Preparation of a thermal insulating material using electrophoretic deposition of silica particles

The electrophoretic deposition (EPD) of silica nanoparticles was performed to prepare consolidated thermal insulating material. Optimal conditions were found considering the loading contents, the suspension medium, and the electric field intensity. The density and thermal conductivity were changed by applying a mechanical pressure before drying of the gel. Density ranged from 120 to 500 kg m-3 with an average porosity comprised between 0.78 and 0.95. According to the porosity, the average pores size of compressed materials was between 7 and 20 nm. Such materials exhibit a thermal conductivity as low as 0.020 W m-1 K-1 at room temperature and 1 atm pressure. Thermal conductivity ranged from 0.020 to 0.045 W m-1 K-1. Minimal conductivity exists for a certain distance between particles. Boundary resistance between adjacent particles was obtained as function of the porosity and its change interpreted as ones of conductive paths though air molecules and across direct solid-solid exchange between particles