Physicochemical and thermo physical characterization of CaO–CaF2–SiO2 and CaO–TiO2–SiO2 based electrode coating for offshore welds

This paper investigates the physicochemical and thermo-physical properties of CaO–CaF₂–SiO₂ and CaO–TiO₂–SiO₂ based electrode coating for welding offshore structures. Twenty-one electrode coating compositions have been formulated using extreme vertices design method. The coating was crushed to powder form. The powder was characterized for weight loss, density, specific heat, enthalpy, thermal conductivity, diffusivity, and specific heat. Coating's structural analysis was done using X-Ray Diffraction and Fourier transformation. X-Ray Fluorescence, Thermogravimetric Analyzer, and Hot disc have been used to characterize the coating mixture. The regression analysis has been used to study the effect of individual constituents and their binary, tertiary interactions on the properties. The obtained output of properties has been optimized using multi-response optimization.     

Effect of BaO substitution for CaO on the structural and thermal properties of SiO2–B2O3–Al2O3–CaO–Na2O–P2O5 bioactive glass system used for implant coating applications

The present study replaced 3.30 and 9.00 mol.% BaO for CaO in a SiO₂–B₂O₃–Al₂O₃–CaO–Na₂O–P₂O₅ bioactive glass system used for implant coating applications. Variations of the glass structure, thermal properties, cytotoxicity, and radiopacity of glasses were studied. As demonstrated by the results, upon adding barium oxide to the glass structure, the weight density increased significantly, while a slight decrease in oxygen density was determined. Introducing barium oxide into glass composition did not cause any considerable change in the spectra of FTIR and Raman. It was demonstrated that the amount of bridging oxygen in the glass structure remained quite unaffected. The hot stage microscopy evaluations revealed further shrinkage of barium-containing frits due to lower viscosity and hence, higher viscous flow of these glasses. By substituting barium oxide for calcium oxide and increasing its concentration, the glass transition temperature (T_g) and the dilatometric softening temperature (T_d) decreased, while the thermal expansion coefficient increased. Moreover, upon substituting 9 mol.% barium oxide for calcium oxide, a 30 °C reduction in maximum sintering temperature (T_ms) of the glass was obtained, whereas the shrinkage rate was increased 1.7 times. It was indicated that the sintering process of barium-incorporated glasses would easily proceed without any phase crystallization. The barium-incorporated glasses exhibited more radiopacity. Additionally, no cytotoxic effect was caused by the substitution, and the Ba-containing glasses could be used for biomedical applications and implant coating as well.     

Corrosion of nickel ferrite refractory by Na3AlF6–AlF3–CaF2–Al2O3 bath

Based on research on cermet inert anodes for aluminium production, it has been suggested that nickel ferrite spinel might be suitable for use as a sidewall refractory in Hall-Héroult cells. A corrosion resistant sidewall would allow elimination of the frozen bath ledge, and has potentially huge benefits in terms of energy savings and increased productivity. However, little work has been done to assess nickel ferrite's suitability as a refractory.Dense nickel ferrite samples were prepared and characterized, and corrosion tests in cryolite based baths were conducted. Results confirm that the spinel does have good corrosion resistance. The corrosion mechanism is complex, involving grain boundary attack and formation of a Ni–Fe alloy. This alloy could pose a risk in terms of contamination of the aluminium. The use of additives to restrict penetration of grain boundaries may be the key to development of a successful spinel based refractory.     

Thermodynamics and crystallization kinetics of REEs in CaO–SiO2–Ce2O3 system

Rare earth elements (REEs) have become increasingly important as ceramic materials. The RE-bearing slags contain massive REEs resources, whereas the lack of thermodynamic and kinetic data of REEs has brought great difficulties to efficient recovery of REEs from RE-bearing slags and the application in ceramics. According to the compositions of the RE-bearing slags in industrial production, the isothermal phase equilibria of CaO–SiO₂–Ce₂O₃ system at 1500°C and 1300°C were constructed by means of liquid-quenching method combined with a series of analyses, which provides the thermodynamic data for the equilibria of REEs. On this basis, the crystallization behaviors of the RE phase (Ce_9.33−xCa_x(SiO₄)₆O_2−0.5x) was investigated, and the temperature range in which the RE phase crystallized singly in RE-bearing slags with a selected compositions was acquired. CCT and TTT diagrams for CaO–SiO₂–Ce₂O₃ system were established to characterize the crystallization kinetics of the RE phase, and the favorable conditions for its crystallization and growth in RE-bearing slags were determined. In this study, the complete thermodynamic and kinetic basic data of REEs in CaO–SiO₂–Ce₂O₃ system are provided for RE-bearing slags.     

