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Oxidation behavior of additively manufactured ZrB2–SiC in air and in CO2 is reported in the temperature range of 700–1000 °C. Observed scale morphologies in air and in CO2 were similar, featuring an outer borosilicate layer and an inner porous zirconia layer containing partially oxidized silicon carbide particles and remnant borosilicate products. Oxide scale thicknesses and parabolic scaling constants in air were approximately twice those observed in CO2 across all studied temperatures. Activation energies for oxidation of 140 ± 20 kJ/mol in air and 110 ± 20 kJ/mol in CO2 were determined, indicating similar diffusion processes that appear to be rate-limiting. The formation of protective scales across wide temperature ranges both in air and in CO2 makes additively manufactured ZrB2–SiC an attractive candidate for high-temperature industrial process applications featuring varied oxidants such as heat exchangers. [ABSTRACT FROM AUTHOR]

Zircon (ZrSiO4) ceramics have been widely used in many fields due to their excellent physical and chemical properties. However, ZrSiO4 ceramics typically possess moderately low mechanical properties, which hinders their wider application. Meanwhile, elevated temperatures (∼1500°C) are required to obtain high‐purity synthetic ZrSiO4 ceramics, which is time‐ and energy‐consuming. In the present study, we prepared mechanically robust ZrSiO4 ceramics at low temperature (∼1170°C) with a low doping level of Mn dopant (<2 mol%). The ZrSiO4 ceramic processed by hot isostatic pressing with.5 mol% Mn dopant achieved the highest flexural strength (512 MPa), elastic modulus (341 GPa), and nanohardness (20.8 GPa). These values are significantly higher than conventional ZrSiO4 ceramics. The strengthening mechanisms of the prepared ZrSiO4 ceramics were attributed to the formation of homogeneously‐distributed nanopores due to incomplete densification and submicron ZrSiO4 grains (∼300 nm). The nanopores avoided stress concentration and deflected microcracks during loading, and the submicron ZrSiO4 grains endowed the ZrSiO4 ceramics with grain refinement strengthening. The results reported in this study would offer guidance to fabricate mechanically robust ZrSiO4 ceramics at low temperatures with a low doping level of dopant. [ABSTRACT FROM AUTHOR]

The present work studied the effect of the addition of SiC microfibers and their influence on interfacial adherence of NiCoCrAlY-7YSZ thermal barrier coatings (TBCs) systems. Two different coatings were fabricated (with and without the addition of SiC microfibers) and exposed to isothermal oxidation heat treatments (OHT) at 950 °C from 50 to 200 h. The microstructure and pull-off test evaluations showed that coatings reinforced with SiC possess a thinner thermally grown oxide (TGO) layer, suggesting an improvement in the oxidation resistance of these samples. In this sense, the coating with SiC also displayed better adherence resistance after 50 and 200 h of exposure. On the other hand, after the pull-off tests, reinforced samples showed a lower percentage of fracture. The above indicates that SiC microfibers enhance the interfacial adherence between the TGO and the ceramic layer (TC) by forming complex oxides resulting from the self-healing reaction mechanism. [ABSTRACT FROM AUTHOR]

The ZrSiO4 has been synthesized with CuO as mineralizer by sol–gel route at low temperature. The mineralization effect of the CuO on mechanism of zircon formation at low temperature has been studied by high-temperature X-ray diffraction method, differential thermal analysis, scanning electron microscopy, and Raman spectroscopy. The temperature of ZrSiO4 formation depends on concentration of CuO and occurs in the range 800–900 °C. The results reveal that the CuO addition accelerates the diffusion processes between the particles of zirconium and silicon oxides by reducing the energy barrier of the chemical reaction and has a significant effect on the crystallization processes taking place in the ZrO2–SiO2 system. A significant decrease in the temperature of formation of the ZrSiO4 phase was shown to associate with the interaction of CuO particles and amorphous phase of ZrO2 with the formation of tetragonal solid solutions Zr1–xCuxO2–δ. The possibility of the formation of solid solutions in the ZrSiO4–CuO system has been discussed and proved. A synthesis technology developed for the production of zircon at low temperatures using an efficient and environmentally friendly mineralizer CuO by the sol–gel method can be applied in various promising applications. [ABSTRACT FROM AUTHOR]

