Silicate Crystals Research Articles

Laboratory time-resolved X-ray diffractometry for investigation of reversible structural changes induced in single crystals by external electric field.

Time-resolved technique of X-ray diffraction curve measurement was implemented at a laboratory X-ray source using a high-speed data acquisition system. The time resolution of up to 100 µs was achieved via this X-ray diffractometry technique in the experiment of rocking curve dynamics measurement in a piezoelectric lanthanum-gallium silicate crystal under the influence of high voltage periodic pulsed electric field with an amplitude of 3.08 kV/mm corresponding to the pre-breakdown state. This perturbation caused a quick angular shift of the rocking curve caused by crystal lattice deformation due to the piezoelectric effect. The absence of the diffraction curve broadening effect was shown as well as the absence of the other significant relaxation-like variations of the curve parameters which are inherent for the migration of charge carriers (ions or vacancies) under the external electric field.

Development of a ReaxFF Reactive Force Field for NaSiOx/Water Systems and Its Application to Sodium and Proton Self-Diffusion

We present the development of a ReaxFF reactive force field for Na/Si/O/H interactions, which enables reactive molecular dynamics simulation of the sodium silicate–water interfaces. The force field parameters were fitted against various quantum mechanical calculations, including equations of state of different NaSiOx crystalline phases, energy barriers of a sodium cation’s transport within the sodium silicate crystal structure, interactions between the hydroxylated silica surface and sodium cation–water systems, and dissociation energies of [NaOH–n(H2O)] (n = 1–6) clusters. After the optimization process, we validated the force field capability through calculating the structures of sodium silicate crystals and glasses and transport properties of sodium ions and protons within the amorphous structures. The force field was also applied to validate the dissociation behavior of sodium hydroxides within the bulk water. Our results with the developed force field are relevant to detailed chemical dissolution mec...

Temperature dependence of Raman shifts and line widths for Q0 and Q2 crystals of silicates, phosphates, and sulfates

Temperature dependence of Raman shifts and line widths for Q0 and Q2 crystals of silicates, phosphates, and sulfates

Kinetic D/H fractionation during hydration and dehydration of silicate glasses, melts and nominally anhydrous minerals

The distribution of hydrogen isotopes during diffusion-driven aqueous processes in silicate glasses, melts and crystals was investigated. Hydration/dehydration experiments were performed on silica glasses at 1000 °C and 1 bar total pressure. Dehydration triggered by decompression-driven bubble nucleation and growth was performed on rhyolitic melts at 800 °C and a few hundred MPa. Hydrogen extraction from a nominally anhydrous mineral (grossular) single crystal was carried out at 800 °C and ambient pressure. After these three series of experiments, pronounced water (sensu lato) concentration profiles were observed in all recovered samples. In the grossular single-crystal, a large spatial variation in H isotopes (δD variation > 550‰) was measured across the sample. This isotopic distribution correlates with the hydrogen extraction profile. The fit to the data suggests an extreme decoupling between hydrogen and deuterium diffusion coefficients (DH and DD respectively), akin to the decoupling expected in a dilute ideal gas (DH/DD ≈ 1.41). Conversely, no measurable spatially- and time-resolved isotopic variations were measured in silicate glasses and melts. This contrasted behavior of hydrogen isotopes likely stands in the different water speciation and solution mechanisms in the three different materials. Glasses and melts contain essentially hydroxyl and molecular water groups but the mobile species is molecular water in both cases. Protonated defects make up most of the water accommodated in grossular and other nominally anhydrous minerals (NAM). These defects are also the mobile species that diffuse against polarons. These results are crucial to accurately model the degassing behavior of terrestrial and lunar magmas and to derive the initial D/H of water trapped in fluid inclusions commonly analyzed in mantle NAMs, which suffered complex geological histories.

