Presence Of Talc Research Articles

Metamorphic peak conditions of eclogites in the Tauern Window, Eastern Alps, Austria: Thermobarometry of the assemblage garnet + omphacite + phengite + kyanite + quartz

Metamorphic peak P– T conditions of five kyanite eclogites from the Tauern Window, Austria, are evaluated on the basis of recent calibrations of the assemblage garnet + omphacite + phengite + kyanite + quartz. Results are about 25 kbar, 630 °C according to the dataset of Holland and Powell [Holland, T.J.B., Powell, R., 1998. An internally consistent thermodynamic data set for phases of petrological interest. Journal of Metamorphic Geology 16, 309–343 (updated 2002)]. Mostly higher P– T values are calculated with the calibrations of Krogh Ravna and Terry [Krogh Ravna, E.J., Terry, M.P., 2004. Geothermobarometry of UHP and HP eclogites and schists—an evaluation of equilibria among garnet–clinopyroxene–kyanite–phengitecoesite/quartz. Journal of Metamorphic Geology 22, 579–592] and Brandelik and Massonne [Brandelik, A., Massonne, H.-J., 2004. PTGIBBS—an EXCEL Visual Basic program for computing and visualizing thermodynamic functions and equilibria of rock forming minerals. Computers and Geosciences 30, 909–923], in part already in the stability field of coesite. However, no indications for this phase are evident from the Tauern samples. The presence of talc is consistent with these P– T values and high H 2O activities. In contrast, the stability limits of paragonite and zoisite are situated at lower pressure and suggest a later formation during the decompression stage. THERMOCALC pseudosections in the NCFMASH system are constructed with the incorporation of fractional crystallization of garnet. Calculated garnet zonations are in better agreement with the observed compositions at peak pressures of about 25 kbar than results at lower pressures. This is also consistent with values from thermobarometry obtained with the same program.

Liquid crystalline adhesives for polypropylene joints

This study was devoted to the investigation of the adhesion of epoxy resins to polypropylene adherends. In particular, the study was carried out as follows: synthesis of both a liquid crystalline (LC) and a bisphenol-A-based resin, their characterization and their further evaluation as adhesives for polypropylene adherends. This was done in order to evaluate the difference between an LC epoxy resin and an isotropic one in adhesive applications. The adherends chosen were neat polypropylene (PP) and polypropylene reinforced with 20 and 40 wt% talc (PP20 and PP40, respectively). The effect of two different pre-treatments (simple degreasing and acid etching) on the polypropylene adherends was also evaluated. It was shown that the adhesion strength of the liquid crystalline adhesive was higher compared to that of the isotropic one. The higher adhesion was related to the extra ductility demonstrated by the LC epoxy resin, which was due to its particular microstructure. Moreover, the acid etching pre-treatment performed on polypropylene adherends prior to bonding improved the adhesion at the interface with the resin. The increased stiffness of the adherends due to the presence of talc turned out to be beneficial to obtain more resistant joints.

Talc as nucleating agent of polypropylene: morphology induced by lamellar particles addition and interface mineral-matrix modelization

The efficiency of talc used as nucleating agent (0.5% by weight) in polypropylene (PP) was determined taking into account the particle size d50, particle morphology and BET specific surface areas. These findings were compared to a mineral with similar properties, pyrophyllite. Talc samples with the finest particle sizes induce a significant increase in the starting crystallization temperature of PP and irrespective of the particle size d50, pyrophyllite was found to be less efficient than talc. X-Ray results show that PP oriented crystallization due to talc or pyrophyllite addition, corresponds to an epitaxial growth whereby the mineral c*-axis is merged with the PP b*-axis. Microscopic observations revealed that in the presence of talc, nuclei density of PP increased strongly. In addition, a large number of nuclei was observed to appear everywhere on the talc surface. A PP-talc interface model is proposed by matching the (001) talc plane and the (010) PP plane. In this model, 3% of PP cell accommodation on talc is necessary with a 15° angle between PP chains elongation and the crystallographic directions of talc. Hexagonal rings on talc surface are believed to represent hydrogen bonds with PP methyl groupings. This fine structure relation between talc and PP is discussed, and is used to characterize the differences observed between the efficiency of talc and that of pyrophyllite.

