Composition Of MgO Research Articles

Leaching efficiency of sulfuric acid on selective lithium leachability from bauxitic claystone

The explosive demand for lithium calls for new lithium resources. A lithium-rich bauxitic clay was selected, and its material composition, phase transformation, lithium leaching efficiency using sulfuric acid were investigated after calcination treatment. In this study, XRF, ICP-AES, ICP-MS, XRD and SEM were employed to characterize bauxitic clay and its calcining products and leaching residues. The results show that bauxitic clay mainly consists of diaspore, illite, montmorillonite and anatase with a major chemical composition of Al2O3 (48.01%), SiO2 (33.06%), K2O (3.88%), TiO2 (2.25%), Fe2O3 (1.07%), MgO (0.46%), and lithium 3170 μg/g. The optimum calcination temperatures were 500 and 600 °C, with 72.34% and 73.61% lithium extracted, respectively, using 15% sulfuric acid leaching for 1 h. The optimal leaching conditions for lithium extraction were a leaching reaction time of 60 min and a 20% (wt/v) sulfuric acid concentration. Lithium leaching in this study was considered to occur via ion exchange instead of mineral dissolution. The findings of this study would be useful and interesting for lithium recovery from bauxitic clay.

Sources and petrogenesis of Late Triassic Zhiduo volcanics in the northeast Tibet: Implications for tectonic evolution of the western Jinsha Paleo-Tethys Ocean

The western Jinsha suture, representing a branch of the Paleo-Tethys, makes the junction between the Songpan-Ganzi Complex and the North Qiangtang Block (NQB). However, the Triassic tectonic evolution of the western Jinsha Paleo-Tethys Ocean is poorly constrained. This paper shows new LA–ICP–MS zircon U-Pb geochronology, major and trace elements, and Sr–Nd–Hf isotopic compositions of the Zhiduo dacitic volcanic rocks in the northern margin of the NQB. LA–ICP–MS zircon U-Pb dating displays that they erupted between 227 ± 2 and 228 ± 1 Ma. These rocks exhibit high silica, medium-K calc-alkalic signature, and low MgO, TiO2, P2O5, Cr, and Ni compositions. They are enriched in light rare earth elements and large-ion lithophile elements with moderate to strong negative Eu anomalies (Eu/Eu* = 0.24–0.56), and depleted in heavy rare earth elements and high field strength elements. They possess relatively low initial 87Sr/86Sr ratios (0.7055–0.7084), positive whole rock εNd(t) (+0.2 to +1.4), and magmatic zircon εHf(t) values (focus on 9.2 ± 2.7) with young Nd and Hf model ages (T2DM (Nd) = 885–983 Ma; T2DM (Hf) = 467–1035 Ma). These features are comparable to those of typical arc volcanic rocks and indicate that they were probably derived from partial melting of a juvenile crust source. The eruption of these volcanic rocks could be attributed to southward subduction of the western Jinsha Paleo-Tethys Ocean. In combination with previous studies, we propose that the subduction of the western Jinsha Paleo-Tethys Ocean initiated at the beginning of the Late Triassic (ca. 228 Ma) and closed at the end of the Late Triassic (ca. 208 Ma). In addition, there is a universal northeastward-younging trend of arc magmas in the northern margin of the NQB, which may indicate a model involving the initial shallow subduction and subsequent slab roll-back.

Bone regeneration of hollow tubular magnesium‑strontium scaffolds in critical-size segmental defects: Effect of surface coatings

