

Since soot particulates are accumulated in the filter during filtration of the filter, it is necessary to periodically remove the particulates to restore the filter to an original operation state, that is, to regenerate the filter. The regeneration process of the filter actually utilizes heat energy to burn off particles deposited in the filter, the regeneration technology can be divided into two categories of regeneration by utilizing the self energy of an internal combustion engine and regeneration by utilizing external energy according to different heat sources, the regeneration of the filter by only relying on the self energy of the internal combustion engine is very difficult, so that the exhaust gas filter of the internal combustion engine is forced to be subjected to thermal regeneration by external energy, and the regeneration efficiency of the electric self-heating regeneration and the microwave regeneration is higher than that of other heating modes, so that the regeneration method which is most applied at present is provided. The electric self-heating regeneration technology is that the filter body is directly used as an electric heating element to electrify and heat the filter body, the carbon smoke particles deposited on the filter body are heated and burnt, and the filter regeneration mode requires that the filter material has certain conductivity: the microwave heating regeneration technology is to utilize microwave energy to heat, so as to burn carbon smoke particles, and during microwave heating, a filter material is required to have certain microwave absorption performance.

The soot particulate filter and the material thereof for internal combustion engines, which have an ideal service life and are favorable for regeneration, should have at least the following characteristics of 1) good thermal shock resistance and high mechanical performance index, 2) good thermal stability and capability of bearing high thermal load, 3) high filtration efficiency and capability of effectively trapping and purifying particulate matters, and 4) required conductivity or microwave absorption characteristic to meet the requirements of regeneration technology.

The carbon smoke filter of the internal combustion engine, which is produced and used more in the prior art, is mainly made of cordierite, aluminum oxide, chrome corundum or silicon carbide, and the problems of poor high temperature resistance and short service life mostly exist in the integral view of the filter. The refractoriness of cordierite is only 1200-1300 ℃, the thermal conductivity coefficient is small, the cordierite is non-conductive, the cordierite cannot be regenerated by utilizing electric self-heating, the microwave absorption performance is poor, the heating temperature rise rate is low in the regeneration process, and the cordierite is not beneficial to filter regeneration. The aluminum oxide has poorer microwave absorption performance and higher thermal expansion coefficient, and during filtering and regeneration, larger internal stress is easily generated in a filter body due to temperature change, so that the material is damaged. The chromium steel jade foamed ceramic filter is still in a trial-manufacture stage, the manufacturing process is difficult to meet the uniformity of the micropore diameter, and the quality is unstable. The silicon carbide filter has good quality, but is difficult to prepare and high in cost.

The foamed ceramic filter produced by the prior art has the problems of unsatisfactory material components, largely unsatisfied performance, long production period and complex production process, the porosity and the pore diameter of the filter produced generally cannot be directly controlled, but are determined by the pore diameter of polyurethane foamed plastic, and the foamed ceramic material with pores smaller than 0.3mm cannot be prepared. The chinese patent office 1992, month 10 and 14, discloses a patent application entitled "ceramic foam material filter and method of making the same," which is filed under the number 92102883.0. The main component of the material is Al₂O₃、SiO₂Or with addition of a small proportion of ZrO₂The process is realized by four steps of slurry preparation, impregnation, drying and sintering. In the preparation of the slurry, Al is selected₂O₃、SiO₂Or with addition of part of ZrO₂Then, Y is added₂O₃And bentonite and carboxymethyl celluloseThe preparation method comprises the following steps of 1) relatively more process steps, high sintering temperature, long production period and high cost, 2) the porosity and pore size of the filter cannot be directly controlled, 3) the high-temperature compressive strength is low, the thermal shock resistance is poor, and 4) the microwave absorption performance of the filter material is poor and the filter material does not have the required conductivity.

The objects and tasks of the invention are: in order to overcome the defects that the prior art for preparing the foamed ceramic filter 1) has complex production method, 2) has long production period, 3) has poor product performance, 4) has short service life and the material system does not have ideal performance required by regeneration technology, and 1) the Self-propagating High-temperature Synthesis (SHS) is utilized to prepare the TiB of the new material system₂+Al₂O₃The method comprises the following steps of (1) simplifying a preparation process of the foamed ceramic filter, (2) simplifying a preparation process of the filter, and (3) enabling the filter material to have conductivity or microwave absorption performance required by a regeneration technology, and (4) controlling the aperture and porosity of a product, so that the production of the foamed ceramic filter with the aperture of 0.1-0.5 mm is realized, and particularly, the technical solution of the invention is provided for the production of the foamed ceramic filter with the aperture of 0.1-0.3 mm.

