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Two types of precursor solutions, including lanthanum nitrate and lanthanum chloride, with zirconium acetate, were used to produce lanthanum zirconate coatings by solution precursor plasma spraying (SPPS). Thermal behavior of the precursor solutions, their rheological properties and atomization patterns were investigated by TGA–DSC, viscosity, surface tension and droplet size measurements, respectively. The chloride precursor led to the formation of impure lanthanum zirconate powder including LaOCl and ZrO2, while the nitrate precursor combined with zirconium acetate produced pure lanthanum zirconate powder after pyrolysis. Increasing the salt concentration from 0.125 to 0.5 M led to the formation of solutions with ~ 2.7 times higher viscosity but ~ 7% lower surface tension. The ethanol based solutions had smaller surface tension compared to the water based (24.3 mN/m vs. 62.7 mN/m), while being more viscous (4.8 cp vs. 3.2 cp). The most significant factor affecting the droplet size in atomized solutions was their viscosity. The 0.5 M water-based solutions with about 28 µm median size droplets injected into the plasma plume produced columnar morphology coatings with ~ 23 vol.% porosity.

Suspension stability is a key parameter that should be considered in any coating process utilizing a suspension as the main feedstock. Application of water as the liquid phase for suspension preparation is promising due to its availability, low cost and no toxicity. In the present study, the effects of three surfactants, polyethyleneimine (PEI), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) and α-Terpineol, on the functional stability of yttria-stabilized zirconia (YSZ) water-based suspensions were investigated. The changes in the suspensions’ zeta potential, pH, viscosity and Turbiscan Stability Index (TSI) were monitored over their aging time of 1 to 7 days. The results showed that α-Terpineol is the most effective surfactant to produce functionally stable suspensions with low viscosity and surface tension values. Plasma spraying of such stable suspensions results in the formation of thermal barrier coatings (TBCs) with columnar morphology having porosity in the range of 17 to 18 vol.%.

We report herein the structural and mechanical properties and in vitro cellular response of hydroxyapatite (HAp)/alginate nanocomposite fibrous scaffolds mimicking the mineralized collagen fibrils of bone tissue. The biomimetically "

Objective As a result of advancements in chairside technology and speed sintering techniques and increased esthetic demands of patients, efforts have been made to produce monolithic zirconia restorations that are highly translucent, strong, and dense. While methods for processing zirconia are well known, there is a tendency to modify the process parameters with the aim of decreasing the overall processing time and, in particular, the sintering time. This review provides clinicians with scientific evidence of the effects of altering sintering parameters used for dental zirconia on its microstructure, phase transformation, and mechanical and optical properties. Materials and methods A systematic search of Embase and Medline using Boolean operators was performed to locate relevant articles. Results Eleven articles were selected for this review. The following characteristics of monolithic zirconia have been confirmed to be affected by alterations in sintering: the microstructure, mechanical properties, optical properties, wear behavior, and low thermal degradation. Conclusions The alteration of sintering parameters has been found to alter the grain size, wear behavior, and translucency of zirconia. There is a lack of clinical studies that investigate the influence of altering sintering parameters or methods on the clinical performance of monolithic zirconia restorations. Clinical significance Alteration of sintering parameters alters the microstructural, mechanical, and optical properties of zirconia. This will consequently impact the clinical performance of zirconia prostheses. Future clinical investigations are encouraged to support these in vitro findings.

This study presents the results of the synthesis and characterization of chemically bonded phosphate ceramics (CBPC) material based on silica residues from furnaces used in power-generation plant enriched with iron (III) oxide and silicon carbide. The sparsely soluble oxide, as required for the successful chemical bonding, was magnesium oxide and the phosphate derivative was ammonium dihydrogen phosphate. Various amounts of water were added. Morphology analysis of the SEM microphotographs revealed the presence of magnesium phosphates and magnesium silicates, confirmed by the MIR spectra. TG/DSC analysis provided an information on the thermal stability of the prepared phosphate ceramics, whereas mechanical tests gave an information on its mechanical strength. The results firmly suggest that silica residues contaminated with iron (III) oxide and silicon carbide (which normally interfere with setting of traditional cements) could find potential applications in CBPC ceramics which can be used inter alia in construction industry.

In suspension plasma spraying (SPS); the use of water based suspensions provides a cheaper; safer and more environmentally friendly alternative to organic liquids. However; due to the physical properties of water; producing a water based SPS coating with desirable microstructure has so far been elusive. In this study; the effects of pH and dispersant on the rheology and stability of YSZ water based suspensions were investigated. PEI; PBTCA and α-Terpineol were used as dispersant polymers. The stabilized suspensions were deposited by Axial III plasma spray system and the relationship between suspension parameters and the atomized droplet size and the final coating microstructure was studied. The results showed that a combination of Terpineol dispersant with pH adjustment to 2.5; could lead to a SPS coating with columnar microstructure having 17.4 vol.% porosity.

