29 research outputs found

    Petrology and origin of the Lar igneous complex of the Sistan suture zone, Iran

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    The Oligocene Lar igneous complex is located in the Sistan suture zone of Iran, being emplaced in Paleocene to Eocene flysch-type rocks. This complex includes mainly intermediate K-rich volcanic (trachyte, latite and andesite) and plutonic (syenite and monzonite) rocks that belong to shoshonitic magma. The geochemical characteristics of the Lar igneous complex, such as an enrichment of LREE and LILE relative to HREE and HFSE, respectively, a negative anomaly of Ti, Ba and Nb and a positive anomaly of Rb and Th are similar to those of arc-type igneous rocks. Tectonic discrimination diagrams also show that rocks of the Lar igneous complex fall within the arc-related and post-collisional fields and K-enrichment of these rocks confirm the post-collisional setting. Based on geochemical features, the Lar igneous complex magma was derived from partial melting of a phlogopite-bearing, enriched and metasomatised lithospheric mantle source and the magma was affected by some evolutionary processes like fractional crystallisation and crustal contamination

    Achieving high thermal conductivity in epoxy composites: Effect of boron nitride particle size and matrix-filler interface

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    For the thermal management of high watt density circuit layers, it is common to use a filled epoxy system to provide an electrically insulating but thermally conducting bond to a metal substrate. An epoxy-thiol system filled with boron nitride (BN), in the form of 2, 30 and 180 ”m platelets, has been investigated with a view to achieving enhanced thermal conductivity. The effect of BN content on the cure reaction kinetics has been studied by differential scanning calorimetry and the thermal conductivity of the cured samples has been measured by the Transient Hot Bridge method. The heat of reaction and the glass transition temperature of the fully cured samples are both independent of the BN content, but the cure reaction kinetics is systematically affected by both BN content and particle size. These results can be correlated with the thermal conductivity of the cured systems, which is found to increase with both BN content and particle size. For a given BN content, the thermal conductivity found here is significantly higher than most others reported in the literature; this effect is attributed to a Lewis acid-base interaction between filler and matrix.Peer ReviewedPostprint (published version

    Recyclable dual-curing thiol-isocyanate-epoxy vitrimers with sequential relaxation profiles

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    Two series of poly(thiourethane)s-poly(thiol-epoxy) hybrids were prepared from dual-curing, stoichiometric thiol:isocyanate:epoxy mixtures. 1-methylimidazole (MI) was used as initiator for the thiol-isocyanate and thiol-epoxy curing reactions. A salt of tetraphenylborate derived from highly basic amine 1,5,7 triazabicyclo [4,4,0]dec-5-ene (TBD) was used as catalyst for the activation of bond exchange reactions. The curing kinetics and the glass transition temperature (Tg) of the samples were studied by differential scanning calorimetry (DSC). Thermal stability was characterized by thermogravimetric analysis (TGA). Stress relaxation dynamics related to the bond exchange reactions were studied by dynamic mechanical analysis (DMA). Recyclability of the fully cured samples according to the DMA results was carried out by hot-pressing at elevated temperatures. The results show that the curing process takes place in a controlled and sequential way: the thiol-isocyanate reaction takes place first, at moderate temperatures, followed by the thiol-epoxy reaction, which is completed at higher temperatures. The analysis of stress relaxation evidences a complex two-step relaxation behavior depending on the contribution of isocyanate and epoxy groups to the mixture. Isocyanate-rich materials show a simple relaxation process corresponding to the trans-thiocarbamoylation exchange reactions. Epoxy-rich materials show, in contrast, a two-step relaxation processes evidencing that trans-thiocarbamoylation alone may not be sufficient to relax the stress completely, due to an apparently permanent network structure. However, complete stress relaxation is possible for epoxy-rich materials through additional bond exchange reactions such as transesterification or dynamic thiol-Michael, but at a slower rate. Depending on the composition and the temperature, full recycling of the material can be achieved at moderate temperatures in a timescale of minutes to hours.This work was funded by the Spanish Ministry of Science and Innovation (MCIN/AEI/10.13039/501100011033) through R&D project PID2020-115102RB-C22, and also by Generalitat de Catalunya (2021- SGR-00154), Spain. X. FernĂĄndez-Francos and O. Konuray acknowledge the Serra-HĂșnter programme (Generalitat de Catalunya).Peer ReviewedPostprint (published version

    Epoxy composites filled with boron nitride: cure kinetics and the effect of particle shape on the thermal conductivity