TiB₂Not only has high melting point, high hardness, excellent corrosion resistance and oxidation resistance, but also has good electrical conductivity and thermal conductivity which are beyond those of other ceramic materials, while Al₂O₃Also has high melting point, high hardness, good chemical stability, but no conductivity, and substantially no absorption of microwave. One of them alone does not satisfy the performance requirements of the filter material for internal combustion engines, and if they are organically combined, an ideal filter having good high-temperature performance and easy implementation of regeneration techniques can be produced. Because the two materials are high melting point and chemically stableGood-performing material, TiB₂Has a melting point of approximately 3000 ℃ and Al₂O₃Has a melting point of over 2000 ℃, and can not be organically combined to form a good-performance material at a temperature of below 2000 ℃ by a prior art sintering method of heating a binder and an activator to manufacture 2000 DEG CThe above high temperature sintering furnace is difficult, and thus mass production of TiB using the prior art is difficult₂+Al₂O₃Ceramic foam filters are not possible.

The invention is based on the principle that the SHS reaction process, the formation of foamed ceramic material, is a highly exothermic chemical reaction process, and utilizes The adiabatic reaction temperature is more than 2000 deg.C, after a certain quantity of additive is added, the necessary energy, i.e. a certain temp. is supplied to system to induce the local chemical reaction of system, then said chemical reaction process is continued under the support of self-released high heat quantity, and finally the combustion reaction wave is spread to whole system so as to control the preparation of required TiB₂+Al₂O₃The foamed ceramic filter has good high-temperatureperformance and required conductivity and microwave absorption performance so as to meet the requirements of the use and regeneration technology of the soot filter of the internal combustion engine.

The basic idea of the invention is that the SHS reaction is utilized, the powder material of the formula of the invention which can complete the SHS reaction does not need to add water and adhesive, and does not need any carrier, the resistivity and the microwave absorption performance of the powder material are controlled by adding the additive with high melting point, and the green body which meets the requirements is directly prepared by controlling the density of the green body, and then the prepared green body is put in a furnace, and the SHS method is utilized to directly ignite to complete the task of the invention.

The self-propagating high-temperature synthesis control preparation A provided by the invention₂O₃+TiB₂A method of making a ceramic foam filter, comprising: production of Al₂O₃+TiB₂The component formula of the foamed ceramic filter is as follows: measuring Al + TiO with the granularity of more than 200 meshes according to the chemical weight₂+B₂O₃The reactant powder and the amount of the reactant powder is 1-20% of the total weight of the reactantsMelting point metal powder Cr, Ti, Zr, or Al₂O₃、SiO₂、ZrO₂Additive powder of ceramic powder; preparation of Al₂O₃+TiB₂The blank of foamed ceramic filter is prepared with the mixture of reactant powder and additive powder and through direct pressing, and has controlled density d_kIs the theoretical density D of the filter material passing through the foamed ceramic₀And the experimental parameters were determined to be d_k=0.20D₀～0.50D₀+ 5% -10%; production of Al₂O₃+TiB₂The process of the foamed ceramic filter comprises the steps of uniformly mixing reactant powder and additive powder in a formula in a ball mill for 15-20 minutes, and directly pressing the mixture in a die by a limiting method to obtain a required blank body shape and density d_kThen, the blank is put into a furnace to be heated to the actual ignition reaction temperature TK, and at the temperature, oxygen-acetylene flame or metal W, Mo wire is used for electric heating to carry out sintering ignition to complete the self-propagating high-temperature synthesis reaction process, namely the prepared Al product₂O₃+TiB₂A ceramic foam filter.

