Quartz Dissolution Rates Research Articles

Synthesis of xonotlite using quartz glass powder waste as a silicon source

Quartz glass powder is a type of silicon-rich industrial waste. Accumulation of this waste has led to resource wastage and environmental pollution. In this paper, quartz glass powder is used as raw material for preparing xonotlite through hydrothermal synthesis. The effects of Ca/Si (C/S) molar ratio, liquid/solid ratio, reaction temperature, and reaction time on the conversion of quartz are studied. The phase and structural changes of glass powder are analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on this, the conversion mechanism of quartz in glass powder is explained. The dissolution rate of quartz in an alkaline solution is a critical factor that restricts hydrothermal reactions. The conversion rate of quartz can be effectively increased by raising reaction temperature and extending reaction time. When the reaction temperature is 240 °C and the reaction time reaches 14 h, the conversion of quartz can reach 94.5 wt%. This study reveals the conversion mechanism of quartz in hydrothermal reactions and provides a theoretical basis for the efficient utilization of glass powder.

Effects of fluid composition and salinity on subcritical crack growth in granite

Using the double-torsion technique, the fracture mechanical response of granite specimens was investigated under the influence of fluid with different electrolyte types and salinities. The fracture toughness (KIC) and critical mechanical energy release rate (G0) of the granite in electrolyte solution are weakened compared to those in distilled water. The KIC in all electrolyte solutions is 2.08–2.28 MPa·m1/2, which is 8.4 % − 16.5 % lower than that in distilled water, and it is insensitive to ion type and salinity. In contrast, the subcritical crack growth index (n) shows different salinity dependence in three salt (AlCl3, CaCl2, and NaCl) solutions. The slight increase in n with rising salinity of the AlCl3 solution is attributed to crack tip blunting caused by over-dissolution of minerals. The n and G0 decrease and then increase with rising salinity of CaCl2 solution, which may be related to the salinity-dependent dissolution rate of quartz and the weakening of repulsive force between crack surfaces. The n and G0 shows a negative correlation with salinity and decrease by 26.4 % and 15.4 %, respectively as the NaCl salinity increases from 0.1 M to 1.0 M. Limitations in the dissolution reactions of the main minerals (albite, biotite and diopside) is accountable for enhancement of n in silica solutions. Experimental results emphasize the critical and subcritical fracture behavior of the granite in response to chemically reactive fluids with implications for both hydraulic fracture stimulations in geothermal fields and caprock integrity for CO2 sequestration. In these applications, the fracture properties of the reservoir rock can be enhanced or weakened by changing the electrolyte type and salinity of the fluid, depending on the actual requirements.

Counterion effects on the alkali dissolution mechanism of quartz

In gold ore, quartz plays an important role in mineral formation by acting as the follower. Understanding counterion release, transport, and deposition in alkali solution is a prerequisite for evaluating the potential role of gold separate from quartz deposits in pretreatment. In this work, the aggregation, retention, and release of counterion in alkali solution media were investigated by kinetic research and pure mineral experiments, the correlation and mechanism of these processes were revealed by combining geochemical theory, interaction energy calculation, and quantum chemistry. The results showed that the retention and release of counterion were closely related to the dissolution and corrosion rate of quartz. The NH4+ and Fe2+ with higher mineral affinity reduced the quartz stability, and the dispersion stability and mobility of the quartz were greatly improved by an alkaline substance due to the enhancement of steric hindrance effects. Quantum chemical calculation results show that ammonium ion promotes the dissolution of quartz stronger than ferrous ion, which is mainly reflected in reducing the activation energy required for the formation of transition state (TS1), which can be verified by kinetic calculation. These findings provide essential insight into the extraction of gold coated by quartz as well as a vital reference for the experiment of gold-loaded quartz leaching in mineral processing.