Segmental defects are formidable challenges for orthopedic surgeons that are caused by large osseous defects such as open injury, comminuted fracture as well as other severe traumas and infection. Current treatment options have practical and clinical shortcomings, calling for innovative bone graft materials. This study is related to hollow tubular magnesium‑strontium (MgSr) alloy scaffolds with autologous morselized bone filled inside and three different coatings were individually applied on MgSr scaffolds, respectively, to study the effects of degradation and bioactivity of the grafts on new bone growth. The optimal coating method was screened using immersion tests, cell proliferation and adhesion, alkaline phosphatase (ALP) assay in vitro, and 4 weeks' implantation in a critical-size segmental defect in vivo. More new bone formation was observed by radiographic tests and histology along the ulna defects, when magnesium scaffold grafts were implanted. Meanwhile, depression occurred for blank control group with only autologous morselized bone filled, because of rapid absorption rate of morselized bone during initial implantation. Therefore, biodegradable MgSr alloy grafts showed their potential application in treating the critical-size segmental defects. As for different coating methods, CaP chemically deposited (CaP) coated sample showed least H2 evolution in vivo, demonstrating highest corrosion resistance and relative stable interfaces, however, the least beneficial ion release meanwhile. Micro-arc oxidation coating (MAO) degraded faster comparing with CaP, while with the main composition of MgO. They both indicate insufficient bioactivity in bone formation. The results suggest superior combination of bioactive surface, beneficial ions release and appropriate corrosion rate of Strontium phosphate conversion (SrP) coating, indicating superior comprehensive oeteoconductive and osteoinductive properties of coatings on hollow tubular MgSr alloy scaffold.

Evidence for multiple 4.0–3.7 Ga impact events within the Apollo 16 collection

AbstractIn a histogram of lunar impact ages from the Apollo 16 site, there is a spike circa 3.9 Ga that has been interpreted to represent either a large number of nearly synchronous events or an abundance of samples that were affected slightly differently by the event that produced the Imbrium basin. To further scrutinize those age relationships, we extracted six centimeter‐sized clasts of impact melt from ancient regolith breccia 60016 and performed petrological and geochronological (40Ar‐39Ar) analyses. Three clasts have similar poikilitic textures, while others have porphyritic, aphanitic, or intergranular textures. Compositions and abundances of relict minerals are different in all six clasts and variously imply Mg‐suite and ferroan anorthosite target sequences. Estimated bulk compositions of four clasts are similar to previously defined group 1 Apollo 16 impact melt rocks, while the other two have higher Al2O3and lower FeO+MgO compositions. All six clasts have similar K2O and P2O5concentrations, which could have been derived from aKREEP‐bearing component among target sequences. Eighteen40Ar/39Ar analyses of the six clasts produced an age range from 3823 ± 75 to 4000 ± 23 Ma, consistent with estimates for the proposed late heavy bombardment. Four clasts have multiple temperature steps that define plateau ages. These ages are distinct, so they cannot be explained by a single impact event, such as the one that produced the Imbrium impact basin. The conclusion that these represent distinct ages remains after considering the possibility of artifacts in defining plateaus.

Manufacture of Water Pipe From Clampshell Powder Materials

<h1>In general, household waste water pipelines use plastic pipes of PVC type that are not environmentally friendly and are relatively expensive. Therefore, this research will design molds and manufacture of composite pipes using raw materials of clampshell powder. The raw material used is clampshell powder with the composition of MgO and CaO compounds which is about 22.28% and 66.70%. The mixture of materials used consisted of clampshell powder with a size of 40 mesh, catalyst, and unsaturated polyester resin as a matrix. The objective of this study is manufacture of water pipes made from polymer composites reinforced by clampshell powder. Composite pipe manufacturing is carried out using the casting method. Pipe molds are made of stainless steel with a diameter of 40.46 mm (1.6 in) and an outer diameter of 50.8 mm (2 in). This mold size follows SNI 06-0084-2002 standards. The results of the study, water pipes from polymer composite material reinforced by clampshell powder with an inner diameter size of 40.64 mm and varying outside diameter. This variation depends on the composition of the clampshell powder in composite materials. The greater the clampshell powder composition, the more easily the maximum pipe wall thickness can be obtained. The average wall thickness variation is 3.35 mm. This variation is still included in the polymer water pipe requirements, which is a minimum of 2 mm.</h1>

Age and geochemistry of Early Ordovician A-type granites in the Northeastern Songnen Block, NE China