The invention is further characterized in that Al is produced₂O₃+TiB₂Ceramic foam filters, the porosity of which is controlled by the density d of the green body_kControlling the control density of the blank to be d when the porosity of the filter is required to be 65-80 percent_k=0.20D₀～0.35D₀+ 5-10%, when the porosity of the filter is required to be 50-65%, the control density of the blank is d_k=0.35D₀～0.50D₀+ 5% -10%; under the condition of porosity of 50-80%, adding different high-melting-point metal additives Cr, Ti, Zr or ceramic additives Al₂O₃、SiO₂、ZrO₂To control Al₂O₃+TiB₂Electricity of foamed ceramic filterThe resistivity is determined by the method when the resistivity of the filter is required to be (1-10) × 10^-4In ohm meter, metal additives Cr or Ti or Zr or Cr + Ti + Zr or any two of them are added into the mixture, the amount is 1-10 Wt%, or when requiredThe specific resistance of the filter is (1-10) × 10^-3In ohm's, the ceramic additive Al should be added into the mixture₂O₃Or SiO₂Or ZrO₂Or Al₂O₃＋SiO₂+ZrO₂Or any two of them, the total amount of which is 1-20%.

The porosity of the foamed ceramic material is generally in inverse proportion to the density, so that when the porosity is required to be in a higher range of 65-80%, experiments determine the control density d of the blank_kCorresponds to 0.20D₀～0.35D₀An interval; when the porosity is required to be in a lower range of 50-60%, the control density d of the blank is determined through experiments_kCorresponds to 0.35D₀～0.50D₀Interval: 5% 10% is for a small volume shrinkage of the material from liquid to solid. The resistivity of the material is adjusted to be (1-10) x 10 by adding conductive metal powder and non-conductive ceramic powder^-4Eumm and (1-10) × 10^-3The range of ohm meters.

The key technology for realizing the invention is as follows: determination of the actual firing temperature Tk, control of green body density, porosity and pore size, and filter performance.

The method for determining the actual ignition temperature Tk comprises the following steps: weighing Al and TiO with the granularity of more than 200 meshes according to the chemical weight₂And B₂O₃Reactant powder and additives accounting for 1-20 wt% of the total weight of the reactants, and the additive is applied to delta H DEG according to the thermal effect of the reactants reacting at 25 ℃ by using the principle of thermodynamics₂₉₈Design the preheating temperature T by adjusting the reaction_0cSo that the adiabatic reaction temperature Tad is not lower than Al₂O₃Melting point 2303K, at which Al in the product₃O₃Including additives with melting points below 2303K, are completely melted. Preheating temperature T according to design_0cDetermining the actual firing temperature Tk of the sintering of the green body, and taking Tk = T_0c+ 300-400 ℃, generally Tk = T_0c+350 ℃. And (4) carrying out ignition operation at the actual ignition temperature Tk to realize the preparation of the foamed ceramic material by using an SHS method.

The method of determining Tk according to the invention will now be described with respect to the general course of the SHS reaction:

calculated by thermodynamic equilibrium equationThe principle is that, assuming the reaction is taking place under adiabatic conditions and 100% of the reactants are undergoing the stoichiometric exothermic SHS reaction, the heat evolved is Δ H °₂₉₈All for heating the product, then, if the reaction takes place at 25 ℃, i.e. under standard conditions, there are:

-ΔH°₂₉₈=∑n_j(H°_Tad-H°₂₉₈)_{i products}

In the formula (H degree)_Tad-H°₂₉₈) Is the relative enthalpy of mol of a substance

n_iMol number of product

ΔH°₂₉₈Thermal effect of reaction at-ambient temperature of 25 DEG C

The physical meaning of the above formula is: the SHS reaction, the thermal effect or enthalpy change of the highly exothermic chemical reaction, heats the product to Tad, i.e., the total amount of enthalpy change of the product from 25 ℃ to the adiabatic temperature Tad is equal to the thermal effect of the reaction.

If, the reactants are preheated to T_0cTemperature, i.e. non-standard, and remixing to react, there are:

∑n_i(H°_T0c-H°₂₉₈)_{i reactant}-ΔH°₂₉₈=∑n_i(H°_Tad-H°₂₉₈)_{i products}

The essential significance of the above formula is that the thermal effect Δ H ° at normal temperature of the standard state for applying the SHS reaction₂₉₈Conveniently calculated, T of the SHS reactant achieved by preheating according to Gauss's law_0cWhen the temperature is reduced to 298K, the heat emitted by the heat-absorbing material is equal to the heat absorbed by the heat-absorbing material, and the sum of sigma n is used_i(H°_T0c-H°₂₉₈)_{i reactant}Expressed, due to the assumed adiabatic process, the heat and thermal effect Δ H °₂₉₈All is absorbed by the product, thereby increasing the temperature of the product.

