A glass-bonded ceramic material from chrysotile (white asbestos)

A process has been developed for bonding chrysotile asbestos into a robust, dimensionally-stable lightweight ceramic material by fusing it with sodium silicate and/or ground waste glass. The chrysotile can retain its desirable properties of fibrous morphology and porosity, but the fibre bundles are stabilized by fusion into a glassy matrix, reducing the respirable fibre concentration. The glass-bonded materials have good resistance to mechanical abrasion, and any resulting dust is found by SEM to be particularly free of fibres. The thermal treatment also converts the chrysotile into crystalline forsterite, which should destroy its cell toxicity. Other methods of glass-bonding chrysotile compacts (hot pressing and impregnating with glaze) were also investigated, and the properties of the resulting materials are reported.     

Thermal transformation in a chrysotile asbestos

Structural changes accompanying thermal transformation in a chrysotile asbestos sample of Indian origin upto a temperature of 900°C have been investigated by x-ray method. The changes in lattice parameters have been systematically measured by applying a least square refinement technique and the crystallite size and strain defects at different stages have been estimated by line profile analysis of the diffraction peaks. The present study also confirms the earlier results on stepwise transformation of chrysotile fibres. This sequence of transformation has been explained assuming two different types of crystallites as reported in kaolinite.     

聚苯硫醚酮(PPSK)热转变行为的初步研究EI

用ＤＳＣ和ＴＧＡ研究了不同分子量ＰＰＳＫ的热转变行为及热分解动力学。结果表明，随着分子量升高，ＰＰＳＫ的玻璃化转变温度（Ｔｇ）、熔点（Ｔｍ）、起始热分解温度以及热分解活化能升高。淬火样品在进行退火处理时，退火温度（Ｔａ）对Ｔｍ有较大的影响，在较低Ｔａ下退火使Ｔｍ下降；但在较高Ｔａ下退火使Ｔｍ升高。     

In situ Raman cell for high pressure and temperature studies of metal and complex hydrides

A novel cell for in situ Raman studies at hydrogen pressures up to 200 bar and at temperatures as high as 400 °C is presented. This device permits in situ monitoring of the formation and decomposition of chemical structures under high pressure via Raman scattering. The performance of the cell under extreme conditions is stable as the design of this device compensates much of the thermal expansion during heating which avoids defocusing of the laser beam. Several complex and metal hydrides were analyzed to demonstrate the advantageous use of this in situ cell. Temperature calibration was performed by monitoring the structural phase transformation and melting point of LiBH(4). The feasibility of the cell in hydrogen atmosphere was confirmed by in situ studies of the decomposition of NaAlH(4) with added TiCl(3) at different hydrogen pressures and the decomposition and rehydrogenation of MgH(2) and LiNH(2).     

玻璃纤维/环氧树脂泡沫夹层板的热解动力学

使用DTG-60(AH)热重分析仪分析了玻璃纤维/环氧树脂泡沫夹层板在不同升温速率和不同氧含量条件下的热分解特性。结果表明,在空气中玻璃纤维/环氧树脂泡沫夹层板的热分解反应可分为三个阶段。随着升温速率的提高,热分解反应的初始反应温度、终止反应温度以及最大质量损失速率温度均向高温方向移动。氧含量的降低对热分解的第三阶段有较大的影响。采用Flynn-Wall-Ozawa法和Starink法进行热解动力学分析,得到玻璃纤维/环氧树脂泡沫夹层板的表观活化能。     

尼龙66及其复合材料的热分解动力学

使用热重分析仪测定尼龙66(PA66)和两种不同玻纤增强尼龙66复合材料(GF/PA)的热分解曲线,用Kissinger法和Crane法研究了PA66和GF/PA的热分解动力学。结果表明:PA66、GF/PA-1和GF/PA-2的热分解反应级数分别为0.949、0.912和0.921,表明均为一阶热分解过程;热分解活化能分别为218.65 kJ/mol、121.81 kJ/mol和132.23 kJ/mol,表明玻纤的加入显著降低了PA66的热分解活化能。在加热速率相同的条件下两种GF/PA达到最大热分解速率的温度都比PA66的低,表明玻纤虽然改善了PA66的性能,但是加快了PA66的热分解过程,说明存在着“灯芯效应”。     

Bio-composites of kenaf fibers in polylactide: Role of improved interfacial adhesion in the carding process