Data-Driven Prediction of Quartz Dissolution Rates at Near-Neutral and Alkaline Environments

Dissolution of silicate-based materials is important to many natural processes and engineering applications, including cement and concrete production. Here, we present a data-driven study to predict the dissolution rates of crystalline silica (i.e., quartz) in near-neutral and alkaline environments. We present a quartz dissolution database containing both dissolution rates and five major dissolution conditions (i.e., temperature, pressure, pH at the experimental temperature T (pHT), and the sodium and alumina content in the solution) via data mining from the literature. We supplement the database with experimental data of quartz dissolution rate in sodium hydroxide solutions (0–5 M) at different target temperatures (25–90°C), which are significantly less covered by the existing literature. We build two data-driven models (i.e., random forest (RF) and artificial neural network (ANN)) to predict the dissolution rate of quartz (i.e., output target) as a function of dissolution conditions (i.e., input features). The results show that both RF and ANN models exhibit high predictive capability, with R2 values of 0.97–0.98, MAPEs of 2.95–4.24% and RMSEs of ∼0.31–0.44 log (mole/m2/s) for the test set. These prediction errors are much smaller than linear regression models (RMSE of ∼1.25 log) also presented here and comparable with those achieved in previous studies using reaction models based on a smaller and less complex dataset (RMSE of ∼0.35–0.44 log). We further evaluate the interpretability and performance of the data-driven models, and the results show that the model predictions are generally consistent with literature observations, including the different impacts of input features on dissolution rate. In particular, the ANN model appears to exhibit a certain level of ability to extrapolate, i.e., making predictions in feature space not covered in the database.

Effect of different ions on dissolution rates of silica and feldspars at high pH

The dissolution kinetics of silica-containing minerals in aggregates influences strongly the process of ASR in concrete. In this paper, the effect of different ions on the dissolution rates of SiO2 (amorphous and quartz) and feldspars at high pH values was studied by following the increase of silicon concentrations in dissolution experiments and with a novel approach of measuring the evolution of scratches of polished surfaces. The second method avoided the problem of precipitation in some systems, such as the formation of C-S-H when calcium was present and lithium silicates in the presence of lithium. At high pH values, lithium, calcium and sulfate increased the dissolution rates of silica and feldspars, while iron, magnesium and additional NaCl, KCl or CsCl showed no significant effect. In contrast, aluminium slowed down significantly the dissolution rates of quartz, amorphous silica and Na and K-feldspar at for all temperatures studies: 20, 40 and 60 °C.

Quartz dissolution in a single phase-high pH Berea sandstone via alkaline injection

A common assertion is that alkaline solution aids oil mobilization by generating in situ soap, or by lowering interfacial tension (IFT) to ultra-low values in synergy with surfactants. This study takes a different approach that involves the alkaline dissolution of detrital quartz grains of sandstone reservoirs to create pathways for oil migration and accumulation. Quartz dissolution via alkaline injection will result in changes in permeability and porosity. This study performed high-pH core flooding on Berea sandstones using core displacement equipment. Silica molybdate spectrophotometry was applied to measure the amount of dissolved silica. Inlet and confining pressure variations were also observed. The molar concentration of NaOH varied at 0.5 M and 1.0 M. The results show higher initial silica dissolution for 0.5 M NaOH (˃200mg/L) compared to 1.0 M NaOH (20 mg/L), which can be attributed to the presence of pre-existing dissolved silica and precipitates in the system prior to the first injection phase. Nonetheless, a steady quartz dissolution rate of 0.4 mg/L/hr for 20 h was only achieved at 1.0 M. Conversely, an abrupt drop in quartz dissolution to below 0 mg/L was recorded for 0.5 M NaOH after 3 h of dissolution. At higher molar concentration of injected alkaline solution, both confining and inlet pressures increased from 8 and 5 bars to 12 and 11 bars as a result of the increased secondary phase of (hydr)oxides or precipitates in the pores. Thus, it can be inferred that the effect of alkaline solution on quartz dissolution is strongly dependent on molar concentration.

