CN109369194B - Low-dielectric and high-strength porous silicon nitride ceramic and preparation method thereof - Google Patents
Low-dielectric and high-strength porous silicon nitride ceramic and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a preparation process for preparing low-dielectric and high-strength porous silicon nitride ceramics by microstructure regulation, which comprises the following steps: preparing gel, forming a blank body, drying the blank body, removing gel from the blank body, and sintering the blank body. The invention aims to improve beta-Si3N4The conversion of (1) is promoted by adding zirconium boride to the slurry3N4To beta-Si3N4Can form high aspect ratio beta-Si3N4The columnar crystal phases are mutually overlapped to form a pore framework of the porous silicon nitride ceramic, so that the strength of the porous silicon nitride ceramic is improved. The preparation process of the porous silicon nitride ceramic provided by the invention is low in cost and simple in process, and the prepared porous silicon nitride ceramic is high in porosity, low in dielectric constant and good in mechanical property. The porosity is more than or equal to 50%, the dielectric constant is 3.3 +/-0.1, and the bending resistance is 99.89-131.67 MPa. The microstructure of the final porous silicon nitride ceramic is shown in the attached drawing.
Description
Technical Field
The invention relates to the technical field of material preparation, in particular to a preparation process of porous silicon nitride ceramics.
Background
The porous silicon nitride ceramic has the advantages of corrosion resistance, high temperature resistance, wear resistance, high specific surface area, low dielectric constant, dielectric loss and the like, and has a very wide application prospect in the fields of high-temperature gas filtration, sensor development, preparation of catalyst carriers and separation membranes, missile radome processing and the like, so that the preparation of the porous silicon nitride ceramic becomes one of the current research hotspots.
The most important characteristic of porous silicon nitride ceramics is that the porous silicon nitride ceramics is porous, and the methods for preparing the porous ceramics commonly used at present, such as a pore-forming agent adding method, a foaming method, a reaction sintering method, an extrusion molding method, gel injection molding and the like, are used for preparing the porous ceramics, and the porous ceramics prepared by the methods have the defects of low void ratio, non-uniform pore size, non-uniform distribution and low strength of the prepared products, or have the defects of harsh drying conditions, high production cost and complex process, so that the requirements of modern production and processing are difficult to meet.
Disclosure of Invention
The invention aims to provide a preparation process of porous silicon nitride ceramics, which has the advantages of simple process, low cost, higher porosity and strength performance and uniform pores, aiming at the defects of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme.
A preparation process of low-dielectric and high-strength porous silicon nitride ceramics comprises the following steps:
(1) preparing gel: silicon nitride powder, zirconium boride powder, a sintering aid, a cross-linking agent, a dispersing agent, a defoaming agent and deionized water are mixed according to the weight ratio of (52-98): (3-9): (2-7): (0.52-0.98): (0.15-1.8), mixing 100 parts of the raw materials, adjusting the pH value to 8.2-11.5 by using 0.01M sodium hydroxide solution, and performing ball milling for 2.5-10 hours to uniformly mix to obtain gel;
(2) and (3) forming of a blank body: carrying out vacuum defoaming treatment on the gel obtained in the step (1) in a vacuum defoaming machine for 10-30 min, injecting the gel into a mold for molding, curing and demolding;
(3) drying the green body: cooling the demolded blank to room temperature, completely freezing the sample, and freeze-drying to obtain a silicon nitride blank;
(4) discharging glue of the blank body: heating the prepared silicon nitride blank in air to discharge glue; heating to 150 ℃ at a heating rate of 1 ℃/min, heating to 400 ℃ at 1.2 ℃/min, heating to 600 ℃ at 1.5 ℃/min, and then preserving heat for 1.5-6 h;
(5) sintering of the green body: putting the green body after the glue discharging into a sintering furnace, heating to 1700-1800 ℃ at a speed of 5 ℃/min under the nitrogen atmosphere, and preserving the heat for 2-3 h; and then raising the temperature to 1800-2000 ℃ for air pressure sintering, and keeping the temperature for 1-2 h to cool along with the furnace to obtain the porous silicon nitride ceramic.
(6) The post-treatment process of the porous silicon nitride ceramic comprises the following steps: the strength of the porous silicon nitride ceramic is improved and the dielectric loss of the porous silicon nitride ceramic is reduced through pre-oxidation treatment and annealing process.