Early Ordovician A-type granites in the northeastern (NE) Songnen Block NE China were studied to better understand the geodynamic settings in this region. This research presents new zircon U–Pb ages and whole-rock geochemical data for the Early Ordovician granites in the NE Songnen Block. Zircon U–Pb dating indicates that the granite in the Cuibei, Hongxing, and Meixi areas in the NE Songnen Block formed in the Early Ordovician with ages of 471–479 Ma. The granites show geochemical characteristics of high SiO2 and K2O compositions and low FeOT, MgO, CaO, and P2O5 compositions. They belong to a high K calc-alkaline series and display a weak peraluminous feature with A/CNK values of 0.98–1.14. The rocks have a ∑REE composition of 249.98–423.94 ppm, and are enriched in LREE with (La/Yb)N values of 2.87–9.87, and display obvious Eu anomalies (δEu = 0.01–0.29). Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm, and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr + Y + Nb + Ce values (324–795 ppm) and Ga/Al ratios consistent with A-type granites. Based on particular geochemical features, such as high Rb/Nb (7.98–24.19) and Y/Nb (1.07–3.43), the studied A-type granites can be further classified as an A2-type subgroup. This research indicates that the Early Ordovician A-type granites were formed by the partial melting of ancient crust in an extensional setting. Lower Sr/Y and (Ho/Yb)N ratios indicate that plagioclase and amphibole are residual in the source, and garnet is absent, implying that the magma was generated at low levels of pressure. By contrast, the contemporaneous granites in the SE Xing’an Block suggest a subduction-related tectonic setting, and its adakitic property indicates a thickened continental crust. We suggest that the Paleo-Asian Ocean plate between the Xing’an and Songnen blocks subducted northward during the Early Ordovician. Meanwhile, the NE Songnen Block was exposed to a passive continental margin tectonic setting.

English

The rocks underlying many parts of Southeastern Nigeria had undergone extensive alterations to form considerable clay deposits. The mineralogical compositions of some of these clay deposits were evaluated with the X-Ray Diffraction (XRD) method to ascertain the suitability of the deposits as raw materials. Results of the analyses indicated that kaolinite (Al2Si2O5 (OH)4) is the dominant clay mineral. Traces of bentonite and dickite were also observed, while the identified non-clay minerals were quartz and iron. Chemical analysis of the clays revealed the predominance of SiO2, Al2O3, Fe2O3 and TiO with values ranging from 31.70 to 56.45%, 19.30 to 29.30%, 3.11 to 29.42% and 2.21 to 7.04%, respectively, while the compositions of CaO, MgO, Na2O, and MnO in the analyzed samples were relatively lower with values ranging from 0.19 to 0.29%, 0.13 to 0.19%, 0.11 to 0.70% and 0.01 to 0.03%, respectively. The Al2O3/TiO2 ratio (3.7 to 13.5) of the studied clays indicated a mafic to intermediate igneous rock origin. Binary plots of TiO2 versus Al2O3 to distinguish between granitic and basaltic sourced clays indicated basalt-rhyolite/granite provenances. The high chemical index of alteration (95.8%), chemical index of weathering (98.3%) and low contents of alkali and alkali earth elements (averaging 0.11%) of the clay-rich sediments, is indicative of a relatively intense weathering source area. The SiO2-K2O/Na2O plots suggested that the sediments in the study area were deposited between passive and active continental margins. In comparison with other reference clays and standard specifications, the clay deposits in the study area possess characteristics satisfactory for economic and some engineering purposes. Key words: Chemical, clay, deposits, economic, mineralogical, potentials, provenance.

α‐Alumina and spinel react into single‐phase high‐alumina spinel in <3 seconds during flash sintering

AbstractIn situ X‐ray diffraction measurements at the Advanced Photon Source show that α‐Al2O3 and MgAl2O4 react nearly instantaneously and completely, and nearly completely to form single‐phase high‐alumina spinel during voltage‐to‐current type of flash sintering experiments. The initial sample was constituted from powders of α‐Al2O3, MgAl2O4 spinel, and cubic 8 mol% Y2O3‐stabilized ZrO2 (8YSZ) mixed in equal volume fractions, the spinel to alumina molar ratio being 1:1.5. Specimen temperature was measured by thermal expansion of the platinum standard. These measurements correlated well with a black‐body radiation model, using appropriate values for the emissivity of the constituents. Temperatures of 1600‐1736°C were reached during the flash, which promoted the formation of alumina‐rich spinel. In a second set of experiments, the flash was induced in a current‐rate method where the current flowing through the specimen is controlled and increased at a constant rate. In these experiments, we observed the formation of two different compositions of spinel, MgO•3Al2O3 and MgO•1.5Al2O3, which evolved into a single composition of MgO•2.5Al2O3 as the current continued to increase. In summary, flash sintering is an expedient way to create single‐phase, alumina‐rich spinel.

