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The characterization of materials surface is essential, as the initial in vivo response is highly dependent on surface properties. Surface topography is a key aspect that influences the response of cells to products resulting from interaction with the surface of a titanium alloy, including parameters such as adhesion, spread, migration, proliferation, and differentiation of cells. Various surface modifications are used to improve the interface properties between MC3T3 and NHDF cells and the Ti–13Nb–13Zr-based surface. Among the techniques discussed in this paper, scanning electron microscopy, laser confocal scanning microscopy, and computed tomography are adequate to investigate materials topography at different scale levels. Chemical characterization of the outer layers of Ti–13Nb–13Zr samples was performed with X-ray photoelectron spectrometry. Studies have shown that the surfaces resulting from the treatment enabling the formation of titanium oxide and zirconium oxide show the lowest cytotoxicity. Implants made from the new generation of titanium alloy, not containing toxic elements, with the use of surface modification could be an essential innovation in implantology. [ABSTRACT FROM AUTHOR]

In this paper, a thorough study is dedicated to the manipulating of nanostructured zirconia thin films prepared by a sol-gel process with the focus on the wetting properties. It is observed that by engineering the amount of cetyltrimethylammonium bromide [[N(CH3)3] Br] (CTAB) and polyethylene glycol (PEG) in zirconium chloride precursor solution, the novel agar-like morphology with random orientation can be grown. Different morphologies are observed by changing the amount of PEG in the solution. All the prepared samples in this method show tetragonal phase after annealing at 500 °C for 1 h. The crystallite sizes have a direct correlation with the ratio of lattice parameters. The optical band gap is estimated by Kubelka-Munk method. Modified ZrO2 thin films at an optimum ratio of PEG to CTAB annealed at 500 °C and present water contact angle lower than 3° (without UV illumination) which indicates their superhydrophilic properties. The analytical results of SEM images of samples annealed at 500 °C are also reported. Spreading and wicking of liquid through the nanochannels which are formed in the vacant spaces between nanorods lead to superior wetting property. Annealing temperature also strongly affects the wettability of agar-like zirconia thin films. Agar-like ZrO2 thin films are obtained with superhydrophilic behavior by annealing at 500 °C. Similar agar-like morphology is also observed with hydrophobic character by annealing at 200 °C. The introduced preparation method in this paper provides an easy route to fabricate superhydrophilic agar-like ZrO2 thin films without further processing. [ABSTRACT FROM AUTHOR]

In this paper, we report an ultralow thermal conductivity and a high-temperature phase stability of the (NdCe)ZrO system over the temperature range from room temperature to 1600 °C and over a wide composition range (0.2 ≤ x ≤ 0.8), and the (NdCe)ZrO system is therefore considered a strong candidate material for the fabrication of next-generation high-temperature thermal barrier coatings. The observed thermal conductivities (0.65-1.0 W/mK) are about 60-40% lower than those of undoped NdZrO over the same temperature range (100-700 °C) and indicate a glass-like behavior. For comparison, the variation in the thermal conductivity with the temperature of the (GdCe)ZrO system with similar point defects was also measured, and the observed behavior was almost the same as that of undoped GdZrO and was mostly determined by phonon-phonon scattering ( λ ∝ 1/ T). The effect of point defect scattering and strong phonon scattering sources (rattlers) on the thermal conductivity is also discussed in this paper. The results of this study suggest that the ultralow thermal conductivity of (NdCe)ZrO can be attributed to the presence of rattlers because of the large difference between the ionic radii of the Nd and Ce ions. [ABSTRACT FROM AUTHOR]

