CN1063410C - Method of preparing foamed ceramic material by self-overgrowth high-temp. synthesis control - Google Patents

Abstract

In the field of materials, a method for preparing foamed ceramic materials controlled by self-propagating high-temperature synthesis (SHS), including taking two or more than two phases according to stoichiometry, can carry out SHS reaction and produce part of the reactant powder; add 1~ 40% additives, sintering is completed by SHS method at TK temperature; the feature is: the formula powder is directly pressed into a green body after mixing, and the prepared foam ceramic material can control its porosity from 50 to 80%. , the aperture is 0.1 ~ 0.5mm. The main advantages are ① short sintering time, ② simple process, no high-temperature sintering furnace is required, ③ good high-temperature performance of the product, and the refractoriness is greater than 1800 ° C, and ④ low cost.

Description

A method for preparing foamed ceramic materials using self-propagating high-temperature synthesis control

The invention relates to the preparation of foam ceramic materials and belongs to the field of materials.

Ceramic foam has good high temperature resistance, developed surface and high activity, and can be widely used in industrial fields such as internal combustion engine exhaust gas filtration and chemical catalyst carrier. Therefore, the study of foamed ceramic materials has always been a frontier topic of research and discussion by material scientists.

On August 28, 1995, China Patent Office accepted the patent application titled "A Method for Preparation of Foamed Ceramic Material by Self-propagating High-temperature Synthesis", and its application number is 95111958.3. The technical route of this patent is: the preparation of foamed ceramic materials by the self-propagating high-temperature synthesis (SHS) method, and the process is realized through four steps of slurry preparation, impregnation, drying and sintering . In slurry preparation, two or more kinds of reactant powders with a particle size greater than 200 mesh are added stoichiometrically, which can carry out SHS reaction and produce a part of the reactant powder with a theoretically calculated value of liquid phase amount θ ₀ , including 1 to 1 40wt% additive, after adding the binder, according to the proportion of the slurry, after adding water, stir evenly to form a slurry; it will be used as a slurry carrier and polyurethane with a pore size of φ0.3～3.0mm The foam plastic is made into the required size and shape, and it is immersed in the slurry for about 10-15 minutes, and the excess slurry is taken out and squeezed out; the polyurethane foam body adhered to the mixture slurry is heated to 200 ~ Dry at 300°C to volatilize the foam and shape the green body; the sintering process is completed by the SHS method. In the completed SHS reaction, the liquid phase amount θ ₁ or θ _1c controlled in the system is 40-80Wt%; The actual ignition temperature for green body sintering by SHS reaction is Tk, and the preparation process is completed by electric heating and ignition with metal W wire or Mo wire at Tk temperature. This invention overcomes the shortcomings of the prior art that can only sinter foam ceramic materials in high-temperature furnaces, and produces foam ceramic materials with short production cycle, relatively simple process, low cost, refractoriness greater than 1800°C and good high-temperature performance, but It also has the following disadvantages: there are relatively many process steps, the porosity and pore size of the prepared finished product can only be determined by the pore size of polyurethane foam, the porosity and pore size cannot be controlled, and it is impossible to prepare foam ceramics with pores less than 0.3mm Material.

The purpose and task of the present invention are: to overcome the many steps in the preparation of foamed ceramic materials in the prior art, and the inability to control the porosity and pore size of the product, and to prepare a simple material formula, simplify the preparation process of the green body, and control the pore size and pores of the product High-efficiency foamed ceramic materials, in order to use the SHS reaction to realize the production of foamed ceramic materials with a pore size of 0.1 to 0.5 mm, especially for the production of a 0.1 to 0.3 mm pore size ceramic foam material, the technical solution of the present invention is proposed.

The present invention is based on the SHS reaction process, and the formation of the foamed ceramic material is a principle of a highly exothermic chemical reaction process. The SHS method is used to provide the necessary energy to the system, that is, under the premise of a certain temperature, to induce a local chemical reaction in the system, and then , because this chemical reaction process continues under the support of its own high heat release, and finally, the characteristics of spreading the combustion reaction wave to the entire system and the characteristics of the experimental relationship between the actual density of the green body and the pore size and porosity of the foam ceramic product, Thereby controlling the preparation of the required ceramic material.

The basic idea of the present invention is to use the SHS reaction to directly prepare the powder that meets the requirements by controlling the density of the green body without adding water and binder or any carrier. The body of the preparation is then placed in the furnace, and the SHS method is used to directly ignite to realize the task of the present invention.

The present invention proposes a method for preparing foamed ceramic materials using self-propagating high-temperature synthesis control, which mainly includes: according to stoichiometry, two or more kinds of particles with a particle size greater than 200 mesh are selected, which can perform SHS reaction and generate a part of the liquid phase. Theoretical calculation The reactant powder of Ti+B or Zr+Cr ₂ O ₃ or Al+TiO ₂ +C or Al+TiO ₂ +B ₂ O ₃ or Al+Cr ₂ O ₃ with a value of θ ₀ and accounts for 1 ～40wt% refractory metal Ti, Cr, Zr, Mo, W powder and ceramic Al ₂ O ₃ , SiO ₂ , ZrO ₂ and SiC powder additives; green body production and sintering methods; self-propagating The 40-80% liquid phase amount θ ₁ or θ _1c controlled in the system in the high-temperature synthesis reaction, and the actual ignition temperature Tk of green body sintering determined by the preheating temperature T ₀ or T _0c , are characterized in that: the green body It is formed by direct pressing after uniform mixing of reactant powder and additive powder. The control density d _k of the green body is determined by the theoretical density D ₀ of the product foam ceramics and the experimental parameters, which is d _k =0.20 D ₀ ~0.5 D ₀ +5%～10%; when the corresponding porosity of the product after reaction is required to be 65～80%, the control density of the green body is d _k =0.2 D ₀ ～0.35D ₀ +5%～10%; When the corresponding porosity of the product after the reaction is 50-65%, the control density of the green body is d _k =0.35D ₀ -0.5D ₀ +5%-10%. The production process of controlling the preparation of foamed ceramic materials is as follows: uniformly mix the materials of the formula of the present invention in a ball mill for 15 to 20 minutes, directly press them into the required shape and density d _k of the green body in the mold with the limit method, and then put the green body The body is placed in a furnace, heated to the actual ignition reaction temperature Tk, and at this temperature, sintered and ignited by electric heating with an oxygen-acetylene flame or metal W and Mo wires, and the self-propagating high-temperature synthesis reaction process is completed, and a foam ceramic material is produced. product.

