| The specific heats, thermal conductivities, and emissivities of powders were measured for use in the Selective Laser Sintering process. Although these data were collected for this process, they have general utility for describing the thermal and optical behaviors of powders.; Differential Scanning Calorimetry was used to test the specific heats of some powders. The Water-Bath Method was developed for measuring the thermal conductivities of the powders from room temperature to 90{dollar}spcirc{dollar}C. The Laser-heated Method, was developed for measuring the thermal conductivity of the powder beds from room temperature to 500{dollar}spcirc{dollar}C.; Emissivities of some powders were tested by the laser-heated method. An equation was derived for the prediction of the emissivity of a powder bed when the emissivity of the solid material which makes up the powder particles and the porosity of the powder are known. The derived equation was compared with the data collected and found to be within {dollar}pm{dollar}30% relative error.; The thermal conductivity data collected were checked against the existing models for the prediction of thermal conductivity of powders in literature.; A new model was developed, and was found to better correlate the thermal conductivity data. The new model may be used to predict the thermal conductive of a powder bed when the particle size, temperature of the powder, the thermal conductivity of the solid which makes up the powder, the thermal conductivity of the fluid which fills up the pores of the powder, and the porosity of the powder are known. The model and data agree with {dollar}pm{dollar}30% over a wide range of materials.; The thermal conductivity prediction equation suggested is used in the SLS modeling program, written by Christian Nelson and revised by Neal Kent Vail at the University of Texas at Austin, to examine the feasibility of using helium as the environmental gas for the SLS process. The result showed that the use of helium as the environmental gas yielded parts of lower porosity than when nitrogen is used. The result indicates the important contribution of gas phase conductivity to the overall bed conductivity. |