1250°C liquidus for the CaO–MgO–SiO2–Al2O3–TiO2 system in air

Ti-bearing blast furnace slags have been regarded as an important secondary material in modern society, and the efficient recycling of Ti oxides from it is of key interest. For this reason, more thermodynamic data is needed regarding the phase relations in different composition ranges and sections. Therefore, the equilibrium phase relations of CaO–MgO–SiO₂–Al₂O₃–TiO₂ system in a low w(CaO)/w(SiO₂) ratio of 0.6–0.8 at 1250 °C in air and fixed concentrations of MgO and Al₂O₃, were investigated experimentally using a high temperature equilibration and quenching method followed by SEM-EDS (Scanning Electron Microscope and Energy Dispersive X-ray Spectrometer) analyses. The equilibrium solid phases of perovskite (CaO·TiO₂), a pseudo-brookite solid solution (MgO·2TiO₂, Al₂O₃·TiO₂)_ss, and anorthite (CaO·Al₂O₃·2SiO₂) were found to coexist with the liquid phase at 1250 °C. The calculated results of Factsage and MTDATA were used for comparisons, and significant discrepancies were found between predictions and the experimental results. The 1250 °C isotherm has been constructed and projected on the CaO–SiO₂–TiO₂-8 wt.% MgO-14 wt% Al₂O₃ quasi-ternary plane of the phase diagram. The obtained results provide new fundamental data for Ti-bearing slag recycling processes, and they add new experimental features for thermodynamic modeling of the high-order titanium oxide-containing systems.     

Fabrication of superhydrophilic self-cleaning SiO2–TiO2 coating and its photocatalytic performance

Generally, superhydrophilic self-cleaning coatings are prepared from semiconductors with photocatalytic properties. Organic pollutants attached to the coating surface can be degraded by its photocatalytic performance realizing a self-cleaning goal. Herein, SiO₂–TiO₂ composite particles were fabricated by the hydrolysis and precipitation of TiOSO₄, and SiO₂ microspheres were chosen as carriers, which are inexpensive and environmentally friendly. Then, superhydrophilic self-cleaning SiO₂–TiO₂ coatings were fabricated by spraying the composites on the surfaces of substrates. The morphology, structure and self-cleaning performance of the SiO₂–TiO₂ coating were characterized and tested. The results revealed that nano-TiO₂ was loaded on the surfaces of SiO₂ microspheres uniformly forming a hierarchical micro/nanostructure. The SiO₂–TiO₂ composite particles exhibited excellent photocatalytic degradation performance, and the degradation rate of methyl orange (10 ppm) was more than 98% under UV irradiation for 40 min. Furthermore, the coating prepared with the SiO₂–TiO₂ composite particles exhibited superhydrophilicity. A water droplet spreads completely on the coating surface in 0.35 s, and the contact angle reaches 0°. In addition, rhodamine B (RhB) and methylene blue (MB) on the coating surface can be degraded efficiently under sunlight irradiation. The SiO₂–TiO₂ composite particles can be sprayed directly on the surfaces of concrete, brick, wood, and glass slides. Therefore, the particles showed good adaptability to different substrates. The superhydrophilic property was due to the hydrophilicity of SiO₂ and TiO₂, the hierarchical micro/nanostructure of the SiO₂–TiO₂ composites, and the photoinduced superhydrophilicity of TiO₂. The above experimental results show that the as-prepared superhydrophilic self-cleaning SiO₂–TiO₂ coating has a large application potential.     

Solubility studies and thermophysical properties of uranium–neodymium mixed oxides system

Uranium–neodymium mixed oxides (U_1−yNd_y)O_2±x (y=0.2–0.85) were prepared by citrate gel-combustion and characterized by XRD. Single phase fluorite structure was observed up to y=0.80. For solid solutions with y>0.80 additional lines pertaining to hexagonal neodymium oxide were observed. Lattice thermal expansion of these samples was investigated by using high temperature X-ray diffraction (HTXRD). The coefficients of thermal expansion for (U_1−yNd_y)O_2±x for y=0.2, 0.4, 0.6, and 0.8 in the temperature range 298–1973 K were found to be 16.46, 16.64, 16.79, and 16.89×10⁻⁶ K⁻¹, respectively. Heat capacity and enthalpy increment measurements were carried out by using DSC and drop calorimetry in the temperature range 298–800 K and 800–1800 K respectively. The C_p,m values at 298 K for (U_1−yLa_y)O_2±x (y=0.2, 0.4, 0.6, and 0.8) are 63.4, 64.3, 61.8, and 58.9 J K⁻¹ mol⁻¹ respectively.     