The specific control range in which the additives added in the ingredients of the present invention account for 1 to 40 wt% of the total weight of the reactants is: for the Ti+B system, Zr, Mo, and W metal powder additives accounting for 1 to 10 wt % of the total weight of the reactants are added And Al ₂ O ₃ , ZrO ₂ ceramic powder additives accounting for 1-15 wt% of the total weight of the reactants, but when mixed and added, the total amount of the two should be 1-15 wt%; for Zr+Cr ₂ O ₃ system, add Al ₂ O ₃ , SiO ₂ ceramic powder additives accounting for 10-30wt% of the total weight of the reactants; for the Al+TiO ₂ +C system, add Ti, Cr, Zr accounting for 1-10wt% of the total weight of the powder , Mo, W metal powder additives and Al ₂ O ₃ , SiO ₂ ceramic powder additives accounting for 1-15wt% of the total weight of the reactants, but when mixed and added, the total amount of the two should be 1-15wt% ; For the Al+TiO ₂ +B ₂ O ₃ system, add Ti, Cr, Zr, Mo, W metal powder additives accounting for 1-10 wt% of the total weight of the reactants and Al ₂ accounting for 1-20 wt% of the total weight of the reactants O ₃ and SiO ₂ ceramic powder additives, but when mixed and added, the total amount of the two added should be 1-20wt%: for the Al+Cr ₂ O ₃ system, add 20-40wt% of the total weight of the reactants Al ₂ O ₃ , SiO ₂ , SiC ceramic powder additives; the upper limit and lower limit of the design preheating temperature T ₀ of the green body or the minimum preheating design temperature T _0c are all guaranteed to exist in the system when the SHS reaction is carried out. Under the premise of ~80% liquid phase amount θ ₁ or θ _1c , it is calculated by thermodynamics. In the SHS reaction of the green body, the 40-80% liquid phase amount θ ₁ or θ _1c controlled in the system is calculated based on the theoretical calculation value of the liquid phase amount θ ₀ , and by controlling the type and amount of additives, after thermodynamic calculation and Determined by experiments; the green body control liquid phase amount θ ₁ or θ _1c should be in the range of 40 ~ 80wt%, specifically; for Ti+B and Zr+Cr ₂ O ₃ systems, θ ₁ or θ _1c should be controlled at 40 ～60Wt% range to calculate T ₀ or T _0c , for Al+TiO ₂ +C system, should control θ ₁ or θ _1c in the range of 50～70Wt% to calculate T ₀ or T _0c : for Al+TiO ₂ + For B ₂ O ₃ system and Al+Cr ₂ O ₃ system, θ ₁ or θ _1c should be controlled in the range of 60-80wt% to calculate T ₀ or T _0c ; In the case of a specified amount of additives, if the preheating temperature changes continuously, the controlled liquid phase quantity θ ₁ also changes continuously within the specified range, and the controlled liquid phase quantity θ ₁ can reach the upper limit and the specified range of the preheating temperature. The lower limit, the upper limit and the lower limit are the upper limit and lower limit of the design preheating temperature T ₀ , Tk should take the average value of the upper limit and lower limit of the design preheating temperature T ₀ ; when adding a specified amount of additives, if the preheating temperature Continuous change, as the temperature rises, the controlled liquid phase quantity θ ₁ cannot reach the upper limit of the specified liquid phase quantity, but can only make θ ₁ reach a stable value θ _1c within the specified liquid phase quantity range, and make all The minimum preheating temperature at which the liquid phase quantity θ ₁ is controlled to reach this fixed value θ _1c is the minimum design preheating temperature T _0c , then Tk should be T _0c plus 300-400°C, usually 350°C.

In order to complete the preparation process of the present invention, the actual ignition temperature Tk of the green body for the SHS reaction is determined under the premise that the amount of additives added under the specified conditions is satisfied so that the specified liquid phase amount is reached during the SHS reaction. For this reason, the determination of Tk should be clearly defined as follows:

① Firstly, the theoretical adiabatic temperature Tad and part of the theoretical liquid phase quantity θ ₀ produced by the SHS reaction when the chemical reaction is carried out at 25°C under the standard state are calculated by using the thermodynamic equilibrium equation,

②Secondly, by adding 1 to 40% of additives to achieve the control of the SHS reaction, there is a specified liquid phase amount θ ₁ or θ _1c of 40 to 80Wt%, and then use the thermodynamic balance equation to calculate the green body Design preheating temperature T ₀ or T _0c

③Finally, according to the design preheating temperature T ₀ or T _0c of the green body, the actual ignition temperature Tk of the final green body during the SHS reaction is determined.

