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The rapid development of the photovoltaic industry has led to increased demand for monocrystalline silicon. Numerous waste graphite devices are generated in the process of crystal pulling, and the waste graphite thermal field contains the largest proportion of graphite. Reports on graphite purification from the waste graphite thermal for photovoltaic crystal pulling are relatively rare. In this study, we purified waste graphite using a combined process of ferric induction roasting and acid-leaching. Through thermodynamic analysis, it is found that the appropriate material ratio is conducive to generating the appropriate target product, namely Fe3Si. Using ball milling mixture as raw material, the calcined product was obtained at 1300℃, 30% iron ratio and 90 min roasting time. XRD, SEM–EDS and XPS analysis methods showed that the calcined product phase was graphitic carbon and Fe3Si, which was consistent with thermodynamic calculation, and then HCl and HF leaching were carried out. High-purity graphite carbon (HPG) with fixed carbon content greater than 99.9% was obtained. The removal rates of Si, Fe, Al, Mg, Zn, Ni, Ti Ca, and Na were 99.58, 99.56, 99.89, 98.32, 99.26, 99.47, 99.62, 98.48, and 98.98%, respectively. Meanwhile, the HPG products with a purity of 99.98% were obtained. [ABSTRACT FROM AUTHOR]

As graphite is an important material for several applications, the evaluation of its properties at very high temperatures is of major importance. Conducting studies at temperatures >2800 K is, however, very challenging, and the amount of available data in the literature is, therefore, very limited. This paper presents a methodology that compares experimental data with simulation results following a progressive increase of the temperature range investigated. The study was conducted on a commercial polycrystalline graphite produced by sintering (EDM-3 from POCO) under high power continuous laser heating (kW ytterbium at a wavelength of 1080 nm). Experiments were done inside a vacuum chamber equipped with pyrometers and cameras allowing fine monitoring of the temperature of the samples. A 3D numerical model has been developed based on the finite element method to analyze the experimental results. The evolution of the thermal and optical properties of EDM-3 with temperature is required for correctly modeling laser/material interactions. By running a sequential comparison of calculation with a dedicated experiment, we achieve better knowledge of such properties. From this study, we obtain estimations of the evolution of thermal conductivity, emissivity, and evaporation rate up to 3800 K of amorphous graphite. [ABSTRACT FROM AUTHOR]

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Preparation of nanomaterials with various morphologies and exploiting their novel physical properties are of vital importance in nanoscientific field. Similarly to the III-N compound semiconductors, Si3N4 nanostructures also could be potentially used for making optoelectronic devices. In this paper, we report on an improved Fe-catalyzed chemical vapour deposition method for synthesizing ultra-long α-Si3N4 nanobelts along with a few nanowires and nanobranches on a carbon felt substrate. The ultra-long α-Si3N4 nanobelts grew via a combined VLS-base and nanobranches via a combined double-stage VLS-base and VS-tip mechanism, as well as nanowires via VLS-tip mechanism. The three individual nanostructures showed variant optical properties as revealed by a cathodoluminescence spectroscopy. A single α-Si3N4 nanobelt or nanobranch gave a strong UV-blue emission band as well as a broad red emission, whereas a single α-Si3N4 nanowire exhibited only a broad UV-blue emission. The results reported would be useful in developing new photoelectric nanodevices with tailorable or tunable properties. [ABSTRACT FROM AUTHOR]