ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The grain size variation in “unseeded” Si3N4 powders, prepared by high-pressure carbothermal nitridation of SiO2 (in stoichiometric 1∶2 proportions with C), has been studied by means of scanning electron microscopy (SEM) and “Sedigraph” measurements. The size is a function of process parameters, of which the reactant surface area was found to be the most important. Specifically, with an SiO2 areaA(SiO2) ≈ 50 m2 g−1 in the reaction mixture, the resulting mean Si3N4 particle diameter,d(Si3N4), is very sensitive to the carbon surface area,A(C), such that the minimumd(Si3N4) ≈ 1 μm was obtained withA(C)=30m2g−1 and the maximumd(Si3N4) ≈ 7μm withA(C)=115m2g−1. Using mixtures withA(SiO2)=50m2g−1 andA(C)=115m2g−1, a slight dependence ofd(Si3N4) on the furnace heating rate was also observed; larger grains (≈ 7 μm) were obtained with 20deg min−1 than with 2deg min−1 (≈5μm). The grain size was found to be virtually independent of nitrogen pressure (in the range 0.3–6.5 MPa), annealing temperature (1470–1830°C) and gas flow rate (2–20 l(stp) min−1).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01160824
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