Calcium Zirconate Research Articles

Exploring the conduction mechanism of multiferroic SrM–BCZT composite

Multiferroic composite of strontium hexaferrite (SrM, SrFe12O19) and barium calcium zirconium titanate (BCZT, Ba0·85Ca0·15Zr0·1Ti0·9O3) have been investigated and the conventional solid-state reaction (SRR) process is utilized to prepare the SrM–xBCZT composite (where x = 0.0, 0.10, 0.20 and 0.30). Diphase stoichiometry was confirmed by the phase analysis, for undoped composition presence of ferromagnetic SrM with complex magnetoplumbite structural phase and hexagonal structural phase with P63/mmc space group was confirmed. Further, doping of BCZT suppressed the secondary phase appeared (Fe2O3) and caused increase in lattice constants. Fourier Transform Infra–Red study revealed the presence of absorption bands of phases. Microstructure analysis suggests the formation of dense composite and confirmed the effect of BCZT as sintering aid. Impedance spectroscopy study suggested two electrical contributions in the microstructure (grain and grain boundary) of charge carriers with short range mobility, while high temperature AC conductivity analysis confirmed double ionized oxygen vacancies conduction. Further, NTCR the negative value of temperature coefficient of resistance and non–Debye type phenomenon is observed, which suggest suitability of these compositions for the heat sensor applications.

In vitro bioactivity, molecular structure and mechanical properties of zirconia-carbonated hydroxyapatite nanobiocomposites sintered at different temperatures

Zirconia-carbonated hydroxyapatite (ZrO2-CHA) nanocomposites powders, with various CHA contents, have been prepared using high energy ball milling. In order to investigate the influence of their exposure to different firing temperatures; namely 800, 1000, 1200, 1400 and 1500 °C on their molecular structure and microstructure, X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), respectively were employed. Additionally, their mechanical properties were also measured. Then, the in vitro bioactivity of the sintered samples, at different temperatures, was examined by FTIR spectroscopy and SEM after their soaking in simulated body fluid for 10 days. The obtained results pointed out that the elevation of sintering temperatures to 1000 °C caused fair densification and good mechanical properties irrespective to the partial degenartion of CHA and the formation of tricalcium phosphate (TCP) and calcium zirconate (CaZrO3) phases. However, further increase of sintering temperature led to dramatic decreases in these properties and then, they were significantly enhanced by the increasing of sintering temperature up to 1500 °C. The formation of the abovementioned phases negatively affected the bioactivity of these nanocomposites. Calculated molecular electrostatic potential confirmed the reactivity of TCP and CaZrO3 phases.

Synthesis and characterization of calcium zirconate nanofibers produced by electrospinning

Calcium zirconate fibers were produced by electrospinning and characterized in this work. The solution was prepared from zirconium and calcium salts, using polyvinyl-pyrrolidone (PVP) as processing aid. The decomposition of the organic fraction and crystallization of calcium zirconate were followed by thermogravimetry and differential scanning calorimetry (TG/DSC). Raman Spectroscopy was used to measure the vibrational modes in the green as well as in the calcined fibers. The final phase composition was studied by means of X-ray diffraction (XRD). The fiber morphology was investigated by confocal laser scanning microscopy (CLS) and scanning electron microscopy (SEM). The formation reaction of calcium zirconate was observed at about 740 °C. Highly crystalline fibers were obtained already at 800 °C, but the crystallinity and calcium zirconate yield improved when the temperature was increased to 1000 °C.

Thermodynamic corrosion behavior of Al2O3, ZrO2 and MgO refractories in contact with high basicity refining slag

Abstract Al 2 O 3 , MgO, and ZrO 2 containing refractories are widely used in the steel industry. The corrosion behavior of high basicity refining slag on three kinds of refractory materials was studied. Regarding the Al 2 O 3 refractory, Al 2 O 3 crucible would partially dissolve into the slag, and form a transition layer composed of CaAl 12 O 19 and CaAl 4 O 7 at the same time. For ZrO 2 refractories, the refining slag and the ZrO 2 crucible produce a transition layer composed of calcium zirconate with the high melting point of CaZrO 3 , CaZr 4 O 9 and Ca 6 Zr 19 O 44 , which prevents the contact between the ZrO 2 crucible and the refining slag to inhibit the further corrosion of the crucible. There is no chemical reaction between the MgO crucible and the refining slag. However, the pores in the MgO crucible matrix are filled with liquid slag. The corrosion mechanisms were studied by experiments combined with thermodynamic calculations, and the relative corrosion model has been established.

