Synthesis and thermoelectric power measurements of TlGaSe 2 single crystals
TlGaSe2single crystals were grown by modified Bridgman method. Thermoelectric power measurement were carried out in a brass working chamber designed for this purpose, allow measurements in a wide range of temperature under vacuum. The experimental results indicates that TlGaSe2 is of p-type conductivity. Throughout these measurements, various parameters such as effective mass of charge carriers, carrier mobility, diffusion coefficient, relaxation time and diffusion length for both majority and minority carriers were found. In addition to these pronounced parameters, the efficiency of the thermoelectric element (figure of merit) was evaluated, which leads to better application in many fields. [A. T. Nagat, S. A. Hussein, S. E. Al Garni. Synthesis and thermoelectric power measurements of TlGaSe2 single crystals. Life Sci J 2014;11(8):418-422]. (ISSN:1097-8135). http://www.lifesciencesite.com. 54
The Growth of p-Type A^{III} B^{III} C_2^{V I} Single Crystals
ABC I 2 single crystals were grown by the modified Bridgman-Stockbarger method, a procedure similar to direct freezing in our crystal growth laboratory. ABC I 2 compounds are collected into two groups (III. group: TI, Ga, In and VI. group: Se, S, Te): 1. TlGaSe2, TlGaS2 and TlInS2 have layer structure. 2. TlInSe2, TlInTe2 and TlGaTe2 have chained structure. The main reasons such crystals grown with this method is similar to the direct freezing method because 1) quality of crystals is the same as crystals grown by other methods, and 2) growth time of crystals is shorter by about 5-10 days. None of the grown crystals had cracks and voids on the surface. Freshly cleaved crystals had a mirror-like surface and there was no need for mechanical or chemical polishing. The X-ray Laue back reflection method was used to test the crystallinity of the prepared samples. It was found that the crystals was p-type by hot probe technique. The ingots produced were single crystals and the useful region of single crystal was approximately 90% of the bulk.
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.