CaO ZrO2 SiO2 Research Articles

Effects of CaO–ZrO2–SiO2–CaF2–TiO2-based electrode coating components on weld chemistry and microhardness

Effects of CaO–ZrO2–SiO2–CaF2–TiO2-based electrode coating components on weld chemistry and microhardness

Structural relaxation of lead and barium-free crystal glasses

The structural relaxation of Na2O–K2O–CaO–ZrO2–SiO2 (NKCZ), Na2O–K2O–ZnO–ZrO2–SiO2 (NKzZ), Na2O–CaO–ZnO–ZrO2–SiO2 (NCzZ), K2O–CaO–ZnO–ZrO2–SiO2 (KCzZ), and Na2O–K2O–CaO–ZnO–ZrO2–SiO2 (NKCzZ) glasses were studied by thermomechanical analysis. The structural relaxation was described by the Tool–Narayanaswamy–Mazurin model (TNMa). The relaxation function of Kohlrausch, Williams, and Watts (KWW) was used. The parameters of relaxation model were calculated by nonlinear regression analysis of thermodilatometric curves measured under cyclic time–temperature regime by thermomechanical analyzer under the constant load. The values of the exponent b of the KWW equation, modulus K, limit dynamic viscosity η 0 of the Mazurin’s expression for relaxation time, and constant B of the Vogel–Fulcher–Tammann viscosity equation were optimized. It was found that TNMa relaxation model very well describes the experimental data. A more detailed analysis of the obtained results showed that the equimolar substitution of SiO2 by ZrO2 (i.e., the increase of the ZrO2 content in the glass) decreases the parameter b, therefore the continuous distribution of the relaxation times spectrum is widening. A wider spectrum of relaxation times was obtained even in the case of substitution of ZnO for CaO and K2O for Na2O. Substitution of ZrO2 for SiO2 decreases the dynamic viscosity limit η 0 that corresponds to an activation energy increase of temperature dependence of isostructural viscosity. Increased content of ZrO2 in the glass caused the increase of the value of the modulus K.

Fundamental investigations on the high temperature corrosion of ZrSiO4-containing andalusite refractories in cement kiln preheater

ZrSiO4-containing andalusite brick after service in cement kiln preheater was analysed by means of XRF, XRD and SEM/EDS techniques in order to determine the corrosion mechanism during 8-months industrial-scale corrosion test in high-alkaline environment at 1100°C. The detailed investigation of the wear mechanism through “post-mortem studies” of the ZrSiO4-containing andalusite brick showed that the K-aluminosilicate phases were formed along with a liquid phase as a consequence of reactions between potassium and andalusite. Ca-aluminosilicate and CaZrO3 phases were also formed.In this paper, a new model of the refractory corrosion was proposed. In modelling the corrosion of zircon-containing andalusite refractory material, ZrSiO4 and Al2SiO5 single grains were used to represent the refractory, so that in all cases the isothermal sections of CaO–Al2O3–SiO2, K2O–Al2O3–SiO2 and CaO–ZrO2–SiO2 systems at 1100°C were used to identify the equilibrium phases and also to explain the mechanism of corrosion.

Phase composition, microstructure and in vitro bioactivity of laser cladding CaO–ZrO2–SiO2 system coatings on titanium alloy

The bioactive coatings were prepared by laser cladding CaO–ZrO2–SiO2 system coatings on titanium alloy (Ti6Al4V). The cross-section morphologies of the coating are cellular crystal and cellular-dendrite structure. With the increase of ZrO2 content, the structure becomes coarse. The coating is mainly composed of CaTiO3, CaO, α-Ca2(SiO4), SiO2 and TiO2. When 5mol% ZrO2 was added, CaZrO3 appears. With the increase of ZrO2 content, ZrO2 appears and CaO disappears. The surface of these coatings are coarse, accidented and partial porous. After soaking in simulated body fluid (SBF), apatite is formed on the coating surface.

Human bone marrow‐derived stromal cells cultured with a plasma sprayed CaO‐ZrO2‐SiO2 coating

The CaO-ZrO2-SiO2 (CZS) coating was prepared by plasma-spraying chemically synthesized CZS powder onto a Ti-6Al-4V substrate. This CZS coating has been demonstrated to have good bioactivity, high bonding strength with the substrate and a low degradation rate. However, the effect of CZS coating on the osseointegration of bone-implant is still unknown. In this study, human bone marrow-derived stromal cells (hBMSCs) were cultured on CZS coating in vitro, and cell behavior was investigated, with the classical hydroxyapatite (HA) coating as a control. Scanning electron microscopy (SEM) and immunofluorescence studies showed that the hBMSCs on the CZS coating spread well with organized cytoskeleton structure at 24 h following cell seeding. The MTT assay and the Alamar Blue assay indicated that CZS coating promoted the attachment and proliferation of hBMSCs. The results of alkaline phosphatase (ALP) activity test and the expression of osteogenic marker genes, such as ALP, collagen I (COLI), osteopontin (OPN), and osteocalcin (OCN), demonstrated that the osteoblastic differentiation of hBMSCs was enhanced more by CZS coating than by HA coating. These results suggest that CZS coating possess excellent biological properties and may have potential in biomedical applications.

