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Ga2O3 is an ultra‐wide‐bandgap semiconductor that is receiving considerable attention due to its promising applications in high‐frequency, high‐power and high‐temperature settings. It can be prepared by calcinating the α‐GaOOH phase at high temperatures. Understanding the significance of hydroxyl groups in α‐GaOOH, dehydroxylation and the structural transition at high temperatures has become a key aspect of preparing high‐quality α‐Ga2O3 crystals, but the underlying mechanism remains unknown. In this research, α‐GaOOH nanorods were hydrothermally synthesized and the structural evolution of α‐GaOOH investigated at high temperatures by in situ X‐ray diffraction. The hydroxyl group in α‐GaOOH squeezes Ga3+ from the center of the [GaO6] octahedron, resulting in deformed [GaO6] octahedra and significant microstrain in α‐GaOOH. The hydroxyl groups are peeled off from α‐GaOOH when the temperature exceeds 200°C, resulting in contraction along the c‐axis direction and expansion along the a‐axis direction of α‐GaOOH. When the temperature exceeds 300°C, the Ga—O bond inside the double chains preferentially breaks to generate square‐wave‐like octahedron chains, and the neighboring chains repack to form hexagonal‐like octahedron layers. The octahedron layers are packed up and down by electrostatic interaction to generate the α‐Ga2O3 structure. This work highlights the role of hydroxyl groups in α‐GaOOH, dehydroxylation and the structural transition on the atomic scale, providing valuable guidelines for the fabrication of high‐quality α‐Ga2O3 crystals. [ABSTRACT FROM AUTHOR]

Thermal treatment of coal byproducts has been shown to improve leaching characteristics of rare earth elements (REEs) in bituminous coal sources due to its influence on the associated minerals. This study investigated the impact of the calcination atmosphere on REE leaching behavior in different density fractions of Baker and Fire Clay seam coarse refuse sources using a thermogravimetric analyzer to create an oxidizing or reducing atmosphere at a desired temperature for 2 h. The effect on leaching characteristics was evaluated using 1.2 M sulfuric acid at 75°C for 5 h at 1% w/v solid concentration. Rare earth element (REE) recovery for the 2.2 specific gravity (SG) sink fraction improved by approximately 15 absolute percentage points at 1000°C relative to the 600°C calcined sample in an inert atmosphere and equilibrated within 10 min from the start of the test. Contrarily, thermal treatment at 1000°C under oxidizing atmosphere significantly reduced the REE recovery due to sintering of the clays, which limited access to the RE minerals for leaching. In general, thermal treatment of heavier fractions in both atmospheres significantly improved the light REE (LREE) recovery while the increase in heavy REE (HREE) recovery was relatively less. As common clay minerals in the coal sources, kaolinite and illite samples were tested under the same conditions and using a digital scanning calorimeter. The findings confirmed that the improvement observed in REE leaching through thermal treatment at 600°C was due to decarbonization for the lighter density fractions and dehydroxylation of clays. [ABSTRACT FROM AUTHOR]

Electronic components made by inorganics (e.g., mica) play key roles in the function exertion of instruments working in outer‐layer space, enduring long‐term β‐ray irradiation. Its damage is vital while explored rarely. Herein, pure muscovite crystals were chosen and irradiated by an electron beam (EB) in air with a dose up to 1000 kGy. Then, micro‐geometry morphology variation in Z‐axis and microstructural transformation mechanism were explored by X‐ray diffraction, Fourier transform attenuated total reflection infrared spectrum, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and CA analysis. Main results reveal that muscovite lattice is unstable to EB irradiation. With dose increases to 1000 kGy, interlayer space d of (0 0 2) lattice varied 2% near 0.2 Å. At low‐dose, irradiation lattice expansion readily occurs, whereas at higher dose, it is lattice shrinkage, showing a transformation from expansion to shrinkage. Concurrently, chemical structure varied, H2O amount increased, and metal element valance and surface wettability were reduced, so dehydroxylation occurred exceeding H2O radiolysis and evaporation, and framework cleavage could be severe. Binding energies of metals of 1000 kGy‐irradiated species decreased by 0.2 eV, and CA of 100 kGy‐irradiated species increased by 10°. Intrinsic mechanisms involve framework destruction, H‐atom migration, hydrogen bond formation/destruction, and H2O radiolysis. At low‐dose irradiation, H‐atom migration and hydrogen bond formation/destruction are predominant, inducing lattice expansion; at higher dose, framework cleavage is intensive and crucial, inducing shrinkage. During which, partial H2O occurred radiolysis, reducing valence. Generally, H‐atom migration and interface cleavage played key roles in microgeometry morphology a variation of muscovite crystal under EB irradiation at 0–1000 kGy. To enhance muscovite geometry‐morphology stability under a long‐term β‐ray irradiation condition, OH and hydrogen bond contents should be reduced and interface region should be strengthened (e.g., lessening vacancies or compacting stacking). This conclusion promotes the design of radiation‐resistant silicate material, guiding the manufacturing of electronic component used in aerospace industry significantly. [ABSTRACT FROM AUTHOR]

Halloysite and kaolinite are dioctahedral TO phyllosilicates that drive the interest of scientists for formulating environmentally friendly materials, and consequently in the field of ceramics. The main scope of this study was the understanding of the texture evolution upon the dehydroxylation reaction and the influence of the presence of halloysite. In situ synchrotron (002) and (111) poles figures were recorded on the DiffAbs beamline at SOLEIL Synchrotron, from room temperature to 1000 °C, on kaolinite and/or halloysite-rich samples shaped by tape casting. Commercial kaolins and halloysite provided by Imerys company were used. The samples were labeled KRG100, KCS100, H100, KRG50H50 and KRG59H50 in relation with the wt. % of kaolin (KRG, KCS) or halloysite (H) clays. In samples KCS100 and KRG100, a strong texture was observed until in situ annealing at 700 °C, with respect to the c-axis of kaolinite. On the contrary, the texture with respect to the c-axis of halloysite for the sample H100 was weak whatever the temperature was. Moreover, this weak texture disappeared before the complete dehydroxylation of halloysite. This is due to the opening of some halloysite tubes. When considering the samples KRG50H50 and KCS50H50, a significant texture was observed with the c-axis preferentially oriented perpendicular to the sample surface. The presence of kaolinite platelets predominated onto the alignment of halloysites tubes. Furthermore, it was noted that the halloysite influenced the (002) diffracted intensity into the temperature range 20 °C to 400 °C. Above 400 °C, the behavior obtained for the (002) reflection in samples KRG50H50 and KCS50H50 was similar to the behavior noticed for pure kaolins KRG100 and KCS100, respectively. The dehydroxylation temperature range appeared to be relevant with combined effect of kaolinite and halloysite transformations arising from KRG100 or KCS100 and H100 samples. Therefore, the onset point of dehydroxylation is 550 °C ± 25 °C for KRG100, KCS100, KRG50H50 and KCS50H50. For the pure halloysite H100 sample, the dehydroxylation starts at the lower temperature 475 °C. It was also noted that during the dehydroxylation of kaolinite, the characteristic portion of ring related to the diffracted intensity of the (111) reflection located at χ = 45° tended to disappear above 550 °C and led to the formation of a new transitory phase with a (111) reflection with perpendicular alignment to the c-axis. Indeed, an epitaxial relationship with the (111) kaolinite reflection could be assumed. Further X-ray scattering experiments allowed highlighting the effective offset temperature of the dehydroxylation, which was identified as close to 720 °C. The metakaolinite achieved structural transformation to another transitory phase at 1000 °C. [ABSTRACT FROM AUTHOR]

