CN102267814A - Preparation method for high-porosity phosphate bonded silicon nitride porous ceramic - Google Patents

Abstract

The present invention is a preparation method of phosphate-bonded silicon nitride porous ceramics with added pore-forming agent, specifically: firstly, 10-50vol.% pore-forming agent is directly mixed with α-silicon nitride powder and oxide powder with ethanol as The ball milling medium is mixed evenly, and then dried to obtain the mixed powder; phosphoric acid is added to the mixed powder according to the stoichiometric proportion of phosphate formed with the oxide powder to obtain the mixed material; the mixed material is processed by molding and cold isostatic pressing, Obtain a molded sample; heat-treat the molded sample at 500-700° C. and keep it warm for 2-5 hours, and then sinter at 800-1200° C. under the protection of a nitrogen atmosphere at normal pressure to obtain the silicon nitride porous ceramic. The invention has the advantages of simple process, good repeatability and low cost, and the prepared silicon nitride porous ceramic material has excellent properties such as uniform pore distribution, small pore size, high porosity and high mechanical strength.

Description

Preparation method of high porosity phosphate bonded silicon nitride porous ceramics

technical field

The invention relates to the field of ceramic materials, in particular to a preparation method of high-porosity phosphate-bonded silicon nitride porous ceramics.

Background technique

Silicon nitride porous ceramics is a new type of "structure-function" integrated ceramic material gradually developed on the basis of research on silicon nitride ceramics and porous ceramics. The performance of this material makes this material have broad application prospects. In addition to the excellent properties of silicon nitride ceramics such as high specific strength, high specific modulus, high temperature resistance, oxidation resistance, wear resistance and thermal shock resistance, silicon nitride porous ceramics also have the following porous characteristics: (1) Good heat resistance and thermal shock resistance; (2) good chemical stability; (3) good mechanical strength and rigidity, under the pressure of air pressure, hydraulic pressure or other stress loads, the shape and size of the pores of the porous body do not change; ( 4) The weight is relatively light compared to other materials.

As a new porous material with excellent comprehensive performance and broad prospects, silicon nitride porous ceramics can be widely used in chemical, environmental protection, biological and other industries as filtration, separation, sound absorption, sensitive materials and bioceramics. In addition, there are many applications in the semiconductor industry, electronics, aerospace, and nuclear industries.

Judging from the current research status, the porosity and pore size adjustment and control of silicon nitride porous ceramics are mainly realized by changing the powder particle ratio, slurry concentration, molding density and sintering process. The pore structure of the fired silicon nitride porous ceramic includes a through-hole structure formed by α-silicon nitride particles bonded in liquid phase and a through-hole structure formed by overlapping β-silicon nitride columnar crystals. The former is mostly prepared by partial sintering method, which leads to the difficulty of controlling the porosity of the material, uneven distribution of pores, large pore size, and low bending strength of the material, but the material has good dielectric properties; the latter makes the mechanical properties of the material It has been greatly improved, but the porosity range is too narrow, the pore size distribution cannot be controlled, and β-silicon nitride has a high dielectric constant and dielectric loss. Since 1970, research on improving the flexural strength of ceramic materials by chemical bonding using phosphate has been gradually carried out. At first, this method was mainly used to prepare high-performance biomaterials such as artificial teeth and artificial joint bones. In 1987, Science Magazine ("Science" Volume 235, Issue 6, author Roy DM) published an article about the use of phosphate to obtain a high-performance cement material with significantly improved mechanical properties through chemical bonding. Since then, through The study of chemical bonding methods to improve the mechanical properties of structural materials has received extensive attention. Research has found that metal oxides such as ZrO ₂ , Al ₂ O ₃ z, SiO ₂ and MgO react with phosphoric acid (H ₃ PO ₄ ) at a relatively low temperature to form a phosphate polycrystalline structure. After high-temperature calcination, it becomes Phosphate ceramics, this kind of phosphate ceramics can be used as a binder to enhance the mechanical properties of the ceramic material matrix due to its high temperature resistance, high bending strength, small thermal expansion coefficient, and good chemical stability.