A vertical p-type 3D silicon nanotube field effect transistor (p-type Si-NTFET) is designed and simulated by using the tool Sentaurus Technology computer-aided design (TCAD). To improve the performance with reduced short channel effects, Si-NTFET device is created with inner and outer gate structures. The performance of the proposed device is analysed in terms of outer gate length. The vertical 3D p-type Si-NTFET gives an on state current (ION) of −2.084 × 10−3 A/µm, off state current of (IOFF) of −2.457 × 10−12A/µm and subthreshold swing of the p-type Si-NTFET device is 53 mV/dec at VDS of −0.3 V. The obtained ION/IOFF ratio of the device is 109. The capacitances (CGD, CGG) and the transconductance (gm) and cutoff frequency (ft) of the device are also analysed. The simulated p-type Si-NTFET device has proved that the device is suitable for low-power applications. [ABSTRACT FROM AUTHOR]

Accident‐tolerant fuels (ATFs) are proposed to provide improved safety response to a loss of coolant accident (LOCA) scenario while maintaining good operational characteristics under normal conditions. In this work, Zr─Me─C (Me═Si or Y) was proposed as candidate coatings for ATF applications. The influence of Si and Y with varied concentration on microstructural evolution, mechanical property, and oxidation resistance of Zr─Me─C coatings were investigated. Based on combined results of X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy, it was found that Si or Y doped ZrC0.55 coatings presented tunable composition and microstructure. Improved air oxidation and spallation resistance were achieved with the incorporation of Me atoms, attributing to the formation of SiO2 and ZrSiO4 and/or the stabilization of zirconia. Under a simulated LOCA condition, decreased weight gains of 13.6 at.% Si and 22.5 at.% Y coated Zry‐4 alloys were achieved. nc‐ZrSiC/nc‐ZrSi (13.6 at.% Si) coating exhibited enhanced mechanical property and oxidation resistance in both high‐temperature air and LOCA conditions, which could be regarded as potential candidate for the applications in ATFs. [ABSTRACT FROM AUTHOR]

Zircon has been widely applied in various traditional and emerging fields due to its distinct physiochemical advantages while monodisperse spherical zircon (MSZ) powders hitherto have not been explored for the tremendous challenges in the control of zircon crystallization and growth. Herein, systematic investigations are presented to reveal the paramount role of halide mineralizers upon the crystallization and growth of MSZ powders synthesized under highly acidic hydrothermal environments (pH <0). A formation mechanism is revealed revolving around the complexation of central Zr4+ with the Lewis basic ligand, fluorine, which forms the F‐containing species of [(OH)1–y·Ry] (R = F, Cl) to replace Zr and generates Zr‐deficient zircons as (ZrO4)1‐xSi[(OH)1‐y·Ry]4x. This finding differs much from conventional views on common fluoro‐hydroxylated hydrothermal zircons, which were generally regarded as Si‐deficient silicates from the substitution of fluoro‐hydroxyls for the [SiO4] tetrahedra. A parameter, Kr=4xy, is first proposed as an index to evaluate the stability of hydrothermal zircons. The MSZ powders demonstrate superb thermal stability at high temperature, superior photo‐reflectance, and thermal insulation over normal zircons, promising attractive prospects to extend zircon applications. [ABSTRACT FROM AUTHOR]

The oxidation and its effect on room-temperature flexural strength were investigated in the hot-pressed ZrB2-SiC composites with 3−7 wt% VC additives exposed to air within the temperature range of 1100−1300ºC, for up to 100 h. The parabolic weight gain versus oxidation time was measured for the period of 10−100 h. The apparent oxidation activation energy was determined to be 70−180 kJ/mol, dependent on the amount of VC. The oxidation products consisted of m-ZrO2, V2O5, and ZrSiO4 at 1100ºC, m-ZrO2, SiO2 (α- or β-cristobalite), ZrV2O7, and ZrSiO4 at 1200ºC and 1300ºC. Moreover, the room-temperature flexural strength of the postoxidized composites varied depending on the amount of VC as well as on oxidation temperature. The change in the strength of the postoxidized composites was associated with the formation of either outermost dense glassy scale or new defects in the oxide layer during the oxidation exposure. [ABSTRACT FROM AUTHOR]