Now illustrate the calculation process of the present invention with respect to the general process of SHS reaction:

The principle of using the thermodynamic equilibrium equation is to assume that the reaction occurs under adiabatic conditions, and the reactant 100% undergoes an exothermic SHS reaction according to stoichiometry, and the heat ΔH° ₂₉₈ released by it is all used to heat the product, then, if The reaction occurs under the standard state at 25°C, then:

-ΔH° ₂₉₈ =∑n _i (H° _Tad -H° ₂₉₈ ) _{i product}

In the formula (H° _Tad -H° ₂₉₈ )- is the relative enthalpy of substance mol

n _i - number of moles of product

Reaction thermal effect at ΔH° ₂₉₈ -25°C

The physical meaning of the above formula is: SHS reaction, that is, the thermal effect or enthalpy change of a highly exothermic chemical reaction, which raises the temperature of the product to Tad, that is, the total enthalpy change of the product from 25°C to the adiabatic temperature Tad is equal to the thermal effect of the reaction .

If the reactant is preheated to T ₀ or T _0c under the non-standard state of temperature, then mix and react, there is:

∑n _i (H° _{TO or Toc} -H° ₂₉₈ ) _{i reactant} -ΔH° ₂₉₈ =∑n _i (H° _Tad -H° ₂₉₈ ) _{i product}

The substantive significance of the above formula is that, in order to apply the thermal effect ΔH° ₂₉₈ of the SHS reaction at normal temperature in the standard state, and to facilitate calculation, according to Gaiss’ law, when the SHS reactant is reduced from T ₀ or T _0c achieved by preheating to 298K, The heat released by it is equal to the heat absorbed by it, represented by ∑n _i (H ° _{TO or Toc} -H ° ₂₉₈ ) _{i reactant} , since it is assumed to be an adiabatic process, this heat and thermal effect ΔH ° ₂₉₈ are all produced by the product Absorption, thereby increasing the temperature of the product.

When an additive is added and preheated to T ₀ temperature, the reaction equilibrium equation becomes:

∑n _j (H° _TO -ΔH° ₂₉₈ ) _{j additive} + ∑n _i (H° _TO -ΔH° ₂₉₈ ) _{i reactant -} ΔH° ₂₉₈ = ∑n _k (H° _Tad -H° ₂₉₈ ) _{k generated substance} +∑n _j (H° _Tad -H° ₂₉₈ ) _{j additive}

In the formula, n _j - the mol number of the additive

n _k - number of moles of product

In the specific calculation, it must be noted that the adiabatic temperature Tad of the SHS reaction and the theoretical liquid phase θ ₀ are closely related to the heat effect of the reaction and the melting point of the product. Now, substance A and substance B react to form substance AB, and the reaction formula is: As an example, to illustrate, if the melting point of AB is T _m(AB) and its latent heat of fusion is △H _m(AB) , then there are three situations for the calculation of Tad and θ ₀ :

In the first case, if:

where C _PS(AB) -AB solid heat capacity

At this time, the thermal effect is small, and when the SHS is completed, the product AB is still solid without melting, and the liquid phase quantity θ ₀ =0, Tad<Tm(AB), the calculation formula is:

In the second case, if:

可求出AB熔化份数，即液相量θ₀第三种情况，若 $-\mathrm{\&Delta;}{H}_{298}>{\&Integral;}_{298}^{T_{m\left(\mathrm{AB}\right)}}{C}_{\mathrm{ps}\left(\mathrm{AB}\right)}\mathrm{dT}+\mathrm{\&Delta;}{H}_{m\left(\mathrm{AB}\right)}$ At this time, the thermal effect ΔH° ₂₉₈ is relatively large, and when the SHS is completed, the product AB is partially melted, Tad=T _m(AB) , and the calculation formula is:

The number of melting parts of AB can be obtained, that is, the liquid phase amount θ ₀ In the third case, if $-\mathrm{\&Delta;}{h}_{298}>{\&Integral;}_{298}^{T_{m\left(\mathrm{AB}\right)}}{C}_{\mathrm{ps}\left(\mathrm{AB}\right)}\mathrm{dT}+\mathrm{\&Delta;}{h}_{m\left(\mathrm{AB}\right)}$

At this time, the thermal effect is large, and when the SHS is completed, the product is completely melted, and Tad>T _m(AB) , the calculation formula is: $-\mathrm{\&Delta;}{h}_{298}={\&Integral;}_{298}^{T_{m\left(\mathrm{AB}\right)}}{C}_{\mathrm{ps}\left(\mathrm{AB}\right)}\mathrm{dT}+\mathrm{\&Delta;}{h}_{m\left(\mathrm{AB}\right)}+{\&Integral;}_{298}^{\mathrm{Tad}}{C}_{\mathrm{ps}\left(\mathrm{AB}\right)}\mathrm{dT}$

where C _PL(AB) -AB liquid heat capacity

In the present invention, the above-mentioned calculation method and the implementation control parameters of each reaction system are listed in the attached table 1. Now use the following two examples (A) and (B) in Attached Table 1 to briefly explain the calculation of Attached Table 1 and the determination of its control parameters:

(A)

(B)

1) Calculate Tad and θ ₀ :

The adiabatic temperature Tad and the theoretical value θ ₀ of the product liquid phase amount are data at 25°C without additives. For formula (A), it can be seen from the trial calculation that it belongs to the second case mentioned above, that is, after the reaction of SHS, Tad is equal to the melting point of the product TiB ₂ 3193K, TiB ₂ is partially melted, and the thermodynamic formula for calculating θ ₀ is:

In the formula -TiB ₂ solid hot melt

_-TiB2 heat of fusion

θ ₀ -TiB ₂ melt fraction wt% is calculated: θ ₀ =35%

For formula (B), it can be seen from trial calculation that after the SHS reaction, Al ₂ O ₃ is completely melted, TiB ₂ is solid, and $\mathrm{Tad}>T_{m\left({\mathrm{al}}_2{o}_3\right)},$ It is similar to the third case mentioned above, the amount of liquid phase can be calculated from the molten Al ₂ O ₃ , considering the heat of fusion and phase transition, after calculating Tad=2465K, Al ₂ O ₃ is completely melted in the reaction, It accounts for 70.8% of the total system, that is, θ ₀ =70.8%

2) Calculate T ₀ or T _0c :

In order to ensure that θ ₁ = 40-80%, when adding 1-40% of additives, calculate T ₀ or T _0c value, at this time, you can add one kind of additives alone or mix multiple additives,

For formula (A), in order to ensure that the system controls the liquid phase amount θ ₁ =40-60%, the additive in the SHS reaction should be 100% melted, and part of TiB ₂ is in a molten state. Therefore, the reaction Tad is the melting point of TiB ₂ , That is Tad=3193K. At this time, the SHS reaction is carried out at different preheating temperatures, and the amount of liquid phase is designed to change continuously between 40% and 60%. Therefore, for (A) formula, taking the addition of 10% Al ₂ O ₃ as an example of the reactant alone, The method of calculating T ₀ is, based on the molar molecular weight of TiB ₂ , the amount of Al ₂ O ₃ that should be added is 7.0 to be converted into a molar fraction of 0.686, the system Tad=3193K, Al ₂ O ₃ is completely melted in the reaction, and according to the thermodynamic equilibrium equation, Calculated by computer, when θ ₁ =40%, the lower limit of T ₀ is 770K. When θ ₁ =60%, the upper limit of T ₀ is 1020K, that is, when the preheating temperature changes between 770K and 1020K, the liquid phase of the system is Varies between 40 and 60%.

Taking (B) formula as an example again below, explaining that metal and pottery are added together, obtain the situation of T _0c , account for reactant gross weight 5%Cr and 10%SiO with adding for _example :

When the system reacts without additives at 25°C, Tad=2465K, θ ₀ =70.8%. After adding additives, when the SHS reaction is carried out at the design preheating temperature, when the design preheating temperature is increased to make Tad>2303K, that is, the melting point of Al ₂ O ₃ , and then continue to increase the design preheating temperature, it can be seen that Tad is greater than 2303K to 3193K, that is, within the melting point of Al ₂ O ₃ and TiB ₂ , the liquid phase is a stable fixed value θ _1c , and θ _1c =74.6%, so this system is only calculated so that θ _1c =74.6% The minimum design preheating temperature T _0c at this time, at this time, Al ₂ O ₃ is completely melted, take Tad=2303K, when calculating, according to the total mol molecular weight of the reactants in the system, the weight of SiO ₂ added is converted into a mole fraction of 1.2mol , the weight of Cr added is converted into a mole fraction of 0.692mol, and T _0C =417K can be calculated from the thermodynamic equilibrium equation.

The formula for calculating T _0c above is:

In the formula, the heat required for solid-state phase transition is not expressed, but it has been taken into account in the calculation. From this formula, the programming computer calculates T _0c = 417K. In the above calculation, the temperature error range is ±5°C.

3) Determination principle of Tk:

When adding a specified amount of additives, Tk takes the average value of the upper limit and lower limit of the design preheating temperature T ₀ that can make the controlled liquid phase θ ₁ reach the specified range or takes the controlled liquid phase θ ₁ to a fixed value θ _1c The minimum design preheating temperature T _0c plus 300 ~ 400 ℃. The empirical method of taking T _0c plus 300-400°C for Tk is: for the Zr+Cr ₂ O ₃ system, generally take the lower limit, that is, take Tk=T _0c +300°C, and for the Al+TiO ₂ +C system, generally take the upper limit, That is, take Tk=T _0c +400°C, for the Al+TiO ₂ +B ₂ O ₃ system, generally take the average value, that is, take Tk=T _0c +350°C.

The key to realizing the idea of the present invention and preparing ideal foamed ceramics is the determination of the green body control density d _k and the process control of the prepared foamed ceramics, that is, the porosity and aperture of the product foamed ceramics are achieved through the control of the green body density. Control, and finally ignite at Tk temperature to complete the SHS reaction.

The system completes the SHS reaction. When Tad is lower than the volatilization temperature of the additive and the product, the total weight of the substance before and after the reaction remains unchanged, and the volume of the green body and the volume of the product are basically unchanged. Therefore, the density of the green body before the reaction indirectly reflects the actual density of the product. Density and porosity are closely related to the pore size of the product at the same time. Therefore, the density of the green body is controlled during the SHS reaction, and the porosity and pore size of the product are also controlled at the same time. The specific instructions are as follows:

Theoretically, according to the actual density of the green body, the theoretical density and porosity of the product can be directly obtained. If the total weight of the substance remains unchanged before and after the reaction, and the volume of the green body is exactly the same as that of the product, then the density of the green body before the reaction is the actual density of the product after the reaction, and the porosity can also be obtained according to the theoretical density of the product. Because the green body has about 5% volume shrinkage before and after the actual SHS reaction, and there are 5% to 10% closed pores in the product, resulting in deviations from the theoretical results in density and porosity. On the basis of experiments, the present invention provides a method for controlling the porosity of the product by controlling the density d _k of the green body according to the theoretical density D ₀ of the product, that is, when d _k =0.2D ₀ ~0.35D ₀ +5%~10% , the corresponding porosity of the product after the ignition reaction is 65%-80%; when d _k =0.35 D ₀ ～0.5D ₀ +5%-10%, the corresponding porosity of the product after the ignition reaction is 50%-65%.