Chemical Dissolution Drilling of Barre Granite Using a Sodium Hydroxide Enhanced Supercritical Water Jet

This experimental study focused on evaluating the technical feasibility of chemically enhancing rock comminution during supercritical hydrothermal jet drilling by increasing pH with additives. Comminution of the crystalline rock samples occurred under supercritical conditions at temperatures and pressures ranging from 535–580 °C and 22.5–27 MPa, respectively, using hydrothermal jets with sodium hydroxide concentrations ranging from 0.0725 to 0.345 mol/kg. Impinging hydrothermal jets induced thermal spallation and rock removal from 21 Barre granite specimens examined. These experimental conditions replicate those that would be encountered in drilling water-filled wells at depths greater than ~ 2300 m. The combination of accelerated mineral dissolution due to the presence of hydroxide ions, high solution temperature increasing reaction rates, and thermal stresses resulted in rates of rock removal up to 5.16 g in 10 min at 410 °C and 0.345 mol/kg NaOH. Comparison with published empirical quartz dissolution rates at high pH suggests granite mass removal primarily resulted from weakening of the rock matrix as a result of the accelerated dissolution of quartz minerals. Experimentally determined heat flux and surface temperature measurements indicated that the rock comminution occurred below the empirically determined minimum levels for the onset of continuous thermal spallation resulting from impinging low-density flame jets or high energy laser heating.

Kyanite far from equilibrium dissolution rate at 0–22 °C and pH of 3.5–7.5

Kyanite is an important and slow-dissolving mineral. Earlier work has measured its dissolution rate at high temperature and acidic pH, but experimental measurements at low temperature and near neutral pH were lacking. The rate equation by Palandri and Kharaka (A compilation of rate parameters of water–mineral interaction kinetics for application to geochemical modeling. US Geological Survey, Open File Report 2004-1068, 2004) indicates that the rate of kyanite dissolution at room temperature and near neutral pH is on the order of 10−17 mol m−2 s−1, orders of magnitudes slower than most common silicate minerals such as albite and quartz. This study used an externally-stirred mixed-flow reactor, which allows high solid:solution ratios, to measure the dissolution rate of kyanite at 0–22 °C and pH of 3.5–7.5. The measured dissolution rate of kyanite is 4.6–7.6 × 10−13 mol m−2 s−1 at 22 °C, and the apparent activation energy is 73.5 kJ mol−1. This dissolution rate is close to the rate of quartz dissolution and four orders of magnitude faster than the prediction by rate equation of Palandri and Kharaka (2004). Based on our new experimental data, we recommend the following rate equation for modeling the dissolution of kyanite at ambient temperatures. $$r = ke^{{\frac{{ - E_{a} }}{R}\left( {\frac{1}{T} - \frac{1}{298.15}}\right)}}$$ where k = 5.08 × 10−13 mol m−2 s−1, and Ea = 73.5 kJ mol−1. Review of literature data (Carroll in The dissolution behavior of corundum, kaolinite, and andalusite: a surface complex reaction model for the dissolution of aluminosilicate minerals in diagenetic and weathering environs. Dissertation, Northwestern University, 1989) led to a recommended rate equation for andalusite as for T = 25 °C and pH = 2–10: $$r = k_{1} a_{{{\text{H}}^{ + } }}^{{n_{1} }} + k_{2} + k_{3} a_{{{\text{H}}^{ + } }}^{{n_{3} }}$$ where k1 = 4.04 × 10−10 mol m−2 s−1, k2 = 7.95 × 10−10 mol m−2 s−1, k3 = 1.01 × 10−17 mol m−2 s−1, n1 = 1.2 and n3 = − 0.6.

