No description available.

No description available.

No description available.

The phase equilibria relationships in the Na₃AlF₆-AlF₃-LiF ternary system have been investigated using a combination of quenching, optical microscopy, DTA, and x-ray powder diffraction techniques. The compatibility relations at 500°C, the binary system Na₃AlF₆-Li₃AlF₆, and the ternary liquidus surface were determined. The liquidus surface was found to contain the following five important invariant points: 1) eutectic - 81% LiF, 9.5% Na₃AlF₆, 9.5% AlF₃ and 685°C 2) eutectic - 56% LiF, 6% Na₃AlF₆, 38% AlF₃ and 585°C 3) eutectic - 37% LiF, 17% Na₃AlF₆, 46% AlF₃ and 620°C 4) peritectic - 30% LiF, 37% Na₃AlF₆, 33% AlF₃ and 660°C 5) reaction point - 65% LiF, 9% Na₃AlF₆, 26% AlF₃ and 675°C The 500°C isothermal section contains 7 three-phase regions and 2 large two-phase regions. The binary system Na₃AlF₆-Li₃AlF₆ contained 2 incongruently melting compounds, many polymorphic transformations, and a eutectic at 690°C and 67 mole % Li₃AlF₆. / Master of Science

The phase equilibria relationships in the Li₃A1F₆-A1₂0₃ binary system, the Li₃A1F₆-Na₃AlF₆-A1₂0₃ ternary system and the LiF-A1F₃-Na₃A1F₆-Al₂0₃ quaternary system have been investigated using a combination of X-ray powder diffraction, DTA, quenching and optical microscopy techniques. The compatibility relations at 500°C for the ternary and quaternary systems, the Li₃A1F₆-A1₂0₃ binary system and the ternary liquidus surface were determined. The binary system was found to have a eutectic at 754°C and 1 mole % Al₂0₃. The liquidus surface was found to contain the following three invariant points: 1. eutectic - 66 mole % Li₃A1F₆, 29% Na₃A1F₆, 5% A1₂0₃ and 670°C 2. peritectic - 51 mole % Li₃A1F₆, 42.5% Na₃A1F₆, 65% A1₂0₃ and 683°C 3. reaction point - 65 mole % Li₃A1F₆, 33% Na₃A1F₆, 2% A1₂0₃ and 693°C. The 500°C isothermal section contains three 3-phase regions and one 2-phase region. The quaternary system contains 7 compatibility tetrahedra at 500°C. / Master of Science

It became the purpose of this study to design, build and test an electronic oscillator capable of exciting an electrodeless discharge in hydrogen in which the Doppler shifts would be exhibited in a regular manner. / M.S.

The focus of this study was to determine the coexistence phase equilibria for three groups of long-chain linear hydrocarbons (n-alkanes, 1-alkenes and 1-alcohols) using Monte Carlo simulation. Three common transferable united-atom force fields were used in the simulations: OPLS-UA (Jorgensen et al., 1984), TraPPE-UA (Martin and Siepmann, 1998) and NERD (Nath, Escobedo, de Pablo and Patramai, 1998). Isothermal phase equilibria was calculated over a temperature range from approximately the normal boiling point up to just below the critical temperature. The liquid and vapour densities and vapour pressures were determined from the simulations. The density results were then fitted using least-squares regression to the scaling law and the law of rectilinear diameters in order to estimate the critical properties. The vapour pressure data were fitted using least-squares to the Clausius-Clapeyron equation to estimate the normal boiling points. The NVT-Gibbs ensemble method was used to simulate the pure-component coexistence of the vapour and liquid phases. The NPT-Gibbs ensemble was used to simulate the n-alkane binary mixtures. Two forms of configurational-bias Monte Carlo (standard CBMC and coupled-decoupled CBMC) were used to increase the number of swap moves accepted during the simulations. Dual-cutoff CBMC was implemented with a second cut-off of sA in order to speed up the CBMC calculations. Minimum image and a spherical potential truncation after 14A were implemented with standard tail corrections. BICMAC and TOWHEE were the two Fortran-77 codes used to simulate the hydrocarbon compounds. BICMAC was used in the simulations of non-polar molecules and TOWHEE was used in the simulations of polar molecules. System sizes ranged from 300 (for the CB'S) down to 100 molecules (for the Czo's). The simulations were typically equilibrated for at least 30000 cycles and production runs ranged from 50000 to 120000 cycles for the different hydrocarbon groups. Standard deviations of the calculated thermophysical properties were between 1-3% for the liquid densities and 10-20% for the vapour densities and vapour pressures. It was found that the coexistence density curves were generally in good agreement with experiment for all the hydrocarbon groups investigated (the OPL5-UA force field being the exception). The chain-length appeared to have littl e effect on the quality of the calculated thermophysical properties. The chain-length did however increase the time required to perform the simulations substantially. The va pour pressures were consistently over-predicted by NERD and TraPPE-UA. The normal boiling pOints were typically under-predicted by 2-5%. The critical tempe ratures and densities were predicted to within 1-5% of experimental values. The n-alkane mixtures were satisfactorily predicted using the NPT-Gibbs ensemble. While both the NERD and TraPPE-UA force fields were shown to be substantially more accurate compared to the OPLS-UA force field, there was little difference between their predictions. Thus, it is likely that the added complexity of using the bond-stretching potential (used by NERD) is unnecessary. The results of this study show that Monte Carlo simulation may be used to predict vapour-liquid coexistence properties of long-chain hydrocarbons and to approximate critical properties. However, current force fields require more refinement in ord er to accurately predict the hydrocarbon thermophysical properties. Plus, faster computing speeds are required before Monte Carlo simulation becomes an industrially viable method. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