为Al₂O₃和TiB₂的分子量，

为Al₂O₃和TiB₂的理论密度，The control density d _k of the green body is the ratio of the weight to the volume of the green body powder before the SHS reaction. The theoretical density of the product can be calculated according to the product composition. Taking Al ₂ O ₃ +TiB ₂ ceramic foam material as an example, the specific calculation method is as follows: When no additives are added, the actual composition of the product is 5Al ₂ O ₃ +3TiB ₂ , converted into a weight ratio, Al ₂ O ₃ : TiB ₂ =710:210, according to the theoretical density of Al ₂ O ₃ and TiB ₂ , The theoretical density of the product can be calculated. The calculation method is: according to the physical performance data of the material, the theoretical density of Al ₂ O ₃ is 3.9g/cm ³ , the theoretical density of TiB ₂ is 4.5g/cm ³ , and the theoretical density of the product is D The calculation formula of ₀ is: ${\mathrm{D.}}_0=\frac{{5W}_{A{l}_2{o}_3}+3W_{\mathrm{Ti}{B}_2}}{\frac{5W_{A{l}_2{o}_3}}{d{\mathrm{Al}}_2{o}_3}+\frac{3W_{\mathrm{Ti}{B}_2}}{\mathrm{dT}{B}_2}}=\frac{5\&times;102+3\&times;70}{5\&times;102/3.9+3\&times;70/4.5}=4.06g/c{m}^3$ In the formula,

are the molecular weights _{of Al2O3} and _TiB2 ,

is _the theoretical density of _Al2O3 and _TiB2 ,

After adding the additives, the theoretical density of the final product can be calculated by the same method as above.

The relationship between the control density of the green body and the product aperture is: the greater the density of the green body, the less the pores between the particles, and the smaller the aperture of the product after the SHS reaction. In the present invention, when the control density of the blank is 25% of the theoretical density of the product %～40%, that is, when d _k =0.2D ₀ ～0.35D ₀ +5%～10%, the pore diameter of the product after the ignition reaction is φ0.25～φ0.5mm, when the blank control density is 40%～55% of the product density %, that is, when d _k =0.35 D ₀ ～0.5D ₀ +5%～10%, the pore diameter of the product after the ignition reaction is φ0.1～φ0.25mm. In summary, the density of the green body is controlled, and at the same time The porosity and pore size of the SHS reaction product are controlled.

The process of the present invention is: uniformly mix the formulation of the material of the present invention in a ball mill for 15 to 20 minutes, then press the mixed powder in a mold to form a body of foamed ceramic material, and then directly place the body In the furnace, heat to the actual ignition reaction temperature Tk, and at this temperature, sinter and ignite with oxygen-acetylene flame or metal W, Mo wire electric heating, complete the SHS reaction process, and make the product, and finally, repair the product Ready to use after passing the test.

Using SHS reaction to prepare foamed ceramic materials, the designed liquid phase amount θ ₁ or θ _1c in the system, the type and amount of additives, the design preheating temperature T ₀ or T _0c of the green body and the actual SHS reaction The range of ignition temperature Tk is listed in Attached Tables 1 to 6, and will not be listed here.

Table 1 is the process parameters of the SHS reaction for the preparation of foamed ceramic materials. The table records in detail 5 kinds of equations for carrying out SHS reaction, theoretical parameters, process control parameters and control quantities.

Table 2 is Calculation example of process parameter control for preparation of ceramic foam material by system. calculated in detail in the table The system uses the SHS reaction to prepare foamed ceramic materials. In the designed system, the amount of different liquid phases θ ₁ and in order to ensure the amount of θ ₁ , different types and different amounts of additives are controlled, the design preheating temperature T ₀ of the green body and the The relationship between the actual ignition temperature Tk of the SHS reaction.

Table 3 is Calculation example of process parameter control for preparation of ceramic foam material by system. The designed liquid phase amount is calculated in detail in the table. With the change of the type and amount of additives, the fixed value θ _1c tends to be stable, and in order to ensure the amount of θ _1c , the different amounts of additives controlled, the minimum of the green body Design the relationship between the preheating temperature T _1c and the actual ignition temperature Tk for SHS reaction.

Table 4 is Calculation example of process parameter control for preparation of ceramic foam material by system. In the table, it is calculated in detail that with the change of additives and their amounts in the system, the change of liquid phase amount also tends to be a fixed value θ _1c , and in order to ensure the amount of θ _1c value, the different additives and their amounts are related to the blank The relationship between the lowest design preheating temperature T _1c of the body and the actual ignition temperature Tk of the reaction of SHS.

Table 5 is Calculation example of process parameter control for preparation of ceramic foam material by system. The table calculates in detail the fixed value θ _1c that the liquid phase amount of the system tends to be stable with the change of different additives and their amounts, and the additives with different amounts and components added in order to ensure the controlled θ _1c value, the minimum Design the relationship between the preheating temperature T _1c and the actual ignition temperature Tk for SHS reaction.

Table 6 is Calculation example of process parameter control for preparation of ceramic foam material by system. The liquid phase amount θ ₁ of the system is calculated in detail in the table, which varies greatly with the type of additives, and the designed liquid phase amount θ ₁ is to ensure the value of θ ₁ . , the relationship between the design preheating temperature T ₀ of the green body and the actual ignition temperature Tk of the SHS reaction.

