Role of dispersion conditions on grindability of yttria stabilized zirconia (YSZ) powders

A precursor for zirconia - 8 mole% yttria (YSZ-ZrO₂-8 m% Y₂O₃) powder was prepared by coprecipitation and the calcination temperature was fixed as 900°C from TG-DTA and XRD studies. The calcined powder could be dry ground only to a mean particle size (D₅₀) of 6 Μm containing substantial amount of coarse agglomerates in the size range 10–100 Μm. The dispersion conditions for its wet grinding were evaluated through zeta-potential and viscosity studies. The zeta-potential variation with pH of the aqueous suspensions of the powder exhibited maximum numerical values at 3 and 11 pH, exhibiting the ideal pHs for dispersion stability through electrostatic columbic repulsion mechanism. Slurries of dry ground powders with solid concentration in the range 15–30 vol.% exhibited pseudo-plastic flow characteristics, indicating presence of flocculates. With progress of grinding, the increase in viscosity of the slurries became less significant with decreasing solid concentration. Even though the particle size of the ground slurries decreased with decreasing solid content, there was little change in it for slurries with solid content < 20 vol.%. Grinding conditions for formation of sinter-active powders of YSZ with sub-micron size (D ₅₀ ∼ 0.7 Μm free of agglomerates of size > 5 Μm) were established. Compacts from this powder could be sintered at 1400°C to translucent bodies with 99% theoretical density.     

Preparation of La2-x Sr x NiO4 (x = 0-1.3) conducting oxides via a citrate route

La_2-x Sr_xNiO₄ (x = 0-1.3) oxide materials were prepared by the citrate and ceramic routes. The citrate precursors and final products were characterized by thermal analysis (DTA + TG), x-ray diffraction, scanning electron microscopy, IR spectroscopy, and specific surface and conductivity measurements. The use of citrate mixtures leads to the formation of amorphous precursors to La₂O₃, NiO, and La_2-xSr_xNiO₄ (x <-0.4); reduces the temperature required for obtaining solid solutions by 150–200‡C as compared to the ceramic route; and enables the preparation of fine powders (≤5 Μm) and dense ceramics. Deceased.     

Advanced ceramics: Combustion synthesis and properties

Fine-particle ceramic powders such as chromites, manganites, ferrites, cobaltites, aluminas (α-Al₂O₃, Cr³⁺/Al₂O₃, zirconia-toughened alumina, mullite and cordierite), ceria, titania, zirconia (t, m, c and PSZ), dielectric oxides (MTiO₃, PZT and PLZT) as well as highT _c cuprates have been prepared by the combustion of redox compounds or mixtures. The combustion-derived oxide materials are of submicron size with a large surface area and are sinteractive.     

A study of two refractories as mould materials for investment casting TiAl based alloys

Interfacial reactions between Ti-46Al (at.%) casting and ceramic shell mould made of ZrO₂ and Al₂O₃ were studied using a range of techniques. On the surface of the TiAl casting, a reaction layer as thick as 230 μm was found in the case of the zirconia mould, whereas there was no visible reaction layer for the alumina mould. Electron probe microanalysis indicated that elements of the two kinds of shell moulds diffused into the alloy melt during casting but to different extents. Metallographic analysis, microhardness measurements and composition analysis showed that alumina was stable and suitable for use as shell moulds when casting TiAl based alloys.     

Science of zirconia-related engineering ceramics

In this paper, we comprehensively review the physical principles behind the improvement of mechanical properties of zirconia (ZrO₂) related ceramics. First, the transformation behaviour of different phases in zirconia is discussed. We next present an overview of two zirconia-related commercially important systems e.g. ZrO₂-MgO and ZrO₂-Y₂O₃. The commercial engineering ceramic materials, generated from these systems, are known as partially stabilized zirconia and tetragonal zirconia polycrystal respectively. The third important material is called zirconia toughened alumina. The evolution, characterization and importance of the microstructure in relation to the basic systems are also presented. Attention is then focussed on to three toughening mechanisms e.g. phase transformation toughening, microcrack toughening and crack deflection toughening. We carefully assess the roles they play in improving toughness. We discussR-curve behaviour arising out of these toughening mechanisms and the implications ofR-curve behaviour in engineering applications. Finally, the subcritical crack growth and tribological behaviour of these materials are discussed.     

