Tungsten Copper Electrode Liquid-phase Sintering Theory (2/2)

From the thermo dynamics of view, Equilibrated at the point of contact of the solid and liquid phases must meet γ_S = γ_SL + γ_Lcosθ. θ is the wetting angle or contact angle, when completely wet, θ = 0 °, then γ_S = γ_SL + γ_L; partial wetting, 0 °< θ < 90 °; completely non-wetting, θ> 90 °, this time γ_S ≥ γ_SL + γ_L. Liquid phase sintering occurs must satisfy θ < 90 °, only with complete wetting liquid or partially wet to penetrate the pores and grain gap, forming a network-like structure of the coating. If θ > 90 °, the liquid produced during sintering will quickly bleed sintered body, densification can not be successfully completed, so that the group of tungsten copper alloy phase changes occurs.

View from the classical liquid-phase humidification theory, Only when we can see the surface energy of the solid and liquid phases is greater than the sum of the solid - liquid interfacial energy, that WSL = γS + γL - γSL in WSL> 0, when the liquid in order to effectively wet the solid surface. Solid phase has certain solubility in the liquid phase will help to improve wettability, promoting an increase in the number of liquid can be carried out by means of liquid mass transfer, and dissolved in a liquid phase in the process of dissolving precipitated solute portion may be carried out to fill the solid phase defects and particle clearance particle surface, thereby further improving the solid phase particle distribution uniformity. The quantity of liquid phase required to meet the solid particles fill the gaps, reduce the porosity of the material, increasing the density of the material, generally 20% -50% of the volume of liquid phase sintering of the best accounts, exceed prone to sintering deformation is insufficient so that the liquid can not be filled solid tungsten skeleton pore and solid particles come into contact with each other and the grains will grow up.