Papers by Keyword: Impurity

Abstract: Al-25%Si has excellent fluidity, which allows for the casting of heat sinks with thin and tall fins. During recycling, the content of impurities such as Fe, Cu, and Mg increases. The effect of these impurities on the fluidity of the alloy was investigated. The results show that the influence of impurity elements on fluidity is small. JIS ADC12 is a popular aluminum alloy that is more economical than Al-25%Si. Si was added to ADC12 to reach a 25% Si content, producing an economical Al-25%Si. The fluidity of Si-added ADC12 was almost the same as that of Al-25%Si. Heat sinks with fin heights of 50 mm, fin top thicknesses of 0.5 mm, and a draft angle of 0.5°, were cast using the Si-added ADC12. The molten metal filled the cavity, but solidification cracks occurred when the fin top thickness was 0.5 mm. When the fin top thickness was increased to 1 mm, solidification cracks did not occur.

Abstract: Impurity incorporation during vapor-phase epitaxy on stepped surfaces was modeled by classifying rate-limiting processes into i) surface diffusion, ii) step kinetics, and iii) segregation. Examples were shown for i) desorption-limited Al incorporation during chemical vapor deposition (CVD) of (0001) SiC, ii) preferential desorption of C atoms from kinks during CVD of Al-doped (000-1) SiC, and iii) segregation-limited C incorporation during metalorganic vapor-phase epitaxy of (0001), (000-1), and (10-10) GaN.

Abstract: During the process of Carbon Capture and Storage, some impurity may be found in the supercritical CO₂ fluid. The changes in corrosion of X70 Steel in water-saturated supercritical CO₂ system caused by impurity has been studied by the simulation experiment. The average corrosion rate was got from weight loss measurement. The morphologies and compositions of corrosion products were analyzed by SEM, EDS and XRD. It was observed that the existence of separate impurity would aggravate the corrosion of X70 steel in the water-saturated supercritical CO₂ system. The average corrosion rate was the highest when NO₂ or SO₂ was included, followed by H₂S, and the average corrosion rate was the smallest when O₂ was contained. Among them, X70 steel suffered local corrosion when NO₂ was contained. The corrosion scale was monolayer structure of FeCO₃ under the supercritical CO₂-H₂O system. After the addition of O₂, Fe₂O₃ appeared in the corrosion scale, indicating that the oxygen corrosion process occurred. While with the addition of H₂S, corrosion scales were double layers. FeS was mainly present in the outer layer. The corrosion process was controlled by CO₂ and H₂S. The corrosion products were mostly FeSO₃·xH₂O and a spot of FeCO₃ when SO₂ was contained. SO₂ mainly governed the corrosion process. Besides, corrosion product was Fe₂O₃ without FeCO₃ in the supercritical CO₂-H₂O-NO₂ system, NO₂ completely controlled the corrosion process.

Abstract: The paper presents the influence of chemical compositions and structure of the deposited metal on its hardness and wear resistance in abrasive-shock conditions. Metal Was deposited by the arc powder wire automatic welding. The studies have shown that increasing nikel contain to 0.65% in the surfaced steel and cobalt additive while reducing carbon contain to 0.17-0.23%, provides martensite and former austenite grain size disintegration. In consequence of multivariate correlation analysis, it was determined dependence to the hardness of the deposited layer and the wear resistance of the mass fraction of the elements included in the flux-cored wires of the system Fe-C-Si-Mn-Cr-Mo-Ni-V-Co. Obtained dependences could be used in predicting hardness and wear resistance of the deposited metal while changing welding metal chemical composition.

Abstract: We have investigated the dependence of the macrostep height on various additives in solution growth of n-type 4H-SiC. Surface modification by adding transition elements in periods 4‒6 (Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, Ce, and W) and group 13‒14 elements (B, Al, Ga, Ge, Sn) was systematically studied to find additives improving smoothness of the growth surface. We found that Sc, Co, Mo, and Ge improved surface smoothness in addition to the already-known additives, such as Al, B, and Sn. Besides, these additives (Sc, Co, Mo, Ge) give no measurable influence on the conductivity of n-type grown crystals. These results demonstrated that Sc, Co, Mo, Ge and Sn are useful additives for solution growth of n-type 4H-SiC.

Abstract: The aim of this paper is to study the photoluminescence spectra and photoluminescence excitation spectra in LiF-O, LiF-WO₃ and LiF-TiO₂ crystals at 20-300 K. It is shown that the luminescence centers in LiF-WO₃ and LiF-TiO₂ crystals are oxygen ions O^2- disturbed by defects. Two absorption bands within 6-4.5 eV and two luminescence bands with maxima at 3.1 eV and 2.64 eV correspond to these centers. The absorption and emission spectra of the oxygen center (3.1 eV luminescence band) are close to those for the (O^2-- V_a) center.

Abstract: A novel method to remove impurity silicon from aluminum melt by the addition of K₂TiF₆ was studied. The mechanism for silicon removal is the formation and sedimentation of Ti(Al_1-x,Si_x)₃ phase and the removal efficiency is mostly decided by the solubility of silicon in TiAl₃ phase, which increases with the increasing of the initial silicon concentration in aluminum melt. The effect of holding temperature on the impurity Si purification efficiency was investigated and the result indicated that the effect of holding temperature is very finite.

Abstract: The experiments have emphasized that additionally introduced impurities of Fe and Pb ions are relevant to the initiation of slow and explosive decomposition of silver azide crystals by the external electric field and UV irradiation. External gas release was used for research purpose. Test-sensitivity is 10⁻¹² mole. Time-to-explosion was measured by a stop watch. It’s been found out that the reaction of slow decomposition in silver azide under the action of electric field turns into explosion faster in samples with the additionally introduced impurities. The samples with additionally introduced Fe are the most explosive ones (time-to-explosion 3 minutes). The authors have assumed that external influence can generate non-equilibrium charge carriers (holes), which become localized on cationic vacancies and support formation of reactive sites. As soon as cut off concentration of these sites is reached, the solid-phase chain reaction turns into explosion. The growing concentration of impurity influences on the number of reactive sites, making their concentration critical. In view of the results obtained in experiments a procedure for monitoring the decomposition of crystals is suggested, which necessitates additional introduction of Fe and Pb ions.

Abstract: In order to design a solvent for high-purity SiC solution growth, the impurity incorporation and the carbon solubility of various solvent materials have been investigated. Among the transition metal elements, the impurity elements of Cr, Ti, V and Hf are more readily incorporate during the solution growth than the other transition metal elements. The thermodynamic calculation revealed that the Y-Si solvent has relatively large carbon solubility, which is comparable to the Cr-Si and Ti-Si solvents often used in the solution growth of bulk SiC crystals. From these results, the Y-Si solvent is expected to be a suitable solvent for the high-purity SiC solution growth. Furthermore, we have demonstrated that the Y-Si solvent can achieve lower incorporation of metal impurity in the grown crystal than the Cr-Si solvent maintaining the growth rate.

Abstract: SiC powders having different purities were prepared by carbothermal reduction under different conditions from traditional process and SiC single crystals were grown by the PVT method from the powders. After crystal growth, boule was cut to wafers and they were polished for chemical and defect analyses. Total impurities including Al, B and Ti which were derived from powders decreased remarkably during crystal growth. The formation of defects including micropipe and dislocations such as TED, TSD and BPD was strongly influenced by impurity content. The effect of impurity seemed to be negligible at below 1ppm level for MPD. On the other hand, dislocations continuously decreased even more when higher purity SiC powder below 1ppm level was used.