Showing papers in "Materials Science Forum in 2008"
TL;DR: The improvements in the design of the HPT tools lead to a well defined torsion deformation and permits, therefore, a comparison with other SPD-techniques.
Abstract: The improvements in the design of the HPT tools lead to a well defined torsion deformation and permits, therefore, a comparison with other SPD-techniques. The design of the tools, the advantages and disadvantages of HPT, as well as the limitation in the sample size are discussed.
121 citations
TL;DR: Based on strain-induced grain refinement, a novel surface mechanical attrition treatment (SMAT) technique was developed to synthesize a nanostructured surface layer on metallic materials in order to upgrade their overall properties and performance without changing their chemical compositions as mentioned in this paper.
Abstract: Based on strain-induced grain refinement, a novel surface mechanical attrition treatment (SMAT) technique has been developed to synthesize a nanostructured surface layer on metallic materials in order to upgrade their overall properties and performance without changing their chemical compositions. In recent several years, the microstructures and properties of surface layer were systematically investigated in various SMAT metals and alloys, including b.c.c., f.c.c. and h.c.p. crystal structures. Different grain refinement approaches and nanocrystalline formation mechanisms were identified in these deformed materials, involving dislocation activities, mechanical twinning and interaction of dislocations with mechanical twins. The properties of the surface layer were measured by means of hardness, tensile, fatigue and wear tests. The enhanced properties of the surface layer are mainly attributed to the strain-induced grain refinement. In this work, we reviewed the microstructures and properties of surface layer in the SMAT materials.
77 citations
TL;DR: In this paper, high power 4H-SiC n-IGBTs have been demonstrated with 13 kV blocking and a low Rdiff of 22 mWcm2 which surpasses the 4HSiC material limit for unipolar devices.
Abstract: For the first time, high power 4H-SiC n-IGBTs have been demonstrated with 13 kV blocking and a low Rdiff,on of 22 mWcm2 which surpasses the 4H-SiC material limit for unipolar devices. Normally-off operation and >10 kV blocking is maintained up to 200oC base plate temperature. The on-state resistance has a slight positive temperature coefficient which makes the n-IGBT attractive for parallel configurations. MOS characterization reveals a low net positive fixed charge density in the oxide and a low interface trap density near the conduction band which produces a 3 V threshold and a peak channel mobility of 18 cm2/Vs in the lateral MOSFET test structure. Finally, encouraging device yields of 64% in the on-state and 27% in the blocking indicate that the 4H-SiC n-IGBT may eventually become a viable power device technology.
72 citations
TL;DR: Results from laboratory cytocompatibility tests undertaken so far on mice fibroblast cells have indicated that nanocrystalline Ti surface has a significantly better property for cell colonisation and healing of tissue consequently.
Abstract: Nanostructured titanium (nTi) with essential enhanced strength and fatigue characteristics is an advanced material for dental implant applications. Nano Ti is commercially pure titanium, that was nanostructured by a special technique of severe plastic deformation. It is bio inert, does not contain even potentially toxic or allergenetic additives and has significantly higher specific strength properties than any other titanium applied in dental implants. Cylindrical threaded screw implants Nanoimplant® sized 2.4 mm in diameter and 12 mm in length were made from nTi. It is the first application of nTi dental implant in the world reported. Recently more than 250 successful clinical applications dealing with surgery on the front teeth were carried out. No complications were noticed during the early postoperative period and early loading. Laboratory cytocompatibility tests undertaken so far on mice fibroblast cells have indicated that nanocrystalline Ti surface has a significantly better property for cell colonisation and healing of tissue consequently.
70 citations
TL;DR: The Ni-Mn-Ga shape memory alloy displays the largest shape change of all known magnetic Heusler alloys with a strain of the order of 10% in an external magnetic field of less than one Tesla as discussed by the authors.
