Eff ect of Activator on Properties of SiC Porous Ceramics

Transcription

1 Ceramic Sciences and Engineering (2018) Original Research Article Eff ect of Activator on Properties of SiC Porous Ceramics Xinhua Yu,Qinqin Tian,Yanfei Li Engineering College, Nanchang University of Technology, Jiangxi, China ABSTRACT In this study, porous silicon carbide ceramics were prepared by using silicon carbide as the main material and sodium carboxymethyl cellulose (CMC) as the pore-forming agent. SiO2-Y2O3-Al2O3 and SiO2-kaolin were used as the builders respectively. This study is about the effect of SiO2-Y2O3-Al2O3 and SiO2-kaolin content on the structure and mechanical properties of porous silicon carbide. SiO2-Y2O3-Al2O3 and SiO2-kaolin affect the porosity, hardness and flexural strength of silicon carbide porous ceramics. In this experiment, the porosity of porous ceramics was measured by Archimedes method. The hardness was measured by Rockwell hardness tester. The flexural strength was measured by universal testing machine. The results show that the properties of silicon carbide porous ceramics prepared by SiO2-Y2O3-Al2O3 are better than that of SiO2-kaolinite when the SiO2-Y2O3-Al2O3 content is 20%. With SiO2-Y2O3-Al2O3 as the combustion agent, porous ceramic with better performance can be prepared at When the SiO2-Y2O3-Al2O3 content is 20%, the prepared silicon carbide porous ceramics has a large porosity and excellent mechanical properties, the opening porosity of 23.73%, hardness and flexural strength of 62 and 15.47MPa, from the fracture can be seen more porous and evenly distributed. KEYWORDS: silicon carbide; SiO2-Y2O3-Al2O3; SiO2-kaolin porous; ceramics 1. Introduction 1.1. Research background Porous ceramics refers to a high temperature firing. The inner part had massively connected to each other or close to the pores of the ceramic material. Its development began in the 1870s, initially used as a bacterial filter material. But because of its excellent performance, porous ceramics has been gradually used in the field of metallurgy, chemical sector, environmental protection, energy and biological aspects [1]. The use of porous ceramic uniform permeability, can be applied to a variety of filters, separation devices, and even can produce a fluid distribution components, mixing elements and exudative components; with porous ceramic developed surface area, it can produce a variety of porous electrode, catalyst carrier, and even can be used in heat exchangers, gas sensors and other fields; the use of porous ceramic absorption of energy performance, can be used as a variety of sound-absorbing materials, shock-absorbing materials; the use of porous ceramic low density, low thermal conductivity, can also be made into a variety of insulation materials, lightweight structural materials, coupled with its high temperature and corrosion resistance, it has aroused great attention in the global material science, and has been developing rapidly. [2]. SiC porous ceramic has the characteristics of high temperature resistance, high oxidation resistance, abrasion resistance, thermal shock resistance, small specific gravity, high thermal conductivity and microwave absorption capacity. In the filter material, catalyst carrier, thermal material, sound absorption material and composite materials that are used in a wide range of materials, and thus the subject leads to more attention [3]. In the preparation of porous ceramics, people always hope that the porous ceramic materials they ve prepared can have a large porosity, but also has excellent mechanical properties, but this causes contradiction. In general, porous ceramic porosity is large, but its mechanical properties are poor. Therefore, the relationship between the porosity of porous ceramics and the mechanical properties is a great significance in the preparation of porous ceramics. There are many factors that affect the porosity and mechanical properties of porous ceramics, such as the content and type of pore-forming agent, the content and type of the builder, the particle size of the material, the firing Copyright This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License ( permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 30