Modifications were undertaken to a static high pressure vapour-liquid equilibrium (VLE) apparatus described by Naidoo [2004]. The alterations were made to improve the sample analysis technique. These modifications included the incorporation of the ROLSITM sampling device into the equilibrium cell, a re-design of the air bath which improved the temperature profile and further alterations described in the text. The equipment has an operating temperature range of 278.15 K to 473.15 K and pressure range of absolute vacuum to 150 bars. The apparatus consisted of an agitated cell in an air-bath. The uncertainties in the temperature and pressure measurements were ±0.02 K and ±4 kPa respectively. A Shimadzu Gas Chromatograph, Model 2010 was used for sample analysis. An initial test of the apparatus was carried out to measure the pure component vapour pressure data for propane and ethane in the temperature range of 279.24 – 360.18K and the results concurred with literature data (absolute relative deviation <0.153%) The experimental procedure used in this study was developed from the technique used by Ramjugernath [2000], with some minor changes implemented only to achieve some requirements for problems encountered during the project. Isothermal binary measurements for the hexafluoroethane (R116) + propane system were used as test system to investigate the accuracy and reliability of the equipment. Three binary isotherms were measured at 291.22 K, 296.23 K and 308.21 K. The measured data compared well with literature data. Particular attention was placed on the fluorinated hydrocarbons. Specific properties of fluorinated hydrocarbons give them many applications in industry, such as solvents, refrigerants, propellants, anaesthetics, etc. Hence, a phase equilibria study of a fluorinated hydrocarbons system was carried out in this project. The commissioning of the equipment was successfully undertaken and the equipment was found to be efficient and reliable. As a consequence measurements were made on the hexafluoropropylene oxide (HFPO) + ethane system. No data has been previously published in literature for this system. Measurements were undertaken at five different temperatures, 283.15 K, 290.15 K, 298.15 K, 308.15 K and 318.15 K. The isotherms were chosen in order to have measurements below and above the critical temperature of ethane, in order to see the transition at the critical temperature. The experimental data were modelled via the direct (phi-phi) method. The Peng-Robinson equation of state was applied, including the Mathias-Copeman alpha correlation with the Wong- Sandler mixing rules incorporating the NRTL activity coefficient model. Good agreement was found between the correlated and the measured data. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