Particulate composition and origin of suspended sediment in the R. Don, Aberdeenshire, UK

Characterising the nature and origin of suspended particulate and colloidal matter in surface waters is a necessary first step in determining the role of these materials in the transport of pollutants. With this aim in mind, samples of suspended sediment were collected from the R. Don, Scotland, and analysed by a combination of X-ray diffraction (XRD) and vertically attenuated infrared spectroscopy (VATIR). Additionally, the carbon and nitrogen contents of the sediment were measured. Samples were collected at eight sites along the river from the headwaters to the mouth, twice during periods of base flow, and once during a storm. During the base flows, the amount of suspended solids was typically no more than 1–10 mg l−1, whereas the high flow samples contained up to 150 mg l−1. XRD showed that the crystalline component of the high flow samples consisted of the clay minerals illite, chlorite, kaolin, hydroxy-interlayered vermiculite, and a 10/14 Å regularly interstratified mica/vermiculite. Non-clay components included quartz, feldspars, amphibole and goethite. Kaolin progressively increased in relative abundance downstream. The clay mineralogy of base flow samples was more or less identical to high flow samples but the non-clay components were reduced and, additionally, talc and calcite were present. The identification of many of the crystalline components was confirmed by VATIR, and amorphous silica was identified, particularly in base flow samples. Organic components were identified as wax, protein, and humate/fulvate. Proportionally more protein and wax components relative to silicates occurred in base flow samples, whereas the humate/fulvate component was most clearly identified in samples from the storm. Organic matter contents ranged from approximately 24% during base flow to 13% during the storm, whilst the C/N ratio showed a progressive decrease downstream, irrespective of flow conditions. Both the characteristics of the mineralogy and the organic matter suggested that topsoils were the primary source of the suspended sediment in the R. Don. However, the presence of talc and calcite were believed to fingerprint ground water sources, which together with the in-stream production of diatoms, may have accounted for a significant mass fraction of the suspended particulate matter during base flows.

Magnesium hydroxide/zinc borate/talc compositions as flame‐retardants in EVA copolymer

The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/talc) has been investigated. The release of water from Mg(OH)2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH)2, appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH)2 loading in ternary compositions. © 2000 Society of Chemical Industry

Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer

The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/talc) has been investigated. The release of water from Mg(OH)2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH)2, appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH)2 loading in ternary compositions. © 2000 Society of Chemical Industry

The effect of talc on the crystallization of isotactic polypropylene

Isotactic polypropylene (iPP) has been crystallized in the presence of talc under the quiescent state and shear flow of injection molding. The resulting morphology has been investigated by means of polarizing microscopy, transmission electron microscopy, and wide angle X-ray diffraction. In the quiescent state, the iPP lamellae grew from the surface of talc and the transcrystalline region was formed at the interface between iPP melt and the talc. The nucleation of iPP was very frequent on the cleavage plane of talc. The X-ray diffraction pattern of the transcrystal showed a*-axis orientation to the crystal growing direction. In injection-molded samples of the talc-filled iPP, the morphology of lamella growing from talc appeared as same as that of the transcrystal. However, the crystalline orientation of injection-molded talc-filled iPP, in which the b axis was oriented to the thickness direction and the a* and the c axis was oriented to the flow direction, was quite different from that of the transcrystal. This b-axis orientation results from the orientation of the plate plane of talc, which induces the nucleation and the crystallization under shear flow. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1693–1703, 2001

Interfacial studies of crosslinked urethanes: Part IV. Substrate effect on film formation in polyester waterborne polyurethanes

These studies examine the effect of substrate surface tension on crosslinking reactions in water-borne polyurethanes (PUR) applied to tin-plated steel, steel, polypropylene (PP), thermoplastic olefin (TPO), and glass. The results show that, relative to tin-plated steel, removal of tin-plating from a steel substrate increases isocyanate (NCO) consumption by 42% near the film-substrate (F-S) interface. When PUR is allowed to crosslink on steel, PP, TPO, and glass, the NCO concentration is greater at the film-air (F-A) interface. Furthermore, crosslinking reactions result in a greater amount of urea-hydrogen bonded species near the F-S interface for all substrates. While an increase of substrate surface tension decreases the amount of urea-hydrogen bonded carbonyl groups near the F-S interface, TPO was found to exhibit different behavior due to talc stratification near the surface. In this case, the presence of talc in WB-PUR coatings or thermoplastic substrates decreases the amount of hydrogen-bonded species and increases NCO consumption.

