Effect of oxidation and residual stress on mechanical properties of SiC seal coated C/SiC composite

The effect of oxidation and thermal residual stress on mechanical properties of SiC seal coated C/SiC composite at ambient temperature and high temperature were studied. The oxidation of SiC seal coated C/SiC composite at 1300 and 1500 °C resulted in carbon fibres burn area near through thickness micro cracks in the SiC seal coating. With the increase in exposure time, the formation of SiO₂ layer in SiC matrix near carbon fibres burns area was found. Residual mechanical properties of SiC seal coated C/SiC composite after exposure in air show significant degradation. First time, a continuous measurement of Young's modulus with temperature of C/SiC composite was carried out using an impulse excitation technique. The effect of relaxation of thermal residual stress on mechanical properties was observed with the help of continuous measurement of Young's modulus as a function of temperature in an inert atmosphere.     

Effect of SiC on the corrosion resistance of electroless Cu–P–SiC composite coating

In this work, Cu–P–SiC composite coatings were deposited via electroless plating with the addition of sodium hypophoshite (NaH₂PO₂) as a reducing agent. The coating compositions deposited were determined by using energy dispersive X-ray spectroscopy (EDX). The surface morphology of the coatings that were analyzed using scanning electron microscopy (SEM) showed that SiC particles were uniformly distributed by virtue of surfactant addition and mechanical stirring. The anti-corrosion properties of Cu–P and Cu–P–SiC coatings in NaCl and HCl solutions were investigated by the weight loss and potentiodynamic polarization techniques. The results showed that the corrosion resistance of Cu–P–SiC coatings was superior to that of electroless Cu–P coatings and carbon steel substrates in various concentrations of NaCl and HCl solutions.     

Wet film application techniques and their effects on the stability of RuO2–TiO2 coated titanium anodes

The effect of wet film application techniques on the physical and electrochemical properties and operational stability of RuO₂–TiO₂ coated titanium anodes was evaluated. Four compositions of RuO₂–TiO₂ coatings were applied to Ti substrates by three different wet coating methods—brush, dip and spin. Changing the coating technique resulted in different morphologies. Electrochemically active surface area of the coatings was related to the morphology. A shift in Ru(III)/Ru(IV) oxidation potential occurred upon changing the application technique. For lower ruthenium content coatings, this shift was related to coating lifetime. Anode stability in accelerated lifetesting showed that dip coated samples lasted up to three times longer than brush coated samples for lower ruthenium content.     

Fabrication of CNT-SiC/SiC composites by electrophoretic deposition

Due to the outstanding mechanical and thermal properties of carbon nanotubes (CNTs), they are considered suitable reinforcement for structural materials. In this study, for the first time, electrophoretic deposition (EPD) was used to deposit (multi-walled) CNTs onto SiC fibres (SiC_f) to form an effective CNT interphase layer for SiC_f/SiC composites. This deposition was followed by electrophoretic infiltration of the CNT-coated SiC fibre mats with SiC powder to fabricate a new CNT-SiC-fibre-reinforced SiC-matrix (SiC_f/SiC) composite for fusion applications. In these EPD experiments, a commercial aqueous suspension of negatively charged CNTs and an optimized aqueous suspension of negatively charged SiC particles were used. The CNT-coatings on the SiC fibres were firm and homogenous, and uniformly distributed nanotubes were observed on the fibre surfaces. In a following step of EPD, a thick SiC layer was formed on the fibre mat when the CNT-coated SiC fibres were in contact with the positive electrode of the EPD cell; however, spaces between the fibres were not fully filled with SiC. Conversely, when CNT-coated SiC fibres were isolated from the electrode, the SiC particles were able to gradually fill the fibre mat resulting in relatively high infiltration, which leads to dense composites.     

A novel IrO<Subscript>2</Subscript> electrode with iridium–titanium oxide interlayers from a mixture of TiN nanoparticle and H<Subscript>2</Subscript>IrCl<Subscript>6</Subscript> solution

A novel IrO₂ anode on titanium substrate with iridium–titanium oxide interlayer (Ti/IrO _x –TiO₂/IrO₂) was prepared and investigated for oxygen evolution. IrO _x –TiO₂ interlayer was coated on titanium substrate by impregnation-thermal decomposition method from a mixture of TiN nanoparticles and H₂IrCl₆ solution at 500 °C. The results showed that the service life of Ti/IrO _x –TiO₂/IrO₂ was a factor of six times longer than that of Ti/IrO₂, which was attributed to the IrO _x –TiO₂ interlayer, it could form a metastable solid solution between IrO _x and thin titanium oxide layer on titanium substrate during calcination. The interlayer contributed to the decrease in migration rate of oxygen atom or molecule toward substrate and the increase in bonding force among IrO₂ layer, interlayer, and substrate. Therefore, besides keeping high electrocatalytic activity, the service life of Ti/IrO _x –TiO₂/IrO₂ electrode was greatly improved, and its overall electrocatalytic performance for oxygen evolution was increased as well.     