According to the novelty search results of domestic and foreign patents and literatures, there is no report on the preparation of porous ceramics with high porosity phosphate combined with silicon nitride.

Contents of the invention

The technical problem to be solved by the present invention is to provide a relatively simple method to prepare high-porosity phosphate-bonded silicon nitride porous ceramics with excellent performance at a relatively low sintering temperature in order to overcome the defects of the prior art.

The present invention solves its technical problem and adopts the following technical solutions:

The preparation method of the phosphate-bonded silicon nitride porous ceramics with the addition of a pore-forming agent provided by the invention, the steps include:

(1) 10-50vol% pore-forming agent is directly mixed with α-silicon nitride powder and oxide powder with ethanol as the ball milling medium, and then dried to obtain the mixed powder;

(2) Phosphoric acid is added to the above-mentioned mixed powder according to the stoichiometric ratio of forming phosphate with the oxide powder to obtain the mixed material;

(3) The mixture is processed by compression molding and cold isostatic pressing to obtain a molded sample;

(4) Heat-treat the molded sample at 500-700°C and keep it warm for 2-5 hours, so that phosphoric acid and oxide powder react to form phosphate and play a bonding role, and the pore-forming agent can be fully removed to obtain a heat-treated product;

(5) The heat-treated product is sintered under normal pressure at 800-1200° C. under the protection of nitrogen atmosphere, the reaction rate is controlled at 50-200° C./hour and the holding time is 2-5 hours, and the silicon nitride porous ceramic is obtained.

In the above steps:

The weight ratio of the pore forming agent, α-silicon nitride powder, oxide powder and ethanol may be (1-5):6:1:10. The pore-forming agent can be cornstarch, naphthalene powder or carbon powder. The average particle diameter of the α-silicon nitride powder is less than or equal to 0.5 μm.

The phosphate is mainly zirconium phosphate, aluminum phosphate, chromium phosphate, lanthanum phosphate or silicon phosphate.

The cold isostatic pressing pressure may be 50-300 MPa.

The silicon nitride porous ceramic prepared by the invention has a density of 0.8-2.0 g/cm ³ .

The present invention uses phosphoric acid and oxides to react at 200-500°C to generate phosphate, and the generated phosphate is used as a binder to promote the bonding between silicon nitride particles; in the range of 400-700°C, the pore-forming agent volatilizes or sublimates A pore structure with uniform structure and mainly open pores is formed, thereby preparing silicon nitride porous ceramics with high porosity, small pore size, uniform pore distribution and high mechanical (bending) strength.

The invention has simple process, good repeatability and low cost, and the prepared phosphate-bonded silicon nitride porous ceramic has excellent characteristics such as uniform pore distribution, high porosity, uniform and controllable pore structure, and high mechanical strength.

Description of drawings

Fig. 1 is the XRD figure of embodiment 1, embodiment 2 and embodiment 3 products.

Fig. 2 is the SEM picture of the product of embodiment 1.

Fig. 3 is the SEM picture of the product of embodiment 2.

Fig. 4 is the SEM picture of the product of embodiment 3.

Detailed ways

The invention provides a method for preparing a high-porosity phosphate-bonded silicon nitride porous ceramic material by adding a pore-forming agent. The method includes mixing, molding, cold isostatic pressing and sintering.

The present invention specifically prepares the silicon nitride porous ceramic material according to the following steps:

(1) The pore-forming agent is directly mixed with α-silicon nitride powder and oxide powder with an average particle size of less than 0.5 μm, using ethanol as the ball milling medium, and the content of the pore-forming agent is 10-50vol.%.

(2) Phosphoric acid is added to the above-mentioned mixed powder according to the stoichiometric ratio of forming phosphate with oxide;

(3) The mold will mix the material by molding and cold isostatic pressing;

(4) heat-treat the molded sample at 500-700°C and keep it warm for 2-5 hours, so that phosphoric acid and oxides can react to form phosphate and play a bonding role, and the pore-forming agent can be fully eliminated;

(5) The product after heat treatment is sintered under normal pressure under the protection of nitrogen atmosphere at 800-1200°C, the reaction rate is controlled at 50-200°C/hour and the holding time is 2-5 hours, and a high-porosity phosphate-bound nitrogen silicon porous ceramic material.