2 Xinhua Yu, et al curve and so on. These factors interact with each other, thus it is difficult to determine the porosity of porous ceramics with excellent porosity and excellent mechanical properties. When the ceramic porous ceramic is prepared by using the sintering agent, the choice of the builder and its content have a great influence on the porosity and mechanical properties of the porous ceramic. The relationship between the porosity of SiC ceramics and its mechanical properties is discussed by selecting the combustion agent and changing the content of the sintering agent. It is very important to prepare porous ceramics with large porosity and excellent mechanical properties. But also to make the preparation of porous ceramic performance more excellent, so that the application of porous ceramics is more wider Properties and Application of Porous Ceramics Porous ceramics has excellent characteristics, due to its excellent characteristics of the porous material it has been widely used, causing widespread concern. In general, the porous ceramic has some common characteristics: (1) well chemical stability; (2) fine mechanical properties and stiffness; (3) good heat resistance; (4) porous ceramic channels evenly distributed [4]. Silicon carbide porous ceramic mainly has the following applications: 1. Filter material The use of porous ceramic aperture through the size of uniformity and uniformity of the characteristics of filtration and separation. SiC porous ceramic with strong acid, high temperature resistance, for strong acid high temperature media filter [5], is now commonly used in industrial wastewater treatment, chemical industry, acidic liquid filtration, futures viscous liquid and compressed air, coke oven gas, car Tail gas and other gas separation and filtration. 2. Catalyst carrier As the porous ceramic has a high specific surface area, porous, heat, high hardness, high strength and so on. It can be used in the catalyst carrier. SiC porous ceramic is a excellent mechanical properties, stable chemical properties, and its chemically active surface as a catalyst carrier Bring new development [6]. 3. Thermal materials Mainly used as insulation materials and heat exchanger insulation material. It uses the porous ceramic s high porosity (mainly closed-cell) heat insulation as a heat exchanger for the use of its huge porosity, large heat exchange area, while the heat and corrosion resistance and other characteristics. 4. Sound absorption material Porous ceramics with mutual through the hole structure, so that the sound into the material inside the internal transmission, due to the viscosity of the air and the inherent damping properties of the material, so that the sound loss, play sound absorption, and SiC porous ceramic has a good The microwave absorption characteristics [7] are a very promising absorbing material. 5. As a composite material of the skeleton material SiC ceramics with high temperature resistance, oxidation resistance, wear resistance, corrosion resistance, good thermal shock resistance, low density and a series of excellent features, and its good adhesion with the aluminum alloy, making SiC ceramic metal composite materials The optimal material for the enhanced phase. Polymer foam impregnated with mud after the high temperature treatment can be obtained with three-dimensional network skeleton structure and the pores through the porous ceramic, with this porous ceramic as a reinforcement phase to ensure enhanced phase three-dimensional network structure continuity, while improving the performance of composite materials [8] Preparation of porous ceramics With the continuous development of industry, people demand for silicon carbide porous ceramics increasing, while the use of silicon carbide porous ceramic materials and the environment put forward higher requirements, thus promoting the preparation of porous ceramic technology development. In this method, it includes the addition of poreforming agent method, foaming method, particle packing method, organic foam impregnation method, sol-coagulation method, and the like. The method comprises the following steps of: Rubber method, in situ oxidation reaction method, reaction sintering method, carbon thermal reduction method [9]. 31

3 Effect of Activator on Properties of SiC Porous Ceramics 1.4. The purpose and significance of this research SiC sintering temperature is very high, pure SiC sintering temperature is at , which makes it difficult without adding any combustion agent in the case of sintering SiC ceramic. If the addition of certain combustion agent in the SiC raw material, the sintering temperature of SiC can be reduced by the principle of liquid phase sintering, which makes the preparation of SiC ceramics easier. Different combustion agent and content, will have a great impact on the SiC ceramic. First, different builders and contents will affect the firing temperature. As the choice of combustion agent is different, then the mechanism of reducing the firing temperature is different, it will affect the