In this study we investigated the effects of process variables on the bond strength, and its dependency upon the interfacial chemistry when the joined $ZrO_2$ toughened $Naeta$"-alumina to $alpha$-alumina using B$_2$$O_3$-$SiO_2$-Al$_2$$O_3$-CaO glass sealant. We observed that bond strength is mainly determined by the strength of the glass, which, in turn, depends on the glass composition established after joining reaction. Joining at $950^{circ}C$ for 15min yielded the highest average bond strength of 66MPa. Different types of interfacial reaction seem to occur at each interface. After joining at $950^{circ}C$ for 15min we found that Ca and Si diffuse much deeper(~15$mu extrm{m}$) into the $eta$"-alumina composite than into the $alpha$-alumina(<1$mu extrm{m}$) as a result of ion exchange reaction and more effective grain boundary diffusion. Thermal expansion coefficient of the glass was found to have changed more closely to those of the $eta$"-alumina composite and $alpha$-alumina, which put the glass under a slight compressive stress.ressive stress.