Abstract: The Ni-Mn-Ga shape memory alloy displays the largest shape change of all known magnetic Heusler alloys with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a 1. Typically, in the Ni-based alloys, the martensitic transformation is accompanied by a systematic change of the electronic structure in the vicinity of the Fermi energy, where a peak in the electronic density of states from the non-bonding Ni states is shifted from the occupied region to the unoccupied energy range, which is associated with a reconstruction of the Fermi surface, and, in most cases, by pronounced phonon anomalies. The latter appear in high-temperature cubic austenite, premartensite but also in the modulated phases. In addition, the modulated phases have highly mobile twin boundaries which can be rearranged by an external magnetic field due to the high magnetic anisotropy, which builds up in the martensitic phases and which is the origin of the magnetic shape memory effect. This overall scenario is confirmed by first-principles calculations.
68 citations
TL;DR: In this article, the magnetic shape memory alloys Ni2Mn1+xSn1-x and 0.4≤x≾0.6 have been studied and shown to undergo a martensitic transition from the high temperature L21 structure to the orthorhombic 4O one.
Abstract: X-ray powder diffraction and magnetization measurements were done on the magnetic shape memory alloys Ni2Mn1+xSn1-x. The alloys with 0≤x≾0.4 crystallize in the cubic L21 structure and exhibit the ferromagnetic behavior. X-ray diffraction patterns indicate that the excess Mn atoms occupy the Sn sites. Furthermore, magnetization measurements make clear that the Mn atoms, which substitute for Sn sites, are coupled antiferromagnetically to the ferromagnetic manganese sublattices. The alloys with 0.4≾x≤0.6 undergo a martensitic transition from the high temperature L21 structure to the orthorhombic 4O one. These alloys show a variety of magnetic transitions. A magnetic phase diagram of Ni2Mn1+xSn1-x system is discussed qualitatively on the basis of the interatomic dependence of the exchange interactions.
55 citations
TL;DR: In this article, a magnetostrictive mechanism of the unusual magnetic and magnetomechanical effects observed in Ni-Mn-Ga alloys is substantiated and a framework of consistent theory of these effects is outlined starting from the fundamental conception of magnetoelasticity and the commonly known principles of ferromagnetism and linear elasticity theories.
Abstract: The giant magnetically-induced deformation of ferromagnetic shape memory alloys results from the magnetic field-induced rearrangement of twinned martensite under the magnetic field. This deformation is conventionally referred to as the magnetic-field-induced-strain (MFIS). The MFIS is comparable in value with the spontaneous deformation of crystal lattice during the martensitic transformation of an alloy. Although the first observations of MFIS were reported more than 30 years ago, it has got a world-wide interest 20 years later after the creation of the Ni-Mn-Ga alloy system with its practically important room-temperature martensitic structure and experimental evidence of the large magnetostriction. The underlying physics as well as necessary and sufficient conditions for the observation of MFIS are the main focus of this chapter. A magnetostrictive mechanism of the unusual magnetic and magnetomechanical effects observed in Ni-Mn-Ga alloys is substantiated and a framework of consistent theory of these effects is outlined starting from the fundamental conception of magnetoelasticity and the commonly known principles of ferromagnetism and linear elasticity theories. A reasonable agreement between the theoretical deductions and available experimental data is demonstrated and, in this way, a key role of magnetoelastic coupling in the magnetomechanical behavior of Ni-Mn-Ga alloys is proved. A correspondence of magnetostrictive mechanism to the crystallographic features of MFIS and the basic relationships of the thermodynamics of solids are discussed.
52 citations
TL;DR: In this paper, a new technique of continuous severe plastic deformation (SPD)-processing, i.e., ECAP (equal channel angular pressing)-Conform, is applied for the first time to produce long-length rods of commercial purity Ti with ultrafine-grained structure.
Abstract: A new technique of continuous severe plastic deformation (SPD)-processing, i.e. ECAP (equal channel angular pressing)-Conform is applied for the first time to produce long-length rods of commercial purity Ti with ultrafine-grained structure. The paper reports on the results of investigation of the microstructure and mechanical properties of Ti rods processed by ECAPConform and the following wire drawing.
52 citations
TL;DR: In this paper, combined techniques of KOH etching and cross-polarizer inspections were used to confirm the absence of micropipes in 4HN-SiC wafers.
