The Study On Low-temperature Sintering Of Alumina Ceramic And Its Metallizing

In order to promote the application of vacuum electron devices, extensive studies on alumina ceramics and its metallizing have been carried out worldwide. In this work, the alumina ceramics and its metalizing, which were sintered at 1400¹550℃using BAS glass (a precursor for glass-ceramic) as the sintering additive, were investigated.. The properties of BAS glass and effects of some factors on sintering of alumina ceramics and its metallizing were analyzed by differential scanning calorimetry, scanning electron microscopy, X-ray diffraction analysis and other testing methods.BAS glass was designed and prepared for sintering additive. It was found that the softening and melting temperature of the designed glass were 1340¹390℃and 1450℃, respectively. The BAS glass was transformed into BaAl₂Si₂O₈ during cooling process, which could be sintered at low temperature by liquid phase sintering. Using the BAS glass as sintering additive, Y₂Si₂O₇, Y₂SiO₅, 3Al₂O₃·2SiO₂ and La₂Zr₂O₇ ceramics were prepared by liquid sintering. The results showed that the composite oxide ceramics can be obtained at low temperatures, and the main crystal phase is the designed composite oxide and the rest is BaAl₂Si₂O₈ crystallized from the glass.Effects of some factors on densification of alumina ceramics adding BAS glass were studied. The densification of ceramics was influenced by glass content, density of green body and sintering process. When the density of green body was 2.7².9g/cm³, the BAS glass content was 5% and the sintering temperature was 1500℃, the relative density of alumina ceramics could reach 97.3%. The result showed that the alumina ceramics with low pore rate, small grain size section, narrow grain size distribution and uniform grain morphology, had excellent mechanical properties.The influences of the Mo particles size, contents of BAS and sintering temperature on the surface status and the properties of metallized alumina ceramics were investigated. Using BAS glass as sintering additive, the Mo metallizing layer was produced on the surface of alumina ceramic. When the Mo particles size was 1³Î¼m, the BAS contents was 15²5%, and the sintering temperature was 1400 ¹570℃, the tensile strength of jointed sample was over 260MPa.The microstructure and elemental distribution of metallized ceramic were analyzed, and the mechanism of metallization was discussed. The results show that both glassy phases migration and Mo sintering act the key roles for the molybdenum metallizing, which could be obtained by liquid phase sintering, using BAS glass as sintering additive.