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Abstract: ZrN–Si3N4 composite powders were synthesised from natural zircon and quartz via carbothermal reduction and nitridation reaction. The effects of various raw material compositions and heating temperatures on phase transformation and product morphologies under flowing nitrogen atmosphere were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The phase equilibrium relationships of the ZrO2–SiO2–C–N2 system at different heating temperatures were also investigated based on the thermodynamic analysis. Products with different phase compositions and morphologies were obtained at different conditions. The products were composed of ZrN, β-Si3N4 and a small amount of c-ZrO2 by carbothermal reduction and nitridation of zircon with less than 20wt.% quartz. With 30wt.% quartz, granular ZrN as well as columnar and acicular β-Si3N4 were detected in the products. With 40wt.% or 50wt.% quartz, the products consisted of ZrN, β-Si3N4, Si2N2O, c-ZrO2 and m-ZrO2. The optimum quartz content for synthesizing ZrN–Si3N4 composite powders was 30wt.%. At heating temperatures below 1600°C, the products were composed of ZrN, β-Si3N4, β-SiC, Si2N2O, m-ZrO2 and c-ZrO2. [Copyright &y& Elsevier]

Self-strengthened mullite ceramics with interlocking columnar grains formed through enhanced anisotropic growth by adding La2O3 were prepared from coal gangue and γ-Al2O3 within the temperature range 1400–1550°C and holding time of 4h. The effects of La2O3 on the bending strength, microstructural evolution, and phase composition were studied. The results showed that the bending strength of the as-prepared ceramics was significantly improved by the addition of La2O3. For samples sintered at 1550°C, the bending strength increased from 64MPa to 218MPa as the La2O3 content increased from 0mol% to 10mol%. X-ray diffraction analysis suggested that the formation temperature of secondary mullite was lowered by about 50°C by adding La2O3. Scanning electron micrographs revealed that the La2O3-added mullite mostly existed in long, columnar form, with aspect ratios of 3–6, forming an interlocking network structure. The interlocking mullite columns, together with the enhanced densification behaviour, contributed to the improved bending strength. [ABSTRACT FROM AUTHOR]

Abstract: β-Si3N4 powder was synthesized via carbothermal reduction nitridation (CRN) method using quartz as starting material. The influence of synthesis temperature, C/SiO2 molar ratio and amount of Fe2O3 additive on the phase transformation and micro-morphology of β-Si3N4 powder was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The results showed that the optimal experimental conditions for the CRN synthesis of β-Si3N4 powder were 3h sintering at 1600°C in flowing nitrogen atmosphere with C/SiO2 molar ratio of 2.0 and amount of Fe2O3 additive of 5.0wt.%. The prepared β-Si3N4 grains present a short hexagonal, rod-like morphology. Changes in experimental parameters affect the phase compositions and the morphology of the product. Excessive carbon promoted the formation reaction of β-SiC. Fe2O3 additive exerted a significant promotion on the formation of β-Si3N4 in CRN process by forming the low melting point eutectics. [Copyright &y& Elsevier]

Objective: In this cross-sectional study, we investigated the frequency tuning properties of sound-evoked vestibular myogenic potentials in extraocular muscles (OVEMPs) in normal human subjects., Methods: Acoustic tone bursts (130 dB pSPL, 10 ms plateau, 1 ms rise/fall) with nine frequencies from 125 to 4000 Hz were presented monoaurally to 12 normal subjects while they sat upright and maintained centre gaze. Using surface electrodes, the OVEMPs were recorded at four locations surrounding the contralateral eye (superior, inferior, nasal, and temporal) and were referenced to an electrode placed at the nape of the neck over C7. To measure the amplitudes of the OVEMP, signals from the electrodes were amplified and sampled at 10 kHz and were averaged over 250 repetitions., Results: We found that the OVEMPs recorded at the four sites exhibited similar well-defined frequency tuning with peak amplitude at ≈ 1000 Hz., Conclusion: Although several studies have examined the frequency tuning of the vestibular evoked myogenic potential measured from the sternocleidomastoid muscles (SVEMP), the reported results are quite variable as regards frequency, which produces peak amplitude. The well-defined OVEMP frequency tuning provides an alternative to the SVEMP for assessing vestibular function via acoustic stimulation. Further studies are needed to identify the extent to which each of the five vestibular end-organs is activated by sound and their contribution to the sound-evoked vestibular myogenic potentials.