Littérature scientifique sur le sujet « Ca-rich glasse »

Abstract Rare Earth (RE)-containing bioactive glasses has recently gained more relevance in the field of biomaterials due to the unique optical, electronic, and chemical properties of the RE elements. In this work, the influence of gadolinium in the thermal properties of bioactive glasses based on the SiO2-Na2O-CaO-P2O5 containing different Na/Ca ratio was studied. The glasses were obtained by melting-quenching, and their properties were evaluated by differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The results evidenced that Gd tends to increase the working temperature (Tc-Tg) in Ca-rich glasses, which leads to a less tendency to devitrification. On the other hand, in Na-rich glasses, Gd did not play an essential role in crystallization, and the thermal properties of Gd-containing Na-rich glasses were similar to their counterparts. In conclusion, we suggested that it is possible to control the influence of Gd in the glass devitrification by changing the Na/Ca ratio in the glass composition. These results may be interesting for further works to which crystallization may be either a desired or undesired phenomena.

This research aims at gaining a further understanding of the impact of accelerating admixtures on the reactivity of supplementary cementitious materials (SCMs), which are widely used as a clinker replacement in blended cements. This was done on synthetic glasses with controlled composition and structure that mimic two types of real SCMs (slag and calcium-rich fly ash). The effects of DEIPA, TIPA, NaSCN and Na2S2O3 on the glass dissolution, hydration kinetics and reaction products were investigated. The obtained results concluded that the pH of the NaOH solution and the composition of the synthetic glass play a key role on the effect of the admixtures. In 0.1 M NaOH (pH = 13.0), all the studied admixtures inhibited the dissolution of slag-like glasses while they enhanced the dissolution of Ca-rich fly ash-like glasses, being Na2S2O3 the admixture that led to the highest increase of the dissolution rate of the Ca-rich fly ash-type glasses. In 1 M NaOH solutions (pH = 13.8), only the alkali admixtures (NaSCN and Na2S2O3) enhanced the degree of reaction of both glasses. In slag-type glasses pastes mixed with 1 M NaOH, the addition of 2% Na2S2O3 induced the highest increase of their reactivity as inferred by the total heat release and the amount of bound water. This is related to the formation of a high amount of S(II)-AFm, in addition to C-A-S-H, that would increase the aluminium undersaturation of the pore solution and consequently the further dissolution of the glass.

AbstractInclusions occurring in leucites from the Oscar and Zirkel Mesa leucite lamproites consist of high (>10 wt.%) and low (<4 wt.%) K2O discrete glass phases which are interpreted to have resulted from silicate liquid immiscibility. Both glasses are quartz-normative and rich in Ti, Fe, Mg, Ca and Ba and poor in Al. The high-K glass is strongly peralkaline. Neither of the glasses have compositions representative of any known lamproites. These inclusions represent the first described examples of silicate-silicate immiscibility shown by glass in alkaline rocks.

AbstractCa- and P-based bioactive glasses are excellent candidates for design and manufacture of biomaterials. Understanding the structure and physico-chemical–thermal behaviour of bioactive glasses is a fundamental step towards the design of a new generation of biocompatible materials. In this study, the structure of SiO2–CaO–Na2O glasses and its derivatives, obtained by substituting Na2O with P2O5 and prepared by melt–quench technique, was studied with neutron and electron diffraction techniques combined with thermal analysis, high-resolution electron microscopy and X-ray photoelectron spectroscopy. Neutron and electron diffraction data were analysed with reverse Monte Carlo simulation and pair distribution function analysis, respectively. Bioactivity of P2O5 substituted glasses was also investigated and proven in vitro using simulated body fluid. Based on the structural analysis, it was found that Si and P atoms are in well-defined tetrahedral units with a bond distance of 1.60 Å for both Si–O and P–O bonds, although P exhibits a higher average coordination number than Si. With increasing phosphate content, tendentious changes in the glass behaviour were observed. Linear increase in Tg, supported by the changes in the average coordination numbers of Si and P, indicates strengthening of network structure with increasing P content and formation of P–O–Ca atomic linkages, which lead to Ca–P-rich atomic environments in the silicate network. These Ca–P-rich environments trap volatile elements and thus decrease the total weight loss during heating at higher P concentrations. In the case of the highest investigated P2O5 content (5 mol%), nanoscale structural inhomogeneity and the formation of Ca–P-rich clusters were also revealed by electron diffraction and atomic resolution imaging. This type of Ca–(Na)–P clustering has a key role in the behaviour of phosphate-substituted silicate glasses under physiological conditions.

