Jaleh Khorami

Comparison of attapulgites from different sources using TG/DTG and FTIR

Abstract Several samples of attapulgites from different sources were analyzed by TG/DTG and FTIR. The thermal behaviour of these clay minerals varies within certain limits according to their origin. For some attapulgite samples, dehydration (bound water) and dehydroxylation occur within the same range of temperature. These differences in thermal behaviour could be related to the various crystal structures, and/or to the chemical compositions of these minerals. We have also observed that associated carbonates in attapulgites decompose in the same temperature zone as the dehydroxylation step. These results could explain the disagreements found in the literature with respect to the quantity of constituent water when comparing the chemical composition of different attapulgite clay minerals.

The adsorption of polyaromatic hydrocarbons on natural and chemically modified asbestos fibers.

Many reports indicate that the carcinogenic (genotoxic) potential of benzo[a]pyrene (B[a]P) may be enhanced several-fold by the promoter (epigenetic) effect of asbestos particles. This promoting effect could be related to the fact that when B[a]P is adsorbed onto the particles, there is a resulting enhanced transport and uptake of the carcinogen into microsomial membranes. These in vitro data bear relevance to the epidemiological studies which indicate an association between exposure to inhaled asbestos dusts and the high incidence of pulmonary cancers in smokers. Using HPLC, it has been observed that B[a]P has great affinity for natural asbestos fibers, and that chemical modification of natural chrysotile with POCl3 results in the complete loss of this adsorption potential of chrysotile for benzo[a]pyrene.

Combined thermogravimetry and fourier transform infrared spectroscopy techniques for gas evolution analysis

Abstract The usefulness of thermogravimetry has been amply demonstrated for a wide variety of material analysis applications. In many instances, however, additional information is required for adequate characterization of the sample and its thermal decomposition behaviour. In this respect, the analysis of evolved gases, or condensed liquids, has proven a highly useful approach. Among the various physical methods used for analysis of the thermal degradation products, infrared spectroscopy has often been found very powerful, being versatile, rapid and widely accessible. In this study, we report a simple new approach in which the evolved gases and condensed liquids from the thermal decomposition of various products are recuperated in an infrared gas cell and on a PVC membrane filter, respectively. The gaseous components were analysed by transmission FT-IR, and the condensed liquid products were examined directly on the PVC membrane by FT-IR in the internal reflexion mode. The technique was used, for example, to examine the pyrolysis products (gases and liquid) of Koberit, a proposed substitute for asbestos. The method was also applied to the study of chemically derivatized asbestos materials in an attempt to unravel the surface chemical modifications.

Microchemical and microstructural investigations of degradation in asbestos-cement sheet

The physical and chemical transformations occurring in asbestos cement (A/C) sheet following a two-year natural exposure to sulfate rich water in a cooling tower have been investigated using a combination of analytical and microstructural techniques. The investigation was conducted on a reference A/C sheet, specimens of the partially degraded A/C sheet and chrysotile fibers recovered from the latter. The methods employed included X-ray diffraction, scanning electron microscopy and EDXA, thermogravimetry, infrared spectroscopy and evolved gas analysis during thermal decomposition. Analysis of the combined data conclusively show that the primary cause of degradation and delamination of the A/C sheet is the formation of gypsum (CaSO4)·2H2O crystals which is accompanied by substantial volume expansion. Apparently, carbonation, yielding calcite and/or vaterite crystals, is a secondary degradation mechanism.

Induced conversion of aluminium silicate fibers into mullite and cristobalite by elevated temperatures: a comparative study on two commercial products

Abstract Aluminium silicate fibers (ALF) are used in a variety of industrial products, including as a substitute for asbestos in insulation materials. Although many studies evaluating the thermal resistance of these compounds have been made, conflicting results were sometimes obtained on the conversion of these amorphous silicates into mullite and cristobalite. For our study, two types of ALF were selected: type I (Triton Kaowool®, Normal grade) and type II (Fiberfrax®; High Specific Area “HSA” grade). These two silicate fibers differ mainly in the percentage of impurities such as iron, titanium, sodium and potassium oxides. As observed by X-ray diffraction, differential thermal analysis and infrared spectroscopy, our results show that both types of ALF are transformed into mullite at 1016°C and 990°C respectively for the type I and type II fibers. With the type I ALF, when heated at 1050°C, the quantity of mullite increased with time. No trace of cristobalite was detected even after a 4 weeks heat treatment at 1050°C. However, for the type II ALF which are richer in oxide impurities, two conversion steps were observed: (a) as with the type I fibers, the quantity of mullite increased with time; (b) after 64 h at 1050°C, the second crystallization step into cristobalite started and increased after the 4 weeks heat treatment. These results indicate that the level of oxide impurities can accelerate the conversion of mullite into cristobalite. Considering the known danger associated with the inhalation of cristobalite, these finding indicate that different ALF might have new biological activities when subjected to elevated temperatures for long periods of times.

Usefulness of Fourier transform infrared spectroscopy in the analysis of evolved gas from the thermogravimetric technique

The usefulness of thermogravimetry has been amply demonstrated for a wide variety of analytical applications. However, in many instances, additional information is required for adequate characterization of the sample and its thermal decomposition behavior. In this respect, the analyses of evolved gases or condensed liquids has been proven a highly useful approach. Among the various physical methods used for the analyses of thermal degradation products, infrared spectroscopy has often been found very powerful, because it is versatile, rapid, and accessible. In this study, we report a simple and new approach to recover evolved gases and condensed liquids after the thermal degradation of fibrous organic materials, using an infrared gas cell and a polyvinyl chloride (PVC) membrane filter, respectively. The gaseous components were analyzed by transmission Fourier transform infrared (FTIR) and the condensed liquids products were examined directly on the PVC membrane by FTIR in the internal mode. For that purpose, several types of synthetic fibers have been selected: polyvinyl alcohol, polyacrylonitrile, polyaramids, and polyolefins. The decomposition products from the combustion of the organic fibers, both in the presence and absence of oxygen, are discussed.

Physicochemical characterization of asbestos and attapulgite mineral fibers before and after treatment with phosphorus oxychloride

Among the hydrous silicates belonging to the serpentine, amphibole, and clay mineral families, chrysotile, crocidolite and attapulgite fibers reacted most strongly with phosphorus oxychloride. While the reactivity of crocidolite was linked mainly to the sodium cations of its structure, the reactivities of chrysotile and attapulgite correlated best with their high hydroxyl group content. The TG/DTG curves of chrysotile and attapulgite revealed significant modifications of their dehydroxylation profiles. IR spectra and specific surface measurements confirmed that, most probably, the phosphorylation process created: (a) a phosphorus coating at the surface of the chrysotile fibers, and (b) an obstruction of the pores by phosphorus compounds with the attapulgite fibers.

Etudes des propriétés adsorbantes des fibres d'amiante modifiées et de fibres proposées comme substitut à l'amiante par chromatographie en phase gazeuse

A study, by vapor phase chromatography, of the adsorption isotherms of benzene on raw and modified asbestos fibers as well as on fibers proposed as substitutes for asbestos shows that there is a marked difference in the behaviour of the various fibers examined. A comparison of the adsorbing power of raw and phosphorylated asbestos fibers, as well as asbestos fibers heated to 700 °C, has been made regarding their behaviour toward solutes bearing various functional groups, and it has shown the existence of physical adsorption as well as chemisorption. The presence of hydroxyl groups in the surface of the asbestos fibers favors the adsorption of organic molecules through hydrogen bonding. [Journal translation]