The dispersant is preferably ammonium polyacrylate with the molecular weight of 3500-4500.
The cross-linking agent is any one of polyvinyl alcohol, polyacrylamide, methyl cellulose and Isabam.
Where Isabam is used as the dispersant and crosslinker, i.e., Isabam is the only organic additive, the solvent is deionized water.
The sintering aid is a mixture of rare earth oxides such as yttrium oxide, lanthanum oxide, cerium oxide, lutetium oxide and praseodymium oxide, and aluminum oxide and silicon dioxide, and the ratio of the rare earth oxides to the aluminum oxide to the silicon dioxide is 1:1: 1.
The defoaming agent is preferably C7-C9 alcohol, and is preferably n-octanol.
Said beta-Si3N4The promoter is zirconium boride powder, and the addition amount is Si3N45-30% of volume content.
In the step (3), the sample is completely frozen and is placed at the temperature of minus 25 ℃ for 24 to 36 hours.
In the step (3), the freeze drying treatment is freeze drying for 15-36h at-60 to-80 ℃.
In the step (2), the curing treatment is to fix the glass fiber in a vacuum drying oven at 55-80 ℃ for 60 min.
The sintering method in the step (5) adopts a two-step sintering method: sintering at 1700-1800 ℃ under normal pressure; sintering at 1800-2000 deg.c and gas pressure of 0.6 MPa.
The post-treatment method of the porous silicon nitride ceramic in the step (6) comprises the following steps: carrying out high-temperature pre-oxidation treatment at 1000-1300 ℃ on the porous silicon nitride ceramic or carrying out annealing process at 500-800 ℃ on the porous silicon nitride ceramic.
Compared with the prior art, the invention has the beneficial effects that:
(1) when the Isobam is used as the only organic additive as the dispersant and the gel, the solvent is deionized water to prepare water-based slurry;
(2) the formed Si3N4 ceramic has the advantages of simple process, less organic additives, environmental friendliness and low price, and can be widely applied to preparation of products with low cost, excellent performance and complex shapes;
(3) the invention adopts zirconium boride powder as beta-Si3N4The accelerant of (2) regulates and controls the microstructure of the porous silicon nitride ceramic;
(4) the invention adopts a two-step sintering method and carries out post-treatment on the porous silicon nitride ceramic, so that the porous silicon nitride ceramic has low dielectric constant and high strength;
(5) the porous silicon nitride ceramic prepared by the invention has high porosity, uniform pores and excellent mechanical and dielectric properties, the porosity is more than or equal to 50%, the dielectric constant is 3.3 +/-0.1, and the bending resistance is 99.89-131.67 MPa.
Drawings
FIG. 1 is the microstructure of the final product of example 1;
FIG. 2 is the mechanical properties of the final product of example 1;
FIG. 3 shows the dielectric properties of the final product of example 1.
Detailed Description
The present invention will be described more fully hereinafter with reference to the following examples. However, the material ratio, the process parameters and the results described in the examples are only for illustrating the present invention and are not to be construed as limiting the present invention.
Example 1
(1) Preparing gel: mixing 52g of silicon nitride powder, 5g of zirconium boride powder, 5g of sintering aid, 3g of Isobam polymer, 1g of defoaming agent and 100g of deionized water, adjusting the pH to 9 by using 0.01M sodium hydroxide solution, and performing ball milling for 3 hours to uniformly mix the components to prepare gel; wherein the sintering aid is a mixture of yttrium oxide, aluminum oxide and silicon dioxide in a ratio of 1:1:1, the cross-linking agent is polyvinyl alcohol, the dispersing agent is ammonium polyacrylate with the average molecular weight of 3500, and the defoaming agent is n-heptanol;
(2) and (3) forming of a blank body: carrying out vacuum degassing treatment on the gel in the step in a vacuum drying oven for 15min, injecting the gel into a mold for molding, fixing the gel in an oven at 55 ℃ for 60min, and demolding;
(3) drying the green body: cooling the demolded blank to room temperature, standing the sample at-25 ℃ for 24h, completely freezing the sample, and freeze-drying the sample at-60 ℃ for 15h to obtain a silicon nitride blank;
(4) discharging glue of the blank body: heating the prepared silicon nitride blank in air to discharge glue; heating to 150 ℃ at a heating rate of 1 ℃/min, heating to 400 ℃ at 1.2 ℃/min, heating to 600 ℃ at 1.5 ℃/min, and then keeping the temperature for 2 hours;
(5) putting the green body after the glue discharging into a sintering furnace, heating to 1700-1800 ℃ at a speed of 5 ℃/min under the nitrogen atmosphere, and preserving the heat for 2-3 h; then raising the temperature to 1800-2000 ℃ for air pressure sintering, keeping the temperature for 1-2 h, and cooling along with the furnace to obtain the porous silicon nitride ceramic;
(6) the post-treatment process of the porous silicon nitride ceramic comprises the following steps: the strength of the porous silicon nitride ceramic is improved and the dielectric loss of the porous silicon nitride ceramic is reduced through pre-oxidation treatment and annealing process.
