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Sintering Behavior and Microstructure Development of Porous Silicon Nitride Ceramics Prepared in an Air Atmosphere Furnace
Author(s) -
Plucknett Kevin
Publication year - 2009
Publication title -
international journal of applied ceramic technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.4
H-Index - 57
eISSN - 1744-7402
pISSN - 1546-542X
DOI - 10.1111/j.1744-7402.2008.02309.x
Subject(s) - sintering , materials science , silicon nitride , microstructure , ceramic , nitrogen , nitride , porosity , atmosphere (unit) , silicon , phase (matter) , chemical engineering , metallurgy , reducing atmosphere , yttria stabilized zirconia , layer (electronics) , composite material , cubic zirconia , chemistry , physics , organic chemistry , engineering , thermodynamics
Porous silicon nitride (Si 3 N 4 ) ceramics have been sintered in a conventional air atmosphere furnace at temperatures between 1500°C and 1700°C, with sintering additions of either 5 or 10 wt% yttria (Y 2 O 3 ). The use of a protective α‐Si 3 N 4 powder bed helps to prevent significant oxidation of the samples during sintering in air, keeping oxidation weight gains below 4 wt% (typically <2.5 wt%). This compares with more typical weight losses when sintering in nitrogen. Samples prepared with a protective α‐Si 3 N 4 powder bed exhibited sintered densities up to ∼89% of the theoretical, which was notably higher than for similar compositions prepared in a controlled nitrogen atmosphere (i.e., ∼70% of theoretical). Increased densification is proposed to arise from the formation of a thin SiO 2 surface layer on individual α‐Si 3 N 4 particles, through passive oxidation, which is expected to promote viscous‐flow densification at lower temperatures. The excess of SiO 2 , relative to the starting composition, is also reflected in the final phase assembly, with Si 2 N 2 O formed in addition to the transformation of α‐ to β‐Si 3 N 4 , when sintering above ∼1550°C. A Si 2 N 2 O gradient occurs, with the surface being approximately 80 vol% Si 2 N 2 O and the bulk predominantly Si 3 N 4 , for samples sintered at 1600°C and 1700°C. Conversely, Si 2 N 2 O is not observed in any measurable volume for similar samples sintered in nitrogen.