Understanding the effects of the process parameters on the distribution behaviour of antimony between metal and slag in the iron blast furnace is critical to develop a universal method of controlling temper embrittlement in commercially pure low alloy steels.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2021 / The ab initio density functional theory and molecular dynamics approach have been used to study the properties of Zr-based systems. In particular Zr-Nb, Zr-Nb-X (X = Co and Sn). We have calculated the structural, elastic, mechanical properties and temperature dependence particularly to determine their stabilities. These alloys are important for a wide range of technological applications, primarily in the nuclear and chemical industries due to their good irradiation stability, wear and corrosion resistance, high mechanical strength and superior neutron economy. The virtual crystal approximation was used to introduce small amounts of either Co or Sn contents on Zr-Nb system. The main idea is to advance high-temperature applications of Zr-Nb system through ternary alloying. Calculations were carried out using the ab initio DFT employing the plane-wave pseudopotential method as implemented within the CASTEP code. The influence of partial substitution for Nb concentration with either Co or Sn concentrations was investigated on the Zr-Nb-X systems of various concentrations. The resulting equilibrium lattice parameters, heats of formation, elastic properties, and the density of states were evaluated to mimic their structural, thermodynamic and mechanical stability trends. The lattice parameters of binary systems Zr99Nb1.0, Zr98.8Nb1.2, Zr98.1Nb1.9, Zr97.5Nb2.5, Zr97Nb3, Zr78Nb22, Zr78Nb22 and Zr50Nb50 gave better agreement with available experimental data to within 5 %, while those for ternary systems have shown a decrease with the introduction of the third element i.e. Co or Sn. The heats of formation were negative (stable) at smaller concentrations of ≤ 1 at. % Co. Moreover, the correlation of electronic stability using the DOS and the ∆Hf calculations has indicated that the systems are thermodynamically stable within ≤ 1 at. % Co for (Zr99Nb1-xCox, Zr98.8Nb1.2-xCox, Zr98.1Nb1.9Cox, Zr97.5Nb1.5-xCox, Zr97Nb3- xCox and Zr78Nb22-xCox) systems. It was found that the increase in Co concentration enhances the thermodynamic, elastic and mechanical stability of the systems and they are found to be stable at small concentrations of about 1 at. % Co. Furthermore, the temperature dependence was carried out using Dmol3 . In particular, the canonical ensemble (NVT) calculations were carried out at different temperatures and we observed their structural behaviour with regard to the binding energy and elastic properties at any given temperature up to 2400 K. We compare the temperature dependence of Zr, Zr50Nb50, Zr78Nb22, Zr78Nb21Co1, Zr78Nb20Co2, Zr78Nb19Co3, Zr50Nb49Sn1, Zr50Nb48Sn2 and Zr50Nb47Sn3 systems. In the case of binary system, the Zr78Nb22 was more promising, showing lower binding energy of - 6.87eV/atom. It was shown that ternary additions with small atomic percentages of Co and Sn have a significant impact on Zr-Nb alloy. Particularly, their elastic properties showed a possible enhancement on the strength and ductility at high temperature. This was observed for 1 at. % since it satisfied the requirements for ductility and strength as specified in literature. The Co and Sn addition on the Zr78Nb22 system is more promising for high-temperature applications, with Sn being more preferable. / National Research Foundation (NRF) and Titanium Centre of Competence (TiCoC)

Thesis (M. Sc. ( Physics)) -- University of Limpopo, 2020 / In this work, we present first-principles calculation on the structural, thermodynamic, mechanical and electronic stabilities of Fe-Al and FeAl-X (X: Pt, Pd, Ru and Ag) alloys at lower and high temperatures. These systems have recently attracted a lot of attention for both scientific and possible technological application in turbines, Steel-It coating, energy sector, boilers, pipes and automotive parts as a potential replacement of steel due to their excellent resistance to oxidation at high temperatures. However, they suffer limited room temperature ductility and a sharp drop in strength above 873 K. We determined the lattice parameters, heats of formation, elastic constants, bulk to shear moduli, density of states, phonon dispersion curve and X-ray diffraction pattern for binary and ternary system at various concentrations between 0 ≤ x ≤ 10. Furthermore, the lattice expansion, elastic constants, Gibbs free energy, X-ray diffraction pattern and radial distribution function were done on the most stable systems to determine the melting point of FeAl-X ternary systems. A systematic investigation was performed on the stability of the Fe-Al alloys at zero K. We employed CASTEP code to evaluate the thermodynamic, elastic