Kinetics of dissolution of sapphire in melts in the CaO–Al2O3–SiO2 system

The dissolution rate of sapphire in melts in the CAS system of varying silica activity, viscosity and degree of alumina saturation has been determined at 1600 °C and 1.5 GPa. After an initiation period of up to 1800 s, dissolution is controlled by diffusion of cations through the boundary layer adjacent to the dissolving sapphire. The dissolution rate decreases with increasing silica activity, viscosity and molar Al2O3/CaO. The calculated diffusion matrix for each solvent melt shows that CAS 1 and 9 which have molar Al2O3/CaO of 0.33 and 0.6 and dissolution rate constants of 0.65 × 10−6 and 0.59 × 10−6 m/s0.5 have similar directions and magnitudes of diffusive coupling: DCaO-Al2O3 and DAl2O3-CaO are both negative are approximately equal. The solvent with the fastest dissolution rate: CAS 4, which has a rate constant of 1.5 × 10−6 m/s0.5 and Al2O3/CaO of 0.31 has positive DCaO-Al2O3 and negative DAl2O3-CaO and the absolute values vary by a factor of 4. Although many studies show that aluminium is added to the melts via the reaction:Si4+=Al3++0.5Ca2+the compositional profiles show that this reaction is not the only one involved in accommodating the aluminium added during sapphire dissolution. Rather, aluminium is incorporated as both tetrahedrally coordinated Al charge balanced by Ca and as aluminium not charge balanced by Ca (termed Alxs). This reaction:AlIV–Ca=Alxs+CaNBOwhere CaNBO is a non-bridging oxygen associated with calcium, may involve the formation of aluminium triclusters. The shape of the compositional profiles and oxide-oxide composition paths is controlled by the aluminium addition reaction. When Alxs exceeds 2%, CaO diffusion becomes increasingly anomalous and since the bond strength of Alxs correlates with CaO/CaO + Al2O3, the presence of more than 2% Alxs leads to significantly slower dissolution than when Alxs is absent or at low concentration. Thus, dissolution is controlled by diffusion of cations through the boundary layer, but this diffusion is itself controlled by the structural modifications required by the addition of new components to the melt. Comparison of quartz dissolution rates in similar melts shows that dissolution is much faster for quartz than for sapphire and that dissolution rates show the same correlation with silica activity and viscosity. We suggest that diffusive fluxes are related to changes in melt structure and the nature of the reaction that incorporates the added component. For the slow eigendirection, SiO2 addition occurs by a single reaction whereas Al2O3 addition requires a more complex two part reaction in which Al is accommodated by charge balance with Ca until Al is in excess of that which can be charge balanced. The Alxs incorporation reaction, is slower than the Si incorporation reaction which inhibits sapphire dissolution relative to quartz in melts of the same composition.

Characterization of Alkali-Induced Quartz Dissolution Rates and Morphologies

A number of studies have investigated the impact of alkali cations on quartz dissolution to increase the understanding of natural rock weathering and enhance the predictability of silica behaviour in reservoir systems. However, there are few evidences for how alkali cations approach the quartz surface. Thus, this study is an attempt to provide empirical evidence on the interaction of electrolytes (\(\hbox {Na}^{+}, \hbox {K}^{+}, \hbox {Ca}^{2+})\) with quartz surface. Bulk quartz grains and clean-faced single quartz crystals were dissolved/etched in varying pH solutions of acidic, near-neutral/neutral and alkali solutions (KOH, NaOH, KCl, NaCl, \(\hbox {CaCl}_{2}, \hbox {CH}_{3}\hbox {COOH}\), HCl). The amount of dissolved silica was measured with molybdate spectrophotometry method, while variations in quartz surface morphology were studied using scanning electron microscopy attached with EDX. Quartz dissolution rates varied with pH, hydrated radius and hydrolysis constants of alkali cations in the order: \(\hbox {Ca}^{2+}<\hbox {Na}^{+}<\hbox {K}^{+}\). Relatively deeper triangular etch pits were observed in quartz dissolved in KOH and NaOH solutions, while shallower pits formed in neutral solutions, and exsolution faces and lamellae were formed in quartz dissolved in low-pH solutions. The results also showed that interfacial secondary phases of cationic silicates play a key role in quartz dissolution.

