Effect of heat treatment in air on the thermal properties of SiC fibre-reinforced composite. Part 1: a barium osumilite (BMAS) matrix glass ceramic composite

The thermal properties have been studied on a glass ceramic composite comprised of a barium osumilite (BMAS) matrix reinforced with SiC (Tyranno) fibres which has been subjected to a heat treatment in air in the range of 700–1,200 °C. Microstructural studies were carried out especially on of the interface between fibre and matrix. The presence of a carbon thin layer in the interface is a typical observation in SiC fibre-reinforced glass ceramic matrix composite systems. The microstructural evaluation and thermal properties showed a degradation of interfacial layer occurred at low heat treatment temperatures, (700–800 °C) this was attributed to the fact that, at those heat treatment temperatures the carbon rich layer formed during processing was oxidised away leaving voids between fibre and matrix, which were linked by isolated silicon-rich bridges. After heat treatment at higher temperatures of 1,000–1,200 °C, the thermal properties were retained or even enhanced by leaving a thick interfacial layer.     

Microstructure property relationship in Pyrex glass composites reinforced with Nicalon fibres

Detailed microstructural studies have been carried out on a series of composites consisting of Pyrex glass reinforced with Nicalon fibres. A variety of techniques has been employed, including X-ray and electron diffraction, electron-probe microanalysis and thin foil analytical electron microscopy. In parallel, mechanical tests have been performed on the composites and measurements have been made of the fibre-matrix bond.Substantial amounts of cristobalite have been identified in the matrix, up to 48% by volume in some cases. At such levels, microcracking is a common occurrence due to the high differential contraction between the matrix constituents upon cooling, which leads to matrix disintegration upon mechanical testing. A second microstructural feature which affects the mechanical behaviour of the composite concerns the fibre-matrix interface and, in particular, the chemistry of the outermost (200 nm) surface regions of the fibre. The amount of graphite here is shown to affect directly the strength of the fibre-matrix bond and, in turn, the degree of fibre pull out and the mechanical properties of the composite.     

Tensile properties of heat-treated Nicalon and Hi-Nicalon fibres

In this study we compare the tensile properties of two types of Nicalon fibres, one with high oxygen content and the other with low oxygen content. Both types of fibre were coated with a carbon layer during manufacture. The fibres were tested at room temperature in the as-received and desized conditions and after heat treatment at 800 and 1200°C in flowing air and argon. Nicalon-607 and Hi-Nicalon fibres exhibited brittle behaviour and a decrease in tensile strength after heat treatment at 1200°C. It was found that Hi-Nicalon fibres had generally higher tensile properties than Nicalon-607 fibres. It was also observed that the high-oxygen-content fibres had more surface defects than the fibres with low oxygen content.     

Improvements in refractoriness and properties of Nicalon fibres by high-temperature heat-treatment

Nicalon SiC fibres were heat-treated in various atmospheres and at various pressures. Initially CO, nitrogen and air were used as the heat-treatment environment at one atmosphere pressure. Microstructural changes and any related strength degradation or improvement were measured for the heat-treated fibres. After heat-treatment in the temperature range 1000°C–1600°C, each sample showed different weight changes. Thus, in air, a weight gain was observed with increasing temperature, whereas in CO and N₂, weight losses were observed but with a smaller weight loss observed for CO. Moreover, carbon monoxide had a significant effect on the strength retention of the fibres. Since the lowest weight loss was observed after heat-treatment in CO at one atmosphere, high pressure CO gas was used to heat-treat Nicalon fibres between 1000°C and 1700°C and the resulting fibres were analysed by single-filament strength testing, scanning electron microscopy, and X-ray diffraction. The results were completely different compared with those in one atmosphere of CO. As the temperature increased, weight and strength increased whereas at one atmosphere pressure, both weight and strength had decreased. The weight increase was because of surface reaction between the CO atmosphere and the SiC fibre and/or because of deposition of carbon from the pressurised CO gas, giving the fibre a surface carbon coating. Carbon coating of a fibre is a beneficial property for CMCs since it provides a weak interface which facilitates pull-out during fracture.     