Phase equilibria in the CaO·SiO2Na2O·SiO2Na2O·Al2O3·6SiO2 system

Equilibrium phase relations in the system CaO·SiO₂Na₂O·SiO₂Na₂O·Al₂O₃·6SiO₂ at 40–80 wt% Na₂O·Al₂O₃·6SiO₂ composition range have been experimentally studied at temperatures between 800 °C and 1200 °C. The liquidus temperature was determined with differential scanning calorimetry. The equilibrated samples were quenched with pressurized nitrogen, and examined with electron probe X-ray microanalysis and X-ray diffraction for identification of microstructure and phase relations. Five primary phase fields, CaO·SiO₂, Na₂O·SiO₂, Na₂O·2CaO·3SiO₂, 2Na₂O·CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ were established. The ternary eutectic point of CaO·SiO₂, Na₂O·2CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ was determined to be at 1030 °C with the composition of 29.0 wt% CaO·SiO₂, 12.0 wt% Na₂O·SiO₂ and 59.0 wt% Na₂O·Al₂O₃·6SiO₂. Peritectic reaction of Na₂O·2CaO·3SiO₂, 2Na₂O·CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ occurred at 930 °C with the composition of 13.0 wt% CaO·SiO₂, 29.0 wt% Na₂O·SiO₂ and 58.0 wt% Na₂O·Al₂O₃·6SiO₂. The liquidus surface projection of the ternary system has been constructed in the composition region important for the bottom ash application.     

Design of multifunctional SiO2–TiO2 composite coating materials for outdoor sandstone conservation

This research was aimed to develop a novel multifunctional SiO₂–TiO₂ composite coating for application in the field of outdoor sandstone conservation. The SiO₂–TiO₂ composite coating derived from the sol–gel reaction of tetraethoxysilan (TEOS) and tetrabutyl orthotitanate (TBOT). Hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and poly(ethylene oxide)-poly(phenylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, F127) surfactant were added to the SiO₂–TiO₂ based materials. The contact angle analysis, scanning electron microscopy measurement, stain resistant test, salt crystallization test and outdoor exposure test were conducted to investigate the effectiveness and durability of this composite coating. Results showed that SiO₂–TiO₂ composite materials created a hydrophobic, crack-free coating with self-cleaning and antibacterial properties on the decayed sandstone surface, allowing their use for practical outdoor sandstone conservation applications.     

Microwave dielectric materials based on the MgO–SiO2–TiO2 system

Ceramics in the system MgO–SiO₂–TiO₂ were prepared by standard mixed oxide route. By adding ZnO–B₂O₃ to the starting mixtures, the firing temperature of the ceramics could be reduced to 1160 °C. Small additions of MnCO₃ and CaTiO₃ improve microwave dielectric properties leading to an increase in insulation resistance and a decrease in temperature coefficient of capacitance. By adding Co₂O₃ grain growth can be inhibited and the dielectric Qf value greatly increased. The resultant ceramic material exhibited low dielectric constant and low dielectric loss: relative permittivity (ε_r): 20±2; temperature coefficient of capacitance (τ_c): 0±30 ppm/°C; Qf: 100,000 (at 10 GHz); insulation resistance: 10¹³ Ω cm:     

Microstructure and properties of CaO–ZrO2–SiO2 glass–ceramics prepared by sintering

For the development of a new wear resistant and chemically stable glass-ceramic glaze, the CaO–ZrO₂–SiO₂ system was studied. Compositions consisting of CaO, ZrO₂, and SiO₂ were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO₃) and calcium zirconium silicate (Ca₂ZrSi₄O₁₂) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca_1.2Si_4.3Zr_0.2O₈. The CaO–ZrO₂–SiO₂ system showed good properties in wear and chemical resistance because the Ca₂ZrSi₄O₁₂ crystals positively affected physical and mechanical properties.     

