Feedstock Mixture Research Articles

Chemical composition of soft vacuum electron beam assisted chemical vapor deposition of silicon nitride/oxynitride films versus substrate temperature

Thin silicon nitride/oxynitride films were deposited on silicon substrates by a soft vacuum electron beam plasma assisted deposition in a triad gas feedstock mixture of silane, ammonia, and nitrogen. Fourier transform infrared spectra, x-ray photoelectron spectra, Auger electron spectra, and secondary ion mass spectra of these thin films were analyzed and compared to determine both the bulk chemical composition and the interfacial properties. Film composition varied from SiO2 to Si3N4 as the substrate temperature (Ts) varied from 50 to 450 °C. Between 150 and 350 °C a stable SiOxNyHz structure formed. The films deposited with NH4–SiH4–N2 mixtures contained large (20%–60%) amounts of N–H bonds, but no detectable Si–H bonds (<0.5%). The total hydrogen content of deposited films decreased by a factor of 10 (to 2%–3%) when only nitrogen and silane were used as source gases, in comparison with that obtained using the triad feedstock mixture.

Two-stage catalytic cracking

This article discusses the use of a scheme in which a mixture of feedstock and cracked product vapor, partially reacted in a cocurrent-flow reactor, comes into contact with regenerated catalysts in the sections of a staged-countercurrent reactor. The proposed two-stage catalytic cracking process is free of the disadvantages of riser cracking, and it offers a means for obtaining considerably greater feedstock conversions and better product quality. The process is distinguished by ''forced'' hydrocarbon regimes in all stages, highly efficient regeneration of the catalyst, and the use of new design elements. Experimental runs were made in the pilot plant and semicommercial units in order to compare the process indexes in two-stage and concurrent cracking. Highly aromatic gasoils can be obtained by two-stage cracking under moderately severe conditions (up to 490/sup 0/C in the cocurrent-flow reactor and 510/sup 0/C in the staged-countercurrent reactor). The process can be conducted in the required direction with respect to feedstock conversion and also with respect to the quality of the end products.