The state and forms of water in dispersed aluminum oxides and hydroxides and products obtained during their treatment are investigated in this paper. It has been found that particles of dispersed aluminum oxides and hydroxides of various water forms are present on surface and in volume. Their classification based on the state of water and the values of Δ H of evaporation has been introduced: "surface-bound" water, "structural" water, and "single OH groups". For micron particles, the presence of predominantly "structural" water is exemplified for gibbsite (Al(OH) 3) and boehmite (AlOOH). For the defective structure of products of heat treatment of gibbsite in air at 250 and 800°С, a low dehydroxylation temperature and high values of Δ H of water evaporation have been found: 71.13 kJ/mol and 67.27 kJ/mol, respectively. For the γ-Al 2 O 3 nanopowder and the products of its treatment, the presence of "surface-bound", "structural" water, and water represented by "single OH groups" has been detected. It has been shown that the treatment of gibbsite or aluminum oxide in a supercritical aqueous fluid at a water/Al 2 O 3 molar ratio of less than 1.5 leads to the formation of tohdite 5Al 2 O 3 •H 2 O, the composition of which is characterized by a low content of structural water in the stable state over a wide temperature range. [Display omitted] • Temperature of reaction between steam and alumina determines the form of bound water. • Forms of water are classified as "surface-bound", "structural" and "single OH groups". • Density of the aqueous medium and water form determines the phase formed. • Products are bayerite, boehmite and todite, as well as γ-Al 2 O 3 and α-Al 2 O 3. • Exchange of oxide matrix with medium determines size and morphology of particles. [ABSTRACT FROM AUTHOR]

Dehydroxylation, alcohols, cyanation, hydroxyl group, nucleophilic substitution Keywords: dehydroxylation; alcohols; cyanation; hydroxyl group; nucleophilic substitution EN dehydroxylation alcohols cyanation hydroxyl group nucleophilic substitution 1593 1596 4 07/31/23 20230815 NES 230815 Graph The cyano group (-CN) is a unique moiety that is commonly found in biologically active molecules [1] and synthetic intermediates. Chem. 1941, 6: 795 26 Erhardt, S. Grushin, V V. Kilpatrick, A H. Macgregor, S A. Marshall, W J. Roe, D C. J. Am. Chem. Soc. 2008, 130: 4828 27 Kim, J. Chang, S. J. Am. Chem. Soc. 2010, 132: 10272 28 Ushkov, A V. Grushin, V V. J. Am. Chem. Soc. 2011, 133: 10999 29 Mondal, B. Acharyya, K. Howlader, P. Mukherjee, P S. J. Am. Chem. Soc. 2016, 138: 1709 30 Zanon, J. Klapars, A. Buchwald, S L. J. Am. Chem. Soc. 2003, 125: 2890 31 Ratani, T S. Bachman, S. Fu, G C. Peters, J C. J. Am. Chem. Soc. 2015, 137: 13902 32 Miwa, N. Tanaka, C. Ishida, S. Hirata, G. Song, J. Torigoe, T. Kuninobu, Y. Nishikata, T. J. Am. Chem. Soc. 2020, 142: 1692 33 Yu, P. Morandi, B. Angew. On the other hand, Ph SB 3 sb P SP + sp I I SP - sp might also directly activate alcohols B D b (path II), permitting a nucleophilic substitution. [Extracted from the article]

Dehydroxylation, alcohols, cyanation, hydroxyl group, nucleophilic substitution On the other hand, Ph SB 3 sb P SP + sp I I SP - sp might also directly activate alcohols B D b (path II), permitting a nucleophilic substitution. Chem. 1941, 6: 795 26 Erhardt, S. Grushin, V V. Kilpatrick, A H. Macgregor, S A. Marshall, W J. Roe, D C. J. Am. Chem. Soc. 2008, 130: 4828 27 Kim, J. Chang, S. J. Am. Chem. Soc. 2010, 132: 10272 28 Ushkov, A V. Grushin, V V. J. Am. Chem. Soc. 2011, 133: 10999 29 Mondal, B. Acharyya, K. Howlader, P. Mukherjee, P S. J. Am. Chem. Soc. 2016, 138: 1709 30 Zanon, J. Klapars, A. Buchwald, S L. J. Am. Chem. Soc. 2003, 125: 2890 31 Ratani, T S. Bachman, S. Fu, G C. Peters, J C. J. Am. Chem. Soc. 2015, 137: 13902 32 Miwa, N. Tanaka, C. Ishida, S. Hirata, G. Song, J. Torigoe, T. Kuninobu, Y. Nishikata, T. J. Am. Chem. Soc. 2020, 142: 1692 33 Yu, P. Morandi, B. Angew. Keywords: dehydroxylation; alcohols; cyanation; hydroxyl group; nucleophilic substitution EN dehydroxylation alcohols cyanation hydroxyl group nucleophilic substitution 1593 1596 4 07/31/23 20230801 NES 230801 Graph The cyano group (-CN) is a unique moiety that is commonly found in biologically active molecules [1] and synthetic intermediates. [Extracted from the article]