When additives are added and preheated to T_0cAt temperature, the reaction equilibrium equation becomes:

in the formula n_jThe mol number of additions

n_kMol number of product

For the SHS reaction of the present invention: design preheating temperature T_0cThe calculation of (c) and the control process of the actual ignition temperature Tk are exemplified as follows:

separately adding Al accounting for 10 percent of the total weight of reactants₂O₃For example, 10% Al is added₂O₃The reduced mol number is 0.706, and the preheating temperature T is designed for the reaction at the moment_0cThe adiabatic reaction temperature Tad is made to be equal to or higher than Al₂O₃Melting point 2303K, Al in the product₂O₃ComprisingAl as an additive₂O₃Complete dissolution, Tad =2303K, calculation of T_0cThe formula of (1) is:

from this equation, T is calculated_0c=444K, temperature error range in the above calculation is ± 5 ℃. Determining the actual firing temperature Tk of the sintering of the green body, and taking Tk = T_0c+350=794K=521℃。

When Tad is lower than the volatilization temperature of the additive and the product, the total weight of the substances before and after the reaction is kept unchanged, and the volume of the blank and the volume of the product are basically unchanged, so that the density of the blank before the reaction indirectly reflects the actual density and porosity of the product, and is closely related to the pore size of the product, thereby controlling the density of the blank during the SHS reaction, and simultaneously controlling the porosity and pore size of the product. Control of the Density d of the inventive bodies_kThe determination method of the porosity and the pore diameter of the foamed ceramic filter comprises the following steps:

theoretically, the theoretical density and porosity of the product can be directly obtained according to the actual density of the blank. If the total weight of the materials before and after the reaction is kept unchanged and the volume of the blank is completely the same as that of the product, the density of the blank before the reaction is the actual density of the product after the reaction, and the porosity of the product can be obtained according to the theoretical density of the product. Due to the fact that SHS is reversedThe volume shrinkage of the blank is about 5 percent before and after the process, and 5 to 10 percent of closed pores exist in the product, so that the density and the porosity deviate from the theoretical resultAnd (4) poor. The invention is based on the experiment and according to the theoretical density D of the product₀Giving control of the density d by the green body_kA method for controlling product porosity, comprising: when d is_k=0.2 D₀～0.35D₀+ 5% to 10%, the corresponding porosity of the product after the ignition reaction is 65% to 80%: when d is_k=0.35 D₀～0.5D₀And when the content is 5-10 percent, the corresponding porosity of the product after the ignition reaction is 50-65 percent.

Controlled density d of the green body_kIs the ratio of the weight to the volume of the blank powder before the SHS reaction, the theoretical density of the product can be calculated according to the components of the product, and Al is used₂O₃+TiB₂The concrete calculation method for the foam ceramic material is as follows: without the addition of additives, the actual composition of the product is 5Al₂O₃+3TiB₂When converted to a weight ratio, Al₂O₃∶TiB₂= 710: 210 based on Al₂O₃And TiB₂The theoretical density of the product can be calculated by the following method: taking Al according to the physical property data of the material₂O₃Has a theoretical density of 3.9g/cm³、TiB₂Has a theoretical density of 4.5g/cm³Theoretical density D of the product₀The calculation formula of (A) is as follows: $D_0=\frac{5W_{A{l}_2{O}_3}+3W_{\mathrm{Ti}{B}_2}}{\frac{5W_{A{l}_2{O}_3}}{d_{{\mathrm{Al}}_2{O}_3}}+\frac{3W_{\mathrm{Ti}{B}_2}}{d_{\mathrm{Ti}{B}_2}}}=\frac{5\×102+3\×70}{5\×102/3.9+3\×70/4.5}=4.06/c{m}^3$ in the formula (I), the compound is shown in the specification,is Al₂O₃And TiB₂The molecular weight of (a) is,

is Al₂O₃And TiB₂The theoretical density of (a) of (b),

the theoretical density of the final product can be calculated in the same way as described above when the additives are added.