final firing temperature and firing temperature range. At the same time, different combustion agents and different content will also affect the porosity of SiC ceramics, thus affecting the mechanical properties of ceramics. Therefore, we can change the type and content of the combustion agent by adding flammable materialz and also have a large porosity and good mechanical properties of SiC porous ceramic, to prepare and to meet the requirements of the use of materials. In this study, SiO2-Y2O3-Al2O3 and SiO2-kaolin were used as the sintering agent to prepare SiC porous ceramics. The sintering conditions and the porosity of the porous materials were investigated by changing the contents of the sintering agents SiO2-Y2O3-Al2O3 and SiO2- And mechanical properties. Furthermore, SiC porous ceramics with excellent porosity and good mechanical properties were prepared by making SiC porous ceramics it is easy to be fired and both had large porosity and good mechanical properties The content of this research In this study, SiC porous ceramics were prepared by using silicon carbide as the main material and sodium carboxymethyl cellulose (CMC) as the pore-forming agent. SiO2-Y2O3-Al2O3 and SiO2-kaolin were used as the builders. Effect of SiO2-Y2O3-Al2O3 and SiO2-kaolin Content on Porosity and Mechanical Properties of SiC Porous Ceramic Materials. The process used in this experiment is: Formula design and calculation material mixing grinding forming sintering performance testing The porosity and strength of SiC porous ceramics prepared by SiO2-Y2O3-Al2O3 and SiO2-kaolin with different content were measured. After comparison and analysis, the porous ceramic ceramics with large porosity and good mechanical properties were prepared. The content of SiO2-Y2O3-Al2O3 and the content of SiO2-kaolin. In this experiment, SiC as the main raw material, CMC as the pore-forming agent, divided into two groups, one group for the SiO2-Y2O3-Al2O3 as the combustion agent, a group of SiO2-kaolin as the combustion agent. The content of SiO2-Y2O3-Al2O3 was 10%, 20%, 30% and 40%, respectively, and SiO2: Y2O3: Al2O3 was 1: 1: After the SiC porous ceramics were prepared, the porosity, flexural strength, hardness, pore size and distribution were measured. The SiO2-kaolin content is 10%, 20%, 30% and 40% respectively, and SiO2: kaolin is 1: 1, and the SiC porous ceramic is prepared. And then its porosity, flexural strength, hardness, pore size and distribution were detected. And finally compared with multiple kind of combustion agent and preparation of SiC porous ceramic with the best performance Overview of domestic and international development DL. Jiang [10] uses SiC and Al2O3 as raw materials, through the accumulation of SiC particles and graphite poreforming agent hole, in situ oxidation of the formation of quartz and mullite phase, the SiC particles combined to prepare high-strength SiC Porous ceramics. The addition of Y2O3 in the raw materials can reduce the formation temperature of mullite, promote the mullite connection phase of the degree and density, improve the mechanical properties of porous ceramics [11]. SiC porous ceramics are obtained by the reaction between the carbon template and the molten Si or gaseous Si and SiO using a carbon template. Reactive sintering can obtain dense SiC, which is very beneficial to improve the mechanical properties, but there are still some residual Si and C and the larger residual stress. In the carbon template technology, the literature [12] directly to the mesoporous carbon as a template, at 1200 ~ 1300 low temperature, and gas phase SiO or Si powder reaction sintered high specific surface area of SiC porous ceramic. The oxidation resistance of SiC porous ceramics prepared by reactive sintering method is poor. By the gas phase diffusion limit, with the gaseous Si or SiO reaction can only be prepared less than 10mm thickness of SiC porous ceramic. Through the reaction between C and SiO2 synthesis of SiC, through the template, sol - gel technology into holes, access to SiC porous ceramic. Andreas Herzog et al. [13] impregnated the silica sol with the porous carbon template obtained by carbonization of wood and then subjected to carbothermal reduction to obtain SiC porous ceramics. The SiC is deposited on the template by chemical vapor infiltration technology, and then the template is removed to obtain SiC porous ceramics. At present, Yoshimi Ohzawa [14] group used this method to prepare SiC porous ceramics. The deposited material was CH3SiCl3 + H2 and pulsed at 1100 C. The main template used is carbon 32