An in-depth understanding of the microstructural transformation that the matrix of clay undergoes prior to the complete dissolution of metal package container is crucial for predicting the effectiveness of the matrix of clay purposed as backfill material in the high-level radioactive waste (HLRW) disposal. Although irradiation can strongly influence microstructure its effect remains unclear. Herein, pure phlogopite single-crystal was chosen as a model material and irradiated in air by an electron beam (EB) at 0–1000 kGy. Variation in chemical/crystalline structure and microstructural transformation mechanism were explored by FT-ATR IR, XRD, TGA, CA and XPS. Key results reveal that irradiation caused extensive octahedral OH cleavage and lattice damage, marginal Si–OH formation and surface wettability elevation. With absorbed dose increases to 1000 kGy the majority of samples exhibited lattice plane expansion while the 200 kGy-irradiated sample exhibited shrinkage. 100 and 200 kGy-irradiated samples exhibited a variation level of ±2.5% (±0.3 Å) and a gap of 0.4 Å in (001) lattice plane. Concurrently, the amount of H 2 O and valance of metal element decreased while surface hydrophilicity increased slightly. 200 kGy-irradiated sample exhibited a CA of 7°, lower the pristine sample near 15°. Overall, phlogopite lattice appears to be unstable to EB irradiation at 0–1000 kGy. Transformation mechanism involves framework cleavage, H-atom migration, hydrogen-bond formation/destruction and reduction of electron. H-atom migration and hydrogen-bond variation played key roles. Normal silicate crystal appears to be unstable to medium-intensity β -ray irradiation. To enhance lattice stability, the number of OH and hydrogen bond should be reduced. This conclusion guides the design of radiation-resistant silicate material for use as backfill or curing material in HLRW disposal. For example, for curing material (e.g., glass), the concentration of OH in matrix base needs to be reduced. This cognization emphasises the role of OH in novel microstructural transformation. [ABSTRACT FROM AUTHOR]

In this work, the thermal decomposition kinetics of howlite were investigated at different heating rates by using Coats-Redfern, Ozawa, and Kissinger-Akahira-Sunose kinetic models under non-isothermal conditions. The thermal decomposition of howlite occurred in two dehydroxylation stages. Results indicated that it decomposes in the first dehydroxylation stage at a very slow rate due to the higher thermal stability of the mineral. Kinetic parameters were determined using the above-mentioned models for all decomposition stages. The activation energies calculated from the Ozawa and Kissinger-Akahira-Sunose isoconversional methods fit well with each other, while the activation energies calculated with the Coats-Redfern method were different. It was also seen that the activation energy of the decomposition reaction changed with the degree of conversion, suggesting that the reaction mechanism is not single-step. [ABSTRACT FROM AUTHOR]

Lithium (Li)-bearing clays have become new types of Li resources, and it is found that the evolution of the mineral structure in Li-bearing clay greatly restricts the extraction of Li. Herein, a Li-bearing clay from Guizhou Province, China, was studied using in situ thermogravimetry–differential scanning calorimetry–mass spectrometry–Fourier transform infrared spectroscopy (TG–DSC–MS–FTIR) (evolved gases), 27Al and 1H magic-angle spinning nuclear magnetic resonance (MAS NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results showed that the Li-bearing clay contained illite, chlorite, kaolinite, pyrite, and anatase. The dehydroxylation reaction of the clay minerals occurred at 450 °C. CH2, CH4, C3H4, C6H5, and C8H9 evolved during the roasting process. The AlO4(OH)2 octahedra transformed to AlO4 tetrahedra due to the reaction between the reductive gases and the residual O in AlO5. The effect of dehydroxylation on the structural stability of different clay minerals differed. After dehydroxylation, kaolinite became amorphous, chlorite reacted with 20% H2SO4, and illite remained stable during the roasting-H2SO4 leaching process. The Li-leaching efficiency increased significantly after dehydroxylation and decreased sharply with the formation of mullite. [ABSTRACT FROM AUTHOR]

The calcination process is the dehydroxylation reaction of the kaolinite mineral into the formation of amorphous metakaolinite phase. The dehydroxylation reaction of kaolinite is affected by various parameters such as calcination temperature, time and particles size. The present work aimed to analyze the kinetics of dehydroxylation reaction of Ethiopian kaolinite during calcination. The effects of temperature (550–675 °C), time (30–210 min) and particles size (0.900–0.106 mm) on the degree of conversion were also investigated. Subsequent to sample preparation and calcination, it was characterized by various analytical techniques such as X-ray diffractometer (XRD), Fourier transformer infrared spectrometer (FTIR), differential scanning calorimeter (DSC), thermogravimetry analyzer (TGA) and scanning electron microscope (SEM). The broadening of the XRD peaks was due combined effects of micro-strain and crystalline size. The crystalline peaks in the XRD curve and the hydroxyl bands in FTIR curve were disappeared in calcined kaolinite which revealed the formation of metakaolinite. In the TGA curve, three endothermic peaks and one exothermic peak were detected from 25 to 1100 °C. The conversion degree increased as calcination temperature and time were increased, and the particles size was reduced. The maximum conversion degree was 0.989 at 625 °C, 0.106 mm and 150 min. The dehydroxylation reaction results were well fitted with pseudo-first-order reaction rate kinetics. For the particles size of 0.900, 0.500, 0.250 and 0.106 mm, the activation energies were 263.105 ± 2.631, 252.831 ± 2.528, 250.727 ± 2.507 and 237.619 ± 2.376 kJ mol−1, respectively, for the pseudo-first-order rate kinetics. [ABSTRACT FROM AUTHOR]

Fluidized roasting is an efficient method to promote vanadium extraction from V-bearing mica in shale. In this study, the transformation behavior of V-bearing sericite during fluidized roasting was explored by combining experimental detections and density functional theory (DFT) calculations. TG-MS, XRD, FTIR, and SEM-EDS were used to investigate the characteristics of the roasted sericite samples. The crystal parameters of V-bearing sericite were calculated with Materials Studio. The results showed that dehydroxylation was the main reaction during roasting, which occurred between 650 °C and 960 °C. After being roasted at 900 °C for 2 h, hydroxyls were completely removed. The calculation results show that −OH was removed between the metal ions in the sericite O-layer, which turned the hexa-coordinate of V3+, Al3+, and Fe3+ into pentacoordinate. Through electronic rearrangement, the bond lengths between two ions connected by −OH were shortened from 0.18~0.20 nm to 0.17 nm. However, some chemical bonds were grown, which indicates that they are weaker and easier to transform. In addition, twisted six-membered rings were formed with obvious angle changes on the (0 0 1) surface. Furthermore, Mulliken's overlap populations of some V-O, Al-O, and Fe-O were decreased. Therefore, dehydroxylation is a determining factor in the destruction of sericite crystals during fluidized roasting, which also promotes vanadium release from shale. [ABSTRACT FROM AUTHOR]

Engineered nanoparticle–support interaction is an effective strategy for tuning the structures and performance of engineered nanoparticles. Here, we show that tuning the dehydroxylation of kaolinite nanoclay as the support could induce zinc oxide–kaolinite interactions. We used free energy theory, electron microscopy, and X-ray photoemission spectroscopy to identify interaction strengths between metal oxides and the underlying nanoclay induced by dehydroxylation. Desirable exposure of nanoparticle sites and the geometrical and crystal structure were obtained by tuning the interface interactions between ZnO nanoparticles and nanoclay. The surface free energy of zinc oxide–nanoclay results in different interfacial interactions, and the properties of the surface free energy electron-donating (γ−) and electron-accepting (γ+) parameters have significant effects on the electron acceptor. This could, in turn, promote stronger interactions between zinc oxide and the kaolinite surface, which produce more active (0001) Zn-polar surfaces with promoting zinc oxide nanoparticles growing along the <0001> direction. Reactive oxygen species, leached zinc ions, and electron transfer can modulate the antibacterial activities of the samples as a function of interface free energy. This further demonstrates the interfacial interactions induced by dehydroxylation. This work has new application potential in biomedicine and materials science. [ABSTRACT FROM AUTHOR]

