The effect of fiber coating on the tensile properties of ionomer-based composites

Asbestos fibers, of the chrysotile variety, were coated with a thin polyamide film by an in situ polycondensation technique. Ionomer-based composites were prepared containing the so-modified asbestos fibers in a random in-plane orientation; results of testing the tensile properties of these asbestos/polyamide/ionomer composites are presented. Parameters investigated comprise the asbestos content in the composite and the polyamide content deposited on asbestos. A significant improvement in the tensile performance was established, especially at the intermediate polyamide content of 3.4 phr. The behavior is discussed in terms of possible interactions between the phases present in the composite material.     

Catalysis of hydrosilylation. XV. A poly(phosphino-organosiloxanyl)silicate-supported rhodium(I) catalyst for gas-phase hydrosilylation of acetylene

Wilkinson's complex [RhCl(PPh₃)₃], anchored to phosphino-organosiloxane macromolecules grafted onto chrysotile asbestos, appeared to be an unusually effective and selective catalyst for the synthesis of vinylsilanes via gas-phase hydrosilylation of acetylene, particularly by methyldichlorosilane in a continuous-flow microreactor as well as in a laboratory reactor. Catalytic and kinetic parameters show an advantage for the catalyst based on the chrysotile-polyorganosiloxane support (catalyst CHR–Rh) over the phosphinated silica (catalyst A).     

Nucleation and Growth of Chrysotile Nanotubes in H2SiO3/MgCl2/NaOH Medium at 90 to 300 °C

Herein, we report new insights into the nucleation and growth processes of chrysotile nanotubes by using batch and semi‐continuous experiments. For the synthesis of this highly carcinogenic material, the influences of temperature (90, 200, and 300 °C), Si/Mg molar ratio, and reaction time were investigated. From the semi‐continuous experiments (i.e., sampling of the reacting suspension over time) and solid‐state characterization of the collected samples by XRPD, TGA, FTIR spectroscopy, and FESEM, three main reaction steps were identified for chrysotile nucleation and growth at 300 °C: 1) formation of the proto‐serpentine precursor within the first 2 h of the reaction, accompanied by the formation of brucite and residual silica gel; 2) spontaneous nucleation and growth of chrysotile between about 3 and 8 h reaction time, through a progressive dissolution of the proto‐serpentine, brucite, and residual silica gel; and 3) Ostwald ripening growth of chrysotile from 8 to 30 h reaction time, as attested to by BET and FESEM measurements. Complementary results from batch experiments confirmed a significant influence of the reaction temperature on the kinetics of chrysotile formation. However, FESEM observations revealed some formation of chrysotile nanotubes at low temperatures (90 °C) after 14 days of reaction. Finally, doubling the Si/Mg molar ratio promoted the precipitation of pure smectite (stevensite‐type) under the same P (8.2 MPa)/T (300 °C)/pH (13.5) conditions.     

Synthesis of Fe‐doped chrysotile and characterization of the resulting chrysotile fibers

This study describes the formation of Fe‐doped chrysotile fibers with partial and total substitution of Mg by Fe. Syntheses were carried out with various starting mixtures (oxides, pure synthetic forsterite) in an externally heated pressure vessel in controlled hydrothermal conditions: temperature, 270 – 400 °C; pressure, 0.5 – 2 kbar; duration of treatment 160 – 480 hours. Pure synthetic forsterite was prepared by the flux growth technique. The starting material and run products were characterized by X‐ray powder diffraction (XRPD), scanning and transmission electron microscopies combined with energy‐dispersive spectrometry (SEM‐EDS and TEM‐EDS), differential scanning calorimetry (DSC) and thermogravimetry (TG). Variations observed in abundance and size of Fe‐doped chrysotile fibers were attributed to different experimental conditions for their synthesis. However, morphological shape turned out to depend on the starting mixtures used. Since natural samples are often difficult to obtain in a sufficiently pure state, these synthetic and well‐characterized Fe‐doped chrysotile fibers can be used for better understanding of the mechanisms involved in asbestos toxicity, as well as of the role of Fe in diseases induced by asbestos phases. These synthetic Fe‐doped chrysotile fibers, together with non‐toxicity testing, may also have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

纤蛇纹石的水热生长机制研究

以氧化镁和二氧化硅为原料,采用水热法在不同反应时间下合成了一系列纤蛇纹石纳米管.利用X-射线衍射(XRD)、红外光谱(IR)、扫描电镜(SEM)、高分辨透射电镜(TEM)等手段研究了纤蛇纹石晶体生长和晶体结构随反应时间的变化过程.X-射线衍射和红外光谱分析表明:随着反应时间的增加所得到的纤蛇纹石样品结晶逐渐完善、卷曲程度逐渐增大;电镜分析表明:获得的纳米管的外径和内径分别为15～40 nm和6～9 nm,长度为50～300 nm,出现了双层管式结构.根据实验结果,结合负离子多面体配位生长理论对纤蛇纹石的生长机理研究表明,纤蛇纹石是由片状逐渐卷曲成管状的.     

