Dehydroxylation Temperature Research Articles

Controlled Hydrothermal Crystallization of Anhydrous Ln2 (OH)4 SO4 (Ln=Eu-Lu, Y) as a New Family of Layered Rare Earth Metal Hydroxides.

Anhydrous hydroxide sulfates Ln2 (OH)4 SO4 (Ln=Eu-Lu, Y) were hydrothermally synthesized as a new family of layered rare earth metal hydroxides (LRHs). They crystallize in the monoclinic system (space group C2/m) with structures built up by alternate stacking of interlayer SO42- and the two-dimensional host layer composed of tricapped [LnO9 ] trigonal prisms along the a axis. In distinct contrast to the recently discovered hydrated LRHs Ln2 (OH)4 SO4 ⋅2 H2 O, which only exist for Ln=La-Dy, the host layers of the anhydrous phase are linked together by sharing edges instead of an O node of the SO42- tetrahedron. Rietveld refinement showed that the cell dimension tends to decrease for smaller Ln3+ , while the axis angle (β=98.78-100.31°) behaves oppositely. Comparative thermogravimetric/differential thermal analysis in air revealed that the dehydroxylation and desulfurization temperatures become gradually higher and lower, respectively, for smaller Ln3+ , and thus the temperature range of Ln2 O2 SO4 existence is narrowed. The newly discovered Ln2 (OH)4 SO4 , together with their hydrated counterparts, allow for the first time green synthesis of Ln2 O2 SO4 with water as the only exhaust for the full spectrum of lanthanides. Calcining Ln2 (OH)4 SO4 in H2 yielded phase-pure Ln2 O2 S for Eu and Gd and a mixture of Ln2 O2 S and Ln2 O3 for the other Ln. The effects of the lanthanide contraction were clearly revealed, and photoluminescence was found for the anhydrous LRHs of Eu and Tb.

Dehydration and dehydroxylation of C-S-H phases synthesized on silicon wafers

Abstract In this work, the synthesis of specific ultrathin Calcium-Silicate-Hydrate (C-S-H) phases on silicon wafers and their transformation into C-S phases is achieved. Specific mineral phases are identified, and the synthesis is successful controlled. Samples are investigated by means of Fourier Transform Infrared (FTIR) spectroscopy and X-ray Diffraction (XRD) and the results are analyzed based on first-principles calculations. When C-S-H phases are transformed into C-S phases, only a few reflexes are detected on XRD, and the coherent scattering domains decrease with the increment of the temperature and time of exposure. This behavior is explained by the Ca/Si changes, which are identified by changes in the FTIR spectra. A thermodynamic analysis is performed with the help of first-principles calculations to underline the influence of the calcium-to-silicon (Ca/Si) ratio in the process of dehydroxylation. To increase the Ca/Si ratio water is partially substituted by methanol at the synthesis. This is observed in the FTIR spectra and is confirmed by lower temperatures of dehydroxylation. The catalytic nature of calcium towards the dehydroxylation is confirmed. The core of this work lies in the preparation of a model, which perfection makes possible to model reactivity, stability and mechanical properties using first-principles calculations, and is the starting point for the synthesis of many others.

Combined interpretation of NMR and TGA measurements to quantify the impact of relative humidity on hydration of clay minerals

Reliability of core measurement and analysis can be highly dependent on the humidity of measurement environment. However, impact of humidity on core measurements is often assumed to be negligible. This paper quantified the influence of relative humidity on the hydration of clay minerals (i.e., montmorillonite, illite, chlorite, and kaolinite) using nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). The influence of clay hydration on the assessment of fluid volume in organic-rich mudrocks was also investigated. The NMR T2 (spin-spin relaxation) magnetic decay of the clay samples showed existence of water even after the samples were dried in an oven at 95°C. The TGA measurements in clay minerals confirmed the weight loss between 95°C and dehydroxylation temperature, which is approximately the same volume as that recorded by NMR measurement in dried samples. This recorded water volume corresponded to desorption of water molecules bound to interlayer cations (i.e., interlayer water). In the case of the hydration water, the NMR-based water vapor adsorption experiments showed that the volume of water accumulated on the surface of clay minerals increased significantly as the relative humidity increased. The cation exchange capacity (CEC) measurements of clay minerals demonstrated that the volume of hydration water was strongly related to the CEC. The volume of interlayer water was, however, not related to the CEC. In the case of organic-rich mudrocks, water vapor adsorption experiments showed >250% change in water volume when relative humidity varies in the range of 0% to 95%, which further verified the significant impact of humidity on core measurements and the necessity of applying corrections for such an impact.

