Solid State Synthesis and Characterization of Carbo-Nitride Materials

摘要

The preparation of stoichiometric sp(sup 2)-bonded amorphous carbon nitride a-C3N4 in gram quantities was successfully achieved by performing a solid-state reaction of cyanuric halides C3N3X3 (X=Cl, F) with lithium nitride L3N at temperatures 300-380 deg C. Addition of boron precursors, e. g., NaBF4, resulted in preparation of a nitrogen-rich BC-N powder of approximately B3C3N7 composition and showing thermal stability up to temperatures of 1000 deg C. The densification of micronized powders by cold isothermal pressing has produced disk-shaped ceramics of C3N4 and B-C-N materials, being lighter than graphite and boron nitride h-BN, respectively. Further modification of the reaction by introduction of porous substrates and templates has led to preparation of a previously unknown material - sphere-shaped nanoscale-size carbon nitride built by stacking of curved C3N4 layers. Preliminary high pressure/high temperature experiments with the C3N4 powder as precursor have demonstrated that the structure of carbon nitride changes under pressures of 8 to 12 Gpa from amorphous to a more ordered graphite-like one, retaining the C3N4 stoichiometry at temperatures up to 500 deg C and losing nitrogen at higher temperatures. The overall amorphous morphology of the carbon nitride has so far precluded the generation of a secondary electron emission by this material during the tests performed. Continuing attempts to prepare crystalline carbo-nitride phases both by the high pressure treatment of amorphous powder precursors and by an appropriate synthetic routes designed are in progress in our laboratory.