Through detection, the porosity of the prepared porous silicon nitride ceramic is 67.23%, and the bending resistance is 100.89 MPa.
Example 2
(1) Preparing gel: mixing 65g of silicon nitride powder, 6g of sintering aid, 3g of cross-linking agent, 0.7g of dispersing agent, 1.2g of defoaming agent and 100g of deionized water, adjusting the pH to 9.5 by using 0.01M sodium hydroxide solution, and performing ball milling for 5 hours to uniformly mix to prepare gel; wherein the sintering aid is a mixture of yttrium oxide, aluminum oxide and silicon dioxide in a ratio of 1:1:1, the cross-linking agent is polyvinyl alcohol, the dispersing agent is ammonium polyacrylate with the average molecular weight of 3750, and the defoaming agent is n-octanol;
(2) and (3) forming of a blank body: carrying out vacuum degassing treatment on the gel in the step in a vacuum drying oven for 15min, injecting the gel into a mold for molding, fixing the gel in an oven at 60 ℃ for 60min, and demolding;
(3) drying the green body: cooling the demolded blank to room temperature, standing the sample at-20 ℃ for 24h, completely freezing the sample, and freeze-drying the sample at-60 ℃ for 15h to obtain a silicon nitride blank;
(4) discharging glue of the blank body: heating the prepared silicon nitride blank in air to discharge glue; heating to 150 ℃ at a heating rate of 1 ℃/min, heating to 400 ℃ at 1.2 ℃/min, heating to 600 ℃ at 1.5 ℃/min, and then preserving heat for 3 h;
(5) putting the green body after the glue discharging into a sintering furnace, heating to 1700-1800 ℃ at a speed of 5 ℃/min under the nitrogen atmosphere, and preserving the heat for 2-3 h; then raising the temperature to 1800-2000 ℃ for air pressure sintering, keeping the temperature for 1-2 h, and cooling along with the furnace to obtain the porous silicon nitride ceramic;
(6) the post-treatment process of the porous silicon nitride ceramic comprises the following steps: the strength of the porous silicon nitride ceramic is improved and the dielectric loss of the porous silicon nitride ceramic is reduced through pre-oxidation treatment and annealing process.
The porosity of the prepared porous silicon nitride ceramic is 66.34% and the bending resistance is 110.72 MPa.
Example 3
(1) Preparing gel: mixing 73g of silicon nitride powder, 6g of sintering aid, 6g of cross-linking agent, 0.7g of dispersing agent, 1.5g of defoaming agent and 100g of deionized water, adjusting the pH value to 10 by using 0.01M sodium hydroxide solution, and performing ball milling for 7 hours to uniformly mix to prepare gel; wherein the sintering aid is a mixture of yttrium oxide, aluminum oxide and silicon dioxide in a ratio of 1:1:1, the cross-linking agent is polyvinyl alcohol, the dispersing agent is ammonium polyacrylate with the average molecular weight of 4000, and the defoaming agent is n-octanol;
(2) and (3) forming of a blank body: carrying out vacuum degassing treatment on the gel in the step in a vacuum drying oven for 20min, injecting the gel into a mold for molding, fixing the gel in the oven at 65 ℃ for 60min, and demolding;
(3) drying the green body: cooling the demolded blank to room temperature, standing the sample at-20 ℃ for 30h, completely freezing the sample, and freeze-drying the sample at-70 ℃ for 20h to obtain a silicon nitride blank;
(4) discharging glue of the blank body: heating the prepared silicon nitride blank in air to discharge glue; heating to 150 ℃ at a heating rate of 1 ℃/min, heating to 400 ℃ at 1.2 ℃/min, heating to 600 ℃ at 1.5 ℃/min, and then preserving heat for 3 h;
(5) putting the green body after the glue discharging into a sintering furnace, heating to 1700-1800 ℃ at a speed of 5 ℃/min under the nitrogen atmosphere, and preserving the heat for 2-3 h; then raising the temperature to 1800-2000 ℃ for air pressure sintering, keeping the temperature for 1-2 h, and cooling along with the furnace to obtain the porous silicon nitride ceramic;
(6) the post-treatment process of the porous silicon nitride ceramic comprises the following steps: the strength of the porous silicon nitride ceramic is improved and the dielectric loss of the porous silicon nitride ceramic is reduced through pre-oxidation treatment and annealing process.