Bio-composites comprised of kenaf fiber reinforced polylactide are fabricated by carding followed by treatment with a 3-glycidoxypropyl trimethoxy silane and hot-pressing. The effects of the silane coupling agent on composite properties was highly beneficial leading to increased moduli and heat deflection temperatures as well as reduced water swelling. Swelling is found to increase with increasing kenaf loading levels but to decrease with increasing coupling agent concentrations. Mechanical properties of the bio-composites at tempertaures above the glass transition are vastly improved in comparison to the base PLA polymer. As little as 10 wt.% kenaf fiber in PLA provides a heat distortion temperature in excess of 140 °C when combined with the coupling agent. The thermal stability towards degradation is slightly decreased relative to the base PLA and the ash content is increased. Thermal properties such as the glass transition, melting temperature, and percent crystallinity of the matrix PLA are largely unaffected by incorporation into the composites. Evidence of successful reaction of the silane with the kenaf fibers is provided by FTIR and implied by decreased swelling in water. A prototypical automotive headliner is fabricated as a means of demonstrating the viability of the present bio-composites in real manufacturing processes.     

A novel decomposition technique of friable asbestos by CHClF2-decomposed acidic gas

Asbestos was widely used in numerous materials and building products due to their desirable properties. It is, however, well known that asbestos inhalation causes health damage and its inexpensive decomposition technique is necessary to be developed for pollution prevention. We report here an innovative decomposition technique of friable asbestos by acidic gas (HF and HCl) generated from the decomposition of CHClF(2) by the reaction with superheated steam at 800 degrees C. Chrysotile-asbestos fibers were completely decomposed to sellaite and magnesium silicofluoride hexahydrate by the reaction with CHClF(2)-decomposed acidic gas at 150 degrees C for 30 min. At high temperatures beyond 400 degrees C, sellaite and hematite were detected in the decomposed product. In addition, crocidolite containing wastes and amosite containing wastes were decomposed at 500 degrees C and 600 degrees C for 30 min, respectively, by CHClF(2)-decomposed acidic gas. The observation of the reaction products by phase-contrast microscopy (PCM) and scanning electron microscopy (SEM) confirmed that the resulting products did not contain any asbestos.     

The role of lattice water in determining the reactivity of various crystalline aluminas

The thermal decomposition of alkali metal chlorides was studied on a series of colloidal and particulate aluminas with different crystalline phases. Decomposition was monitored by differential thermal and thermogravimetric analysis and the resulting phase development by X-ray diffraction. It was found that the presence of strongly bound lattice water in colloidal gel bohemite alumina caused significantly lower decomposition temperatures and increased reactivity towards compound formation. This has been attributed to the simultaneous loss of water via a hydrolysis reaction with the metal chloride, and subsequent phase transformation of the pseudo-bohemite into γ-alumina, forming the aluminate at a much reduced temperature. This revised version was published online in November 2006 with corrections to the Cover Date.     

Leached asbestos materials: precursors of zeolites

Zeolites have been synthesized from the Alix materials obtained by acid leaching of chrysotile asbestos having a magnesium leaching degree (MLD) larger than 60%. Above removal of 60% of Mg, acid-leaching results in a rapid morphological degradation of the asbestos fibers leading to a more porous and noncrystalline solid, comparable, when the MLD approaches 100%, to the highly siliceous zeolites or silicalite in terms of surface area, density, and hydrophobicity. Such microporous silica materials constitute excellent matrices for the growth of submicron zeolite particles. The rate of water uptake of the resulting zeolite A is much faster than that of commercial zeolite A, which can be used in applications for soil conditioning. The presence of Mg in the zeolites results in improved catalytic conversion of methanol to light olefins.     

An innovative energy-saving in-flight melting technology and its application to glass production

The conventional method used for glass melting is air-fuel firing, which is inefficient, energy-intensive and time-consuming. In this study, an innovative in-flight melting technology was developed and applied to glass production for the purposes of energy conservation and environmental protection. Three types of heating sources, radio-frequency (RF) plasma, a 12-phase alternating current (ac) arc and an oxygen burner, were used to investigate the in-flight melting behavior of granulated powders. Results show that the melted particles are spherical with a smooth surface and compact structure. The diameter of the melted particles is about 50% of that of the original powders. The decomposition and vitrification degrees of the prepared powders decrease in the order of powders prepared by RF plasma, the 12-phase ac arc and the oxygen burner. The largest heat transfer is from RF plasma to particles, which results in the highest particle temperature (1810 °C) and the greatest vitrification degree of the raw material. The high decomposition and vitrification degrees, which are achieved in milliseconds, shorten the melting and fining times of the glass considerably. Our results indicate that the proposed in-flight melting technology is a promising method for use in the glass industry.     