Advanced refractories for titanium metallurgy based on calcium zirconate with improved thermomechanical properties

Calcium zirconate refractories exhibit a promisingly high corrosion resistance in contact with titanium alloy melts. In the present article, we improved the thermomechanical properties of calcium zirconate based refractories by altering their microstructure and chemical composition. In a full factorial experimental design we investigated the effects of an insitu phase formation, of the addition of coarse grained MgO aggregates as well as the addition of SrCO3. Based on these factors, the chemical, physical, mechanical and thermomechanical properties as well as the resulting microstructure were thoroughly characterized. Strikingly, the addition of SrCO3 resulted in significantly improved mechanical properties before and after thermal shock. The improved thermal shock resistance can be attributed to a lower determined thermal expansion coefficient, a homogeneous pore size distribution with a reduced pore size and a better bonding between the matrix and the coarse grained aggregates.

Chemical synthesis of materials based on calcium zirconate for solid oxide fuel cells (SOFC)

AbstractFuel cells allow the production of energy from a clean electrochemical reaction. Among various types, the solid oxide fuel cell (SOFC) operates at high temperatures, allowing the conversion of hydrogen fuel into electricity, where water is generated as a by‐product. Strontium‐doped lanthanum manganite (La1‐xSrxMnO3, LSM) is commonly used as a cathodic material in traditional high‐temperature solid oxide fuel cells. Nowadays, the operating temperature of SOFCs should be reduced to 600–800°C due to improved fine electrolyte production techniques and the use of some intermediate temperature electrolytes. The LSM is not a suitable cathode for SOFCs operating in this temperature range, since it does not have a high enough conductivity and its electrochemical activity is very low as well. In this article, the performance improvement of LSM is described by mixing with calcium zirconate. The composite ceramic materials CaZrO3−La0.6Sr0.4MnO3, CaZrO3−NiO, and CaZrO3 were synthesized by combustion method, for application as a SOFC single cell. The results prove that the synthesized materials have potential to be used in a SOFC cell. At 800°C, was confirmed the CaZrO3 formation. Through Electrochemical impedance spectroscopy, the analysis presented low activation energy and the materials have been demonstrated to be compatible, an important fact to construct a suitable SOFC cell. The obtained activation energy was 0.90, 0.85, and 0.51 eV for the electrolyte, the anode and the cathode, respectively.

Characterization and investigation of in vitro properties of antibacterial copper deposited on bioactive ZrO2 coatings on zirconium

In this study, porous and rough bioceramic structures were coated on commercial pure Zr by PEO (plasma electrolytic oxidation). Then, Cu was deposited onto the PEO surfaces without any morphological changing by TE (thermal evaporation). Mainly, meta-stable Ca0.15Zr0.85O1.85 (calcium zirconium oxide), cubic-ZrO2 (zirconia) and perovskite-CaZrO3 (calcium zirconate) were observed on the surfaces by powder-XRD (powder X-ray diffraction) and TF-XRD (thin film XRD) analyses as the phases of Zr and Cu2(P2O7) (copper pyrophosphate) were detected as a trace amount on the Cu-deposited PEO surface. The average thicknesses of the PEO coating and TE layer were measured as approximately 21.8 ± 2.4 μm and 20 nm, respectively. The Cu-deposited PEO surfaces indicated superhydrophobic character while the PEO surface exhibited hydrophilic behavior. The apatite-forming abilities on both coatings were evaluated by surface and cross-sectional SEM (scanning electron microscopy) and surface EDS (energy dispersive X-ray spectroscopy)-mapping analyses at post-soaking in SBF (simulated body fluid) up to 10 days. However, apatite formed on the Cu-deposited PEO surfaces was thicker and more homogenous than the PEO surface. Thus, in vitro bioactivity was considerably improved by Cu-deposition on the PEO. In vitro microbial adhesion test of both surfaces was investigated by bacterial adhesions for Gram positive and Gram negative bacteria. The bacterial adhesions on the Cu-deposited PEO surfaces were lower compared to the PEO surfaces for all bacteria types.