The porosity of the prepared porous silicon nitride ceramic is 65.16% and the bending resistance is 115.89 MPa.
Example 4
(1) Preparing gel: mixing 85g of silicon nitride powder, 7g of sintering aid, 7g of cross-linking agent, 0.8g of dispersing agent, 1.8g of defoaming agent and 100g of deionized water, adjusting the pH to 10.5 by using 0.01M sodium hydroxide solution, and performing ball milling for 7 hours to uniformly mix to prepare gel; wherein the sintering aid is a mixture of yttrium oxide, aluminum oxide and silicon dioxide in a ratio of 1:1:1, the cross-linking agent is polyvinyl alcohol, the dispersing agent is ammonium polyacrylate with the average molecular weight of 4000, and the defoaming agent is n-octanol;
(2) and (3) forming of a blank body: carrying out vacuum degassing treatment on the gel in the step in a vacuum drying oven for 20min, injecting the gel into a mold for molding, fixing the gel in an oven at 70 ℃ for 60min, and demolding;
(3) drying the green body: cooling the demolded blank to room temperature, standing the sample at-20 ℃ for 36h, completely freezing the sample, and freeze-drying the sample at-80 ℃ for 30h to obtain a silicon nitride blank;
(4) discharging glue of the blank body: heating the prepared silicon nitride blank in air to discharge glue; heating to 150 ℃ at a heating rate of 1 ℃/min, heating to 400 ℃ at 1.2 ℃/min, heating to 600 ℃ at 1.5 ℃/min, and then keeping the temperature for 4 h;
(5) putting the green body after the glue discharging into a sintering furnace, heating to 1700-1800 ℃ at a speed of 5 ℃/min under the nitrogen atmosphere, and preserving the heat for 2-3 h; then raising the temperature to 1800-2000 ℃ for air pressure sintering, keeping the temperature for 1-2 h, and cooling along with the furnace to obtain the porous silicon nitride ceramic;
(6) the post-treatment process of the porous silicon nitride ceramic comprises the following steps: the strength of the porous silicon nitride ceramic is improved and the dielectric loss of the porous silicon nitride ceramic is reduced through pre-oxidation treatment and annealing process.
The porosity of the prepared porous silicon nitride ceramic is 62.69% and the bending resistance is 127.25 MPa.