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    Thermally conducting and electrically insulating materials have been prepared by filling an epoxy–thiol system with boron nitride (BN) particles of different shapes (platelets and agglomerates) and sizes (from 2 to 180 ”m), and hence with different specific surface areas. The cure kinetics has been studied by differential scanning calorimetry in both non-isothermal and isothermal modes, and it has been shown that there is a systematic dependence of the cure kinetics on the BN content, the cure reaction generally being retarded by the addition of the BN particles. For filler loadings greater than about 30 vol%, the retardation of the cure, in both isothermal and non-isothermal mode, appears also to decrease as the specific surface area decreases. For the smallest (2 ”m) platelets, which have a significantly higher specific surface area (10 m2 g-1), the retardation is particularly pronounced, and this aspect is rationalized in terms of the activation energy and frequency factor of the reaction. The thermal conductivity of the cured epoxy–thiol–BN composites has been measured using the transient hot bridge method and is found to increase in the usual way with increasing BN content for all the particle types and sizes. For the platelets, the thermal conductivity increases with increasing particle size, mirroring the effect of BN content on the cure kinetics. The agglomerates, though, give the highest values of thermal conductivity, contrary to what might be expected in the light of their specific surface areas. Scanning electron microscopy of the fracture surfaces of the cured composites has been used to show that the interface between epoxy matrix and filler particles is better for the agglomerates. This, together with the reduced interfacial area, explains their higher thermal conductivity.Postprint (published version

    Frequency of Kidney Stone Different Compositions in Patients Referred to a Lithotripsy Center in Ilam, West of Iran

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    Introduction: Ilam is one of the provinces with the highest prevalence of kidney stone. The aim of this study was to calculate the frequency percentage of kidney stones by composition in Ilam.Materials and Methods: This cross-sectional study was conducted on 160 patients referred to the lithotripsy center of Ilam for the treatment of kidney stones from 2014 to 2015 (9 months). A two-part questionnaire including demographic information and stone type was used for collecting data. Finally, the obtained data were analyzed with SPSS version 17.Results: The frequency of kidney stones was 68% in men and 31.8% in women. The prevalence of kidney stones was higher in men than women, but there was no significant relationship between gender and the stone type. The highest prevalence of the stone was in the age group 31-41 years (33.7%) and there was a significant relationship between age and the stone type (P=0.001). The frequency of calcium oxalate (CaOx), mixed, uric acid, and cysteine kidney stones was 61.25%, 36.25%, 1.9%, and 0.6%, respectively. The most prevalent mixed stone was uric acid together with calcium oxalate stones (21.8%) followed by CaOx together with calcium phosphate stones (10.6%).Conclusions: The prevalence of CaOx and uric acid and CaOx stones was high. It is likely the increase in mixed stones in Ilam, especially uric acid and CaOx stones, is due to the nutritional pattern of subjects. More studies are required to determine the relationship between the stone type and diet in this area.Keywords: Kidney stones; Nephrolithiasis; Urolithiasis; Calcium phosphate; Calcium oxalate; Struvite; Uric aci

    Thiol-Ene Networks with Tunable Dynamicity for Covalent Adaptation

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    To be fully recyclable, covalent adaptable networks must ultimately be able to overcome all topological restrictions and flow. By using a statistically based method, it was shown that the extent of stress relaxation in disulfide-containing thiol-ene polymers is closely correlated to the fraction of permanent cross-links. Given sufficient disulfide content, the cured materials can be recycled at moderate temperatures with no apparent loss in tensile properties. Since the materials also feature ester bonds, even when the disulfide content is low, one can increase the reprocessing temperature to trigger transesterification reactions which ensure full stress relaxation and recyclabilityPeer ReviewedPostprint (published version

    Experimental and Numerical Analysis on TIG Arc Welding of Stainless Steel Using RSM Approach

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    This study involves the validating of thermal analysis during TIG Arc welding of 1.4418 steel using finite element analyses (FEA) with experimental approaches. 3D heat transfer simulation of 1.4418 stainless steel TIG arc welding is implemented using ABAQUS software (6.14, ABAQUS Inc., Johnston, RI, USA), based on non-uniform Goldak’s Gaussian heat flux distribution, using additional DFLUX subroutine written in the FORTRAN (Formula Translation). The influences of the arc current and welding speed on the heat flux density, weld bead geometry, and temperature distribution at the transverse direction are analyzed by response surface methodology (RSM). Validating numerical simulation with experimental dimensions of weld bead geometry consists of width and depth of penetration with an average of 10% deviation has been performed. Results reveal that the suggested numerical model would be appropriate for the TIG arc welding process. According to the results, as the welding speed increases, the residence time of arc shortens correspondingly, bead width and depth of penetration decrease subsequently, whilst simultaneously, the current has the reverse effect. Finally, multi-objective optimization of the process is applied by Derringer’s desirability technique to achieve the proper weld. The optimum condition is obtained with 2.7 mm/s scanning speed and 120 A current to achieve full penetration weld with minimum fusion zone (FZ) and heat-affected zone (HAZ) width

    Stress-relaxing thermosets with easily regulated bond exchange kinetics

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    We have carried out stress-relaxation experiments on poly(acrylate) and poly(thiol-ene) based thermosets prepared from in-house synthesized epoxy-acid adducts with acrylate (for the former) and ene functionalities (for the latter). The adducts contain disulphide bonds at their center which allow their cured thermosets to undergo disulphide metathesis when heated above a certain temperature [1]. The possibility of concurrent transesterification, albeit at a significantly lower rate, between ester and hydroxyl moieties present in the components is not discardedPeer ReviewedPostprint (published version
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