The use of massive nylon as a material for bearing liners is limited by its low melting point ( 260 °C) and its low thermal conductivity (0.172 Btu per hour - square foot - °F per foot). This combination of defects results in the formation of hot spots at points of stress., and since the material does not conduct away the heat from such spots rapidly enough., the nylon tends to expand and stick to the shaft. If it were not for this difficulty., more use would be made of nylon bearings., since it has excellent resistance to corrosive substances such as sea water and is capable of resisting repeated mechanical shock. The purpose of this investigation was to determine the extent to which the degree of crystallinity of nylon could be increased by cold-rolling and annealing, and the change :in thermal conductivity resulting from these treatments. A survey was made of the literature on the thermal conductivity of nylon in particular and non-metallic solids in general., of the internal structure of nylon., of the effect of physical treatment on the internal structure and physical properties of nylon., and on test methods. The duPont Company reported the thermal conductivity of its nylon molding compounds, and stated that an average value for Nylon FMl.0001 is 0.15 Btu per hour - square foot - °F per foot. Austin and Eucken agreed in stating that on theoretical and experimental evidence the thermal conductivity of an inorganic compound is in general higher when the substance is in crystalline form than when it is in amorphous form. Jakob stated that in nonmetallic solids heat is conducted by transfer of vibrations from molecule to molecule, and that in crystals heat is also conducted by a wave-like vibration of the lattice as a 'Whole. Austin stated that the thermal conductivity of inorganic compounds is dependent on the strength of chemical bonding in the compounds. Rehner suggested that the thermal conductivities of organic polymers are all of about the same magnitude since heat is conducted mainly along the molecular chains, which contain primary valence bonds of about the same strength. Many investigators have shown that nylon is microcrystalline in nature, containing crystalline regions about 1000 Angstroms in diameter imbedded in a matrix which is essentially a supercooled liquid. Thus nylon is a two-phase system. The density of nylon has been investigated repeatedly and has been shown to be a measure of the degree of crystallinity. The degree of crystallinity is defined as the percentage of crystalline material present. Direct comparison of the reported densities has not been possible because the samples tested have not been completely characterized as to previous physical treatment. It has been shown that the method of forming affects the density, and samples which have been cooled slowly from the melt have a smaller number of crystal nuclei and a higher degree of crystallinity. Annealing., stretching., solvent swelling., and rolling increase the density and degree of crystallinity., and more drastic physical treatment tends to cancel out the effect of previous milder treatment. Bunn and Garner have established tre crystal form and crystal parameters of nylon 66 and 610 and demonstrated the nature of the orientation that takes place on cold-rolling and annealing. The nylon molecules tend to lie in the plane of the rolled sheet :in the direction of rolling. The experimental part of the work consisted of testing methods of increasing the thermal conductivity of nylon., measuring the thermal conductivity., and determining the changes in internal structure which caused the changes in conductivity. The thermal conductivities of two samples of nylon 66 were determined. One was a slab of cast nylon 1/4-inch thick. The other was prepared from the first by cold-rolling it to half the original thickness and then annealing for two hours at 240°C. To determine the effect of physical treatment on the internal structure the density and degree of crystallinity -were detennined and x-ray diffraction patterns of the samples were made. The material which was tested., nylon 66., was a practically pure chemical compound. It is lmown as polyhexamethylene adipamide., and is the most common nylon of commerce. Standard laboratory procedures were used in all the tests. The thermal conductivity was measured using the ASTM Method Cl77-45, the guarded hot plate method. In this method two sheets of nylon five inches square were sandwiched between an electrical heater and two brass cooling blocks. The quantity of heat which flowed through the samples under the temperature difference set up by the apparatus was measured by measuring the electric power input to the heater. The temperature drop across the samples was measured by means of thermocouples. The sample thickness and area were measured, and from these quantities the thermal conductivity was calculated. The density was determined by weighing six-gram samples in air and in water, according to the standard method. The degree of crystallinity was calculated from the density of dried samples by assuming a linear relationship between density and degree of crystallinity. This method of calculation was worked out by Hermans for cellulose, but has never before been used for nylon. The results of this investigation showed that when nylon slab was rolled and annealed, the degree of crystallinity was increased, confirming the conclusions of previous investigators. On the other hand, the thermal conductivity was affected mainly by an orientation of the molecules produced by rolling rather than by the change in degree of crystallinity. Because of an orientation of the molecules in the direction of rolling, the nylon thermal conductivity became anisotropic. The conductivity was apparently increased in the direction of rolling at the expense of the other directions. These results support Rehner's hypothesis that the thermal conductivity of polymers is mainly dependent on the strength of the primary bonds in the molecular chain, and that thermal conduction in polymers is mainly molecular conduction, not lattice conduction. This hypothesis was questioned at the beginning of the investigation, but the results seem to confirm it. Rolled nylon would be superior to cast nylon for use in bearings since it could better conduct heat away from hot spots. The lower conductivity in the direction through the thickness of the liner would not be a drawback in bearings provided with fluid lubrication since the heat generated by friction is not conducted away through the walls but is carried away by the lubricant. The nylon would have to be annealed after rolling to eliminate residual strains caused by rolling which make it brittle, even though annealing caused some decrease in the degree of orientation of the molecules, with accompanying decrease in the effect of anisotropy of conductivity. The following conclusions were reached from tests made on nylon 66 slab characterized by an intrinsic solution viscosity of 2.53 in 90 percent formic acid, indicating a degree of polymerization of 148. / M.S.

