Silicon nitride porous ceramic composition and preparation method thereof

A technology of porous ceramics and silicon nitride, applied in the field of silicon nitride porous ceramics formulation and preparation, can solve the problems of unpleasant hydrocarbon gas, unfavorable environmental protection, toxicity, etc., achieve superior economy and reliability, and shorten process time , the effect of avoiding environmental pollution

Inactive Publication Date: 2008-09-03

XI AN JIAOTONG UNIV

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Problems solved by technology

The debinding process presents some serious problems

First, the debinding process is very time-consuming, especially for large-sized products, which often takes several days, resulting in a decrease in production efficiency

Second, the improper heating system ...

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Method used

As can be seen from Table 2, Fig. 1 and Fig. 2, due to the addition of yttrium oxide sintering aid, the intergranular phase increases, the porosity of the sintered body decreases, and the flexural strength also improves.

[0023] Bentonite content is preferably 5 to 30%. If it is less than 5%, the corresponding mud material may not have good plasticity, which is not conducive to extrusion. If it exceeds 30%, the silicon nitride content will decrease accordingly, the intergranular phase will increase after sintering, and the mechanical properties will decrease. The said bentonite is c...

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Abstract

The invention discloses a porous silicon nitride ceramics composing prescription and a method for the products thereof, containing the following components by weight: 50-70 per centsilicon nitride powder, 5-30 per cent bentonite, 0-10 per cent sintering additives and 20-30 per cent water. The sintering additives, contain at least one of Y2O3, Al2O3 and MgO and the method includes: weighing the components except water before placing into a ball mill for dry mixing-grinding to make a mixed powder which is then put into a wheel roller for wheel grinding and kneading to obtain a pug; putting the pug into an extruder for extrusion forming to obtain a shaped body; then drying the shaped body before putting into an atmosphere oven where the shaped body is heated to a temperature of 1700-1850 DEG C in the nitrogen at a heating rate of 10 DEG C/min and then insulation sintered for 1 to 3 hours at a nitrogen pressure of 1-6 atmospheric pressure to obtain a sintered body . The porous silicon nitride ceramics of the invention can be widely used as matrix of filters for gas separation at high temperature and in corrosive atmosphere and as heat-resistant or enhanced materials for power generation gas turbines, engines and space shuttles.

Technology Topic

Silicon nitrideGas separation +13

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[0021] The present invention will be further described in detail below in conjunction with specific embodiments.

[0022] A silicon nitride porous ceramic composition, as shown in Table 1, in Examples 1 to 9 shown in Table 1, the silicon nitride powder content is generally 50 to 70%, if less than 50%, the nitrogen in the sintered body The silicon nitride content is also small, the reinforcing effect of the rod-shaped silicon nitride grains is limited, and the mechanical properties of the fired body are reduced. If it is greater than 70%, the amount of bentonite added will be reduced accordingly, and the plasticity of the corresponding mud will be poor, and liquid phase migration will easily occur during extrusion, resulting in large fluctuations in the density of the extruded green body. The average particle diameter of silicon nitride powder is preferably 0.5-1 micron, and its crystal form can be expressed as different Si 3 N 4 particles. Such as α-type, β-type, or amorphous Si 3 N 4 Both can be used, as well as mixtures of silicon nitride and precursors.

[0023] The content of bentonite is preferably 5-30%. If it is less than 5%, the corresponding mud material may not have good plasticity, which is not conducive to extrusion. If it exceeds 30%, the silicon nitride content will decrease accordingly, the intergranular phase will increase after sintering, and the mechanical properties will decrease. The said bentonite is characterized by montmorillonite-based hydrous clay ore, including sodium-based, calcium-, magnesium-based bentonite, or sepiolite clay ore. Adding an appropriate amount of bentonite in the prescription of the present invention can not only endow the ceramic mud with good plasticity, which is convenient for the smooth progress of the extrusion process, but also has an auxiliary sintering effect in the sintering process of ceramic products. 2 o 3 、Al 2 o 3 Or in the case of MgO, it can also promote the formation of silicon nitride porous ceramic products at a lower temperature.