Phase equilibria studies in the CaO–SiO2–Al2O3–MgO system with CaO/SiO2 ratio of 0.9

Phase equilibria and liquidus temperatures in the CaO–SiO₂–Al₂O₃–MgO system at a CaO/SiO₂ weight ratio of 0.9 in the liquid phase have been experimentally determined employing high-temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Isotherms at 1573, 1623, 1673, and 1773 K were determined and the primary phase fields of wollastonite, melilite, olivine, periclase, spinel, and corundum have been located. Compositions of the olivine and melilite solid solutions were analyzed and discussed. Comparisons between the newly constructed diagram, existing data, and FactSage predicted phase diagrams were performed and differences were discussed. The present study will be useful for guidance of industrial practices and further development of thermodynamic modeling.     

Effect of ZrO2 addition on in-vitro bioactivity and mechanical properties of SiO2–Na2O–CaO–P2O5 bioactive glass-ceramic

Herein, a multicomponent bioactive glass (0Z, 46SiO₂–30CaO–18Na₂O–6P₂O₅, wt.%) is prepared via melting. ZrO₂ is introduced into the bioglass using two different methods, and then three types of glass-ceramic bulks are manufactured using low-cost pressureless sintering. The effect of ZrO₂ addition on the bioactivity and mechanical properties of the bioactive glass-ceramic is assessed. The results indicate that the main crystalline precipitate from the bioactive glass-ceramic is Na₂Ca(Si₂O₆). The crystallisation ability of the 5Z glass-ceramic, bioactive glass-ceramic with ZrO₂ added during melting at high temperature, is reduced because ZrO₂ participated in the reconstruction of the glass network. Further, the ZrO₂ addition led to a low rate of cation release when soaked in simulated body fluid, indicating a decreased bioactivity. At the same time, the 5Y bioactive glass-ceramic, prepared by mixing YSZ particles with 0Z using ball-milling, possesses not only the highest mechanical strength (about twice the strength of 0Z) but also a high bioactivity. This study presents a promising method for the production of excellent bioactive glass-ceramic and a candidate (5Y) for the clinical applications where load bearing is required.     

Effect of ZnO content on the physical,mechanical and chemical properties of glass-ceramics in the CaO–SiO2–Al2O3 system

The objective of this study was to evaluate the effect of ZnO content on the physical, mechanical and chemical properties of CaO–Al₂O₃–SiO₂ (CAS) glass-ceramics produced from Colombian wastes, such as fly ash, granulated blast furnace slag and glass cullet. The CaO/SiO₂ molar ratio of the mixtures was held constant (0.36). ZnO was added to the mixtures in proportions of 4, 7 and 10 wt%. The glass-ceramics were produced by the controlled crystallization of a parent glass. The values of crystallization temperature (T_p) show a fall up to 7 wt% and then shoots up with 10 wt% concentration of ZnO, but in general, ZnO addition lowers the temperature required for the formation of crystalline phases. In general, anorthite (CaAl₂Si₂O₈) is the main phase observed in all heat treated samples, in addition to albite (Na(AlSi₃O₈)) and labradorite (Na_0.45 Ca_0.55 Al_1.55 Si_2.45 O₈). The crystalline phases hardystonite (Ca₂ZnSi₂O₇) and willemite (Zn₂SiO₄) were also identified in the samples with 7 and 10 wt% ZnO. The densities of the glass-ceramics were between 2658 and 2848 kg/m³, and it was found that ZnO helps to increase the density of glass-ceramics. The elastic modulus was in the 100–105 GPa range, the fracture toughness was between 0.45 and 0.64 MPa m^1/2, and the Vickers microhardness was between 632 and 653 MPa. With regards to the durability, the weight loss of the glass-ceramics immersed in alkaline solution (NaOH) did not exceed 1.5 wt% after immersion for 6 h at 80 °C. The results of this study confirm that the vitrification process is a favorable option to utilize these industrial wastes.     