4 Xinhua Yu, et al fiber, cellulose, cotton, cotton and so on. With the increase of the number of pulses, the thickness of SiC layer increases, the strength increases and the porosity decreases. In the appropriate time, remove the carbon template by oxidation, it does not affect the pore structure, but the strength decreased. SJ. XIE et al. [13] prepared a three-dimensional network SiC Reinforced Cu-based composites with a conventional hot press using three-dimensional web SiC as a reinforcement. Since the three-dimensional network SiC forms a hard micro-protrusion on the wear surface and acts as a bearing, the plastic deformation and high temperature softening, reduce the contact with the matrix alloy, reduce the adhesion wear, and conducive to the oxide film in the wear surface of the retention, so the composite material shows good dry friction and wear properties. SiC porous ceramics prepared by solid-state sintering are mainly used in special functional materials. For example, high purity SiC powder can be obtained by solid-phase sintering porous structure and photoluminescence effect of porous ceramics. Fan Zimin et al [16] in the SiC powder by adding the right amount of other materials, through the accumulation of particles into the hole, at 2230 solid phase sintering prepared with conductive heating function of SiC porous ceramic. 2. Experiment 2.1. Experimental raw materials Table 1. Experimental materials Name of drug manufacturer Grade Manufacturer Silicon carbide (SiC) 1000 (Al 2 O 3 ) Pure analysis (Y 2 O 3 ) Pure analysis (SiO 2 ) Pure analysis Tianjin Branch Coso Chemical Reagent Development Center Tianjin Branch Coso Chemical Reagent Development Center Tianjin Branch Coso Chemical Reagent Development Center (CMC) Pure analysis Kaolin (PVA) Pure analysis 2.2. Experimental apparatus and equipment Electronic balance beaker straw mortar mold (26 8 8) vernier caliper Press (Model Y41-10B Tianjin second forging machine tool plant equipment electrical parameters: power supply rated voltage 380V phase 3 frequency 50Hz) Microscope (Figure 2.2-1) Rockwell Hardness Tester Vacuum sintering furnace (Figure 2.2-2) SCR temperature controller (Figure Model KSY-12D-18 Shanghai, China Research Institute Electric Furnace Co., Ltd. Electrical parameters: Maximum control power 8KW Maximum output current 150A Maximum control temperature 1800 ) 2.3. Process The main process of this study is: Formula design and calculation material mixing grinding forming sintering performance testing 33

5 Effect of Activator on Properties of SiC Porous Ceramics Selection of preparation methods As the pure SiC ceramic is difficult to sintering, so this experiment selected a certain amount of combustion agent to reduce the sintering temperature. Specifically, SiO2-Y2O3-Al2O3 and SiO2-kaolin are used as the builder. The mechanism of the two sintering agents reduce the sintering temperature is to produce liquid phase at lower temperature, through the liquid phase sintering, making SiC at low temperature densification. At the same time, because the object of this study is SiC porous ceramic, so we use the method of adding pore-forming agent to prepare SiC porous ceramic. This method is in the SiC aggregate to add a certain amount of pore-forming agent, in the sintering, due to the temperature rise, the pore-forming agent will produce gas, leaving the ceramic body in the pores, become porous ceramics. The advantage of adding pore-forming agent to prepare porous ceramics is that different shapes can be used to prepare articles with different shapes and different pore structures [17]. This process is relatively simple, relatively low cost. In this study, SiC porous ceramics were prepared by using SiO2 as the master batch and using CMC as the pore former. SiO2-Y2O3-Al2O3 and SiO2-kaolin were used as the builder. The effects of different SiO2-Y2O3-Al2O3 and SiO2-kaolin content on the sintering temperature, porosity and mechanical properties of SiC porous ceramics were studied Determination of firing curve In the first experiment, we used the calcination curve as shown in Figure , the furnace process parameters: from room temperature by 60min heating to 300, heat 100min, then 60min heating to 600, heat 30min, after 80min, heated to 1000, heat 30min, and finally by 100min, heated to 1400, heat 180min, with the furnace cooled to room temperature. Figure Burning curve In this experiment, the final burned products, has no strength, breaks off easily. Our analysis may be due to the fact that the sintering temperature is too low and the holding time is not long enough. So, we changed the firing curve, and made a second experiment. In the second experiment, we used the firing curve as shown in Figure to raise the maximum temperature to 1500 C and extend the holding time to 360 min. Furnace process parameters: from room temperature by 60min heating to 300, heat 100min, and then heated to 600min 60min, heat 30min, after 80min, heated to 1000, heat 30min, the last 100min, heated to 1500, heat 360min, With the furnace cooled to room temperature. In this experiment, the final fired products, compared with the first have a greater strength, good sintering, so as shown in Figure for the final firing curve. Figure 1. Sintering curve II 34