Investment casting of titanium alloys with calcium zirconate moulds and crucibles

Titanium alloys are very difficult to process via investment casting due to their high melting temperature and reactivity. The objective of the present work was to evaluate new shell mould materials for the suitability for titanium casting in comparison to conventional materials. A new corrosion-resistant material for crucibles and shell moulds based on calcium zirconate (CaZrO3) is proposed with the aim of improving the casting quality of titanium alloys. Tilt casting trials into CaZrO3 shell moulds using three different crucible materials were conducted. The results were compared to a commercial shell system containing silica. The reactivity with the titanium melt was extensively studied as a function of melt temperature, part dimensions and shell mould temperature by hardness profiles and oxygen measurements. The reaction of the CaZrO3 shell was very low, indicated by small oxygen contents and thereby low surface hardness. The formation of an α-case was avoided by choosing appropriate casting parameters.

Synthesis, characterization and hydration analysis of Ba2+-, Cu2+- or Bi3+-doped CaO\u2013Al2O3\u2013ZrO2-based cements

This paper deals with the design, synthesis, hydration mechanism and hydration products of novel Ba2+-, Cu2+- or Bi3+-doped CaO–Al2O3–ZrO2-based cementitious materials used for heavyweight concrete mixes. The results of the heating microscopy thermal analysis indicated that both Cu and Bi in a Ca7ZrAl6O18-based cement clinker can effectively reduce the sintering temperature by 150–200 °C. Incorporation of barium for the synthesis of calcium zirconium aluminate-based hydraulic binder increased its thermal resistance since Ba2+-doped Ca7ZrAl6O18 along with accessory (Ca,Ba)ZrO3 with a perovskite‐type structure and BaAl2O4 phases having high melting points were formed. The presence of metal ions, i.e., Cu2+ or Bi3+, created conditions which were favorable for the formation of hexagonal calcium aluminate hydrates rather than the cubic one, as confirmed by coupled DSC–TG/EGA–MS thermal analysis techniques and X-ray diffraction. For the Ba2+ doping ions, this effect was the least noticeable. The effect of metal ions including Ba2+, Cu2+ and Bi3+ on microstructural features of cement pastes was investigated by SEM–EDS. These doping ions strongly affected the morphologies of Ca–Al hydrates.

The effect of calcium zirconate modifications on the microstructure and functional properties of sodium niobate thin films prepared by chemical solution deposition

Sodium niobate thin films doped with manganese (NN), and NN films modified with 5 or 10 mol % calcium zirconate (CZ) on platinized silicon substrates were prepared by chemical solution deposition. The 250-nm-thick films crystallize in a perovskite phase with fine, equiaxed grains. The NN films exhibit well-shaped ferroelectric loops with a remanent polarization and coercive field of ∼10 μC/cm2 and ∼100 kV/cm, respectively. The modification with CZ strongly influences the ferroelectric response of the films: the remanent polarization progressively decreases to around 2.5 μC/cm2. The absence of an anti-ferroelectric response, which has previously been confirmed in bulk NN-CZ ceramics, is attributed to the nanoscale microstructure and residual thermal stresses. All the studied films exhibit a piezoelectric response with the highest piezoelectric d33 coefficient of 35 pm/V at 300 kV/cm bias field for the NN modified films with 5 mol % CZ, making them candidates for lead-free piezoelectric thin-film applications.