Regularities of phase formation, structure and properties of chemically and thermally resistant ceramic materials

Based on the compositions of MgO—Al2O3—TiO2—SiO2 system, the chemically and thermally resistant ceramic was obtained at a firing temperature of 1250 °C by the directed synthesis of tialite and mullite phases. The influence of alternative raw materials of natural and technogenic origin on the operational properties and phase composition of porous and densely-sintered ceramic materials was studied. The using expediency of pyrophyllite containing waste of quartzite mining and ferrotitanium production wastes as the phase forming components of ceramic masses is established. The mechanism of structure- and phase formation of tialite and mullite-tialite ceramics was investigated. It was established that, stabilization of the tialite phase at a temperature of 1200—1250 oC occurs while maintaining the ratio of TiO2/Al2O3 oxides ~ 1.4 and the presence of 1.3 wt. % Fe2O3, as the mineralizing component included in the waste. The possibility of obtaining tialite containing ceramic materials at a lower firing temperature (1200 oC) due to the formation of a tialite solid solution (Mg0.3Al1.4Ti1.5O5) while maintaining the ratio of MgO : TiO2 oxides = 0.18 was proved. Technological principles of the production of chemically and thermally resistant ceramics both with the densely-sintered and with the porous structure, the total porosity of which is respectively 0.41 and 60 %, have been developed. The permeability of porous ceramic materials of mullitе-tialite composition was determined (water permeability coefficient P = 5.39∙10-5 cm2/s), as well as parameters of sorption processes (diffusion rate of Cr2O7-2 and MnO4- ions is 6.38∙10-6 and 1.06∙10-5 cm2/s respectively). This indicates the possibility of using the developed porous ceramics for the manufacture of industrial wastewater filters. Complex studies of the phase composition, structure and properties of the developed ceramic materials confirmed the promise of their use for the manufacture of parts of equipment operating in corrosive environments.

Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt

To investigate possible reactions between differently coated carbon-bonded alumina filters and an AZ91 magnesium alloy melt, immersion tests were carried out. Uncoated as well as MgAl2O4-, Al2O3-, nano- (carbon nano tubes/alumina nano sheets) and MgO-C-coated filters were tested. Thermodynamic calculations showed that only magnesia (MgO) and carbon are stable against molten magnesium; alumina (Al2O3) and spinel (MgAl2O4) will be reduced under the formation of magnesia. Optical and scanning electron microscopy as well as EDX analysis were performed near and at the filter-magnesium alloy-interface of the cooled and sectioned filter samples after their immersion into the AZ91 melt. The results of the thermodynamic calculations were confirmed by the experiments. The MgO-C-coated filter was the only one that did not show an in situ-formed layer on its surface after being in contact with the magnesium alloy melt. The alumina- or spinel-containing filter surfaces displayed platelet-like in situ layers after their contact with the molten AZ91. The results of the EDX analysis of these layers suggest their composition of MgO, since notable respective Mg and O contents were detected, as predicted by the calculations.