Abstract: Recent advances in PVT c-axis growth process have shown a path for eliminating micropipes in 4HN-SiC, leading to the demonstration of zero micropipe density 100 mm 4HN-SiC wafers. Combined techniques of KOH etching and cross-polarizer inspections were used to confirm the absence of micropipes. Crystal growth studies for 3-inch material with similar processes have demonstrated a 1c screw dislocation median density of 175 cm-2, compared to typical densities of 2x103 to 4x103 cm-2 in current production wafers. These values were obtained through optical scanning analyzer methods and verified by x-ray topography.
49 citations
TL;DR: In this article, the authors observed variations in the instability in the threshold voltage, VT, of SiC metaloxide semiconductor field effect transistors (MOSFETs) from various sources and/or processes due to gate bias stressing as a function of temperature.
Abstract: We have observed variations in the instability in the threshold voltage, VT, of SiC metaloxide semiconductor field-effect transistors (MOSFETs) from various sources and/or processes due to gate-bias stressing as a function of temperature. In some cases we see a dramatic increase in the instability with increasing temperature, consistent with interfacial charge trapping or de-trapping. In other cases the temperature response is very slight, and in still other cases we actually see VT instabilities that move in the opposite direction with bias, indicating the presence of mobile ions.
46 citations
TL;DR: In this paper, the DC characteristics and reverse recovery performance of 4H-SiC junction barrier Schottky (JBS) diodes capable of blocking in excess of 10 kV with forward conduction of 20 A at a forward voltage of less than 4 V are described.
Abstract: DC characteristics and reverse recovery performance of 4H-SiC Junction Barrier Schottky (JBS) diodes capable of blocking in excess of 10 kV with forward conduction of 20 A at a forward voltage of less than 4 V are described. Performance comparisons are made to a similarly rated 10 kV 4H-SiC PiN diode. The JBS diodes show a significant improvement in reverse recovery stored charge as compared to PiN diodes, showing half of the stored charge at 25°C and a quarter of the stored charge at 125°C when switched to 3 kV blocking. These large area JBS diodes were also employed to demonstrate the tremendous advances that have recently been made in 4H-SiC substrate quality.
TL;DR: In this paper, the influence of KCl, K2CO3 and K2SO4 on the initial stages of corrosion of 304-type (Fe18Cr10Ni) stainless steel was investigated at 600°C in 5% O2 + 40% H2O.
Abstract: The influence of KCl, K2CO3 and K2SO4 on the initial stages of corrosion of 304-type (Fe18Cr10Ni) stainless steel was investigated at 600°C in 5% O2 + 40% H2O. Small amounts of salt (1.35 .mol K+/cm2) were added before exposure. The exposures were carried out in a thermobalance. Exposure time was 24 hours. Reference exposures were carried out in 5% O2 and in 5% O2 + 40% H2O. The oxidized samples were analyzed by SEM/EDX, XRD and IC. KCl and K2CO3 are very corrosive towards 304L, producing thick non-protective scales. Corrosion is initiated by the reaction of the potassium salts with the protective, chromium-rich oxide forming K2CrO4. This depletes the oxide in chromia and converts it into iron-rich non-protective oxide. In contrast, K2SO4 does not accelerate corrosion significantly.
TL;DR: The twinning disconnection is a line defect similar to dislocation but located at an interface and exhibiting a step character besides a dislocation character as mentioned in this paper, and it is the elementary carrier of magnetic-field-induced deformation.
Abstract: Magnetic shape-memory alloys owe their exceptional properties primarily to the accompanying effects of a martensitic phase transformation. The twinning disconnection as elementary carrier of magnetic-field-induced deformation is the starting point of the present study. A disconnection is a line defect similar to a dislocation but located at an interface and exhibiting a step character besides a dislocation character. The mutual interaction of disconnections is fully tractable by the theory of dislocations. Due to the martensitic transformation, a hierarchical twin microstructure evolves, details of which are controlled through disconnection-disconnection interaction. Depending on the mutual orientation of twin boundaries on different hierarchical levels, twinning disconnections are incorporated in higher hierarchical twin boundaries forming disclination walls, or they stand off individually from those interfaces. Disconnections which stand off from interfaces contribute to magnetoelasticity, i.e. recoverable magnetic-field-induced deformation. Disconnections in disclination walls contribute to magnetoplasticity, i.e. permanent magnetic-field-induced deformation, if the twin thickness is large. In self-accommodated martensite with very thin twins, resulting from a martensitic transformation without training, the deformation is fully magnetoelastic and small. In single-domain crystals, resulting from effective thermo-magnetomechanical training, the deformation is fully magnetoplastic and large. Between these limiting cases, there is a continuous spectrum where, as a rule, the fraction of magnetoplastic strain and the total strain increase with increasing effectiveness of training.
