Protecting nuclear graphite from liquid fluoride salt and oxidation by SiC coating derived from polycarbosilane

Modification process has been conducted on commercial nuclear graphite IG-110 (Toyo Tanso Co., Ltd., Japan) by impregnation and pyrolysis of polycarbosilane (PCS) solution for getting the modified IG-110 (M-IG-110) coated by dense SiC coating for molten salt reactor. The microstructure and properties of graphite were systematically investigated and compared before and after the modification process. Results indicated that the M-IG-110 possessed of more excellent integrated properties including molten salt barrier property and oxidation resistance than bare IG-110 due to the filling effect of SiC particles in the pores of M-IG-110 and dense SiC coating adhering to the surface of M-IG-110. The fluoride salt infiltration amount of M-IG-110 under 5 atm was only 1.1 wt%, which was much less than 14.9 wt% for bare IG-110. The SiC coating derived from PCS exhibited remarkable compatibility with graphite substrate under high temperature and gave rise to excellent oxidation resistance of M-IG-110.     

Fabrication of micro-scale textured grooves on green ZrO2 ceramics by pulsed laser ablation

The green ZrO₂ ceramics were fabricated by cold isostatic pressing. Pulsed laser ablation with a wavelength of 1064 nm was performed to fabricate micro-scale textured grooves on the surface of green ZrO₂ ceramics. The influence of laser parameters on surface quality was studied. The heat-affected zone around the machined grooves and micromorphology of laser-irradiated surface were investigated. Results showed that micro-scale textured grooves with a width of 30–50 µm and a depth of 15–50 µm on the green ZrO₂ ceramic surfaces were successfully fabricated by pulsed laser ablation. The laser parameters had a profound influence on the surface quality of micro-scale textured grooves. Better surface quality could be obtained with frequency below 40 Hz, power below 6 W, and scanning velocity above 200 mm/s. A sintering layer was found on the laser-irradiated surfaces when frequency was above 60 Hz, power was above 10 W, and scanning velocity was below 150 mm/s. Analysis of this sintering layer revealed clear melting and resolidification of ZrO₂ particles.     

Calcium phosphate substrates with emulsion-derived roughness: Processing,characterisation and interaction with human mesenchymal stem cells

Calcium phosphates (CaP) have been the subject of several studies that often lack a systematic approach to understanding how their properties affect biological response. CaP particles functionalised with a pH-responsive polymer (BCS) were used to prepare microporous substrates (porosity between 70 and 75% and pore sizes of 5–20 μm) through the aggregation of oil-in-water emulsions by controlling solid loading, emulsification energy, pH, drying and sintering conditions. The combined effect of surface roughness (roughness amplitude, R_a between 0.9–1.7 μm) and chemistry (varying Hydroxyapatite/β-Tricalcium phosphate ratio) on human mesenchymal stem cells was evaluated. HA substrates stimulated higher cell adhesion and proliferation (especially with lower R_a), but cell area increased with β-TCP content. The effect of surface roughness depended of chemistry: HA promoted higher mineralising activity when R_a ～ 1.5 μm, whereas β-TCP substrates stimulated a more osteogenic profile when R_a ～ 1.7 μm. A novel templating method to fabricate microporous CaP substrates was developed, opening possibilities for bone substitutes with controlled features.     

Interfacial microstructure and performance of nano-diamond film/Ti-6Al-4V joint brazed with AgCuTi alloy

The CVD nano-diamond film and Ti-6Al-4V alloy were successfully brazed with AgCuTi active brazing filler. The interfacial microstructure was investigated by SEM, EDS, XRD and TEM. Typical interfacial microstructure of brazed joint was conformed as Ti-6Al-4V/diffusion layer/Ti₂Cu + TiCu + Ti₃Cu₄/Ag(s,s) + Cu(s,s) + Ti₂Cu₃/TiCu + TiC/nano-diamond film. The effects of brazing temperature on interfacial microstructure and mechanical properties of the brazed joints were analyzed. With the increasing brazing temperature, the thickness of reaction layers adjacent to Ti-6Al-4V substrate and nano-diamond film increased obviously. Moreover, the Ti₂Cu₃ phase coarsened and aggregated in brazing seam at higher temperature. The joint was formed by the diffusion and reactions between atoms, and the microstructure evolution of brazed joint was discussed. In addition, a slight graphitization of nano-diamond film occurred during brazing process, and the highest shear strength can reach 25 MPa when the joint was brazed at 880 °C for 10 min. Finally, the fracture positions and fractographs of brazed joints were also discussed.     