In the present paper, triethylamine-assisted (CZS) and reference (CZ)-doped CeO-ZrO mixed oxides were prepared by co-precipitation. The prepared samples were characterized by N adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM and HRTEM), powder X-ray diffraction (XRD), Raman spectroscopy, and H temperature-programmed reduction (TPR). The results showed an improved thermal stability of CZS in textural properties with surface area of 32 and 12 m g after aging at 1000 and 1100 °C for 10 h, respectively. Investigation of the sintering behavior disclosed that the sintering of crystallites during high-temperature thermal aging might be related to the packing mode of the grains, since the looser structure of CZS compared to that of CZ hindered the grain growth at high-temperature calcination. The results of XRD and Raman revealed identical structural properties for both materials which suggested a cubic phase in fresh samples and a mixture of cubic and tetragonal phases after thermal aging at severe high temperatures (1000 and 1100 °C). The TPR results showed reduction peaks with rather low-temperatures, which was 414 °C after thermal aging at 1000 °C and 367, 577 °C at 1100 °C. This suggested a high thermal stability of CZS in reduction property. Consequently, the high thermal stability of the mixed oxide in both textural and reduction properties would contribute to the stability of the catalytic activity of the Pd-only three-way catalyst after high-temperature thermal aging, that is, Pd/CZS-a exhibits conversion temperatures of the pollutants (T and T) 10-20 °C lower than Pd/CZ-a. [ABSTRACT FROM AUTHOR]

Pyroelectric materials are widely investigated for thermal devices. As an efficient standard for evaluation, the pyroelectric figures of merit (FoM) for specific thermal-related applications can clearly represent the performance of voltage responsivity and detectivity. In this paper, six congruent lithium niobate (CLN) single crystals with different ZrO doping concentrations were grown by the top-seeded melt growth method including pure CLN. In order to analyze the dielectric and pyroelectric performances, the concentrations, and occupations were extensively studied by ultraviolet and infrared absorption spectra. Our results present an efficient way to improve the FoM of CLN by using zirconia doping. The working temperature of Zr:CLN thermal device can be widened obviously. [ABSTRACT FROM AUTHOR]

This paper presents the micro-shot peening of zirconia (ZrO)-advanced ceramics applicable for bio-medical, dental, automotive and aerospace sectors. A ZrO-advanced ceramic was micro-shot blasted with selected parameters as a first-step investigation focused on the topography, microstructure, surface hardness and the surface fracture toughness ( K) characteristics. A new technique of micro-blasting was conducted using a portable shot blaster. A white-light interferometer, scanning electron microscopy and Vickers indentation technique were employed for the analysis. This was followed by determining the K using an empirical equation. Surface roughness was improved by 34 % after micro-shot blasting treatment. No surface cracking was present which generally exists due to the brittle nature of the ceramic. The hardness, however, reduced by 5.6 % with a reduction in the Vickers crack length of 9 %. This improved the K by 3 % when comparing the micro-shot peened surface to the original, as-received surface. It is difficult to conclude if the ZrO-advanced ceramic has undergone plastic deformation and the movement of dislocations increased to strengthen the ZrO ceramic at this stage. However, based on the results, it can be predicted that a level of surface compression was induced beneath the micro-shot peened layer as indicated from the result of the surface topography and integrity. This would justify the hardness modification and the enhancement in K. [ABSTRACT FROM AUTHOR]

A series of binary CeO-ZrO compounds with the composition of Ce/Zr = 1:1 (molar ratio) were reduced by graphite powders at various reducing temperatures (1173 ≤ T ≤ 1573 K) for 24 h in a self-made reducing device. The reduced products obtained at various T were characterized by X-ray diffraction and Vibration Spectrum. In the case of 1223 ≤ T ≤ 1573 K, the reduced phase is identified as the k-CeZrO phase with the space group of P23, in which Ce and Zr ions are in an ordered arrangement similar to that of the pyrochlore CeZrO and the ordering level between Ce and Zr ions in the pyrochlore-type k-CeZrO phase decreased with the decreasing T. The phase is stabilized without decomposition down to room temperature; the reason is attributed to the reducing atmosphere retention caused by graphite until the end of experiment. In the case of T < 1223 K, a phase transition from k-CeZrO phase to t′-CeZrO phase was observed. The formation of t′ phase is due to the fact that the reducing atmosphere is too weak to severe enough to yield Zr/Ce cation ordered configurations. The graphite reducing mechanism is discussed in the paper. [ABSTRACT FROM AUTHOR]

