JOURNAL OF MATERIALS SCIENCE 18 (1983) 2087-2094 Formation and characterization of oxynitride glasses in the Si-Ca-AI-O-N and Si-Ca-AI,B-O-N systems PAUL E. JANKOWSKI*,SUBHASH H. RISBUD Department of Ceramic Engineering and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Oxynitride compositions in the Si-Ca-AI-O-N and Si-Ca-AI, B-O-N systems were melted and furnace-cooled in BN crucibles at temperatures from ~ 1650 to 1850 ~ C under dry nitrogen atmospheres. Glass formation, phase stability and crystallization were studied by characterizing the cooled melts by X-ray diffraction, DTA, and electron micro- scopy. Oxynitride batches with nitrogen content up to ~ 11 at % formed glasses in the Si-Ca-AI-O-N system. Glasses in the Si-Ca-AI, B-O-N system could be formed only when the B203 content of the batch was less than ~ 3 wt %. Oxynitride glasses in these boron~ontaining systems were characteristically inhomogeneous, difficult to process, and prone to crystallization. In both the systems, glasses exhibited glass transitions beginning at ~ 1000 ~ C and crystallization at ~ 1300 to 1500 ~ C. Nitrogen-containing crystalline phases were identified in devitrified glasses via microstructural and micro- mechanical analyses. 1. Introduction Burgeoning interest in nitrogen ceramics in the last two decades has resulted in considerable efforts being directed towards the fabrication and proper- ties of Si3N4 and several multicomponent materials in Si-metal-O-N systems. One of the many fascinating aspects of these developments is the growing enthusiam for investigating a new set of non-crystalline materials generally referred to as oxynitride glasses [1-15]. In the present work we have investigated glass formation and stability in the oxynitride systems Si-Ca-A1-O-N and Si-Ca-A1, B-O-N. The goals were to obtain and characterize glasses in these systems with respect to thermal stability, crystallization, and microstructure. 2. Experimental procedures 2.1. Materials synthesis Appropriately batched oxide and nitride ceramic 2.2. Materials characterization powders were charged into BN crucibles (~ 2.5 Materials were characterized by *Now at Coming Glass Works, Coming, New York 14830, USA. t!Mode11000A, Astro Industries Inc., Santa Barbara, California, USA. 0022--2461/83 $03.00 + .12 1983 Chapman and Hall Ltd. cm diameter x 5 cm height) and lightly pressed. The crucible was jacketed by a graphite sleeve and the assembly loaded into the chamber of a high temperature graphite element furnace? capable of operating up to ~ 2500 ~ C. A schematic sketch of the furnace and the experimental set-up used is shown in Fig. 1. Crucibles were heated in the fur- nace at ~ 30 ~ C min -1 under an atmosphere of dry nitrogen (flow rate ~ 500cm 3 min -I) until the melt processing temperature (~ 1650, 1750 or 1850~ was reached. Following a 7h soak at this temperature, the furnace was shut off and allowed to cool. The average cooling rate of the crucible was 32~ -1 down to 800~ at which time the crucible was removed and quenched in water. Some melts were lowered into a nitrogen glove box and allowed to cool in flowing nitrogen. differential 2087