Refinement of industrial kaolin by removal of iron-bearing impurities using thiourea dioxide under mechanical activation

This study reports a series of experiments conducted to evaluate the suitability of thiourea dioxide (TD) under mechanical activation, in bleaching iron-bearing impurities from raw kaolin. The optimum conditions for the maximum whiteness of 76.32% were determined as follows: rotation speed of ball mill, 400rpm; activation time, 1.5h; TD dosage, 0.8% of kaolin mass; solid-to-liquid ratio, 1:2; pH, 8.0; room temperature. The effect of grinding causes the partial surface amorphization of kaolin particles and a decrease in the dehydroxylation temperature. The assistance of grinding leads to a higher iron removal when compared with the conventional bleaching method using sodium hydrosulfite.

Rehydroxylation in smectites and other clay minerals observed in-situ with a modified thermogravimetric system

Dehydroxylation-rehydroxylation experiments were performed on various dioctahedral aluminous 2:1 layer clay minerals using the precise thermogravimetry (TG) system equipped with a continuous N2 gas flow enriched with H2O vapor of controlled concentration. The setup and rehydroxylation conditions applied are specifically sensitive to study in-situ rehydroxylation of smectites with various octahedral compositions and vacancy, saturated with counterions in various sizes and valences. Under the conditions applied, the pyrophyllite structure does not rehydroxylate, illite shows a minor ability to rehydroxylate, and smectites present an entire range of potential rehydroxylation, from remaining in the completely dehydroxylated state to an almost complete rebuild of the octahedral sheet.The mass gained during single- or multi-isotherm rehydroxylation matches the mass lost during the subsequent (secondary) dehydroxylation. In smectites, the Al-pyrophyllite-like arrangement is preferentially rehydroxylated, but at higher degrees of rehydroxylation, OH groups in other octahedral arrangements are also rebuilt. Among the temperatures tested, smectites and illite rehydroxylate most intensively during isothermal heating at 400°C (H2O content=0.28molH2O/m3), which is the onset temperature of dehydroxylation of their rehydroxylated forms. The smectites capability to rehydroxylate comes from an interplay of the counterions' size, the tetrahedral substitution in the 2:1 layers, and the negative charge generated in the former-octahedral sheet that controls the ability of cations to move from the surface of the tetrahedral sheet or from the octahedral sheet back to the interlayer.The conventional (time)1/4 power law and the logarithmic kinetic models of rehydroxylation produced good fits of the experimental data. Calculation of activation energies (Ea) for the rehydroxylation reaction produced values from 30kJ/mol to 173kJ/mol, highly dependent on the interlayer cation, 2:1 layer structure, and the experimental protocol. The kinetic models developed for rehydroxylation at temperature near ambient remain valid for the experiments up to 400°C. At 500°C the mechanism of rehydroxylation is influenced by other factors.

Dendrimers-containing organoclays: Characterisation and interaction with methylene blue

The structure of organoclays composed of synthesized phosphorus-based dendrimers, which was endowed with peripheral ammonium groups, and stevensite- or montmorillonite-rich clays was examined using X-ray diffraction, high resolution transmission electron microscopy, thermal analysis and solid-state nuclear magnetic resonance. The interactions between methylene blue (MB) and the organoclays or Na+-saturated clay minerals were investigated. The results showed that both dendrimers adsorbed on Na+-saturated clay minerals by cation exchange, and that the organoclays, particularly those of the first generation dendrimers, were mainly composed of intercalated nanocomposites. As a result of the adsorption of the dendrimers, the clay hydrophilicity reduced and the dehydroxylation temperature of the clay minerals increased. Regarding the adsorption of MB on the organoclays, the results pointed out that MB mainly adsorbed as MB+ and MBH2+, and the electronic environments of AlIV of montmorillonite and that of AlVI of stevensite were disturbed. For some organoclays, ordered structures were formed, and the Si4+ substituent (Al3+) left the tetrahedral sheet. The thermodynamic data indicated that MB adsorbed spontaneously (−11.3<∆G°<−0.9kJ/mol) and the uptake of MB by montmorillonite-based organoclays was believed to occur by chemisorption. In contrast, for stevensite-based organoclays MB adsorption seemed to be accomplished by physisorption.