6 Xinhua Yu, et al Sample preparation In this experiment, method of adding a builder and a pore former was used to prepare SiC porous ceramics. The first group is SiO2-Y2O3-Al2O3 as the combustion agent, the content of 10%, 20%, 30%, 40%, pore-forming agent CMC, the content of 15%. Weighing a certain amount of SiC, Al2O3, SiO2, Y2O3 and CMC in the mortar for grinding, grinding for 1h, and then add 5% PVA, continue grinding for 1h, to be completely mixed evenly, into the mold, On the forming. After molding, as shown in Figure The second group is SiO2-kaolin as the combustion agent, the content of 10%, 20%, 30%, 40%, pore-forming agent CMC, its content is 15%. Weigh a certain amount of SiC, SiO2, kaolin and CMC in the mortar for grinding, grinding 1h, then add 5% PVA, continue grinding 1h, to be completely mixed evenly, into the mold, and then in the press molding The After molding, as shown in Figure Experimental steps Figure 2. Sample II In the first group of experiments, SiO2-Y2O3-Al2O3 as the combustion agent, due to SiO2-Y2O3-Al2O3 is different, so the following four formulations, as shown in Table In this set of experiments, the experimental steps are as follows: 1. In accordance with the formula with an electronic balance accurately weighed a certain quality of SiC, SiO2, Y2O3, Al2O3 and CMC into the mortar, grinding 1 hour, so that the material fully mixed. Then add 5% PVA to improve the molding properties of the feedstock and continue grinding for 1 hour to stir evenly. 2. Weigh 1.1g of material into the abrasive, and then molded on the press, pressed into strips, according to the burning agent SiO2-Y2O3-Al2O3 content of 10%, 20%, 30%, 40%, respectively For A1, A2, A3, A4, the recipe is shown in Table The pressed sample was placed in a vacuum furnace and sintered in a vacuum atmosphere at a firing temperature of 1400 C. The firing curve is shown in Figure In this firing curve, the resulting product, no strength, breaking off, can be seen from the cross-section, only the surface of the product appeared sintering, and in the product is no sintering. The product is shown in Figure After analysis, I think this is due to the fact that the sintering temperature is too low and the holding time is not enough. To this end, I changed the sintering curve and carried out a second experiment. Table 2. First set of experimental recipes Group SiC% SiO 2 % Y 2 O 3 % Al 2 O 3 % CMC% PVA% A1 70% 2.5% 2.5% 5% 15% 5% A2 60% 5% 5% 10% 15% 5% A3 50% 7.5% 7.5% 15% 15% 5% A4 40% 10% 10% 20% 15% 5% 35

7 Effect of Activator on Properties of SiC Porous Ceramics Figure 3. The first test of the product The second experiment, the formula is still as shown in Table , the experimental steps and the same as the first experiment. The second experiment uses the firing curve shown in Figure This experiment is a good way to overcome the lack of the first experiment, the product has a higher strength, density is much higher than the first time. But the second experiment is also a problem, the surface of the product there are a lot of macroscopically visible pores, and the emergence of significant expansion and greater cracks. The product is shown in Figure After analysis, I think this is CMC in the low temperature volatile a lot of gas caused by the teacher s guidance, I conducted a third experiment. The third experiment, the formula is still as shown in Table , firing curve shown in Figure In the experimental steps, to take some improvement measures. First, the use of buried, that is, in the sintering, the product buried in the Al2O3 powder below, which can effectively slow down the low temperature sintering, CMC volatile gas rate. Second, this experiment was fired in a high temperature furnace (SCR temperature controller) as shown in Figure 2.2-3, and the atmosphere at the time of sintering was air. The experimental product, compared with the previous two have improved significantly. Products have a higher strength, high density, at the same time, the product surface is more smooth, no large pores, no significant expansion and cracks. The product is shown in Figure After that, the product was tested for performance. Figure 4. The product obtained in the second experiment 36