Optical and dielectric properties of lanthanide titanium tantalate and niobate ceramic composites

The xPrTiTaO₆ (1 − x) YTiNbO₆ dielectric ceramic composites are fabricated through the solid state ceramic route. The compositions are calcined in the temperature range 1,200–1,260 °C and sintered in the range 1,350–1,410 °C. Structural analysis of the materials is done using X-ray Diffraction analysis. The composites contain both aeschynite and euxenite orthorhombic phases. The surface morphology of the sintered pellets is examined by scanning electron microscopy. The dielectric constant, conductance and loss factor are measured in the radio frequency region. The UV–visible spectra are recorded and the band gap is calculated. The photoluminescence spectra of the compositions are recorded and the transitions causing emission are identified. The elemental composition of the composites is confirmed using energy dispersive spectroscopy. The materials are suitable for substrate and optoelectronic applications.     

Preparation of Y-TZP ceramic fibers by electrolysis-sol-gel method

Polycrystalline yttria stabilized tetragonal Zirconia (T-ZrO₂) fibers were obtained by pyrolysis of gel fibers using zirconium oxychloride octahydrate as raw material. The spinnable zirconia sol was prepared by electrolyzing the zirconium oxychloride octahydrate solution in the presence of acetic acid and sugar (sucrose, glucose or fructose), in which the molar ratio of CH₃COOH/ZrOCl₂ · 8H₂O and sugar/ZrOCl₂ · 8H₂O was in the range of 1.0–4.0 and 0.2–0.4, respectively. The relation of spinnability to the shape of colloidal particle was discussed. The as-prepared zirconia fibers sintered at different temperatures show smooth and crack-free surface with the diameter of 5–10 μm. Slow heating rate below 600 °C and then sintering at 1,400 °C for 30 min were necessary to obtain the dense tetragonal zirconia ceramic fibers, the particles composed the fibers had the size of ∼150 nm.     

Production of opaque frits with low ZrO<Subscript>2</Subscript> and ZnO contents and their industrial uses for fast single-fired wall tile glazes

The amounts of zirconium and zinc oxides, which raise the production costs of ceramic glazes, were decreased in fast single-fired wall tile frit compositions and an industrial frit production was conducted. Opacity of the fired frit-based glazes was accomplished by compositional modifications of frits with no other nucleating agent. It was determined that the ratios of Al₂O₃/ΣR₂O, Al₂O₃/ΣRO, and Al₂O₃/B₂O₃ have significant effects on decreasing ZrO₂ and ZnO levels in the frit composition. A reduction of 25% in both zirconia and zinc oxide contents of frit batches, with respect to the reference frit (R) containing 6–10% ZrO₂ and 6–10% ZnO for a glossy white opaque wall tile glaze, was achieved in the ZD glaze consisting of 4.5–7.5% zirconia and 4.5–7.5% ZnO in its frit composition. It was concluded that zircon was the main crystalline phase of the glaze contributing the opacity. The ZD frit-based glaze has a thermal expansion coefficient value of 61.13 ± 0.32 × 10⁻⁷ °C⁻¹ at 400 °C which well matches to that of the wall tile body. TS EN ISO 10545 standard tests were also applied to the final ZD glaze. It is confirmed that the production cost of a fast single-fired wall tile glaze can be decreased by 15–20% with the successful new frit developed.     

Bone-like apatite coating on Mg-PSZ/Al2O3 composites using bioactive systems

A biomimetic method was used to promote bioactivity on zirconia/alumina composites. The composites were composed of 80 vol% Mg-PSZ and 20 vol% Al₂O₃. Samples of these bioinert materials were immersed in simulated body fluid (SBF) for 7 days on either a bed of wollastonite ceramics or bioactive glass. After those 7 days, the samples were immersed in a more concentrated solution (1.4 SBF) for 14 days. Experiments were also performed without using a bioactive system during the first stage of immersion. A bone-like apatite layer was formed on the surface of all the materials tested, using wollastonite the bioactive layer was thicker and its morphology was close to that observed on the existing bioactive systems. A thinner apatite layer consisting of small agglomerates was obtained using bioactive glass. The thickness of the ceramic layers was within the range of 15 to 30 μm.     