Metal occupancy and its influence on thermal stability of synthetic saponites

Due to high surface acidity and thermal stability, saponite has important applications in various fields. In this study, saponites with different Mg/Zn ratios (0–6) and a fixed Si/Al ratio of 5.43 were synthesized under hydrothermal condition. The resultant synthetic saponites were characterized by using XRD, FTIR, TG, SEM and MAS NMR. The characterization results demonstrated that, with a decrease of Mg/Zn ratio, both the crystallinity and layer stacking order of saponite were increased, and rose-like morphology was observed in Zn-saponite. Al3+ preferentially occupied tetrahedral sites in Si-O tetrahedral sheet in all synthetic saponites. A decrease of Mg/Zn ratio in octahedral sheet could improve the substitution extent of Al3+ for Si4+ and resulted in an increase of Al(IV)/Al(VI) ratio in the resultant saponite, which might be a crucial factor to control the crystal growth of saponite. The dehydroxylation temperature of saponite depended strongly on the Mg/Zn ratio and the replacement of Al3+ for Mg2+ and Zn2+ in octahedral sheets, due to their different bond strength. A ‘one-to-one’ mode was proposed for the substitution of Al3+ for Mg2+ and Zn2+ in octahedral sheets of the synthetic saponites.

Surface and Bulk Thermal Dehydroxylation of FeOOH Polymorphs.

In this study, bulk and surface thermal decomposition of synthetic iron oxyhydroxides to iron oxides was followed using the temperature-programmed desorption (TPD) technique. Submicron-sized akaganéite (β-FeOOH), rod- and lath-shaped lepidocrocite (γ-FeOOH), and goethite (α-FeOOH) particles were heated in vacuo in the 30-400 °C range, and their OH vibrational modes were monitored by Fourier transform infrared (FTIR) spectroscopy while H2O(g) release was monitored by quadrupole mass spectrometry. Peak thermal dehydroxylation temperatures were larger in the order of lath lepidocrocite (200 °C) < akaganéite (200/260 °C) < rod lepidocrocite (268 °C) < goethite (293 °C). Pre-equilibration of these particles to aqueous solutions of HCl increased dehydroxylation temperatures of all minerals except goethite by 13-40 °C. These shifts were explained by (1) the dissolution of particles or regions of particles of lower degree of crystallinity by HCl, as well as (2) the strengthening of the hydrogen bond environment in the akaganéite bulk. The latter is a means of facilitating H2O(g) formation via interactions between two adjacent OH groups. Strongly analogous forms of interactions at the FeOOH particle surfaces were also shown to facilitate the release of singly coordinated (-OH) hydroxo groups to the gas phase at temperatures lower than 125 °C, thus creating OH vacancies that may be actively involved in the transfer of bulk to surface OH groups during thermal dehydroxylation. Doubly- (μ-OH) and triply- (μ3-OH) coordinated hydroxo groups were however resilient to exchange under those conditions, and their dehydroxylation was strongly congruent with that of bulk OH groups. By resolving the bulk and surface thermal decomposition of FeOOH polymorphs, this work provides clearer insight into the fate of these materials in natural and technological settings where important thermal gradients are commonplace.

Silylation of saponite with 3-aminopropyltriethoxysilane

A series of saponites (Sap) with a fixed Si/Mg ratio and varied Al contents were synthesized by using hydrothermal methods. The spectral, structural and morphology characters of the obtained products were characterized by a combination of XRD, FTIR, TG-DTG, TEM, 29Si MAS NMR, 13C NMR etc. before and after 3-aminopropyltriethoxysilane (APTES) grafting. XRD patterns showed that well-ordered Sap were obtained with starting Si/Al ratios of 5.43 and 7.89. Silylation reactions have little or no effect on the layered structure of Sap at the used dosage of APTES. The existence of the –CH2 stretching bands at around 2937cm−1 in IR spectra clearly showed the incorporation of silane in the grafted samples. TG–DTG curves revealed that the samples with higher crystallinity displayed higher dehydroxylation temperature, as expected. A new mass loss located at around 420°C in silylated Sap was ascribed to the volatilization of the alkyl group in silane. The 29Si NMR spectroscopy showed a series of signals of T structures, ascribed to the different silylation modes between silane and Sap. Furthermore, silylation procedures led to a decrease of the intensity of the signals at ca. −84ppm along with an increase of the intensity of Q3 signals. A further increase in the silane concentration did not decrease the resonance at −84ppm any further. This phenomenon confirmed the coexistence of Q2 structure with Q3Si(2Al) structure, which resulted from the broken bonds at the edge surfaces of the synthesized Sap.