PURPOSE The marginal fit is an essential component for the clinical success of prosthodontic restorations. The aim of this study was to investigate the influence of different abutment finish line widths and crown thicknesses on the marginal fit of zirconia crowns fabricated using either standard or fast sintering protocols. MATERIALS AND METHODS Six titanium abutments were fabricated for receiving zirconia molar crowns. Crowns were designed virtually and milled from partially sintered zirconia blanks and divided into 12 groups (n = 10/group). Crowns in groups 1 to 6 were sintered by standard sintering, while those in groups 7 to 12 were sintered by fast sintering. Groups were further categorized according to abutment finish line and crown thickness: G1/G7 (0.5 mm chamfer, 0.8 mm thick); G2/G8 (0.5 mm chamfer, 1.5 mm thick); G3/G9 (1.0 mm chamfer, 0.8 mm thick); G4/10 (1.0 mm chamfer, 1.5 mm thick); G5/G11 (1.2 mm chamfer, 0.8 mm thick); G6/G12 (1.2 mm chamfer, 1.5 mm thick). The marginal gaps were assessed at 8 locations using digital microscopy. The linear mixed effect model analysis was performed at a significance level of 0.05. RESULTS All vertical marginal gaps were within the clinically acceptable range (∼11-52 μm). G8 (FS, 0.5 mm chamfer, 1.5 mm thick) demonstrated the largest gaps (47.95 μm, 95% CI: 44.57-51.23), whereas G3 (SS, 1.0 mm chamfer, 0.8 thick) had the smallest marginal gap (14.43 μm, 95% CI: 11.15-17.71). A linear mixed effect models showed significant differences for the interaction between finish line × crown thickness × sintering (F = 18.96, p < 0.001). The lingual surfaces showed the largest gaps in both sintering protocols, while the mesial and mesiobuccal surfaces demonstrated the smallest gaps. CONCLUSIONS There was a significant interaction between finish line widths, crown thickness, and sintering protocol on the marginal gaps in both sintering protocols; 1.0 mm finish line preparations with either 0.8 mm or 1.5 mm occlusal reduction had better marginal fit in both sintering protocols compared to 0.5 mm or 1.2 mm finish lines. Smaller marginal discrepancies were observed for standard sintering crowns with a 0.5 mm finish line and 1.5 mm occlusal reduction. Conservative occlusal reduction should be accompanied with a 1.2 mm finish line to obtain better marginal fit for full-contoured zirconia crowns.

In this work we investigated a novel approach to prepare Li-La-Zr-O solid-state electrolyte films by the suspension plasma spray process. This process offers several advantages that make it a promising low-cost, rapid and robust production method for garnet-type Li-ion conductors. A cubic garnet-type, Li6.75La3Zr1.75Nb0.25O12, ethanol-based suspension was plasma sprayed on stainless-steel substrates using two torch power levels, 30.9 and 77.1 kW, at different stand-off distances. Solid-state electrolyte films of ~14 μm thickness were deposited in ~0.1 h of spraying. Maximum Li-ion conductivity as high as 7.3·10−6 S cm−1 at 22 °C has been obtained for the samples sprayed at 30.9 kW and stand-off distance of 25 mm. These samples contained a majority of amorphous phase (67.0 wt%), 20.2 wt% of Li6.75La3Zr1.75Nb0.25O12, and the balance of 12.8 wt% of the pyrochlore phase (La2Zr2O7). We associate this result with the relatively high value of Li number density, 2.2·1022 cm−3, and the lowest content of La2Zr2O7. The higher torch power level and/or longer stand-off distance leads to a reduction in Li number density and higher content of La2Zr2O7, likely due to evaporative loss of Li species during the spray process. These factors also translate to a decrease in Li-ion conductivity. The knowledge that has been acquired in this preliminary study provides guidelines for further development and optimization of this rapid deposition technique of garnet-type solid-state electrolyte films.

Molybdenum disilicide (MoSi2) rapidly oxidizes at 400–600 °C, which given enough time, can lead to its disintegration. Above 1000 °C, MoSi2 exhibits better oxidation resistance due to the formation of a continuous SiO2 layer (or alumina layer for the materials doped with aluminum). However, during high-temperature service, the protective layer on MoSi2 could be damaged, e.g. due to erosion, volatilization, and micro-cracks in thermal cycling, or due to exposure to reducing atmospheres. In this study, the oxidation characteristics of MoSi2 based materials were investigated in air, with the pre-oxidized protective layer removed to simulate such surface damages. Five different, commercially available, MoSi2 based heating elements, i.e. Kanthal Super (labelled by the manufacturer as KS-1700, KS-1800, KS-1900, KS-ER and KS-HT) were exposed to 300 to 900 °C isothermally, for 12 to 240 h, and their mass changes determined. Scanning Electron Microscopy, Energy-dispersive X-ray spectroscopy, and X-ray diffraction analyzed the microstructure, chemical composition and phase composition of the oxidized samples. It was found that the oxidation behavior of the different materials under investigation depended strongly on their chemical and phase composition, exposure time and temperature. KS-ER, KS-1800 and KS-1700 showed better resistance against the low temperature (300 to 900 °C) degradation for up to 240 h, while KS-HT and KS-1900 underwent significant degradation after 240 h of air exposure within the same temperature range. For rapid comparison of the materials damage sensitivity we propose a novel Cumulative Mass vs Temperature Index CMTI, including both mass gain and loss at temperatures ranging from 300 to 900 °C. The index allows quick ranking of the materials under consideration.

