CN101323526A - Preparation method of porous silicon nitride-silicon dioxide wave-transparent material - Google Patents

Abstract

The invention discloses a method for preparing a porous silicon nitride-silicon dioxide wave-transmitting material. Firstly, Si ₃ N ₄ powder with an average diameter of 0.1-0.6 microns and phenolic resin are made into a mixed powder, which is ball milled and dried. After crushing, it is molded into a green body; then oxidized and sintered in a high-temperature tube furnace to prepare porous Si ₃ N ₄ -SiO ₂ composite ceramics; the porous Si ₃ N ₄ -SiO ₂ composite ceramics are impregnated multiple times Dry the silica sol after drying; sinter the porous Si ₃ N ₄ -SiO ₂ composite ceramics impregnated with silica sol at 1200-1300°C for 2-3 hours in nitrogen flowing at normal pressure to make porous Si ₃ N ₄ -SiO ₂ Wave-transparent material. The invention repeatedly impregnates the porous Si ₃ N ₄ -SiO ₂ multi-phase ceramics with silica sol, and the bending strength of the Si ₃ N ₄ -SiO ₂ multi-phase ceramics is increased from 96.2 MPa in the prior art to 101-124 MPa.

Description

Preparation method of porous silicon nitride-silicon dioxide wave-transparent material

technical field

The invention relates to a preparation method of a silicon nitride-silicon dioxide wave-transmitting material.

Background technique

Si ₃ N ₄ -SiO ₂ composite material is a kind of high-temperature wave-transparent material with great potential.

The document "Preparation of Si ₃ N ₄ /SiO ₂ Composite Materials by Pressureless Sintering, Xu Changming, Wang Shiwei, Huang Xiaoxian, Guo Jingkun, Journal of Inorganic Materials, 21(2006), pp.935-938" discloses a method for preparing Si ₃ N ₄ - SiO ₂ composite ceramics method, adding 5vol.% Si ₃ N ₄ into SiO ₂ powder, and adopting a pressureless sintering method to sinter Si ₃ N ₄ -SiO ₂ composite ceramics at 1370°C. The bending strength of the ceramic is 96.2 MPa, and the dielectric constant is 3.63-3.68. Its dielectric constant meets the requirement that the dielectric constant of the wave-transparent material is less than 4.0, but its bending strength is poor, and the sintering temperature is high, and there is almost no porosity.

Contents of the invention

In order to overcome the deficiencies of poor bending strength in the prior art, the present invention provides a preparation method of porous silicon nitride-silicon dioxide wave-transmitting material, by repeatedly impregnating porous Si ₃ N ₄ -SiO ₂ multiphase ceramics with silica sol, which can Improve the flexural strength of Si ₃ N ₄ -SiO ₂ composite ceramics.

The technical solution adopted by the present invention to solve the technical problem: a method for preparing a porous silicon nitride-silicon dioxide wave-transmitting material, comprising the following steps:

(a) Si ₃ N ₄ powder with an average diameter of 0.1 to 0.6 microns and phenolic resin are made into a mixed powder, wherein phenolic resin accounts for 10 to 20% of the mass content of the mixed powder, and the rest is Si ₃ N ₄ powder, and then For every 100 grams of powder, add 200-300 ml of absolute ethanol and 15-25 alumina balls with a diameter of 8-12 mm, mill together for 15-20 hours, and dry at 80-100 °C for 8-10 hours , preparing a mixed powder with a mass percentage of Si ₃ N ₄ of 80% to 90%; crushing the mixed powder, passing through a 40 to 60 mesh sieve, and molding under a pressure of 80 to 100 MPa to form a green body;

(b) Put the green body into a high-temperature tube furnace and raise the temperature to 1200-1300°C under a nitrogen atmosphere, and then keep it in static air for 2-3 hours for oxidative sintering to prepare a porous Si ₃ N ₄ -SiO ₂ composite phase ceramics;

(c) Impregnate the porous Si ₃ N ₄ -SiO ₂ composite ceramics with silica sol for 1 to 5 times, each time for 30 to 60 minutes. Finally, dry in an oven at 80-100°C for 3-5 hours;

(d) Sinter the porous Si ₃ N ₄ -SiO ₂ multiphase ceramics impregnated with silica sol at 1200-1300°C for 2-3 hours in flowing nitrogen at normal pressure to make a porous Si ₃ N ₄ -SiO ₂ wave-transparent material .

The beneficial effects of the present invention are: due to repeatedly impregnating silica sol to the porous Si ₃ N ₄ -SiO ₂ multiphase ceramics, the bending strength of the Si ₃ N ₄ -SiO ₂ multiphase ceramics is increased from 96.2MPa in the prior art to 101~ 124MPa, see the table below.