High temperature gas turbine sealing is an important issue for increasing the thermal efficiency of gas turbine. In this purpose, layered structured LaPO has been selected as the soft phase to add into the commercialized thermal barrier coating material 7 wt% yttria stabilized zirconia (7YSZ). The consequent thermal conductivities and mechanical properties versus the content of LaPO have been researched systemically in this paper. Phase composition and microstructure of the high-temperature sintered LaPO/7YSZ composites were characterized. The thermal conductivity decreases significantly due to the second phase effects and the interface thermal resistance was also strongly involved according to the composite model. The hardness decreased by composed LaPO phase so that to reduce attrition of the vanes at high temperature. The slight increase of fracture toughness and bending strength in the results were also favored in operation. The experimental results demonstrate that the LaPO/7YSZ composite will be an excellent candidate abradable sealing material for high temperature gas turbine. [ABSTRACT FROM AUTHOR]

A reverse-flow reactor enables the pyrolysis of hydrocarbons at temperatures up to 2000 °C to high value petrochemical products. Materials in the reactor hot zone, exposed to such extreme temperatures, are also subject to rapid oxidative cycling over a period of several seconds between a regeneration (heat addition) step that is mildly oxidizing and a pyrolysis (cracking) step that is strongly carburizing. This paper addresses the performance of a class of zirconate ceramics such as BaZrO, SrZrO, and LaZrO that have been tested in a laboratory scale reverse-flow reactor and compares the results with thermodynamic predictions. It is observed that zirconate ceramics degrade by decomposition to zirconia and the second oxide, vaporization of the second oxide, and ceramic dusting corrosion of zirconia that involves carbide-oxide inter-conversion and carbon precipitation. The pyrolysis reaction promotes carbon deposition and carburization of zirconia leading to the formation of a non-protective porous carbide layer. The regeneration reaction converts the carbide layer partially back to oxide while also oxidizing away some of the deposited carbon. Repeated cycles of pyrolysis and regeneration steps eventually result in the breakup of the bulk zirconate ceramic structure into powder or dust. [ABSTRACT FROM AUTHOR]

This paper describes the preparation of crack-free stainless steel 316L/alumina functionally graded material (SUS316L/AlO FGM) by spark plasma sintering (SPS). The sintering of individual powders and their composites was first studied to find an optimum SPS condition to get both materials and their mixtures highly dense. Sintering of cylindrical-shaped FGM pellets (ϕ20 mm) with various numbers of interlayers of 1, 2, 3, 4, and 9 was then carried out where the kind of and location of related cracking were carefully examined. The FGMs faced the problem of cracking mainly in the radial direction near the AlO-rich layers regardless of the number of layers or the gradient compositional profile. An yttrium-stabilized zirconia (3Y-ZrO) was added thereafter to the gradient on the expense of AlO content (up to 50 vol.%) and no radial cracking was found. Defects-free FGM pellets were successfully produced by interposing 19 interlayers between the SUS316L and AlO ends. The Vickers hardness profile was determined throughout the cross-section of sintered FGM and it was varying steadily through the gradient from 2.0 GPa at the SUS316L surface to 14.4 GPa at the AlO surface. [ABSTRACT FROM AUTHOR]

In this paper, the densification of a ceramic powder matrix that contained large macropores of the size much larger than the average grain size of the matrix was studied. The grain-boundary diffusion controlled sintering models of ceramic matrix contained large macropores were first established. A sintering potential associated with the macropores was also verified and introduced into the models. The experimental data were collected for the sintering of porous 8 mol% yttria-stabilized zirconia system with 20 vol% large pores. The predictions of the model were found in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The processing of yttria-stabilised zirconia (Y-ZrO2)-based ceramic nanocomposites by means of pulsed electric current sintering (PECS) is described. A nanometer-sized electrically conductive secondary TiCN phase was added to the insulating zirconia matrix in order to make the composite electrically conductive. The paper focuses on the importance of processing conditions and highlights the benefits of the PECS method as compared to more traditional hot pressing. The mechanical and microstructural properties of the ZrO2–TiCN composites have been determined, and the benefits of using an electrical current to densify these composites were explained in terms of the evolution of the electrical properties of the densifying powder compact. [ABSTRACT FROM AUTHOR]