The Effect of Sintering Temperature Variation on the Superconducting Properties of ErBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Superconductor Prepared via Coprecipitation Method

The effect of heat treatment on the superconducting properties of ErBa₂Cu₃O_7−δ (ErBCO) ceramic materials has been studied. The nano-metal oxalate precursor was prepared using coprecipitation (COP) method. The prepared materials were subjected to calcination process at 900 °C for 12 h and then sintered under oxygen environment for 15 h at 920 °C, 930 °C, 940 °C, and 950 °C, respectively. All samples showed a metallic behavior and single-step transition in the R–T curves. The best zero critical current, T _C(R=0)=91.4 K, was for the sample sintered at 920 °C. XRD data showed single phase of an orthorhombic structure. As the sintering temperature increases, the formation of nonsuperconducting phases (impurities) was observed when the samples sintered above 920 °C. The formation of nano-oxalate powders via COP method is a very efficient procedure to produce high-quality superconductors with less processing temperature required.     

Characterization of the interface between (U,M)O2±x and yttria-zirconia

Solid-state electrochemical cells have been prepared by co-sintering pre-reacted electrode and electrolyte materials together. The electrodes investigated were the non-stoichiometric oxides of the general formula (U, M)O_2±x (M = Sc, Y) and the electrolyte used was yttria-stabilized zirconia. The specimens were characterized by X-ray diffraction, Rutherford back-scattering spectrometry, scanning electron microscopy with energy-dispersive analysis by X-rays, and optical microscopy. For M = Sc, an intermediate phase is formed at the interface and is responsible for the strong bonding of the electrode layer to the electrolyte. The thickness of the intermediate layer was about 2 to 3Μm. Considerable loss of uranium, which in some cases led to destabilization of the fluorite phase, was observed from the surface of the uraniascandia electrode layers. The intermediate phase is thought to be formed as a result of reaction between the electrolyte and volatile uranium-containing species produced by decomposition of the urania-scandia electrode material. For M = Y, no evidence for the formation of such a phase was found and the adhesion of the electrode to electrolyte was poor.     

Dynamic fatigue and strength characterization of three ceramic materials

Fracture strength and fatigue parameters of three ceramic materials submitted to dynamic fatigue were evaluated. A machinable leucite-reinforced dental ceramic, aluminum oxide, and yttria-stabilized zirconia (YSZ) were tested. The inert strength of the materials was determined in air (25 °C) at stressing rates of 70, 250, 400 MPa/s for Porcelain, Alumina and YSZ respectively. The data was analyzed using a two-parameter Weibull distribution. The Weibull modulus (m) and the characteristic of fracture (σ ₀) parameters were determined for each material. Specimens were also tested in 3-point bending at different stressing rates in distilled/deionized water at 37 °C (dynamic fatigue) in order to calculate the fatigue parameters n and ln B. The strength for each material was characterized using Strength–Probability–Time (SPT) diagrams for 1 day, 1 year and 10 years. YSZ showed a high-fracture strength σ ₀ (1,459 MPa) at a failure probability of 63.2% and high resistance to subcritical crack growth. YSZ and alumina showed better resistance to slow crack growth than porcelain, indicating less susceptibility to strength degradation by stress corrosion. Lifetime predictions after 10 years indicate a reduction of 50%, 36% and 29% in strength for porcelain, alumina and YSZ respectively. YSZ seems to be a very promising material for long-term dental and biomedical applications.     

Femtosecond laser directly writing microholes in Bi(Nb<Subscript>0.998</Subscript>V<Subscript>0.002</Subscript>)O<Subscript>4</Subscript> ceramic and multi-photon induced large scale nanometer wires array

Femtosecond laser pulse directly writing microholes by the matrix microholes ablation technique (MMAT) in a high permittivity microwave ceramic Bi(Nb_0.998V_0.002)O₄ were systematically investigated. The feasible micro-fabricating parameters-output power intensity, writing intervals ΔR and step depth ΔZ, and writing velocity-were discussed and optimized. A large scale crystalline wires array at several hundred nanometers induced by multi-photon absorption was observed and analyzed. The tropism of nanometer array was similar to the epitaxy technique but perpendicular to the writing path. The experiment demonstrated the flexibility and efficiency to micro-fabricated superfine and complex configurations in ceramic materials by femtosecond laser.     