Product of carbonitriding of leucoxene concentrate

The grain, phase, and chemical compositions and the microstructure of tusin (a mixture of titanium carbonitride TiC_1-xN_x (x ≈ 0.4 - 0.5) and silicon carbide SiC), used as the base of a new kind of refractory that is the product of carbonitriding of leucoxene concentrate, are presented. It is shown that titanium carbonitride and silicon carbide intergrow finely, which hampers phase separation. Chemical treatment of tusin yields technical silicon carbide. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 25–27, January, 2000. RF Patent No. 2100317.     

Thermal characteristics of high-strength and thermostable aromatic fibres

The thermal characteristics of para-aramid, polyoxadiazole, and polyimide fibres were comparatively investigated by dynamic thermogravimetric analysis, differential scanning calorimetry, and thermomechanical analysis. It was shown that thermooxidative degradation of these types of fibres began at 400–450 °C and intensified at higher temperatures. The fibres investigated are characterized by size stability up to the initial temperature of thermooxidative processes (400–450 °C). With respect to thermal stability, these fibres are in the following order: polyimide > polyoxadiazole, and carbocyclic para-aramid fibres. The correlation of the “hydrogen index” I_H and “aromaticity index” I_Ar for thermostable fibres with their thermal stability was demonstrated. Translated from Khimicheskie Volokna, No. 3, pp. 72–74, May–June, 2008.     

Use of chemical fibres in drying screens for the paper industry

The basic types of chemical fibres for the development and production of drying screens for paper machines were selected and their properties were determined. Polyester fibres are the most appropriate type for fabrication of drying screens due to their elevated mechanical properties and thermohydrolytic stability. Optimum designs for drying screens based on polyester monofilaments and complex fibres with a polymer coating with defined permeability were developed. To decrease the markability of paper web, it was suggested that the outer supporting surface of the screen be coated with soft fibres or a fibrous layer of Nitron fibres. Translated from Khimicheskie Volokna, No. 2, pp. 43–47, March–April, 1998.     

Effect of SiC and Al2O3 particles on the electrodeposition of Zn, Co and ZnCo: II. Electrodeposition in the presence of SiC and Al2O3 and production of ZnCo–SiC and ZnCo–Al2O3 coatings

SiC or Al₂O₃ microsized particles were added to acid sulfate-based solutions for the electrodeposition of Zn, Co, and ZnCo. Initially, their effects on the electrochemical processes were evaluated. The Zn electrodeposition rate was increased in both SiC and Al₂O₃-loaded solutions. The Co electrodeposition rate was also increased by SiC. However, Al₂O₃ decreased it, especially at the beginning. Both SiC and Al₂O₃ influenced the electrodeposition of ZnCo positively at moderate loadings. The factors involved in producing ZnCo–SiC and ZnCo–Al₂O₃ composites were evaluated. ZnCo–SiC composites could be deposited with a higher [Co/Zn] ratio in the metal matrix than for pure ZnCo. In ZnCo–Al₂O₃, the [Co/Zn] ratio was smaller than in ZnCo and ZnCo–SiC. It was necessary to reduce the CoSO₄ concentration to improve the Al₂O₃ co-deposition. The variation in [Co/Zn] ratio could, in principle, be related to the effects of SiC and Al₂O₃ on the individual Zn and Co electrodeposition.     

Microstructure and mechanical properties of SiC fibres after exposure at elevated temperature

To understand the service behaviour of SiC fibres, the effects of ambient environment and temperature on the microstructure, mechanical property and oxidation behaviour of these fibres were investigated. The result shows that, the surface of SiC fibres becomes rough after exposure in air from 973 to 1573?K due to the formation of small SiO₂ particles, and a smooth SiO₂ film will be formed on the SiC fibre at 1773?K. In Ar atmosphere, SiC fibres will change into clusters of large SiC crystals after heat treatment for 2?h at 2373?K. The tensile strength of SiC fibres decreased by 66 and 95% when the fibres were exposed at 1773?K for 5?min in air and 2373?K for 2?h in Ar, respectively. This degradation is associated with the evaporation of CO and SiO from the fibres as well as with SiC grain growth in the fibres.     