Effect of heat treatment on surface properties of polyacrylonitrile-based activated carbon fibres

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

热处理时间对聚甲基丙烯酰亚胺(PMI)泡沫结构和性能的影响EI北大核心CSCD

以甲基丙烯酸丁酯(BMA),丙烯酰胺(AM)为反应单体,丙烯酸(AA)作为第三单体和交联剂,在不同热处理时间下,通过自由基本体聚合制备聚甲基丙烯酰亚胺(PMI)泡沫。采用傅里叶变换红外光谱(FT-IR)、扫描电子显微镜(SEM)、热重分析(TGA)、差示扫描量热分析(DSC)等手段对其结构和性能进行表征。结果表明:随着对BMA/AM/AA共聚物热处理时间增加,分子链间发生重排反应生成六元酰亚胺环,经过交联固化后得到PMI泡沫,其特征吸收峰与文献值能较好地吻合。泡沫热处理5 h后得到孔径为100~200μm致密硬质闭孔泡沫,其力学性能良好,压缩强度为8.160 MPa,拉伸强度达到12.95 MPa。泡沫的玻璃化转变温度(Tg)为255℃,热失重10%时热分解温度Td10高达280℃,345℃时泡沫仍能残留80%以上,其导热系数为0.05424 W/(m·K),说明对共聚物热处理5 h后得到了具有优异的耐高温性能和隔热性能的泡沫。     

Effect of heat treatment on structure and properties of dispersed-type dental amalgam

Effect of heat treatment of Ag–Cu–Pd dispersant particles on the structure, mechanical properties and mercury vapor release rate of an Ag–Cu–Sn/Ag–Cu–Pd-based dental amalgam has been investigated. Experimental results indicate that crystallinity of dispersant Ag-Cu–Pd alloy increases with increasing HTT, with most notable increase occurring between 100 and 200 °C. Increasing HTT of Ag–Cu–Pd alloy does not change much of the mercury/alloy ratio for amalgamation, but largely reduces working/setting time of the amalgam. The Ag–Cu–Pd particles in 7 d-aged amalgam are comprised primarily of an outer Sn/Cu/Pd-rich zone and an inner Ag/Cu/Pd-rich zone with eutectic-type morphology and chemical distribution. The annealing-enhanced Pd segregation effect is most significantly observed in the amalgam derived from 300 °C-annealed Ag–Cu–Pd dispersant. This amalgam also has the highest compressive strength, highest DTS, and lowest creep rate. Higher annealing temperature causes mechanical property of the amalgam to deteriorate. The initial mercury vapor release rates of amalgams derived from 100, 200 and 300 °C-annealed Ag–Cu–Pd dispersant are significantly lower than that derived from 400 °C-annealed dispersant.     

Effect of the chemical heat treatment in a semianthracite char on the textural properties and the gasification in air

The effects of the chemical heat treatments of a semianthracite char (AC) on the textural properties and the gasification in air they are investigated. Sample AC first was treated with the LiCl/KCl mixture or the mixture formed by LiCl/IKCl and a metallic oxide, M _{n = 1, 2}O (MgO, CaO, FeO, CoO, NiO, Cu₂O or ZnO) at 743, 873 or 1173 K and products obtained they were then washings carefully with water distilled. The information on the textural modifications was deduced of isotherms of CO₂ adsorption to 273 K. The reactivity tests were taken to the temperature 808, 823 and 838 K. As resulting from the AC treatments, on developed the microporosity and on increase the air reactivity, in particular, the first effect is greater whim the used mixture went LiCl/KCl/CoO at 1173 K and the second effect are greater when the used mixture went LiCl/KCl/Cu₂O at 1173 K.     

Effects of coating treatment on mechanical properties of carbon fibres and reinforced silicon carbide composites

Abstract

Three-dimensionally braided carbon fibre reinforced SiC matrix composites have been fabricated and the effects of coating treatment on the mechanical properties have been investigated. It has been found that pyrocarbon coating can improve the strength of the heat treated carbon fibres. When the coating thickness was 0.5 m, the composites had better mechanical properties: a flexural strength of 643 MPa and a fracture toughness of 17.9 MPa m12. The composites also exhibited a toughening fracture mode.     

Effect of heat treatment on structure and magnetic properties of FeCoNi/CNTs nanocomposites

Fe₄₆Co₃₅Ni₁₉/CNTs nanocomposites have been prepared by an easy two-step route including adsorption and heat treatment processes. We investigated the effect of heat treatment conditions on structure, morphology, nanoparticle sizes and magnetic properties of the Fe₄₆Co₃₅Ni₁₉ alloy nanoparticles attached on the carbon nanotubes by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). When the reducing temperature changes from 300–450°C, a transition of the crystalline structure from bcc phase to fcc-bcc dual phase and an increase in particle size of Fe₄₆Co₃₅Ni₁₉ nanoparticles together with a local maximum at 350°C are observed. Meanwhile, the saturation magnetization (M _s) for Fe₄₆Co₃₅Ni₁₉ nanoparticles increases with the increase of reducing temperature and the coercivity (H _c) decreases rapidly with a local minimum at 350°C. When the reducing time (tr) changes from 2–5 h, bcc phase is predominant in the Fe₄₆Co₃₅Ni₁₉ alloy particles. Both the particle size and M _s have a maximum at tr = 3 h, and the H _c reaches a maximum at tr = 4 h.     