Massive nylon lends itself to many applications because of its outstanding toughness, abrasion-resistance, and chemical resistance. These properties make it a satisfactory bearing material, and in some applications it is superior to metallic bearings. However, the disadvantages of low melting point and low thermal conductivity prevent nylon from being used more extensively. A previous investigation of the effect on thermal conductivity of change in crystallinity brough about by rolling and annealing nylon 66 indicated that it exhibits anisotropy of conductivity and that its thermal conductivity depends on primary physical factors related to its molecular structure. The purpose of this investigation was to determine the relationships of anisotropy of thermal conductivity, bond strength, degree of crystallinity, molecular orientation, and the changes resulting from the rolling-annealing treatment of nylon 66. A survey was made of the literature on the thermal conductivity of nylon in particular and non-metallic solids in general, of anisotropy of thermal conductivity, of the internal structure of nylon, of the effect of physical treatment on the internal structure and physical properties of nylon, and on test methods. The experimental part of the work consisted of measuring the thermal conductivity of nylon along three directions of heat flux, and the changes in internal structure and thermal conductivity in the three directions of heat flux resulting from rolling and annealing treatment. The thermal conductivity of six samples of nylon 66 was determined. The first three samples were cut from a slab of cast nylon ¼ inch thick. The conductivity was measured in a direction perpendicular to the plane of the sample and to the greatest length of the slab, in the plane of the sample, but perpendicular to the greatest length of the slab, and in the plane and in the direction of the greatest length of the slab. The other three samples were prepared from a ¼-inch thick cast slab which had been cold-rolled to half the original thickness and then annealed for two hours at 240 °C. To determine the effect of physical treatment on the internal structure and thermal conductivity, the density and degree of crystallinity were determined and x-ray diffraction patterns of the samples were made. Standard laboratory procedures were used in all of the tests. The thermal conductivity was measured using the ASTM method Cl77-45, the guarded hot plate method. In this method two sheets of nylon five inches square were sandwiched between an electrical heater and two brass cooling blocks. The quantity of heat which flowed through the samples was measured by measuring the electric power input to the heater. The temperature drop across the samples was measured by means of thermocouples. The sample thickness and area were measured, and from these quantities the thermal conductivity was calculated. The density was determined by weighing one to six-gram samples in air and in water, according to the standard method. The degree of crystallinity was calculated from the density of dried samples by assuming a linear relationship between density and degree of crystallinity. This method of calculation was worked out by Hermans for cellulose and used by Snow for nylon. The results of this investigation showed that when nylon slabs were rolled and annealed, the degree of crystallinity was increased, confirming the conclusions of previous investigators. The thermal conductivity was affected mainly by an orientation of the molecule produced by rolling rather than by the change in degree of crystallinity. Because of a preferential orientation of the molecules in the direction of rolling, the nylon thermal conductivity became anisotropic. These results support Rehner’s hypothesis that the thermal conductivity of polymers is mainly dependent on the strength of the bonds in the molecular chain, and that thermal conduction in polymers is mainly molecular conduction, not lattice conduction. The following conclusions were reached from tests made on the nylon slabs. / Master of Science

