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Many features of aluminosilicate glasses incorporating a rare-earth ( RE) ion are dictated by its mass and cation field strength ( CFS). Sc- Al- Si- O glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass of all RE3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass-transition temperature ( Tg), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc2 O3- Al2 O3- SiO2 system. The glasses exhibit uniform and unexpectedly low Tg-values (≈875°C), but a high microhardness (≈9.3 GPa) that correlates with the Sc2 O3 content. 29 Si magic-angle spinning ( MAS) nuclear magnetic resonance ( NMR) spectroscopy shows enhanced deshielding and a minor glass-network ordering as either the Al or Sc content of the glass increases. 27 Al MAS NMR reveals that besides the expected AlO4 tetrahedra, substantial amounts of AlO5 (31%-35%) and AlO6 (≈5%) polyhedra are present in all Sc- Al- Si- O glass structures. 45 Sc isotropic chemical shifts (≈92 ppm) derived from MAS and 3 QMAS (triple-quantum MAS) NMR experiments are consistent with ScO6 environments. [ABSTRACT FROM AUTHOR]

Abstract: We report physical properties of density, glass transition temperature, Vickers hardness and refractive index for 15 La–Al–Si–O glasses within the compositional region 10–28mol% La2O3, 11–30% Al2O3 and 45–78% SiO2. The glass transition temperature varies only slightly between 871 and 883°C. Both the density (3.25–4.33gcm−3) and refractive index (1.59–1.70) display similar compositional dependencies and are primarily dictated by the La2O3 content. The hardness (6.4–9.0 GPa) increases with decreasing SiO2 content and to a minor extent also with the amount of La2O3 of the glass. The physical properties, in particular the hardness, are discussed with reference to glass structure. The similarity in the observed properties between the present oxide-based glasses and those of analogous rare-earth (RE) element-containing RE–Si–(Al)–O–N oxynitride glasses is highlighted and discussed in relation to the apparent, but hitherto largely neglected, role of RE-ions to primarily control many enhanced physical properties of oxynitride glasses. [Copyright &y& Elsevier]

Abstract: Mixed alkali earth element containing high nitrogen content oxynitride glasses (Ca1− xAEx )1.2(1)SiO1.9(1)N0.86(6), with AE =Mg, Sr, Ba, x ≤0.30 for Mg and x ≤0.46 for Sr and Ba, and nominally constant (Ca/AE):Si:O:N ratios were prepared in order to investigate the compositional dependencies of physical properties on alkali earth element composition. The glasses were prepared by melting mixtures of AEH2, CaH2, SiO2 and Si3N4 powders in nitrogen atmosphere at 1600–1700°C and characterized by X-ray powder diffraction and scanning and transmission electron microscopy. Cation and anion glass compositions were determined by respectively energy dispersive X-ray analysis and combustion analysis. The determined physical properties were density, glass transition temperature, Vickers hardness, and refractive index. The physical properties were found to vary linearly with the degree of substitution of Ca by the AE elements. The density of the glasses increases substantially upon substitution by Sr and Ba, up to 3.99g/cm3. Glass transition temperatures are found to be higher for Mg and Sr substituted glasses, ca. 900°C, in comparison with Ba substituted glasses, ca. 850°C. The hardness increases upon substitution by Mg, up to 12.2 GPa at x =0.46, and decreases upon substitution by Sr and Ba. The refractive index increases upon substitution by Sr and Ba, up to 1.97 for Ba at x =0.46, and decreases upon substitution by Mg. The transparency of the glasses was found to increase upon increasing substitution by Mg and completely transparent glasses were obtained for x =0.24. [Copyright &y& Elsevier]

Abstract: Vickers hardness and refractive index was determined for Ca–Si–O–N glasses with 14.6–58 e/o N and 19–42 e/o Ca. By applying slow cooling rates, transparent glasses were obtained for compositions near Ca9.94Si10O17.73N8.14, while the majority of the glasses were opaque due to small inclusions of elemental Si and/or Ca-silicide. Determined glass densities varied between 2.80 and 3.25g/cm3. Hardness was found to vary from 7.3 to 10.1GPa at a load of 500g and, respectively increase and decrease linearly with N and Ca content. The refractive index was found to increase linearly with N content from 1.62 to 1.95 and showed no significant dependence on Ca content. [Copyright &y& Elsevier]

In developing elongated α-sialon grains, a nitrogen-rich liquid phase sintering method was introduced by using CaH2 as a sintering aid, so as to vary the N/O ratio of the liquid phase formed in the sintering process while keeping the Si/Al ratios constant. With increasing addition the phase contents changed from single β-sialon to dual β/α-sialons and to single Ca-α-sialon. At low N/O ratios the microstructures contained mainly equiaxed β-sialon grains, and at high N/O ratios well faceted elongated Ca-α-sialon grains. The improved toughness ( KI C=7.8 MPa·m1/2) and hardness ( HV10=17.5 GPa) properties can be attributed to the formation of interlocked microstructures. High-temperature compressive deformation tests indicated that the deformation onset temperature is determined mainly by the Si/Al and N/O ratios, whereas the deformation rate is affected by the microstructure, i.e., the morphology and amounts of elongated α-sialon grains and residual glass phase, especially for the sialons with low N/O ratios. [ABSTRACT FROM AUTHOR]

Abstract: Vickers hardness and refractive index have been determined for a series of La-Si-O-N oxy-nitride glasses containing 30–62e/o of La and 9–68e/o of N. The hardness varies between 7.7 and 11.5GPa at a load of 1kg and is dependent of the N content, while the La content does not influence it significantly. The increase of the hardness with N content is, contrary to reported findings for other oxy-nitride glasses, found not to be linear over the whole compositional range. The refractive index varies between 1.8 and 2.3 and increases non-linearly with increasing N content. The compositional variations of hardness and refractive index are compared with previously published results. [Copyright &y& Elsevier]

Nitrogen-rich Ca–α-SiAlON ceramics with nominal compositions Ca xSi12−2 xAl2 xN16 and 0.2≤ x≤2.6, extending along the Si3N4–1/2Ca3N2:3AlN tie line, were prepared from Si3N4, AlN, and CaH2 precursors by hot pressing at 1800°C. 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–α-SiAlONs form continuously within the compositional range x=0 to at least x=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 CaH2 as a precursor, grain growth was kinetically enhanced, resulting in self-reinforced microstructures with elongated grains. The obtained Ca–α-SiAlON ceramics demonstrate a combination of both high hardness ∼21 GPa, and high fracture toughness ∼5.5 MPa·m1/2. [ABSTRACT FROM AUTHOR]

Abstract: Ca and Sr-based oxynitride glasses with very high nitrogen content have been synthesized using metal hydrides as primary precursors. Values of Young''s modulus, shear modulus, bulk modulus and Poisson''s ratio were determined by means of ultrasonic echography. Vickers micro-indentation has been used to characterize hardness and indentation fracture toughness behaviour. Elastic moduli were found to increase linearly with nitrogen content, with the highest value of Young''s modulus at 135GPa, for a Ca-glass with 58 e/o of nitrogen. The Sr-glasses exhibit lower elastic moduli than Ca glasses. Poisson''s ratio, hardness, indentation fracture toughness, crack initiation load and surface damage resistance were found to increase with increasing nitrogen content for both glass series. [Copyright &y& Elsevier]