Chemical and mineralogical characterization of soils derived from ophites in mediterranean climate (North of Spain)

We have studied the chemical and mineralogical characteristics of ophites located in a diapiric formation in Burgos (North of Spain), and the soils derived from them. The ophites studied show mineralogical uniformity. Their main components are clinopyroxenes, plagioclases, biotite, and olivine. Generally, they show deuteric alteration mainly affecting the olivine. The presence of talc is attributed to an outpouring of basic magma (ophite) in an evapotiric environment of Keuper facies. Chemically, they are basic rocks, of basaltic nature, poor in silicon dioxide (SiO2) and rich in magnesium oxide (MgO) and ferric oxides (Fe2O3). The weathering of the ophites results in clay consisting of chlorite, vermiculite, and interlayer chlorite‐vermiculite‐smectite inherited from original material. Small amount of extractable silica (Si), aluminum (Al), and iron (Fe) show the scarcity of amorphous material attributed to the high content in organic carbon (C) which prevents formation of allophane, and to the xeric moisture regime of soils in this location.

Crystallization kinetics of poly(L-lactide-co-meso-lactide)

The crystallization kinetics of poly(L-lactide-co-meso-lactide) were determined over a range of 0% to 9% mesolactide. The kinetics were fit to the nonlinear Avrami equation and then to the Hoffman–Lauritzen equation modified for optical copolymers. The theory was found to fit the data well. The crystallization half-time was found to increase about 40% for every 1 wt % meso-lactide in the polymerization mixture. The change in crystallization rate is driven mainly by the reduction in melting point for the copolymers. The copolymer crystallization kinetics were also determined in the presence of talc, a nucleating agent for polylactide. The theory again fit the data well, using the same growth parameters and accounting for the talc only through the nucleation density term. © 1996 John Wiley & Sons, Inc.

Occurrence of talc in soils with high iron content from the south-west of Spain

The mineralogy of the clay fractions of 2 soil profiles classified as an Alfic Dystric Eutrochrept (Soil I) and a Xerochreptic Haploxeralf (Soil II) has been determined. A notable feature of these soils is the presence of talc and the high iron content as goethite, hematite, lepidocrocite, and maghemite. Talc was the most abundant non-iron mineral of the clay fraction of Soil II. In Soil I, talc occurs as a residual phase from the parent material with its persistence in the profile aided by coatings of iron oxides, which inhibit further weathering. In these soils there is a high proportion of goethite accompanied by hematite. In Soil I the proportion of iron oxides changes within the profile. Another notable feature of this profile is the presence of maghemite in the upper horizons where this is the predominant iron oxide mineral.

Removal of phenol from coupling of talc and peroxidase. Application for depollution of waste water containing phenolic compounds

AbstractThe degradation of phenol by a combination of horseradish peroxidase/hydrogen peroxide in the presence of talc, a natural abundant and low cost mineral, was investigated. Adsorption of the reaction products on the talc effectively protected the biocatalyst against contamination by oxidative products, thereby prolonging its catalytic action and leading to almost complete elimination of phenols in aqueous media. Suitable conditions for depollution of waste water containing phenolic substances were developed after optimization of various parameters (type and amount of talc, reaction duration).

Talc: an indicator of recent anthropogenic activity

AbstractTalc is very often an important constituent of suspended matter in marine and lacustrine environments but is rarely detected in sediments. The presence of talc is usually attributed to its industrial and agricultural application. Its recent anthropogenic use, long residence time in the water column due to its small particle size, transport by surface currents and winds, and its tendency to resuspension from the sediment are factors which contribute to the preferential detection of talc in suspended matter.

Sedimentalogical and stratigraphic analyses of the Lagoa Feia Formation, rift phase of Campos Basin, offshore Brazil

The Campos Basin is located offshore the State of Rio de Janeiro along the Southeast Brazilian Continental Margin. It comprises an approximate area of 100,00 km 2 up to 3,400 m Isobath. The Lagoa Feia Formation comprises mainly the rift phase sediments of the basin. Intense tectonic activity generated normal faulting with a preferential northeastern direction and great vertical displacement. Large basalt flows, with ages varying between 120 Ma and 130 Ma, represent the onset of the rift system forming the basement upon which Lagoa Feia formation sediments were deposited. The lack of marine fossils indicates non-marine depositional environments for this formation. The formation can be subdivided into four deposition sequences: Basal Clastic Sequence, Talc-Srevensltic Sequence, Coquinas Sequence, and Clastic-Evaporitic Sequence. Sediments of the three basal sequences are indicative of typical lacustrine environments. The presence of talc and stevensite clay-minerals, and the diagenetic assemblage of the Coquinas Sequence suggest that this lake had alkaline brackish to saline waters. Alluvial fans and their associated facies deve loped on the western border and adjacent to other highs of the basin. Sand flat and mud flat facies compose the marginal portions of the lake, while in deeper waters hydrocarbon generating shales were deposited. The Coquinas Sequence represents an expressive amount of pelecipod calcirudites, and calcarenites deposits, which now are important hydrocarbon reservoirs. An important and regionally widespread erosional unconformity separates the Coquinas Sequence of the overlying Clastic-Evaporitic Sequence, which is characterized by shallow water sedimentation defined through stromatolitic and nodular limestones associated with extensive deposition of alluvial fans. The top of the Lagoa Feia Formation is marked by a thick evaporitic layer deposited under hot arid to semi-arid climate and relative ly stable tectonic conditions, connected with the ocean at the south.