This work deals with the melt blend of 60/40 PHB/PET (p-hydroxybenzoic acid and polyethylene terephthalate) and 80/20 PHB/PET copolyesters in a 50:50 weight% ratio. Specifically, the interest was to determine as to how do the mechanical properties of the injection-molded parts from the blend compare with that of 70/30 PHB/PET composition and to find out if the melt blend obtained after a single extrusion pass represents an equilibrium composition blend. To determine the anisotropic mechanical properties, injection-molded plaques were obtained by injection-molding the blend at different temperatures. It was found that the tensile properties (tensile strength, modulus and elongation at break in the machine direction) of the blend increase with the increase in the injection-molding temperature (from 300 to 320°c) and then decrease. The flexural modulus of the injection-molded plaques (at an injection-molding temperature of 330°c) of a 50:50 blend of 60/40 PHB/PET and 80/20 PHB/PET mixed only in the injection-molded unit was 2.2 x 10⁶ psi which is 40% higher than that reported for the 60/40 PHB/PET, 100% higher than reported for either 80/20 PHB/PET or 70/30 PHB/PET. To determine the equilibrium nature of the blend, samples with different residence time in the extruder and the 70/30 PHB/PET samples were analyzed by means of Differential Scanning Calorimeter (DSC), Dynamic Mechanical Analysis (DMA), Thermal Mechanical Analysis (TMA), Scanning Electron Microscope (SEM) and Rheometrics Mechanical Spectrometer (RMS), and the mechanical properties of the injection-molded plaques were also determined. The DSC thermogram of the four extrusion pass blend showed multiple melting endotherms. Similar behavior was observed for a number of samples which had been annealed above the melt temperatures for different lengths of time. The formation of multiple peaks was attributed to the incomplete transesterification reaction in the extruder. The OMA results also indicated a substantial decrease in the melting temperatures with the increase in the number of extruder passes. A similar decrease in the melting temperatures has been reported in the literature for various polyesters undergoing transesterification reaction. The TMA results showed that the modulus versus temperature profiles (softening profiles) of one, two and three extrusion pass samples were the same but that of the four extrusion pass film was different and was closer to the softening profile of the 70/30 PHB/PET film. The softening profile of the four extrusion pass sample indicated the presence of crystallites of varying degrees of development, which corresponds well with the splitting peak phenomenon observed in the corresponding DSC thermograms. Thus, it is clear that a chemical reaction is occurring in the extruder. It is suspected that the observed decrease in the flexural properties with the increase in the number of extruder passes is due the transesterification reaction occurring in the extruder. Transesterification studies were also carried out in a cone & plate geometry in the RMS in a no-shear (simple melt annealing) and shearing environment on a larger time scale. From a comparison of the thermal behavior of the blend (as a function of the reaction time) in different environments, it was concluded that the transesterification reaction proceeds faster in the presence of deformation such as occurs in the extruder or in a simple shear flow and with an increase in temperature. Finally, to compare the rheological properties of the multiple extrusion pass and the 70/30 PHB/ PET samples, dynamic frequency sweeps were performed in the RMS at different temperatures. At a given frequency, the complex viscosity, storage modulus and loss modulus increased with an increase in the number of extrusion passes. This increase is unexpected. A number of explanations have been proposed to account for this increase in the rheological properties. / Master of Science

No description available.

Areas which require high-temperature MOS circuits are instrumentations for geothermal and petroleum well-logging, space exploration, aero-propulsion systems, and other hostile environments. MOS digital circuits at high temperature are examined as well as the maximum operating temperature of MOS devices. Factors affecting high-temperature operation of these devices, including threshold voltage sensitivity, mobility degradation, leakage current characterization and interactions, zero-TC current in analog applications and reliability considerations, are discussed. Methods to reduce threshold voltage sensitivities, process modifications to reduce leakage current density at high temperature, circuit techniques to eliminate the leakage current effects, diode compensation, CMOS thermal latch-up and MOS scaling rules at high temperature are investigated. Experimental results of epitaxial diodes to verify the leakage current reduction effect are discussed.

With electronic packaging becoming more complex, simple hand methods to model the thermal performance of the package are insufficient. As computer aided modeling methods came into use, a test system was developed to verify the predictions produced by such modeling methods. The test system is evaluated for operation and performance. Further, the premise of this type of test (the accurate calibration of packaged temperature-sensitive-parameter devices can be done) is investigated using a series of comparative tests. From this information, causes of possible/probable errors in calibration are identified and related to the different methodologies and devices used. Finally, conclusions are presented regarding the further improvement of the test system and methodologies used in this type of testing.

