CaO-SiO2 System Research Articles

Evaluation of Thermodynamic Activity of a Metallic Oxide in a Ternary Slag from the Sulphide Capacity of the Slag

The correlation between the activity of a metallic oxide in a ternary slag system and the sulphide capacity of the slag was investigated. The solubility of sulphur in the binary systems CaO-SiO2 and Al2O3-CaO along with its sulphide capacity of the Al2O3-CaO-SiO2 system respectively have been used to estimate the activities of CaO at the compositions of some Al2O3-CaO-SiO2 intermediate compounds. Estimation has been carried out assuming that the Gibbs free energy of fusion for the ternary composition is additive of those for pure substances. The estimated values of the activities are in good agreement with the measured values. This correlation is not only used to evaluate the activity but also, by comparing the estimated activities with the measured ones, it is possible to elucidate the applicability of Henry's law to the activity of a metallic sulphide and to determine the order in the affinity of a cation to sulphur between two metallic oxides in a slag.

Chemical potentials of oxygen within four‐phase assemblages of the system CaO–SiO2–Al2O3–FeO

Within the system CaO + SiO2+ Al2O3+ FeO, there are a number of four‐phase assemblages. Chemical potentials of oxygen within such assemblages have been determined by using an electrochemical technique incorporating zirconia solid electrolyte.

Thermal and chemical properties of diopside-wollastonite glass-ceramics in the SiO2–CaO–MgO system from raw materials

The crystallization process of ternary system SiO2–CaO–MgO from waste raw materials was investigated by DTA and polarizing microscope and characterized by chemical durability for glasses and glass-ceramics. The effects of compositional changes on bulk crystallization and growth morphology were also studied. β-wollastonite and diopside, were identified after heat-treatment. The coarse grained morphology with directional surface crystallization was observed. Studying of chemical durability shows that, the weight loss increased by increasing CaO content on the expense of MgO in both acidic or alkaline solution.

Experimental study of phase equilibria in the PbO-ZnO-“Fe2O3”-CaO-SiO2 system in air for high lead smelting slags (CaO/SiO2=0.35 and PbO/(CaO + SiO2)=5.0 by weight)

Experimental studies on phase equilibria in the multicomponent system PbO-ZnO-CaO-SiO2-FeO-Fe2O3 in air have been conducted to characterize the phase relations of a complex slag system used in commercial lead oxidation smelting. The liquidus in the pseudo-ternary section ZnO-"Fe2O3"-(PbO + CaO + SiO2) with the CaO/SiO2 weight ratio of 0.35 and the PbO/(CaO + SiO2) weight ratio of 5.0 has been constructed using results of over 100 high-temperature equilibration and quenching experiments followed by electron probe X-ray microanalysis. The liquidus in this pseudoternary section contains primary phase fields of spinel (zinc ferrite) ZnxFe3-xO4+y, zincite ZnuFe1-uO, melilite PbvCa2-vZnwFe1-wSi2O7, hematite Fe2O3, magneto-plumbite PbFe10O16, and dicalcium silicate Ca2-t PbtSiO4. The laboratory results are compared with the slags obtained from an industrial reactor.

Thermochemical Modeling of Oxide Glasses

A modified associate species approach is used to model the liquid phase in oxide systems. The relatively simple technique treats oxide liquids as solutions of end‐member and associate species. The model is extended to representing glasses by treating them as undercooled liquids. Equilibrium calculations using the model allow the determination of species activities, phase separation, precipitation of crystalline phases, and volatilization. In support of nuclear waste glass development, a model of the Na2O–Al2O3–B2O3–SiO2 system has been developed that accurately reproduces its phase equilibria. The technique has been applied to the CaO–SiO2 system, which is used to demonstrate how two immiscible liquids can be treated.

