Most of the world’s solar cells in photovoltaic industry are currently fabricated using crystalline silicon.
Czochralski-grown silicon crystals are more expensive than multicrystalline silicon crystals. The future of solar-grade Czochralski-grown silicon crystals crucially depends on whether it is usable for the mass-production of high-efficiency solar cells or not. It is generally believed that the main obstacle for making solar-grade Czochralski-grown silicon crystals a perfect high-efficiency solar cell material is presently light-induced degradation problem. In this work, the substitution of boron with gallium in p-type silicon single crystal is studied as an alternative to reduce the extent of lifetime degradation.
The diamond-wire sawing technology is employed to slice the silicon ingot. In this paper, the quality of the diamond wiresawn gallium-doped silicon wafers is studied from the chemical, electrical and structural points of view. It is found that the characteristic of gallium-doped silicon wafers including texturing behavior and surface metallic impurities are same as that of conventional boron-doped Czochralski crystals.
In this research, cubic zirconia is synthesized with a refined CaO from shells as a stabilizer through Skull melting method. The proper process time and concentration are defined by Hydration reaction to produce the refined CaO after two different treatments using 0.1 mol% of HCl respectively with Cockle shell. The highest purity of CaO is reached when the shell is immersed in 1 mol% HCl. In Hydration reaction step, the pure Ca(OH)2 is produced at 45oC for 24 hours.
The highest purity of CaO is measured when the Ca(OH)2 is treated by heat at 1200oC for 5 hours. The single crystals are grown through Skull melting method by adding the different contents of the refined CaO from 10 mol% to 30 mol% into ZrO2. The frequency of High-frequency oscillator used for Skull melting method is 3.4 MHz. The descending speed of the single crystal is 3 mm/hour. The grown length of the single crystal is 4 cm. As a result of this study, 15 mol% of CaO has the best crystallinity
Sapphire wafers are used as an important substrate for the production of blue LED (light emitting diode) and the LED’s performance largely depends on the quality of the sapphire single crystals. There are several crystal growth methods for sapphire crystals and Kyropoulos method is an efficient way to grow large diameter and high-quality sapphire single crystals with low dislocation density. During Kyropoulos growth, the convection of molten melt is largely influenced by the hot zone geometry such as crucible shape, heater and refractory arrangements. In this study, CFD (computational fluid dynamics) simulations were performed according to the bottom/side ratios (per unit of the crucible surface area) of heaters. And, based on the results of analysis, the molten alumina flows and remelting phenomena were analyzed.
Mechanical alloying was carried out to produce CrSi2 thermoelectric compound using a mixture of elemental Cr33Si67 powders. An optimal milling and heat treatment conditions to obtain the single phase of CrSi2 compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry measurement. CrSi2 intermetallic compound with a grain size of 70 nm could be obtained by MA of Cr33Si67 powders for 70 hours and subsequently annealed at 650oC. Consolidation of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at 600~1000oC under 60 MPa. The shrinkage of MA samples during SPS consolidation process increased gradually with increasing temperature up to 1000oC and relatively significant at about 600oC. We tend to believe that these behaviors are deeply related to form a CrSi2 compound during heating process, as can be realized from the DSC measurement. Electrical conductivity and Seebeck coefficient of sintered bodies were measured up to 900oC. Seebeck coefficient and power factor of Cr33Si67 compact prepared by MA and SPS at 1000oC showed the maximum value of 125 μV/K at 400oC and 4.3 × 10−4 W/mK2 at 350oC, respectively.
The upconversion (UC) luminescence of Li+/Er3+/Yb3+ co-doped CaWO4 phosphors and effects of Yb3+ concentration are investigated in detail. Single crystallized CaWO4 : Li+/Er3+/Yb3+ phosphor can be obtained, co-doped up to 35.0/5.0/30.0mol% (Li+/Er3+/Yb3+) by solid-state reaction. Under 980 nm excitation, CaWO4 : Li+/Er3+/Yb3+ phosphor exhibited strong green UC emissions visible to the naked eye at 530 and 550 nm induced by the intra 4f transitions of Er3+ (4H11/2, 4S3/2 → 4I15/2).
The optimum doping concentrations of Yb3+ that would result in the highest UC luminescence were determined, and a possible UC mechanism that depends on the pumping power is discussed in detail.
In this study, the effect of addition of waste glassy slag produced from recycling of spent catalyst (denoted as waste glass hereafter) on the physical properties of artificial aggregates made of coal bottom ash and dredged soil (7 : 3 by weight base) was evaluated. Especially, the bloating behavior of artificial aggregates was analyzed by performing the relation study between the apparent density, water absorption and microstructure. The apparent density of artificial aggregates increased slightly with sintering temperature at 1050~1150oC, but decreased above 1150oC showing bloating phenomenon. The bloating behavior of artificial aggregates was decreased so the apparent density increased with amount of waste glass added. Also, the water absorption of artificial aggregates decreased with sintering temperature. Above 1200oC,big fissure and much liquid were formed at the surface of artificial aggregates and these phenomena could be suppressed by increasing amount of waste glass added. The artificial aggregates fabricated in this study had an apparent density of 1.1~1.6 and water absorption of 8~22 % which meet KS requirements for the artificial lightweight aggregates.
The purpose of this study is to enhance the mechanical strength of specimens containing fly ash from fluidized bed type boiler, which the recycling rate will be eventually increased. Specimens containing fly ash in a certain portion were made and aged for 3, 14, and 28 days. Specimens were carbonated under the supercritical condition at 40oC. The carbonation process under the supercritical condition was performed to enhance the mechanical property of specimens by filling the voids and cracks existing inside cement specimen with CaCO3 reactants. The additional aging effect after the supercritical carbonation process on mechanical strength of specimens was also investigated by comparing the compressive strength with and without 7 day extra aging. Under the supercritical condition and additional 7 day aging specimens were very effective for enhancement of mechanical strength and compressive strength increased by 44 %.