The main advantages of the present invention are: ①Simple process, no high-temperature sintering equipment, no need to add water and binder in the material formula, the green body is directly formed, saving energy and investment, and low cost; ②The production cycle can be greatly shortened, and the general sintering time Only 10 to 40 seconds, ③ the prepared product has good high temperature resistance and thermal shock resistance, and the refractoriness is greater than 1800 ° C, ④ high temperature strength, 1000 ° C compressive strength is 2 ~ 5 MPa, ⑤ can control the prepared pore size at 0.1 ~0.5mm foam ceramic material.

Below in conjunction with the specific example of the present invention, further illustrate the details of the present invention:

Example 1:

A ceramic foam filter used for exhaust gas purification tests of internal combustion engines. Its performance requirements are: pore size 0.2mm, porosity greater than 60%, refractoriness greater than 1200°C, compressive strength at room temperature 4.0MPa, high temperature thermal shock resistance More than 50 times at 1000°C, and the size is φ150×50mm. The existing technology cannot prepare such a small-pore ceramic foam material. The method of the present invention is used to prepare it. The steps are as follows:

Step One, Ingredients

The five systems given in Attached Table 1 can be used to make filter materials, here Al ₂ O ₃ and TiB ₂ are selected, according to the SHS reaction equation: According to the size of the ceramic foam filter, its weight can be roughly estimated to be 1400-1800 grams. Therefore, 200-270 mesh commercial supply powders are taken respectively, including 648g of Al powder, 576g of TiO ₂ powder, and 504g of B ₂ O ₃ powder. The additive is Al ₂ O ₃ , accounting for 10wt% of the total amount of the above-mentioned reactants, 172.8g is taken, and neither water nor any binder is added. Put the powder directly into the ball mill and mix for 20 minutes to prepare the required powder with a total weight of 1900.8 grams.

The second step, bad body preparation

In order to calculate the theoretical density, the addition of 10% Al ₂ O ₃ additives is converted into a mole number of 0.705, so the final composition of the product is 5.705Al ₂ O ₃ +3TiB ₂ , and the theoretical density of Al ₂ O ₃ is 3.9g/cm ^3. The theoretical density of TiB ₂ is 4.5g/cm ³ , according to the calculation formula of the theoretical density D ₀ of the product, D ₀ is 4.03g/cm ³ :

Generally, the porosity of foam materials is in a large range, and the operability is good. The filter requires a porosity greater than 60%. _Therefore , the control density of the green body d _k =0.35D _{0 ~} 0.50D ₀ +5%~10 _% . And 5%-10% is used to balance the error caused by about 5% volume shrinkage, and 8% is 0.08. Considering comprehensively, it is desirable to take d _k =0.4D ₀ +8%, and calculate d _k =1.69g/cm ³ .

The product size is φ150×50mm, and its volume can be calculated as 883.1cm ³ , which is the volume of the green body. From this, the powder weight of the green body can be calculated as 883.1×1.692=1494.2 grams. Considering the actual loss and easy operation, You can take 1500 grams of powder, and save the remaining powder for reuse. Due to a small amount of volume shrinkage, take an A3 steel mold with an inner diameter of 150.2mm, an outer diameter of 180mm, and a height of 110mm, put 1500 grams of powder into the mold, and press the powder into a shape of φ150.2×50mm by the limit method. Take out the green body, control the density d _k to be 1.69g/cm ³ The foamed ceramic material green body has just been prepared.

The third step is to determine the ignition temperature

1. Calculate Tad and θ ₀

According to thermodynamic calculations or directly look up the data given in Table 1 and Table 5, the theoretically calculated value θ ₀ of the liquid phase amount of the system when it reacts at 298K and has no additives is 70.8%, and the adiabatic temperature T _ad =2465K, which is taken as Tad=2303K.

2. Calculate T _0c

In order to ensure that the liquid phase quantity _θ1c is controlled at _60-80Wt %, the added _Al2O3 and the generated _Al2O3 are all melted. At this time, when the temperature of the system rises so that the adiabatic temperature _exceeds 2303K, the controlled liquid phase quantity It is a stable value θ _1c , and θ _1c = 73.5% can be calculated according to the aforementioned thermodynamic theory. Substituting it into the formula for calculating T _0c , the minimum design preheating temperature T _0c = 444K can be calculated.

3. Determination of the actual ignition temperature Tk

According to Table 5 Remark column 1), Tk=T _0c +350 is taken for the Al+TiO ₂ +B ₂ O ₃ system, so the actual ignition temperature of the green body is Tk=444+350=794K, that is, 521°C.

The fourth step, sintering operation

Put the prepared body of foamed ceramic material into a box-type resistance furnace and heat it to 521°C±5°C. At this temperature, use a φ0.5mm W wire to heat it electrically, and ignite it at one end of the body. At this time, the voltage of the W wire is 40V, and the current is 50A. After one end is ignited, the combustion wave rapidly expands to the unreacted area, and the SHS reaction is completed in about 33 seconds, and the required foam ceramic material filter is prepared.

The fifth step, product testing

After testing, the pore size of the filter is 0.16-0.24mm, the porosity is 62%, and its active ingredients are: Al ₂ O ₃ 73.5%, TiB ₂ 26.5%. The impact is greater than 50 times, and the refractoriness is greater than 1800°C. It is actually applied to the exhaust gas purification test of the internal combustion engine, and the filtering effect is good.

