No description available.

Spent Nuclear Fuel (SNF) is a by-product of existing nuclear reactors; SNF consists of long-lived radioactive actinides which have an average half-life of several thousand years (e.g. Plutonium-239 with a half-life of 24,000 years, and Americium-243 with a half-life of 7,360 years). Several multinational organizations are making an attempt to extract the energetic value out of these nuclear stockpiles in order to minimize the risk of nuclear proliferation and reduce waste volume. The Inert Matrix Fuel (IMF) concept is being considered as an option to reuse the radioactive actinides present in spent nuclear fuel by means of a transmutation process. Due to the volatile nature of these radioactive actinides, it is expected that the high-temperature conventional processing of IMFs will result in a significant loss of material. This study investigates microwave sintering of inert matrix material (excluding actinide fuel) as an alternative route to conventional processing. It was observed that microwave sintering showed a reduction of 300°C in temperature required for full densification when compared to conventional sintering. The reduction in sintering temperatures did not show any significant variation in the resulting properties (hardness and grain size). While these results satisfy the need for the application, it is important to understand why microwaves enhance the sintering phenomena. It is speculated (by many researchers) that the electric field associated with microwave energy is enhancing flux leading to accelerated densification during microwave sintering. This study has observed a decrease in the activation energy (for sintering 8YZ) with the increase in the magnitude of the applied electric field. / Ph. D.

ESI-MS spectra of Ni(II), Co(III), Mg(III), and Fe(II) porphyrin solutions in methanol show porphyrin monomer species with different charge states, such as [Ni(II)TPPS+H]3-, [Co(III)TPPS]3-, [Mn(III)TPPS]3-, [Mn(III)TPPS+H]2-, [Fe(II)TPPS+H]3-, and [Fe(II)TPPS+2H]2- ions. Collision-induced dissociation (CID) of these monomer species produced primarily losses of neutral SO3 and SO2. The mechanisms, in which these dissociation pathways took place, were investigated by the means of DFT calculations of the corresponding dissociation of neutral and ionized benzenesulfonate (B3-LYP/6-31+G(2d, p) level) and porphyrin monomer (B3-LYP/6-31+G(2d, p)+LANL2DZ//PM7 level). RRKM fitting of the CID breakdown curves showed that the activation energies of the reactions that experience a loss of SO2 from [Co(III)TPPS]3- and [Mn(III)TPPS]3- were similar, but of a lower magnitude than those for a loss of SO3. On the other hand, for [Ni(II)TPPS+H]3- and [Fe(II)TPPS+2H]2-, the activation energies of the reaction leading to a loss of SO2 were also similar, but this time were larger than those leading to SO3 loss. These results are consistent with a mechanism by which the SO2 loss starts with -C6H4SO3-, while the SO3 loss has to begin with -C6H4SO3H. To lose this SO3, extra energy is required for [Co(III)TPPS]3- and [Mn(III)TPPS]3- in order for them to overcome the barrier of H transfer from the porphyrin ring to -SO3-, but this is irrelevant when it comes to [Ni(II)TPPS+H]3- and [Fe(II)TPPS+2H]2- since the C6H4SO3H moiety already exists. In addition, the reaction of [Fe(II)TPPS+H]3- losing H leads to a unique dissociation mechanism.

Diamond is a unique material with many exceptional properties. It has therefore been proven to be an important material for many applications. Moreover, the introduction of dopant species into the gas phase during the CVD growth process has been shown to strongly influence not only the properties and morphology of diamond, but also the growth rate. The purpose with the theoretical part of the present study has been to support and explain the experimental observations regarding the effect of various dopants (nitrogen, phosphorous, sulphur, and boron) on the diamond growth rate. Commonly observed H-terminated diamond surfaces [(111), (110) and (100)-2×1], were thereby carefully investigated using density functional theory under periodic boundary conditions. Based on the assumption that the hydrogen abstraction reaction is the growth rate-limiting step, both the thermodynamic and kinetic aspects of the diamond growth process were found to be severely affected by various dopants. More specifically, the results showed that nitrogen and phosphorous dopants (positioned within the 2nd, 3rd or 4th carbon layer) will cause an enhancement in the growth rate (as compared with non-doped situations). On the other hand, any growth rate improvement does only occur when positioning boron in the 2nd, and sulphur in the 4th, atomic carbon layer. With boron, and sulphur, positioned within the other atomic carbon layers, the growth rates were observed to decrease. In addition, the main purpose with the experimental part of the present study has been to investigate the effect of one specific dopant precursor (TMB) on the boron-doped diamond growth process. The result has shown that the increasing mass flow of TMB will not affect the mechanism of the HFCVD growth process of boron doped diamond. However, a linear boron carrier concentration in the diamond film vs. mass flow rate of TMB was observed.

There are many products, including hard drives, which require trace amounts, on the order of several mg, of lubricants for proper operation. The following study investigated the evaporation rates of pump oil and several alkanes, which have a wide range of applications, using a thermogravimetric machine. Both static and dynamic temperature tests were conducted. The rate of evaporation of the test specimen was determined as the percentage of mass loss per unit time. Using the Arrhenius Equation, the activation energy of the evaporation process, Ea, can be calculated as the slope of the best fit line for a plot of the ln(k) vs. 1/T (where k represents the rate of the evaporation). These values were shown to have good agreement with the enthalpy of vaporization calculated from the Clausius Clapeyron Equation and with the activation energy calculated using the Freeman and Carroll Method. The alkanes were compared using the rate of evaporation and the amount of activation energy required for evaporation as model systems. Further investigations were conducted to determine the relationship of surface area of the evaporating liquid and the rate of evaporation. It is suggested that the surface area is a function that depends on the activation, bonding, and interfacial energies of the liquid. However, the wetting angle, which aids in the description of the surface area, depends on the surface energy. Subsequent modeling was conducted in an attempt to predict the evaporation characteristics of other lubricants for the purpose of comparison.