Material analysis and TL dating of a Renaissance glazed terracotta Madonna statue kept in the Museum of Fine Arts, Budapest

Abstract A glazed terracotta statue depicting the Virgin and the Child, dated to the turn of the 15th and 16th centuries, is a prominent object of the Collection of Sculpture before 1800 of the Museum of Fine Arts, Budapest. The provenance of the statue is unknown, it may stem from the place of its 19th-century purchase, Florence or its environs. This paper presents the material analysis and TL dating of the statue and compares the technological features to the glazed sculptural ceramics produced by the della Robbia and Buglioni workshops in the Renaissance Florence. The yellowish ceramic body was made from highly calcareous clay (25 wt% CaO content) and its mineralogical composition indicates an apparent firing temperature of ∼900–950 C. The white tin glaze is of lead-alkali type with 19.2–20.7 wt% SnO2, 26–31 wt% PbO and 4.7–7.4 wt% Na2O + K2O content. Tiny green spots occur sporadically in the white glaze, where the colour is due to the presence of dissolved copper. In these spots, newly-formed potassium-aluminium silicate, calcium-tin silicate and calcium silicate crystals occur at the body-glaze interface and in the glaze. The violet-coloured glaze on the base of the statue contains a lower amount of tin oxide and a higher amount of lead oxide (11.8 wt% SnO2, 40 wt% PbO) compared to the white glaze covering the statue. The colour was achieved by addition of manganese, and the violet-coloured glaze was applied on a white glaze covering the body of the base. Based on the TL dating, the statue is unambiguously authentic with an age of 0.58 ± 0.06 ka.

Porous glass-ceramics from alkali activation and sinter-crystallization of mixtures of waste glass and residues from plasma processing of municipal solid waste

Abstract Alkali-activated aqueous slurries of fine glass powders, mostly deriving from the plasma processing of municipal solid waste (‘Plasmastone’), were found to undergo progressive hardening at low temperature (75 °C) owing to the formation of C S H (calcium silicate hydrate) gels. Before complete setting, slurries could be easily foamed by vigorous mechanical stirring, with the help of a surfactant; finally, the resulting open-celled structure could be ‘frozen’ by a subsequent sintering treatment, with crystallization of Ca Fe silicates. The densification of the struts upon firing was enhanced by mixing Plasmastone with up to 30 wt% recycled glasses and increasing the firing temperature from 800 to 1000 °C. A total porosity exceeding 75 vol%, comprising both well-interconnected macro- and micro-sized pores on cell walls, was accompanied by good compressive strength, well above 1 MPa. The stabilization of pollutants generally increased with increasing firing temperature and glass content, with some exceptions; no practical leaching was observed from samples deriving from Plasmastone combined with 30 wt% boro-alumino-silicate glass from the recycling of pharmaceutical vials.

A Physical Model for Three‐Phase Compaction in Silicic Magma Reservoirs

AbstractWe develop a model for phase separation in magma reservoirs containing a mixture of silicate melt, crystals, and fluids (exsolved volatiles). The interplay between the three phases controls the dynamics of phase separation and consequently the chemical and physical evolution of magma reservoirs. The model we propose is based on the two‐phase damage theory approach of Bercovici et al. (2001, https://doi.org/10.1029/2000JB900430) and Bercovici and Ricard (2003, https://doi.org/10.1046/j.1365-246X.2003.01854.x) because it offers the leverage of considering interface (in the macroscopic limit) between phases that can deform depending on the mechanical work and phase changes taking place locally in the magma. Damage models also offer the advantage that pressure is defined uniquely to each phase and does not need to be equal among phases, which will enable us to consider, in future studies, the large capillary pressure at which fluids are mobilized in mature, crystal‐rich, magma bodies. In this first analysis of three‐phase compaction, we solve the three‐phase compaction equations numerically for a simple 1‐D problem where we focus on the effect of fluids on the efficiency of melt‐crystal separation considering the competition between viscous and buoyancy stresses only. We contrast three sets of simulations to explore the behavior of three‐phase compaction, a melt‐crystal reference compaction scenario (two‐phase compaction), a three‐phase scenario without phase changes, and finally a three‐phase scenario with a parameterized second boiling (crystallization‐induced exsolution). The simulations show a dramatic difference between two‐phase (melt crystals) and three‐phase (melt‐crystals‐exsolved volatiles) compaction‐driven phase separation. We find that the presence of a lighter, significantly less viscous fluid hinders melt‐crystal separation.