Hafnium silicate (HfSiO4; hafnon) is under consideration as an environmental barrier coating material for high‐temperature applications. However, its rate of formation from mixtures of monoclinic HfO2 and crystalline (β‐cristobalite) SiO2 powders is unknown. Here it has been synthesized and its formation rate measured during their solid‐state reaction at temperatures from 1250°C to 1400°C. Rietveld refinement of X‐ray diffraction patterns indicates that at 1250°C the hafnon phase fraction increases linearly with time, while at the highest reaction temperature, the hafnon phase fraction exhibited a parabolic dependence upon time. Between these two limiting temperatures, a region of linear behavior preceded a transition to parabolic kinetics, with the transition occurring at an earlier time as the reaction temperature increased. Arrhenius relations fitted the kinetics of hafnium silicate formation in both the linear and parabolic regimes. Scanning electron microscopy indicated that the reaction proceeded by diffusion of SiO2 into HfO2, similar to the mechanism by which zirconium silicate has been formed from vitreous SiO2 and tetragonal ZrO2. The initial linear rate of reaction is consistent with the growth of the contact area between the SiO2 and HfO2 particles combined with rapid permeation of the Si4+ and O2− through the initial, incompletely formed hafnon. After a thin hafnon layer had formed between the reactants, the rate of hafnium silicate growth slowed and further growth was governed by the rate of diffusion of Si4+ and O2− through the reaction product consistent with the observed parabolic dependence of the phase fraction upon time. [ABSTRACT FROM AUTHOR]

The C@ZrSiO4 pigments offer a viable alternative to spinel black pigments, but they have poor tinting strength due to low encapsulation rate. The aggregate and irregular morphology limits their application. Herein, as a three‐in‐one solution for the above issues, we report a highly dispersed submicronic inclusion black pigment with deep dark hue by double‐shell reaction sintering method for the first time. The morphological advantage of spherical CSs (carbon spheres) @ZrSiO4 pigments has successfully stimulated a significant increase in chromatic performance with L* value of 13.58. In addition, the suspension stability of the pigments in solution was verified, and the effect of the order of double shell on the encapsulation efficiency was studied. [ABSTRACT FROM AUTHOR]

The effect of thermal cycling exposure on room temperature flexural strength was examined in hot‐pressed ZrB2–SiC composite undergone cyclic heating‐cooling test at 1200 and 1400°C in air for up to 1000 or 500 cycles. For the post‐tested samples at 1200°C, the flexural strength of the composite initially increased and subsequently degraded with increase of number of thermal cycles (N). The strength retention displayed by the composite after N = 1000 cycles was approximately 80%. For the post‐tested samples at 1400°C, however, the flexural strength decreased with increase of N. After N = 500 cycles, the strength retention was approximately 45%. The strength decrease was associated with the formation and coarsening of defects in the oxidized reactive layer and the delamination of the outermost thinner dense oxide layer. [ABSTRACT FROM AUTHOR]

Layered zircon and hafnon are observed at the surface of gels resulting from the complete alteration of Zr‐ or Hf‐bearing borosilicate glasses at 90°C and pH 1. The unusually low temperature of formation may arise from the similarity of the local structure around Zr in the gel (from the altered glasses), the leaching solution and the zircon structure, in particular, the majority eight‐coordination of Zr and the connectivity of Zr‐sites with their surroundings. Similar behavior is expected for Hf, which mimics Zr speciation in solution and hafnon structure. This work expands the known formation methods of zircon and hafnon at low temperature, underlining the importance of amorphous precursors to facilitate crystal growth under unusual conditions. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured C/SiC/ZrB2–SiC oxidation protective gradient coating was prepared by a two‐step reactive melt infiltration method. In order to reduce production cost, ZrB2 phase was synthesized by the in situ reactive that included low‐cost ZrO2 and B2O3 powders as raw materials. High‐temperature oxidation behavior of coatings was evaluated by isothermal oxidation test at 1773 K in air for 10 hours. Thermodynamical behavior of the coatings at various temperatures during oxidation test and coating process was predicted by HSC Chemistry 6.0 software. Compressive residual stresses of 36.9 MPa and 41 MPa were calculated for in situ and ex situ coatings by Williamson‐Hall method. After 10 hours of isothermal oxidation at 1773K, in situ and ex situ coatings showed 12.84% and 15.69% of weight losses with oxidation rates of 1.87 × 10−2 g cm−3 h−1 and 0.91 × 10−2 g cm−3 h−1, respectively. These results indicated that the oxidation protection ability of the coating produced by the in situ method was very close to ex situ coating. [ABSTRACT FROM AUTHOR]