A study on the impact of SO2 on CO2 injectivity for CO2 storage in a Canadian saline aquifer

Potential effects of SO2 as an impurity on CO2 injectivity for CO2 storage in a targeted sandstone saline aquifer in western Canada were investigated. Batch experiments using rock and brine samples in contact with supercritical CO2 and CO2 mixtures with SO2 were conducted in high-pressure reactors for 45days. The results suggest that SO2 increased precipitation of sodium chloride and calcium sulfate dehydrate, and also increased the dissolution of quartz. Moreover, the precipitation of sodium chloride appeared to be concurrent with the dissolution of quartz, the predominant constituent of the rock. The concurrent precipitation of sodium chloride and dissolution of quartz could be attributed to taking up of water by H4SiO4 that reduces the number of water molecules in the hydration shells of Na+ and Cl− ions in highly concentrated brine. According to this view, the dissolution of quartz, which would be much slower than the reassociation of dissolved sodium chloride ions, is limiting the rate of sodium chloride precipitation. The rate of quartz dissolution was estimated based on the present experimental data, which could be used to assess salt precipitation and determine suitable operation conditions for CO2 injection. The findings of this work should also be applicable to acid gas injection in oil and gas industry.

Rate equations for sodium catalyzed quartz dissolution

Quartz dissolution rate data were fit to an equation that predicts the dissolution flux (J, mol/m2sec) as a function of temperature (T, K), sodium concentration (mNa+, molal), and hydrogen ion activity (aH+). J=0.64610-748002.303R1T+6.6410-880002.303R1TmNa+0.331aH+0.441The same data fit equally well to an equation that expresses the rate as a function of temperature, sodium concentration, and hydroxide ion activity (aOH-). J=0.64610-748002.303R1T+1120010-716002.303R1TmNa+0.326aOH-0.441These equations are more convenient to use than those given by Bickmore et al. (2008) because rates can be predicted without the implementation of a surface speciation model. They predict that at 25°C quartz dissolves more than 200 times faster in seawater than in pure water.These two equations fit the data just as well as five other equations from Bickmore et al. (2008) that are based on surface species concentrations. All of these rate equations contain information about the reaction mechanism(s) for quartz dissolution but that information is ambiguous because the independent variables used to develop the equations are correlated. This means that rate equations alone cannot be used to infer the dissolution mechanism. Existing surface complexation, surface charge, terrace-ledge-kink, and Lewis acid-base models must be modified and amalgamated in order to develop a reliable model of the reaction mechanism(s).

Dissolution kinetics of quartz in water at high temperatures across the critical state of water

The steady-state dissolution kinetics of quartz in water has been measured at temperatures from 20 to 435°C at pressures of 23 and 33MPa using a continuous stirred-tank reactor. Dissolution rates were found to increase with increasing temperature from 20 to 374°C at 23MPa, giving an Arrhenius expression of logk+=−1.6478−13,573.1/T(K), but then decreased on further increasing the temperature beyond 374°C. At 33MPa, the rates increased with temperature up to 400°C, giving an Arrhenius expression of logk+=−1.325−14,124/T(K), but then decreased on further increasing the temperature. At a constant temperature below 350°C, quartz dissolution rates were found to increase with increasing pressure. At around the critical state of water, the dissolution rates fluctuated as a result of sharp changes in the properties of the medium (e.g., density, dielectric constant, ionic product).

Dissolution Rate and Diffusivity of Silica in SiMn Slag

The dissolution rate and solubility of quartz in silicomanganese slag were studied in the temperature range of 1673 K to 1823 K (1400 °C to 1550 °C) under an inert atmosphere of argon. The dissolution rate of quartz was measured using a rotating rod technique; while quartz solubility was examined using static experiments. Solubility of silica in slags was also calculated using multi-phase equilibrium thermodynamic software developed by CSIRO. Effects of additives (CaO, MnO, SiO2, and Al2O3) on the quartz dissolution rate and solubility were also examined. Under the experimental conditions employed the dissolution rate of quartz was controlled by mass transfer of silica in the slag. Silica diffusion coefficients in silicomanganese slag varied from 0.9 × 10−7 to 1.3 × 10−6 cm2/s, depending on temperature and slag composition. Activation energy for the diffusion of silica in silicomanganese slag was found equal to 367 kJ/mol. The addition of 10 wt pct CaO decreased activation energy to 115 kJ/mol, while addition of 10 wt pct Al2O3 increased the activation energy to 430 kJ/mol. Effect of slag composition on silica diffusivity was examined in relation with structure of molten slag.