Evaluation of Crystals’ Morphology on Detection Efficiency Using Modern Classification Criterion and Monte Carlo Method in Nuclear Medicine

Crystals used in medical imaging systems play a key role in obtaining images for the improvement of diagnoses in medicine. We investigated crystal material characteristics in detection efficiency, and a reliable definition of efficiency proposed for improving spatial resolution. In this study, bismuth germanate (BGO), lutetium oxyortho silicate, gadolinium silicate, and lutetium yttrium oxyortho silicate crystals have been evaluated to compare their special characteristics using Monte Carlo simulation. Additionally, a new criterion is introduced as scattering frequency at which the ratio of the number of Compton interaction to the minimum traversed distance of photons in crystal is suggested. This frequency is based on random numbers, Compton scattering, energy of γ-ray, geometry and material of crystal. The sensitivity of crystals as a function of crystal width at various incident angles of the photon is investigated. The simulated results have demonstrated that at a distinct width of crystal, the detection efficiency of the BGO crystal was more than that of other crystals in which the amount of scatter and random coincidences decreased. Crystal width at various applications, however, must be optimized with respect to the trade off among the signal-to-noise ratio, spatial and temporal resolutions, efficiency, and the untrue coincidences. Determining crystal width and material may be useful in collimator design to improve spatial resolution and efficiency.

Crystal growth, low-temperature spectroscopy and multi-watt laser operation of Yb:Ca3NbGa3Si2O14

We report on the crystal growth, structure, room- and low-temperature (6K) absorption and emission spectroscopy of a 3at% Yb3+-doped trigonal ordered langasite-type silicate crystal, Ca3NbGa3Si2O14 (Yb: CNGS). The Rietveld refinement data are presented. Absorption, stimulated-emission and gain cross-sections are determined for the Yb3+ ion in CNGS for π and σ polarizations. The maximum stimulated emission cross-section amounts to σSE = 0.97 × 10−20cm−2 at 1014nm (σ-polarization). The Stark splitting of the Yb3+ multiplets is resolved. Microchip laser operation is obtained with both a-cut and c-cut 3at% Yb: CNGS samples under end-pumping at 976nm by a Volume Bragg Grating-stabilized diode laser. For the latter cut, the maximum output power reaches 7.61W at 1048–1060nm with a slope efficiency of 59%. By varying the output coupling, multi-watt emission over a 50nm-broad spectral range is achieved.

Direct Crystallization of Layered Silicates on the Surface of Amorphous Silica.

We overview the entire surface coverage of amorphous silica with layered silicates (smectite-like) using the direct crystallization technique under hydrothermal conditions. Various shapes (e. g., microspheres, fibers, microcapsules) have been available as the silica substrates, which involve partial dissolution triggered by the hydrolysis of urea for supplying a source of the layered silicates. Other sources (e. g., Li+ , Mg2+ , Al3+ ) have been supplied from aqueous solutions, participating the heterogeneous nucleation of the layered silicates. Because of partial dissolution of the silica substrates, the original shape has been preserved after the hydrothermal reactions. Cation exchange reactions, usually observed for conventional smectite systems, occurred by replacing the interlayer cations in the silicates with metal (a rare-earth ion) and organic (a quaternary long-chain alkylammonium, methylene blue, and a tris-chelated complex) cations. We have discussed the mechanism of the crystallization and displayed some applications of the hybrids (e. g., chiral discrimination, filtering, and magnetic recovery).

