Preparation Of Porous Alumina Ceramics And Discussion On The Pore-Making Mechanism Of Aluminum

The preparation of porous alumina ceramics with aluminum powder as pore forming agent is a new technology proposed in recent years.The advantage of this process is that Al2O3,the product of pore forming agent,is an important component of porous alumina ceramics,so the introduction of aluminum powder into ceramic materials will not lead to the deviation of ceramic components.However,as the process is still in the exploratory stage,there are still many problems to be solved,such as the pore forming mechanism of aluminum powder is unknown.The paper uses aluminum powder to prepare porous alumina ceramics,thoroughly discuss the influence of aluminum powder on the performance of porous alumina ceramics,and explore its pore forming mechanism.In this paper,porous alumina ceramics were prepared by dry pressing.The effects of the amount of aluminum powder,the size of aluminum powder and forming pressure on the properties of ceramics were studied.It is found that with the increase of the amount of aluminum powder,the firing shrinkage of ceramic materials decreases gradually until the sintering shrinkage reaches 0%,and the ceramic materials expand when aluminum powder is added continuously.With the increase of the amount of aluminum powder,the apparent porosity increase and bending strength of ceramics decrease gradually.With the increase of the particle size of aluminum powder,the firing shrinkage of ceramic materials gradually increased,the apparent porosity gradually decreased,and the bending strength gradually increased.With the increase of forming pressure,the shrinkage of ceramic materials decreases,both of the apparent porosity and the bending strength increase.In this paper,tetraethyl silicate(TEOS)is used as the coating material,and Si O2 produced by hydrolysis is used as the coating material to coat and modify the aluminum powder,so as to enhance its water resistance,and effectively solve the defect that aluminum powder is easy to hydrate and is not suitable for wet process to prepare porous ceramics.The aluminum content of the coated aluminum powder was measured by gas capacity method in acid environment,and the coating rate of the aluminum powder was calculated.It is found that with the increase of the quality ratio of coating materials(TEOS / Al),the coating rate of aluminum powder increases gradually.Porous alumina ceramics were prepared by using coated aluminum powder as pore forming agent.The effect of the amount of coated aluminum powder and TEOS / Al quality ratio on the properties of the ceramics was investigated.It is found that the coated aluminum powder completely meets the needs of wet forming porous high aluminaceramics and has good foaming effect in high alumina ceramics.The pore forming regularity is similar to that of non coated aluminum powder in high alumina ceramic materials,with the increase of the amount of coated aluminum powder,the firing shrinkage of the ceramic materials gradually decreased,the apparent porosity gradually increased,and the bending strength gradually decreased.The influence of TEOS / Al mass ratio on the properties of ceramics was studied.It was found that with the increase of TEOS / Al mass ratio,the firing shrinkage of ceramics first decreased and then increased,the apparent porosity first increased and then decreased,and the bending strength first decreased and then increased.In this paper,SEM was used to observe the microstructure of ceramic materials at different firing temperatures.It was found that when the firing temperature was 1100 ℃,there was no liquid phase in the green body,and there were holes with explosive open structure in the ceramic materials.It was believed that this was the result of oxidation and evaporation boiling of aluminum powder at this temperature;when the firing temperature was raised to 1250 ℃,there was liquid phase in the green body,and there were spherical bubbles in the ceramic material,The results show that the void formed by high temperature oxidation and evaporation boiling of aluminum powder is effectively wrapped by high viscosity liquid phase.According to the comprehensive analysis,the pore forming mechanism of aluminum powder in ceramic matrix is the result of the synergistic action of two mechanisms: explosion pore forming and oxidation expansion pore forming of aluminum powder.