This paper proposes a gate-all-around silicon nanowire dopingless field-effect transistor (FET), utilizing a gate-stacked technique. The source and drain regions are formed by employing a charge plasma concept, with the application of appropriate work functions for metal contacts. The charge plasma approach reduces the need for doping control during fabrication, and thus reduces the thermal budget, while the gate-stacked structure solves the problem of scaling limitations with respect to the SiO2 dielectric thickness (< 2 nm). The simulation results show that the proposed device, when compared with a conventional junctionless nanowire FET (JL-NWFET), possesses enhanced performance parameters, with improved immunity to short-channel effects. The random dopant fluctuations (RDFs) of the proposed device are analyzed and compared with those of a conventional JL-NWFET. The conventional device has a high doping concentration, and as a result suffers from higher RDFs, whereas the proposed dopingless device possesses lower RDFs. The process parameters used to measure sensitivity to RDFs include the radius, doping concentration and gate oxide thickness. When the radius of the nanowire is varied by + 30%, changes in threshold voltage, on-state current and subthreshold slope of 66, 63 and 12%, respectively, are observed in the JL-NWFET, versus 5, 22.6 and 1.8% for the proposed dopingless device (CP-NWFET). Similar variations in doping concentration and gate oxide thickness are seen with the JL-NWFET, whereas the CP-NWFET is largely unaffected. Thus, the proposed gate-stacked dopingless CP-NWFET solves the issue of both doping control and scaling limitation of the gate oxide layer, which paves the way for easier fabrication, with exceptional immunity against parametric variations, making it a good candidate for future nanoscale devices. [ABSTRACT FROM AUTHOR]

We have successfully synthesized for the first time a Ti-doped ZrSiO4 powder (stoichiometry Zr0.95Ti0.05SiO4) via a sol-gel route. The structural and vibrational properties have been characterized by X-ray diffraction, electron microscopy and Raman spectroscopy. Zr0.95Ti0.05SiO4 has a tetragonal zircon-type structure with a = 6.5981(2) Å and c = 5.9810(2) Å. Eight of its Raman-active modes have been measured and assigned. We also performed high-pressure synchrotron X-ray diffraction experiments. The structural behavior was studied up to 31 GPa. At this pressure, we found evidence of the onset of a phase transition, coexisting the low-pressure polymorphs (zircon) with the typical high-pressure polymorph of ZrSiO4 (reidite-type). From the analysis of unit-cell volume versus pressure using a Birch-Murnaghan equation of state, in the quasi-hydrostatic pressure regime (P < 10.5 GPa), we have determined a bulk modulus of 297 GPa. This magnitude represents an enhancement of a 30% in the value of this parameter if compared with un-doped zircon-type ZrSiO4 (bulk modulus < 227 GPa). The low compressibility of Zr0.95Ti0.05SiO4 converts this compound in a very good candidate for many technological applications. The effect of pressure on the linear compressibility of the lattice parameters is also analyzed. [ABSTRACT FROM AUTHOR]

Zircon (i.e., ZrSiO) was synthesized by a sol-gel route at a low temperature with assistance of soft mechano-chemical activation of derived precursors in a high-energy density stirred bead mill. The reaction of precursors pretreated by soft mechano-chemical at different time in sol-gel process was analyzed. The samples were characterized by X-ray diffraction, Fourier transfer infrared spectroscopy, nitrogen gas adsorption method (BET), thermogravimetry, scanning electron microscopy and high-resolution Si nuclear magnetic resonance spectroscopy. The results show that zircon powder with a high crystallinity and a small grain size can be formed via soft mechano-chemical pre-activation and sol-gel route at a lower temperature. The specific surface area of calcined powder increases and the average crystalline size and mean surface particle size decreases with increasing the soft mechano-chemical treatment time. It is indicated that the soft mechano-chemical activation can accelerate the dehydration/dehydroxylation reactions, reduce the bonding degree of Si-O bonds, and break a certain extent of [SiO] tetrahedral three-dimensional network, which is formed in the sol-gel reaction, thus enhancing the reactivity of precursors and facilitating the formation of ZrSiO from Zr ions with [SiO] tetrahedra during the subsequent thermal treatment at a lower temperature (i.e., 700 °C). Graphical Abstract: XRD patterns of all the ground precursors fired at 700 °C. Soft mechano-chemical activation of precursor prepared in sol-gel route could decrease the subsequent sintering temperature of ZrSiO. Compared to the precursor unactivated, ZrSiO powder with a high crystallinity was formed at a lower sintering temperature (i.e., 700 °C) for the precursor activated for 6 h. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate for the first time a 300-mm indium–gallium–arsenic (InGaAs) wafer on insulator (InGaAs-OI) substrates by splitting in an InP sacrificial layer. A 30-nm-thick InGaAs layer was successfully transferred using low temperature direct wafer bonding (DWB) and Smart Cut™ technology. Three key process steps of the integration were therefore specifically developed and optimized. The first one was the epitaxial growing process, designed to reduce the surface roughness of the InGaAs film. Second, direct wafer bonding conditions were investigated and optimized to achieve non-defective bonding up to 600 °C. Finally, we adapted the splitting condition to detach the InGaAs layer according to epitaxial stack specifications. The paper presents the overall process flow that achieved InGaAs-OI, the required optimization, and the associated characterizations, namely atomic force microscopy (AFM), scanning acoustic microscopy (SAM), and HR-XRD, to insure the crystalline quality of the post transferred layer. [ABSTRACT FROM AUTHOR]