Colour and toxic characteristics of metakaolinite–hematite pigment for integrally coloured concrete, prepared from iron oxide recovered from a water treatment plant of an abandoned coal mine

A metakaolinite-hematite (KH) red pigment was prepared using an ocherous iron oxide sludge recovered from a water treatment plant of an abandoned coal mine. The KH pigment was prepared by heating the kaolinite and the iron oxide sludge at kaolinite's dehydroxylation temperature. Both the raw sludge and the KH specimen were characterised for their colour properties and toxic characteristics. The KH specimen could serve as a pigment for integrally coloured concrete and offers a potential use for the large volumes of the iron oxide sludge collected from mine water treatment plants.

Characterization of silver-kaolinite (AgK): an adsorbent for long-lived (129)I species.

Bentonite is a preferred buffer and backfill material for deep geological disposal of high-level nuclear waste (HLW). Bentonite does not retain anions by virtue of its negatively charged basal surface. Imparting anion retention ability to bentonite is important to enable the expansive clay to retain long-lived 129I (iodine-129; half-life = 16 million years) species that may escape from the HLW geological repository. Silver–kaolinite (AgK) material is prepared as an additive to improve the iodide retention capacity of bentonite. The AgK is prepared by heating kaolinite–silver nitrate mix at 400 °C to study the kaolinite influence on the transition metal ion when reacting at its dehydroxylation temperature. Thermo gravimetric-Evolved Gas Detection analysis, X-ray diffraction analysis, X-ray photo electron spectroscopy and electron probe micro analysis indicated that silver occurs as AgO/Ag2O surface coating on thermally reacting kaolinite with silver nitrate at 400 °C.

Silica/Methylaluminoxane/(n‐BuCp)2ZrCl2: Effect of Silica Dehydroxylation Temperature on HDPE Morphology

SummaryMorphology and particle size distribution (PSD) of high density polyethylene (HDPE) produced in slurry and gas phase ethylene homopolymerisations have been analysed in connection with the catalytic activity of silica supported (n‐BuCp)2ZrCl2/Methylaluminoxane (MAO) catalysts. It has been shown that the silica dehydroxylation temperature affects the catalytic activity of these silica supported catalysts in ethylene homopolymerisation which, in turn, affects the polymer morphology and PSD. Thick fibrous HDPE is observed in all the polymer samples produced via slurry phase process, whereas, the gas phase process HDPE samples did not show such fibrous structures. PSD of the polymers replicate the PSD of silica support and shifts towards larger particle size with increase in productivity which is related to silica dehydroxylation temperature.

Silica/MAO/(n-BuCp)2ZrCl2 catalyst: effect of support dehydroxylation temperature on the grafting of MAO and ethylene polymerization

This study reports the role of silica dehydroxylation temperature on the performance of Silica/MAO/(n-BuCp)2ZrCl2 catalysts in ethylene homopolymerization.

The possibility of using dredging sludge in manufacturing cements: Optimization of heat treatment cycle and ratio replacement

This study aims to produce an eco-cement by using heat treated dam’s sludge as an additive to clinker. Different heat treatment cycles were applied to the dam’s sludge: three temperatures selected in the range between the dehydroxylation and decarbonation temperatures (600, 700 and 800°C) reached by adopting different heating rates (5, 10 and 20°C/min). The analysis of DRX, DSC–TG, FTIR results show that the heat treatment cycles let to the change of the sludge structure allowing its use as a pozzolanic additive to produce cements. The optimal heat treatment cycle is 600°C with a holding time of 5h and a heating rate 20°C/min. Normalized mortars have been designed using modified cements constituted by 5% of gypsum, different percentage of heat treated sludge (5–10% and 15%) and clinker. The compressive strengths at 28days lead to the choice of blending 85% clinker, 10% heat treated sludge and 5% gypsum to produce modified cements. The influence of the thermal activation of the dam’s sludge on the technical properties such as normal consistency, fineness, setting time, heat of hydration, compressive strength have been investigated and tests were conducted according European standards. Results reveal that heat treatment at 600°C with a rate of 20°C/min conducts to an activated sludge with no emission of carbon dioxide and the higher strength resistance when added to clinker at 10%. However, whatever the fineness or the rate of heat treatment, the percentage of kaolinite (11%) existing in the natural sludge is not sufficient to develop by heat treatment at 600°C hydration products allowing significant improve of mechanical resistance of modified cements by comparison to CEMI.