The primary focus of this study is the measurement and modeling of binary and ternary VLE data. The measurements of binary and ternary systems were undertaken on a fully automated dynamic VLE apparatus. The glass dynamic VLE still was modified to handle pressures ranging from 0 to 500 kPa, however, the safest maximum pressure to which tests had been conducted was 350 kPa. Thus, this limit was not to be exceeded during the measurement of experimental data. The systems under investigation included the binary and ternary combinations of the following chemicals: n-hexane, 1-hexene and n-methyl-2-pyrrolidone (NMP) at isothermal conditions. A test system consisting of ethanol + cyclohexane was measured at 40 kPa, as well as the system of 1-hexene + NMP at 363.15 K and n-hexane + NMP at 363.15 K. Published literature data for these test systems were employed to verify the measured data for the test systems complied with thermodynamic consistency. All other data constitutes new data, currently unavailable in literature. The following isotherms were measured: 1) 1-hexene (1) + NMP (2) at 323.15, 343.15, 353.15 and 363.15 K 2) n-hexane (1) + NMP (2) at 353.15, 363.15, 378.15 and 383.15 K 3) 1-hexene (1) + n-hexane (2) at 343.15, 363.15 and 373.15 K, and 4) 1-hexene (1) +n-hexane (2) + NMP (2) at 363.15 K All system measurements were carried out on the glass low-to-medium pressure VLE still of Lilwanth (2011), with the exception of the test system ethanol + cyclohexane, which was carried out on the low pressure VLE glass still of Hirawan (2007). The two VLE stills, utilized to carry out measurements in this work, can operate isobarically and isothermally. The temperature on the stills of Hirawan (2007) and Lilwanth (2011) were controlled to within ±0.425 and ±0.089 K respectively and the accuracy of pressure control is to within ±0.320 and ±0.440 kPa respectively. In addition, for the calibration of the various systems: ethanol + cyclohexane, 1-hexene + NMP, n-hexane + NMP, 1-hexene + n-hexane and 1-hexene + n-hexane + NMP, the accuracies are: ±0.002, ±0.0034, ±0.0033, ±0.0066 and ±0.0083 of a mole fraction respectively. The binary interaction parameters obtained from modeling the three binary systems were used to predict the ternary system data. Thereafter, the experimentally measured data for the ternary system was then compared to the model prediction, which was completed on Dortmund Data Bank (DDB, 2011). The measured binary data was regressed utilizing the combined and the direct methods. For the direct method, the cubic equations of state (CEoS) used to describe the vapour phase included the Peng-Robinson (1976) and Soave-Redlich-Kwong (1972) equations combined with the mixing rule of Wong and Sandler (1992) in conjunction with the Gibbs excess energy models, namely the NRTL (1968) and UNIQUAC (1975) models, to describe the liquid phase non-idealities. For the combined method, the Gibbs excess energy activity coefficient models mentioned above were employed to represent the liquid phase imperfections and the vapour phase nonidealities were represented by cubic equations of state, as mentioned above, as well as the Hayden and O‟Connell (1975) virial equation of state for the calculation of the virial coefficients. To verify whether the measured data is thermodynamically consistent the point and direct tests were applied. Even though the direct test is a more stringent approach to testing thermodynamic consistency, for the systems 1-hexene + NMP and n-hexane + NMP, the point test was utilized as the primary means by which to quantify the data, as the associative effects of the NMP molecule effect the results obtained. For the system 1-hexene + n-hexane the direct test was used as the primary means to test the consistency of data, as no cross- or self-association is present. After extensive modeling was carried out, it was found that for the systems 1-hexene + NMP and n-hexane + NMP the model which enabled the best fit of the experimental data are the NRTL activity coefficient model in conjunction with the Hayden and O‟Connell virial equation of state (EoS). For the system 1-hexene + n-hexane the overall best fit model is the Peng-Robinson EoS in conjunction with the Wong-Sandler mixing rule and the NRTL activity coefficient model. A single set of binary interaction parameters for each of the three binary systems was obtained (via regression on Aspen Plus®) using the NRTL-HOC models. However, since Aspen Plus® cannot predict ternary system behaviour using the binary interaction parameters of the constituent systems, DDB was utilized. Further, DDB did not have available the HOC virial EoS (for enabling predictions), thus, it was decided to use the ideal gas model for representation of the vapour phase in conjunction with the NRTL activity coefficient model. The use of the ideal gas model does not compromise the integrity of the prediction in any way since the ternary system measurements were carried out in the dilute NMP region. Thus, since the main components in the ternary mixture at any one instant were 1-hexene and nhexane, and these components behave ideally, the ideal gas model is applicable. After the predicted behaviour for the ternary system was compared to the experimental data for the same system, the maximum percentage error encountered between the two data sets is 5%. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012