The present invention will be further described below in conjunction with implementation examples.

Embodiment 1: (1) Starch, α-silicon nitride, zirconium dioxide and ethanol ball milling are mixed, and their weight ratio is 1: 6: 1: 10; After drying, the weight concentration is 85% phosphoric acid Mix with the above powder, zirconium dioxide and phosphoric acid in a stoichiometric ratio; (2) preform the material through 10MPa molding treatment, and finally form it after cold isostatic pressing; (3) heat-treat the molded product at 550 ° C and keep it warm for 2 hours, make phosphoric acid react with zirconium dioxide to generate zirconium phosphate, and remove cornstarch to form pores; 2 hours, cool with the furnace. A zirconium phosphate bonded silicon nitride porous ceramic with a porosity of 32% and a bending strength of 80 MPa can be obtained.

Analytical testing shows (see Figure 2): the main phase of the product is α-silicon nitride, which maintains the main phase of the raw material without phase transition. Zirconia reacted with phosphoric acid to form zirconium phosphate (ZrP ₂ O ₇ ) to act as a cohesive agent, and the cornstarch was removed more cleanly. The zirconium phosphate bonded silicon nitride porous ceramic prepared by this method has relatively uniform pore distribution and high porosity.

The analysis test shows (see Fig. 3): the prepared silicon nitride porous ceramic material has high porosity, uniform pore distribution and small pore size.

Embodiment 2: (1) Starch, α-silicon nitride, zirconium dioxide, and ethanol ball milling are mixed, and their weight ratio is 2: 6: 1: 10; After drying, the weight concentration is 85% Phosphoric acid is mixed with the above powder, zirconium dioxide and phosphoric acid are in stoichiometric ratio; (2) The material is preformed by 10MPa molding treatment, and finally formed by cold isostatic pressing; (3) The molded product is heat-treated at 550°C and kept for 2 hours, make phosphoric acid react with zirconium dioxide to generate zirconium phosphate, and remove cornstarch to form pores; 2 hours, cool with the furnace. An aluminum phosphate bonded silicon nitride porous ceramic material with a porosity of 47% and a bending strength of 71MPa can be obtained.

Analytical testing shows (see Figure 2): the main phase of the product is α-silicon nitride, which maintains the main phase of the raw material without phase transition. Zirconia reacted with phosphoric acid to form zirconium phosphate (ZrP ₂ O ₇ ) to act as a cohesive agent, and the cornstarch was removed more cleanly. The zirconium phosphate bonded silicon nitride porous ceramic prepared by this method has relatively uniform pore distribution and high porosity.

The analysis test shows (see Fig. 4): the prepared silicon nitride porous ceramic material has high porosity, relatively uniform pore distribution and small pore size.

Embodiment 3: (1) naphthalene powder, α-silicon nitride, zirconium dioxide, and ethanol ball milling are mixed, and their weight ratio is 2: 6: 1: 10; After drying, the weight concentration is 85% The phosphoric acid is mixed with the above powder, wherein zirconium dioxide and phosphoric acid are in a stoichiometric ratio; (2) the material is preformed by 10MPa molding treatment, and finally formed by cold isostatic pressing; (3) the molded product is heat treated at 550°C and Keep warm for 2 hours, make phosphoric acid react with zirconium dioxide, react to generate zirconium phosphate, and oxidize and remove starch at the same time, and keep warm for 2 hours; (4) The product after heat treatment is sintered under normal pressure under the protection of nitrogen atmosphere at 1000 ° C, and the heating rate is 100°C/hour, keep warm for 2 hours, and cool with the furnace. A silicon nitride porous ceramic material with a porosity of 45% and a bending strength of 68MPa can be obtained.

Analytical testing shows (see Figure 2): the main phase of the product is α-silicon nitride, which maintains the main phase of the raw material without phase transition. Zirconium oxide reacts with phosphoric acid to form zirconium phosphate (ZrP ₂ O ₇ ) for bonding, and naphthalene powder is removed relatively cleanly. The zirconium phosphate bonded silicon nitride porous ceramic prepared by this method has relatively uniform pore distribution and high porosity.