TL;DR: The use of technologically byproduct agricultural wastes in various segments of the brick and tile industry is increasing continuously as mentioned in this paper, adding extra thermal energy from inside the mixture decreasing the energy requirements of the manufacturing process.
Abstract: The use of technologically byproduct agricultural wastes in various segments of the brick and tile industry is increasing continuously. The additives, mixed into the raw clay ignite during the firing process, adding extra thermal energy from inside the mixture decreasing the energy requirements of the manufacturing process. Added to this, through the combustion of the bio-wastes the porosity increases enhancing the thermal insulation properties of the final product. We have investigated some common, agricultural wastes to determine their effect on the thermal properties of bricks. In our experiments industry relevant amounts of additives (sawdust, rice-peel, seed-shell) were added to the basic clay composition. We have prepared mixtures with additive concentrations of 0, 4, 7 percentage by weight. The preparations of the samples were (milling, drying and firing) following industrial standard procedures. Precise thermal conductivity data were gathered from all samples using a RAPID-K type static thermal conductivity measuring instrument. Our measurements show that by increasing the amount of the organic byproducts in the clay mixture it is possible to significantly decrease their thermal conductivity, leading to an improved insulation capability of commercial brick products. On the other hand, there was only a minor reduction in the mechanical strength found during previous works. The investigated agricultural byproducts were also ranked based on their effect on the product's thermal properties. It was found that the largest decrease to the thermal conductivity was caused by the sunflower seed-shell additive. Mixing 7 % wt. seed shell to the clay, we can decrease the thermal conductivity of the fired product from 0,27 W/m·K to 0,17 W/m·K (36%). We have found that under the same conditions the sawdust caused the least improvement, only a decrease of 0,27 W/m·K to 0,23 W/m·K (16%) was measured.
TL;DR: In this article, the formation and volatilisation of Cr2O2(OH)2 is shown to account quantitatively for chromium loss from thin alloy foils reacted with air-steam mixtures over periods of 103 h.
Abstract: Water vapour interacts with growing chromia scales in several different ways. Formation and volatilisation of Cr2O2(OH)2 is shown to account quantitatively for chromium loss from thin alloy foils reacted with air-steam mixtures over periods of 103 h. In the shorter term, water vapour is shown to refine the grain structure of Cr2O3 scales grown on Ni-25Cr. Scaling kinetics are at the same time accelerated by an additional, larger contribution to diffusion by a grain boundary species, either OH- or H2O. A slight increase in scaling rate observed at low water vapour partial pressures in H2/H2O gases is thought to be due to hydrogen doping.
TL;DR: In this paper, the development of knowledge of microstructure-property relationships in silicon nitride materials is outlined, particularly recent advances in understanding the effects of grain boundary chemistry and structure on mechanical properties.
Abstract: Silicon nitride is one of the major structural ceramics that has been developed following many years of intensive research. It possesses high flexural strength, high fracture resistance, good creep resistance, high hardness and excellent wear resistance. These properties arise from the processing of the ceramic by liquid phase sintering and the development of microstructures in which high aspect ratio grains and intergranular glass phase lead to excellent fracture toughness and high strength. The glass phase softens at high temperature and controls the creep rate of the ceramic. The purpose of this review is to examine the development of silicon nitride and the related sialons and their processing into a range of high-grade structural ceramic materials. The development of knowledge of microstructure–property relationships in silicon nitride materials is outlined, particularly recent advances in understanding the effects of grain boundary chemistry and structure on mechanical properties. This review should be of interest to scientists and engineers concerned with the processing and use of ceramics for structural engineering applications.
TL;DR: In this paper, the microstructural properties of a precipitation hardenable Al 7075 alloy subjected to rolling at liquid nitrogen temperature and room temperature were studied by using tensile tests and hardness.