8 Xinhua Yu, et al Figure 5. The product obtained in the third experiment In the second group of experiments, SiO2-kaolin as the combustion agent, due to different SiO2-kaolin, so the following four formulations, as shown in Table Table 3. The second set of experimental recipes Group SiC% SiO 2 % 高岭土 % CMC% PVA% B1 70% 5% 5% 15% 5% B2 60% 10% 10% 15% 5% B3 50% 15% 15% 15% 5% B4 40% 20% 20% 15% 5% The second group of experiments due to the experience of the first group of experiments, as shown in Figure using the firing curve, using Figure high temperature furnace (SCR temperature controller), using Buried and other methods. The specific experimental steps are as follows: 1. According to the formula with an electronic balance accurately weighed a certain quality of SiC, SiO2, kaolin, CMC into the mortar, grinding 1 hour, so that the material fully mixed. Then add 5% PVA to improve the molding properties of the feedstock and continue grinding for 1 hour to stir evenly. 2. Weigh 1.1g of the material into the abrasive, and then formed in the press, pressed into strips, according to SiO2 - kaolin builders content of 10%, 20%, 30%, 40%, respectively, numbered B1, B2, B3, B4, the formula shown in Table The pressed sample was placed in a high-temperature furnace and sintered in an air atmosphere at a firing temperature of 1500 C. The firing curve was shown in Figure The products obtained in this experiment are better, the products have higher strength and higher density. At the same time, the surface of the product is relatively flat, there is no large pores, no deformation, obvious expansion and crack. The product is shown in Figure Subsequently, the product was tested for performance. 3. Performance testing 3.1. Detection of porosity The experiment uses the Archimedes method to detect the porosity of the product, the specific method is: 37

9 Effect of Activator on Properties of SiC Porous Ceramics 1. Measure the dry weight of the product. 2. The product into the water soak for 5 minutes, and then come out, with a saturated wet towel to dry the surface of the product, measured wet weight m2. 3. Measure the volume of the product by the drainage method. 4. Use formula 1 to measure the porosity of the product. Porosity = (m2-m1) / (ρ water V) Formula 1 In the first set of experiments, I measured the porosity calculated in Table From Table 3.1-1, we see that the porosity varies according to the SiO2-Y2O3-Al2O3 content. I think that a slight change in porosity may be caused by the different degree of Al2O3 coverage when the individual is buried. Table 4. The porosity of the product when SiO2-Y2O3-Al2O3 is used as the builder Group porpsity A % A % A % A % In the second set of experiments, I measured the porosity calculated in Table From Table 3.1-2, we see that the porosity varies according to the SiO2-kaolin content. I think that a slight change in porosity may be caused by the different degree of Al2O3 coverage when the individual products are buried, and the porosity is slightly larger when SiO2-kaolin is used as a builder, and this is probably due to the fact that kaolin Water content is relatively large reason Hardness testing Table 5. The porosity of the product when SiO2-kaolin is used as the builder Group Porosity B % B % B % B % The hardness of the two sets of samples was mm and the load was 60Kg. The hardness of SiC porous ceramics prepared with SiO2-Y2O3-Al2O3 as the builder is shown in Table As can be seen from Table 3.2-1, when the SiO2-Y2O3-Al2O3 content is 20%, the hardness reaches a maximum value of 62, while the SiO2-Y2O3-Al2O3 content continues to increase and the hardness decreases drastically. The hardness of SiC porous ceramics prepared with SiO2-kaolin as the builder is shown in Table Table 6. Hardness of SiC porous ceramics with SiO2-kaolin as the builder Group B1 B2 B3 B4 Hardness As can be seen from Table 3.2-2, when the SiO2-kaolin content is 20%, the hardness also reaches a maximum of 55, while the SiO2-kaolin content continues to increase, the hardness decreases. In contrast to Table and Table 3.2-2, it can be seen that SiO2-Y2O3-Al2O3 is the builder, the hardness is larger than that of SiO2-kaolin as the builder, and this is also a consistent with the porosity of the two sets of samples When the SiO2-Y2O3-Al2O3 was used as the builder, the porosity was larger and the porosity was negatively correlated with the mechanical properties of the porous ceramic. When SiO2-Y2O3-Al2O3 is used as the builder, and its content is 20%, the hardness reaches a maximum value of Flexural strength test The three-point flexural strength of SiC porous ceramics was measured on a universal material testing machine with a span of 20 mm and a loading speed of 0.5 mm / min. SiC porous ceramic sample is 28mm 8mm 8mm long strip. The flexural strength of the product when SiO2-Y2O3-Al2O3 is used as the builder is shown in Table