Preparation and Characterization of CaO-ZrO2-SiO2 Coating for Potential Application in Biomedicine

In this paper, chemically synthesized CaO-ZrO2-SiO2 (CZS) powder was plasma sprayed onto a Ti-6Al-4V alloy substrate for its potential applications in biomedicine. Surface morphology and phase composition were analyzed by scanning electron microscopy (SEM) and x-ray diffraction (XRD). The degradation behavior of the coating in biological environment was in vitro appraised in Tris-HCl buffer. The mass loss was much lower than that of the wollastonite coating (WC) and close to that of the hydroxylapatite coating (HC). The bond strength with titanium alloy substrate was 31.8 ± 4.7 MPa. In vitro bioactivity appraisement results showed that apatite could be formed on the surfaces after soaking in simulated body fluid (SBF) for 14 days. Canine marrow stem cells (MSCs) also showed well adhesion and proliferation on the coating surfaces. In summary, results suggest that the coating possesses well cytocompatibility and may be an appropriate candidate for application in biomedicine.

Environmental stability of the YSZ layer and the YSZ/TGO interface of an in-service EB-PVD coated high-pressure turbine blade

Hot corrosion of an in-service EB-PVD coated 1st stage high-pressure turbine (HPT) blade following an interactive CaSO4 infiltration/CMAS deposition process has produced reactive interfaces with the yttria stabilized zirconia (YSZ) top coat and the TGO layer which were investigated by analytical scanning and transmission electron microscopy (TEM). Despite complete CaSO4 infiltration of the coating macroscopic damage of the airfoil was confined to the pressure surface close to the trailing edge. Since the bulk composition of the CaSO4/CMAS deposits exhibited a high lime-to-silica ratio CaSO4/CMAS/YSZ interfaces typically involved a Ca–Zr-rich layer followed by fine-grained Ca-FSZ particles enveloping rounded YSZ column tips. No interfacial reaction was observed between the YSZ column walls and the CaSO4 pore fillings. Possible terms for the formation of this unique CaSO4/CMAS microstructure are evaluated. Zirconia destabilization upon hot corrosion is discussed in the light of phase compatibilities in the systems CaO–Y2O3–ZrO2 and CaO–ZrO2–SiO2 and put into perspective with previous work on both, natural and synthetic hot corrosion deposits.

Structure, magnetic and positron lifetime studies on CaO–ZrO2–SiO2 glass system doped with vanadium oxide

The structure of CaO–ZrO2–SiO2 glasses doped with V2O5 (0.1–2 mole%) was studied using density and molar volume measurements. It was observed that the molar volume increased while the density decreased with increasing V2O5 content. Magnetic susceptibility measurements showed the diamagnetic behaviour of this glass system. The free volume was probed using ortho-positronium pick-off annihilation lifetime parameters. The mean free volume and fractional free volume have also been calculated from the positron annihilation lifetime data. The overall measured parameters from the structural and/or positron annihilation spectra indicated that the majority of the vanadium ions in the range 0–0.5 mole% of V2O5 are in the V5+ valence state which act as a glass former. On the other hand, the majority of the vanadium ions in the range 0.7–2 mole% of V2O5 are the V3+ and V4+ states acting as a glass modifier.

Sintering and crystallisation of vanadium doped CaO–ZrO2–SiO2 glass-ceramics

The effect of addition of V2O5 on densification and crystallisation of glass powder compacts in the system CaO–ZrO2–SiO2 has been investigated. A well crystallized material of relatively high density (95% of theoretical density) was obtained after sintering at 900 °C for 1h by adding 5mol% V2O5. Crystalline phases identified were wollastonite, calcium zirconium silicate and calcium zirconium oxide. The addition of V2O5 was shown to reduce the sintering temperature and also to enhance the electrical conductivity of the base CaO–ZrO2–SiO2 glass-ceramic. Possible applications of the present vanadium containing glass-ceramics are the production of coloured glazes and in coatings and enamels with “anti-static” behaviour.

Bulk Crystallization of Glasses Belonging to the Calcia-Zirconia-Silica System by Microwave Energy

This paper reports results that show the effect of microwave absorption on the bulk crystallization of two glasses in the CaO—ZrO2—SiO2 system. The glass samples were devitrified using either microwave or conventional heating, to compare the results obtained from the two different techniques. Remarkably different crystallization paths were observed, depending mostly on the composition of the glass. This observation was especially true when microwave heating was used, where the dielectric losses observed in silicate glasses are related to the ZrO2 content. X-ray diffraction analysis was performed on the powdered samples, to determine the crystalline phases present. The microstructure and microanalysis results of these glass-ceramic compositions are presented and are related to the different ZrO2 contents.

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–ZrO 2 –SiO 2 system was studied. Compositions consisting of CaO, ZrO 2 , and SiO 2 were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO 3 ) and calcium zirconium silicate (Ca 2 ZrSi 4 O 12 ) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca 1.2 Si 4.3 Zr 0.2 O 8 . The CaO–ZrO 2 –SiO 2 system showed good properties in wear and chemical resistance because the Ca 2 ZrSi 4 O 12 crystals positively affected physical and mechanical properties.

Effect of silicon carbide whisker reinforcement on CaO–ZrO2–SiO2glass–ceramic system

AbstractAn industrial frit formulated in the new CaO–ZrO2–SiO2 glass–ceramic system was studied as a matrix for whisker reinforced composites. The frit was ball milled in acetone and wet ultrasonically mixed with 5, 10, 20, and 30 vol.-% SiC whiskers in order to overcome whisker agglomeration and obtain intimate mixing of the two phases. The samples were hot pressed at 14 MPa in graphite dies, using a N2 atmosphere, for 2 h at 1280°C. In order to investigate the effect of whiskers as a reinforcement, flexural strength as well as crack configuration and propagation were taken into consideration. Whisker orientation perpendicular to the hot pressing direction was found by SEM observation, and no carbon layer at the whisker/matrix interface was detected by EPMA. Further characterisation of the specimens involved physical (density, elastic modulus) and microstructural properties (XRD, SEM, TEM). The result of glass devitrification was inter locked wollastonite crystals.