Porosity(%) Density (g/cm ³ ) Bending strength (MPa) Fracture toughness (MPa·m ^1/2 ) Permittivity Dielectric loss (×10 ^-3 ) Example 1 30±1 1.87±0.02 101±4 0.8±0.1 3.56 3.59 Example 2 27±1 1.91±0.02 108±5 1.0±0.1 3.62 3.48 Example 3 23±1 1.97±0.02 116±4 1.2±0.1 3.72 3.16 Example 4 20±1 2.02±0.02 124±3 1.4±0.1 3.80 3.11

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Description of drawings

The accompanying drawing is a flow chart of the preparation method of the porous silicon nitride-silicon dioxide wave-transmitting material of the present invention.

Detailed ways

Embodiment 1: 80 grams of Si ₃ N ₄ powder with an average particle diameter of 0.6 microns are mixed with 20 grams of phenolic resin, poured into 300 milliliters of dehydrated alcohol, and add 15 alumina balls with a diameter of 8 to 12 millimeters, After ball milling for 15 hours, take it out and put it in a drying oven for 10 hours at 80°C. The dried powder is taken out and ground and passed through a 40-mesh sieve to obtain a mixed powder with uniform particle size. Pour 6 grams of mixed powder into a steel mold, and use a pressure of 80 MPa to mold the mixed powder into a bar-shaped green body. Put the body into a high-temperature tube furnace, raise the temperature to 1300°C under the protection of high-purity nitrogen, then keep it in static air for 2 hours, and finally cool it down to room temperature in static air to obtain porous Si with a porosity of 45%. ₃ N ₄ -SiO ₂ composite ceramic samples. Immerse the sample in a beaker filled with silica sol, and immerse it in a vacuum dish with a pressure of 4KPa for 30 minutes; take it out, put it in a beaker filled with water, ultrasonically clean it for 3 minutes, and then put it in a drying oven at 80°C for 3 hours. The sample was repeatedly dipped in silica sol and dried, and then sintered at 1200°C for 3 hours under the protection of high-purity nitrogen to obtain a porous Si ₃ N ₄ -SiO ₂ composite ceramic with a porosity of 30±1%.

Tested at room temperature, the density of the ceramic is 1.87±0.02g/cm ³ , the flexural strength is 101±4MPa, the fracture toughness is 0.8±0.1MPa·m ^1/2 , the dielectric constant is 3.56, and the dielectric loss is 3.59×10 ^-3 .

Embodiment 2: 85 grams of Si ₃ N ₄ powders with an average particle diameter of 0.3 microns are mixed with 15 grams of phenolic resin, poured into 250 milliliters of dehydrated alcohol, and add 20 alumina balls with a diameter of 8 to 12 millimeters, After ball milling for 18 hours, take it out and put it in a drying oven at 90°C for 9 hours to dry. The dried powder is taken out and ground and passed through a 40-mesh sieve to obtain a mixed powder with uniform particle size. Pour 5 grams of mixed powder into a steel mold, and use a pressure of 90 MPa to mold the mixed powder into a bar-shaped green body. Put the body into a high-temperature tube furnace, raise the temperature to 1250°C under the protection of high-purity nitrogen, then keep it in static air for 2.5 hours, and finally cool it down to room temperature in static air to obtain porous Si with a porosity of 43%. ₃ N ₄ -SiO ₂ composite ceramic samples. Immerse the sample in a beaker filled with silica sol, and immerse it in a vacuum dish with a pressure of 4KPa for 40 minutes; take it out, put it in a beaker filled with water, ultrasonically clean it for 4 minutes, and then put it in a drying oven at 90°C for 4 hours. The sample was dipped in silica sol twice and dried, and then sintered at 1250°C for 2.5 hours under the protection of high-purity nitrogen to obtain porous Si ₃ N ₄ -SiO ₂ composite ceramics with a porosity of 27±1%.

Tested at room temperature, the density of the ceramic is 1.91±0.02g/cm ³ , the flexural strength is 108±5MPa, the fracture toughness is 1.0±0.1MPa·m ^1/2 , the dielectric constant is 3.62, and the dielectric loss is 3.48×10 ^-3 .