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy (Metallurgical Engineering) 2017 / The alloy Ti-2.7Al-5.7Fe-6Mo-6V (wt%), commercially known as Timetal 125, is used as a high strength fastener in aerostructure assemblies. Very little information is available on its properties and processing, and this study investigated its consolidation from low cost elemental powders, to achieve the minimum mechanical properties for use as a high strength fastener. Reactions during alloying and its beta transus were investigated by differential thermal analysis. The α+β phase region was established to lie between 590oC and 800oC by thermal analysis, metallography and XRD. The alloy was consolidated to ~99% theoretical density by semi-centrifugal casting, and spark plasma sintering of the blended powders. Various heat treatments were undertaken, and the microstructures were evaluated by optical and scanning electron microscopy. Tensile properties, hardness and density were measured after each heat treatment, to establish the optimal combination of mechanical properties. The experimental Timetal 125 style alloy was found to be a metastable beta titanium alloy, which could be strengthened by ageing. It had a microstructure consisting of alpha grains with fine beta precipitates in the as-cast condition, while the sintered samples had acicular precipitates and larger grains, due to the unusually long period that was required to sinter the samples. The ultimate tensile strength was >1500MPa, and elongation was ~3% in the as-cast condition, thus failing to conform to the Airbus EN6116 standard’s specification for ultimate tensile strength and elongation for a high strength fastener in the as-cast or sintered condition. After annealing the castings at 900oC for 1 hour, the ultimate tensile strength decreased to ~760MPa, while elongation increased to ~15%, which still did not conform to the Airbus standard, due to the low strength. The alloy was solution-annealed at 900oC, followed by water quenching to retain a fully βTi microstructure. The minimum properties for the Airbus standard were achieved after ageing between 500oC and 590oC for 1 hour, with an ultimate tensile strength of ~1285MPa, and elongation of ~6.3%. The strengthening depended on the amount and morphology of αTi precipitates from ageing. The αTi/βTi ratio increased with increasing temperature and holding time (shown by XRD), up to 590oC where the precipitates progressively transformed to βTi. Extending isothermal holding time coarsened the precipitates, which was deleterious to strength. There was generally a positive correlation between mean grain size and temperature or holding time, although competing transformations suppressed grain growth, particularly after heat treatment close to transformation temperatures. Although grain size had an effect on the strength of the Timetal 125 style alloy, the main mechanism was precipitation hardening by the secondary αTi. Extended ageing resulted in the formation of allotriomorphic alpha titanium, and a corresponding decrease in the ultimate tensile strength. It was not possible to subject the sintered samples to tensile testing, due to their shape. However, the sintered samples were less porous and had higher Vickers’ values than the castings, suggesting they had similar, if not higher tensile strengths. The acicular precipitates in the sintered samples were possibly martensite or omega titanium (ωTi, Pearson symbol hP3 and space group P6/mmm) although they were too fine to be detected by X-ray diffraction and too fine analyse separately by energy dispersive X-ray spectrometry. / MT 2017

by Guo Wenhua. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

"Apr 2002." / The numerals in title is subscript. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Polymer-layered silicate nanocomposites based on a variety of polymer matrices and several organoclays were prepared by melt processing. A detailed characterization of the thermal degradation of several commercial and experimental organoclays often used to form polymer nanocomposites was reported. The surfactant type, loading, and purification level of organoclay significantly affect their thermal stability; however, broadly speaking, the results suggest that these differences in thermal stability do not appear to have much effect on the morphology and properties of the nanocomposites formed from them. It seems that the thermal stability of organoclays is not the key factor in organoclay exfoliation in melt processed polymer nanocomposites, since the exfoliation/dispersion process may have been completed on a time scale before the degradation of surfactant progresses to a detrimental level. Polymer nanocomposites have been made from a variety of polymers; however, few matrices have demonstrated the ability to readily exfoliate the organoclay as well as nylon 6, especially for highly hydrophobic materials like polyolefins. Hence, a significant part of this research work was devoted to explore various routes to improve polyolefinorganoclay interactions, and thus, organoclay exfoliation in these systems. Amine grafted polypropylenes and a conventionally used maleic anhydride grafted polypropylene were used as compatibilizers for polypropylene based nanocomposites to improve the organoclay exfoliation. A series of ethylene vinyl acetate copolymers, the polarity of which can be adjusted by varying their vinyl acetate contents, based nanocomposites were prepared as the model system to address the relationship between the polarity of the polymers and their preferences over various organoclay structures. Attempts were made to explore the effect of degree of neutralization of acid groups in ionomers on the morphology and properties of nanocomposites, and it seems that the ionic units on the polymer chain provide a more favorable interaction between the polymer matrix and the organoclay compared to acid units and, thus, lead to better dispersion of the clay particles. It was determined that surfactants whose structure lead to more shielding of the silicate surface result in improved levels of exfoliation in all the above mentioned unmodified and modified polyolefin based nanocomposites. / text