Microstructural, mechanical and biological properties of hydroxyapatite - CaZrO3 biocomposites

The biofunctionalization of metal implants with bioactive ceramics arises as an appealing strategy for promoting their osseointegration, without impairing implants’ good mechanical resistance. In this work, biocomposites of hydroxyapatite - CaZrO3 were obtained by rate controlled sintering and their microstructure, mechanical properties, biological as well as the effect of stoichiometric calcium zirconate dopant on the decomposition of HA were analysed. The results obtained showed that the addition of CaZrO3 stabilizes the hydroxyapatite at least up to 1300 °C and inhibits the appearance of the α- and β-TCP phases. Moreover, the mechanical properties of the hydroxyapatite were improved with 10 wt% of CaZrO3, despite the increase of porosity. The in vitro assays demonstrated that the biocomposites were biocompatible, since they favoured human osteoblast cells adhesion and proliferation. All the data obtained emphasize the potential of these biocomposites for the aimed biomedical application.

Investigation of the interactions between titanium and calcium zirconium oxide (CaZrO3) ceramics modified with alumina

Powdered mixtures of CaO, ZrO2 and Al2O3 in various ratios were hot pressed. The mixtures reacted with titanium at 1600?C for 30min in argon to evaluate the suitable ceramic crucibles for casting of titanium. The interfacial microstructures between titanium and ceramic composites were characterized using X-ray diffractometer, scanning and transmission electron microscope. The produced hot pressed mixtures that were chemically bonded together, contained calcium aluminate (CaAl2O4), calcium dialuminate (CaAl4O7), cubic zirconia (c-ZrO2), and calcium zirconium oxide (CaZrO3). The increase in Al2O3 amount led to the decrease in CaZrO3 amount and an increase in the amount of CaAl2O4, CaAl4O7 and c-ZrO2 due to the reaction of CaO and Al2O3. At the end of the reaction of the ceramic mixtures with Ti at 1600?C for 30min, the acicular ?-Ti and ??-Ti were formed at the interface of Ti and the composites containing up to 10 vol.% Al2O3. In composites containing more than 20 vol.% Al2O3, Ti3Al5 was found at the interface instead of ?-Ti and ??-Ti. Furthermore, CaZrO3, ZrO2 and Ca3Al2O6 existed on the sides of the ceramic far away from the interface. CaZrO3/Al2O3 composites with less than 20 vol.% Al2O3 could be a potential crucible or mould material for productive applications in titanium casting.

Влияние спекающей добавки Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- на электропроводность протонного электролита CaZr-=SUB=-0.95-=/SUB=-Sc-=SUB=-0.05-=/SUB=-O-=SUB=-3-delta-=/SUB=-

The effect of the sintering additive Al2O3 on the electrical conductivity of a polycrystalline proton electrolyte based on calcium zirconate, CaZr0.95Sc0.05O3-δ (CZS) was studied. It is shown that the introduction of the sintering additive Al2O3 makes it possible to obtain dense ceramics by the combustion method at a relatively low temperature (1470 ° С). The introduction of 0.1–0.5 wt% Al2O3 leads to an increase in the grain size of ceramics from 100 nm to 1-2 μm. Al2O3 additives up to 0.3 wt% increase the electrolyte conductivity. It has been established that with the introduction of Al2O3, calcium aluminates are formed at the grain boundaries. The proton character of charge transfer was revealed both in the volume of grains and at the grain boundaries of the electrolyte in humid air.

Antiferroelectricity in new silver niobate lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01)

The critical need for clean energy has led to the development of lead-free electroceramics. However, lead-free antiferroelectrics seldom have been reported because of the difficulties in materials fabrication and their low electrical performance. In this work, we successfully synthesized lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01) using the solid state reaction method in flowing oxygen (O2) atmosphere. Calcium zirconate (CaZrO3) dopant effectively stabilized the antiferroelectricity of silver niobate (AgNbO3) by dramatically decreasing the tolerance factor t. Additionally, we identified an orthorhombic Pbcm structure similar to that of pure AgNbO3. With the introduction of CaZrO3, phase transition temperatures M1–M2, M2–M3 and the freezing temperature Tf decreased. The shift of the M1–M2 phase transition temperature and Tf was the result of the restriction of the M1 phase due to CaZrO3 substitution. The compositions of x < 0.001 displayed a double hysteresis loop with a raised critical field EF. However, when the doping concentration exceeded 0.002, the double hysteresis loop with a higher polarization could not be obtained until the breakdown strength of EB exceeded 200 kV/cm because of the tremendously enhanced free energy barrier between the virgin antiferroelectric state and the field-induced ferroelectric state. We also evaluated the polarization hysteresis loops are also evaluated at temperatures up to 100 °C for the compositions x = 0.00–0.005. With an elevated temperature, at which the free energy barrier was reduced, the double hysteresis loop was obtained at a lower electric field when compared with that at room temperature for the compositions x = 0.004 and 0.005. These results demonstrated that by adjusting the tolerance factor t and average electronegativity difference X, the antiferroelectricity could be predicted in AgNbO3-based lead-free solid solution systems, thus providing a new strategy for designing a new class of antiferroelectric materials.

