Title

Supercritical carbon dioxide processing of vitrified bonded abrasives

Date of Completion

January 2004

Keywords

Engineering, Chemical|Engineering, Environmental

Degree

Ph.D.

Abstract

Supercritical CO2 (scCO2) was investigated for use in the processing of vitrified bonded abrasives. In this study, two novel technologies were developed; selective extraction of pore inducers from vitrified bonded abrasives and thin film deposition of lubricants into vitrified bonded abrasives from supercritical solutions. ^ Highly porous vitrified grinding wheels were produced by selective extraction of pore inducers with dense CO2. This technology was developed as an alternative to the conventional thermal technique. Green grinding wheels were made with CO2 soluble pore inducers which were subsequently subjected to scCO2. The extraction rate was a function of temperature, flow rate, and flow direction. The vanishing kinematic viscosity of scCO 2, combined with the relatively large solubility of the pore inducers, led to strong natural convention currents. The system was modeled using a coupled set of equations for external mass transfer and internal diffusion, with an average absolute error of 3.4%. Grinding tests demonstrated the scCO 2 extracted wheels performed as well if not better then conventional pore induced wheels. ^ Supercritical CO2 was used for the deposition of fine films within vitrified bonded grinding wheels. Vitrified bonded abrasives were placed in a solution of lubricant dissolved in scCO2. Upon depressurization, the solution passed through the cloud point and the lubricant precipitated out of solution and was deposited within the pore matrix of the grinding wheel. The mass of material impregnated was only a function of concentration in solution, indicating the deposition was uniform and the thickness of the deposits was controllable. The impregnated grinding wheels were subjected to grinding tests and had superior performance compared to grinding wheel standards. ^ In order to investigate the phenomena governing the deposition within the wheel, a glass pore was developed to model the system. The effect of supersaturation was investigated by altering the rate of approach to the cloud point. Rapid expansion led to high supersaturations and micron to submicron particles deposited uniformly throughout the pore. Deposition by temperature quench led to both heterogeneous and homogeneous nucleation. The entire pore area was found to be covered with heterogeneously nucleated submicron particles, which were affected by surface imperfections on the glass. ^