The effects of In3+ doping on the properties of precipitated goethite

Indium-doped goethite samples were synthesized by the precipitation method at pH 12 using an organic alkali tetramethylammonium hydroxide (TMAH) and investigated using different instrumental techniques. In3+-for-Fe3+ substitution in the goethite structure was confirmed by the measurement of the unit cell expansion by XRD and the reduction of the hyperfine magnetic field by Mössbauer spectroscopy. Maximum substitution was estimated at about 8 mol%. Indium substitution in goethite also caused an increase in the size of crystallites and particles, a shift in the position of bands in FT-IR and UV–Vis–NIR spectra and a rise in goethite dehydroxylation temperature (observed by TGA-DTA).

Use of thermal analysis to determine the hydration products of oil well cement pastes containing NaCl and KCl

This paper evaluates the hydration of oil well cement pastes containing sodium chloride (NaCl) and potassium chloride (KCl) using thermal analysis. Pastes were designed containing up to 36 % of NaCl and up to 34 % of KCl by the mass of water and water to cement ratio of 0.44. The curing was performed at 60 °C up to 7 days. X-ray diffraction was used with a complementary technique to identify the products formed. The results show that the pastes with salt addition presented the formation of Friedel’s salt due to the interaction of the ion Cl− with the aluminate phases. The dehydroxylation temperature of calcium hydroxide lowered with the increment of percentage of salt addition. At the first hours of curing, NaCl and KCl have accelerated the hydration reactions. For later ages, NaCl addition has retarded the hydration reactions and KCl has not modified significantly this property. Exceptions from these were observed for saturated pastes (36 % NaCl and 34 % KCl) that had the hydration reactions retarded in all ages evaluated.

Influence of Grinding and Sonication on the Crystal Structure of Talc

AbstractTalc is an important industrial mineral with a broad range of applications. Particle size and crystal structure have a significant influence on the potential uses. The present study examined the influence of grinding and ultrasound treatment on talc from a new deposit, Gemerská Poloma, in Slovakia. The general knowledge that grinding produces progressive structural disorder leading to amorphization, whereas sonication has a negligible effect on the talc crystal structure, was confirmed by X-ray diffraction (XRD), infrared (IR) spectroscopy, and transmission electron microscopy (TEM). Partial reduction of particle size along with delamination was observed by XRD after sonication, low-angle laser light scattering (LALLS), scanning electron microscopy (SEM), and TEM. The specific surface area (SSA) increased slightly after prolonged sonication, but grinding initially caused a rapid increase in SSA followed by a drastic decrease after prolonged grinding time of up to 120 min which was attributed to the aggregation of amorphized talc. Sonication and grinding had different influences on the thermal behavior of the talc studied. Sonication decreased slightly the dehydroxylation temperature, whereas grinding added a significant mass loss at low temperature, arising from the dehydration of hydrated Mg cations released from the talc structure during amorphization. The initial high whiteness value of talc decreased slightly after grinding or sonication. Thermogravimetry was suggested as a useful tool to track and predict changes in the talc structure upon sonication and grinding.

Effect of dry grinding on chemically modified kaolin

The effect of dry grinding on the morphology and structure of kaolin particles treated with potassium acetate (KAc) and dimethyl sulfoxide (DMSO) has been investigated. After treatment with KAc, the d-spacing of kaolin increased from 0.72 to 1.03, 1.30, and 1.38nm due to the combined effects of humidity and orientation of KAc molecules. The d-spacing was increased to 1.13nm in the case of DMSO treatment. A combination of XRD, TGA, and FT-IR showed that the crystalline structure of kaolin–DMSO and kaolin–KAc were significantly altered by grinding. The intensity of XRD diffraction peaks of ground samples was decreased due to the deterioration of the crystalline structure, and for longer grinding times those peaks almost disappeared. After grinding, the dehydroxylation temperature generally shifted to lower values and a smaller weight loss was observed. The variations of particle size and surface characteristics were also investigated.

Lithium ion assisted hydration of metal ions in non-aqueous sol–gel inks for high performance metal oxide thin-film transistors

Enhanced hydration lowers the dehydroxylation temperature of the sol–gel inks, resulting in high-performance metal oxide thin film transistors.

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

A successive anchoring of Ti(NMe2)4, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800°C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, 13C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands.