Carbon-nitrogen ratios pyrolysis

The carbon snpport was synthesized by the drying and pyrolysis of a resorcinol-formaldehyde aqueous gel, following a procedure developed in a previous study [8] the R/C (resorcinol/sodium carbonate) molar ratio of the gel precursor solution was chosen equal to 1000, while all other synthesis variables (from gel preparation to pyrolysis conditions) were kept identical as in the above-mentioned study. In brief, resorcinol and sodium carbonate were solubilized in water and then formaldehyde was added. Gelation and ageing were performed at 85°C (72 h), and were followed by evaporative drying (60-150°C, 1 day) and pyrolysis (800°C, 2 h) under nitrogen flow. 

Accordingly, a 0-1 molar solution of phthalic anhydride in benzene (100 ml.) was pyrolyzed at 690° under nitrogen at a steady rate of 30 ml/hr (Fields and Meyerson, 1965). The pyrolysis tube was Vycor, filled with Vycor beads contact time was 11 5 sec, which gave a 58% conversion of the phthalic anhydride. Acetylene was steadily evolved, along with carbon dioxide and carbon monoxide in a 1 1 ratio these were identified in the gas stream by mass-spectral analysis of samples taken at regular intervals. The benzene was distilled off and the products boiling over 180° (2 g) were analyzed by mass spectrometry on a Consolidated Model... 

Summary Polysilacarbosilanes and polysilasilazanes prepared according to a copolymer strategy offer an easy, coherent approach to polycarbosilanes and silazanes, precursors of SiC and SiCN-based materials with variable C/Si and C/Si/N ratios. In contrast with the polysilazane route which leads, upon pyrolysis, to carbon-containing silicon nitride, the synthesized polycarbosilazanes are finally converted into nitrogen-containing silicon carbide. 

In the activation by hydroxide, the main variables affecting the final porous texture are hydroxide/carbon ratio, heating rate, temperamre, and time of pyrolysis. Moreover, there are two additional parameters that have recendy been reported [24, 25] nitrogen flow rate and the washing stage (washing with water or washing with hydrochloric acid), which have an important role in porosity development. 

---