Glass of the Si – Na – Ca – P system has been synthesized by normal melting and annealing technique. The obtained glass powders and annealed blocks were showed to be amorphous by X-ray diffraction (XRD). The thermal properties of glasses were analyzed by differential scanning calorimetry (DSC), it showed that the glass transformation temperature (Tg) was 556.3°C. The behavior of annealed glass discs in simulated body fluid solution (SBF) was studied in polyethylene containers at a constant temperature of 37°C for different time up to 14 days. The changes in the surface morphology and composition were observed by electronic probe microanalyzer (EPMA) associated with energy dispersive spectroscopy (EDS). Glass surface changed quickly as soon as immersion took place, and after longer soaking time, it showed different superimposed internal and external layers, which were identified as SiO 2-rich and CaO – P 2 O 5-rich layers, and on the external layer, spherical particles were also discovered.

This study compares the in vitro behaviour in SBF of glasses from two different systems, TiO2-CaO-P2O5 and SiO2-CaO-P2O5 with the same TiO2 and SiO2 molar content, in order to evaluate the effect of TiO2 and SiO2 on the surface reactivity of those glasses. The glass formation regions in both systems were observed for compositions with less than 40 mol% TiO2 and 40 mol% SiO2, respectively. Four glasses with similar TiO2 and SiO2 molar contents have been selected for comparison. These glasses are equimolar in CaO and P2O5 with TiO2 or SiO2 varying from 4 to 33 mol %. Powder glasses were immersed in Simulated Body Fluid (SBF) and kept at 37°C for different times, up to 14 days. Surfaces were observed by Scanning Electron Microscopy (SEM) and specimen ion leaching to SBF was studied by Inductively Coupled Plasma (ICP) spectroscopy. Preliminary spectroscopic studies by Raman were performed to identify the structure of the glasses. For glasses of the SiO2-CaO-P2O5 system a significant dissolution of all ions was observed together with the formation of phosphoric acid. In opposition, the immersion of TiO2-CaO-P2O5 glasses produced a small Ca consumption and stable Ti and P concentrations, indicating the formation of a Ca-P rich layer on these glasses. The observed differences in the dissolution behaviour are tentatively explained in terms of the glass structures obtained by spectroscopy.

This paper studies the blast furnace slag glass phase structure by a series of analysis methods. In glass phase, both Si and Al ions are confirmed to occupy only tetrahedral sites, while the [SiO4]4- and [AlO4]5- are separated by Ca and Mg. Furthermore, the glass structure corresponds to micro-crystal model, which means it contains some nano-scaled micro-crystals in the glass phase. In addition, the slag glass may separate into two phases: a calcium rich phase and a silica rich phase. According to devitrification experiment, it has been inferred that the chemical composition and structure of silica rich phase are close to that of akermanite,which means most of Si is distribute around Mg.

AbstractTransmission electron microscopy of ultramicrotomed thin-sections of Pleistocene and Eocene glass shards revealed the neoformation of (i) illite and (ii) halloysite at the glass periphery. According to previous experimental studies, halloysite neoformation in marine environments can occur on glass shards deposited in Si-rich sediments; an excess of Ca tends to inhibit the reaction.

The effect of alloy composition on the glass forming ability (GFA) of the Ca-Zn-Mg alloys has been investigated in the present study. The alloy compositions investigated are near Ca-rich ternary eutectic composition; Ca60Mg15Zn25, Ca65Mg10Zn25, Ca65Mg15Zn20, Ca65Mg20Zn15, and Ca70Mg15Zn15. Bulk metallic glass (BMG) samples with the diameter larger than 5 mm are fabricated by conventional copper mold casting method in air atmosphere. Among the parameters representing the glass forming ability, Trg and γ parameters exhibit good correlation with the maximum diameter of the fully amorphous structure in the alloy compositions investigated in the present study.

