Removal of low molecular weight components during thermal debinding of powder compacts

Abstract

This paper discusses the thermal removal of a low molecular weight component in a stainless steel powder-binder compact. A two-component binder composed of stearic acid (SA) and polypropylene (PP) with widely different debinding temperatures was chosen as a model system. Thermogravimetric analysis was used to determine separately the debinding kinetics of SA. Strong evidence was found that the mechanism which determines the debinding rate is the diffusion of stearic acid in the polymer. The diffusion length is half the distance between neighbouring pores which allow the evaporation products of stearic acid to move out of the compact. The differences with debinding mechanisms in ceramic powder compacts are discussed. Upper thresholds of the activation energy of diffusion of SA in liquid and solid PP are calculated to be 70 and 122 kJ mol⁻¹, respectively. The diffusivity atT= 167 °C was estimated as 8×10⁻⁹ cm² s⁻¹.