The effect of Eu-loading on the some physical features of CdO

The Eu-loaded CdO thin films were coated on the glass substrates with a sol-gel spin coating method by using Cd(CH₃COO)₂·2H₂O and EuCl₃·6H₂O salts. The effect of Eu-loading ratio varied from 0 to 4 at% in the step of 1 at% on the structural, morphological, electrical, and optical features of cadmium oxide had been evaluated with XRD, Raman study, SEM, AFM, Four Point Probe, and UV/VIS analysis. The coated films were polycrystalline with (111) preferential orientation and they had a cubic cadmium oxide structure. The granular-structure was observed from SEM and AFM images. The sizes of granules were in the range of 15–220 nm. It was observed that the homogeneity of granule distribution deteriorated with Eu-content. The RMS roughness value increased from 4.1nm to 284 nm with Eu-doping. The minimum sheet resistance was found to be 4.8 × 10² Ω for 2 at% Eu-content, but the maximum optical band gap was determined to be 2.61 eV for 1 at% Eu-content. The Urbach energy varied between 366 meV and 658 meV. As a result of this work, Eu-doping has an important effect on the properties of cadmium oxide.     

Effect of Na-doping on thermoelectric and magnetic performances of textured Bi2Sr2Co2Oy ceramics

Bi₂Sr_2-xNa_xCo₂O_x (x = 0.0, 0.025, 0.050, 0.075, 0.100, and 0.125) samples were prepared through the solid-state route and textured using the laser floating zone technique. Microstructural analysis of as-grown samples showed well oriented grains and a relatively high amount of secondary phases due to their incongruent melting. Annealing procedure has drastically decreased the number and amount of secondary phases. Moreover, Na-doping has further decreased the secondary phases content and improved grain alignment. These modifications have been reflected in a large decrease of electrical resistivity with the annealing procedure. The maximum power factor values have been obtained in 0.075 Na-doped annealed samples, 0.20 mW/K²m, which are much higher than the best values obtained in textured materials through hot uniaxial pressing. Magnetic properties were very similar for all samples, with paramagnetic Curie temperature and effective magnetic moment values of ?48.6 K and ≈2 μ_B, respectively.     

Controlling microstructure and film growth of relaxor-ferroelectric thin films for high break-down strength and energy-storage performance

The relaxor ferroelectric Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ (PLZT) thin films were deposited using pulsed laser deposition, and their microstructures, break-down field strengths and energy storage performances were investigated as a function of the buffer layer and electrode. A large recoverable energy-storage density (U_reco) of 23.2 J/cm³ and high energy-storage efficiency (η) of 91.6% obtained in the epitaxial PLZT film grown on SrRuO₃/SrTiO₃/Si are much higher than those in the textured PLZT film (U_reco = 21.9 J/cm³, η = 87.8%) on SrRuO₃/Ca₂Nb₃O₁₀-nanosheet/Si and the polycrystalline PLZT film (U_reco = 17.6 J/cm³, η = 82.6%) on Pt/Ti/SiO₂/Si, under the same condition of 1500 kV/cm and 1 kHz, due to the slim polarization loop and significant antiferroelectric-like behavior. Owing to the high break-down strength (BDS) of 2500 kV/cm, a giant U_reco value of 40.2 J/cm³ was obtained for the epitaxial PLZT film, in which U_reco values of 28.4 J/cm³ (at BDS of 2000 kV/cm) and 20.2 J/cm³ (at BDS of 1700 kV/cm), respectively, were obtained in the textured and polycrystalline PLZT films. The excellent fatigue-free properties and high thermal stability were also observed in these films.     

Structure and electrical insulation characteristics of plasma-sprayed alumina coatings under pressure

In this work, alumina coatings were fabricated on 316LN austenitic stainless steel by a plasma spray technique. The pressure dependence of the surface electrical resistivity of alumina coatings was investigated in detail. A combination of scanning electron microscopy and X-ray diffraction was employed to understand the microstructure and properties of the as-sprayed alumina coatings. The coatings can endure high pressures under a practical working environment. The surface electrical resistivity of the alumina coatings decreases continuously with an increase in pressure to 250 MPa. Interestingly, the surface resistivity is still greater than 10⁷ Ω·mm for 250 MPa, demonstrating that the coatings have good electrical insulation properties and can be fully utilized in the magnet support of ITER.     