The analysis test shows (see Fig. 5 ): the prepared silicon nitride porous ceramic material has high porosity, uniform pore distribution and small pore size.

Embodiment 4: (1) Starch, α-silicon nitride, aluminum oxide, and ethanol ball milling are mixed, and their weight ratio is 3: 6: 1: 10; After drying, the phosphoric acid with a weight concentration of 85% Mix with the above powder, alumina and phosphoric acid are in a stoichiometric ratio; (2) The material is preformed by 10MPa molding treatment, and finally formed by cold isostatic pressing; (3) The molded product is heat-treated at 550°C and kept for 2 hours, Make phosphoric acid react with alumina to form aluminum phosphate, and remove cornstarch to form pores; (4) sinter the heat-treated product under normal pressure at 1000°C under the protection of nitrogen atmosphere, with a heating rate of 100°C/hour and heat preservation for 2 hours. Cool in the furnace. A silicon nitride porous ceramic material with a porosity of 53% and a bending strength of 54MPa can be obtained.

Embodiment 5: (1) Starch, α-silicon nitride, silicon oxide, and ethanol ball milling are mixed, and their weight ratio is 3: 6: 1: 10; After drying, the weight concentration is 85% phosphoric acid Mix with the above powder, wherein silicon oxide and phosphoric acid are in stoichiometric ratio; (2) The material is preformed by 10MPa molding treatment, and finally formed by cold isostatic pressing; (3) The molded product is heat-treated at 550°C and kept for 2 hours , make phosphoric acid react with alumina, react to form aluminum phosphate, and at the same time oxidize and remove starch, and keep warm for 2 hours; (4) Sinter under normal pressure at 1000°C under the protection of nitrogen atmosphere, the heating rate is 100°C/hour, keep warm for 2 hours , cooling with the furnace. A silicon nitride porous ceramic material with a porosity of 57% and a bending strength of 50 MPa can be obtained.

Claims (7)

1. a preparation method of silicon nitride porous ceramics is characterized in that a kind of phosphate adding pore-forming agent is combined with the preparation method of silicon nitride porous ceramics, and the steps of the method comprise: (1) 10-50vol.% pore-forming agent is directly mixed with α-silicon nitride powder and oxide powder with ethanol as the ball milling medium, and then dried to obtain the mixed powder; (2) Phosphoric acid is added to the above-mentioned mixed powder according to the stoichiometric ratio of forming phosphate with the oxide powder to obtain the mixed material; (3) The mixture is processed by compression molding and cold isostatic pressing to obtain a molded sample; (4) Heat-treat the molded sample at 500-700°C and keep it warm for 2-5 hours, so that phosphoric acid and oxide powder react to form phosphate and play a bonding role, and the pore-forming agent can be fully removed to obtain a heat-treated product; (5) The heat-treated product is sintered under normal pressure at 800-1200° C. under the protection of nitrogen atmosphere, the reaction rate is controlled at 50-200° C./hour and the holding time is 2-5 hours, and the silicon nitride porous ceramic is obtained. 2. The preparation method of silicon nitride porous ceramics according to claim 1, characterized in that: the weight ratio of the pore forming agent, α-silicon nitride powder, oxide powder and ethanol is (1～5) :6:1:10. 3. The preparation method of silicon nitride porous ceramics according to claim 1, characterized in that: the pore-forming agent is corn starch, naphthalene powder or carbon powder. 4. The preparation method of silicon nitride porous ceramics according to claim 1, characterized in that: said phosphate is mainly zirconium phosphate, aluminum phosphate, chromium phosphate, lanthanum phosphate or silicon phosphate. 5 . The method for preparing silicon nitride porous ceramics according to claim 1 , characterized in that: the pressure of cold isostatic pressing is 50-300 MPa. 6. The method for preparing porous silicon nitride ceramics according to claim 1, characterized in that: the average particle size of the α-silicon nitride powder is less than or equal to 0.5 μm. 7 . The method for preparing porous silicon nitride ceramics according to claim 1 , characterized in that: the density of the porous silicon nitride ceramics is 0.8-2.0 g/cm ³ .

Images