Submicron barium calcium zirconium titanate ceramic for energy storage synthesised via the co-precipitation method

Monodisperse submicron barium calcium zirconium titanate [(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3] powders with homogeneous spherical microstructure were synthesised via the co-precipitation method. The (Ba + Ca)/(Zr + Ti) molar ratio and concentrations of reactants and NaOH used in the synthesis process were adjusted to obtain a single phase. Thermogravimetric analysis, X-ray diffraction, infrared and Raman spectroscopies and transmission electron microscopy were used to analyse the phase formation temperature, crystalline structure and reaction mechanism of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 formation at room temperature. The results suggested that the pure perovskite phase formation temperature was approximately 900–950 °C, which is considerably lower than that of BCZT powders synthesised using the conventional solid-state reaction (1250 °C). The dense phase-pure ceramics synthesised at 1320 °C displayed high recoverable energy storage performance (0.25 J/cm3) and breakthrough field (100 kV/cm). This work provides a new strategy to lower the synthesis temperature and improve the electrical properties of perovskites as well as revealing a possible formation mechanism.

Dielectric and piezoelectric properties of porous lead-free 0.5Ba(Ca0.8Zr0.2)O3-0.5(Ba0.7Ca 0.3)TiO3 ceramics

Porous barium calcium zirconate titanate 0.5Ba(Ca0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) lead-free ferroelectric ceramics were fabricated via a burnt polymer spheres (BURPS) technique by introducing corn starch as the pore-forming agent. The effect of porosity on the microstructure, dielectric, and piezoelectric properties of the porous materials were investigated. An increase in porosity volume fraction from 10% to 25% resulted in an increase in the hydrostatic charge coefficient (dh), which was 140 to 560% higher than that of the dense BCZT material. An increase in porosity fraction from 10% to 25% also lead to a decrease in relative permittivity that was 16.7% to 60.4% lower than the dense material. These two changes in properties provided a significant enhancement of the hydrostatic figure of merit (dh∙gh) for the porous ceramic; for example the dh∙gh of the 25 vol.% porous BCZT ceramic was 158 times more than the dense ceramic and demonstrates the potential of porous lead-free ferroelectrics for piezoelectric transducer devices. Reasons for the significant enhancement in piezoelectric performance of the porous ceramics are discussed.

Characterization of Phase Evolution, Microstructure and Electrical Properties of Sol-Gel Auto-Combustion Derived BCZT Ceramics.

This work aims to study the effect of sintering temperature on properties of barium calcium zirconate titanate (BCZT) ceramics. The BCZT is a Pb-free material that shows excellent piezoelectric properties. In this study, BCZT ceramics were prepared from BCZT powders synthesized from barium nitrate, calcium nitrate, zirconium (IV) oxynitrate hydrate, titanium (IV) butoxide and citric acid precursors by the sol-gel auto-combustion method. The BCZT powder was calcined at the temperature ranging from 700 to 1000 °C. Green bodies were sintered at various temperatures (1200-1450 °C). The X-ray diffraction patterns showed only non-crystalline phase of as-burnt powder. For the calcined powders, XRD patterns showed that the amount of crystalline, perovskite phase increased with increasing calcination temperature. The crystalline particles have a spherical shape and the size in the range of 25-35 nm. For the BCZT ceramics sintered at 1200-1300 °C, the density tended to increase with increasing sintering temperature. Very high bulk densities of 5.62-5.63 g/cm3 (which were higher than those of the ceramics synthesized by the wet-chemical method) were achieved at the sintering temperature of 1400-1450 °C. Ceramics produced at these temperatures possessed fully-developed microstructures, very good dielectric properties as well as high response of polarization and strain to applied electric field.