10 Xinhua Yu, et al Table 7. Flexural strength of SiC porous ceramics with SiO2-Y2O3-Al2O3 as builder Group A1 A2 A3 A4 Pressure Strength(MPa) As can be seen from Table 3.3-1, the flexural strength of SiC porous ceramics is low, which I think may be related to the pore-forming agent CMC. CMC volatile too much, at , volatile a lot of gas, making the embryo body produced a large number of holes, the contact between the particles become not close, greatly affected the high temperature sintering, and ultimately lead to products cannot be completely sintered, Bending strength is low. However, it can be seen from Table that the SiC porous ceramics produced have a maximum flexural strength when the SiO2-Y2O3-Al2O3 content is 20%, which I think this may be due to the SiO2-Y2O3-Al2O3 content of 20 %, And the sintering temperature is 1500, the sintering of the product is the densest, and SiO2-Y2O3-Al2O3 for other content, there is a low degree of sintering or over-burning, thus affecting the product s flexural strength. The flexural strength of the product when SiO2-kaolin is used as a builder is shown in Table The It can be seen from Table that the flexural strength of SiC porous ceramics is also extreme when SiO2-kaolin is used as the builder, and the flexural strength is the largest when the SiO2-kaolin content is 20% is 11.27MPa, And when the SiO2-kaolin content increases or decreases, the flexural strength decreases. The flexural strength of SiC porous ceramics is negatively correlated with the porosity of SiO2-kaolin as the activator, and the porosity is large and the flexural strength is small, and the porosity is small and the flexural strength is large. And Table and Table to compare, we can see that SiO2-Y2O3-Al2O3 as a builder, the flexural strength than SiO2-kaolin for the combustion agent, and this also with the two The porosity is in good agreement with SiO2-Y2O3-Al2O3 as the combustion agent, the porosity is smaller than that of SiO2-kaolin. It can be seen that the porosity of SiC porous ceramics is negatively correlated with its mechanical properties. SiO2-Y2O3-Al2O3 as the combustion agent, the overall porosity is small, and the bending strength is larger. (23.73%) and the maximum flexural strength (12.47 MPa) were obtained when the content was 20% at And SiO2 - kaolin as a sintering agent, the overall porosity is larger, greater bending strength Crystal phase analysis The fracture structure of the sample was observed under a 100-fold microscope. The first group of experiments, with SiO2-Y2O3-Al2O3 as the combustion agent of the sample structure shown in Figure 3.4-1, 3.4-2,3.4-3, Figure 6. Specimen containing 10% SiO2-Y2O3-Al2O3 under microscope From the first group of experiments can be seen from the crystal phase, with SiO2-Y2O3-Al2O3 as the combustion agent, the resulting products of the pores of the pores is small, the distribution is more uniform, while the pore 39

11 Effect of Activator on Properties of SiC Porous Ceramics distribution and SiO2-Y2O3-Al2O3 content Is not close, and with the SiO2-Y2O3-Al2O3 content increased, the pore size of a slight increase in the trend. And some samples of local stomatal is more intensive or scarce, which may be caused by uneven mixing. The crystal phase analysis is also consistent with the hardness and flexural strength of the previous test, with SiO2-Y2O3-Al2O3 as the combustion agent, the cross-sectional morphology is better, the hardness and bending strength of the products are larger. Figure 7. Sample containing 20% SiO2-Y2O3-Al2O3 under microscope Figure 8. Sample containing 30% SiO2-Y2O3-Al2O3 under microscope 40