Abstract: The mechanical properties and microstructural characteristics of a precipitation hardenable Al 7075 alloy subjected to rolling at liquid nitrogen temperature and room temperature are reported in this present work. The Al 7075 alloy was severely rolled at cryogenic temperature and room temperature and its mechanical properties were studied by using tensile tests and hardness. The microstructural characterization of Al 7075 alloy were made using SEM/EBSD, TEM and DSC. The cryorolled Al 7075 alloys have shown improved mechanical properties as compared to the room temperature rolled Al alloy. The cryorolled Al alloy after 90% thickness reduction exhibits ultrafine grain structure as observed from its TEM micrographs. It is observed that the strength and hardness of the cryorolled materials (CR) at different percentage of thickness reductions are higher as compared to the room temperature rolled (RTR) materials at the same strain due to suppression of dynamic recovery and accumulation of higher dislocations density in the CR materials.
TL;DR: In this article, the DC characteristics of 4H-SiC p-channel IGBTs capable of blocking -12 kV and conducting -0.2 V at 25°C are demonstrated for the first time.
Abstract: DC characteristics of 4H-SiC p-channel IGBTs capable of blocking -12 kV and conducting -0.4 A (-100 A/cm2) at a forward voltage of -5.2 V at 25°C are demonstrated for the first time. A record low differential on-resistance of 14 mW×cm2 was achieved with a gate bias of -20 V indicating a strong conductivity modulation in the p-type drift region. A moderately doped current enhancement layer grown on the lightly doped drift layer effectively reduces the JFET resistance while maintains a high carrier lifetime for conductivity modulation. A hole MOS channel mobility of 12.5 cm2/V-s at -20 V of gate bias was measured with a MOS threshold voltage of -5.8 V. The blocking voltage of -12 kV was achieved by Junction Termination Extension (JTE).
TL;DR: In this paper, the melting temperature of any nanoparticle basically depends on the ratio of surface atoms to the total atoms, and significant melting temperature suppression is observed when the particle size approaches the sub-20 nm range.
Abstract: The present paper reports a simple calculation of the size and shape dependent melting temperature of nanoparticles. The melting temperature of any nanoparticle basically depends on the ratio of surface atoms to the total atoms. Significant melting temperature suppression is observed when the particle size approaches the sub-20 nm range. The behavior of melting temperature is similar for the larger nanoparticles of all considered shapes but differs significantly for small nanoparticles. Different melting temperature is predicted for the nanoparticles of the same size in different shapes.
TL;DR: In this paper, X-ray microbeam diffraction experiments performed by the authors using synchrotron xray microbeams determined the elastic strains within the cell interiors.
Abstract: Backstresses or long range internal stresses (LRIS) in the past have been suggested by many to exist in plastically deformed crystalline materials. Elevated stresses can be present in regions of elevated dislocation density or dislocation heterogeneities in the deformed microstructures. The heterogeneities include edge dislocation dipole bundles (veins) and the edge dipole walls of persistent slip bands (PSBs) in cyclically deformed materials and cell and subgrain walls in monotonically deformed materials. The existence of long range internal stress is especially important for the understanding of cyclic deformation and also monotonic deformation. X-ray microbeam diffraction experiments performed by the authors using synchrotron x-ray microbeams determined the elastic strains within the cell interiors. The studies were performed using, oriented, monotonically deformed Cu single crystals. The results demonstrate that small long-range internal stresses are present in cell interiors. These LRIS vary substantially from cell to cell as 0 % to 50 % of the applied stress. The results are related to the Bauschinger effect, often explained in terms of LRIS.
TL;DR: In this paper, a review of methods of hydrophobic wafer bonding is presented, showing that removing the oxide layer from the surfaces of crystalline silicon substrates causes the formation of a dislocation network in the interface.
Abstract: The paper reviews methods of hydrophobic wafer bonding. Hydrophobic surfaces are obtained by removing the oxide layer from the surfaces of crystalline silicon substrates. Bonding such surfaces causes the formation of a dislocation network in the interface. The structure of the dislocation network depends only on the misalignment (twist and tilt components). The different dislocation structures are discussed. Because wafer bonding offers a method to the reproducible formation of such networks, different applications are possible
TL;DR: In this article, the development of thermal barrier coatings (TBCs) over the past 30 years is briefly reviewed, together with a summary of the current understanding of failure mechanisms; highlighting the challenges and prospects in TBCs research.