Development of bioactive organic–inorganic hybrid for bone substitutes

Bioactive glasses and glass–ceramics have been attractive because they spontaneously bond to living bone when implanted in bony defect. However, they are much more brittle and much less flexible than natural bone. Hybridization of essential constituents of bioactive glasses and glass–ceramics with flexible polymer can solve this problem. The present topic is devoted to the design of organic–inorganic hybrids that can bond to living bone. Previous studies reported that the condition for bioactive glasses and glass–ceramics to achieve direct bond to living bone is formation of a bone-like apatite layer on their surfaces after exposure to the body fluid. The same type of apatite formation can be observed even in a simulated body fluid (Kokubo solution) proposed by Kokubo and his colleagues. Glasses in the binary system CaO–SiO2 showed the apatite formation in Kokubo solution. The formation of the surface apatite is induced both by dissolution of calcium ions from the bioactive glass, and by silanol (Si–OH) group in the hydrated silica gel formed on the surface. These findings bring an idea that incorporation of calcium ion (Ca2+) and Si–OH group into organic substances leads to a bioactive hybrid. It was confirmed that organic–inorganic hybrids containing calcium salt, which were synthesized from vinyltrimethoxysilane (VS) or 3-methacryloxypropyltrimethoxysilane (MPS), showed the apatite formation in Kokubo solution. Such type of organic–inorganic hybrids can be blended with organic polymer. An organic–inorganic hybrid was synthesized from MPS and 2-hydroxyethylmethacrylate (HEMA) at a composition of MPS/HEMA=0.1:0.9. The MPS–HEMA hybrid also formed the apatite layer when the hybrid was incorporated with calcium chloride. Incorporation of MPS and calcium salt also provides conventional PMMA-based bone cement with the ability of apatite formation. These findings indicate that novel bioactive materials can be developed from organic–inorganic hybrids obtained by incorporation of calcium ion and specific kinds of functional groups such as Si–OH.

Electrochemical evaluation of resistance to localised corrosion of vitreous coatings containing particles applied on metallic substrates for biomedical applications

CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spontaneously form passive oxide films when immersed in physiological environments. The stresses resulting from the use of the prosthesis can cause fracture and abrasion of the oxide film that covers the surface. This can result in crevice corrosion, with the corresponding decrease in pH leading to severe attack. Protective coatings deposited onto the metals would minimise the release of metallic ions from the substrate and the incorporation of bioactive particles would enable the adhesion to the bone tissue. This work describes the electrochemical behavior of CrCoMo alloys (F75) as cast, covered by a hybrid silica coating obtained by sol–gel. The silica sol–gel coating contains bioactive glass ceramic and vitreous particles of the system CaO–SiO 2–P 2O 5 previously obtained by fusion, crystallization and milling. The performance of the alloy with and without coating is evaluated in simulated body fluid (SBF) pH 7.31 at 37 °C. As cobalt base alloys are susceptible to crevice attack, coated pieces are also tested in SBF acid solution (pH 0.7) in order to simulate the acidic media and the high chloride concentrations that develop when a crevice is formed. The electrochemical behavior has been evaluated by potenciodynamic polarization and electrochemical impedance spectroscopy. It was found that for both pH conditions the samples coated with double layer of glass ceramic particles showed lower passive current densities than those with monolayers. The coating improves the protection potential of the base material in the neutral solution. Besides, in the acidic solution, all the samples remain passive but the protection potential shifts to potentials more active than those measured in the neutral SBF.

In vivo and in vitro evaluation of vitreous coatings on cobalt base alloys for prosthetic devices

This work describes the electrochemical and biological response of wires of CrCoMo surgical alloys (F75) covered by two layers of SiO 2 coating prepared by sol–gel to evaluate their properties in simulated body fluids and implanted in Lew rats for the in vivo evaluation. Wires were coated by a single layer of hybrid silica (that means that the coating contains Si–CH 3 groups) covered by another similar layer containing a suspension of bioactive glass-ceramic particles in the system CaO–SiO 2–P 2O 5 to provide fixation to bone. Standard electrochemical tests were conducted for the in vitro measurements and showed smaller current density for the covered samples than for the uncovered ones after 30 days of immersion. For the in vivo tests the coated wires were inserted in the tibia cortical bone by a press fit technique in Lew rats and analysed after 53 days of being implanted. We observed that none of the wires created an inflammatory response. Moreover the covered wires developed neo formed bone in the surroundings of the samples made of collagen with a vascular development. Uncovered wires did not develop new histionic structure.

