Indigenous and institutional profile: Limpopo River Basin

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First principles calculation of structural and magnetic properties for Fe monolayers and bilayers on W(110)

Structure optimizations were performed for 1 and 2 monolayers (ML) of Fe on a 5 ML W(110) substrate employing the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The magnetic moments were also obtained for the converged and optimized structures. We find significant contractions ($\sim$ 10 %) for both the Fe-W and the neighboring Fe-Fe interlayer spacings compared to the corresponding bulk W-W and Fe-Fe interlayer spacings. Compared to the Fe bcc bulk moment of 2.2 $\mu_B$, the magnetic moment for the surface layer of Fe is enhanced (i) by 15% to 2.54 $\mu_B$ for 1 ML Fe/5 ML W(110), and (ii) by 29% to 2.84 $\mu_B$ for 2 ML Fe/5 ML W(110). The inner Fe layer for 2 ML Fe/5 ML W(110) has a bulk-like moment of 2.3 $\mu_B$. These results agree well with previous experimental data

Failure mechanism and lifetime of various laser-drilled APS-TBC systems under LCF conditions

Laser drilling is a highly efficient method to produce cooling holes in TBC systems. Low-Cycle Fatigue tests on APS TBC-coated nickel-based superalloy specimens were performed for undrilled and laser-drilled samples, using a long-pulsed and an ultra-short pulsed laser method at two different angles. The tests were conducted at 850 °C with two mechanical strain ranges of 0.38% and 0.67% to analyse the influence of the quality of the laser drilled holes on failure mechanism and lifetime. Ultra-short pulsed laser and inclined cooling holes showed longer life time compared to the other drilled variants

Oxidation Studies of Anodes Layer Microstructures in Metal Supported Solid Oxide Fuel Cells

The effect of oxidation on the microstructural and mechanical stability of ceramic layers in metal supported solid oxide fuel cells is reported. Half-cells that are produced with a reduced nickel based anode are oxidized for different times and temperatures in order to assess stability limits. Samples are analyzed in terms of the effective cell curvature and microstructure, where further insight is obtained via the observation of microstructures before and after oxidization. The interpretation is aided by a comparison to the behavior of structures without electrolyte layer. Electrolyte cracking and anode delamination are observed after oxidation, where the latter is absent in case of oxidation experiments without electrolyte layer, highlighting the failure relevance of strain induced by electrolyte deposition

Yb203 and Gd203 doped strontium zirconate for thermal barrier coatings

Yb2O3 (10 mol%) and Gd2O3 (20 mol%) doped SrZrO3 was investigated as a material for thermal barrier coating (TBC) applications. The thermal expansion coefficients (TECs) of sintered bulk Sr(Zr0.8Yb0.1)O-2.95 and Sr(Zr0.8Gd0.2)O-2.9 were recorded by a high-temperature dilatometer and revealed a positive influence on phase transformations of SrZrO3 by doping Yb2O3 or Gd2O3. The results for the thermal conductivities of Sr(Zr0.9Yb0.1)O-2.95 and Sr(Zr0.8Gd0.2)O-2.9 indicated that both dopants can reduce the thermal conductivity of SrZrO3. Mechanical properties (Young's modulus, hardness, and fracture toughness) of dense Sr(Zr0.9Yb0.1)O-2.95 and Sr(Zr(0.8)d(0.2))O-2.9 showed lower Young's modulus, hardness and comparable fracture toughness with respect to YSZ. The cycling lifetimes of Sr(Zr0.9Yb0.1)O-2.95/YSZ and Sr(Zr0.8Gd0.2)O-2.9/YSZ double layer coatings (DLC), which were prepared by plasma spraying, were comparable to that of YSZ at operating temperatures 1300 degrees C. (c) 2008 Elsevier Ltd. All rights reserved