Effect of CaO doping on the properties and crystallization behavior of Y2O3–Al2O3–SiO2 glass

Nowadays, Y₂O₃–Al₂O₃–SiO₂ (YAS) glass joining is considered to be a promising scheme for nuclear-grade continuous silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC). CaO has great potential for nuclear applications since it has low reactivity and low decay rate under nuclear irradiation. In this paper, the effect of CaO doping on the structure, thermophysical properties, and crystallization behavior of YAS glass was systematically studied. As the CaO doping content increased, the number of bridge oxygens and the viscosity at high temperatures reduced gradually. After heat treatment at 1400 °C, the main phases in YAS glass were β-Y₂Si₂O₇, mullite, and SiO₂ (coexistence of crystalline and glass phases), while that with 3.0% CaO doping turned into a single glassy phase under the same treatment conditions. Moreover, a structural model and the modification mechanism were proposed, which provided a theoretical basis for the subsequent component design and optimization.     

Gas sensing properties of asymmetrically reduced Na1/2Bi1/2TiO3–based ceramics

We report the gas sensing properties of a type of new materials, Na_1/2Bi_1/2TiO₃ (NBT)-based ceramics. After the NBT-based ceramics were asymmetrically reduced and coated with Au electrodes, the materials exhibit relatively large electrical responses when exposed to oxygen and some oxidizable gases at a relatively low temperature (≤300 °C). An electric voltage ～60 mV is measured in the mixture of O₂ and N₂ (1% O₂). In oxidizable gases, a negative response can be obtained. The measured voltages are ?45 mV and ?98 mV in the mixtures of H₂/air (1000 ppm H₂) and C₂H₅OH/air (1000 ppm C₂H₅OH), respectively. The electrical responses are proportional to the logarithm of the concentrations of the analyzed gases. Also, the electrical responses to oxygen and oxidizable gases have opposite signs, and the model of mixed-potential is proposed to explain the gas sensing phenomenon. This study provides a new material and a simple design for gas sensors. The proposed gas sensor comprises a reduced NBT-based ceramic wafer with the same electrodes on the opposite surfaces. Additional components in traditional gas sensors, such as sensing or reference electrode, are unnecessary.     

Improvement of gold electrode conductivity after cofiring with CaO–B2O3–SiO2 green tapes for LTCC application

The cofiring process of Au paste containing various amount of glass additive with different properties and CaO–B₂O₃–SiO₂ (CBS) green tapes was investigated. The initial shrinkage temperature of Au paste was strongly associated with the softening point and the content of glass additive. The swell of sample and its mechanism during cofiring process was reported. The sheet resistivity of Au electrode was greatly depended on the content of CBS glass additive. When the content of CBS glass additive with the softening point of 704 °C was 3 wt %, the Au electrode exhibited the highest conductivity with the sheet resistivity of 2.4 mΩ/sq. The results obtained in this paper revealed the relationship between the glass additive and cofiring defects of Au electrode in the metal/ceramic multilayer structure, which gave an avenue to manufacture Low temperature co-fired ceramics (LTCC) modules with good quality.     

Effect of TiO2 on microphase development during phase separation and crystallization in Na2O–B2O3–SiO2 glass system

This study examines the incorporation of TiO₂ into sodium borosilicate glasses and its effect on the formation of glassy and crystalline microphases. Glasses in the composition range: 7Na₂O–23B₂O₃–(70 - X)SiO₂–XTiO₂ (where X = 0–14.6 mol.% TiO₂) which exhibit phase separation were investigated. Raman studies confirm the formation of two different TiO₂ coordinations depending on the molar content of TiO₂. Thermal properties of glasses are unaffected by TiO₂ addition. The domain size of microphase development in TiO₂-containing glass indicates competition between phase separation and crystallization. Enrichment of titanium on the interphase between glassy microphases reduces the mass transfer and consequently limits the growth rate of glassy phases. This competes with the formation of anatase for which a nucleation-controlled mechanism is proposed.     

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.     

SiO2–Al2O3–CaO glass-ceramics: Effects of CaF2 on crystallization,microstructure and properties

The effects of fluorine content on the nucleation and crystallization behavior of SiO₂–Al₂O₃–CaO glass ceramics system have been investigated. The crystalline phases were determined by X-ray diffraction (XRD). The crystallization kinetics was determined by differential thermal analysis (DTA). The microstructures were examined by using scanning electron microscope (SEM). Fourier transformed infrared spectra (FTIR) analysis was used to study the glass structure. The results showed that by increasing the fluorine content, both the crystallization peak temperature (T_p) and activation energy (E) decreased. Wollastonite, anorthite and gehlenite are the main crystalline phases that exist in the glass ceramics system. The study shows that fluorine promoted initial crystallization of glass and can be used as an effective nucleating agent in the SiO₂–Al₂O₃–CaO system.