Oxidation protective MoSi2-SiC-Si coating for graphite materials prepared by slurry dipping and vapor silicon infiltration

A novel kind of dense MoSi₂-SiC-Si coating was prepared on the surface of graphite substrate by slurry dipping and vapor silicon infiltration process. Mo-SiC-C precoating was fabricated via slurry dipping method, and then MoSi₂-SiC-Si coating with dense structure consisting of Si, MoSi₂ and SiC was obtained by vapor silicon infiltration process. The isothermal oxidation tests at temperatures from 800 to 1600 °C and TGA test from room temperature to 1500 °C were used to evaluate the oxidation resistance ability of the MoSi₂-SiC-Si coating. The experimental results indicate that the prepared coating has good oxidation protection ability at a wide temperature range from room temperature to 1600 °C. Meanwhile, the oxidation of the coated samples is a weight gain process at temperatures from 800 to 1500 °C due to the formed SiO₂ layer on the surface of coating. After oxidation for 220 h at 1600 °C, the weight loss of the coated sample was only 0.96%, which is considered to be the excessive consumption of the outer coating and the appearance of defects in the coating. Two layers can be observed in the coating after oxidation, namely, SiO₂ layer and MoSi₂-SiC-Si layer.     

Effects of pH value and temperature on the corrosion behavior of a Ta2N nanoceramic coating in simulated polymer electrolyte membrane fuel cell environment

To improve the corrosion resistance and electrical conductivity of Ti-6Al-4V bipolar plates used in polymer electrolyte membrane fuel cells (PEMFCs), a novel electro-conductive Ta₂N nanoceramic coating was developed by reactive sputter-deposition using a double cathode glow discharge plasma technique. The microstructure of the coating consisted of fine equiaxed Ta₂N grains with an average grain size of ∼13 nm, which exhibited a strong (101) preferred orientation. To explore the influence of both pH values and temperatures on the corrosion resistance of the coating, the electrochemical behaviors and electronic properties of passive films grown on the Ta₂N coating were systematically investigated using different electrochemical techniques in simulated PEMFC operating environment. It was shown that either increasing the acidity or the temperatures of the solution, the corrosion potential (E_corr) decreased and the corrosion current density (i_corr) increased. At a given temperature or pH value, the Ta₂N coating had a higher E_corr and lower i_corr as compared with uncoated Ti-6Al-4V. The results of EIS measurements showed that with increasing temperature or acidity of the solution, the resistance of the passive film (R_p) formed on the Ta₂N coating decreased slightly, being of the order of magnitude of 10⁷ Ω cm², which was an order of magnitude higher than that of uncoated Ti-6Al-4V. The interfacial contact resistance (ICR) values were found to increase with increasing pH value or decreasing solution temperature, and the ICR values of the Ta₂N coating were markedly lower than that of uncoated Ti-6Al-4V, due to the thinner thickness of passive films. Furthermore, the Ta₂N-coated Ti-6Al-4V is more hydrophobic than bare Ti-6A1-4V, which was favorable for both the simplification of water management and improving corrosion resistance in PEMFC operating environment.     

Effect of carbon contamination on the sintering of alumina ceramics

The present work aimed with the carbon contamination in alumina ceramics and its influence on sinterability of alumina in low vacuum and atmospheres of argon and nitrogen. The commercially available alumina was coated with carbon and sintered at different atmospheres to investigate the effect of carbon presence on alumina sintering behaviour. The sintering conditions were: heating/cooling rates 5 °C/min and 1.7 °C/min until the maximum temperature of 1400 °C and a dwell time of 2 h. The microstructure of the samples was investigated from fracture and surface, prior to polishing, chemical or thermal etching. The non-densified (porous) surface layer was found in the samples sintered in nitrogen and vacuum, however, sintering in argon atmosphere showed a negligible effect on the surface. The core of investigated specimens exposes a transgranular/intergranular fracture mode and is dense in all cases. In the case of vacuum sintering, the strong carbon diffusivity was also noticeable by the dark grey color of the samples. Interestingly, the formation of aluminium nitride took place during sintering of carbon coated alumina samples in a nitrogen atmosphere at 1400 °C. The thickness of the reactive porous layer was approximately 15 μm beneath the surface. Such a porous layer is inappropriate to the desired features of final ceramic products. Presented results lead to better understanding of the sintering behaviour of ceramic and to suitable selecting of the set-up by densification conditions.     

