Glass-ceramic pressure sensor support base and its fabrication

Abstract

A dry pressing and slip casting process is provided for the manufacture of glass-ceramic components of the type used in sensors. Both process on starts with a powder composition of SiO (42-59 wt. %), Al O (17-35 wt. %), MgO (2-25 wt. %) and also BaO (0-20 wt. %), TiO (0-12 wt. %), ZnO (0-10 wt. %), CaO (0-10 wt. %), B O (0-5 wt %), P O (0-5 wt. %), ZrO (0-5 wt. %), alkali oxides such as K O, Na O (0-3 wt. %) and other small amounts (0-1 wt. %) of additives such as Fe O , As O . Fe O , V O , As O . Some of the ingredients (e.g. Mg, Ba, Ca) can also be present in the form of fluoride, e.g., MgF , BaF , CaF , to up to 10 wt. %. Additional ceramic additives up to 30 wt. %, which are as second phase (e.g., Al O , Y O doped ZrO , SiO , mullite, zircon, carbides, nitrides, and a combination of the above), are not part of the glass composition, but are introduced to enhance both the mechanical strength and toughness and to further modify the coefficient of thermal expansion. In the dry pressing process the powder is milled, blended with a binder and then subjected to a drying/granulation process. A die cavity of a desired shape is then filled with the powder. Pressure is then applied to die for a period of time. After the pressure is removed, the green ceramic part is ejected and then sintered to become a finished ceramic cover or header. In the slip casting process, the powder is milled and dispersed in a water. The slip is then poured or pumped into a permeable casting mold of a desired shape made of Gypsum. When either the liquid has been completely sucked away by the mold or the desired depositing thickness has been reached, the cast green ceramic part is removed from the mold, dried and then sintered into a finished ceramic cover or header.