Raman microspectroscopy of blue‐green historical beads: Comparative study of undamaged and strongly degraded samples

AbstractConfocal Raman microspectroscopy is used to substantially supplement existing experimental data on historical blue‐green beads with respect to the presence and distribution of potassium antimony silicate (KSS) crystals. Problem of degradation of blue‐green beads on historical artifacts accounts for topicality of the work. The reasons for possible short‐term (several years) degradation of beads and the presence of neighboring damaged and undamaged beads on a single item remain unknown in spite of multiple experimental works on various glasses. Presence of KSS microcrystals may serve as a reason for degradation of beads. Raman measurements at several depths are used to determine the distribution and estimate sizes of KSS microcrystals. Such distributions are different for undamaged and strongly degraded beads. For degraded beads, Raman data show the depth dependence of the concentration of (non)bridged oxygens in the near‐surface layer with a thickness of 3–4 μm (i.e., inhomogeneity of glass matrix). The results prove the growth of KSS microcrystals in historical blue‐green beads, which may cause internal stress and, hence, degradation. The results can be used for optimization of storage conditions and restoration procedures for historical items.

Dynamic observations of vesiculation reveal the role of silicate crystals in bubble nucleation and growth in andesitic magmas

Bubble nucleation and growth control the explosivity of volcanic eruptions, and the kinetics of these processes are generally determined from examinations of natural samples and quenched experimental run products. These samples, however, only provide a view of the final state, from which the initial conditions of a time-evolving magmatic system are then inferred. The interpretations that follow are inexact due to the inability of determining the exact conditions of nucleation and the potential detachment of bubbles from their nucleation sites, an uncertainty that can obscure their nucleation location – either homogeneously within the melt or heterogeneously at the interface between crystals and melts. We present results of a series of dynamic, real-time 4D X-ray tomographic microscopy experiments where we observed the development of bubbles in crystal bearing silicate magmas. Experimentally synthesized andesitic glasses with 0.25–0.5wt% H2O and seed silicate crystals were heated at 1atm to induce bubble nucleation and track bubble growth and movement. In contrast to previous studies on natural and experimentally produced samples, we found that bubbles readily nucleated on plagioclase and clinopyroxene crystals, that their contact angle changes during growth and that they can grow to sizes many times that of the silicate on whose surface they originated. The rapid heterogeneous nucleation of bubbles at low degrees of supersaturation in the presence of silicate crystals demonstrates that silicates can affect when vesiculation ensues, influencing subsequent permeability development and effusive vs. explosive transition in volcanic eruptions.

Failure Mechanism of Yttria Stabilized Zirconia Atmospheric Plasma Sprayed Thermal Barrier Coatings Subjected to Calcia-Magnesia-Alumino-Silicate Environmental Attack

The contribution focuses on the description of failure mechanism of atmospheric plasma sprayed multilayer thermal barrier coatings subjected to calcia-magnesia-alumino-silicate (CMAS) environmental attack. To identify exothermic and endothermic reactions which occurred during heating/cooling by means of calorimetry was also utilized initial yttria stabilized zirconia (YSZ) powder subsequently used for thermal spraying of multilayer thermal barrier coating system (TBCs), CMAS powder later on utilized for thin layer deposition and its mixture. Atmospheric plasma spray technique was used to produce the TBCs on a grit blasted nickel-based superalloy substrates, where CoNiCrAlY powder was used for deposition of a bond coat and YSZ powder was sprayed as a top coat. In accordance to the aerospace standard the thin layer of CMAS was deposited on as sprayed TBCs samples surface from its colloidal solution by paint brush method. Burner-rig test, utilizing direct propane-oxygen flame, was used for thermal cyclic exposition of the multilayer coated samples at the temperature of 1150 °C. Samples after thermal cyclic exposure test were investigated by means of materialographic analysis approaches. The significant reduction in life-time of CMAS coated YSZ top coat was observed due to lower melting point phase formation and molten silicate crystallization within the pores providing the spallation identified as a major mechanism of TBCs failure.