In this paper, two precipitation methods of silica, i.e., sol–gel method and silica polymer precipitation, were compared in terms of their impact on the thermal properties of impregnated cellulose fibers. Additionally, the pre-treatment process consisting in dipping the cellulose fibers in NaOH solution to increase the fibers porosity was examined. Three molar phosphoric acid and Flodur 3 (ester hardener based on ethylene glycol diacetate) were used as the sol–gel precipitation agents and 20 wt% aqueous solution of sodium acrylate was used as the polymer precipitation agent. The silica provider was sodium water glass type D. The obtained results have shown that the silicate layer fully covered the cellulose fibers, as confirmed by the scanning electron microscope microphotographs and mid-infrared spectra. Even after thermal treatment at 700 °C, the silicate species still remained in the ash as confirmed by the infrared bands characteristic for sodium silicates, i.e., at 960 and 880 cm−1. Thermogravimetric analysis revealed no significant difference in the weight loss of the cellulose samples treated with different precipitation mixtures, as well as between the raw and pre-treated samples. All weight losses oscillated between 40–50 wt% at 700 °C. Differential thermal analysis curves showed that the pre-treatment process shifts the temperature range in which the different phenomena occur towards higher values. We believe that these results could contribute to the development of cellulose materials with enhanced thermal properties and the process could be an attractive substitute for coatings based on orthosilicates and their derivatives.

Objective To test the effects of addition of polyacrilonitrile (PAN) nanofibers and nanocrystal cellulose (NCC)-containing PAN nanofibers on flexural properties of experimental dental composites. Methods 11 wt% PAN in dimethylformamide (DMF) solution was electrospun at 17.2 kVA and 20 cm from the collector drum. NCC was added to the solution at 3 wt%. Fiber mats were produced in triplicates and tested as-spun. Strips (5 cm × 0.5 cm) were cut from the mat in an orientation parallel and perpendicular to the rotational direction of the collector drum. Tensile tests were performed and ultimate tensile strength (UTS), elastic modulus (E) and elongation at maximum stress (%) were calculated from stress/strain plots. Fiber mats were then infiltrated by resin monomers (50/50 BisGMA/TEGDMA wt%), stacked in a mold (2 × 15 × 25) and light-cured. Beams (2 × 2 × 25 mm) were cut from the slabs and tested in a universal testing machine. Data were analyzed by multiple t-test and one-way ANOVA (α = 0.05). Results Addition of 3% NCC resulted in higher tensile properties of the fibers. Fibers presented anisotropic behavior with higher UTS and E when tested in perpendicular orientation. The incorporation of 3% NCC–PAN nanofibers resulted in significant increase in work of fracture and flexural strength of experimental dental composite beams. Significance NCC was found to be a suitable nanoparticle to reinforce experimental dental composites by incorporation via nanofiber. This fundamental study warrants future investigation in the use of electrospun nanofibres as a way to reinforce dental composites.

Injectable bone cements have been well characterized and studied in non-load bearing bone fixation and bone screw augmentation applications. Current calcium phosphate cement or poly(methyl methacrylate) cement have drawbacks like low mechanical strength and in situ exothermic properties. This leads especially in patients with osteoporosis to worsening contact between implant and bone and can finally lead to implant failure. To improve these properties, a calcium silicate cement (CSC) was prepared, which additionally contained the bisphosphonate risedronate (RA) to promote osteoblast function. Cement setting rate and compressive strength were measured and found to be reduced by RA above 0.5 wt%. X-ray diffraction, Rietveld refinement analysis, scanning electron microscopy, and porosity measurements by gas sorption revealed that RA reduces calcium silicate hydrate gel formation and changes the cement's microstructure. Cumulative release profiles of RA from CSC up to 6 months into phosphate buffer solution were analyzed by high-performance liquid chromatography, and the results were compared with theoretical release curves obtained from the Higuchi equation. Fourier transform infrared spectra measurements and drug release studies indicate that calcium-RA formed within the cement, from which the drug can be slowly released over time. An investigation of the cytotoxicity of the RA-CSC systems upon osteoblast-like cells showed no toxic effects of concentrations up to 2%. The delivery of RA from within a CSC might thus be a valuable and biocompatible new approach to locally deliver RA and to reconstruct and/or repair osteoporosis-related bone fractures.

The fundamental building blocks of hierarchically structured bone tissue are mineralized collagen fibrils with calcium phosphate nanocrystals that are biologically “engineered” through biomineralization. In this study, we demonstrate an original invention of dicalcium phosphate anhydrate (DCPA)/poly(lactic acid) (PLA) composite nanofibers, which mimics the mineralized collagen fibrils via biomimetic in situ synthesis and electrospinning for hard tissue regenerative medicines. The interaction of the Ca2+ ions and the carbonyl groups in the PLA provides nucleation sites for DCPA during the in situ synthesis process. This resulted in the improved dispersion of DCPA nanocrystallites in the intrananoporous PLA nanofibers through electrospinning, compared to the severely agglomerated clusters of DCPA nanoparticles fabricated by conventional mechanical blending/electrospinning methods. The addition of poly(ethylene glycol), as a copolymer source, generated more stable and efficient electrospun jets and aided in the electrospinability of the PLA nanofibers incorporating the nanocrystallites. It is expected that the uniformly distributed DCPA nanocrystallites and its unique nanocomposite fibrous topography will enhance the biological performance and the structural stability of the scaffolds used for hard tissue reconstruction and regeneration. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 514–522, 2014.

