Sintering aids with the formulation of ytterbium woehlerite J(Yb),YB_4Si_2O_7N_2, and its solid solutions with Al_2O_3 J(Yb),Yb_4Si_2_xAl_xO_7+xN_2-x, were introduced into silicon nitride toobtain high density bodies by gas pressure sintering. Partialstabilisation of α-Si_3N_4 (up to ≈18/100) was achieved bycontrolled thermal oxidation of the initial powder mixtures. Theresulting materials with J(Yb) as an intergranular phase showed goodsinterability, invariably reproducible phase formation And excellentoxidation resistance up to 1400 deg.C in air. Overall, secondaryphases with J(Yb) Formulation show promise as sintering aids thatallow Si_3N_4-based ceramics to be sintered to high Density withoutcompromising intrinsic mechanical and thermal properties.
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