Effect of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> additions on the power loss of NiZn ferrites

Nickel–zinc ferrite system, Ni_0.65Zn_0.35Fe₂O₄ + x Nb₂O₅ where x varies from 0.0 wt% to 1.5 wt% in steps of 0.3 wt%, has been prepared by conventional ceramic technique. The samples were sintered at 1250 °C for 4 h in air atmosphere followed by natural cooling. The power loss and microstructures of these materials are examined. Microstructures reveal that niobium oxide additions promoted grain growth with an increase in grain size from 4 μm to 13.2 μm with the increase in niobium concentration. The measured power loss at frequencies from 100 kHz to 10 MHz under different exciting flux densities from 5 mT to 30 mT was found to be low up to 3 MHz, thus making the materials suitable for power applications up to this frequency. In the total power loss, hysteresis loss is predominant below 500 kHz and eddy current loss component is much higher at higher frequencies.     

Inflammatory reaction in rats muscle after implantation of biphasic calcium phosphate micro particles

Several studies have shown that macro micro porous bioceramics ectopically implanted promote bone tissue formation. This study aims at investigating the inflammatory response towards biphasic calcium phosphate (BCP) ceramic micro particles. BCP composed of hydroxyapatite (HA) and beta-tricalcium phosphate, HA/β -TCP ratio of 50/50, were prepared by sintering at 1200°C for 5 h. After crushing, 3 fractions of BCP micro particles < 20, 40–80 and 80–200 μ m were sieved. The micro particles were carefully characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser scattering. The inflammatory reactions induced by BCP micro particles implanted in quadriceps muscles of rats for 7, 14 and 21 days were studied by histology (n = 8/group). A fibrous tissue encapsulation of the BCP micro particles implanted in muscle tissue was observed and fibrosis was similar for the 3 groups of micro particles. The comparison of the cellular response indicated that the total number of cells was significantly higher for BCP < 20 μ m than for 40–80 and 80–200 μ m (p < 0.0001). The number of macrophages was relatively higher for the smallest than for the intermediate and largest fractions (p < 0.0001). The relative percentage of giant cells was higher for the intermediate and largest size of particles than for the smallest. The number of lymphocytes was comparable for the 3 fractions and after the 3 delays. Therefore, the BCP micro particles < 20 μ m initiated an inflammatory response which might play an important role in osteogenesis.     

Improvement of the rheological properties of the zirconia/polypropylene system for ceramic injection moulding using coupling agents

In order to improve the rheological properties of the zirconia/polypropylene system for ceramic injection moulding, the zirconia powder was surface-treated with aluminate (A), silane (S) and titanate (T) coupling agents dissolved in toluene. 2% additions of these coupling agents decreased the torque,T _h, for compounding the zirconia filled-polypropylene after 1 h at 180°C. The surface treatment also reduced the viscosity, η_a, of the compound, the effectiveness of the coupling agents on viscosity reduction being T > S > A. On the contrary, the apparent activation energy,E _a, for flow of the compound increased when fluidity was promoted by surface treatment. Rheological measurements in systems with different titanate concentrations showed that the three parameters,T _h, η_a, andE _a, remained nearly constant for coupling agent additions of over 2%. This critical concentration of 2% showed good correspondence to the optimum concentration evaluated from thermogravimetric analysis of the powders.     

BaTiO3 (BTO)–CaCu3Ti4O12 (CCTO) substrates for microwave devices and antennas

The solid state procedure was used to produce bulk ceramics of BTO (BaTiO₃), CCTO (CaCu₃Ti₄O₁₂) and BTO_0.5–CCTO_0.5 that were studied in the medium-frequency (MF) range (100 Hz–1 MHz) and in the microwave range of frequencies. The presence of BTO is decreasing the dielectric constant (ε_r) of the BTO–CCTO composite. The CCTO and BTO samples present a strong tendency to the increase of the loss with frequency. The BTO substrates are presenting higher values of the ε_r in the range of 1–4 GHz (around 140). For pure CCTO the dielectric constant is around 37.6. Similar behaviour observed at the MF range, that the higher dielectric constant is also associated to the higher loss is also present in the microwave region. The study of a planar microstrip antenna, that uses the BTO _X –CCTO_(1−X) ceramic as a high ε_r substrate was done. Therefore, these measurements confirm the potential use of such materials for small high dielectric planar antennas (HDA). These materials are also very promising for capacitor applications and certainly for microelectronics, microwave devices (cell mobile phones for example), where the miniaturization of the devices is crucial.     