Dielectric spectroscopy technique is used in this work to study the structural changes inside lead zirconate titanate (Pb (Zr,Ti)O3 or PZT) exposed to hydrogen for 24 h at 550 °C, at constant pressure p = 0.13 bar. The results show that even after hydrogen treatment, there are still spontaneous dipoles (TiO or ZrO) inside the PZT. However, the dielectric constant is only about half of that of the as-received sample. After the hydrogen treatment, two relaxation peaks were observed in the dissipation factor curves. While the kinetics of one of the relaxation peaks obeys the classical Arrhenius law, the other peak shows a non-monotonic relaxation kinetics. Possible reasons for the formation of these peaks have been discussed.

Osteoporosis greatly impairs bone fracture restoration with bone cement because the accelerated resorption decreases the osseointegration between bone and implants. In this study, we designed a new drug delivery system based on the third generation bisphosphonate risedronate (RA) and the osteogenic calcium phosphate silicate cement (CPSC). The impact of RA on CPSC's material properties and microstructure was evaluated by different characterization methods (μCT, XRD, FTIR, SEM and gas sorption). In addition, in vitro biocompatibility of RA-added CPSC was evaluated (MTT assay, flow cytometry, real-time PCR). In an in vivo study of osteoporotic rabbits, osteoporosis- and bone resorption-related biomarkers were measured over time (ELISA) and local osteogenic and anti-osteoporotic effects investigated (x-ray, CT, histology, PCR arrays). RA decreased the setting rate and compressive strength of CPSC by impeding the hydration of calcium silicate. The overall porosity of CPSC was also decreased with RA. The RA-added CPSC was biocompatible and improved osteoblast proliferation and differentiation. The slow release of RA from CPSC reduced the prevalence of osteoporosis in rabbits and improved peri-implant bone formation and osseointegration. In conclusion, RA-containing CPSC demonstrates its potentials to improve fractural restoration under osteoporotic conditions and should be further engineered to increase its effectiveness in fractural restoration.

The effect of Cr 2 O 3 particle size on the densification of magnesia refractories was investigated. Magnesia grains ( 2 O 3 (2 μm) and nano-Cr 2 O 3 particles (10–20 nm) and sintered at 850–1450 °C, for 5 h in air. The progress of the densification and phase evolution of samples was studied with the support of X-ray diffraction phase analysis (XRD), Fourier transformer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was shown that the densification of magnesia was enhanced by reducing the particle size of the added chromia to the range of 20 nm. According to the phase analysis results, the higher dissolution rate of Cr 2 O 3 in MgO in the MgO–Cr 2 O 3 system was responsible for the faster densification of nano-Cr 2 O 3 containing mixes.

A novel calcium phosphate silicate bone cement (CPSC) was synthesized in a process, in which nanocomposite forms in situ between calcium silicate hydrate (C-S-H) gel and hydroxyapatite (HAP). The cement powder consists of tricalcium silicate (C(3)S) and calcium phosphate monobasic (CPM). During cement setting, C(3)S hydrates to produce C-S-H and calcium hydroxide (CH); CPM reacts with the CH to precipitate HAP in situ within C-S-H. This process, largely removing CH from the set cement, enhances its biocompatibility and bioactivity. The testing results of cell culture confirmed that the biocompatibility of CPSC was improved as compared to pure C(3)S. The results of XRD and SEM characterizations showed that CPSC paste induced formation of HAP layer after immersion in simulated body fluid for 7 days, suggesting that CPSC was bioactive in vitro. CPSC cement, which has good biocompatibility and low/no cytotoxicity, could be a promising candidate as biomedical cement.

Providing a reliable hot surface ignition system (glow plug, GP) for natural gas-direct injection engines is challenging. This paper presents experimental results of aging all-ceramic Si3N4-based GPs in an engine, continuing previously published results on electric and gas burner rigs. The microstructural modifications of the ceramic heater, leading to degradation and ultimately to failure, are effected by four synergistic mechanisms: electrical, chemical, mechanical, and thermal. GP lifetime in engine follows the general Arrhenius law, with activation energy of 5.2 eV, (vs 9.1 V on burner rig and 13.8 eV on electric rig, as reported previously), suggesting additional factors contributing to GP failure in the engine.

Lead–zirconate–titanate Pb(Zr,Ti)O3 (PZT)-based actuators are being evaluated by the automotive industry for advanced fuel injection systems, including injection of hydrogen. However, hydrogen can penetrate PZT lattice with deleterious effects on the functionality and properties of PZT. The effect of long-term (200–1200 h) high-pressure (100 bar) hydrogen exposure on the microstructure and electrical properties of PZT has been investigated in the present work. It is found that while the hydrogen atmosphere has only superficial effects on the microstructure of bare PZT plates, it has considerable deleterious effects on the microstructure of electrode/PZT/electrode assembly. The degradation consisted of the development of a porous layer just beside the electrodes on the PZT surface, detachment of the electrodes from the PZT, and extensive damage to the Ag/Pd electrodes. The effect of hydrogen on the capacitance of the electrode/PZT/electrode assembly was also studied by online monitoring of the changes in capacitance in H2; no noticeable changes were observed in capacitance during the hydrogen treatment under the given conditions.

