Abstract: A method of preparing fully dense silicon nitride based ceramic articles comprises the steps of blending a metal oxide component and silicon nitride, wherein a portion of the silicon nitride comprises acicular crystals; comminuting the powder mixture to reduce the aspect ratio of the acicular crystals to an average of less than about 3; pressing the comminuted powder to form a compact; and pressureless sintering the compact to a fully dense ceramic body. Powder mixtures and powder compacts for forming fully dense silicon nitride based ceramic bodies are also disclosed.

Abstract: Novel optical fibers are formed from glass compositions enclosed by the iso-composition lines, 2 and 18 mole percent P.sub.2 O.sub.5, 30 and 70 mole percent Al.sub.2 O.sub.3 and 20 and 60 mole percent B.sub.2 O.sub.3 or glass compositions bounded by lines connecting the compositions 28 m% Al.sub.2 O.sub.3 -- 72 m% P.sub.2 O.sub.5 -- 0 m% B.sub.2 O.sub.3 ; 5 m% Al.sub.2 O.sub.3 -- 45 m% P.sub.2 O.sub.5 -- 50 m% B.sub.2 O.sub.3 ; 10 m% Al.sub.2 O.sub.3 -- 30 m% P.sub.2 O.sub.5 -- 60 m% B.sub.2 O.sub.3 and 42 m% Al.sub.2 O.sub.3 -- 58 m% P.sub.2 O.sub.5 -- 0 m% B.sub.2 O.sub.3. The glass compositions forming the optical fibers can contain the usual oxide modifiers.