An authors index for 2013 issues of the periodical "Institute of Electrical and Electronics Engineers (IEEE) Transactions on Electron Devices" is presented.

An author index for the December 2012 issue of periodical "IEEE Electron Device Letters" is presented.

Abstract  Self-diffusion of Si under anhydrous conditions at 1 atm has been measured in natural zircon. The source of diffusant for experiments was a mixture of ZrO2 and 30Si-enriched SiO2 in 1:1 molar proportions; experiments were run in crimped Pt capsules in 1-atm furnaces. 30Si profiles were measured with both Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis with the resonant nuclear reaction 30Si(p,γ)31P. For Si diffusion normal to c over the temperature range 1,350–1,550°C, we obtain an Arrhenius relation D = 5.8 exp(−702 ± 54 kJ mol−1/RT) m2 s−1 for the NRA measurements, which agrees within uncertainty with an Arrhenius relation determined from the RBS measurements [62 exp(−738 ± 61 kJ mol−1/RT) m2 s−1]. Diffusion of Si parallel to c appears slightly faster, but agrees within experimental uncertainty at most temperatures with diffusivities for Si normal to c. Diffusion of Si in zircon is similar to that of Ti, but about an order of magnitude faster than diffusion of Hf and two orders of magnitude faster than diffusion of U and Th. Si diffusion is, however, many orders of magnitude slower than oxygen diffusion under both dry and hydrothermal conditions, with the difference increasing with decreasing temperature because of the larger activation energy for Si diffusion. If we consider Hf as a proxy for Zr, given its similar charge and size, we can rank the diffusivities of the major constituents in zircon as follows: D Zr D Si D O, dry D O, ‘wet’. [ABSTRACT FROM AUTHOR]

Self-supported zircon (ZrSiO4) coatings have been deposited by means of atmospheric pressure plasma spraying, a high growth rate deposition method. However, it is well known that ZrSiO4 dissociates into ZrO2 and SiO2 in the high-temperature plasma torch during plasma spraying, the rapid quenching preventing reverse combination of both components into ZrSiO4. Usually, high-temperature annealing (1,600–1,900 K) is applied to recombine SiO2 and ZrO2 into ZrSiO4. In this contribution, we investigate an attractive technological alternative to recombine SiO2 and ZrO2 into ZrSiO4 by laser treatment with a scanning continuous wave CO2 laser. By carefully adjusting the CO2 laser treatment parameters (laser power density and scanning velocity), we show that the SiO2 and ZrO2 phases indeed recombine into ZrSiO4, however, with a very low recombination rate. Thus, we have investigated the addition of SiO2-rich glassy particles to the plasma spray powders to facilitate the recombination of ZrO2, and SiO2 into ZrSiO4 during the laser treatment. Furthermore, the beneficial role of the glassy particles addition to substantially lower the annealing temperature during classical heat treatments has been studied. Available evidence indicates that the glassy particles melt during heat treatment, and thus favor the mobility and availability of silica at the ZrO2 grains, which results in a lowering of the reaction temperature and an enhancement of the reaction kinetics. [ABSTRACT FROM AUTHOR]

The MoSi2-ZrB2 coatings were prepared on Nb-Si based alloy by atmospheric plasma spraying with the spraying power 40, 43 and 45 kW. The effect of spraying power on the microstructure and oxidation resistance of MoSi2-ZrB2 coating at 1250 °C were studied. The results showed that the main constituent phases of coatings were MoSi2 at all spraying power. The coating became more compact as the spraying power increased. The coating prepared at 45 kW was dense and uniform, which exhibited the best oxidation resistance due to the formation of a dense and uniform glass layer consisting of SiO2 and ZrSiO4. [ABSTRACT FROM AUTHOR]

In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer's cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents. [ABSTRACT FROM AUTHOR]