Graded coatings on ceramic substrates for biomedical applications

Bioactive glasses and particles reinforced composites were used to coat alumina substrates, in order to combine the mechanical properties of the high-strength alumina with the bioactivity of the coatings. The coatings were either monolithic glass or glass-matrix/zirconia particle composite and were prepared by a low-cost firing method. A multilayer approach was applied to minimize crack propagation at the interface between the coating and the substrate. Functionally graded structures were developed to achieve a compliant material to withstand the stresses due to the expansion coefficient mismatch between the substrate and the coatings. The sequential coating of the alumina with glass-matrix/zirconia particle composite layers produced a structurally stable composite structure. A systematic study revealed that multiple layers were necessary to provide a gradual compliance of the thermal expansion coefficient. The glass-matrix/zirconia particles composites layers were also essential for the control of the Al3+ diffusion from the substrate through the glass. This is in accordance with the experimental results of previous works. Thus, the alumina content in the coating should be maintained as low as possible in order to preserve its bioactivity. The composite layers were further coated by a glass belonging to the system SiO2–CaO–P2O5–Na2O–MgO–F−, known for its bioactivity. The experimental results were substantiated by optical and scanning electron microscopy (SEM) with compositional analysis (EDS) and by a mechanical characterization. The in vitro behavior of the coated samples was investigated by means of soaking in simulated body fluid (SBF) followed by SEM observation and XRD analysis.

Preparation and Characterisation of Biocompatible Vitroceramic–Metal Systems for Applications in Medicine

Vitroceramic coatings from the oxide system SiO2–CaO–Na2O–B2O3 50;TiO2 were obtained on metallic supports (titanium and austenitic steels with high Cr and Ni contents). The coating technology was classical enamelling. The metallic support is coated by either immersion or painting with a slurry layer resulting from a mixture of a frit (having the best oxide composition for each metallic support) with a liquid, fired at the enamelling temperature and then subjected to a thermal treatment for crystallisation. Good adherence between the two different materials is achieved when their thermal expansion coefficients are close to each other. The vitroceramic coating–metallic support system was characterised by optical microscopy, SEM, and X-ray diffraction. The adherence of the vitroceramic layer to the metallic supports was determined using microhardness tests carried out at the interface. Evidence of the processes occurring at the interface (gas bubbles, micropores, chemical binding, etc.) was also found. The coating layers are types of biocompatible and bioactive vitroceramic materials.

Wollastonite polytypes in the CaO-SiO 2 system.

This work deals with the identification and kinetics of crystallisation of the wollastonite polytypes which form in the system CaO-SiO2 in the temperature range 700–1000 °C. The kinetics of phase transformations in the system have been determined from analysis of in situ synchrotron X-ray powder diffraction data. Two different systems with the same compositions were investigated: one is more reactive, having grains with a larger surface area per unit volume, the other is less reactive, being composed of grains with a smaller surface area per unit volume. 1T-wollastonite forms first and progressively transforms in an intermediate 1Td-wollastonite disordered form. Both phases in turn transform into 2M-wollastonite polytype. Differences in the polytypes forming and reaction kinetics were observed for the two systems. In the more reactive system, the conversion 1T to 1Td polytypes is the dominant process. The kinetic parameters calculated using the Avrami models fully describe the reaction process of formation of both polytypes and transformation of one polytype into the other.

The effect of compositional changes on the crystallization behaviour and mechanical properties of diopside–wollastonite glass-ceramics in the SiO2–CaO–MgO (Na2O) system

The crystallization process of ternary system SiO2–CaO–MgO (Na2O) was investigated by DTA, XRD and SEM techniques and by strength measurements. The ability of Cr2O3+Fe2O3 as nucleating agents in inducing bulk nucleation via formation of a spinel phase was proved. Wollastonite and diopside are two major phases that were identified after two-stage heat treatment. The spherulitic growth morphology was observed by SEM. At high growth temperatures for long times the recrystallization process was observed too. The kinetic parameters, such as activation energy and Avrami exponent, were calculated by Kissinger equation.