Example 5
(1) Preparing gel: mixing 98g of silicon nitride powder, 9g of sintering aid, 7g of cross-linking agent, 0.98g of dispersing agent, 1.8g of defoaming agent and 100g of deionized water, adjusting the pH to 11.5 by using 0.01M sodium hydroxide solution, and performing ball milling for 10 hours to uniformly mix to prepare gel; wherein the sintering aid is a mixture of yttrium oxide, aluminum oxide and silicon dioxide in a ratio of 1:1:1, the cross-linking agent is polyvinyl alcohol, the dispersing agent is ammonium polyacrylate with the average molecular weight of 4500, and the defoaming agent is n-octanol;
(2) and (3) forming of a blank body: carrying out vacuum degassing treatment on the gel in the step in a vacuum drying oven for 30min, injecting the gel into a mold for molding, fixing the gel in an oven at 80 ℃ for 60min, and demolding;
(3) drying the green body: cooling the demolded blank to room temperature, standing the sample at-20 ℃ for 36h, completely freezing the sample, and freeze-drying the sample at-80 ℃ for 36h to obtain a silicon nitride blank;
(4) discharging glue of the blank body: heating the prepared silicon nitride blank in air to discharge glue; heating to 150 ℃ at a heating rate of 1 ℃/min, heating to 400 ℃ at 1.2 ℃/min, heating to 600 ℃ at 1.5 ℃/min, and then keeping the temperature for 6 h;
(5) putting the green body after the glue discharging into a sintering furnace, heating to 1700-1800 ℃ at a speed of 5 ℃/min under the nitrogen atmosphere, and preserving the heat for 2-3 h; then raising the temperature to 1800-2000 ℃ for air pressure sintering, keeping the temperature for 1-2 h, and cooling along with the furnace to obtain the porous silicon nitride ceramic;
(6) the post-treatment process of the porous silicon nitride ceramic comprises the following steps: the strength of the porous silicon nitride ceramic is improved and the dielectric loss of the porous silicon nitride ceramic is reduced through pre-oxidation treatment and annealing process.
The porosity of the prepared porous silicon nitride ceramic is 59.58 percent and the bending resistance is 131.67 MPa.
Claims (2)
1. A preparation method of low-dielectric and high-strength porous silicon nitride ceramics is characterized by comprising the following steps:
(1) preparing gel: mixing 52g of silicon nitride powder, 5g of zirconium boride powder, 5g of sintering aid, 3g of Isobam polymer, 1g of defoaming agent and 100g of deionized water, adjusting the pH to 9 by using 0.01M sodium hydroxide solution, and performing ball milling for 3 hours to uniformly mix the components to prepare gel; wherein the sintering aid is a mixture of yttrium oxide, aluminum oxide and silicon dioxide in a ratio of 1:1: 1; the defoaming agent is n-heptanol;
(2) and (3) forming of a blank body: carrying out vacuum degassing treatment on the gel prepared in the step (1) in a vacuum drying oven for 15min, injecting the gel into a mold for molding, fixing the gel in the oven at 55 ℃ for 60min, and demolding;
(3) drying the green body: cooling the demolded blank to room temperature, standing the sample at-25 ℃ for 24h, completely freezing the sample, and freeze-drying the sample at-60 ℃ for 15h to obtain a silicon nitride blank;
(4) discharging glue of the blank body: heating the prepared silicon nitride blank in air to discharge glue; heating to 150 ℃ at a heating rate of 1 ℃/min, heating to 400 ℃ at 1.2 ℃/min, heating to 600 ℃ at 1.5 ℃/min, and then keeping the temperature for 2 hours;
(5) putting the green body after the glue discharging into a sintering furnace, heating to 1700-1800 ℃ at the speed of 5 ℃/min under the nitrogen atmosphere, and preserving the heat for 2-3 h; then raising the temperature to 1800-2000 ℃ for air pressure sintering, keeping the air pressure at 0.6MPa, and carrying out furnace cooling for 1-2 h to obtain the porous silicon nitride ceramic;
(6) the post-treatment process of the porous silicon nitride ceramic comprises the following steps: the strength of the porous silicon nitride ceramic is improved and the dielectric loss of the porous silicon nitride ceramic is reduced through pre-oxidation treatment and annealing process.
2. The method for preparing a porous silicon nitride ceramic according to claim 1, wherein the post-treatment process of the porous silicon nitride ceramic in the step (6) comprises: carrying out high-temperature pre-oxidation treatment at 1000-1300 ℃ on the porous silicon nitride ceramic and carrying out annealing process at 500-800 ℃ on the porous silicon nitride ceramic.
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| CN112279670A (en) * | 2020-11-10 | 2021-01-29 | 衡阳凯新特种材料科技有限公司 | Low-shrinkage porous silicon nitride ceramic and preparation method thereof |
| CN112661519A (en) * | 2021-01-28 | 2021-04-16 | 威海圆环先进陶瓷股份有限公司 | Production technology of silicon nitride ceramic pile |
| CN113773091B (en) * | 2021-08-11 | 2023-10-24 | 臻金新材(深圳)有限公司 | Aluminum nitride ceramic casting slurry, aluminum nitride ceramic substrate and preparation method |
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