Research On The Composite, Microstructure And Thermal Properties Of Alumina-cordierite Ceramics For Heat Exchanger

Inorganic-nonmetallic ceramic heat exchangers are wildly used in many fields of manufacturing industry for advantages such as low cost, excellent heat resistance and chemistry performance, long service and low coefficient of thermal expansion. However, thermal shock resistance and thermal conductivity of ceramic heat exchangers are poor than metal heat exchangers, which limits ceramic heat exchangers’further application in industry.Alumina ceramics have series of excellent performance; however, poor thermal shock resistance limits their applications in the field of heat exchangers. In this paper, based on the related project, cordierite-aluminum ceramics for heat exchanger were prepared by industrial raw materials and slip casting process. The X-ray diffraction, scanning electron microscope, laser flash thermal analyzer, thermal shock resistance test, sintering properties test, mechanical properties test are used to analysis the effects of compositions and sintering additives on the relative density, porosity, bending strength, the main crystalline phase, microstructure, thermal conductivity and thermal shock resistance.The effects of cordierite on the microstructure and properties of cordierite-aluminum ceramics were studied. The results showed that with the increase of cordierite between10wt%and50wt%, the relative density and bending strength were decreased, porosity was increased; XRD showed cordierite was increased, α-Al2O3was decreased gradually, and a small amount of mullite appeared. There was a plate structure of microstructure of the ceramic fracture with out significant grain boundary. Round grains of cordierite existed. Small air holes distributed evenly. The thermal conductivity was decreased gradually, and the thermal shock resistance was increased firstly and then decreased. When cordierite content was30wt%, the ceramic sintered at1350℃had the best thermal shock resistance performance, the number of the thermal shock cycle was12; the thermal conductivity rate reached to the maximum,9.385W· m-1K-1, at room temperature.The effects of MgO-TiO2sintering additives on the microstructure and properties of cordierite-aluminum ceramics were studied. The results showed that with the increased of TiO2/MgO ratios, the relative density was decreased and porosity was increased, when ceramics sintered at1250℃and1300℃; when ceramics sintered at1350℃, the relative density was first increased and then decreased, porosity was first decreased and then increased, when TiO2/MgO=0.5, the relative density was increased to the maximum82.68%, porosity was decreased to the minimum13.51%; the bending strengths of all the ceramics were more than100MPa.With the increased of TiO2MgO ratios, XRD showed cordierite was decreased, mullite was increased and α-Al2O3was changed little, when ceramics sintered at1250℃and1300℃; cordierite completely disappeared, mullite and alumina was basically unchanged. There was a plate structure of microstructure of the ceramic fracture with out significant grain boundary, and mullite crystals precipitated. With the increased of TiO2/MgO ratios, the thermal conductivity was increased gradually when ceramics sintered at1250℃and1300℃; the thermal conductivity of ceramics sintered at was increased1350℃was increased firstly and then decreased. The thermal shock resistance was increased firstly and then decreased. When TiO2/MgO=0.5, the ceramic sintered at1350℃had the best thermal shock resistance performance, the number of the thermal shock cycle was18; the thermal conductivity rate reached to the maximum,12.624W· m-1K-1, at room temperature.