Abstract: Thermal barrier coatings (TBCs), which comprise metallic and ceramic multilayers, have been widely used in the hot section of aeroturbine engines to increase turbine efficiency and to extend the life of metallic components. An improvement in TBCs requires a better understanding of the complex changes in their structure and properties that occur under harsh operating conditions that eventually lead to their failure. In this paper, the developments of TBCs over the past 30 years are briefly reviewed. A description of materials issues involved in the state-of-art and next generation TBCs systems is presented, together with a summary of the current understanding of failure mechanisms; highlighting the challenges and prospects in TBCs research.
TL;DR: In this article, a mechanism based on hydrogen embrittlement and a cathodic hydrogen charging experiment was proposed to prevent spontaneous interfacial decohesion in bulk alumina and bulk aluminides.
Abstract: Alumina scale adhesion to high temperature alloys is known to be affected primarily by sulfur segregation and reactive element additions. However, adherent scales can become partially compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to moisture can lead to spontaneous interfacial decohesion, occurring while the samples are maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS) are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are reviewed for thermal barrier coatings (TBCs), culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylation of aluminum from the alloy interface appears to be the relevant basic reaction.
TL;DR: In this paper, the feasibility of using I-ECAP for nanostructuring of plates rather than bars was investigated and a 3D finite element simulation has been performed which shows the importance of restricting material flow in the direction of plate width.
Abstract: Batch severe plastic deformation (SPD) processes are mainly used for laboratory purposes. More industrially oriented are continuous processes among which the new SPD process of Incremental Equal Channel Angular Pressing (I-ECAP) is an attractive option. This paper investigates the feasibility of using I-ECAP for nanostructuring of plates rather than bars. First, a 3D finite element simulation has been performed which shows the importance of restricting material flow in the direction of plate width. A laboratory rig has been designed, which converts the vertical movement of the machine crosshead into an oblique movement of the reciprocating punch. Preliminary trials of I-ECAP have been carried out on a 4x30x100mm Al 1070 plate. Metallurgical samples after 4 and 8 passes of I-ECAP (route A) have been investigated using TEM. In conclusion, the new SPD process of I-ECAP is capable of processing plates, which opens up new possibilities of nanostructuring metals on an industrial scale.
TL;DR: In this article, electric discharge machining (EDM) was used for silicon carbide (SiC) single crystal cutting and the EDM realized not only high speed and smooth cutting but also lower surface damage.
Abstract: In this study, we report electric discharge machining (EDM) as a new cutting method for silicon carbide (SiC) single crystals. Moreover, we discuss characteristics and usefulness of the EDM for the SiC. The EDM realized not only high speed and smooth cutting but also lower surface damage. Defect propagation in the EDM SiCs have been also estimated by etch pits observation using molten KOH, however, we confirmed the EDM has caused no damage inside the SiCs in spite of high voltage and high temperature during the machining.
TL;DR: In this paper, the microstructure of slurry aluminide coatings was studied by scanning and transmission electron microscopy and X ray diffraction, showing that after several thousands hours of exposure to steam, the coating was mostly composed of α-Al2O3.
Abstract: Slurry iron aluminide coatings are very resistant to steam oxidation at 600-650o C. These coatings can be used to protect new generation Ultra Super Critical (USC) steam power plant ferritic/martensitic steel components. The microstructure of the initially deposited coating changes as a function of time, mainly due to coating-substrate interdiffusion, going from mostly Fe2Al5 to FeAl, causing the precipitation of AlN in those substrates containing a minimum content of N and moreover, developing Kirkendall porosity at the coating-substrate interface. Steam oxidation at 650o C causes the formation of a protective thin layer of hexagonal χ-Al2O3 phase along with some α- and γ-Al2O3 after the first few hours of exposure. However, despite the relatively low temperature, and after several thousands hours the protective layer was mostly composed of α-Al2O3. A study of the evolution of the microstructure of slurry aluminide coatings deposited on P92 and exposed to steam at 650o C has been carried out by scanning and transmission electron microscopy and X ray diffraction.