Tailoring interfacial interaction through glass fusion in glass/zinc-hydroxyapatite composite coatings on glass-infiltrated zirconia

In the current study, the biocompatibility and mechanical characteristics of glass-infiltrated zirconia were improved via a simple composite coating made of Zn-doped hydroxyapatite (ZnHA) ceramic and a silicate-based glass. During thermal treatment, significant reaction and crystallisation occurred and some of the ZnHA was transformed into β-tricalcium phosphate, calcium oxide phosphate, and calcium zirconium oxide. Moreover, the glass crystallised into a sodium calcium aluminium silicate phase. The mechanical properties were investigated and the results indicated that the amount of glass in the composite and in the glass-infiltrated zirconia layer strongly affected the flexural strength and adhesion of the coating layer. The composite coatings on the glass-infiltrated zirconia displayed better mechanical properties than the pure ZnHA coating due to the newly formed crystalline phases. Murine pre-osteoblastic (MC3T3-E1) cells adhered to and spread well on the composite coating surfaces. The cell viability results revealed that the glass/ZnHA composites demonstrated a superior bioactivity of osteoblast cells compared to uncoated zirconia. These results show that the glass/ZnHA composites on the glass-infiltrated zirconia structure are suitable for use as hard tissue implant coatings due to their morphological and mechanical stability and enhanced bioactivity to pre-osteoblastic cells.

Functional coatings for titanium casting molds using the replica technique

The quality of titanium cast parts depends not only on the corrosion reaction of the mold in contact with the titanium alloy melt, but also on the dimensional accuracy and the surface quality of the investment casting mold. Usually, the ceramic mold is produced by dip-coating. This contribution investigated the coating properties of green calcium zirconate (CaZrO3) coatings produced by the replica technique. Thus, the effect of different coating slurries as well as different coating technologies on important coating properties was analyzed. In all cases, centrifuging and spraying produced thinner coatings compared to dip-coating. Using an appropriate coating slip, particularly centrifuging revealed a cohesive homogeneous coating surface and is therefore a promising technology for the production of functional coatings for titanium casting molds.

Novel Calcium Zirconate Silicate Cement Biomineralize and Seal Root Canals.

This study evaluated the sealing ability of gutta-percha (GP) with a calcium silicate-based sealer and a novel calcium zirconate containing calcium silicate cement (ZC). The root canals of the extracted premolars were prepared, which were then randomly allocated to three experimental groups (12 root canals per group) for obturation by continuous wave of condensation with the GP and AH 26 sealer (CW); obturation using a single GP with a calcium silicate-based EndoSequence BC sealer (SC); or obturation with ZC. The roots were inserted into sterile Eppendorf tubes, which were inoculated coronally with Porphyromonas gingivalis. The amount of endotoxin leakage into the apical reservoirs were measured using the Limulus Amebocyte Lysate (LAL) assay over 21 days, with comparisons made using one-way ANOVA and Scheffe’s tests (α = 0.05). After 21 days, 75% of the canals that had been obturated by SC, 50% of those obturated by CW and 42% of those obturated by ZC showed endotoxin leakage. The amount of leakage was higher in the SC canals than in the CW (p = 0.031) or ZC (p = 0.03) canals, although there was no significant difference in the amount of leakage for CW and ZC (p > 0.05). X-ray diffraction revealed the presence of tricalcium silicate (Ca3SiO5) and calcium zirconate (CaZrO3) in the synthesized ZC. Scanning electron microscopy revealed mineralized precipitates on the dentin of canals obturated by ZC. The novel calcium zirconate silicate cement appears to promote biomineralization and seal root canals at least as effectively as the conventional sealer.