A comparative study on the effect of carbon-based and ceramic additives on the properties of fiber reinforced polymer matrix composites for high temperature applications

Ablative composites have been in use for thermal protection of space vehicles for decades. Carbon-phenolic composites have proven to perform exceptionally well in these applications. However with development in aerospace industry their performance needs improvement. In this field, different carbon-based and ceramic additives have been introduced into ablative composite systems. This review article gives a comparative analysis of researches done in this field in the recent past. Density, ablative, thermal and mechanical properties of ablative composites with different ultra-high temperature ceramic particles i.e. ZrSi₂, Cenosphere, nano-SiO₂, BN etc. and carbon-based nanoparticles i.e. CNTs, nano-Diamonds, Graphene oxide etc. used as additives, have been compared and discussed. Emphasis is put on carbon-phenolic composite systems although some epoxy matrix systems have also been discussed for comparison.     

Effects of mean stress and fibre volume content on the fatigue-induced damage mechanisms in CFRP

The effect of the load type (tension and compression) in quasi-static and of the applied mean stress in fatigue tests on the mechanical behaviour and on the damage mechanisms in unidirectional (UD) carbon/epoxy laminates has been studied in combination with the influence of fibre volume content. Results show that the fibre volume content increases the mechanical properties in tension–tension fatigue tests for all tested angles 0°, 45° and 90°. The tensile damage mechanisms of off-axis specimens depend on the fibre volume content and change from matrix cracking and matrix–fibre debonding to fibre-pull out with an increasing amount of fibres as investigated in detail in a previous work. In tension–compression tests, higher fibre volume contents are only beneficial in fatigue tests at angles of 0° and 45°. Fatigue strengths of UD 90° specimens in tension–compression tests are not significantly improved by the fibre volume content which can be ascribed to breakage of entire fibre bundles and crushed fibres on the fracture surfaces.     

A review of advanced proton-conducting materials for hydrogen separation

This paper provides a comprehensive overview of developments and recent trends in H₂ separation technology that uses dense proton–electron conducting ceramic materials and their associated membranes. Various proton–electron conducting materials and their associated membranes are summarized and classified into several important categories, such as Ni-composite proton-conducting materials, as well as tungstate-based, BaPrO₃-based, LaGaO₃-based, and niobate/tantalite composite metal oxide-based ceramic materials/membranes. Various membrane designs, including asymmetric ceramic membranes (supported and self-supported) and surface-modified membranes, are also reviewed. Several important properties of ceramic materials and membranes, such as proton and electron conductivity and performance (i.e., H₂ transport flux and lifetime stability), are also discussed. To highlight the technical progress in this area, all possible ceramic materials and associated membranes are summarized, along with their properties and performance, to help readers quickly locate the information they are looking for. Based on this review, several challenges hindering the maturation of this technology are analyzed in depth, and possible research directions for overcoming these challenges are suggested.     

On the mechanical response of woven para-aramid protection fabrics

The initial condition of the structure of the fabric's knitting form, before applying a load, is closely correlated with the performance of the fabric under loading. The present study focuses on the mechanical response of para-aramid protection fabrics under tensile loading and suggests a knitting angle as a considerable factor for the behavior of the fabric. A global and a local method are applied to monitor the effect of this angle on the fabric's performance and deformation mechanism. The experimental results indicate that this angle affects both the fracture propagation mode and the fracture toughness. A failure onset detection mode, based on this angle, is also suggested, followed by a calculation of the further feasible deformation of a permanently deformed zone until the next failure.     

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO₂ films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti⁴⁺ cations by S⁶⁺ ions into TiO₂ structure of the doped samples. SO₄^2? groups were observed on the surface. S-TiO₂ film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO₂ films. The results supported the idea that the sulfur-doped TiO₂ films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.     

Preparation and characterization of Cf/Pollucite composites through geopolymer precursors

Continuous carbon-fibre-reinforced Cs-geopolymer composite (C_f/CsGP) were prepared, and its in-situ conversion was investigated during high-temperature treatments. The effect of treatment temperature on the thermal evolution process and mechanical properties of the resulting products were systematically evaluated. The results indicated that the crystallization temperature of C_f/CsGP composite was considerably delayed because the amorphous structure of carbon fibres was not conducive as a nucleation substrate for pollucite derived from the CsGP matrix. Moreover, the integrity of the corresponding resulting products derived from the C_f/CsGP composite were damaged due to thermal shrinkage that occurred during the high-temperature treatment process. When treatment temperature was ≤1200^oC, the mechanical properties of the corresponding products exhibited an upward trend, which was ascribed to the improvement of the densification degree of the resulting composite and well interface-bonding state between carbon fibres and pollucite. However, the mechanical properties of the resulting composites decreased with the treatment temperature continued increased from 1200 to 1400^oC. This phenomenon was attributed to the impairment of fibre properties caused by interfacial reactions.     

Ni–Fe mixed oxides prepared by calcination of layered double hydroxides: Potential pigments for the ceramic industry

Mixed Ni,Fe oxides have been prepared by calcination of precursors with the hydrotalcite-type structure which had been prepared by the reverse micelle method using different surfactants. The solids have been characterized by several physicochemical techniques: Powder X-ray diffraction, nitrogen adsorption–desorption at −196 °C for specific surface area assessment, particle size distribution, UV–vis spectroscopy, and temperature-programmed reduction. The solids are formed by NiO and NiFe₂O₄ (spinel) and their properties depend on the experimental conditions used to prepare the hydrotalcite-type precursor. The crystallite size is larger for the spinel crystallites than for the NiO crystallites and in all cases depends on the surfactant used and the pH during the synthesis. The original, uncalcined samples, show intense mainly yellow color, but on calcination almost all of them change to dark brown or even almost black; only when using a cyclic surfactant the color is markedly different from that obtained when linear surfactants are used.     

Synthesis of hydroxyapatite fibers using electrospinning: A study of phase evolution based on polymer matrix

Hydroxyapatite (HA) is considered as the most promising biomaterial candidate to replace and regenerate hard tissues. A small amount of β-tricalcium phosphate (β-TCP) phase is advantageous for rapid bonding of the artificial bones to natural ones due to its high solubility compared to hydroxyapatite. Synthesizing HA nanofibers from electrospinning of sol-gel is considered as a widely researched topic. Motivation of the current work was to investigate the influence of polymeric binder in the final phase evolution after heat treatment of electrospun nanofibers. Calcium phosphate nanofibers were fabricated by electrospinning sols using gelatine and polyvinylpyrrolidone as carrier polymers and subjected to heat treatment. It was realized that carrier polymers facilitate preferential calcium phosphate phase formation by forming hydroxyapatite as major phase while PVP was used and β-TCP with HA as secondary phase while gelatine was employed. XRD and thermal analyses were performed to ascertain the reason behind this interesting behaviour.