Crystallisation Kinetics and Phase Relations of Wollastonite by Real Time Synchrotron Powder Diffraction

The crystn. kinetics of 1T-wollastonite in the CaO-SiO2 system starting from a stoichiometric glass was investigated in situ by x-ray synchrotron powder diffraction at 800-900�. At higher temp., 1T-wollastonite converts into the 2M polytype. The collected data were analyzed by the Avrami models and kinetic parameters seem to indicate a nucleation deceleratory controlled mechanism with 1D growth. The preliminary results of this study are part of a general project aimed to investigate polymorphism and polytypism of wollastonite and the related phases, esp. the role of the kinetic parameters in the formation of the polytypes in the pyroxenoid series. [on SciFinder(R)]

Low-temperature synthesis, structure, and bioactivity of gel-derived glasses in the binary CaO-SiO2 system.

Glasses in the binary system CaO-SiO2 for which the molar fraction of CaO is 0 < or = x < or = 0.50, were prepared by means of a sol-gel route starting from tetraethylorthosilicate and calcium nitrate. The textural features of the monoliths obtained were characterized using N2 gas adsorption, helium ultrapycnometry, and mercury porosimetry. In vitro bioactivity tests were performed in simulated body fluid (SBF). The ionic concentration of the SBF after glass immersion was analyzed using inductively coupled plasma atomic emission spectroscopy. The surfaces of the specimens were characterized using X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray analysis before and after in vitro testing. The textural characterization revealed that the glasses were mesoporous with cylindrical pores with average diameters ranging from 25 to 663 A depending on the molar fraction of CaO. The in vitro studies showed that all binary CaO-SiO2 gel-glass compositions produced were bioactive. These results indicate that the binary gel-derived CaO-SiO2 system exhibits a level of bioactivity over a similar molar range of SiO2 content as the previously studied ternary CaO-P2O5-SiO2 system.

Thermodynamic Modeling of the Miscibility Gaps and the Metastable Liquidi in the MgO‐SiO2, CaO‐SiO2, and SrO‐SiO2 Systems

A range of compositions and temperatures below the monotectic temperature exists where there are thermodynamic restrictions that prevent the equilibrium solid from forming directly from the undercooled homogeneous liquid. In this region, the solid can form only after liquid‐liquid phase separation has occurred. As suggested by earlier research, the thermodynamic restrictions on the crystallization process may be useful to control the crystallized grain structure in glass‐ceramic systems. Thus, understanding the thermodynamic limitations on the formation of the solid in monotectic systems could have commercial significance. In the present paper, the metastable liquidus boundaries, liquid miscibility gaps, and spinodal curves in binary MgO‐SiO2, CaO‐SiO2, and SrO‐SiO2 systems are calculated by using analytical expressions for the Gibbs free energies of the liquid phases. Calculating the metastable liquidus rather than using a simple extrapolation as originally proposed in the aforementioned previous research provides greater control of the heat‐treatment processes and, thus, greater control over the resulting microstructure.

In Situ Temperature Measurement of Oxide Melt in an Arc Imaging Furnace by a Monochromatic Radiation Pyrometer.

An arc imaging furnace has various advantages as an apparatus for ceramic synthesis. However, the disadvantage of this furnace is the difficulty of in situ temperature measurement of the sample, because of a very small heating spot in the furnace and the effect of infrared radiation from the light source on the measurement, a monochromatic radiation pyrometer is used. In this paper, a technique for in situ temperature measurement by monochromatic radiation pyrometer is proposed and applied to the melts of a CaO-SiO2 system above 1700°C. Heating up was performed in an arc imaging furnace equipped with a Xenon lamp. The monochromatic radiation pyrometer was proven to work appropriately for in situ temperature measurement of the melting samples above 1750°C, because it can focus on a small melting drop 2-3mm in diameter, and also because it can avoid the effect of infrared radiation from the Xe lamp, by using a 5μm wavelength to detect the radiation from the sample melts.

Influence of SO3 on the Phase Relationship in the System CaO–SiO2–Al2O3–Fe2O3

The influence of the additive SO3 on the phase relationships in the quaternary system CaO‐SiO2‐Al2O3‐Fe2O3 was investigated by observing the change of volume ratio of 3CaOSiO2 (C3S) to 2CaOSiO2 (C2S) + CaO (C) in the sintered material with the increase of SO3 content. The primary phase volume of C3S in the quaternary phase diagram shrank with the increase of SO3 and disappeared when the SO3 content exceeded 2.6 wt% in the sintered material. Changes in the peritectic reaction relationship between CaO (C), 2CaOSiO2 (C2S), 3CaOSiO2 (C3S), 3CaOAl2O3 (C3A), 4CaOAl2O3Fe2O3 (C4AF), and liquid were also observed and discussed.

