INITIAL FRACTURE MECHANISMS IN NICKEL ALLOYED PM STEEL

Abstract— Initial fatigue crack propagation mechanisms at near threshold conditions were studied for four nickel-alloyed, powder-metallurgy (PM) steels. Fatigue fracture surfaces were obtained by testing smooth rectangular specimens at 30 Hz and under constant amplitude and zero mean stress conditions. Materials based on Distaloy AE were used in two densities, namely 7.15 and 7.45 g/cm³.
All the fracture surfaces were composed of three morphological regions (i) a macrocrack initiation region Rl where cracks propagated preferentially through particles (ii) a macrocrack growth region R2 and (iii) an unstable crack growth region R3 where cracks propagated preferentially between particles. Initial fatigue crack growth, in region R1, was controlled by the propagation of short cracks whose dimensions were comparable to the material microstructure. The subsequent fatigue crack growth in regions R2 and R3 was controlled by ductile rupture between microvoids. Transparticle fracture in region R1 was independent of pore distribution, while interparticle fracture in regions R2 and R3 was dependent on pore distribution.     

Sulfur in chromia

The solubility of sulfur in chromia has been studied in H₂-H₂O-H₂S tagged with³⁵S at 973 and 1173 K at low oxygen and sulfur partial pressures typical for coal gasification-systems. For monocrystalline samples, it has been shown that sulfur-containing species are only present adsorbed on the surface of the specimens and can be removed by ultrasonic cleaning in acetone. The surface coverage after 4 weeks of exposure to H₂-H₂O-H₂S was between 2.8 and 19.3% of a monolayer. In polycrystalline chromia, sulfur was located only in pores and cracks of the sample. In dense, compact areas of the specimens the solubility of sulfur was below the detection limit of autoradiography, which was estimated to be better than 0.17 ppm.     

Synthesis of Thermally Stable χ-Alumina by Thermal Decomposition of Aluminum Isopropoxide in Toluene

Thermal decomposition of aluminum isopropoxide in toluene at 315°C resulted in χ-alumina that had high thermal stability, whereas the reaction at lower temperatures resulted in formation of an amorphous product. The χ-alumina thus obtained directly transformed to α-alumina at ∼1150°C, bypassing the other transition alumina phases, whereas the amorphous product transformed to γ-alumina and then to θ-alumina before final transformation to α-alumina. When the χ-alumina, solvothermally synthesized at 315°C, was recovered by the removal of the solvent at the reaction temperature, thermal stability of the product was improved further. This procedure is convenient because it avoids bothersome work-up processes that yield large-surface-area and large-pore-volume alumina.     

Direct Observation of Internal Structure in Spray-Dried Alumina Granules

The internal structure of spray-dried alumina granules was characterized by optical microscopy by immersing them in a liquid having a refractive index close to that of alumina. This method provides a unique technique for the detailed analysis of the internal structure of spray-dried granules.     

可降解多孔β-磷酸钙生物陶瓷的制备研究

本文采用湿法制备β-磷酸三钙（β-TCP）粉末，以玻璃为黏结剂，经高温烧结后，添加造孔剂混合后热压铸成型，经过高温处理，制备出可生物降解的β-TCP多孔材料。经X-射线衍射和扫描电镜形貌分析，证明材料主晶相是β-TCP，材料内部有大量连通的均匀微孔。溶解测试表明材料具有一定的溶解性。材料的制备工艺可实现规模化生产。     

Phase-Separated Polyzwitterionic Hydrogels with Tunable Sponge-Like Structures for Stable Solar Steam Generation

Solar steam generation (SSG) through hydrogel-based evaporators has shown great promise for freshwater production. However, developing hydrogel-based evaporators with stable SSG performance in high-salinity brines remains challenging. Herein, phase-separated polyzwitterionic hydrogel-based evaporators are presented with sponge-like structures comprising interconnected pores for stable SSG performance, which are fabricated by photopolymerization of sulfobetaine methacrylate (SBMA) in water-dimethyl sulfoxide (DMSO) mixed solvents. It is shown that driven by competitive adsorption, the structures of the resulting poly(sulfobetaine methacrylate) (PSBMA) hydrogels can be readily tuned by the volume ratio of DMSO to achieve phase separation. The optimized phase-separated PSBMA hydrogels, combining the unique anti-polyelectrolyte effects of polyzwitterionic hydrogels, demonstrate a rapid water transport capability in brines. After introducing photothermal polypyrrole particles on the surface of the phase-separated PSBMA hydrogel evaporators, a stable water evaporation rate of ≈2.024 kg m⁻² h⁻¹ and high solar-to-vapor efficiency of ≈97.5% in a 3.5 wt.% brine are obtained under simulated solar light irradiation (1.0 kW m⁻²). Surprisingly, the evaporation rates remain stable even under high-intensity solar irradiation (2.0 kW m⁻²). It is anticipated that the polyzwitterionic hydrogel evaporators with sponge-like porous structures will contribute to developing SSG technology for high-salinity seawater applications.     

Unmodified SBA-15 adsorbents for the removal and separation of Th(IV) and U(VI) ions: the role of pore channels and surface-active sites

ABSTRACT

The removal of Th(IV) and U(VI) by calcinated, non-calcinated, and methyl grafted SBA-15 (abbreviated as SBA-15, SBA-15-NC and SBA-15-MG, correspondingly) were compared to elucidate the role of pores and surface adsorption sites on SBA-15 adsorbents. It was proposed that the contribution of pores and surface-active sites of SBA-15 increases its higher adsorption capacity with respect to the other examined adsorbents. The kinetic studies revealed that the adsorption and also desorption occurred initially on the surface and then to the pores. Adsorption/desorption of the ions into pores was occurred with slow kinetics.     

Effective Medium Theory of the Porosity Dependence of Bulk Moduli

Effective medium theory is used to obtain a closed- form expression for the porosity dependence of the bulk moduli of ceramics. The theory is illustrated with an application to data for high-purity alumina that spans a volume fraction of porosity ranging from 0.5% to 90%.     

Defect Chemistry and Microstructure of Hydrothermal Barium Titanate

Hydrothermal powders of BaTiO₃ and (Ba,Ca)(Ti,Zr)O₃ contain large amounts of protons in the oxygen sublattice. The proton defects are compensated by vacancies on metal sites. When the powder is annealed, water is released and the point defects disappear in the temperature range of 100°–600°C. Metal and oxygen vacancies combine to small nanometer-sized intragranular pores. At temperatures of >800°C, the intragranular pores migrate to the grain boundaries and disappear. In multilayer ceramic capacitors that have been prepared from hydrothermal powders, the intragranular pores are preferentially collected at the inner electrodes, which results in "bloating," cracks, and delamination.