水热法合成掺杂铁离子纤蛇纹石纳米管

本工作研究了在水热条件下纤蛇纹石纳米管的人工合成，通过掺杂Fe³⁺离子替代了纤蛇纹石晶格中的Mg²⁺离子。采用X-射线衍射、扫描电镜、透射电镜、红外光谱和电子自旋共振谱等手段研究了掺杂离子对纤蛇纹石晶体生长和晶体结构的影响。X-射线衍射分析表明随着掺杂Fe³⁺离子量的增加所得到的纤蛇纹石样品其晶胞参数b值逐渐减小。电子自旋共振谱、红外光谱分析表明Fe³⁺离子部分替代了Mg²⁺离子和Si⁴⁺离子进入纤蛇纹石的八面体和四面体结构单元。透射电镜研究表明掺杂前后所得到的纤蛇纹石内径分别为6～8 nm和8～15 nm。     

Facile synthesis and characterization of Chrysotile/SnO2 nanocomposite for enhanced photocatalytic properties

SnO₂ nanocrystals grown on chrysotile surfaces could be facilely synthesized in large quantities through a direct precipitation process coupled with a calcination treatment. The as-synthesized chrysotile/SnO₂ nanocomposites showed a smaller band gap energy (2.88 ev) and relatively strong light absorption than the individually dispersed SnO₂ nanocrystals. Due to the narrow gap and chemical passivation aroused by inherently negative charges on the surface of chrysotile, chrysotile/SnO₂ nanocomposite was endowed with superior performance to chrysotile nanotube and SnO₂ nanocrystals.     

Raman spectroscopy of the nickel silicate mineral pecoraite—an analogue of chrysotile (asbestos)

The molecular structure of the mineral pecoraite, the nickel analogue of chrysotile of formula Ni₃Si₂O₅(OH)₄, was analysed by a combination of Raman and infrared spectroscopies. A comparison is made with the spectra of the minerals nepouite and chrysotile and a synthetic pecoraite. Pecoraite is characterised by OH stretching vibrations at 3645 and 3683 cm⁻¹ attributed to the inner and inner surface hydroxyl stretching vibrations. Intense infrared bands at around 3288 and 3425 cm⁻¹ are assigned to the stretching vibrations of water strongly hydrogen‐bonded to the surface of the pecoraite. The asbestos‐like mineral is characterised by SiO stretching vibrations at 979, 1075, 1128 and 1384 cm⁻¹, OSiO chain vibrations at 616 and 761 cm⁻¹ and Ni O(H) vibrations at 397 and 451 cm⁻¹. Copyright © 2008 John Wiley & Sons, Ltd.     

Tubular-shaped stoichiometric chrysotile nanocrystals

Stoichiometric chrysotile tubular nanocrystals have been synthesized as possible starting materials for applications toward nanotechnology, and as a standard reference sample for the investigation of the molecular interactions between chrysotile, the most utilized asbestos, and biological systems. Chrysotile nanocrystals have been synthesized under controlled hydrothermal conditions, and have been characterized by chemical, morphological, structural, spectroscopic and microcalorimetric analyses. They show a constant "cylinder-in-cylinder" morphology constituted by two or three concentric subunits. Each single nanocrystal has a tubular shape of about 49+/-1 nm in outer maximum diameter, and a hollow core of about 7+/-1 nm. Structural investigation carried out on an X-ray powder pattern allowed to improve the structural model proposed for chrysotile mineral samples. Synthetic chrysotile crystallizes in the monoclinic Cc space group with a=0.5340(1) nm, b=0.9241(1) nm, and c=1.4689(2) nm, beta=93.66(3) degrees.     

Interaction of bovine serum albumin with chrysotile: spectroscopic and morphological studies

The biodurability of chrysotile fibers, which is related to their cytotoxicity and mutagenic responses, is strongly affected by the surface chemical adsorption of biological molecules. Natural chrysotile is a heterogeneous material in both structure and composition. The availability of synthetic stoichiometric chrysotile of constant structure and uniform morphology has allowed us to investigate its interaction with bovine serum albumin (BSA). By using transmission electron microscopy (TEM) and atomic force microscopy (AFM), we have obtained the first morphological evidence of albumin adsorption onto chrysotile nanocrystals. FTIR spectroscopy was used to quantify modifications of BSA secondary structure that were induced by the surface interaction. The protein transition to beta-turns allows a stronger interaction between the protein hydrophilic side-chains and the charged asbestos surface, which is consistent with hydrogen bonds involving the superficial OH groups. Synthetic stoichiometric chrysotile nanocrystals were shown to be an ideal reference standard with which to study the interaction of asbestos fibers with biological systems, in order to elucidate the chemical mechanisms of asbestos toxicity.