Review and modeling of viscosity of silicate melts: Part I. Viscosity of binary and ternary silicates containing CaO, MgO, and MnO

A structurally related model for the calculation of the viscosity of silicate melts is proposed based on the general behavior of the viscosity of binary silicate melts. It relates viscosity to the degree of polymerization, as represented by the three types of oxygen in the melts. The model parameters for binary systems were optimized to give best fit to the experimental values. For ternary systems, it was assumed as a first approximation that the model parameters were linear functions of the parameters of the two binary silicate systems. The model has been applied to the CaO-SiO2, MgO-SiO2, and MnO-SiO2 binary systems and the CaO-MgO-SiO2 and CaO-MnO-SiO2 ternary systems. Good agreement was obtained between calculated values and experimental data over the composition and temperature ranges in which experimental data exist. Comparison was made between the present model and the Urbain model. The present model has the capability of representing changes in viscosity due to substitution of cation species in silicate melts.

Reactions between cement and As(III) oxide: The system CaOSiO 2As 2O 3H 2O at 25°C

Arsenic-bearing wastes are common by-products of mineral processing and smelting. As arsenic is well known to be highly toxic, it is important that these wastes should be treated in an ecologically acceptable manner. As(III) is the species of principal concern. One treatment system uses Portland cement as a containment and chemical immobilization matrix. A review of the literature revealed the solid phases of relevance, and solubility data were critically evaluated. Based upon these data, computer-based modelling was used to identify stable phase assemblages in the CaOSiO 2As 2O 3H 2O system at 25°C and calculate equilibrium solubilities. An experimental program was undertaken to verify the modelling predictions within the CaOAs 2O 3H 2O sub-system, and experimentally-obtained solubility data were, in turn, used by the modelling program. Solubility data thus derived were critically compared with those of the literature and although there are some differences between the data sets recast in the form of phase diagrams, the two are numerically in good agreement. The solubility of As is limited by reaction with calcium hydroxide and CSH gel to ∼0.0007 mmol kg −1, or approx. 0.075 mg l −1 as arsenite (AsO 2 −), by formation of CaAsO 2OH.

5564823 Method and apparatus for separation and volume measurement of components for lightweight concrete : Holik Karl Litchfield Park, United States assigned to Rastra Technologies Inc

The purpose of this investigation is to determine the reaction of different cement components and sulfoaluminate in mixtures and their mutual influence on the hydration. The components used are silicates, C3S and β-C2S, aluminates, C3A, C12A7 and CA2, ferrites, C4AF and C2F, and sulfoaluminate, C4A3S̄. The investigation includes separate components as well as combinations of two components. These combinations include one component from each of the following groups: silicate, aluminate, ferrite and sulfate. All combinations have been made with or without addition of gypsum. All eight hundred different combinations of the components have been investigated for one day, seven days, twenty-eight days and one year.The relations between the products of hydration and the oxide compositions of the cement components in system CaO  SiO2  Al2O3  Fe2O3 were explored. The different components were mixed at water/solid ratio of 0.5. The specimens were not protected from CO2, consequently monocarboaluminate, C4AC̄H11, was formed. The hydrate phases developing during hydration have been observed qualitatively by X-ray diffraction technique.In a neat paste of C3A, di- and tetracalcium aluminate hydrates were formed. After a while C3AH6 crystals appeared, according to the following scheme: High-sulfate form (ettringite) forms in hardened cement, a result of interaction of calcium sulfate with aluminates or ferrites, changing to monosulfate hydrate with time. When there are both gypsum and lime (the lime that is released from C3S or β-C2S during the hydration) the reactivity of C4AF is reduced. The lime seems to stabilize the ettringite crystals somewhat. In the presence of C3S and gypsum, the hydration of the sulfoaluminate yields a product with a greater quantity of ettringite than that from the pastes without C3S.The new phase of gehlenite hydrate, C2ASH8, found in a different system, seems to be a result of the hydration of C3S or β-C2S in alumina saturated solution (alumina components), C4A3S̄.