Influence of strontium and niobium on the physical and biological performance of hydroxyapatite as a bioactive coating on implant materials

The coating of hydroxyapatite (HAP) on the surface of bio-inert metallic implants to augment their bioactivity is in use for the last two decades. Substitution of various materials in HAP further improves the functionality of these coatings. We demonstrate coating of Ti6Al4V alloy sheets with strontium and niobium reinforced HAP using microwave (MW) irradiation technique. Physical characterization revealed, uniform semicrystalline hydroxyapatite coating with enhanced surface roughness and microhardness. The increased surface roughness was accompanied by higher wettability and more protein adsorption. Electrochemical corrosion assessment showed a dramatic increase in corrosion potential and a noticeable decline in corrosion current density suggesting an enhanced anticorrosive behaviour. These implants also exhibited improved hemocompatibility and bacteriostatic properties. Cell viability and confocal microscopy studies of the coated samples showed enhanced cell attachment on the surface. We propose microwave irradiation as a fast and hassle-free alternative for one-pot synthesis and deposition of ionic substituted HAP on metallic implants.     

Human primary osteoblast behaviour on microrough zirconia-toughened alumina and on selectively etched microrough zirconia-toughened alumina

Hip arthroplasty cementless acetabular components require excellent mechanical properties, biocompatibility, low friction and good osseointegration with surrounding bone tissue. Zirconia-toughened alumina (ZTA) fulfils these demands but requires combination with a rough metal shell for adequate osseointegration. Surface modifications of ZTA could allow a metal-free solution, thus preserving the bone stock for an eventual revision surgery. In this study, selective chemical etching proved to be an innovative method for the introduction of nano-features on micro-rough surfaces obtained by injection moulding. Results suggest that micro-roughness, fluorine enrichment and nano-porosity at the surface of ZTA play a synergistic role on human osteoblast (hOb) maturation. Among the tested groups, hydrofluoric acid etched “medium” roughness (Sa = 330 nm) ZTA showed the highest and/or earliest ALP expression at both the protein and gene level, while microroughness alone induced only minor effects on hOb maturation on ZTA.     

Dip Coating of Calcium Hydroxyapatite on Ti-6Al-4V Substrates

Ti-6Al-4V alloy is the most commonly used metallic material in the manufacture of orthopedic implants. The main inorganic phase of human bone is calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA). To achieve better biocompatibility with bone, metal implants made of Ti-6Al-4V are often coated with bioceramics. Dip-coating techniques scarcely are used to apply HA onto metallic implants. New dipping-solution recipes to be used for HA coatings are described in this work. Scanning electron microscopy and X-ray diffractometry have been used for sample characterization.     

Enhancement in the extraction efficiency and resisting electrostatic discharge ability of GaN-based light emitting diode by naturally grown textured surface

GaN-based light-emitting diodes (LEDs) with naturally textured surfaces were grown by metal-organic chemical vapor deposition (MOCVD). A naturally textured p-GaN surface layer was fabricated by controlling the growth temperature. The output power of light from the naturally textured surface GaN-based LED, whose p-GaN layer was grown at 850 °C, was 48.6% higher than that from a commercial GaN-based LED. The GaN-based LED with a naturally textured surface and a thick p-GaN layer with a thickness of 300 nm, which was grown at a high growth temperature, exhibited improved electrostatic discharge (ESD) resistance and could resist a reverse bias voltage of as high as 3500 V. The experimental results demonstrate that the naturally textured growth method combined with a p-GaN layer grown at high temperature is suitable for manufacturing high-efficient low-cost GaN-based LEDs.     

Investigation on La2Zr2O7 multilayers by chemical solution deposition

The preparation of 80 nm, 140 nm, and 200 nm La₂Zr₂O₇ (LZO) multilayers on biaxially textured Ni-5 at% W (Ni5W) substrates using chemical solution deposition (CSD) was studied. The performance of multilayers was studied by means of X-Ray Diffraction (XRD), Electron Back Scattering Diffraction (EBSD), and Auger Electron Spectrometry (AES). The as-grown buffer layers exhibit sharp texture with texture components (0°−10°) about 96.7%, 98.9%, and 98.8%, respectively. The full-width at half maximum (FWHM) values of the ω-scans decreases with the number of layers, close to that of Ni5W substrates. The films exhibit dense, smooth, crack-free surface with a roughness Ra 3–5 nm, and sufficient barrier function against metal ionic diffusion from Ni5W substrates into buffer layers. The performance of LZO multilayers was confirmed by YBa₂Cu₃O_7−x (YBCO) films deposited by CSD technology.     