by Clive Hau Ming Shiu. / On t.p., "x" and "1-x" are subscript. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves [126]-[130]). / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / TABLE OF CONTENTS --- p.iii / Chapter Chapter 1 --- INTRODUCTION --- p.1 / Chapter Chapter 2 --- THEORY --- p.3 / Chapter 2.1 --- Fundamentals of GaAs and AlGaAs --- p.3 / Chapter 2.1.1 --- Crystal structure and properties of GaAs --- p.4 / Chapter 2.1.2 --- General properties of GaAs at 300K --- p.5 / Chapter 2.1.3 --- Temperature dependence of bandgap for GaAs --- p.6 / Chapter 2.1.4 --- Dopants of GaAs --- p.7 / Chapter 2.1.5 --- Properties of AlGaAs --- p.8 / Chapter 2.2 --- Phase Equilibrium of GaAs and AlGaAs --- p.10 / Chapter 2.2.1 --- Phase diagram of Ga-As binary system --- p.11 / Chapter 2.2.2 --- Phase diagram of Al-Ga-As ternary system --- p.13 / Chapter 2.3 --- Principle of LPE growth --- p.17 / Chapter 2.3.1 --- General concept of liquid phase epitaxy --- p.17 / Chapter 2.3.2 --- Fundamental methods of LPE growth --- p.19 / Chapter 2.4 --- Dopants in GaAs and AlGaAs system --- p.21 / Chapter 2.4.1 --- Common dopants in GaAs --- p.22 / Chapter 2.4.2 --- Tellurium in GaAs --- p.23 / Chapter 2.4.3 --- Silicon in GaAs --- p.24 / Chapter 2.4.4 --- Tellurium and Tin in AlGaAs --- p.26 / Chapter Chapter 3 --- LPE SYSTEM FOR GaAs AND AlGaAs --- p.28 / Chapter 3.1 --- Basic requirements for horizontal sliding LPE system --- p.30 / Chapter 3.2 --- Cleaning process of the LPE system --- p.37 / Chapter 3.2.1 --- Cleaning procedures of the quartz parts --- p.37 / Chapter 3.2.2 --- Cleaning procedures of the stainless steel tubing --- p.38 / Chapter 3.2.3 --- Cleaning procedures of the graphite boat --- p.39 / Chapter 3.3 --- Final examination for LPE growth --- p.41 / Chapter 3.3.1 --- Examining the sealing of the system --- p.41 / Chapter 3.3.2 --- Examining the palladium hydrogen purifier --- p.41 / Chapter 3.3.2.1 --- Measuring the dew point --- p.41 / Chapter 3.3.2.2 --- Measuring the content of oxygen and nitrogen --- p.42 / Chapter 3.3.3 --- Adjusting and measuring the isothermal zone in the fumace --- p.42 / Chapter 3.3.4 --- Measuring of background impurity --- p.43 / Chapter 3.3.5 --- Inspection of the operating chamber --- p.44 / Chapter Chapter 4 --- EXPERIMENTALS --- p.45 / Chapter 4.1 --- Determination of GaAs and AlGaAs content in the source melt --- p.45 / Chapter 4.2 --- Calculation of GaAs and AlGaAs content in the source melt --- p.45 / Chapter 4.3 --- Experimental determination of source melt composition --- p.48 / Chapter 4.4 --- LPE growth method --- p.49 / Chapter 4.5 --- Thickness control of LPE epilayers --- p.49 / Chapter 4.6 --- Experimental procedures --- p.50 / Chapter Chapter 5 --- RESULTS AND DISCUSSIONS --- p.63 / Chapter 5.1 --- Growth condition studies of GaAs --- p.63 / Chapter 5.1.1 --- Experimental --- p.63 / Chapter 5.1.2 --- Phase equilibrium of GaAs in the range of 780 to 840 °C --- p.63 / Chapter 5.1.3 --- Results of undoped GaAs epilayers --- p.67 / Chapter 5.1.4 --- Results of Si doped GaAs epilayers --- p.72 / Chapter 5.2 --- Growth condition studies of AlxGa1-xAs for x=0.1 to 09 --- p.73 / Chapter 5.2.1 --- Phase equilibrium of AlxGa1-xAs for x=0.1 to 09 --- p.73 / Chapter 5.2.2 --- Relation between saturation of solution and he flatness of interface between epilayer and substrate --- p.79 / Chapter 5.2.3 --- Determination of composition x in AlxGa1-xAs --- p.82 / Chapter 5.2.4 --- Relation between epilayer thickness and x in AlxGa1-xAs --- p.84 / Chapter 5.3 --- High AlxGa1-xAs with x ´ 0.9 ° at 780 °C --- p.87 / Chapter 5.3.1 --- Deposition rate of high AlxGa1-xAs epilayer versus cooling rate --- p.87 / Chapter 5.3.2 --- Thickness profiles of epilayers versus cooling rate --- p.89 / Chapter 5.3.3 --- Spectroscopic refractive index of high AlxGa1-xAs in the visible light spectrum --- p.94 / Chapter 5.3.4 --- Rocking curves of high AlxGa1-xAs --- p.96 / Chapter 5.4 --- Tellurium doped AlxGa1-xAs with x ranging from 0.1 to 09 --- p.98 / Chapter 5.4.1 --- Carrier concentration versus composition x in AlxGa1-xAs --- p.98 / Chapter 5.4.2 --- Carrier concentration of Al0.3Ga0.7As versus Te mole fraction --- p.100 / Chapter 5.4.3 --- Donor activation energy of Te Versus x in AlxGa1-xAs --- p.102 / Chapter 5.4.4 --- Refractive index of Te doped AlxGa1-xAs at 300K --- p.105 / Chapter 5.4.5 --- Dependence of solubility upon Te doping level --- p.106 / Chapter 5.5 --- Heavily tellurium doped Al0.3Ga0.7As --- p.107 / Chapter 5.5.1 --- Diffractometry study of heavily Te doped Al0.3Ga0.7As --- p.108 / Chapter 5.5.2 --- Morphological studies and interface studies of heavily Te doped Al0.3Ga0.7As --- p.112 / Chapter Chapter 6 --- CONCLUSION --- p.119 / APPENDIX Photoluminance Analysis at room temperature / REFERENCE