This paper summarises the work that has been done in the framework of the French programme PROMETHEREF. This programme was concerned with the thermomechanical properties at high temperature of two industrial refractories: fused-cast materials for glass melting and alumina castables for steel production. At high temperature, both materials exhibit creep, that has been characterised by tension, compression and bending tests. The microstructural mechanisms of deformation have been investigated and allowed the macroscopic viscoplasticity to be understood. Both types of materials exhibit damage processes that have also been characterised mechanically and microstructurally. The nature and the adhesion of the aggregates have been shown to have a great influence on the mechanical behaviour of the castables, as well as the continuous zirconia skeleton observed in high-zirconia fused-cast refractories by X-rays tomography. [ABSTRACT FROM AUTHOR]

Yttria stabilized zirconia (7YSZ) solution precursor has been successfully used in the deposition of high durability thermal barrier coatings. In this paper, the thermal and crystallization behaviors of 7YSZ precursor were investigated by TG-DTA, FTIR and XRD. The results show that the precursor decomposition and crystallization temperatures greatly depend on heating rate e. g. 74°C for the crystallization temperature when tripping the heating rate. With a 10 °C/min heating rate, the weight loss due to precursor pyrolysis occurs predominantly at temperatures below 500 °C. A small weight loss due to the oxidation of residual carbon is detected from 800 °C to 950 °C. The complete crystallization of the tetragonal phase was determined to be around 500 °C by DTA and XRD analyses with a 10 °C/min heating rate. The crystallization kinetics and the activation energy of amorphous 7YSZ precursor were investigated by variable heating rate DTA. The calculated activation energy is 66.2 kJ/mol. The Avrami parameter value was determined to be 2.68, which indicates that crystallization nucleation and growth is diffusion-controlled. The crystalline phase of 7YSZ coatings deposited by the Solution Precursor Plasma Spray process was identified by XRD and Raman spectrum. The average YSZ grain size in the SPPS coating was determined to be 61 nm. [ABSTRACT FROM AUTHOR]

The polymer composites filled with nanoparticles have good friction and wear properties and widely used in many fields. The performances of nanocomposites are influenced extensively by the nanoparticles morphology, size, volume fraction and dispersion. Nanometer ZrO2 particles have good properties, lower prices and shows good foreground in resist-materials of polymer composites. In this paper, the nanometer ZrO2 particles are treated by silane coupling agent of N-(2-aminoethyl)-γ-aminopropylmethyl dimethoxy silane. The effect of nanometer ZrO2 content and silane coupling agent on the friction and wear properties of BMI copmposites filled with nanometer ZrO2 are investigated. The composites filled with untreated ZrO2 and treated ZrO2 are prepared by the same way of mechanical high shear dispersion process and casting method. The sliding wear performance of the nanocomposites is studied on an M-200 friction and wear tester. The experimental results indicate that the frictional coefficient and the wear rate of the composites can be reduced by filled with nanometer ZrO2. The composites containing treated nanometer ZrO2 have the better tribological performance than that containing untreated nanometer ZrO2. The results are explained from the SEM morphologies of the worn surface of matrix resin and the composites containing nanometer ZrO2 and the TEM photographs of the nanometer ZrO2 dispersion in the matrix. [ABSTRACT FROM AUTHOR]

This paper presents an exploratory investigation of a production route for thermal barrier coatings (TBCs) from a stable zirconia nanopowder suspension by means of electrophoretic deposition (EPD) on a low carbon steel substrate, followed by a consolidation by hybrid microwave sintering. Since the thickness of the green deposit is restricted to a critical thickness, which depends on the curvature of the substrate, a method of repeated deposition and sintering was applied in order to produce thick coatings. The low electric conductivity of the sintered ceramic coating does not inhibit the deposition of additional layers. This method enabled the production of porous coatings with a sintered thickness of 150–300 μm. A finite element model was applied to evaluate the thermal conductivity of the coatings. Values of the order of 0.8 W/mK were obtained which is comparable to that of coatings deposited by other techniques. Hence, the multiple deposited coatings with their thick and porous microstructure have a high potential for thermal barrier coating (TBC) applications. [ABSTRACT FROM AUTHOR]