In the development of advanced natural gas and hydrogen direct injection combustion engines, a challenge is providing reliable hot-surface (glow plug, GP) ignition systems; most promising are GPs with silicon nitride-based heaters. This paper presents experimental results of accelerated degradation tests of the GPs on natural gas-burning rig, continuing previously published results on GP degradation in air. Degradation, ultimately leading to GP failure, occurs through the synergistic effects of electric field and chemical reactions in the combustion environment. The resulting microstructural modifications of the ceramic heater, studied by SEM/EDS, are a combination of sintering additive ions migration and surface oxidation.

All-ceramic glow plugs (GP) based on sintered-silicon nitride are evaluated as hot surface ignition systems for natural gas and hydrogen direct injection combustion engines. This paper presents experimental results of the accelerated degradation tests of the GPs in air, wherein GP is heated solely by dc electricity. The complex degradation process has been linked mostly to the redistribution of the sintering additives in Si3N4/Yb2O3 system under an influence of dc electric field and temperatures over 1300°C, as experienced by GP in-service. Ytterbium ions migration varies with time, temperature, and voltage. The microstructural damage was studied primarily by SEM microscopy.

The solid solubility of magnesia in magnesium aluminate spinel and magnesium aluminate spinel in magnesia does not change with temperature thus not creating bonds or precipitation over periclase grains in a single stage sintering process. In comparison, the precipitated spinels in magnesia-chromia refractories form complex spinel due to inversion in the position of bivalent and trivalent cations within the structure, making them more stable at high temperature than either normal or inverse spinel. Additives form low-temperature compounds that diffuse into the spinel structure and create defects that change the properties of spinel solid solution. In the present study, magnesia and alumina powders along with tetravalent oxide additives were analyzed for their role in reactive densification of spinel in a single stage firing process in order to achieve a better binding system for magnesia-based refractories. These tetravalent oxides on reaction with magnesia form spinel solid solution with MgAl 2 O 4 as they have similar crystal structure. The spinel solid solution formed using oxide additives is expected to have higher solubility in magnesia than magnesium aluminate spinel, resulting in improvement of the bonding during sintering through increased in solid solubility at elevated temperatures followed by precipitation of secondary spinel phases, similar to the complex spinel in magnesia-chrome refractories. The formation of spinel during firing remains as a second phase that retards the grain growth of periclase. The changes in unit cell dimensions with temperature and amount of additive were analyzed using Reitveld method and correlated with the densification behaviour at different temperatures.

Aluminum, one of most reactive metals, rapidly corrodes in strong acidic or alkaline solutions but passivates at pH of about 5–9. We have determined that the passivation of aluminum in this range of pH, and in particular in regular tap water, can be substantially prevented after milling of aluminum with water-soluble inorganic salts (referred to as “WIS”), such as KCl or NaCl. Ensuing corrosion of Al in tap water, with accompanying release of hydrogen and precipitation of aluminum hydroxide, at normal pressure and moderate temperatures (∼55 °C) is rapid and substantial. For example, ∼92% of the Al in the Al–WIS system when milled for 1 h and ∼81% when milled for 15 min, corrodes in 1 h, with the release of 1.5 mol of hydrogen per each mole of Al consumed in the reaction. Besides gaseous hydrogen, only solid aluminum hydroxides were formed as the reaction byproducts, opening up the possibility of straightforward recycling of the system. The effects of WIS concentration, chemistry of other additives, powder particle size, temperature, and milling conditions on the reaction kinetics are reported.

One approach to lower the cost of solid oxide fuel cells (SOFCs) is to lower the operating temperatures below 1073 K to allow the use of robust and comparatively inexpensive stainless steels not only for interconnects but also for SOFC support structures. The metal supports must be sufficiently porous to facilitate gas flow toward the reactive sites in the electrodes. Gas flow and electrical conductivity must remain adequate during any oxidation that occurs during operation. In order to identify microstructures most suitable for use as SOFC supports, a series of gas permeation and surface profilometry experiments was conducted to determine the permeability and surface roughness of porous steels (AISI 430) having different pore structures. The materials were also characterized by a variety of porosity measurement methods, each yielding complementary information on the three-dimensional structures. A combination of moderately low surface roughness and high gas permeability was found to represent a good combination of properties for metal-supported SOFC application.

For small particles of aluminum ( 5%) is observed to corrode before passivation occurs at moderate temperatures (>50 °C) in de-ionized water within 1 h. Ball-milling of the aluminum powders with aluminum oxide or water soluble salts results in a significant increase in both the rate of corrosion and the extent of corrosion before passivation. The resulting release of hydrogen gas is of commercial interest for portable hydrogen supply systems. This paper investigates the effect of temperature increase, pH shift, and change of surface area during milling, on the corrosion rate of aluminum powders in water.

