Fabrication And Properties Of MAS Glass-ceramics Byaqueous Tape Casting

The MAS glass substrate were fabricated via aqueous tape casting usingMAS powders obtained by high temperature solid state reaction between the rawmaterials of MgO, Al2O3and SiO2. The dispersing behavior and mechanism ofthe MAS powder in the liquid were discussed. Influnce of bonding agent?plasticizer and solid content on the rheology behavior of the slurry weresystematically investigated. The TG-DTA curve of the green tape were examinedto optimize the binder burnout process. The the co-firing between MAS powderand Ag electrode was achieved by studying the influence of sintering temperatureon the properties of MAS glass substrate. The sintering temperature andshrinkage of Si3N4ceramic were lowerd by incroporating MAS powders, and theeffect of Si3N4volume on the sinterability, mechaical properties of the compositewere discussed.MAS glass powder could be dispersed by triammonium citrate effectivelyaccording to the result of Zeta potential which the maximum potential absolutevalue can reach more than40mv. The apparent viscosity of the suspensionsshowed "V" changes and increased with the dispersant content and solid contentincreased, respectively; Slurry exhibits shear thinning property, and viscosityincreases with the binder content and solid content, yet, viscosity showed a trendof first increasing and then decreasing with plasticizer content added. Butanolcan be used as a defoaming agent added to slurry, due to it can reduce the surfacetension of water.The distribution of PVA was different for different parts of green tapes. PVApresent filiform and net distribution for top and bottom surfaces, respectively.The bulk density of the green tape increased with solid loading while the averagepore diameter and porosity exhibited crosscurrent. XRD analysis showed that themain phases of the sintered samples were SiO2and glass at low temperature(850oC), only ?-cordierite was detected at high temperature (900-950oC). Thedensity of the substrate increased with sintered temperature while the shrinkageexhibited crosscurrent. The coefficient of thermal expansion decreased with theincreasing sintered temperature which was matched to Si. The substrate possessed excellent dielectric properties including low dielectric constant andloss. The substrate could be co-fired with Ag at900oC though the diffuse of Agwas detected.Viscosities of MAS/Si3N4slurries increase as the increasing of Si3N4content while the green tapes display single peak distribution. All the organicsubstance will be removed completely above550?. Only alpha-cordierite phaseand alpha-Si3N4phase exist in the composites, and no reaction was taken place.Both sintering shrinkage and densities of the composites descend asincreasing of Si3N4content. Strength increases and the begining and then reducesas increasing of Si3N4content, and the highest bend strength is145MPa;Dielectric constant descend as increasing of Si3N4content while dielectric lossappear oppsite tendency. The dielectric constant and loss decreased abruptly at5MHz because of the relaxation polarization.