Oceanic and Continental Mantle Fragments in Ophiolites of the Northwestern Pacific Margins: Composition, Age, and Genesis of Sakhalin Peridotites

The paper presents the results from a study of original and published data on the chemical composition and age of mantle peridotites from Sakhalin Island ophiolites. The material and genetic proximity of peridotites from the Berezovsky and Shelting plutons, on the one hand, and melange zone serpentinites, on the other, have been established. In composition and Fe2O3 and MgO variations, Sakhalin peridotites differ radically from those of the Northeast Asia ophiolite complexes (Krasnogorsky Massif, Karaginsky Island Massif, etc.), which are fragments of Pacific Plate mantle. Conversely, Sakhalin peridotites have a subcontinental genesis and are compositionally close to xenoliths of lherzolites from Hankai Microcontinent mantle (southern Sikhote-Alin). The rythmics of alternation in compression and expansion at the margin of the Asian continent in the last 180 million years, caused by cyclical changes in the Pacific spreading rate, have been considered. According to data obtained by U-Pb dating of zircons, the formation of the Berezovsky Massif took place 169–154 Ma ago during Jurassic expansion of the continental margin. Matching age and composition data demonstrate that the Sakhalin ophiolites formed within the marginal sea basin during riftinduced destruction of the periphery of the Hankai Craton. The assumed tectonic setting was close to that reconstructed for the Jurassic Josephine ophiolites of the California margin of the North American continent. The continental genesis of the studied ophiolites agrees with the age and tectonic mode of ophiolite formation for Sakhalin Island.

High performance Ni-Fe-Mg catalyst for tar removal in producer gas

A Ni-Fe-Mg material, supported on a ceramic substrate, suitable for application in a gasifier or reforming reactor was evaluated as a catalyst for tar decomposition via steam reforming. Experiments were conducted in a laboratory-scale fixed-bed reactor using simulated producer gas containing toluene and ethylene as tar surrogates. The catalyst was prepared by wet-impregnation and characterized by analytical techniques to include: BET, XRD, TPR, and SEM. The elemental composition of Ni, Fe, and MgO was optimized for maximum activity and stability. The optimized catalyst composition contained Ni, Fe, and MgO in the ratio 45:21:34 by weight. The observed catalyst activity was superior in comparison to other alkaline earth metal promoters: CaO, SrO, and BaO as well as a reference catalyst, Ni-K-MgO, in the temperature range between 600 and 800 °C. Time on stream with the optimized composition showed sustained tar (toluene + ethylene) conversion of near 100% at 750 °C for at least 48 h, indicating no coke formation. The coke formation affinity of Ni was reduced by the presence of the FeNi3 alloy. The enhanced performance with MgO is attributed to the strong adsorption of H2O forming Mg(OH)2 species facilitated on the oxide ion vacancy site of MgO acting as oxygen exchange site.

X-ray absorption spectroscopy investigation of relationship between Mg vacancy and magnetic properties of MgO powder

This paper reports on the ferromagnetism of MgO powder and degraded powder at room temperature. The starting material, Mg(OH)2, was analyzed by X-ray fluorescence (XRF) spectrometry and then calcined at 450 °C for 5 h to obtain fresh MgO powder. The calcined powder was separated into two batches (i) kept in vacuum sealed (MgO-F) and (ii) kept at ambient environment (30–32 °C at 45–55% relative humidity) for 2 days (MgO-D). The samples were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and X-ray absorption spectroscopy (XAS) including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). XRD and EXAFS confirmed that MgO phase in MgO-F. Both Mg(OH)2 and MgO compositions were found in MgO-D. The origin of ferromagnetism at room temperature of MgO-F and MgO-D is attributed to the Mg vacancies in the MgO structure that revealed and verified by XANES and EXAFS results.

Low temperature MIR to submillimeter mass absorption coefficient of interstellar dust analogues