The relationship between the green body control density and the pore size of the foamed ceramic filter is as follows: the larger the density of the blank is, the fewer the pores among the particles are, and the smaller the pore diameter of the product after the SHS reaction is, in the invention, when the density of the blank is controlled to be 25-40% of the theoretical density of the product, namely d_k=0.2 D₀～0.35D₀When the density is 5-10%, the aperture of the product after the ignition reaction is phi 0.25-phi 0.5mm, and when the blank density is controlled to be 40-55% of the product density, namely d_k=0.35 D₀～0.5D₀And when the pore diameter is + 5% -10%, the pore diameter of the product after the ignition reaction is phi 0.1-phi 0.25mm, and in conclusion, the density of the blank body is controlled, and the porosity and the pore diameter of the SHS reaction product are also controlled.

Al prepared by the invention₂O₃+TiB₂A ceramic foam filter, the product mainly comprises Al₂O₃And TiB₂In which Al is₂O₃Is non-conductive, TiB₂Is a material with good conductivity and the resistivity thereof is 10^-8An order of magnitude. Although the integral filter isa porous material, experimental results show that under the condition of no additive, the pore diameter and the porosity of the material have little influence on the resistivity and the microwave absorption performance of the material, and the additive has larger influence on the resistivity and the microwave performance. Thus, Al produced by the present invention₂O₃+TiB₂The foamed ceramic filter is characterized in that the resistivity and the microwave absorption performance of the filter are controlled by adding 1-10% of metal powder additives or 1-20% of ceramic powder additives.

The production process of the filter comprises the following steps: the ingredients of the formula are evenly mixed in a ball mill and directly pressed into a required blank body shape and density d in a die_kThen placing in a furnace, heatingTo the actual ignition reaction temperature TK, and at the temperature, using oxygen-acetylene flame or metal W, Mo wire to electrically heat for sintering ignition, completing the SHS reaction process, thus preparing the present inventionBright Al₂O₃+TiB₂A ceramic foam filter.

The main advantages of the invention are: 1) simple process, no high-temperature sintering equipment, no need of adding water and binder in material formula, direct forming of blank, energy and investment saving, low cost, 2) greatly shortened production period, generally sintering time of only 10-40 seconds, 3) prepared Al₂O₃+TiB₂The foam ceramic filter has good high temperature resistance and thermal shock resistance, the refractoriness is more than 1800 ℃,4) the high temperature strength is high, the compression strength at 1000 ℃ is 2-5 MPa,5) the foam ceramic material with the aperture of 0.1-0.5 mm can be prepared by controlling, 6) Al₂O₃+TiB₂Ceramic foam filters have desirable electrical resistivity and microwave absorption properties.

The details of the invention are further illustrated below with reference to specific examples of the invention:

example 1:

a foamed ceramic filter for an internal combustion engine exhaust gas purification test has the following performance requirements: the pore diameter is 0.1mm, the porosity is more than 60%, the refractoriness is more than 1200 ℃, the compressive strength at normal temperature is 4.0MPa, the high-temperature thermal shock resistance is more than 50 times at 1000 ℃, the filter is regenerated by adopting an electric self-heating regeneration mode, and the electrical resistivity of the filter is required to be (1-4) multiplied by 10^-3The Eumm, the size is phi 150 x 50mm, the prior art can not prepare the foamed ceramic filter, the preparation method of the invention is adopted, the steps are as follows:

first, preparing the ingredients

The filter material is made of Al₂O₃And TiB₂Composition according to SHS reaction equation: meanwhile, the weight of the foamed ceramic filter can be roughly calculated to be about 1500 g according to the size and approximate density of the foamed ceramic filter, so that 200-270-mesh commercial supply powder is respectively taken, wherein the weight of Al powder is 540g, and the weight of TiO powder is 540g₂Powder 480g, B₂O₃420g of powder, additive Al₂O₃Accounting for 10 wt% of the total amount of the reactants, 144g of the mixture is taken, and no water or any binder is added. Directly putting the powder into a ball millMixed for 20 minutes to prepare the required powder, and the total weight of the powder is 1584 grams.