This dissertation investigates the self assembly and automatic oscillation of intelligent poly (N-isopropylacrylamide) [PNIPAM] microgel particles. The equilibrium phase diagram as a function of temperature and concentration was constructed for the charged PNIPAM spheres. The PNIPAM microgel particles display rhythmic size oscillations when covalently coupled to a nonlinear chemical reaction, the Belousov-Zhabotinsky (BZ) reaction. The nonequilibrium dynamics of PNIPAM microgels in the presence of BZ reaction was studied by the systematic variation of substrate concentrations and temperature. In addition, the BZ chemical reaction was modeled to reveal the existence of upper temperature limits for nonlinear chemical systems. The experiments employ environment sensitive PNIPAM particles that are sensitive to temperature, pH, and ionic strength. The PNIPAM particles have been demonstrated here to behave as hard spheres at low pH values and soft spheres at high pH. This is done by measuring the freezing and melting boundary of fluid-crystal coexistence region with a new technique which is simpler and quicker compared to the traditional sedimentation method. A novel method was developed to achieve size uniformity of PNIPAM gel particles with covalently-bound tris(bipyridyl)ruthenium(II) via the coordination chemistry between a ruthenium complex and the monodispersed PNIPAM gel particles bearing bipyridine ligands. The correlation between the dynamic behavior of BZ reaction induced mechanical oscillations of PNIPAM particles and substrate concentrations was presented in a ternary phase diagram. In particular, the dependence of oscillation frequency and induction time on the substrate concentrations was studied. The temperature dependency of the induction time and oscillatory frequency of the BZ reaction in this polymerimmobilized catalyst system were compared to the bulk BZ reaction with the catalyst in the solution phase. Prolonged induction times were observed for the immobilized catalyst, compared with free catalyst, while little difference was observed on the oscillation frequency. A theoretical improvement has been achieved by incorporating the temperature dependence in the BZ Oregonator model. Bifurcation has been calculated in the phase space spanned by initial reagents concentration ratio, stoichiometric factor and temperature. The existence of upper temperature limits has been demonstrated.

The glass forming ability (GFA) of the lightweight Mg65Cu25Y10 alloy has been widely studied. This alloy contains a medium sized Mg matrix (0.16 nm in atomic radius), a small sized Cu (0.14 nm) and a large sized Y (0.18 nm). The glass transition temperature Tg, supercooled temperature range

Recently, wet sand blasting on coated cutting tool inserts has drawn interest to the tooling industry due to its positive effects on cutting performance and tool life. This performance boost has partly been attributed to the buildup of compressive residual stresses in the coating during the blasting process. However, the mechanism of forming residual stresses in ceramic coatings during sand blasting is not fully understood. This work utilize x-ray diffraction as the main tool to study the formation and relaxation of residual stresses after wet sand blasting and annealing on 001, 012 and 110 textured α-Al2O3 coatings. To minimize the influence of stress gradients in the samples, all stress measurements were set up with a fixed analysis depth of 2 µm. Sand blasting was made with an alumina based slurry at 2, 3.2 and 4 bar pressure and the anneal was done at temperatures from 400 to 1000 °C for 2 hours or more. The coating hardness was evaluated by nanoindentation. Finally, the activation energy for the relaxation of residual stresses was estimated using the Zener-Wert-Avrami function. The results reveal the highest compressive residual stress with up to -5.3 GPa for the 012 texture while the stresses for the 001 and 110 textures peaked at -3.1 and -2.0 GPa, respectively. Further, a hardness gradient was present after blasting of the 001 and 012 textured samples indicating a higher stress at the surface of the coating. The 110 textured sample is the most brittle resulting in flaking of the coating during sand blasting. The different deformation mechanisms are related to difference in active slip planes between coatings with different textures. Both the stress and hardness decreased after heat treatment and the activation energy for stress relaxation was found to be as 1.1 ± 0.3 eV, 1.9 ± 0.2 eV and 1.2 ± 0.1 eV for the 001, 012 and 110 textures, respectively.

No description available.

Nanocrystalline materials are polycrystalline solids with grain size in the nanometer range (< 100nm), which have been found to exhibit superior properties such as high magnetic permeability and corrosion resistance, as well as a considerably increase of strength when compared with their coarse grain counterparts. All those improved properties are attributed to the high volume fraction of grain boundaries (GBs). However, the high density of GBs brings a large amount of excess enthalpy to the whole system, making the nanostructures unstable and suffer from severe thermal or mechanical grain growth. In order to maintain the advantageous properties of nanocrystalline materials, it is necessary to stabilize GB and inhibit grain growth. While alloying has been found to be an effective way of achieving stabilized nanocrystalline metal alloys experimentally, the direct quantification of solute effects on GB motion still poses great challenge for investigating thermal stability of general nanocrystalline materials. In this research, impurity segregation and solute drag effects on GB motion were investigated by extending the interface random-walk method in direct molecular dynamics simulations. It was found that the GB motion was controlled by the solute diffusion perpendicular to the boundary plane. Based on the simulation results at different temperatures and impurity concentrations, the solute drag effects can be well modeled by the theory proposed by Cahn, Lücke and Stüwe (CLS model) more than fifty years ago. However, a correction to the original CLS model needs to be made in order to quantitatively predict the solute drag effects on a moving GB.