12 Xinhua Yu, et al Figure 9. Sample containing 40% SiO2-Y2O3-Al2O3 under microscope Figure 10. Sample containing 10% SiO2-kaolin under a microscope The structure of SiC porous ceramics is shown in Figure 3.4-5, 3.4-6, 3.4-7, when SiO2-kaolin is used as the builder. It can be seen from the crystal phase obtained from the second group of experiments that when the SiO2-kaolinite is used as the builder, the resulting pores are larger and larger. At the same time, when the SiO2-kaolin content is increased, the pore and pore size Evenly, and even some stomata connected to each other, the formation of large pores. With the increase of SiO2-kaolin content, the pore size of the product becomes larger, and the stomatal distribution becomes more uneven, local dense, local sparse. When the SiO2-kaolin content is 40%, we can see that there are a large number of large pores, uneven distribution in the sample section, which we do not want to get. I think that this may be kaolin containing water, moisture in the initial sintering volatilization, the formation of more pores, and these stomata also affected to the late sintering, making the product less compact. Compared with the first group of experiments, that is, SiO2-Y2O3-Al2O3 for the combustion of the product compared to the burned, its surface morphology is poor, which 41

13 Effect of Activator on Properties of SiC Porous Ceramics is consistent with the previous porosity, hardness, flexural strength of the test to SiO2-Y2O3-Al2O3 for the combustion agent to get the products, less pores, the distribution is more uniform, its hardness and flexural strength are higher. And SiO2 - kaolin as the combustion agent, the pores more, uneven distribution, hardness, bending strength is low. 4. Conclusion When the SiC porous ceramic is prepared by using SiO2-kaolin as the activator, the porosity is larger, but the pore size is larger and the pore distribution is inhomogeneous. The hardness and flexural strength of SiC porous ceramic are low. The flexural strength of SiC porous ceramics prepared with SiO2-kaolin as the activator was 11.27MPa and the opening porosity was 24.72%. Therefore, the use of SiO2 - kaolin as a sintering agent to prepare SiC porous ceramic, the resulting mechanical properties of poor products. When the SiC porous ceramic is prepared by using SiO2-kaolin as the sintering agent, the kaolin contains certain moisture, which makes the porosity of the product larger. At the same time, the temperature of the liquid phase of SiO2 and Al2O3 is higher ( ), So that the uses of liquid phase sintering of the combustion effect is not obvious, the product at 1500 sintering level is not high, resulting in poor mechanical properties of products. When the SiC porous ceramic was prepared by SiO2-Y2O3-Al2O3 as the sintering agent, the porosity was slightly smaller, but the pore size was smaller and the pore distribution was more uniform. The hardness and flexural strength of the SiC porous ceramic were higher The Therefore, SiO2-Y2O3-Al2O3 as the combustion agent, can be prepared at 1500 better performance of SiC porous ceramic. When the content of SiO2-Y2O3-Al2O3 is 20%, the flexural strength of SiC porous ceramic is 15.47MPa, the hardness is 62, and the opening porosity is 23.73%. And from the fracture can be seen, more pores, smaller, and evenly distributed, both large porosity and excellent mechanical properties. References 1. SZ. Zhu, ZB. Zhao, GQ. Liu. Preparation technology of porous ceramic materials [J]. Materials Science and Engineering. 1996,14 (3): S. Y, SH. Tan, DL. Jiang. Preparation and Catalytic Performance of Porous Silicon Carbide [J]. Acta Metallurgica Sinica, 2003,18 (4): R. ZHANG, SL. FU, LU Hong-xia et al. Effect of Sintering Temperature on SiC Porous Ceramics [J]. Chinese Journal of Ceramics, 2000,5: XW. Zhu, DL. Jiang. Organic Foam Impregnation Process - A Kind of Economical and Practical Preparation of Porous Ceramics [J]. Chinese Journal of Ceramics, 2000,3: Schwartzwalder and A.V. Somess. United States Patent. US QB. Ye, DP. Xia, HD. Liu. Preparation of silicon carbide foam ceramic filter [J].1995,5: XW. Zhu, DL. Jiang, SH. Tan. Preparation of Silicon Carbide Mesoporous Porous Ceramics [J]. Chinese Journal of Inorganic Materials, 2000,15 (6): Chinese Journal of Ceramics, 2004,32 (2): (in Chinese with English abstract) [J]. Chinese Journal of Ceramics, 2004,32 (2): Sundeman and J.V iedt. United States Patent. US Aoki Y and Mc Enaney B. SiC foams produced by siliciding carbon foams [J]. Britsh Ceramic Transactions, 1995, 94 (4): XL. Zhu, XQ. Su. Porous ceramic materials [J]. Chinese Ceramics, 2000,36 (4): YM. Wang, WQ. Cai. Porous ceramic filter material [J]. Jiangsu Ceramics, 2003,36 (1): JS. Zhang, XM. Cao, LX. Ma, etc. Chinese Patent Publication No. CN A 14. JZ. Wu, SY. Yi, Ouyang stick. Journal of Ceramics, 1993, (12) 3: P.Sepulveda and J.G.P.Binner.Processing of cellular ceramics by foaming and in situ Polymensation of organic monomers [J].J.European Ceramic Society, 1999, 19: Aoki Y and Mc Enaney B.SiC foams Produeed by siliciding carbon foams [J].British Ceramic Transactions, 1995,94 (4): J.-H. She, J.F. Yang, N. Kondo, T. Ohji, S. Kanazaki, Z.-Y. Deng, High strength porous silicon carbide ceramics by an oxidation-bonding technique, J. Am. Ceram. Soc. 85 (11) (2002)