Second step, green body preparation

To calculate the theoretical density, 10% Al is added₂O₃The mol number of the additive is 0.705, so that the final composition of the product is 5.705Al₂O₃+3TiB₂Taking Al₂O₃Has a theoretical density of 3.9g/cm³、TiB₂Has a theoretical density of 4.5g/cm³The theoretical density D of the product₀The calculation formula of (A) is as follows: $D_0=\frac{5.705W_{A{L}_2{O}_3}+3w_{\mathrm{Ti}{B}_2}}{\frac{5.705W_{{\mathrm{Al}}_2{O}_3}}{d_{A{l}_2{O}_3}}+\frac{3W_{\mathrm{Ti}{B}_2}}{d_{\mathrm{Ti}{B}_2}}}=\frac{5.705\×102+3\×70}{5.705\×102/3.9+3\×70/4.5}=4.03g/\mathrm{cm}$

the porosity of the common foam material is in a larger range, and the operability is good. Because the porosity of the filter is required to be more than 60 percent, the green body control density is controlled by d_k=0.35D₀～0.50D₀+ 5% -10% determination, taking blank out and controlling density d_k=0.4D₀+ 10%, calculate d_k=1.69g/cm³。

The product size is phi 150 multiplied by 50mm, and the volume can be calculated to be 883.1cm³The weight of the powder of the blank is 883.1 x 1.692=1494.2 g, which is the volume of the blank, 1500 g of powder can be taken out in consideration of actual loss and convenient operation, and the rest of powder is stored and reused. Due to a small amount of volume shrinkage, an A3 steel die with the inner diameter of 150.2mm, the outer diameter of 180mm and the height of 110mm is taken, 1500 g of powder is put into the die, and the powder is pressed into a phi 150.2 multiplied by 50 shape by a limiting method. Taking out the blank and controlling the density d_kIs 1.69g/cm³The foamed ceramic material green body is prepared.

Third, the ignition temperature is determined

According to thermodynamic calculation, the system addsAdditive Al₂O₃After that, Al is formed₂O₃And added Al₂O₃All melt, therefore, the design preheat temperature is calculated as T, taking the system Tad =2303K_0c=444K, take T_0c+300 as the actual firing temperature of the blank, i.e. TK =744K =471 ℃.

The fourth step, sintering operation

Putting the prepared green body of the foamed ceramic material into a box-type resistance furnace, heating to 471 +/-5 ℃, electrically heating by using a W wire with the diameter of 0.5mm at the temperature, and igniting one end of the green body, wherein the voltage of the W wire is 40V and the current is 50A. One end is ignited, the combustion wave rapidly expands to the unreacted area for about 33 seconds, the SHS reaction is completed, and the required foam ceramic material filter is prepared.

The fifth step, product detection

The filter prepared by detection has the pore diameter of 0.08-0.14 mm and the porosity of 62 percent, and comprises the following effective components: al (Al)₂O₃73.5％,TiB₂26.5%, the filter has a normal temperature compressive strength of 4.3MPa, a thermal shock resistance of more than 50 times at 1000 deg.C, a refractoriness of more than 1600 deg.C, and a resistivity of 3.7 × 10^-3The Eumm has good filtering effect when being applied to a tail gas purification test of an internal combustion engine.

Example 2:

the performance requirements of the foamed ceramic filter for the automobile exhaust purification test are as follows: the pore diameter is 0.35mm, the porosity is more than 70%, the refractoriness is more than 1400 ℃, the compressive strength at normal temperature is 3.6MPa, the high-temperature thermal shock resistance is more than 50 times at 1000 ℃, the regeneration is carried out by adopting a microwave heating regeneration mode, the microwave loss coefficient is 0.4-0.6, the dielectric constant is 23-28, the size requirement is phi 60 x 40, the prior art can not prepare the foamed ceramic filter, and the preparation method disclosed by the invention comprises the following steps:

first, preparing the ingredients

According to the SHS reaction equation: meanwhile, the weight of the foam ceramic filter can be roughly calculated to be about 150 g according to the size and the approximate density of the foam ceramic filter, and therefore, 200E to E are respectively taken135g of 270 mesh Al powder, TiO₂120g of powder, B₂O₃105g of powder, wherein the additive is that Zr and Cr respectively account for 5 wt% of the total amount of the reactants, and 18g of the powder is taken respectively without adding water or any binder. The powder is directly put into a ball mill to be mixed for 20 minutes to prepare the required powder, and the total weight is 396 g.