Context.The submillimeter spectral domain has been extensively explored by theHerschelandPlancksatellites and is now reachable from the ground with ALMA. A wealth of data, revealing cold dust thermal emission, is available for astronomical environments ranging from interstellar clouds, cold clumps, circumstellar envelops, and protoplanetary disks. The interpretation of these observations relies on the understanding and modeling of cold dust emission and on the knowledge of the dust optical properties.Aims.The aim of this work is to provide astronomers with a set of spectroscopic data of realistic interstellar dust analogues that can be used to interpret the observations. It pursues the experimental effort aimed at characterizing the spectroscopic properties of interstellar dust analogues at low temperature in the mid-infrared (MIR) to millimeter spectral domain. Compared to previous studies, it extends the range of studied dust analogues in terms of composition and of structure of the material.Methods.Glassy silicates of mean composition (1−x)MgO –xSiO2withx= 0.35 (close to forsterite, Mg2SiO4), 0.50 (close to enstatite, MgSiO3) and 0.40 (close to Mg1.5SiO3.5or MgSiO3:Mg2SiO4= 50:50) were synthesized. The mass absorption coefficient (MAC) of the samples was measured in the spectral domain 30–1000μm for grain temperature in the range 300–10 K and at room temperature in the 5–40μm domain.Results.We find that the MAC of all samples varies with the grains temperature and that its spectral shape cannot be approximated by a single power law inλ−β. In the FIR/submm, and above 30 K, the MAC value at a given wavelength increases with the temperature as thermally activated absorption processes appear. The studied materials exhibit different and complex behaviors at long wavelengths (λ≥ 200 to 700μm depending on the samples). These behaviors are attributed to the amorphous nature of dust and to the amount and nature of the defects within this amorphous structure. We do not observe MAC variations in the 10–30 K range. Above 20μm, the measured MAC are much higher than the MAC calculated from interstellar silicate dust models indicating that the analogues measured in this study are more emissive than the silicates in cosmic dust models.Conclusions.The underestimated value of the MAC deduced from cosmic dust models in the FIR/submm has important astrophysical implications because masses are overestimated by the models. Moreover, constraints on elemental abundance of heavy elements in cosmic dust models are relaxed.

Enhanced dielectric and piezoelectric responses in Zn1-xMgxO thin films near the phase separation boundary

Dielectric and piezoelectric properties for Zn1-xMgxO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn1-xMgxO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane (d33,f) and in-plane (e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectric coefficients is accompanied by a 35% increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. The enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn1-xMgxO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.

Study of the Corrosion and Surface Film Growth on AZ63 Magnesium Alloy in MgSO4 Solution

Comprehending the mechanism of corrosion film growth on the anode in electrolytes is a foundation in the tailoring of a desirable delayed action in magnesium–manganese dioxide (Mg/MnO2) primary batteries. The formation and growth evolution of the corrosion film on AZ63 magnesium alloys in 2 mol L−1 MgSO4 aqueous solution was investigated by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Results indicate that corrosion preferentially occurred on the α phase adjacent to the β phase of the alloy before spreading to the area away from the β phase. The β phase acted as a micro cathode that accelerates the corrosion dissolution. The film consisted of a base film and mosaic particles with amorphous mixed compositions of MgO, Mg(OH)2, (MgCO3)4·Mg(OH)2·4H2O, and Mg(OH)2·2MgSO4. The formation and growth of the film on the AZ63 magnesium can be divided into three stages: film formation, film composition transformation, and film structure breakdown. A film growth model was also proposed for interpreting the corrosion evolution of the AZ63 alloy.

Conduction mechanism and dielectric properties of ZnO/MgO solid composites

In this paper, (1−x)ZnO/xMgO solid composites, where x = 0, 10 and 20%, were prepared at high temperature 1200 °C by a solid-state method. The effect of increasing MgO content on structural, morphological, dielectric and the electrical properties of the ZnO/MgO composites has been investigated. The X-ray diffraction analysis indicates that all the samples have a prominent hexagonal crystalline structure with (002) and (101) as preferred growth directions and the segregation of MgO cubic phase took place for an MgO composition x ≥ 10 wt%. Analysis of infrared (IR) is in agreement with the diffraction results of X-ray diffraction. Morphological properties showed that the grain size was decreased with increasing MgO content. For the dielectric properties, a strong dispersion of permittivity constants was observed at low frequency, which can be attributed to interfacial relaxation. For the electrical properties, the frequency dependence of ac conductivity is interpreted in terms of Jonscher’s law. The ac electrical conduction in ZnO/MgO composites is analyzed by different processes, which can be attributed to several models, the hopping correlated barrier (CBH) for the undoped ZnO sample, and the hopping correlated barrier (CBH) and the overlapping large polaron tunneling model for both composites ZnO/MgO:10% and ZnO/MgO:20%.

