Fabrication, microstructural characterisation and mechanical properties of glass compacts containing controlled porosity of spheroidal shape

Addition of hollow glass microspheres to a glass powder and densification of the mixture by hot-pressing is shown to be an attractive technique to fabricate porous glass compacts with isolated porosity of controlled shape. The microspheres are deformed in viscous state under the uniaxial pressure during matrix densification, leading to spheroidal pores dispersed in the glass matrix. By changing the hot-pressing parameters, it is possible to manipulate the shape of the pores, i.e., to change their axial ratio. Pore axial ratios between 1 and 0.1 were obtained, with porosity volume fractions of up to 0.35. The mechanical properties of the porous glass compacts (Young's modulus and flexure strength) were determined and the influence of pore content, shape and orientation on the measured property values was discussed. It was observed that pores acted as fracture origins. The fabricated porous materials, containing spheroidal pores of well-defined shape and orientation, are shown to be very useful to test the validity and prediction capability of theoretical models. Other possible application areas of these porous materials with closed, isolated pores are discussed.