Redox polymerization of methyl acrylate in absence and in presence of some inorganic silicon compounds

AbstractThe polymerization of methyl acrylate in water using ammonium, potassium, and sodium persulphates with sodium bisulphite as redox initiation system was studied. It has been found that ammonium persulphate had the least activity on the rate of polymerization and resulted in the formation of the highest viscosity average molecular weights for the obtained polymers. The rate of polymerization was found to increase with sodium bisulphite concentration in the redox system, but the viscosity average molecular weights were found to decrease with the increase of sodium bisulphite concentration. Addition of some inorganic silicon compounds (containing the same weight equivalent of SiO2) resulted in increasing the rate of polymerization and decreasing the induction period. The average molecular weights obtained in presence of china clay were found to be the highest and those obtained in presence of talc were the least.

Structure and properties of talc‐filled polyethylene and nylon 6 films

AbstractWater vapor transmission rates can be reduced by as much as 50% in polyethylene by using talc as a filler. The oxygen permeability as well as water vapor transmission rates are similarly reduced by talc in nylon 6 films. The films show low elongation at break and reduced breaking strenth in the presence of talc. The yield strength and the modulus increase with the amount of talc, whereas the elongation at yield decreases. The mechanical and the barrier properties change with the size of the filler, the smaller size being more favorable. Talc probably acts as a nucleating agent and increases the crystallinity in polyethylene and nylon. Polyethylene unit cells in talc‐filled films are oriented with the (110) planes parallel to the (001) planes of talc. Nylon 6 crystals, which are in the α form in the presence of talc, are oriented with the hydrogen bonded sheets, the (002) planes, parallel to the (001) planes of talc. In both polyethylene and nylon 6, talc is oriented with the c‐axis normal to the plane of the film, i.e., with the broad faces of talc flakes in the plane of the film. Lattice matching between the polymer and talc suggests epitaxy to be a contributing factor for the observed orientation of polyethylene and nylon 6 crystals.

Surface powders on surgical gloves.

Four different instrumental techniques were used to analyze the microscopic particles on the patient-contact surfaces of a variety of surgical gloves. The presence of talc was confirmed on most, but not all, gloves tested. The presence of talc, when it occurred, seemed to be due to design by the manufacturer rather than by accident, and it was predominantly on the patient-contact surfaces. The intentional inclusion of talc on modern surgical gloves has been unexpected up to now. A washing and wiping procedure showed that talc was more difficult to remove than starch-based powder. A powder-stripping procedure showed that powder that resisted removal by washing could be mechanically dislodged. Thus, a shedding hazard might exist during a surgical procedure even if the glove surfaces have been washed and wiped.

The mineralogy and origin of the talc deposits near Winterboro, Alabama

The north and south talc bodies near Winterboro, Alabama, are associated with Cambrian dolomite. The north body lies like a blanket in residual clay which overlies the dolomite bedrock, and the lense-shaped south body is oriented along a fracture in the dolomite with a strike of N 65 degrees W and a dip of 43 degrees NE. The nature and distribution of insoluble residues in the dolomite as well as textural and field evidence suggest that hydrothermal solutions and metasomatic processes produced talc in and near fractures in the dolomite. These solutions are apparently also responsible for the production of chlorite in the dolomite and in associated shales and sandstones, or chlorite metasomatites, beneath the south body. Weathering exposed the north body and part of the south body and produced brecciation and silicification as well as a residuum of talc and chlorite in the vicinity of the orebodies.Insoluble residues in dolomite obtained from diamond drill cores suggest that a mineralized halo of talc and chlorite extends at least 200 feet from the main orebody, with the talc to chlorite ratio increasing as the talc body is approached. This feature, the presence of talc in the residual soils overlying the dolomite, and the associated chlorite and chlorite metasomatites may be useful in prospecting for Winterboro-type talc deposits.

Drug permeation through membranes V: Interaction of diazepam with common excipients

The effects of common tablet excipients on the permeation of diazepam through polydimethylsiloxane membranes and on the turnover time of goldfish were studied. The permeability coefficient decreased and the turnover time increased in the presence of talc, polysorbate 80, and, possibly, fumed silicon dioxide, but these parameters were unaffected by lactose, microcrystalline cellulose, and starch.