Concomitant selective dehydroxylation during the transformation of flavones into pyrazoles with hydrazine is determined by the A‐ring substitution pattern and propensity to keto enol tautomerization. The obtained pyrazoles show varied tyrosinase inhibition properties, including one nanomolar inhibitor. [ABSTRACT FROM AUTHOR]

Materials with grain sizes of less than 63 μm from the quarries (Cebeci, Cendere and Arnavutköy) in Istanbul (Turkey) are considered as waste and cannot be utilised in any area. In this study, we aimed to determine the expansion potential of the wastes and the factors that trigger the expansion. The grain sizes of the sandstone-shale wastes from the Cebeci (CB), Cendere (CN) and Arnavutköy (AR) quarries range between 2 and 71 µm, 2 and 56 µm and 2 and 77 µm, respectively. The mineral paragenesis of the wastes from the investigated regions is the same and consists of quartz, albite, muscovite, chlorite and calcite. Expansion tests show that quarry waste samples expanded at temperatures between 1200 and 1210 °C. The wastes were subjected to expansion tests in the range of 2–8 min, and their expansion rates were determined every minute. It was determined that the expansion rate of the quarry wastes in the Cendere region is higher than those of the Cebeci and Arnavutköy regions. Thermal analysis results indicate that the OH‾ release (dehydroxylation) of chlorite and muscovite minerals in waste samples occurred at approximately 560 °C. As a result of dehydroxylation, the wastes undergo partial melting and thus form a viscous structure that can trap gases and provide expansion in the samples. With the formation of a viscous structure, H2O and CO2 gases released from chlorite, muscovite, calcite minerals and organic matter in the range of 1200–1210 °C were trapped in the samples and allowed them to expand. [ABSTRACT FROM AUTHOR]

A strategically distinct dehydroxylative alkylation reaction of α‐hydroxy carboxylic acid derivatives with alkenes is developed. The reaction starts with the attack of a 4‐dimethylaminopyridine (DMAP)‐boryl radical to the carbonyl oxygen atom, followed by a spin‐center shift (SCS) to trigger the C−O bond scission. The resulting α‐carbonyl radicals couple with a wide range of alkenes to furnish various alkylated products. This strategy allows for the efficient conversion of a wide array of α‐hydroxy amides and esters derived from several biomass molecules and natural products to value‐added compounds. Experimental and computational studies verified the reaction mechanism. [ABSTRACT FROM AUTHOR]

A strategically distinct dehydroxylative alkylation reaction of α‐hydroxy carboxylic acid derivatives with alkenes is developed. The reaction starts with the attack of a 4‐dimethylaminopyridine (DMAP)‐boryl radical to the carbonyl oxygen atom, followed by a spin‐center shift (SCS) to trigger the C−O bond scission. The resulting α‐carbonyl radicals couple with a wide range of alkenes to furnish various alkylated products. This strategy allows for the efficient conversion of a wide array of α‐hydroxy amides and esters derived from several biomass molecules and natural products to value‐added compounds. Experimental and computational studies verified the reaction mechanism. [ABSTRACT FROM AUTHOR]

Natural zeolite clinoptilolite CLIN with a framework ratio of Si/Al ≥ 4 containing mainly potassium and calcium ions in its internal channel system was used as a starting material. The acidic HCLIN catalysts were prepared under soft conditions avoiding the use of environmental less-benign mineral acids. The starting material was ion exchanged using a 0.2 M aqueous ammonium nitrate solution at a temperature 80 °C for 2 h. The obtained NH4CLIN was converted into the acid HCLIN catalyst by calcination at 300–600 °C. The obtained samples were characterized by XRD, FTIR, SEM/TEM, AAS, and EDX element mapping. The state of aluminium and silicon was studied by 27Al- and 29SiMAS NMR spectroscopy. The textural properties of the catalysts were investigated by nitrogen adsorption and desorption measurements. The Brønsted acidity of the HCLIN catalysts was studied by temperature-programmed decomposition of the exchanged ammonium ions releasing ammonia as well as 1H MAS NMR, {1H–27Al} Trapdor, and {1H–27Al} Redor experiments. The strongly agglomerated samples were crystalline and thermally stable up to >500 °C. Although a part of the clinoptilolite framework is maintained up to 600 °C, a loss of crystallinity is already observed starting from 450 °C. The specific surface areas of the starting CLIN and ammonium exchanged NH4CLIN are low with ca. 26 m2/g. The pores are nearly blocked by the exchangeable cations located in the zeolite pores. The thermal decomposition of the ammonium ions by calcination at 400 °C causes an opening of the pore entrances and a markable increase in the specific micropore area and micropore volume to ca. 163 m2/g and 0.07 cm3/g, respectively. It decreases with further rising calcination temperature indicating some structural loss. The catalysts show a broad distribution of Brønsted acid sites (BS) ranging from weak to strong sites as indicated the thermal decomposition of exchanged ammonium ions (TPDA). The ammonium ion decomposition leaving BS, i.e., H+ located at Al–O–Si framework bridges, starts at ≥250 °C. A part of the Brønsted sites is lost after calcination specifically at 500 °C. It is related to the formation of penta-coordinated aluminium at the expense of tetrahedral framework aluminium. The Brønsted sites are partially recreated after repeated ammonium ion exchange. The catalytic performance of the acidic HCLIN catalysts was tested in the etherification of glycerol as a green renewable resource with different C1-C4 alcohols. The catalysts are highly active in the etherification of glycerol, especially with alcohols containing the branched, tertiary alkyl groups. Highest activity is observed with the soft activated catalyst HCLIN300 (300 °C, temperature holding time: 1 min). A total of 78% conversion of glycerol to mono and di ether were achieved with tert-butanol at 140 °C after 4 h of reaction. The mono- and di-ether selectivity were 75% and 25%, respectively. The catalyst can be reused. [ABSTRACT FROM AUTHOR]

