Semiconductor Cystal Growth: Sb-doped Ge A report of a junior lab. Fall'98
Brittle Fracture of Glass A lab report from a junior lab. Spring'99
Mechanical Testing of Unidirectional Composite Another report from a junior lab. Spring'99
Nitinol Heat Engine A design project from a material engineering class. Spring'99
Abstract: Many thin film fabrication techniques have been used to produce thin-film high temperature superconductors. Pulsed laser deposition or laser ablation is one of the methods that is carried out in many applications. Because of its several advantages, PLD has been widely used. This review paper therefore focuses on the process and techniques of PLD method in several aspects. The discussions include the mechanical and theoretical description of the process, the general deposition process, the equipment that is used in the process with its description and its importance to the film quality, some of the techniques that can affect the quality of superconductors, and the major problems of the method including some of the solutions of those problems.
The full paper is in PDF file: htsc.pdf
Abstract: Solar cells are widely used in many technological applications such as calculators, powering communication equipment and satellites. The most important part of solar cells is the semiconductor layer. The quality of a solar cell depends greatly on the solute distribution in the semiconductor. Uniform solute distribution gives high quality solar cells, i.e. high efficiency. Therefore, understanding the limits of applicability of growing a semiconductor is important. This experiment studied the limits of applicability of growing a semiconductor by growing a single crystal Sb-doped Ge and determining the solute distribution in the single crystal. An Sb-doped Ge crystal was formed by the Bridgman melt technique. The amount of Sb and Ge were calculated base on the volume of the desired crystal. The predicted results and the theoretical calculation of the expected compositional profile were presented. A non-uniform solute-concentration profile was expected due to the effects of convective mixing in the liquid.
The full paper is in PDF file: crystal_growth.pdf
Abstract: Many types of glass are used vastly in everyday life. Several applications require high strength and safety. Since the actual strength of glass is different from the theoretical strength by two to three orders of magnitude if small flaws or microcracks on the surface are present, understanding the effects of surface flaws to the strength of glass is important. This experiment investigated the effects of different surface treatments on SLS-glass rods. Five surface treatments were performed on soda-lime silicate glass rods; then, the five sets of samples and one set of controlled samples were tested in four-point bending in the Instron testing machine. The average strengths and elastic modulus of the glass rods obtained from the calculations were satisfied in most cases. Some deviations in the results were obtained in all samples. The Weibull modulus verified such deviations in the strength values of different samples by explaining the variability of a material's properties. The results confirmed that ion exchanging and etching the glass rods increased the strength of glass. Conversely, interacting the glass rods with water and abrading the surfaces of the glass rods reduced the strength of glass.
The full paper is in PDF file: glass_fracture.pdf
Abstract: Composite materials are used in many applications such as sporting goods, automotive parts, and aircraft structures. The properties of composite materials are superior to those of the constitutes. High strength and stiffness, long life, low density, corrosion resistance, and wear resistance are some of their properties. The mechanical properties of composites depend on the orientation of the loading axis relative to the fiber. Composites can be very stiff and strong under one loading direction but very weak in another direction. Catastrophic failure can happen if this behavior is not considered in designing process. This experiment studied mechanical properties of two types of unidirectional composites, boron/epoxy and boron/aluminum composites under different loading orientations. Tensile and four-point bending tests were carried out to determine the tensile strength and elastic modulus of each material. The results were satisfactory. Both composites were strongest in the orientation that the loading direction was parallel to the fiber direction and weakest in the in the orientation that the loading direction was perpendicular to the fiber direction. The results suggested from almost all cases that the boron/aluminum composite is stronger and stiffer than the boron/epoxy composite.
The full paper is in PDF file: composite.pdf
Energy is an important
factor for everyone's life. Electricity in households and gasoline or diesel
engines in cars are the primary energy sources that are used everyday.
Pollution and efficiency are problems associated with these sources. Many
efforts have been made to find substitute energy sources that will cause
no pollution and will have more efficiency; however, no real solution has
yet been found.
Since sunlight is free and causes no pollution, many researchers have tried to convert it into electric current by several designs such as solar cells. However, many applications besides solar cells can also be achieved to produce electric current from solar energy. One approach is to use a shape memory alloy to produce mechanical work, which is then converted to electric current by a generator. This approach has the potential to be useful for remote areas that are sunny and hot and require a moderate amount of energy power.
Nitinol1, Nickel Titanium Naval Ordnance Laboratory, is an alloy of nickel and titanium that exhibits a shape memory effect. When a Nitinol sample is physically deformed to a new shape, the sample will recover its original shape when heated to its transformation temperature2. Mechanical work can be obtained during the return to the material's original shape. Therefore, this alloy can be used to produce mechanical work when it is thermally cycled between hot and cold reservoirs.
In this design project, the problem was to design a device using a shape memory alloy to produce mechanical work. It was assumed that an effective generator was available and the only design to be done was the device. The preliminary goal of the design was to get a power output of 10 kW from of the engine.
The full paper is in PDF file: nitinol.pdf