Effect of heat treatment on structure evolution and properties of nano zinc titanate ceramics

Nano zinc titanate ceramics are prepared using a conventional solid state method. The obtained compacts are sintered at 800, 900, 1000 and 1100 °C for 3 h. The prepared compacts are analyzed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM) for structural and microstructural studies. Based on the X‐ray diffraction (XRD) data, it is observed the coexistence of ZnTiO₃ and α‐Zn₂TiO₄ phases together at low temperature (800 °C) without the presence of TiO₂ (rutile) contradicting the general mechanism stating the transformation of ZnTiO₃ to α‐Zn₂TiO₄ and TiO₂ at higher temperatures. A new mechanism is proposed to explain the formation of nano ZnTiO₃ and α‐Zn₂TiO₄ structures depending on the role of TiO₂ in achieving this mission. According to this mechanism, we propose a partial diffusion of TiO₂ in the ZnO lattice forming the ZnTiO₃ phase. The second part of TiO₂ acts as a catalyst that facilitates the transformation of nano ZnTiO₃ to nano α‐Zn₂TiO₄. The catalytic power of rutile is achieved from its enhanced tensile stress that induces the phase transition from nano ZnTiO₃ to nano α‐Zn₂TiO₄.     

Mechanical properties of date palm fibres and concrete reinforced with date palm fibres in hot-dry climate

The study examines four types of date palm surface fibres and determines their mechanical and physical properties. In addition, the properties of date palm fibre-reinforced concrete, such as strength, continuity index, toughness and microstructure, are given as a function of curing in water and in a hot-dry climate. The volume fraction and the length of fibres reinforcement were 2–3% and 15–60 mm respectively. Increasing the length and percentage of fibre-reinforcement in both water and hot dry curing, was found to improve the post-crack flexural strength and the toughness coefficients, but decreased the first crack and compressive strengths. In hot-dry climate a decrease of first crack strength with ageing was observed for each concrete type. Water curing decreased the global degree of the voids and cracks with time for each concrete type, but increased it in hot-dry climate.     

Effect of fibre/matrix interface structure on strength and plasticity of boron aluminium reinforced with discontinuous fibres

The variation of strength characteristics of boron aluminium were studied in relation to the structure of the fibre-matrix interface. It was found that effects of optimal discrete reinforcement of boron aluminium may be realized to a certain extent if such structural characteristics of the interface as density of interphase bonds, , are purposefully changed. In the case where =0.340, the effect of discrete reinforcement is the largest for both failure work and elongation, if the composite strength remains relatively high. Failure work of discrete reinforced boron aluminium is five times higher than that of the continuously reinforced one, but relative elongation reaches 10%.     

Effect of barium on the structure and dielectric properties of multicomponent ceramics based on ferroelectric relaxors

High-density ceramic samples of mPb(Mg_1/3Nb_2/3) · yPb(Zn_1/3Nb_2/3) · nPb(Ni_1/3Nb_2/3) · xPbTiO₃ (m = 0.4541, y = 0.0982, n = 0.1477, x = 0.3) solid solutions, unmodified and barium-modified, with the composition lying in a morphotropic phase region, have been prepared by a conventional ceramic processing technique. We demonstrate that barium substitution for 5% of the lead on the A site allows one to obtain ceramics containing no pyrochlore phase. Modification with barium shifts the solid solution from the morphotropic to a tetragonal phase region. In addition, barium doping increases the average grain size of the ceramic from 2–3 to 3–4 μm and changes the type of fracture from intergranular to mixed (intergranular and transgranular). Modification with barium increases the relative dielectric permittivity ?/?₀ (at E = 0) of the material by more than a factor of 2 (from 4300 to 9100). We conclude that materials based on the ceramics studied can find practical application and examine ways of further improving their piezoelectric performance.     

Impact properties of polyurethane and glass fibres reinforced composites

Impact resistance of the polyurethane matrix and composites with glass fibres of various volume fractions was investigated. The theory of linear elastic fracture mechanics (LEFM) was successfully applied to obtain a quantitative assessment of a parameter of toughness, the critical strain energy release rate (G _c), which was determined from the energy (W ^*) required to fracture sharply-notched specimens by taking into account specimen dimensions and notch depth. It is found that the G ^* is not a linear function of reinforcement concentration. The impact resistance with low volume fraction _f=0.045 of glass fibres decreases as compared to that of the matrix. However, with further incorporation of glass fibres, the impact resistance gradually increases, reaching its maximum for the volume fraction _f=0.158. An explanation of this non-linear behaviour is provided in this paper.