Common clay deposits contain a variety of minerals that provide low and unpredictable reactivity even after calcination. This study aims to enhance the reactivity of such low-grade clay via alkali thermal fusion, where clay was co-calcined with different dosages of NaOH to achieve superior reactivity. The effects of such co-calcination on the formation of reactive aluminosilicates were monitored using high-temperature in-situ X-ray Diffraction (XRD). Additionally, the role of different alkali dosages on the characteristics of the calcined clays was studied using ex-situ XRD, FTIR, ICP-OES, and 29Si NMR. The co-calcination process significantly enhanced the Al and Si dissolution from the calcined clays, which subsequently improved their pozzolanic properties. All of the alkali-fused SCMs satisfied the modified strength activity index (SAI) requirement and the lower dosages of alkali-containing samples (5 % NaOH) showed 50 % reduction in expansion due to alkali silica reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dry synthesis method for utilizing active sites of cobalt oxides on alumina. • Combined alumina dehydroxylation and solid-state impregnation for dry synthesis. • Active control of hydroxyl groups and Al penta sites over γ-Al 2 O 3 surface. • Enhanced redox property via selectively favored Co 3 O 4 phase formation. • Designing catalyst where strong support-metal interaction has negative effects. Alumina-supported cobalt oxide excels as an oxidation catalyst, however, strong metal-support interactions (SMSI) of cobalt and alumina can lead to inactive phases such as cobalt aluminate. To avoid the formation of the inactive phase, it was hypothesized that reducing the number of hydroxyl group anchoring sites on the alumina would enable a higher ratio of active cobalt oxide than inactive phases. We devised a dry synthesis method combined with alumina dehydroxylation and solid-state impregnation of cobalt. Characterization results including XRD, XPS, and Raman spectroscopy confirm the formation of the desired active phase on the dehydroxylated alumina. The resultant catalysts demonstrate a surprising decrease in the cobalt content (max. tenfold from 20 wt.% to 2 wt.% of cobalt loading) for oxidations of NH 3 and CO, respectively, suggesting practically useful synthesis method for highly active supported catalysts. [ABSTRACT FROM AUTHOR]

The thermal characteristic behaviors of two kaolinite samples selected from Qingshuihe region in Inner Mongolia in China were studied through thermogravimetry, derivative thermogravimetry, and differential scanning calorimetry (TG–DTG–DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The activation energies of dehydroxylation for the two kaolinite samples (determined as Kaol-1 and Kaol-2) were calculated based on KAS and FWO methods. The XRD results indicated that Kaol-1 and Kaol-2 both were determined as kaolinite, and a small amount of quartz, but the Kaol-2 presented many amorphous organic matters. The TG–DSC results displayed the adsorbed water desorption and dehydroxylation with the temperature increased from 200 to 1100 °C. The dehydroxylation is followed as the intensities decrease in the bands at 3690 cm−1, 3620 cm−1 and 914.0 cm−1 attributing to the stretching mode of inner surface hydroxyls, and which disappeared when the temperature reached at 600 °C. The endothermic peak temperature of dehydroxylation for Kaol-2 presented higher than that of Kaol-1, which may be attributed to present of amorphous organic matter and was in agreement with the XRD data. The maximum endothermic temperature of dehydroxylation increased both for Kaol-1 and Kaol-2 with the increase in heating rate, which was attributed to more sufficient decomposition as the decrease in heating rate. The thermal kinetic analysis indicated that the dehydroxylation reaction of Kaol-1 should be a single kinetic mechanism, but the E of Kaol-2 decreased as α increasing from 0.2 to 0.5 and then gradually increased with the increase of α. The average E of dehydroxylation for Kaol-2 both was lower than that of Kaol-1 based on Kissenger–Akahira–Sunose and Flynn–Wall–Ozawa methods, which was attributed to the relatively higher organic carbon content in Kaol-2. [ABSTRACT FROM AUTHOR]

The thermal-decomposition behavior of a sodium-bentonite sample was investigated in this study. Non-isothermal pyrolysis tests were performed through simultaneous thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis to characterize the thermal-behavior of the bentonite sample in a temperature range from ambient to 750°C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) were used to determine the changes in mineralogy, structural features and morphology of bentonite before and after pyrolysis at 750°C. Iso-conversional methods were used to obtain kinetic-parameters such as the activation energies whereas Coats-Redfern (CR) method was used to find the most probable reaction mechanisms involved on the bentonite pyrolysis. XRD analysis showed that bentonite sample was mainly composed of sodium montmorillonite and a minority of other minerals such as quartz, plagioclase, alkali feldspar, cristobalite and calcite. Structural collapse of the clay mineral due to the thermal treatment was confirmed through XRD, FT-IR and SEM. Results indicated that thermal-decomposition of bentonite is carried out in two stages: a dehydration following a diffusion-controlled kinetics with an average activation energy of 72.23 kJ/mol, and a dehydroxylation characterized by a second-order kinetics with an average activation energy of 228.28 kJ/mol. [ABSTRACT FROM AUTHOR]

Mössbauer, Raman, X-ray diffraction and X-ray photoelectron spectroscopies were used to examine the effects of temperature on the structure of two aluminoceladonite samples. The process of oxidation of Fe2+ to Fe3+ ions started at about 350 °C for the sample richer in Al and at 300 °C for the sample somewhat lower Al-content. Mössbauer results show that this process may be associated with dehydroxylation or even initiate it. The first stage of dehydroxylation takes place at a temperature > 350 °C when the adjacent OH groups are replaced with a single residual oxygen atom. Up to ~500 °C, Fe ions do not migrate from cis-octahedra to trans-octahedra sites, but the coordination number of polyhedra changes from six to five. This temperature can be treated as the second stage of dehydroxylation. The temperature dependence on the integral intensity ratio between bands centered at ~590 and 705 cm−1 (I590/I705) clearly reflects the temperature at which six-coordinated polyhedra are transformed into five-coordinated polyhedra. X-ray photoelectron spectra obtained in the region of the Si2p, Al2p, Fe2p, K2p and O1s core levels, highlighted a route to identify the position of Si, Al, K and Fe cations in a structure of layered silicates with temperature. All the measurements show that the sample with a higher aluminum content and a lower iron content in octahedral sites starts to undergo a structural reorganization at a relatively higher temperature than the less aluminum-rich sample does. This suggests that iron may perform an important role in the initiation of the dehydroxylation of aluminoceladonites. [ABSTRACT FROM AUTHOR]

The dehydroxylative functionalization of alcohols is synthetic appealing, but it remains a long-term challenge in the synthetic community. Low-valent titanium has shown the power to produce carbon radicals from alcohols via homolytic cleavage of the C–OH bonds and thus offers the potential to overcome this problem. In this perspective manuscript, we summarized the recent advance on radical dehydroxylative transformation of alcohols either promoted or catalyzed by titanium. The limitation and outlook of the studies in this field are also provided. 1 Introduction 2 Recent Developments in Dehydroxylative Functionalization of Alcohols 2.1 Stoichiometric Titanium Complexes Mediated Homolysis of Alcohols 2.2 Radical Dehydroxylative Functionalization of Alcohols by Ti Catalysis 3 Summary and Outlook [ABSTRACT FROM AUTHOR]