The properties of hydroxyapatite ceramic coatings produced by plasma electrolytic oxidation

Calcium phosphate coatings produced on the surface of Ti6Al4V by plasma electrolytic oxidation (PEO) using different concentrations of hydroxyapatite (HA) in a 0.12 M Na₃PO₄ (NAP) electrolyte solution was investigated. It was found that the amount of calcium phosphate particles infiltrated into the coating layer as well as the thickness and the surface roughness of the coating increased with increasing HA concentration. The porosity of the ceramic coatings indicated an inverse relationship with the concentration of HA particles dispersed in the NAP solution. The result also demonstrates that higher scratch adhesive strength was achieved using 1.5 g/L HA solution, producing a critical load of 2099 mN, while 0 g/L HA only produced a critical load of 1247 mN. The adhesion becomes independent of thickness when the concentration of HA exceeds 1.5 g/L. The failure of the coating was characterized by large periodic hemispherical chipping, while intermittent delamination was noticed with the coating embedded with HA particles. This study demonstrate the viability of using PEO to produce a thin layer of HA ceramic coating on Ti6Al4V suitable for biomedical applications.     

Texturing behaviours of (K0.47Na0.51Li0.02)(Nb0.8Ta0.2)O3 piezoelectric ceramics produced using NaNb1-xTaxO3 templates

Textured (K_0.47Na_0.51Li_0.02)(Nb_0.8Ta_0.2)O₃ (KNLNT20) piezoelectric ceramics were prepared using NaNb_1?xTa_xO₃ templates. The highest degree of grain orientation (97%) and piezoelectric constant (342 pC/N) were obtained upon adding 3 wt% of the NaNb_0.8Ta_0.2O₃ (NNT20) template and sintering at 1150 °C for 1 h. Back-scattered scanning electron micrographs of the textured KNLNT20 samples sintered at 1150 °C for 1 h indicated the presence of templates similar in size to the original ones within the cores of the textured grains. The peak value of the dielectric constant corresponding to the NNT20 core decreased after prolonged holding at 1150 °C, owing to a decrease in the size of the NNT20 core because of the interdiffusion of K, Na, and Li ions between the NNT20 core and KNLNT20 shell. This interdiffusion also decreased the piezoelectric constant, d₃₃ value of the textured KNLNT20 samples by inducing a change in the chemical composition of the shell region.     

Low temperature degradation of laser patterned 3Y-TZP: Enhancement of resistance after thermal treatment

The aim of this study is to characterize the resistance to low temperature degradation (LTD) of the surface of dental-grade zirconia (3Y-TZP) patterned with a Nd:YAG laser (532 nm harmonic and pulse duration of 10 ns) employing an interference setup.Laser patterning decreases the resistance to LTD of 3Y-TZP because of the presence of monoclinic phase and residual stresses, induced by the thermal shock during laser-material interaction. A thermal treatment (1 h at 1200 °C) anneals the affected microstructure and increase the resistance to LTD of laser patterned 3Y-TZP. Transformation delay may be attributed to monoclinic phase reversion, texture in the tetragonal phase and the existence of a net of shallow microcracks on the surface, accommodating autocatalytic transformation.     

Synthesis and characterization of nanocrystalline NiO-GDC via sodium alginate-mediated ionic sol-gel method

In this study, nanocrystalline nickel oxide gadolinium-doped ceria (NiO-GDC) powder was synthesized in-situ using Na-Alginate as the template via ionic sol-gel technique. The effects of calcination time and temperature on the particle size and the physiochemical properties of nanocrystalline NiO-GDC are presented in this paper. Using this method, gel beads were formed by contacting sodium alginate solution as the gelling template and metal (gadolinium/cerium/Ni) nitrates as the precursor. The obtained nanocrystallites were characterized using Field Emission Scanning Electron Microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, thermo gravimetric analysis, nitrogen adsorption/desorption analysis, and Fourier transform infrared spectroscopy. It was observed that the increasing calcination temperature had affected both the particle size and the surface area of the NiO-GDC, whereas the increasing calcination time had only impacted the size of the particles. The smallest mesoporous nanocrystalline NiO-GDC powder (12.1225 ± 0.005 m²/g surface area), composed of cubic GDC (5.18 nm crystallite size) and cubic NiO (7.99 nm crystallite size) were synthesized at a calcination temperature of 500 °C for 2 h. This study hopes to inspire more researches on the ionic-gelation method for synthesizing other metal nanostructures as well as other reaction parameters.