ABLATION AND CHEMICAL ALTERATION OF COSMIC DUST PARTICLES DURING ENTRY INTO THE EARTH’S ATMOSPHERE

ABSTRACT Most dust-sized cosmic particles undergo ablation and chemical alteration during atmospheric entry, which alters their original properties. A comprehensive understanding of this process is essential in order to decipher their pre-entry characteristics. The purpose of the study is to illustrate the process of vaporization of different elements for various entry parameters. The numerical results for particles of various sizes and various zenith angles are treated in order to understand the changes in chemical composition that the particles undergo as they enter the atmosphere. Particles with large sizes (> few hundred μm) and high entry velocities (>16 km s−1) experience less time at peak temperatures compared to those that have lower velocities. Model calculations suggest that particles can survive with an entry velocity of 11 km s−1 and zenith angles (ZA) of 30°–90°, which accounts for ∼66% of the region where particles retain their identities. Our results suggest that the changes in chemical composition of MgO, SiO2, and FeO are not significant for an entry velocity of 11 km s−1 and sizes <300 μm, but the changes in these compositions become significant beyond this size, where FeO is lost to a major extent. However, at 16 km s−1 the changes in MgO, SiO2, and FeO are very intense, which is also reflected in Mg/Si, Fe/Si, Ca/Si, and Al/Si ratios, even for particles with a size of 100 μm. Beyond 400 μm particle sizes at 16 km s−1, most of the major elements are vaporized, leaving the refractory elements, Al and Ca, suspended in the troposphere.

Synthesis and Characterization of CaO-SiO<sub>2</sub>-MgO Bioactive Glass Produced by Sol-Gel

Bioactive glasses have widely used in biomedical applications such as bone filler due to their excellent biocompatibility, bioactivity and osteoconduction characteristics. In this work, a silicate-rich glass was synthesized by the sol-gel method with 60% SiO2 – 30%CaO – 10% MgO composition where fumed silica acts as the silica precursor. This new method was hypothesized to reduce the gel formation time, due to the high surface area of the fumed silica. In addition, this would presumably increase the nanoporosity of the glass. For comparison purposes, we used a glass of the same composition, but with the conventional silica precursor, tetraethyl orthosilicate (TEOS), through the sol gel method. Both were heat treated at 450°C. FT-IR analysis before and after heat treatment at 450°C showed the presence of nitrate groups, especially in the TEOS samples. This is consistent with the more hygroscopic aspect of those samples. The fumed silica samples had significantly less pronounced peaks corresponding to the nitrate groups, consistent with the more porous structure and the less hygroscopic aspect. The fumed silica samples indeed had a lower gelling time and showed similar results obtained by XRD and FT-IR analyses, showing that the use of fumed silica is viable and advantageous in the glass synthesis by the sol-gel process

An Alternative Quality Control Technique for Mineral Chemistry Analysis of Portland Cement-Grade Limestone Using Shortwave Infrared Spectroscopy

Shortwave infrared (SWIR) spectroscopy can be applied directly to analyze the mineral chemistry of raw or geologic materials. It provides diagnostic spectral characteristics of the chemical composition of minerals, information that is invaluable for the identification and quality control of such materials. The present study aims to investigate the potential of SWIR spectroscopy as an alternative quality control technique for the mineral chemistry analysis of Portland cement-grade limestone. We used the spectroscopic (wavelength position and depth of absorption feature) and geochemical characteristics of limestone samples to estimate the abundance and composition of carbonate and clay minerals on rock surfaces. The depth of the carbonate (CO3) and Al-OH absorption features are linearly correlated with the contents of CaO and Al2O3 in the samples, respectively, as determined by portable X-ray fluorescence (PXRF) measurements. Variations in the wavelength position of CO3 and Al-OH absorption features are related to changes in the chemical compositions of the samples. The results showed that the dark gray and light gray limestone samples are better suited for manufacturing Portland cement clinker than the dolomitic limestone samples. This finding is based on the CaO, MgO, Al2O3, and SiO2 concentrations and compositions. The results indicate that SWIR spectroscopy is an appropriate approach for the chemical quality control of cement raw materials.