Abstract REE bearing carbonate systems at high pressure: an experimental study Carbonatites are important sources of Rare Earth Elements (REE). REE mainly reside in Ca-bearing phases carbonates, apatites, Ca-Nb oxides, Ca-silicates and in accessory phases such as monazite, burbankite, bastnäsite. At liquid phases, carbonate melts display remarkable physical properties. In particular, carbon-rich and silica-poor melts, i.e. transitional melts, are efficient metasomatizing agents of carbon between the mantle and the crust. This study focuses on two main issues: I) the effect of REE such as La and Y on the structure and melting behavior of transitional carbonate-silicate melts, which has been investigated in simple model with variable CaCO3:SiO2 ratio at 1 GPa; and II) the stability and mineral physics of REE-bearing carbonates at high pressure, in particular of La-burbankite. Few experimental works have explored phase relations, structure and the role of REE in carbonate-rich melts. The typical unquenchable nature of carbon-rich melts makes for a difficult, determination of the structure of carbon-rich glasses. Wyllie and Jones (1986) synthesized a REE-bearing carbonatite glass in a series of experiments performed in the system CaO–CaF2–BaSO4–CO2–H2O–La(OH)3 using a composition similar to carbonatites ore deposits in Mountain Pass (California). At 0.1 GPa the investigated carbonatite composition starts to melt at temperatures as low as 550°C. As today, there are no data available regarding melting behavior, structural properties of melts, and the stability of REE-bearing phases in model system of hydrous carbon-rich low silica. Furthermore, although in alkali free systems a complete miscibility between silicate and carbonate liquids is expected, the compositional threshold at which carbonate-silicate liquids might form a glass, i.e. are quenchable, is still scarcely explored in simple model systems. In this study, I investigated i) how viable is the quenching of a carbon-rich melt as a function of the bulk SiO2:CaCO3 ratio, ii) the structure of these glasses, iii) and the role of REE in the molecular structure(La, Y). I also determined the CO2 solubility in transitional melts by micro-Raman spectroscopy. Single stage and end-loaded piston cylinder experiments have been performed at 1 GPa in two model systems: CaO–SiO2–La2O3–H2O–CO2 in the range 700–1250°C, and CaO–SiO2–Y2O3–H2O–CO2 in the range 1200–1250°C. The starting materials were prepared as a powder mixture of La2(CO3)3 or La2O3 or Y2O3 and amorphous SiO2 and CaCO3 with approximately 5-10 wt.% of H2O. Different bulk compositions with different SiO2:CaCO3 ratio have been considered. Run products were characterized by backscattered electrons images (BSE), X-ray diffractometry, micro-Raman spectroscopy, nuclear magnetic resonance (NMR) of selected experiments, and chemically analyzed by electron microprobe. At subsolidus conditions (T < 1000°C), all bulk compositions in CaO–SiO2–La2O3–H2O–CO2 system contain calcite and quartz coexisting with a Ca-La silicate phase with an apatite-type structure of general formula between La3Ca2(Si3O12)OH and La4Ca(Si3O12)O. Liquidus conditions have been observed in runs on bulk compositions with SiO2:CaCO3 = 0.28 1.4 at T >1150°C for both investigated systems. Homogeneous quenched glasses have been retrieved for composition with up to SiO2:CaCO3=0.28 ratio, whereas at lower ratio (0.12) dendritic textures are visible. Deconvolution of Raman spectra of glasses reveal a CO2 content up to 20.40% in the CaO–SiO2–La2O3–CO2–H2O system and up to 10.80% in the CaO–SiO2–Y2O3–CO2–H2O system classifying the melts as carbonate-silicate transitional melt. While studiyng the behavior of Ca-rich carbonatitic hydrous glasses with REE, we also investigated the influence on the REE distribution of an alkaline carbonate, burbankite [(Na,Ca)3(Sr,Ba,Ce,REE)3(CO3)5], at upper mantle conditions. Recently, the alkaline-carbonate system has been observed at High Pressure and High Temperature (HP-HT) by Shatzky et al., (2016); they found a new class of Ca-rich alkaline-alkaline earth carbonates and burbankite with the latter being abundantely presents in carbonatites that constitutes important ore concentrations of strategic metals, including Nb and REE elements on Earth’s surface. A La rich burbankite [Na3Ca2La(CO3)5] was synthesized at 5 GPa and 1000°C, to scope out the possibility that REE can enter the structure of this carbonate also at upper mantle conditions. Furthermore, the elastic properties of the synthesized La-burbankite have been determined by in-situ HP and HT single crystal X-ray diffraction measurements at synchrotron facilities using a diamond-anvil cell for HP experiments and a quartz-glass capillary for the HT experiments. The determination of these thermoelastic parameters allowed to calculate the possible density of this phase at upper mantle conditions, that is ca. 3.2 g/cm3 at 5.5–6.0 GPa and 900–1000°C. Results suggest that potentially the La-burbankite could fractionate at HP and HT from a carbonatitic melt, because the latter has a lower density (ca. 2.1-3.1 g/cm3) and may constitute a REEs reservoir at upper mantle conditions.