Measurement of porosity in ceramic coatings by thermogravimetric volatilization of liquids

A simple gravimetric method was developed to determine the open porosity in ceramic coatings, The coating's pore space was filled with a liquid and the weight loss on volatilization of the liquid was measured in a thermogravimetric analyzer. This thermogravimetric volatilization of liquids (TVL) method was used to characterize the porosity in titania coatings, alumina/aluminum phosphate coatings, and free-standing films of alumina, Several liquids mere used; ethylene glycol and 1,3-propanediol gave the best results due to their low volatilities at room temperature, The measured porosities of the ceramic coatings ranged from 30% to 80% and the pore sizes (as determined by SEM and mercury porosimetry) ranged from 0.1 to 15 mu m. The standard deviation of the TVL measurement was smaller for thicker coatings (e.g., greater than or equal to 20 mu m). Porosities determined by TVL mere within typically 5-10 % of those determined by mercury intrusion porosimetry on identical samples, Characterization of a series of alumina/aluminum phosphate coatings showed a decrease in porosity consistent with expectations based on density and SEM observations, TVL is nondestructive, can be used for small volumes of sample, and when combined with SEM, provides a good means to characterize coating porosity and pore structure.