Dielectric and piezoelectric characterization of PSZT–BT ceramics for capacitor applications

The ceramic compositions (1 − x)Pb_0.9875Sr_0.0125(Zr_0.53Ti_0.47)O₃ –xBaTiO₃ where x = 0.2, 0.4, 0.6 and 0.8, fabricated through solid state reaction method were investigated for phase formation, microstructure, density, dielectric and piezoelectric properties. The X-ray diffraction patterns indicated that introduction of BaTiO₃ in isovalent donor Sr modified PZT lattice, diminished the tetragonality. All the specimens were homogenous in nature due to the coarse grains of BaTiO₃, which had undergone inter-granular growth and were homogeneously distributed within the PSZT–BT lattice. Introduction of BaTiO₃ in PSZT perovskite lattice resulted in enhanced grain growth till x = 0.6 (2.03 μm). Dielectric properties (ε_RT, Tanδ and T _c) were influenced by both BaTiO₃ and Sr. The maximum ε_RT = 1588 and ε_Tc = 10478 were found in 0.2PSZT–0.8BT ceramic system. The optimum dielectric permittivity at room temperature with a low Curie transition temperature was found in 0.2PSZT–0.8BT composition. Piezoelectric properties are very sensitive to isovalent substitutions, where isovalent donor Sr modification and BT concentrations in PZT, affected the piezoelectric properties (k _p and d ₃₃) in the ceramic system. Thus, the series PSZT–BT compositions could be ideal candidates for capacitors and suitable sensor applications.     

Composites of amorphous calcium phosphate and poly(hydroxybutyrate) and poly(hydroxybutyrate-co-hydroxyvalerate) for bone substitution: assessment of the biocompatibility

Composites of amorphous carbonated apatite and poly-(R)-3-hydroxybutyrate (PHB) and poly-(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate (PHBHV), respectively, were studied by pH monitoring upon immersion in water and by long-term osteoblast culture. For comparison, α-tricalcium phosphate (α-TCP), one glass ceramic (GB 9N), and one bioglass (Mg 5) were subjected to the same experiments. Excellent cell proliferation was found on the composite of calcium phosphate with PHB and on the reference materials (α-TCP, glass ceramic, bioglass). In contrast, cell death was observed repeatedly on the composite with PHBHV. A composite of amorphous calcium phosphate and PHB appears to be well suited as slowly biodegradable bone substitution material.No benefit of any kind will be received either directly or indirectly by the authors.W. Linhart and W. Lehmann contribute equally and therefore share first authorship     

Effect of combined doping (y<Superscript>3 +</Superscript> + fe<Superscript>3 +</Superscript>) on structural features of nanodispersed zirconium oxide

Fully stabilized zirconium dioxide is widely used. One of the basic requirements to this material is the thermal stability of the structure. The most effective stabilizer for zirconium oxide is yttrium oxide. However, the structure of Y-ZrO₂ degraded at low temperature. Partial substitution of Fe^{3 +} for Y³⁺ decreases both the crystallization and sintering temperature of zirconia ceramic. The aim of present work is the investigation of structural peculiarities of zirconium oxide stabilized by combined dopant depending on chemical composition, synthesis conditions and heat treatment. The polymorphic composition of a ZrO₂-based materials has been determined in series of samples that correspond to the formula [1−(x+y)]ZrO₂⋅xY₂O₃⋅yFe₂O₃ in the temperature range 620–1570 K. It has been found that at the same molar ratio ZrO₂ : doping oxides, the degree of ZrO₂ stabilization increases, and the low-temperature degradation process is retarded by the partial substitution of Fe^{3 +} for Y³⁺. Nonequivalent sites of Fe^{3 +} ions have been identified: two with octahedral coordination for CPH and three with octa-, penta- and tetrahedral coordination for SPH. The possibility of cluster distribution of Fe³⁺ ions and the dependence of the number of vacancies on synthesis conditions have been shown.