Tetragonally stabilized, polycrystalline zirconia (TZP) is an interesting material for dental applications due to the tooth-like appearance, biocompatibility and, compared with other advanced ceramics, high bending and tensile strength. At present fully sintered TZP dental crowns or bridges can only be made via CAD-CAM supported mechanical milling processes, but the high costs and long processing times are disadvantageous. In contrast to this process a less expensive preparation is possible via near net-shape electrophoretic shaping from aqueous suspensions and consecutive sintering. As the deposition rate for electrophoretic deposition (EPD) is independent of particle size, bimodal starting powders can be used for optimizing the green density of the compact. Thus the shrinkage during sintering can be minimized. Furthermore, the pore structure can be controlled. In this paper the preparation of dental crowns via EPD is shown. With a combination of commercially available micron-sized Ce-stabilized zirconia (Ce-ZrO2) powder, nanosized zirconia powder (nano-ZrO2), and a submicron alumina powder (Al2O3) compacts with relative green densities up to 78% could be achieved. These compacts could be completely sintered at 1,600 °C with a linear shrinkage of less than 9%. [ABSTRACT FROM AUTHOR]

The emission spectrum of a-alumina in the spectral range between 13900 and 14250 cm-1 is characterized by several bands which are much weaker than the two intense and sharp R1 and R2 bands appearing at 14400 and 14430 cm-1, respectively; these latter are known as Ruby lines and they are the emission bands used in the Ruby laser. Furthermore these bands shift in frequency with stress (Piezo-Spectroscopic effect). In this paper, for the first time, the stress-dependent peak frequency of the weaker bands in the 13900-14250 cm-1 range is calibrated, and the results are presented as Piezo-Spectroscopic coefficients. The calibration is performed by reporting the frequency shift of each investigated band as function of varying stresses. The stresses, residual in nature, are obtained by fabricating composite materials where a-alumina is mixed in various amounts with (i) Ceria-Stabilized Tetragonal Zirconia Polycrystals (Ce-TZP) and (ii) silicon carbide, SiC. The composite materials are prepared at high temperature (1500°-1800°C); due to the difference in thermal expansion, upon cooling to room temperature a-alumina develops compressive and tensile stresses, when mixed with Ce-TZP and SiC, respectively. The stress values necessary for the calibration are obtained from the frequency shift of the R2 band, using its well-established Piezo-Spectroscopic coefficient (7.6 cm-1/GPa). Then the newly obtained Piezo-Spectroscopic coefficients of the bands in the 13900-14250 cm-1 range are tested to retrieve the stresses in two sets of composites; finally the stress values are compared with those obtained in the same samples from the frequency shift of the R2 band. The comparison shows a very good agreement, thus providing evidence that the bands in the 13900-14250 cm-1 range can be used to monitor stresses in a-alumina-based materials. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells are currently constructed using a yttria stabilised zirconia electrolyte membrane. However, zirconia has a number of disadvantages associated with its use, such as the high operational temperatures required for it to exhibit acceptable levels of ionic conductivity. Alternative ceramics such as doped cerium oxide show promise as electrolytes capable of operating at reduced temperatures, but introduce additional problems such as electronic conduction and inferior mechanical properties. This paper describes the manufacture and characterisation of a number of prototype electrolytes consisting of a mixture of yttria stabilised zirconia and gadolinium doped ceria. Traditional ceramic processing techniques were used to produce the samples, which were then examined using dilatometry, impedance spectroscopy and X-ray diffraction. Results show a lowering of the ionic conductivity of zirconia with the addition of doped ceria. X-ray diffraction patterns obtained from the samples suggested that this effect could be attributed to the formation of a solid solution of ceria in zirconia. [ABSTRACT FROM AUTHOR]

Oxygen sensors provide valuable information for improving the efficiency of, and thus reducing harmful emissions from, combustion processes, such as in internal combustion engines. Oxide materials can be used in different ways to generate an oxygen partial pressure dependent output. The type of sensor in which a particular oxide is used depends on the ionic and electronic defects in the oxide, which can be, to some extent, controlled by doping. In this paper, the issues in selection of an oxide for use in resistive-type, potentiometric-type and amperometric-type oxygen sensors are reviewed. Prototypical examples of materials, specifically titania and zirconia, commonly used in these sensors are discussed to illustrate the effects of doping and defect interaction on the electrolytic and transport properties of oxide materials for use in oxygen sensors. [ABSTRACT FROM AUTHOR]