Second step, green body preparation

5% Zr and 5% Cr are added as additives, the mol number of Zr is 0.376 and that of Cr is 0.692, so that the final composition of the product is 5Al₂O₃+3TiB₂+0.376Zr +0.692Cr, the theoretical density of which can be calculated: d₀=4.27g/cm³Taking the controlled density d of the blank_k=0.4D₀+ 5%,calculate d_k=1.79g/cm³。

The product size is phi 60 multiplied by 40, and the volume can be calculated to be 113.0cm³The weight of the powder of the green body is calculated to be 113 × 1.79=202.3 g, 204 g of the powder can be actually taken, and the rest of the powder can be stored and reused. Considering a small amount of volume shrinkage, an A3 steel mold with an inner diameter of 60.1mm, an outer diameter of 75mm and a height of 75mm is taken, 204 g of powder is put into the mold, and the powder is pressed into a phi 60.1X 40 shape by a limiting method. Taking out the blank and controlling the density d_kIs 1.79g/cm³The foamed ceramic material green body is prepared.

Third, the ignition temperature is determined

According to thermodynamic calculation, Al is generated after the system is added with additives₂O₃And all the added Zr and Cr are melted, therefore, taking the system Tad =2303K, the designed preheating temperature is calculated as T_0c=204K, take T_0c+350 as the actual firing temperature of the blank, i.e. TK =554K =281 ℃.

The fourth step, sintering operation

Putting the prepared green body of the foamed ceramic material into a box-type resistance furnace, heating to 281 +/-5 ℃, electrically heating by using a W wire with the diameter of 0.5mm at the temperature, and igniting one end of the green body, wherein the voltage of the W wire is 40V and the current is 50A. One end is ignited, the combustion wave rapidly expands to the unreacted area for about 30 seconds, the SHS reaction is completed, and the required foam ceramic material filter is prepared.

The fifth step, product detection

The filter prepared by detection has the pore diameter of 0.16-0.24 mm and the porosity of 62 percent, and comprises the following effective components: al (Al)₂O₃64.45％,TiB₂26.5 percent, 4.55 percent of Zr and 4.55 percent of Cr, the normal-temperature compressive strength of the filter is 4.3MPa, the heat shock resistance at 1000 ℃ is more than 50 times, the refractoriness is more than 1500 ℃, the microwave loss coefficient is 0.52, the dielectric constant is 25.4, and the filter has good filtering effect when being applied to the tail gas purification test of an internal combustion engine.

The following examples 3 and 4 are similar to examples 1 and 2 in preparation steps, and therefore, the preparation steps of the examples are briefly described, and refer to examples 1 and 2. Only an analysis of the key control parameters of the preparation and the final product composition is given for the following examples 3, 4, 5.

Example 3:

a foamed ceramic filter for internal combustion engine exhaust gas purification, the performance requirements of which are as follows: the pore diameter is 0.4mm, the porosity is 80%, the refractoriness is more than 1100 ℃, the compressive strength at normal temperature is 4.0MPa, the high-temperature thermal shock resistance is more than 50 times at 1000 ℃, the filter is regenerated by adopting an electric self-heating regeneration mode, and the electrical resistivity of the filter is required to be (5-10) multiplied by 10^-3The Eumm, the size requirement is phi 150 x 70mm, and the control parameters and steps are briefly described as follows:

the additive is Zr accounting for 1 percent of the total weight of the reaction materials, and according to thermodynamic calculation, when Tad =2303K in the system, the preheating temperature T is designed_0c=155K, the actual green body firing temperature Tk =155+400=655K, i.e. 382 ℃.

The procedure of example 1 or 2 was followed to produce a ceramic foam filter having the following effective components: al (Al)₂O₃70.1％,TiB₂28.9 percent of Zr, 1.0 percent of Zr, 0.37 to 0.43mm of pore diameter and 84 percent of porosity, the normal-temperature compressive strength of the filter is 4.2MPa, the heat shock resistance at 1000 ℃ is more than 50 times, the refractoriness is more than 1300 ℃, and the resistivity is 7.85 multiplied by 10^-3The Eumm has good filtering effect when being applied to a tail gas purification test of an internal combustion engine.

