Self‐Reinforced Nitrogen‐Rich Calcium–α‐SiAlON Ceramics

Abstract

Nitrogen-rich Ca-a-SiAlON ceramics with nominal compositions Ca x Si 12À2x Al 2x N 16 and 0.2rxr2.6, extending along the Si 3 N 4 -1/2Ca 3 N 2 :3AlN tie line, were prepared from Si 3 N 4 , AlN, and CaH 2 precursors by hot pressing at 18001C. The x values attained were determined by energy-dispersive X-ray (EDX) microanalysis and X-ray powder diffraction (XRPD) data using the Rietveld method. The results show that Ca-a-SiAlONs form continuously within the compositional range x 5 0 to at least x 5 1.82. Phase assemblages, lattice parameters, Vickers hardness, and fracture toughness were determined and correlated to the calcium content, x. Owing to a high sintering temperature and the use of CaH 2 as a precursor, grain growth was kinetically enhanced, resulting in self-reinforced microstructures with elongated grains. The obtained Ca-a-SiAlON ceramics demonstrate a combination of both high hardness B21 GPa, and high fracture toughness B5.5 MPa . m 1/2 .

Synthesis of Ca-α-SiAlON phosphors by a mechanochemical activation route

“…The Eu 2+ ion (radius: 116 pm) is too large to be thermodynamically incorporated into the a-SiAlON structure, although the Eu 2+ could be incorporated into a-SiAlON structure with a smaller stabilizing cation such as Y 3+ or Ca 2+ [24]. In preliminary work on Eu 2+ -doped a-SiAlON phosphors, the main focus has been on the photoluminescence spectra and more efficient synthetic approaches [1,2,[17][18][19][20]; little attention has been paid to the crystal structural evolution of these materials. In fact, the distribution of Eu 2+ in host structure plays an important role in the photoluminescence of phosphors.…”

“…Recently, in the course of fundamental studies on rare-earth-doped systems, a new potential application of a-SiAlONs as luminescent materials has emerged. Among them, Eu-doped Ca-a-SiAlON, which exhibits yellow emission (570-600 nm) by excitation in the UV to blue spectral region (300-460 nm), is attracting considerable attention in the electronics industry for use as a wavelength-conversion phosphor for white LEDs [1,2,[17][18][19][20].…”

Thermal properties of the nitrogen-rich Ca-α-Sialons

“…The present work deals with the preparation of some nitrogen-rich Ca-␣-Sialon (Ca x Si 12−2x Al 2x N 16 ) ceramics that exhibit improved toughness that in turn can be attributed to the formation of elongated ␣-Sialon grains. 3,4 In addition, increased resistance to high temperature deformation was also observed in nitrogen-rich Ca-␣-Sialons, i.e. nitrogen-rich Ca-␣-Sialons exhibited about 150 • C higher deformation onset temperature than those of their oxygen-rich counterparts.…”

“…3 16 , with x = 0.2, 0.4, and 0.8, 1.2 and 1.6, respectively, were ball milled (planetary ball mill PM 100, Retsch, Germany) in hexane and these samples are denoted as CCH02, CCH04, CCH08, CCH12, and CCH16. The mixed powders were vacuum-dried at 105 • C for 6 h then pre-compacted in a steel die in an argon-filled glove box, and finally hot pressed using a pressure of 35 MPa and a holding time of 4 h at 1800 • C. In order to reveal the reaction subsequences, starting powders of CCH16 composition were hot pressed in the temperature range 600-1800 • C for 2 h using a pressure of 35 MPa, followed by an X-ray powder diffraction analysis.…”

“…It has been shown that nitrogen-rich Ca-␣-Sialons (Ca x Si 12−2x Al 2x N 16 ) ceramics can be prepared from the mixtures of Si 3 N 4 , AlN and CaH 2 powders. 3 Based on the positive effects of increasing nitrogen content vis-a-vis the properties of the formed oxynitride glass with respect to glass transition temperature, hardness, toughness, etc., CaH 2 has been used as Ca source in stead of CaO that traditionally has * Corresponding author. Tel.…”