SiC Nanorods Grown on Electrospun Nanofibers Using Tb as Catalyst: Fabrication, Characterization, and Photoluminescence Properties

Well-crystallized β-SiC nanorods grown on electrospun nanofibers were synthesized by carbothermal reduction of Tb doped SiO₂ (SiO₂:Tb) nanofibers at 1,250 °C. The as-synthesized SiC nanorods were 100–300 nm in diameter and 2–3 μm in length. Scanning electron microscopy (SEM) results suggested that the growth of the SiC nanorods should be governed by vapor-liquid-solid (VLS) mechanism with Tb metal as catalyst. Tb(NO₃)₃ particles on the surface of the electrospun nanofibers were decomposed at 500 °C and later reduced to the formation of Tb nanoclusters at 1,200 °C, and finally the formation of a Si–C–Tb ally droplet will stimulate the VLS growth at 1,250 °C. Microstructure of the nanorod was further investigated by transmission electron microscopy (TEM). It was found that SiC <111> is the preferred initial growth direction. The liquid droplet was identified to be Si₈₆Tb₁₄, which acted as effective catalyst. Strong green emissions were observed from the SiC nanorod samples. Four characteristic photoluminescence (PL) peaks of Tb ions were also identified.     

Electrochemical treatment of ammonia in wastewater by RuO<Subscript>2</Subscript>–IrO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti electrodes

This study investigated the removal of ammonia in wastewater by an electrochemical method using titanium electrodes coated with ruthenium and iridium (RuO₂–IrO₂–TiO₂/Ti) with low chlorine evolution over-voltage. The effects of operating parameters, including chloride ion concentration, current density and initial pH, were also investigated. The results were evaluated primarily by considering the efficiency of the elimination of NH₄⁺-N. The removal of ammonia by electrochemical oxidation mainly resulted from the indirect oxidation effect of chlorine/hypochlorite produced during electrolysis. The direct anodic oxidation efficiency of ammonia was less than 5%, and the current efficiency was less than 10%. The ammonia removal followed pseudo-first-order kinetics. The electrochemical process can be applied successfully as a final polishing step, or as an alternative method to biological nitrification. The process seems to be most beneficial for small coastal cities     

Synthesis of nanocrystalline TiO<Subscript>2</Subscript>-coated coal fly ash for photocatalyst

In order to more easily separate TiO₂ photocatalyst from treated wastewater, TiO₂ photocatalyst is immobilized on coal fly ash by precipitation method. The titanium hydroxide precipitated on coal fly ash by neutralization of titanium chloride is transformed into titanium dioxide by heat treatment in the temperature range of 300–700 ‡C. The crystalline structure of the titanium dioxide shows anatase type in all ranges of heat treatment temperature. The crystal size of anatase increases with increasing heat treatment temperature, with the drawback being the lower removal ability of NO gas. When the coal fly ash coated with 10 wt% of TiO₂ was calcined at 300 and 400 ‡C for 2 hrs, the average crystal size of anatase appeared about 9 nm, and the removal rates of NO gas were 63 and 67.5%, respectively. The major iron oxide, existing in coal fly ash as impurity, is magnetite (Fe₃O₄). Phase transformation of magnetite into hematite (Fe₂O₃) by heat treatment improves the removal rate of NO gas for TiO₂-coated coal fly ash.     

Investigations on the thermal behaviours of SiC-ZrC continuous ceramic fibres

In this study, nanoscale composite SiC-ZrC ceramic fibres, derived from polyzirconocenecarbosilane (PZCS) via melt spinning, electron beam crosslinking, pyrolysis and sintering were investigated in detail. Compared with several commercial products of second-generation SiC fibres, the produced composite fibres exhibit improved thermal stability, mechanical properties and oxidation resistance. SiC grains in the fibre grew from 9.8 nm to 33.9 nm after annealing in an inert atmosphere at 1800 °C for 1 h, as well as decomposition of the SiC_xO_y phase and the growth of SiC grains affected the mechanical properties of the fibres, and the mechanical properties of the fibres were maintained at 1.1 GPa, accompanied by an increase in the modulus. After the fibres were oxidized at 1100～1400 °C for 1 h, a dense oxide layer of SiO₂-ZrO₂ was formed on the surface of the fibres, which slowed down the rate of further fibre oxidation, thus, the fibres exhibited excellent oxidation resistance.     

Oxidation of polyvinyl alcohol fibres in the presence of phosphorus-containing compounds

The oxidation temperature-time regime that results in carbon fibre materials (CFM) with a yield of approximately 30% and a 94–95% concentration of carbon was established based on a study of the fundamental characteristics of thermal transformations of polyvinyl alcohol (PVA) fibres in the presence of phosphorus-containing compounds. It was shown that the effective active energy of decomposition of oxidized PVA fibres and their capacity for coke formation increase in the presence of [NH ₄]₂HPO₄. The effect of the increase in the elasticity of CF caused by the action of the phosphorus-containing compound on cross-linking of the carbon during high-temperature treatment was determined. Translated from Khimicheskie Volokna, No. 2, pp. 14–18, March–April, 1997.     