The thermal transformation of Man Made Vitreous Fibers (MMVF) and safe recycling as secondary raw materials (SRM)

This work describes the high temperature reaction sequence of commercial Man Made Vitreous Fibers (MMVF) Cerafiber, Superwool, Rock wool and Glass wool which may be used as substitute for asbestos in some industrial applications. Knowledge of the reaction path and transformation sequence is very important to assess whether carcinogenic crystalline phases are formed during devitrification, which may occur when used as insulators. In addition, knowledge about the nature of the phases formed at high temperature is mandatory to assess if thermally transformed MMVF can be safely recycled as secondary raw material (SRM). In this scenario, this study provides useful information for the optimization of the industrial annealing process aimed to attain a safe, recyclable product. The results of this work show that one of the high-temperature products of Cerafiber and Superwool is cristobalite which is classified as a carcinogenic. It was possible to define the temperature interval at which Cerafiber and Superwool fibers can be safely used as thermal insulators (e.g. insulators in tunnel and/or roller kilns, etc.). As cristobalite is formed in both synthetic fiber products at temperatures higher than 1200 degrees C, their use should be limited to devices operating at lower temperatures. Rock and Glass wool melt upon thermal treatment. As far as the industrial process of inertization is concerned, a maximum firing temperature of 1100 and 600 degrees C is required to melt Rock wool and Glass wool, respectively, with the high-temperature products that can be safely recycled as SRM. Recycling of these products in stoneware tile mixtures were subsequently attempted. The addition of 1-2 wt.% of the melts of Rock and Glass wool gave promising results in terms of viscous sintering reactions and resistance to staining with the only weak characteristic being the color properties of the fired bodies which tend to worsen.     

Effect of pre-heat treatment and cobalt doping of hydrargillite on the kinetics of the hydrargillite-corundum transformation in supercritical water fluid

We have studied the kinetics of corundum formation in supercritical water fluid from aluminum hydroxide (hydrargillite) and from the products of its thermal decomposition at 300°C over a period of 5 h. In all cases, the reaction involves the formation of boehmite, AlOOH, as an intermediate. The use of the product of the thermal decomposition of hydrargillite as a precursor considerably increases the reaction rate and reduces the induction period in comparison with the parent hydrargillite. Cobalt doping further increases the reaction rate and reduces the induction period. When the product of the thermal decomposition of hydrargillite is used as a precursor, the temperature dependence of the reaction rate constant shows Arrhenius behavior, whereas that for synthesis from uncalcined aluminum hydroxide has a more complex character.     

Studies on Mechanical, Friction, and Wear Characteristics of Kevlar and Glass Fiber-Reinforced Friction Materials

Asbestos possesses properties that are ideally suitable for use as a friction material in automotive and a number of other applications. Animal and human studies carried out since the early 1900s have established that asbestos is carcinogenic and that exposure to especially asbestos dust causes a large number of diseases. Realizing the health hazards posed by asbestos, many countries started phasing out asbestos from all asbestos-containing products since the 1980s. Some of them imposed a total ban in the 1990s on the use of asbestos-containing friction products. This situation forced many manufacturers to look for alternatives to asbestos. But the efforts have only been partly successful. The search is, therefore, still on to find suitable substitutes for asbestos. Though steel wool, Kevlar, glass, and a number of other mineral fibers have been tried out on an experimental basis over the last two decades, glass and Kevlar fibers, in particular, have shown promise as potential substitutes for asbestos. These days, therefore, studies on polymer-based friction materials reinforced with glass, Kevlar, and ceramic fibers are being pursued with much fervor. However, conflicting views are prevailing even today as to the suitability of asbestos-free composites for automotive applications and freedom from the concomitant health risks posed by them. In the present work, therefore, phenolic resin matrix samples reinforced with different amounts of glass and Kevlar fibers were produced and characterized for their mechanical, physical, friction, and wear properties to assess their suitability for light passenger car applications. The study establishes that composites based on glass and Kevlar fibers show good mechanical, physical, friction, and wear characteristics, enhancing thereby their suitability for automotive applications. The property improvements achieved are correlated to the composition, microstructure, and the changes taking place on the surface of the friction composites.     