The effect of synthesis and thermal treatment on phase composition and ionic conductivity of Na-doped SrSiO3

The structural and electrochemical properties of Sr1-xNaxSiO3 were studied. Powders with different compositions (0.1≤x≤0.45) were prepared by solid state reaction. Mixing of SrCO3, Na2CO3 and SiO2 was carried out in different media in order to explore the effect of solvents on the formation of secondary phases. X-ray diffraction was employed to study the phase composition of mixtures treated in air at different temperatures in the range 850–1050°C for at least 12h. Various heating schemes were applied to help the incorporation of Na in the monoclinic SrSiO3 structure.Pressed pellets were sintered at 1000°C for at least 12h and electroded with Ag paste for electrochemical characterization.For most compositions and thermal treatments, the formation of the insulating Na2Si2O5 phase was observed, as reported in literature.Highest conductivity and degradation rate was obtained when synthesis was carried out in acetone with single calcination step at 850°C, due to the crystallization of Na2Si2O5 from glass. Double calcination limited conductivity but increased its thermal stability. When ethanol was used for powder mixing and double calcination was applied, the material exhibited higher conductivity after long term ageing at 650°C, also thanks to its low activation energy, without appreciable crystallization of other silicates.

Wollastonite-diopside-carbon composite foams from a silicone resin and inorganic fillers

A novel multiphasic ceramic composite was developed in the form of highly porous open-celled foams, starting from a silicone-based mixture, incorporating micro-sized fillers and fired in N2 atmosphere. Highly homogeneous mixtures were first foamed at 350°C, in air, and later fired at 1100°C. The process yielded a final ceramic with two silicate phases (wollastonite, CaSiO3, and diopside, CaMgSi2O6), embedded in an amorphous matrix, exhibiting a particularly remarkable compressive strength (exceeding 20MPa), and a residual open porosity of about 65% (with pore diameters ranging between 300 and 500µm). This result cannot be attributed to the formation of a homogeneous silicon oxycarbide (SiOC) matrix; on the contrary, the amorphous material surrounding the silicate crystals consisted of a nano-composite, with C domains immersed in a silicate glass phase. Very preliminary cell culture studies performed in vitro showed encouraging results.

First investigations on the quaternary system Na2O-K2O-CaO-SiO2: synthesis and crystal structure of the mixed alkali calcium silicate K1.08Na0.92Ca6Si4O15

In the course of an exploratory study on the quaternary system Na2O-K2O-CaO-SiO2 single crystals of the first anhydrous sodium potassium calcium silicate have been obtained from slow cooling of a melt in the range between 1250 and 1050 °C. Electron probe micro analysis suggested the following idealized molar ratios of the oxides for the novel compound: K2O:Na2O:CaO:SiO2 = 1:1:12:8 (or KNaCa6Si4O15). Single-crystal diffraction measurements on a crystal with chemical composition K1.08Na0.92Ca6Si4O15 resulted in the following basic crystallographic data: monoclinic symmetry, space group P 21/c, a = 8.9618(9) Å, b = 7.3594(6) Å, c = 11.2453(11) Å, β= 107.54(1)°, V = 707.2(1) Å3, Z = 2. Structure solution was performed using direct methods. The final least-squares refinement converged at a residual of R(|F|) = 0.0346 for 1288 independent reflections and 125 parameters. From a structural point of view, K1.08Na0.92Ca6Si4O15 belongs to the group of mixed-anion silicates containing [Si2O7]- and [SiO4]-units in the ratio 1:2. The mono- and divalent cations occupy a total of four crystallographically independent positions located in voids between the tetrahedra. Three of these sites are exclusively occupied by calcium. The fourth site is occupied by 54(1)% K and 46%(1) Na, respectively. Alternatively, the structure can be described as a heteropolyhedral framework based on corner-sharing silicate tetrahedra and [CaO6]-octahedra. The network can build up from kröhnkite-like [Ca(SiO4)2O2]-chains running along [001]. A detailed comparison with other A2B6Si4O15-compounds including topological and group-theoretical aspects is presented.