Hydroxyapatite coatings on 316L stainless steel substrates were prepared using ultrasonic spray deposition with substrate temperature kept at 300 °C. Two spray patterns, continuous and pulsed (intermittent), were used coupled with precisely control of substrate movement. It was determined that the ability to form continuous and relatively dense, well bonded coatings, was related primarily to the control of the flowrate of precursor solution and temperature and movement of the substrate. The microstructure and bonding strength of the coatings were evaluated in relationship with continuous and pulsed (intermittent) spray routes. Coatings prepared by continuous spray contained relatively large cracks while coatings by pulse spray exhibited finer cracks and higher bonding strength.

A new process for ∼200 μm thick multilayer dielectric films on aluminum was developed via chemically bonded composite sol–gel. The sol–gel process used alumina and chemical bonding used phosphoric acid and aluminum phosphates. An interlayer was introduced between the coatings and aluminum substrate to decrease the thermal expansion mismatch between the ceramic and the substrate. The dielectric breakdown voltage of about 2500 V was measured for the films at room temperature.

Calcium zirconate (CaZrO 3 , CZ) was prepared using a solid-state reaction with mechanochemical activation through vibro-milling, aiming at completing the reaction CaO+ZrO 2 = CaZrO 3 at relatively low calcination temperatures. Changes in the crystallite size and homogeneity of the mixed components CaO and ZrO 2 in the starting mixtures were observed with different milling times. The influence of milling on the incipient temperature of CZ formation and completion of CZ formation was investigated. It is concluded that milling of the reactants for 20 h lowered the incipient temperature of CZ formation from 800° to 600°C, and the temperature of complete CZ formation from above 1100° to 800°C.

The repair of bone defects is still a pressing challenge in clinics. Injectable bone cement is regarded as a promising material to solve this problem because of its special self-setting property. Unfortunately, its poor mechanical conformability, unfavorable osteo-genesis ability and insufficient osteo-inductivity seriously limit its clinical application. In this study, novel experimental calcium phosphate silicate bone cement reinforced by carbon fibers (CCPSC) was fabricated and characterized. First, a compressive strength test and cell culture study were carried out. Then, the material was implanted into the femoral epiphysis of beagle dogs to further assess its osteo-conductivity using a micro-computed tomography scan and histological analysis. In addition, we implanted CCPSC into the beagles' intramuscular pouches to perform an elementary investigation of its osteo-inductivity. The results showed that incorporation of carbon fibers significantly improved its mechanical properties. Meanwhile, CCPSC had better biocompatibility to activate cell adhesion as well as proliferation than poly-methyl methacrylate bone cement based on the cell culture study. Moreover, pronounced biodegradability and improved osteo-conductivity of CCPSC could be observed through the in vivo animal study. Finally, a small amount of osteoid was found at the heterotopic site one month after implantation which indicated potential osteo-inductivity of CCPSC. In conclusion, the novel CCPSC shows promise as a bioactive bone substitute in certain load-bearing circumstances.

Vertebral compression fractures can be successfully restored by injectable bone cements. Here the as-yet unexplored in vitro cytotoxicity, in vivo biodegradation, and osteoconductivity of a new calcium phosphate silicate cements (CPSC) are studied, where monocalcium phosphate (MCP; 5, 10, and 15 wt%) is added to calcium silicate cement (CSC). Setting rate and compressive strength of CPSC decrease with the addition of MCP. The crystallinity, microstructure, and porosity of hardened CPSC are evaluated by X-ray diffractometer, Fourier transform infrared spectroscopy, and microcomputed tomography (CT). It is found that MCP reacts with calcium hydroxide, one of CSC hydration products, to precipitate apatite. While the reaction accelerates the hydration of CSC, the formation of calcium silicate hydrate gel is disturbed and highly porous microstructures form, resulting in weaker compressive strength. In vitro studies demonstrate that CPSC is noncytotoxic to osteoblast cells and promotes their proliferation. In the rabbit tibia implantation model, clinical X-ray and CT scans demonstrate that CPSC biodegrades slower and osseointegrates better than clinically used calcium phosphate cement (CPC). Histological studies demonstrate that CPSC is osteoconductive and induces higher bone formation than CPC, a finding that might warrant future clinical studies.

In this study, a polymer bond layer was incorporated between the chemically bonded composite sol–gel coating (CB-CSG) and stainless steel substrate to form sandwich structure coatings for improving the coating's corrosion resistance in aqueous solutions. The low processing temperatures of CB-CSG coatings and a specified high temperature polymer (siloxane) make it possible to prepare polymer/CB-CSG composite coatings with an unusual combination of mechanical properties and corrosion resistance. Compared with non-polymer CB-CSG coatings, the ceramic/polymer sandwich coatings exhibit lower hardness and elastic modulus due to the infiltration of polymer into the CB-CSG ceramic coatings. However, the polymer layer of the sandwich structure coatings may remarkably reduce the residual stress in the coatings. Electrochemical characterization and salt spray tests indicate that the polymer layer is very efficient for improving the overall corrosion resistance.