Genetic relationships between ferralsols, podzols and white kaolin in Amazonia

SummaryWhite kaolin has frequently been observed to be associated with ferralsol‐podzol soil systems in Amazonia. In order to evaluate whether such systems favour kaolin genesis and to identify the associated genetic processes, we studied soil organization, mineralogy and groundwater properties of a ferralsol‐podzol soil system with white kaolin located in the High Rio Negro Basin, Brazil. We found that the kaolin was situated near the ferralsol‐podzol transition and that its thickness was related to the depth of landscape incision by regressive erosion. The kaolin was characterized by silicon, iron and titanium (Ti) leaching and aluminium (Al) absolute accumulation. The groundwater that percolates from the podzol to the kaolin can enhance kaolinite precipitation, by supplying Al originating from kaolinite dissolution in the overlying Bh, and kaolin bleaching, by low pH and Eh of the percolating waters favouring iron reduction. The system dynamics imply that the quartz dissolution rate in the kaolin is of at least the same order of magnitude as the kaolinite dissolution rate in the overlying Bh. Within the whole system, Ti appeared to be very mobile.

Hypogenic speleogenesis in quartzite: The case of Corona 'e Sa Craba Cave (SW Sardinia, Italy)

The paper presents a detailed study demonstrating the hypogenic origin of the Corona 'e Sa Craba quartzite cave in SW Sardinia (Italy). Although the quartzite host-rock of this cave derived from silicification of Cambrian dolostones and dissolution of carbonate remnants could have had a role in the speleogenesis, detailed morphologic and petrographic investigation revealed clear evidence of quartz dissolution without signs of mechanical erosion by running waters. Thin section microscopy and scanning electron microscope (SEM) images show pervasive dissolution morphologies, such as pits and notches on quartz crystals causing the deep arenization of the cave walls, suggesting that the dissolution of quartz had a primary role in the formation of the void. The study of secondary cave minerals and the sulfur isotopic composition of sulfates and sulfides, coupled with data on fluid inclusions, allowed reconstruction of the peculiar speleogenetic history of this hypogenic hydrothermal quartzite cave. The cave formed by reduced hydrothermal fluids, probably under basic–neutral pH in phreatic conditions. The presence of abundant cations of Ba2+ in reduced Cl-rich fluids enhanced the quartz dissolution rate, allowing the formation of the voids in deep settings. During the Late Oligocene uplift of the area, the hydrothermal fluids in the cave reached oxygen-rich conditions, thus a minerogenetic phase started with the deposition of barite when the temperature of the fluid was ≤50°C. The presence of cinnabar crusts in the lower part of the cave walls and on the boulders suggests a later volcanic phase with Hg-rich vapors ascending from below. Other minerals such as alunite, basaluminite, gypsum and halloysite (typical of an acid sulfate alteration environment), and phosphates were formed in a final, much more recent stage. The δ34S values of the cave sulfate minerals indicate that S is derived from the remobilization of original Precambrian Pb–Zn Mississippi Valley Type ores. These last two stages did not significantly affect the morphology of the cave. The Corona 'e Sa Craba appears to be the world's first example of a hypogenic cave in quartzite where the speleogenetic mechanisms have been studied and reconstructed in detail, using a variety of modern methods. This study confirms that dissolution of quartz by thermal alkaline fluids at depth can produce large dissolutional voids in the apparently poorly soluble quartzite rocks.