Example 4:

a ceramic foam filter for purifying the tail gas of IC engine has the following performance requirements: the pore diameter is 0.5mm, the porosity is 80%, the refractoriness is more than 1200 ℃, the compressive strength at normal temperature is 4.0MPa, the high-temperature thermal shock resistance is more than 50 times at 1000 ℃, the regeneration is carried out by adopting a microwave heating regeneration mode, the microwave loss coefficient is 0.2-0.4, the dielectric constant is 10-16, the size requirement is phi 150 x 65, the prior art can not prepare the foamed ceramic filter, and the preparation method disclosed by the invention comprises the following steps:

the additive is Al₂O₃And SiO₂Each account for 10 percent of the total weight of the reaction materials, and according to thermodynamic calculation, when the Tad =2303K of the system, the preheating temperature T is designed_0c=645K, the actual green body ignition temperature Tk =645 +300 =945K, i.e. 672 ℃.

The procedure of example 1 or 2 was followed to produce a ceramic foam filter having the following effective components: al (Al)₂O₃67.35％,TiB₂24.3％,SiO₂8.35 percent, the pore diameter is 0.48-0.52 mm, the porosity is 81 percent, the normal-temperature compressive strength of the filter is 4.34MPa, the heat shock resistance at 1000 ℃ is more than 50 times, the refractoriness is 1350 ℃, the microwave loss coefficient is 0.29, the dielectric constant is 14.7, and the filter has good filtering effect when being applied to the tail gas purification test of the internal combustion engine.

It should be noted that about 1% of impurities in the reactants were not included in the calculation of the composition of the examples, and this effect was not considered in the thermodynamic calculation.

Claims (3)

1. Self-propagating high-temperature synthesis control preparation of Al₂O₃+TiB₂A method of making a ceramic foam filter, comprising:

a)Al₂O₃+TiB₂the component formula of the foamed ceramic filter is as follows: measuring Al + TiO with the granularity of more than 200 meshes according to the chemical weight₂+B₂O₃The reactant powder and high-melting-point metal powder Cr, Ti, Zr or Al accounting for 1-20% of the total weight of the reactants₂O₃、SiO₂、ZrO₂Of ceramic powdersThe additive powder material is added into the mixture,

b) preparation of Al₂O₃+TiB₂The blank of foamed ceramic filter is prepared with the mixture of reactant powder and additive powder and through direct pressing, and the blank has density dk controlled via the theoretical density D of the foamed ceramic filter material₀And experimental parameters determined as dk =0.20D₀～0.50D₀+5％～10％，

C) Production of Al₂O₃+TiB₂The process of the foamed ceramic filter comprises the steps of uniformly mixing reactant powder and additive powder in a formula in a ball mill for 15-20 minutes, directly pressing the mixture into a required blank body shape and density dk in a die by a limiting method, then heating the blank body in a furnace to an actual ignition reaction temperature Tk, and performing sintering ignition by using oxygen-acetylene flame or metal W, Mo wire electric heating at the temperature to complete a self-propagating high-temperature synthesis reaction process, wherein the product is the prepared Al₂O₃+TiB₂A ceramic foam filter.

2. Self-propagating high-temperature synthesis control Al preparation according to claim 1₂O₃+TiB₂Method for manufacturing a ceramic foam filter, characterized in that Al is produced₂O₃+TiB₂The porosity of the ceramic foam filter is controlled by the control density dk of the blank, and when the porosity of the filter is required to be 65-80%, the control density dk of the blank is =0.20D₀～0.35D₀+ 5% -10%: when the porosity of the filter is required to be 50-65%, the control density of the green body is dk =0.35D₀～0.50D₀+5％～10％。

3. Self-propagating high-temperature synthesis control Al preparation according to claim 1₂O₃+TiB₂The method for manufacturing the foamed ceramic filter is characterized in that under the condition that the porosity is 50-80%, different high-melting-point metal additives Cr, Ti and Zr or ceramic additives Al are added₂O₃、SiO₂、ZrO₂To control Al₂O₃+TiB₂The resistivity of the foamed ceramic filter is determined by the following method,when the resistivity of the filter is required to be (1-10) × 10^-4In ohm meter, adding metal additives Cr or Ti or Zr or Cr + Ti + Zr or any two of them into the mixture, wherein the amount of the metal additives is 1-10 Wt%; or when the specific resistance of the filter is required to be (1-10) x 10^-3In ohm's, the ceramic additive Al should be added into the mixture₂O₃Or SiO₂Or ZrO₂Or Al₂O₃+SiO₂+ZrO₂Or any two of them, the total amount of which is 1-20%.