Example 2:

The performance requirements of the foam ceramic filter used in the test are: pore size 0.35mm, porosity greater than 70%, refractoriness greater than 1400°C, compressive strength at room temperature 3.6MPa, high temperature thermal shock resistance greater than 50 times at 1000°C, The size is φ60×40mm. It is difficult to prepare such a small-pore ceramic foam material in the prior art. It is prepared by the method of the present invention, and its steps are as follows:

Step One, Ingredients

The five systems given in Attached Table 1 can be used to make filter materials, and now _TiB2 ceramic materials are used to make them. For this reason, according to the reaction formula At the same time, according to the size of the ceramic foam filter, its weight can be roughly calculated to be 100-150 grams. Therefore, 96g and 44g of Ti powder and B powder with a particle size of 250-320 mesh were taken respectively, and the additive was Al ₂ O ₃ powder. Above-mentioned reactant total weight 15%, is 21g. Without adding water or any binder, the powder was directly put into a ball mill and mixed for 15 minutes to prepare the required powder with a total weight of 161 grams.

The second step, green body preparation

To calculate the theoretical density, the 15% Al ₂ O ₃ addition is converted into a mole number of 0.103, so the final composition of the product is 0.103 Al ₂ O ₃ +3TiB ₂ , and the theoretical density of Al ₂ O ₃ is 3.9g/cm ³ , The theoretical density of TiB ₂ is 4.5g/cm ³ , according to the calculation formula of the theoretical density D ₀ of the product, D ₀ is 4.41g/cm ³ .

Generally, the porosity of foam materials is in a large range, and the operability is good. The filter requires a porosity greater than 70%. Therefore, the control density of the green body adopts d _k =0.25D ₀ ～0.30D ₀ +5%～10%, and the value in the formula is 0.25D ₀ ～0.30D _0. The value is 0.25D ₀ , and 5% to 10% is used to balance the error caused by about 5% volume shrinkage, and 8% is 0.08. Considering comprehensively, it is desirable to take d _k =0.25D ₀ +8%, and calculate d _k =1.18g/cm ³ .

The product size is φ60×40mm, and its volume can be calculated as 113.0cm ³ , which is the volume of the green body. From this, the powder weight of the green body can be calculated as 113×1.18=133.5 grams. Considering the actual loss and the convenience of operation, You can take 135 grams of powder, and save the remaining powder for reuse. Due to a small amount of volume shrinkage, take an A3 steel mold with an inner diameter of 60.1mm, an outer diameter of 75mm, and a height of 75mm, put 135 grams of powder into the mold, and press the powder into a shape of φ60.1×40mm by the limit method. Take out the green body, control the density d _k to be 1.18g/cm ³ The foamed ceramic material green body has just been prepared.

The third step is to determine the ignition temperature

1. Calculate Tad and θ ₀

According to thermodynamic calculations or directly look up the data given in Table 1 and Table 2, the theoretical calculation value of liquid phase amount θ ₀ is 35% when the system reacts at 298K without additives, and the adiabatic temperature T _ad =3193K.

2. Calculate T ₀

It can be known from Table 2 that in order to ensure that the liquid phase quantity θ ₁ of the Ti+B system is controlled at 40-60Wt%, 15% additive Al ₂ O ₃ is added. When the liquid phase quantity θ ₁ = 40%, the design preheating temperature The lower limit of T ₀ is 1150K. When controlling the liquid phase amount θ ₁ =60%, the upper limit T ₀ of the design preheating temperature is 1380K.

3. Determination of the actual ignition temperature Tk

It can be seen from Table 2 that the average value of the upper and lower limits of the green body design preheating temperature T ₀ is taken for the Tk of the Ti+B system, and Tk=1265K=992°C.

The fourth step, sintering operation

Put the prepared green body into a box-type resistance furnace and heat it to 990°C±5°C. At this temperature, use 0.5mm W wire to heat it electrically, and ignite one end of the green body. At this time, the temperature of the W wire The voltage is 30V and the current is 45A. After one end is ignited, the combustion wave rapidly expands to the unreacted area, and the SHS reaction is completed in about 24 seconds, and the required foam ceramic material filter is prepared.

The fifth step, product testing

After testing, the pore size of the filter produced is 0.27-0.33mm, and the porosity is 74%. Its active ingredients are: TiB ₂ accounts for 87.0%, Al ₂ O ₃ accounts for 13.0%, mechanical properties: normal temperature compressive strength is 4.4MPa, 1000℃ The thermal shock resistance is greater than 50 times, and the refractoriness is greater than 1800°C. It is actually applied to the exhaust gas purification test, and the effect of trapping soot particles is good.

Below embodiment 3,4,5, because its preparation step is completely with the step of embodiment 1,2, therefore, the embodiment preparation step is briefly described, can refer to embodiment 1,2. The following examples 3, 4, and 5 only give the analysis of the key control parameters of the preparation and the composition of the final product.

Example 3:

A foam ceramic filter used for cleaning the exhaust gas of internal combustion engines. Its performance requirements are: pore size 0.4mm, porosity 80%, refractoriness greater than 1100°C, compressive strength at room temperature 4.0MPa, high temperature thermal shock resistance More than 50 times at 1000°C, the size requirement is φ150×70mm, and the steps are briefly described as follows:

The filter is made of Al ₂ O ₃ , Cr and SiO ₂ materials. The SHS reaction equation is: , the additive is SiO ₂ accounting for 40% of the total weight of the reaction mass. According to thermodynamic calculation or Table 6, it is known that the system Tad=2303K, the upper limit of the design preheating temperature _T0 is 775K, and the lower limit is 990K, and the actual ignition operation temperature TK=883K, that is, 610°C±5°C.