[0024] Formulation and sintering process conditions of silicon nitride porous ceramics of the present invention

[0025]

[0026] The addition amount of the sintering aid in the composition of Table 1 is 0-10wt%. If it exceeds 10 wt%, the shrinkage rate of the porous ceramic increases, resulting in a decrease in porosity and a large amount of intercrystalline glass phase. The sintering aid mentioned here refers to a metal oxide that changes into glass in the high temperature range of sintering. The embodiment of table 1 adopts Y 2 o 3 、Al 2 o 3 Or at least one of MgO, and a mixture of two or three of the above can also be added.

[0027] For liquid phase water, the amount added is generally 20-30%, preferably 23-27%. If it is less than 20%, the plasticity of the mud is relatively poor and cannot be extruded smoothly. If it exceeds 30%, the mud material is too soft, and the green body strength after extrusion is low, and deformation is easy to occur.

[0028] According to the preparation method of the silicon nitride porous ceramics of the formula in Table 1, the silicon nitride powder, bentonite, and sintering aid are first weighed to obtain the initial powders of Examples 1-9, which are respectively put into a ball mill for dry mixing to obtain 9 uniformly mixed powders of different recipes. After passing the mixed powder of each formula through a 200-mesh sieve, add the corresponding proportion of water in Table 1, put them into the wheel rolling machine, and knead the wheel into a uniform mud. The mud material of each formula is put into the extruder and pressurized at 1 MPa, and the mud is smelted for 3 times, and then extruded to obtain the required molded body. Place the molded bodies of the above-mentioned formulas in an oven at 120 degrees to dry, put the dried molded bodies into an atmosphere furnace, and heat them to 1700-1850 degrees at a heating rate of 10-50 degrees per minute under nitrogen , kept at a nitrogen pressure of 1-6 atmospheres for 1-3 hours to obtain a sintered body. The specific process parameters of the sintering process are shown in Table 1.

[0029]The sintering temperature of the square molded bodies of the above-mentioned embodiments is 1700-1850 degrees under nitrogen atmosphere. If the temperature is less than 1700 degrees, the phase transformation of silicon nitride cannot be completely completed. If the temperature exceeds 1850 degrees, the aspect ratio of silicon nitride grains may be reduced and the mechanical properties may be reduced. The heating rate is preferably 10-30 degrees/minute, if it is lower than 10 degrees/minute, it will increase the sintering time and reduce the production efficiency. If it is higher than 50 degrees per minute, it may cause the green body to crack. If the holding time is less than 1 hour, the phase transition cannot be completely completed, and if it is longer than 3 hours, the microstructure will not change much, resulting in waste of energy. Therefore, the best holding time is 1-3 hours.

[0030] The three-point bending strength at room temperature was measured for the silicon nitride porous ceramic sintered body sample obtained by the above method. The Archimedes drainage method was used to determine the open porosity. Mercury porosimetry was used to test the pore size. Scanning electron microscope was used to observe the microstructure on the section of the sample (Example 2-4). The performance results of these porosity, pore size and mechanical strength are shown in Table 2.

[0031] It can be seen from Table 2 that when sintered at a temperature range of 1700-1850 degrees, the sintered body exhibits a high bending strength at a porosity of 30-60%, up to 172MPa.

[0032] from figure 1 and figure 2 It can be seen that due to the increase of bentonite content, the intergranular phase in the sintered body increases, but it has no effect on the growth of rod-shaped crystals of the material.

[0033] From Table 2, figure 1 and figure 2 It can be seen that due to the addition of yttrium oxide sintering aid, the intergranular phase increases, the porosity of the sintered body decreases, and the flexural strength also increases.

[0034] Table 2 Performance of silicon nitride porous ceramic sintered body of the present invention

[0035] Open porosity

[0036] Example 3

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Classification and recommendation of technical efficacy words

Avoid environmental pollution
Shorten process time

Silicon nitride porous ceramic composition and preparation method thereof

AI-Extracted Technical Summary

Problems solved by technology

Method used

Abstract

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Examples

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Description & Claims & Application Information

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