The effects of potassium addition on the rate of quartz dissolution in the CMAS and CAS systems

Quartz dissolution in melts in the KCAS and KCMAS systems results in the formation of a silica- and potassium-enriched boundary layer next to the dissolving crystals. The presence of potassium in CAS melts has no discernible effect on dissolution rate compared with that in K-free melts with otherwise similar composition despite a small decrease in the diffusivity of silica in the potassium-bearing melts. The decrease in silica diffusivity is offset by an increase in the solubility of silica in the K-bearing melts. Addition of potassium to CMAS melts results in a large decrease in the dissolution rate of quartz. Even though the solubility of silica is enhanced, the addition of potassium leads to large changes in the structure of the melt in the boundary layer (as measured by NBO/T), which results in a large decrease in the diffusivity of silica and thus slower dissolution. There is significant diffusive coupling of Al2O3, CaO and MgO during dissolution, which leads to local uphill diffusion of these components. K2O is decoupled from the other components, as shown by its much thicker diffusion zone. Potassium moves through the boundary layer as a result of two homogeneous reactions: uphill diffusion in which potassium diffuses into the silica-enriched melt adjacent to the dissolving quartz crystal and downhill diffusion in the region furthest from the crystal–melt interface where SiO2 and K2O diffuse away from the interface together.

Numerical study on double‐frequency TMF in Cz silicon growth

AbstractIn a typical Cz set‐up, the silicon melt sustained in a fused silica crucible is exposed to oxygen dissolving from the hot crucible walls. The reduction of oxygen incorporation into the growing silicon crystal poses one of the crucial challenges. Quartz dissolution rate can be minimized and SiO evaporation rate enhanced if melted silicon is exposed to double‐frequency upwards travelling magnet fields (TMFs) generated within KRISTMAG® heater magnet modules (HMMs) positioned around the crucible. Our numerical results show the shift of the maximum of the Lorentz force density and consequently velocity away from the crucible walls. The obtained flow patterns can be advantageous for the oxygen control in Cz silicon growth due to accelerated transport of dissolved oxygen towards melt free surface without simultaneous enhancement of oxygen dissolution rate from the silica crucible walls. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effects of quartz particle size and water-to-solid ratio on hydrothermal synthesis of tobermorite studied by in-situ time-resolved X-ray diffraction

Hydrothermal synthesis process of tobermorite (5CaO·6SiO 2·5H 2O) has been investigated by in-situ X-ray diffraction using high-energy X-rays from a synchrotron radiation source in combination with a purpose-build autoclave cell. Dissolution rates of quartz were largely affected by its particle size distribution in the starting mixtures. However, the composition (Ca/Si) of non-crystalline C–S–H at the start of tobermorite formation was identical regardless of the quartz dissolution rate. An effect of water-to-solid ratio (w/s) was investigated for samples using fine particle quartz. Tobermorite did not occur with w/s of 1.7 but occurred with w/s higher than 3.0. Surprisingly, however, the dissolution curves of quartz were nearly identical for all samples with w/s from 1.7 to 9, indicating that the dissolution rate is predominated by surface area. Possible reaction mechanism for tobermorite formation will be discussed in terms of Ca and/or silicate ion concentration in the liquid phase and distribution of Ca/Si in non-crystalline C–S–H.

In situ time-resolved X-ray diffraction of tobermorite synthesis process under hydrothermal condition

Hydrothermal synthesis process of tobermorite (5CaO.6SiO2.5H2O) has been investigated by in situ X-ray diffraction (XRD) using high-energy X-rays from a synchrotron radiation source in combination with a laboratory-made autoclave cell and a photon-counting pixel array detector. Three types of quartz sand having different particle size distributions were used. Not only the dissolution rate of quartz but also that of portlandite (Ca(OH)2) were largely affected by particle size distribution of quartz in starting mixtures. The effect of γ-Al2O3 on quartz dissolution and tobermorite formation was also investigated. In all cases, portlandite dissolved completely before the tobermorite formation, while a certain amount of quartz remained undissolved at the timing for tobermorite to start to be detected (denoted as T0). However, the composition (Ca/Si) of non-crystalline C-S-H at T0 was identical regardless of the quartz dissolution rate. Possible reaction mechanism for tobermorite formation has been discussed in terms of distribution of Ca/Si in non-crystalline C-S-H.