Embodiment 3: 90 grams of Si ₃ N ₄ powder with an average particle diameter of 0.3 microns are mixed with 10 grams of phenolic resin, poured into 200 milliliters of dehydrated alcohol, and add 20 alumina balls with a diameter of 8 to 12 millimeters, After ball milling for 19 hours, take it out and put it in a drying oven at 90°C for 8 hours. The dried powder is taken out and ground, and then passed through a 50-mesh sieve to obtain a mixed powder with uniform particle size. Pour 5 grams of mixed powder into a steel mold, and use a pressure of 90 MPa to mold the mixed powder into a bar-shaped green body. Put the body into a high-temperature tube furnace, raise the temperature to 1250°C under the protection of high-purity nitrogen, then keep it in static air for 2.5 hours, and finally cool it down to room temperature in static air to obtain porous Si with a porosity of 42%. ₃ N ₄ -SiO ₂ composite ceramic samples. Immerse the sample in a beaker filled with silica sol, and immerse it in a vacuum dish with a pressure of 4KPa for 50 minutes; take it out, put it in a beaker filled with water, ultrasonically clean it for 4 minutes, and then put it in a drying oven at 90°C for 4 hours. The sample was impregnated with silica sol three times and dried, and then sintered at 1250°C for 2 hours under the protection of high-purity nitrogen to obtain a porous Si ₃ N ₄ -SiO ₂ composite ceramic with a porosity of 23±1%.

Tested at room temperature, the density of the ceramic is 1.97±0.02g/cm ³ , the flexural strength is 116±4MPa, the fracture toughness is 1.2±0.1MPa·m ^1/2 , the dielectric constant is 3.72, and the dielectric loss is 3.16×10 ^-3 .

Embodiment 4: 90 grams of Si ₃ N ₄ powders with an average particle diameter of 0.1 micron are mixed with 10 grams of phenolic resin, poured into 200 milliliters of dehydrated alcohol, and add 25 alumina balls with a diameter of 8 to 12 millimeters, After ball milling for 20 hours, take it out and put it in a drying oven for 8 hours at 100°C. The dried powder is taken out and ground, and passed through a 60-mesh sieve to obtain a mixed powder with uniform particle size. Pour 5 grams of mixed powder into a steel mold, and press the mixed powder into a bar-shaped green body with a pressure of 100 MPa. Put the body into a high-temperature tube furnace, raise the temperature to 1200°C under the protection of high-purity nitrogen, then keep it in static air for 3 hours, and finally cool it down to room temperature in static air to obtain porous Si with a porosity of 41%. ₃ N ₄ -SiO ₂ composite ceramic samples. Immerse the sample in a beaker filled with silica sol, and immerse it in a vacuum dish with a pressure of 3KPa for 60 minutes; take it out, put it in a beaker filled with water, ultrasonically clean it for 5 minutes, and then put it in a drying oven at 100°C for 5 hours. The sample was impregnated with silica sol four times and dried, and then sintered at 1300°C for 2 hours under the protection of high-purity nitrogen to obtain porous Si ₃ N ₄ -SiO ₂ composite ceramics with a porosity of 20±1%.

Tested at room temperature, the density of the ceramic is 2.02±0.02g/cm ³ , the flexural strength is 124±3MPa, the fracture toughness is 1.4±0.1MPa·m ^1/2 , the dielectric constant is 3.8, and the dielectric loss is 3.11×10 ^-3 .

Claims (1)

1, a kind of preparation method of porous silicon nitride-silicon dioxide transmitted wave material is characterized in that comprising the steps:

(a) with average diameter be 0.1～0.6 micron Si ₃N ₄Powder and phenolic resins are made mixed powder, and wherein phenolic aldehyde accounts for 10～20% of mixed powder mass content, and all the other are Si ₃N ₄Powder adds the alumina balls of proportioning and 8～12 millimeters of 15～25 diameters of 200～300 milliliters absolute ethyl alcohol then with per 100 gram powders, ball milling is 15～20 hours together, dries 8～10 hours at 80～100 ℃, prepares Si ₃N ₄The quality percentage composition is 80%～90% mixed powder; After the mixed powder fragmentation, cross 40～60 mesh sieves, be pressed into base substrate at 80～100MPa pressure counterdie;

(b) base substrate is put into high temperature process furnances and under nitrogen atmosphere, be warming up to 1200～1300 ℃, in still air, be incubated then 2～3 hours and carry out oxidation and sinter, prepare porous Si ₃N ₄-SiO ₂Complex phase ceramic;

(c) to porous Si ₃N ₄-SiO ₂1～5 Ludox of complex phase ceramic dipping, each dip time is 30～60 minutes, wants ultrasonic cleaning 3～5 minutes between per twice dipping process, after cleaning in baking oven 80～100 ℃ dried 3～5 hours;

(d) to having flooded the porous Si of Ludox ₃N ₄-SiO ₂Complex phase ceramic 1200～1300 ℃ of sintering 2～3 hours in the nitrogen of atmospheric flow are made porous Si ₃N ₄-SiO ₂Electromagnetic wave transparent material.

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