TL;DR: Corrosion field tests have been carried out in the superheater region of a commercial waste-fired 75MW CFBC boiler using air cooled probes Exposure time was 24 and 1000 hours The effect of adding sulphur to the fuel on the corrosion of two high alloyed steels and a low alloyed steel was studied as discussed by the authors.
Abstract: Corrosion field tests have been carried out in the superheater region of a commercial waste-fired 75MW CFBC boiler using air cooled probes Exposure time was 24 and 1000 hours The effect of adding sulphur to the fuel on the corrosion of two high alloyed steels and a low alloyed steel was studied The fuel consisted of 50% household waste and 50% industrial waste The exposed samples were analyzed by ESEM/EDX and XRD Metal loss was determined after 1000 hours Both materials suffered significant corrosion in the absence of sulphur addition and the addition of sulphur to the fuel reduced corrosion significantly The rapid corrosion of the high alloyed steel in the absence of sulphur addition is caused by the destruction of the chromium-containing protective oxide by formation of calcium chromate Adding sulphur to the fuel inhibited chromate formation and increased the sulphate/chloride ratio in the deposit Iron(II) chloride formed on the low alloyed steel regardless of whether sulphur was added or not
TL;DR: In this article, a mechanistic model that interprets the transition in oxidation behavior of zirconium diboride as the temperature is varied from 600°C to 2500°C is presented.
Abstract: A mechanistic model that interprets the transition in oxidation behavior of zirconium diboride as the temperature is varied from 600°C to 2500°C is presented. Available thermodynamic data and literature data for vapor pressures, oxygen permeability in boria, and viscosity of boria were used to evaluate the model. Three regimes and the temperatures of transition between them were identified. In the intermediate temperature regime, viz., 1000°C to 1800°C, good correspondence was obtained between theory and experiments for weight gain, recession, and scale thickness as functions of temperature and oxygen partial pressure. In this regime, the rate-limiting step is the diffusion of dissolved oxygen through a film of liquid boria in capillaries at the base of the oxidation product. At lower temperatures, an external boria scale forms, but it was not found to contribute significantly to oxidation resistance. Comparison with literature data on recession is very good, but weight gain is predicted to be higher than experimentally observed unless flow of viscous boria is included. At higher temperatures, the boria is lost by evaporation, and the oxidation rate is limited by diffusion of molecular oxygen through the capillaries between nearly columnar blocks of the oxide MO2.; this regime is soon followed by a rapid acceleration of recession due to vaporization of the oxide MO2 itself.
TL;DR: In this article, the origin of giant step bunching on 4˚ off-axis 4H-SiC (0001) faces was investigated and it was shown that it occurs during hydrogen etching and epitaxial growth at extremely low or high C/Si ratios with an excessive supply of SiH4 or C3H8.
Abstract: To elucidate the origin of giant step bunching on 4˚ off-axis 4H-SiC (0001) faces, we carried out hydrogen etching and epitaxial growth under various conditions. We found that giant step bunching occurs during hydrogen etching and epitaxial growth at extremely low or high C/Si ratios, i.e., with an excessive supply of SiH4 or C3H8. From these results, we have proposed that the origins of giant step bunching are asymmetry in the step kinetics in etching and Si or C cluster generation on terraces during growth.
TL;DR: In this paper, the authors present a brief review of today knowledge about electronic properties of dislocations in silicon and dislocation-related luminescence in connection with possible application of this luminecence for silicon infrared light-emitting diodes (Si-LEDs).
Abstract: There is a growing demand for a silicon-based light emitters generating a light with a wavelength in of 1.3-1.6 μm range, which can be integrated into silicon chips and used for in-chip opto-electronic interconnects. Among other possibilities, the D1 luminescence at about 1.55 m, caused by dislocations in Si, can be a suitable candidate for such in-chip light emitters. Here we present a brief review of today knowledge about electronic properties of dislocations in silicon and dislocation-related luminescence in connection with possible application of this luminescence for silicon infrared light-emitting diodes (Si-LEDs).