Papers by Keyword: Re-Oxidation

Abstract: The microstructure, especially porosity, of PTC (positive temperature coefficient) thermistor based on BaTiO₃ was controlled with a forming pressure. The relationship between theirPTCR properties and microstructureswas investigated with an optical and SEM (Scanning Electron Microscope) images and digital multimeter. Disk samples were fabricated by pressinguniaxially at various pressures of 100~15000kg/cm² and sintering at 1265°C in reducing atmosphere and finally re-oxidizing at 700°C in air. The porosity of the samples decreased rapidly from 45% to 8% with increasing the forming pressure from 100 to 1000kg/cm²andbecame 4% at 15000kg/cm²with slowdecreasing of porosity in the pressure range of 1000~15000kg/cm².With increasing the forming pressure, the resistivity jump of samplesdecreased rapidlyfrom 0.5 to 2.9 at about1000kg/cm²that corresponds tothe porosity of 15% and was saturated above this pressure. It is considered that there is a critical amount of porosity for having PTCR effect, which was about 15% in our samples. In addition, the porosity of the sample has a greater influence on the resistivity jump than on theresistivity at room temperature, which is due to the oxidation of grain boundary through a favorable channel of oxygen such as a pore.

Abstract: Abstract. One of the everlasting problems existing in alloy steel plant is clogging of Submerged Entry Nozzle(SEN) due to accumulation of De-oxidized/Re-oxidized products while casting Medium Carbon Re-Sulfur Steel grades(forging grades).After complete De-sulphurization and De-oxidation, liquid steel have been subjected to Ca-treatment which promote deep De-oxidation and deep De-sulphurization in addition to inclusion morphology control. Finally liquid steel have been injected with sulfur cored wire for chemistry requirement of 0.02-0.035%. All these conditions encourage thermodynamically favorable conditions for formation of various combination of oxide and sulphide inclusions which are highly detrimental to castability in continuous casting of integrated steel mill. This becomes one of the major process interruptions which directly terminate production capacity day by day and also affects the quality of cast product. As well said before “Best Slag Maker Is Best Steel Maker”, we mainly focused on secondary steel making slag at different stages, and found the relation of castability with respect to slag behavior. We arrived at optimal slag nature for better castability in continuous casting of steel.

Abstract: Electrical properties, positive temperature coefficient of resistivity (PTCR), and microstructures of (Ba_m-0.007Sm_0.007)TiO₃ (BST) with different Ba-site/Ti-site (A/B) ratio sintered in a reducing atmosphere and reoxidized in air are investigated. The results reveal that the room temperature resistivity of the semiconducting BST ceramics first decreases and then increases with increasing of A/B ratio (m), particularly when m is equal to 1.006, the semiconducting BST ceramics which have been sintered in a reducing atmosphere and reoxidized at 800°C exhibit significant PTCR effect with a resistance jumping ratio of 3 orders magnitude, and achieve a lower room temperature resisitivity of 80.8 Ω∙cm, in addition, the grain size distribution of the Ti-excess specimens is much better than that of the Ba-excess ones.

Abstract: Re-oxidation is an important thermal process to minimize oxygen vacancies and produce high reliable Ni-MLCCs. The re-oxidation of these devices is then investigated with a series of “in-situ” impedance measurements between 400 and 500 °C in air. From the relative impedance change, chemical diffusion coefficients, associated activation energy and effective equivalent circuit model are determined. Those values were found to be reasonable compared with previous researchers’ data. Moreover, the proposed effective equivalent circuit model successfully represents the real Ni-MLCC morphology. From transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), it is found that the electrical properties and reliabilities of the Ni-MLCCs re-oxidized under different conditions are identical.

Abstract: Solid Oxide Fuel Cells (SOFCs) with electrical efficiencies above 50 % are considered as very promising option for future decentralized energy conversion. At the Forschungszentrum Juelich (FZJ) planar SOFC stacks are currently being developed and tested at 800°C and up to 10000 h using H2 and methane as fuel. Stacks in the kW class routinely reach power densities of 700 W/cm². Typically the layered material composite of the FZJ-stack consists of cells with yttria stabilized zirconia (YSZ) electrolyte, Ni-YSZ anode and a cathode of lanthanum strontium manganite. The cells are mounted between ferritic steel interconnects. The fuel and air compartment are sealed by glass-ceramics and more recently also by metal brazes. Significant progress in reliable stack operation has been achieved over the past decade. However, problems with thermo-chemical and thermo-mechanical compatibility still remain a major challenge. To illustrate the complexity of material interactions in SOFCs, selected problems related to mechanical failure processes are presented. The role of residual stresses is addressed and fracture phenomena of cell and sealant are described in greater detail.