Study Of Macroporous Ceramic Pipes Prepared In Cold Isostatic Pressing

Ceramic filters offer a number of excellent properties including high temperature stability, resistance to chemical corrosion, high filtering precision, as well as convenient backwashing and regeneration, so show a bright future of development and utilization in areas of new energy development, catalyst support, high-performance filters. As core component of porous ceramic filter, for the sake of dust particles removal, Porous ceramic pipe is necessary to withstand the environment of flue gases, thermal stress and exhibit the characteristics of high collection efficiency, high airflow quantity and low pressure drop. Oxides and non-oxide (SiC) porous ceramic pipes with diameter 50μm, filtering accuracy greater than 10μm, and a certain bending strength were prepared in the subject. In this paper, by means of corundum powder and SiC powder as aggregates, carbon black as pore former, macroporous ceramic pipes were prepared in Cold Isostatic Pressing method.Forming process of macroporous ceramic pipe in CIP was explored from coarse aggregates. Both external pressing method and internal pressing method dies were designed based on the target sizes and compression ration of the powder; effects of powder properties, molding pressure, demolding and drying on green body were investigated; common defects such as non-uniform in neck, decentration in inner diameter, abscission of the blined end and rupture in the middle were summed up; furthermore, the reasons that led to these were briefly analyzed.Porous ceramic pipes on dimension ofφ60mm×φ40mm×400mm,φ60mm×φ40mm×1000mm were prepared with 220μm corundum as aggregate and carbon black as pore-former in CIP method, of which the average pore size was 70μm, the bending strength was more than 20MPa, and a large amount of pores bigger than 200μm existed. The air flow-pressure drop curve were determined by simple device. It is shown that pore-former enables the rearrangement of the aggregates to form framework; when the additions are 5wt.%, 10wt.%, the averge pore diameters are 65μm, 70μm, respectively; the bending strength reaches the maximum at 5wt.% carbon black addition, and drops subsequently. Morever, with addition of 7wt.% CMC, the body strength reaches the maximum; if more, the demolding is difficult, and even leads to green body fracture.Silicon carbide ceramic pipes on dimention ofμ60mm×μ40mm×400mm were prepared with aggregates A(180～150μm, 90mesh), B(250～212μm, 74mesh), C(300-250μm, 60mesh) and D(355-300μm, 54mesh). The effects of aggregate size, pore-former, binder and sintering system were investigated. The results show that when sintered at 1200℃, the pore diameter is in the rang of 20～40μrn, and average pore diameter is 30um, also the contents of large pores(d > 100μm) increace. When soaked for 120min at 1150℃, the bonding strength is lower, so abscission on the surface is general; while soaked for 120min at 1300℃, glass transition on the surface leads to drop of porosity, at the same time the bending strength rises because of the oxidation of SiC. At 800℃the oxidation of black carbon into CO₂ stimulates the formation of circular, open pores; when reached at 1300℃, the pores turn into ellipse. The dehydration and decomposition of Kaolin at the high temperature increases the pore volnme and probability of the formation connective pore.