High-temperature flexural strength of I-CVI processed Cf/SiC composites with variable interphases

The effect of single-layer pyrocarbon (PyC) and multilayered (PyC/SiC)_n=4 interphases on the flexural strength of un-coated and SiC seal-coated stitched 2D carbon fiber reinforced silicon carbide (C_f/SiC) composites was investigated. The composites were prepared by I-CVI process. Flexural strength of the composites was measured at 1200 °C in air atmosphere. It was observed that irrespective of the type of interphase, the seal coated samples showed a higher value of flexural strength as compared to the uncoated samples. The flexural strength of 470 ± 12 MPa was observed for the seal coated C_f/SiC composite samples with multilayered interphase. The seal coated samples with single layer PyC interphase showed flexural strength of 370 ± 20 MPa. The fractured surfaces of tested samples were analyzed in detail to study the fracture phenomena. Based on microstructure-property relations, a mechanism has been proposed for the increase of flexural properties of C_f/SiC composites having multilayered interphase.     

Preparation and evaluation of RuO2–IrO2, IrO2–Pt and IrO2–Ta2O5 catalysts for the oxygen evolution reaction in an SPE electrolyzer

IrO₂–RuO₂, IrO₂–Pt and IrO₂–Ta₂O₅ electrocatalysts were synthesized and characterized for the oxygen evolution in a Solid Polymer Electrolyte (SPE) electrolyzer. These mixtures were characterized by XRD and SEM. The anode catalyst powders were sprayed onto Nafion 117 membrane (catalyst coated membrane, CCM), using Pt catalyst at the cathode. The CCM procedure was extended to different in-house prepared catalyst formulations to evaluate if such a method could be applied to electrolyzers containing durable titanium backings. The catalyst loading at the anode was about 6 mg cm⁻², whereas 1 mg cm⁻² Pt was used at the cathode. The electrochemical activity for water electrolysis was investigated in a single cell SPE electrolyzer at 80 °C. It was found that the terminal voltage obtained with Ir–Ta oxide was slightly lower than that obtained with IrO₂–Pt and IrO₂–RuO₂ at low current density (lower than 0.15 A cm⁻²). At higher current density, the IrO₂–Pt and IrO₂–RuO₂ catalysts performed better than Ir–Ta oxide.     

Evaluation of corrosion behaviour of Ti–25Mo alloy in chloride medium

The corrosion behaviour of Ti–25Mo alloy in 0.9 wt% NaCl was evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and compared with that of commercially pure titanium (CP-Ti). The corrosion behaviour of Ti–25Mo alloy has been reported for the first time in this paper. The microstructure and structural characteristics were also examined using optical microscopy and X-ray diffraction (XRD), respectively. The study reveals that Ti–25Mo alloy possesses a β-phase microstructure. The Ti–25Mo alloy exhibits higher passivation range, lower average passive current density (i_pass) and higher charge transfer resistance (R_ct) compared to that of CP-Ti. Based on the corrosion protection ability, Ti–25Mo alloy can be a suitable alternative material for orthopaedic implant applications.     

Large-scale Synthesis of β-SiC Nanochains and Their Raman/Photoluminescence Properties

Although the SiC/SiO₂ nanochain heterojunction has been synthesized, the chained homogeneous nanostructure of SiC has not been reported before. Herein, the novel β-SiC nanochains are synthesized assisted by the AAO template. The characterized results demonstrate that the nanostructures are constructed by spheres of 25–30 nm and conjoint wires of 15–20 nm in diameters. Raman and photoluminescence measurements are used to explore the unique optical properties. A speed-alternating vapor–solid (SA-VS) growth mechanism is proposed to interpret the formation of this typical nanochains. The achieved nanochains enrich the species of one-dimensional (1D) nanostructures and may hold great potential applications in nanotechnology.     

Fabrication of short carbon fibre reinforced SiC multilayer composites by tape casting

Silicon carbide multilayer composites containing short carbon fibres (C_sf/SiC) were prepared by tape casting and pressureless sintering. C fibres were dispersed in solvents and then mixed with SiC slurry to make green C_sf/SiC tape. Triton X-100 was found to be the best one for Toho Tenax HTC124 fibres (with water soluble coating) among BYK-163, BYK-410, BYK-2150, BYK-9076, BYK-9077 and Triton X-100 dispersants. C_sf/SiC multilayer composites containing 5 vol.% fibre (mean fibre length of 3, 4.5, and 6 mm) were obtained. Addition of short C fibres seems to worsen the densification process in the C_sf/SiC multilayer composites, whereas anisotropy shrinkage in C_sf/SiC was also observed. Open pores size was increased slightly after the addition of C fibre but it decreased with the mean fibre length. Mechanical properties were affected by high residual porosity. The addition of short C fibre has not changed the crack deflection at weak interfaces. C_sf/SiC multilayer composites containing longer fibres (4.5 and 6 mm) presented higher elastic modulus, bending strength and Vickers hardness as compared to shorter fibres (3 mm). Improved sintering performance and fibre content are necessary to improve mechanical properties.