Two‐step chemical vapor deposition (CVD) method is a promising technique for industrial fabrication of low‐hydroxyl silica glass ingot, in which a porous silica preform is first synthesized by flame hydrolysis deposition, which is subsequently sintered and vitrified to form silica glass. During sintering hydroxyls can be easily removed through the small pores in porous silica preform, which is called dehydroxylation. A deep understanding of the heat and mass transport characteristics involved in the dehydroxylation process is prerequisite to its controlling. In our previous work, a numerical model was developed to simulate the sintering and dehydroxylation of porous silica preform considering heat and mass transfer in porous media at high temperatures, chemical reaction of dehydroxylation, and volume shrinkage of preform. The results revealed that the dehydroxylation effect largely depends on the temperature fields in the furnace. In present work, the influences of thermal environments, including heating curve, heater position, and crucible structure on the dehydroxylation process of porous silica preform are systematically studied by numerical methods. Based on the results, increasing temperature at either stage is helpful for hydroxyl removal as well as increasing the hydroxyl distribution uniformity. However, long‐time exposure to 1500°C will instead worsen the dehydroxylation effect. Compared to top or bottom heating, side heating is more beneficial to hydroxyl removal. To improve the dehydroxylation condition at the bottom of porous silica preform, a novel crucible structure is designed which shows better performance than the ordinary crucible. At last, an optimized heating scheme is proposed in this study, which obtains much better dehydroxylation effect than other cases. [ABSTRACT FROM AUTHOR]

Thermal treatment of clay minerals is used to produce building materials like supplementary cementitious materials (SCM). New, environmentally friendly binders, that are alkali activated materials (AAM) or geopolymers can be produced with calcined clay minerals, too. Four typical reactions occur during thermal treatment of clay minerals, namely dehydration, dehydroxylation, breakdown of structure, and recrystallization of high temperature phases. Heating to temperatures below the breakdown of structure makes rehydration and rehydroxylation of the clay minerals possible, ass observed in ancient bricks and pottery. As swellable clay minerals or mixtures of different clay minerals come into focus as precursors for geopolymers or as SCM, it is important to pay attention to rehydroxylation in this context as well. This work studied the rehydration and rehydroxylation of three different homoionic (Na+, Ca2+, Mg2+) exchanged trans- and cis-vacant dioctahedral smectites at equal relative humidity (75% r.H.) at different temperatures (22, 40, and 60 °C) after calcination at 700 °C. Simultaneous thermal analysis was used to determine the amount of H 2 O uptake (after 4, 24, 48, 72, and 168 h) due to rehydroxylation. Rehydroxylation between 8.7% for a Na+ exchanged sample and up to 37.3% for a predominantly Mg2+ exchanged sample took place within 7 d. The process of rehydroxylation could be further verified by X-ray diffraction, these measurements should be part of future studies. The α-free isoconvertional approach resulted in E a of rehydroxylation in the range 32–90 kJ/mol for Ca2+ exchanged samples. • Rehydroxylation of smectites takes place at ambient conditions. • Degree of rehydroxylation increased with time and temperature. • Ca2+ and Mg2+ exchanged samples showed larger values for rehydroxylation than Na+ exchanged ones. • Activation energies of rehydroxylation in the range 32–90 kJ/mol for Ca2+ exchanged samples. [ABSTRACT FROM AUTHOR]

This study presents novel characterisation techniques to evaluate the effects of mechanical activation (MA) on the kaolinite structure. MA was achieved with a planetary ball mill at various times and rotation speeds to get different activation degrees. A thermal activation was performed for comparison purposes. The results of X-ray diffraction and selective area electron diffraction demonstrated that the kaolinite content was significantly reduced as the amorphous phase increased. Illite, K-feldspars, and quartz impurities were extensively modified as well. The morphology of kaolinite particles is altered. Furthermore, the mechanical treatments significantly affected the hydroxyls, losing bonding strength with the structure, as stated with 1H nuclear magnetic resonance. Thermogravimetric analysis and infrared spectroscopy also revealed that water molecules could be formed due to the reaction of hydroxyls between them or with the atmosphere. This work improves the comprehension of MA on kaolin by clearly confirming with new techniques that the mechanical treatments distort the kaolinite structure. • Mechanical activation strongly modifies kaolin's structure. • X-ray diffraction reference intensity ratio is useful to monitor the activation effect. • Amorphization is assessed with transmission electron microscopy selective area electron diffraction. • The hydroxyls are separated from the structure and the chemical bonds are weakened. • The presence of water formed through hydroxyls reaction is confirmed. [ABSTRACT FROM AUTHOR]

High–temperature treatment of smectite minerals leads to the dehydroxylation process. One of the consequences of this process is the loss of sorption ability, which is an interesting, but not fully understood, phenomenon. A combination of static and dynamic quantum–chemical methods was used to analyze structural changes associated with the dehydroxylation of smectite layers. The work aims in the determination of multi–path reaction mechanism. The Nudged Elastic Band (NEB) method allowed for the recognition of intermediate structures, transition states and activation energies in the studied reaction mechanisms. Born–Oppenheimer Molecular Dynamics (BOMD) was used to investigate the interatomic distances time–evolution of atoms involved in the dehydroxylation process at different temperatures. The simulations were carried out in the crystalline phase, for which the computational model was prepared based on the dioctahedral structure of smectites with the chemical formula: Ca2+Al 4 Si 8 O 22 (OH) 2. It was found, that the process requires a proton transfer to the oxygen atom of the hydroxyl group located in the octahedral sheet, which results in the release of water molecule from the layer. In addition, it has been shown that the process of a water molecule formation on the surface is also possible. The process occurring inside the layer is more energetically favoured than that on the surface. However, high activation energies were obtained in both cases, what proves that the dehydroxylation reaction takes place only at a relatively high temperatures. It has also been demonstrated that this process can follow several different mechanisms. [Display omitted] • Smectite structure dehydroxylation process in the light of multi–path reaction mechanism. • Dynamic nature of proton migration. • Water formation on the inner and external sides of the mineral layer. • Energetically more favourable are reactions inside the layers than on the surface. • Six independent reaction pathways were recognized. [ABSTRACT FROM AUTHOR]