According to the steps in Example 1 or 2, a ceramic foam filter can be produced, the final composition of which is 35.4% for Al ₂ O ₃ , 36.0% for Cr, and 28.6% for SiO ₂ .

Example 4:

A ceramic foam filter used for exhaust gas purification of internal combustion engines, its performance requirements are: pore size 0.5mm, porosity 80%, refractoriness greater than 1200°C, compressive strength at room temperature 4.0MPa, high temperature thermal shock resistance 1000 The temperature is greater than 50 times at ℃, and the size is φ150×65mm. The steps are briefly described as follows:

Use ZrO ₂ +Cr and Al ₂ O ₃ materials as additives to make filters, and the SHS reaction equation is: , the additive Al ₂ O ₃ accounts for 10% of the total weight of the reaction materials. According to the thermodynamic calculation or look-up table 3, it is known that the system Tad=2303K, the liquid phase quantity θ _1c =41.8% is controlled, the minimum design preheating temperature T _0c =350K is calculated, and the actual green body ignition temperature Tk=650K is taken, that is 377°C±5°C.

According to the steps in Example 1 or 2, the ceramic foam filter can be produced, and the final composition is: ZrO ₂ accounts for 58.1%, Cr accounts for 32.8%, and Al ₂ O ₃ accounts for 9.1%.

Example 5:

A ceramic foam filter used for cleaning the exhaust gas of internal combustion engines. Its performance requirements are: pore size 0.1mm, porosity 60%, refractoriness greater than 1250°C, compressive strength at room temperature 4.0MPa, high temperature thermal shock resistance More than 50 times at 1000°C, the size is φ150×40mm, and the steps are briefly described as follows:

Select Al ₂ O ₃ +TiC ceramic material, use Ti and SiO ₂ as additives to prepare filters, according to the reaction equation , the additives Ti powder and SiO ₂ powder each account for 5% of the additives. According to thermodynamic calculations or look-up table 4, it is known that the system takes Tad=2303K, and the liquid phase quantity θ _1c is controlled to be 57.4%. The minimum design budget is calculated. The heating temperature is T _0c =535K, and the actual billet ignition temperature is TK=935K, that is, TK=662±5°C.

According to the steps in Example 1 or 2, the ceramic foam filter can be produced, and the final composition is: Al ₂ O ₃ accounts for 48.3%, TiC accounts for 42.6%, SiO ₂ accounts for 4.55%, and Ti accounts for 4.55%.

表2. 体系制备泡沫陶瓷材料工艺参数控制计算例

表3   体系制备泡沫陶瓷材料工艺参数控制计算例

表4   体系制备泡沫陶瓷材料工艺参数控制计算例表5   体系制备泡沫陶瓷材料工艺参数控制计算例表6   体系制备泡沫陶瓷材料工艺参数控制计算例

It should be noted that about 1% of impurities in the reactants are not included in the calculation of the components in the examples, and this effect is not considered in the thermodynamic calculations. Table 1 prepares the technical parameters of foam ceramic material SHS reaction

Table 2. Calculation example of process parameter control for preparation of ceramic foam material by system

table 3 Calculation example of process parameter control for preparation of ceramic foam material by system

Table 4 Calculation example of process parameter control for preparation of ceramic foam material by system table 5 Calculation example of process parameter control for preparation of ceramic foam material by system Table 6 Calculation example of process parameter control for preparation of ceramic foam material by system

Claims (1)

1. A method for preparing foamed ceramic materials using self-propagating high-temperature synthesis control, which mainly includes: taking two or more kinds of particles with a particle size greater than 200 mesh according to stoichiometry, capable of performing self-propagating high-temperature synthesis reactions and generating a theoretically calculated value of partial liquid phase θ ₀ Ti+B or Zr+Cr ₂ O ₃ or Al+TiO ₂ +C or Al+TiO ₂ +B ₂ O ₃ or Al+Cr ₂ O ₃ reactant powder and accounts for 1 to 40% of the total weight of reactants % high-melting point metal Ti, Cr, Zr, Mo, W powder and ceramic Al ₂ O ₃ , SiO ₂ , ZrO ₂ and SiC powder additives; the production and sintering method of the green body; after completing the self-propagating high-temperature synthesis The 40-80% liquid phase amount θ ₁ or θ _1c controlled in the system during the reaction, and the actual ignition temperature Tk of green body sintering determined by the preheating temperature T ₀ or T _0c are characterized in that: a) The green body is formed by uniform mixing of the reactant powder and the additive powder, and then directly pressed. The control density d _k of the green body is determined by the theoretical density D ₀ of the product foam ceramics and the experimental parameters, which is d _k =0.20 D ₀ ～0.5D ₀ +5%～10%; when the corresponding porosity of the product after the reaction is required to be 65～80%, the control density of the green body is d _k =0.2 D ₀ ～0.35D ₀ +5%～10 %; when the corresponding porosity of the product after the reaction is required to be 50-65%, the control density of the green body is d _k =0.35D ₀ ～0.5D ₀ +5%-10%, b) The production process of controlling the preparation of foamed ceramic materials is: uniformly mix the materials of the formula in a ball mill for 15 to 20 minutes, directly press them in the mold with the limit method to form the required shape and density d _k of the green body, and then put the green body The body is placed in a furnace, heated to the actual ignition reaction temperature Tk, and at this temperature, sintered and ignited by electric heating with an oxygen-acetylene flame or metal W and Mo wires, and the self-propagating high-temperature synthesis reaction process is completed, and a foam ceramic material is produced. product.