Partially yttria stabilized zirconia (PYSZ) is the state-of-the-art material for current thermal barrier coating (TBC) applications at aircraft engines. It introduces intrinsic properties leading to increased lifetime of superalloy turbine blades and engine efficiency. The new generation turbines generate higher gas temperatures, which seriously affects the thermal stability of the state-of-the-art TBC materials, mainly because of considerable phase transformation- and/or sintering-induced volume changes. These processes cause degradation of columnar microstructure of electron-beam physical vapor deposited (EB-PVD) coatings and raise modulus of elasticity and as a result, the internal stresses. One of the suggested strategies for the improvement of sintering resistance is to infiltrate TBCs with another oxide. This aims to reduce the diffusion rate at the nano-structured feather-arm features and to avoid inter-columnar pore closure. This paper deals with infiltration of EB-PVD PYSZ-structures with a liquid-phase precursor based on alumina and titania to inhibit sintering. After heat-treatment of infiltrated coatings at 1000 and 1100 °C, microstructure is characterized by SEM/EDX and compared with as-coated state-of-the-art material aged under same conditions. The mechanism, which may stop or inhibit the sintering at TBCs is discussed. Attributions to the thermal stability and the potential use of the infiltration technique in EB-PVD-coatings are addressed.

Chemically bonded composite sol–gel coatings have been recently proposed as a novel, low-cost method of protection of metals against corrosion and wear. However, the process operates in mildly acidic (pH = 3–4) conditions sufficient to initiate corrosion of mild steel during heat treatment of the coating at 300 °C. Therefore, there is a need to protect surface of steel from contact with the coating slurry. To achieve this, a protective film of iron phosphate was produced on mild steel substrate surface using commercial product (Crystcoat 747). The film also improved bonding between the substrate and the ceramic layer. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterized the microstructure of the iron phosphate coating and the ceramic coating.

This work investigates hydration behavior of hydratable alumina in the presence of several forms of magnesia used for production of refractory castables. The mixtures of hydratable alumina with reactive magnesia, fused magnesite and deadburnt magnesite were hydrated at 20 °C and 110 °C. The hydration products were determined with X-ray diffractometer and the hydration extent was calculated from thermogravimetric analysis. The results revealed significant difference in the hydration products between the hydratable alumina-reactive magnesia mixture and the hydratable alumina-fused magnesite or deadburnt magnesite mixtures under the hydration conditions. The relationships of the compositions of hydrotalcite-like hydrates with different types of magnesias are elucidated. The bonding formed between hydratable alumina and magnesite aggregate in castables and its effect on the strength of the castables dried at 110 °C and fired at 816 °C was discussed.

MgAl 2 O 4 spinel precursor was prepared by a novel method combining a sol-gel process with the "traditional" precipitation process. The thermal decomposition and phase development of the precursor were analyzed, and the degree of agglomeration of the calcined powder was assessed by determining its particle size and crystal size. The optimum calcination temperature was determined based on the variation of specific surface areas, crystal size, and particle size. Completely crystallized ultrafine spinel powder (d 5 0 =600 nm, specific surface area=105 m 2 /g) was obtained after calcination at 900°C.

MgAl2O4 spinel precursor was prepared using a heterogeneous sol–gel process. The effect of high-energy milling on the precursor decomposition and spinel formation was investigated. The milling decreased the Al(OH)3 dehydroxylation temperature from 190° to about 130°C. The activation energy for spinel formation decreased from 688 kJ/mol for the as-prepared precursors to 468 kJ/mol for the precursors milled for 5 h. Milling of the precursor lowered the incipient temperature of spinel formation from 900° to 800°C, and the temperature of complete MgAl2O4 spinel formation from >1280° to ∼900°C.

This communication introduces chemically bonded (CB) composite sol–gel (SG) technology. The composite includes majority (>80 vol%) particulate filler, the balance being SG-derived bonding phase. Ceramic bond formation in such a composite is induced through chemical reaction rather than through sintering. In the particular variant of the process presented here, the reactivity of the SG-derived alumina ceramics toward phosphates, such as aluminum phosphate or phosphoric acid, is explored to produce a ceramic (reaction) bond in the system without sintering. This allows attaining structural integrity of the composite at relatively low temperatures of 300°C. Several examples of 40–200 μm thick films of CB alumina on stainless steel, Mg and Al, Ni, and on carbon fiber-reinforced epoxy are discussed.

Observation of p-type gas sensitivity in undoped titanium oxide thin-films is reported. Layers of titanium oxide were sol–gel deposited on thermally oxidized Si wafers. The deposits were annealed at 500 °C for 60 min. XRD tests revealed the films to be mainly of anatase with an average grain size of ∼15 nm, and the SEM micrographs indicated an average particle size of 30 nm. The four-point-probe test, carried out at 320 °C, indicated the oxide semiconductor layer to be of p-type, and the Arrhenius diagram of electrical conduction resulted in an activation energy of 0.2 eV. The gas sensing properties of the layers were investigated on sample resistive gas sensors fabricated based on TiO x –SiO 2 –Si–SiO 2 chips mounted on temperature-controlled micro-heaters. Operated at 320 °C, the resistance of the sample devices increased as ethanol vapour contamination was introduced into the surrounding atmosphere. The sensitivity to ethanol is high; ∼100% resistance increase was recorded for 50 ppm contamination. The sample sensors were capable of detecting ppm ethanol levels reversibly but concentrations above 3000 ppm affected the layers irreversibly. Increasing the partial pressure of oxygen had an inverse effect and reduced the resistance of the device as expected for a p-type oxide semiconductor.

