Grish Chandra

Alkyl- and arylsilsesquiazanes: effect of the R group on polymer degradation and ceramic char composition

A series of alkyl- and arylsilsesquiazanes [RSi(NH)3/2] was prepared by the ammonolysis of the corresponding RSiCl3. Each polymer was pyrolysed to 1200° C in an inert atmosphere to give amorphous Si-C-N ceramic chars. The major volatile products in the pyrolysis effluent were identified and quantified by a combination of TGA-GCMS, TGA-GCFTIR and pyrolysis-capillary GC techniques. Mechanistic aspects correlating the alkyl/aryl group on the polymer structure, decomposition and ceramic char composition were studied. Oxidative stability of the ceramic chars fits percolation theory. The oxygen contents of ceramic chars containing ⩽ 25 wt% carbon increased 1 to 2% after 12 h at 1200° C. At higher levels of carbon the chars were completely oxidized to SiO2.

The atmospheric partitioning of decamethylcyclopentasiloxane(D5) and 1-hydroxynonamethylcyclopentasiloxane(D4TOH) on different types of atmospheric particles

A series of outdoor chamber experiments using different types of atmospheric particles were conducted to investigate the atmospheric gas-particle partitioning behavior of decamethylcyclopentasiloxane (D5) and its hydroxylated compound, 1-hydroxynonamethylcyclopentasiloxane (D4TOH). This was undertaken because the phase in which a compound exists directly influences its lifetime in the atmosphere, its deposition to the surface of the earth, and ultimately its potential impacts on human health. To treasure the phase distribution, or partitioning, between the gas and particle phases, aerosol systems were created in either the 190 m3 or 25 m3 outdoor Teflon film chambers at the UNC chamber facility in Pittsboro, NC. Diesel, wood, and coal soot were used as organic combustion particle sources, while Arizona fine dust was used as an inorganic particle source. The gas-particle partition coefficient, Kp, was used as a measure of the phase distribution. Kp can be expressed as Kp = (Cp/TSP)/Cg, where Cp(ng/m3) and Cg(ng/m3) are the concentrations in the particle and gas phases respectively, and TSP (μg/m3) is the total suspended particulate matter concentration. The effect of temperature is considered to be the key parameter that affects the partitioning coefficient. Chamber data showed for both D5 and D4TOH partitioning, that temperature was very important and could influence partitioning to the particle phase by two orders of magnitude in going from 25 to 0°C. It was also found that relative humidity (RH) was an important parameter affecting D4TOH partitioning especially with mineral dust particles.

Low Temperature Ceramic Coatings for Environmental Protection of Integrated Circuits

A novel concept for improved environmental protection of integrated circuits uses thin, in-situ formed ceramic layers on the circuit surface. Metastable ceramic precursors, hydrogen silsesquioxane and silacyclobutane, convert to pure silica and amorphous silicon carbide dielectric films respectively upon processing at temperatures from 175 to 250oC. These twolayer ceramic films were shown to protect silicon CMOS circuits from industry-recognized autoclave and HAST exposure environments for more than 400 hours whereas unprotected circuits always failed within 200 hours.