In this study we report on the addition of a waste, a real spent corundum abrasive powder collected after testing, to a metakaolin-based alkali activated binder. The waste has been chosen as representative of spent grits produced by industrial blasting processes. In this model system based on metakaolin, the effect of corundum powder in the environment of high alkaline media was investigated in terms of 3D reticulation of the aluminosilicate amorphous structure of the consolidated geopolymeric mixes. A number of microstructural techniques (FT-IR, XRD, TGA/DTA) have been used in combination with less conventional one, such as the ionic conductivity measurements of the eluate produced after 24 h of immersion of the sample in water. The overall 3D aluminosilicate frame typical of MK-based geopolymer is retained also after 50 wt% addition of recycled corundum, as shown by FT-IR, XRD, and TGA/DTA. The traces of ceramic materials abrasion present in the waste showed good reactivity, as shown by the disappearance of their characteristic peaks in the XRD patterns. Ionic conductivity of the eluates evidenced the most extended reactivity of the alkaline activator solution in the case of 10 and 20 wt% addition of the waste. While the role of 20, 30 and 40 wt% addition of the waste to the MK-based matrix produced the highest compressive strength in the consolidated mortars after 28 days comparable to those of Ordinary Portland cement concretes. It was proved that, when produced using a partially reactive waste with well-formulated mix designs, metakaolin alkali-activated binders or mortars are an important aluminosilicate source for room temperature produced construction materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porous dehydroxyl cobalt phytate displays superior OER stability with a V- t test for 80 h. • The role of dehydroxyl temperature in improving the OER performance is critical. • The OER activity and stability of cobalt phytate are even comparable to commercial RuO 2. Phytic acid (PA) is a six-fold dihydrogenphosphate ester of inositol with cost-effective, environmentally friendly, and safe properties. Here, we successfully synthesize the dehydroxyl cobalt phytate (PA-Co-400) using PA as phosphorus sources by a one-pot wet-chemistry strategy to prepare the precursor PA-Co and then heat treatment at 400 °C under an N 2 atmosphere for dehydroxylation. The average diameter, specific surface area, surface element distribution, and catalytic activity of the catalyst are significantly affected by dehydroxylation temperature. The specific surface area increases first and then decreases with the treatment temperature from 200 °C to 600 °C. The SEM results indicate that the average diameter of PA-Co-400 particle is 68.90 nm. The as-prepared samples are used as an anode catalyst for electrocatalytic oxygen evolution reaction (OER). The PA-Co-400 exhibits splendid OER performances with an overpotential of 310.31 mV at j 10 (η 50 = 349.35 mV, η 100 = 367.20 mV), which are even comparable to commercial RuO 2 (η 10 = 310.54 mV, η 50 = 389.80 mV, η 100 = 450.60 mV). Moreover, the PA-Co-400 has a small Tafel slope of 53.27 mV dec−1, which is lower than commercial RuO 2 (81.71 mV dec−1). The ultra-long durability of PA-Co-400 was tested for over 80 h at current densities of 10 mA cm−2 without a significant reduction in 1 M KOH. [ABSTRACT FROM AUTHOR]

This work aims to assess the potential reactivity of a mechanically activated kaolin for its use as an alternative cement precursor. The mechanical activation was successfully achieved by grinding at different rotation speeds (250, 300, and 350 rpm) and times (60, 90, and 120 min), obtaining a highly amorphous and reactive material. The amorphization was monitored through XRD with amorphous content estimation and FTIR deconvolution. The potential reactivity was evaluated through chemical attacks, obtaining SiO 2 and Al 2 O 3 availabilities up to 95 wt% and 93 wt% of total SiO 2 and Al 2 O 3 content. XRD and FTIR also allowed the identification of the non-reactive phases on the insoluble residue after chemical attacks. NMR analysis revealed that part of the aluminium was in IV coordination, limiting the reactivity in the alkali activation process. This work demonstrated the effectiveness of mechanical activation as a greener treatment than thermal dehydroxylation to increase the raw kaolin's reactivity. • The effect of mechanical activation (MA) in kaolin's reactivity was evaluated. • MA enhances the reactivity of kaolin. • Grinding time and rotation speed's influence on kaolin's reactivity was revealed. • The MA of kaolin could lead to a higher amorphous content than in metakaolin. • The results demonstrate that activated kaolin is suitable as cement precursor. [ABSTRACT FROM AUTHOR]

• Water content in the glasses is intimately related to the melt viscosity. • Temperature and time of dehydroxylation has been optimized for the title glass. • The method of dehydroxylation has shown to be efficient for up to 50 g of glass. • The Nd 2 O 3 doped glass showed excellent optical characteristics and laser performance. • Nd3+ ions may be present in two structural environments within the glass matrix. A photograph of an as-melted dehydroxylated Nd 2 O 3 doped laser phosphate glass where inset shows the time-evolution of stimulated emission pulses at pump energies of 28 mJ and 45 mJ and pump pulse at 802 nm wavelength. [Display omitted] In this work, we have studied the preparation and properties of an alumino-phosphate glass with composition 13Na 2 O-13K 2 O-16BaO-4Al 2 O 3 -54P 2 O 5 (mol%). The first part of the work deals with the study of the processing conditions of the dehydroxylation of the phosphate glass, which was performed by remelting under N 2 flow using graphite crucibles. Glass samples from 5 to 50 g and Nd 2 O 3 doped were submitted to dehydroxylation and the influence of temperature, time, mass of glass and viscosity were correlated with the content of water in the glasses through the coefficient of absorption of OH ions. The network structure of the glasses was also determined by means of 31P and 27Al 1D/2D nuclear magnetic resonance and the local environment of Nd3+ ions was probed by electron paramagnetic resonance. The optimized conditions of processing were then used to obtain a dehydroxylated glass with a 2.5 wt% Nd 2 O 3 whose spectroscopic and laser emission properties were studied. The spectroscopic properties of Nd3+ ions which include, Judd-Ofelt calculation, stimulated emission cross-section of the laser transition, lifetime, and quantum efficiency are presented. Site-selective laser spectroscopy and stimulated emission obtained under selective wavelength pumping along the 4I 9/2 →4F 5/2 absorption band were performed to determine the distribution of crystal field in which the rare earth is located, together with its influence in the pump wavelength dependence of the spontaneous and laser emissions of Nd3+ in this glass matrix. [ABSTRACT FROM AUTHOR]

• Water molecules and Ca2+ ions located between mineral layers play a significant role in the dielectric response. • Nontronite annealed approx. 350 °C rebinds water very easily. • Nontronite annealed up to 440 °C partially loses its water–binding capacity. • Total loss of the water–binding ability and tenfold reduction of electrical permittivity is observed after exceeding 643 °C. • The results obtained from TG, XRD, and dielectric measurements are consistent. The effect of annealing temperature on the ability to rebind water by nontronite was investigated. Nontronite is a type of layered mineral that belongs to the smectite group of clay minerals. It was found that annealing the mineral at temperatures lower than 350 °C causes loss of the interlayer water. However, after moisten water is reabsorbed to a large degree. When the mineral was annealed at approx. 640 °C, it loses definitely the ability to bind water. [Display omitted] [ABSTRACT FROM AUTHOR]

