<P> This thesis is concerned with the investigation of the diffusion controlled reaction between MgO and β-quartz in the temperature range 1200 - 1450 °C in wet and dry atmospheres. The reactions were studied by placing known faces of quartz crystals in direct contact with Mg0 powder, heat treating them, and then investigating the cross sections. The product layer was investigated by both reflected light and thin section metallography, electron - microprobe and X- ray diffraction. Using Wagner's and Schmalzried's ideas on solid state reactions, a theoretical model for the diffusion controlled formation of silicates was developed. With this model, a mechanism for the diffusion controlled formation of forsterite from MgO and β-quartz was advanced. </P> / Thesis / Master of Science (MSc)

The temperature profile needed to complete the reaction between the sodium-diamine complex and the isocyanate terminated prepolymer has been established. The sodium diamine complex has the advantage of blocking the nearly instantaneous reaction between the diamine and isocyanate from taking place until it is released at elevated temperatures. Because of its low melting temperature (~40 °C) and its low molecular weight (low viscosity), this chain extension reaction is not dependent on the participation of the prepolymer. Instead, the rate of reaction is dependent on the dissolution of the 4,4’-methylenedianiline (MDA) complex into the system. The dissolution of the MDA complex has been demonstrated to be strongly dependent on particle size. Both the plasticizer Bis(2-ethylhexyl) adipate and the quaternary ammonium compound found in soy lecithin play crucial roles for this reaction. The quaternary ammonium compound is crucial in the dissolution of the complexes. Although the plasticizer has been shown to dissolve the complex to a small extent, the principal role of the plasticizer is to disperse the complexes and to prevent their agglomeration. Other additives such as Dimethyl Sulfoxide (DMSO) have demonstrated to be highly efficient in dissolving the complex. However its effectiveness limits the mixing window needed before reaction take place, resulting in a disadvantage.