The change in strength of hydratable alumina-bonded castable refractories in the presence of magnesia powder and magnesia aggregate, after heat treatment at 110∘ and 816∘C, and the relationship between the strength and morphology and thermal decomposition behavior of the hydrates in the castables are investigated. The mechanism of bonding facilitated by the presence of magnesite in hydratable alumina-bonded castables after drying is discussed. The contribution of polycondensation process occurring after dehydroxylation of the hydrates in the castables after firing at 816∘C is proposed as the principal mechanism for strength development.

Aluminum phosphate products formed by the reactions of alumina and alumina-gel systems with acidic phosphates were analyzed. Drying of alumina-gel to form microcrystalline boehmite and conversion to γ-alumina by thermal treatment was indicated by the appearance of octahedral, pentacoordinate, or tetrahedral sites, which were established using 27Al magic-angle-spinning solid-state nuclear magnetic resonance spectroscopy. Crystalline aluminum phosphate products and amorphous material were identified using this technique. α-alumina and heat-treated alumina-gel that were reacted with phosphate in an Al:P ratio of 1:1 yielded dramatically different aluminum orthophosphate:aluminum metaphosphate product ratios of 8.2:1 and 1:1.1, respectively. When alumina-gel was heat-treated with phosphate, an abundance of aluminum orthophosphate, aluminum metaphosphate, and hydrated aluminum phosphate products were affected by varying conditions of temperature and time of heat treatment and by the amount of phosphate present. An α-alumina/alumina-gel composite sol–gel phase that was reacted with phosphoric acid (H3PO4) in a Al:P ratio of 1:1 exhibited an increased quantity of aluminum metaphosphate products compared with an α-alumina:H3PO4 ratio of 1:1 and a higher percentage of reaction (79%) compared with the reactions of an α-alumina:H3PO4 ratio of 1:1 or an alumina-gel:H3PO4 ratio of 1:1. The morphologies of aluminum triphosphate hydrate and aluminum metaphosphate product phases were observed using scanning electron microscopy.

A novel method for the processing of sol–gel-derived titanium dioxide composites has been developed and investigated for the purpose of producing thick films and self-supported photocatalysts. The processing of the composite sol–gel (CSG) photocatalysts, prepared as “coating” and self-supported “bulk” bodies involved utilizing precalcined commercial titania (Degussa P-25 and Aremco) as filler mixed with the sol and then, heat treatment at relatively low temperature (up to 700 °C). The resulting photocatalyst exhibited relatively high surface area and enhanced mechanical stability and integrity. Scratch adhesion tests performed on the CSG photocatalysts showed very good mechanical integrity and scratch resistance of about 5–10 N, far greater than the 0–0.2 N observed for P-25 and Aremco photocatalysts. Photocatalytic activities of the developed composites were evaluated through the oxidation of a known and standard air contaminant trichloroethylene (TCE), which has been widely investigated by many researchers in the field of photocatalysis. The CSG photocatalysts coatings provided TCE removals ranging up to 90% of that provided by P-25. However, the better mechanical integrity offered by the CSG photocatalysts make them viable alternatives for commercial applications that require long term stability and good mechanical properties.

The friction and wear behaviour of a new developed, pressureless sintered TiB 2 ceramic was studied in comparison to SiC against SiC and Al 2 O 3 balls under unlubricated conditions at room temperature. Special attention was paid to the influence of relative humidity on friction and wear results. For both ceramics the coefficient of friction against both ball materials decreases with increasing humidity and is higher in tests against alumina than against SiC. The wear rate is affected significantly by humidity and decreases by one order of magnitude for Al 2 O 3 /SiC system and by 2 orders of magnitude for SiC/SiC system. For TiB 2 wear rates are nearly not affected by humidity against both ball materials and are much smaller than for SiC.

BaTiO3 ceramic thin films were prepared by sol–gel processing and their humidity sensitive characteristics have been investigated. The films were formed on Al2O3 substrates with comb type Au electrodes by spin coating. It was found that the impedance of the thin films decreases with increasing relative humidity (RH). The humidity sensitivity of the sensor depends on the applied frequency of the electric signal and the activation energy for conduction is reduced with water adsorption. The BaTiO3 thin films show a negligible hysteresis under cyclic humidity changes with a good long-term stability and fast response time. It appears that the sol–gel process produces films that can be used as efficient humidity sensors.

Titanium dioxide (TiO 2 ) coatings have been long considered as biocompatible interfaces to promote the physico-chemical bonding between the bone tissues and implant material (e.g., titanium and stainless steel). Monodispersed TiO 2 (anatase, the low temperature polymorph of TiO 2 ) microspheres, produced in the form of colloidal precipitates, were deposited on different substrates and apatite formation was induced on the resulted surface by immersing the coated substrates in simulated body fluid solution. Analytical and microstructural investigations, conducted by X-ray diffraction, energy depressive X-ray spectroscopy and scanning electron microscopy techniques, showed considerable higher rates of apatite formation, in vitro, on the anatase microspheres compared to the sol–gel-derived thin films of the same oxide. We concluded that the particular surface morphology of the packed TiO 2 microspheres, promotes a faster apatite formation in vitro.

Ultra-fine spheres of TiO2 are synthesized through sol–gel colloidal processing. Compared to previous studies, the present work shows a considerable achievement in controlling the shape of the produced particles as well as a relatively narrow size distribution.