• Thermal treatment of hydrous volcanic glass (rhyolite) causes moisture, molecular weather and hydroxyl release at different temperature. • Frasier-Suzuki method was applied to deconvolute 3 processes and calculate their kinetic triplet values (Ea, A, f(a)). • Moisture release follows 3D Ginstling-Brounstein D4 diffusion model, and molecular water and hydroxyl group release following Zhuravlev model. • Heated samples present higher a* (redness) and b* (yellowishness) coordinates' values compared to raw volcanic glass. Thermal decomposition of hydrous volcanic glass occurs through the release of different water species under overlapping processes over wide temperature range. Its investigation is of practical interest since it constitutes integral processing part towards its valorization as source for the production of high-quality porous material for various applications. The study presents investigation of thermal decomposition of hydrous rhyolite through the non-isothermal solid-state kinetics approach. Rhyolite decomposition occurs through three partially overlapping processes, where loosely held and chemically bound water, as well as hydroxyl release at different temperature regions and through different mechanisms. The separation of overlapped thermal curves was done through peak deconvolution method using Frazier-Suzuki equation. Subsequently, the isoconversional (model-free) Friedman, generalized master-plots and Kissinger methods were applied for the determination of apparent activation energy (E a), reaction model (f(a)) and pre-exponential factor (A) for each individual reaction step considered. Using the kinetic triplet values of each process, the kinetic rate equations were combined allowing precise simulation of the dehydration and dihydroxylation processes. A comparison of model results with thermogravimetric (TG) data, as well as data from the literature, showed the satisfactory accuracy of the model in the simulation of the process and the successful prediction of each water type fraction, during the process evolution. Spectroscopy techniques in UV―VIS and NIR (near infra-red) spectral ranges were applied to raw rhyolite and sample with different water content allowed calculation of color coordinates and its correlation with dehydration and dehydroxylation degrees, and also identification of water species. [ABSTRACT FROM AUTHOR]

In view of the reduction of the environmental impact due to cement production and towards the attenuation of supplementary cementitious materials (SCMs) production cost, new, non-kaolin SCMs have been introduced. This work investigated the structural changes of the minerals present in two Greek palygorskite clays and the pozzolanic reactivity following calcination and grinding. The combination of x-ray diffraction (XRD), thermogravimetric (TG) analysis and Fourier-transform infrared (FTIR) techniques shed light on the effect of calcination and grinding time on minerals' structure and pozzolanic reactivity. The results showed that the thermal and mechanochemical dehydroxylation led to the structural disorganization of palygorskite crystal structure that commenced immediately following 3 h calcination and 15 min grinding. Thermally and mechanically treated clays demonstrated similar Ca(OH) 2 (CH) consumption, ranging between 665 and 755 and 577–761 mg CH/g clay respectively. Therefore, the pozzolanic reactivity of the treated clays was competitive with high-purity and commercial metakaolin, mechanically treated kaolin and higher than that of calcined zeolite suggesting that the thermal and mechanical treatment of palygorskite clay produced a SCM with enhanced pozzolanic reactivity, which may be an alternative to widely known pozzolanic materials. • Thermal and mechanical treatment induces the dehydroxylation of palygorskite. • Both treatments reduce or eliminate the palygorskite and smectite crystallinity. • Both treatments produce highly reactive pozzolans, competitive with metakaolins. • Palygorskite pozzolanic reaction produces tobermorite gel. [ABSTRACT FROM AUTHOR]

The present paper explores the methods of transforming low grade kaolinitic clay, sandstone clay, into supplementary cementitious material (SCM). The sandstone clay is the waste product in the sand manufacturing from sandstone mineral. Thermal calcination at 600–900 °C was applied to activate the initial sandstone clay. Microstructure characterization was then carried out on the obtained activated sandstone clays (ASCs) to study the microstructure and chemical changes during the thermal activation. The pozzolanic reactivity of ASCs were assessed by direct methods (isothermal calorimetry test and lime consumption test) and indirect method (strength measurement of ASC blended mortar). The compressive strength of the ASCs blended cement based mortar showed that ASCs possessed high pozzolanic reactivity through the dehydroxylation and the alternation of Al and Si coordination environments during thermal activation. Agglomeration occurred after the sandstone clay calcination, however the particle size was reduced. Even at a short time calcination for 1 h, the pozzolanic reactivity of ASCs improved as the calcination temperature increased from 600 to 900 °C. Mortar strength test results confirmed that the ASCs with a fineness similar to OPC, can be used as high quality SCMs. Further isothermal calorimetry results indicated that ASCs not only contributed to pozzolanic reaction but also had a good filler effect in the early hydration stage due to the existence of micro-quartz. [ABSTRACT FROM AUTHOR]

• Presents the fundamentals pertaining to the microwave treatment of ultramafic ores. • High temperature X-ray diffraction analysis showed the transition to heazlewoodite. • Conventional heating tests and thermodynamic modelling supported the microwave tests. The mining of ultramafic ores is required to meet society's continued demand for nickel. These deposits, however, are difficult to process due to their high serpentine content. Serpentine, a gangue mineral, increases slurry viscosity, slime-coats the valuable Ni-bearing mineral pentlandite, and reports to and dilutes the froth during flotation via the formation of bubble-fibre aggregates. Microwave pre-treatment can be used to convert the serpentine gangue to olivine, which should improve ore processing. However, the fundamental microwave properties and heating behaviour of ultramafic ores must be understood to develop a robust process. Microwave heating curves were developed for, and high temperature permittivity analysis was conducted on, two ultramafic nickel ores (Pipe and OK ore). Subsequently, TGA/DSC (thermogravimetric analysis/differential scanning calorimetry) and HTXRD (high-temperature x-ray diffraction) tests, along with a thermodynamic analysis using FactSage 7.3, were done to explain the heating behaviours and permittivity data. An unusual peak in the permittivity data was detected at 950 °C for the Pipe ore with both increasing and decreasing temperature; however, no phase transitions were detected in the TGA/DSC analysis. HTXRD of the Pipe ore revealed the presence of heazlewoodite at higher temperatures (950 to 1100 °C). Thermodynamic modeling of the Pipe ore system suggests that melting at higher temperatures is responsible for the decrease in the permittivities of this ore. To mitigate the melting and clumping of the ore particles, it is necessary to ensure that the processing temperature does not exceed 800 °C during microwave treatment. The OK ore, which contained less microwave response minerals than the Pipe ore, reached a maximum temperature of 500 °C after only 5 min of heating time, and therefore overheating was not an issue. [ABSTRACT FROM AUTHOR]