Highly-efficient laser operation of a novel trigonal silicate crystal Yb^3+:Ca_3NbGa_3Si_2O_14

A novel trigonal ordered langasite-type silicate crystal, Yb3+:Ca3NbGa3Si2O14 (Yb:CNGS), is characterized with respect to absorption and stimulated-emission cross-sections as well as Raman spectra using polarized light. Thanks to its excellent thermo-mechanical properties, highly-efficient multi-watt lasing is demonstrated. A compact a-cut 5 at .% Yb:CNGS crystal diode-pumped at 978 nm generated a maximum output power of 7.27 W at 1062-1068 nm with a slope efficiency of 78%. These values represent record parameters for ~1 μm lasers based on langasite-type crystals. The very broad and smooth gain cross sections of Yb:CNGS are attractive for ultrashort pulse and broadly tunable lasers at ~1 μm.

Effect of carboxylic and hydroxycarboxylic acids on cement hydration: experimental and molecular modeling study

Most concrete produced includes chemical admixtures such as air entrainers, set modifiers, water reducers, etc., many of which include organic molecules. Hydroxycarboxylic acids, in particular, retard portland cement hydration. The interaction of such acids with hydrating cement phases is a complex, multi-parameter problem. To elucidate the interaction of hydroxycarboxylic and carboxylic acid retarders on hydration of cement, a combined experimental and molecular-computational approach was used. Glycolic acid, acetic acid, calcium glycolate and calcium acetate were used as model compounds. Molecular dynamics simulations were performed to simulate the interactions of select test compounds with the (001) surface of the portlandite crystal (calcium hydroxide) and the (040) surface of the tricalcium silicate crystal. Hydrogen bond density profiles and binding energies were evaluated. The adsorption isotherm for chelate complexes was determined experimentally by equilibrating aqueous solutions of the agents in the presence of various amounts of solid-phase calcium hydroxide. Finally, isothermal calorimetry experiments were used to quantify effects on hydration rate. The glycolic acid shows significant cement retardation, whereas acetic acid does not retard. Glycolic acid was found to retard hydration via calcium chelation and surface adsorption that involves the adsorption of the calcium chelate complex preferentially on tricalcium silicate. Simulation results reveal that calcium glycolate forms a strong hydrogen bonding network near to calcium hydroxide and hydrated tricalcium silicate surfaces and are responsible for its strong adsorption on these surfaces. While acetic acid forms a strong calcium chelate, it does not associate with calcium hydroxide or unhydrated or hydrated tricalcium silicate surfaces.

Diode-pumped passively Q-switched self-frequency-doubled Nd:CNGS laser.

With Cr4+:YAG as a saturable absorber, a passively Q-switched self-frequency-doubled (SFD) laser based on a trigonal Nd:Ca3NbGa3Si2O14 (Nd:CNGS) silicate crystal was demonstrated for the first time. The maximum average output power at 532 nm was 16.2 mW, and the corresponding pulse repetition frequency, single pulse energy, pulse duration and peak power were 2.25 kHz, 7.2 μJ, 13.7 ns, 0.53 kW, respectively. We also present a rate-equation model of such a passively Q-switched SFD laser showing a good agreement with the experiment. Nd:CNGS is a promising pulse SFD material for miniature all-solid-state visible light sources.

Preparation of Glass Ceramics by Reactive Crystallization with Waste Glass and Spinel

Magnesium silicate glass ceramics were prepared by reactive crystallization with mixed powder of waste glass and spinel. The effects of spinel content and sintering temperature and holding time on the crystal phase and morphology of magnesium silicate glass ceramics were investigated. The reactive crystallizing behavior between waste glass powder and spinel was studied using energy dispersive spectrdmeter during the holding process. The result show that the optimum preparation conditions were as follows: the addition of 30 wt% spinel used as crystallization promoting agent, sintering temperature of 900 oC and holding time of 2 h. The magnesium silicate and alumina crystals were formed via an interaction between glass powder and spinel instead of direct precipitation from the parent glass. With increasing of the holding time, the Al and Mg element contents of the glass were increased, on the contrary, that Si element content was decreased in the glass phase. It shows that the Si element is diffused from glass into spinel phase and subsequently magnesium silicate crystals are formed.