and electronic stability. Virtual crystal approximation was used to determine various atomic concentrations (0 ≤ x ≤ 5) of both Pt and Ru; this allowed more precise predictions on the materials’ behaviour. Further analysis was done on the density of states to describe the behaviour of each phase near the Fermi level; these phases were observed at different percentage compositions. A supercell approach, DMol3 was also used to evaluate these systems at a larger scale (0 ≤ x ≤ 50). VASP and LAMMPS codes were used to determine the stability of these FeAl-X ternary systems at concentrations (0 ≤ x ≤ 10). It was found that the equilibrium lattice parameters of the binary systems are in good agreement to within 2% with the available experimental data. The heats of formation showed that β2 FeAl phase was the most energetically stable system since it displayed the lowest value compared to all other binary systems. This observation accord well with the experimental phase diagram. It was also confirmed from the corresponding electronic DOS behaviour near the Fermi level. Furthermore, the shear modulus (C’) of these Fe-Al binary systems, i.e. FeAl, Fe2Al5, Fe4Al13, Fe5Al8, Fe2Al and FeAl3 were found to be positive fulfilling the condition of stability. The Fe2Al5 system was found to be the second most stable phase, followed by the monoclinic structure Fe4Al13. This observation was confirmed from the total DOS (where the Fermi level falls in the pseudogap, condition of stability). We further employed virtual crystal approximation and supercell approaches to model various atomic compositions at 0 ≤ x ≤1 and 0 ≤ x ≤ 50 for Ag, Pt, Pd and Ru. The heats of formation, density of states and elastic constants were determined to describe the structural, thermodynamic and mechanical stability of these systems. It was found that the addition of Ag, Pt, Pd and Ru enhances the stability at lower atomic percentage composition below 0.5%. Interestingly, the addition of Pt and Ru was found to significantly improve the ductility of the ternary FeAl-X compound for 0.2 and 0.5 at. % compositions. These systems showed that the Fe-sublattice was the preferred doping site with promising improvement in strength on the properties. It was further deduced that Ag and Pd stabilize the FeAl-X system at atomic percentage compositions of 0.5 and 0.7 respectively. Furthermore, a molecular dynamics-based LAMMPS-EAM was employed to model Fe50-XXXAl doped systems with either Ag, Pt or Pd. The lattice site preferences of the dopant were deduced from their energy landscape. More importantly, Ag and Pd doped systems gave comparable transition temperatures to experimental findings of 1273 K and 1073 K, respectively. Their thermodynamic and mechanical stability trends showed promising properties for industrial applications, displaying stability at a high temperature below 1300 K. This was evident for Ag, Pt (0.5 at %) and Pd (0.7 at %) doping as was the most stable systems with respect to Cij, ΔG, and RDF’s which indicated to influence the elastic instability above 1200 K as well as the ductility of these systems. The XRD confirmed that the doped systems preserved the structural symmetry as expected.

Supersaturated substitutional alloys formed by ion implantation and rapid liquid-phase epitaxial regrowth induced by pulsed-laser annealing have been studied using Rutherford-backscattering and ion-channeling analysis. A series of impurities (As, Sb, Bi, Ga, In, Fe, Sn, Cu) have been implanted into single-crystal (001) orientation silicon at doses ranging from 1 x 10^15/cm2 to 1 x 10^17/cm2. The samples were subsequently annealed with a Ω-switched ruby laser (energy density ~1.5 J/cm2, pulse duration 15 x 10-9 sec). Ion-channeling analysis shows that laser annealing incorporates the Group III (Ga, In) and Group V (As, Sb, Bi) impurities into substitutional lattice sites at concentrations far in excess of the equilibrium solid solubility. Channeling measurements indicate the silicon crystal is essentially defect free after laser annealing. The maximum Group III and Group V dopant concentrations that can be incorporated into substitutional lattice sites are determined for the present laser-annealing conditions. Dopant profiles have been measured before and after annealing using Rutherford backscattering. These experimental profiles are compared to theoretical model calculations which incorporate both dopant diffusion in liquid silicon and a distribution coefficient (k') from the liquid. It is seen that a distribution coefficient (k') far greater than the equilibrium value (k0) is required for the calculation to fit the experimental data. In the cases of Fe, Zn, and Cu, laser annealing causes the impurities to segregate toward the surface. After annealing, none of these impurities are observed to be substitutional in detectable concentrations. The systematics of these alloys systems are discussed.