Factors affecting the resistance of cementitious materials at high temperatures and medium[0] heating rates

The resistance of mortars made of dolomite and quartz aggregate with and without polypropylene fibers has been studied at a nominal heating rate of 30^∘C/min from room temperature up to 1000^∘C. It is demonstrated that the key parameters that affect the performance of plain mortars are volume instability, phase transformation, aggregate dissociation, and permeability. Experimental results point at the major role of aggregate type on mass loss, porosity, volume instability, microstructure, cracking pattern, and mechanical properties. Three thermal zones are identified; low (up to about 300^∘C), intermediate (about 300 to 600^∘C), and high (>600^∘C). It is shown that in the low thermal zone, the mechanical properties are about the same or better than those at room temperature. The intermediate thermal zone is characterized by a moderate decline of mechanical properties, whereas a rapid decline is registered in the high thermal zone. Explosive spalling due to pressure built-up of volatiles took place at temperatures over 200^∘C. Addition of polypropylene fibers prevents spalling due to the occurrence of porous and permeable interface between the fibers and the matrix rather than fiber shrinkage or melting. An erratum to this article can be found at     

热分解动力学在含能材料中的应用

文章主要介绍了热分解动力学在含能材料中的重要性,列举了热分解动力学的主要分析方法及几种常用的反应机理,并对其进行简要分析。热分析技术具有快捷简便、准确度高以及适用范围广的特点,在含能材料的热分解动力学中发挥重要作用。热分解动力学广泛应用于含能材料的动力学参数的求解、反应机理的推断以及动力学补偿效应的确定,为其有效使用寿命的预测以及安全性能的评定等提供科学依据。同时,热分析技术的自身完善以及与其他技术的联机使用将促进热分解动力学的不断发展。     

Kinetics of thermal decomposition of hydroxyapatite bioceramics

The mechanism and kinetics of thermal decomposition of injection moulded hydroxyapatite ceramics were studied over the temperature range of 1473–1758 K. At temperatures below 1473 K the sintering and transformation of hydroxyapatite to hydroxyoxyapatite proceeded to a conversion degree of 0.4 to 0.5. At temperatures between 1473 and 1758 K the hydroxyapatite was decomposed to -TCP, H₂O and CaO. The decomposition of HOA started on the surface of the HOA ceramics. The rate of increase in the thickness of the reaction products (-TCP) was described by the parabolic law. The kinetic analysis of the time dependence of HOA conversion to TCP by means of the J-M-A-J-K equation also showed that the thermal decomposition of HOA ceramics was controlled by diffusion of water from the reaction zone to the surface of the ceramic sample. The activation energy of the thermal decomposition of HOA ceramics amounted to 283.5 kJ/mol.     

Effect of content of Mg(NO3)2 x 6H2O on fabrication of alpha-alumina nanopowders by thermal decomposition of ammonium aluminum carbonate (AACH)

An alpha-Al2O3 and MgAl2O3 spinel phase doped alpha-Al2O3 nanopowders were fabricated by the thermal decomposition and synthetic of ammonium aluminum carbonate hydroxide (AACH). Crystallite size of 5 to 8 nm were fabricated when reaction temperature of AACH was low, 8 degrees C, and the highest [NH4+][AlO(OH)2-][HCO3] ionic concentration of pH 10 from the ammonium hydrogen carbonate (AHC) aqueous solution. The phase transformation of amorphous-s, theta-, alpha-Al2O3, MgAl2O3 spinel phases was examined at each temperature according to the amount of Mg(NO3)2 x 6H2O and AACH. A time-temperature-transformation (TTT) diagram for thermal decomposition in air was determined. Homogeneous, spherical alpha-Al2O3 nanopowders with a particle size of 60 nm were obtained by firing the crystallites, which had been synthesized from AACH at pH 10 and 8 degrees C, at 1050 degrees C for 6 h in air.     

Synthesis, characterization and properties of nitrogen-rich salts of trinitrophloroglucinol

Five different nitrogen-rich salts of trinitrophloroglucinol (H(3)TNPG) have been prepared by the reaction of ammonia, aminoguanidine (AG), carbohydrazide (CHZ), semicarbazide (SCZ) and 5-aminotetrazo (ATZ) with trinitrophloroglucinol in aqueous solution through the heating method of water bath, with the yield up to 80%. These salts were characterized by elemental analysis, FT-IR, DSC and TG-DTG techniques. Their melting temperature is consistent with the thermal decomposition temperature. Their thermal decomposition process and kinetic parameters from 323 to 673K were investigated under a linear heating rate by DSC. The thermal decomposition of these salts undergoes an intensive exothermic decomposition stage to evolve abundant gas products and the enthalpies of exothermic decomposition reaction are high. The tests of sensitivity properties show these salts are insensitivity. All the properties of five nitrogen-rich salts appeared to depend on molecule structures and interconnection. It can be concluded that the five compounds are worthy of further in-depth studies as the gas-generating composition, emission reagents and propellants.