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In this study, nanostructured titania (TiO2; n-TO) and nanostructured alumina-titania (Al2O3-13 wt.%TiO2; n-ATO) coatings were successfully deposited on the 6061 aluminum alloy by applying the high-velocity oxy-fuel process. The n-TO coating showed limited pores or microcracks accompanied by both partially and fully melted areas within splats. The n-TO coating exhibited about 25% higher microhardness compared with the n-ATO coating. The agglomerated non-molten nanostructured TiO2 particles that are randomly dispersed and embedded within the n-TO coating microstructure act as arresters of cracks through either branching or blunting crack tips, resulting in about 17% higher bonding strength, as compared to the n-ATO coating with a looser microstructure. The n-TO coating demonstrated superior hardness, higher wear resistance, and smoother wear scar than the n-ATO and uncoated Al substrate. The electrochemical test indicated that the n-ATO coating had about a 50% higher corrosion rate than the n-TO coating because of its looser structure. The immersion test revealed that the n-ATO coating had been severely attacked by blistering and deep cracks corrosions, whereas limited attacks could be distinguished using the n-TO coating in the substrate interface. Based on the results, the n-TO coating can effectively protect the Al alloy substrate against 3.5 wt.% NaCl solution.

One of the high potential material, lanthanum zirconate (LZ) is deposited on superalloy 625 due to its excellent phase stability, low thermal conductivity as well as the high melting point. However, microstructural defects were detected due to lamellar structure behaviour exhibited from the plasma-sprayed coating techniques. This paper investigated the effect of surface modification on LZ thermal barrier coating (TBC) by using laser glazing method. The double ceramic layer (DCL) TBCs are composed of NiCoCrAlYTa bond coating formed via the HVOF process while 8YSZ ceramic top coat and La2Zr2O7 as the third layer were produced by utilizing the APS technique. Nd:YAG pulsed laser has been used to modify the surface layer of plasma-sprayed LZ coatings. The microstructural morphologies of both as-sprayed and laser glazed samples were investigated using Scanning Electron Microscopy (SEM). The phases of the coatings were analysed with X-ray Diffractometry (XRD). The results showed that the laser glazing process reduced surface roughness attributed to the sealing of porosities and other structural defects of the coating. Finally, the impacts of laser energy input and laser distance on the characterization of the glazed layer are discussed.

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.

A protective novel (MgO) oxide layer (with 91.92% corrosion protection efficiency) was successfully applied on Mg–0.4%Ca alloy using protective oxidation at 390°C (without any pre-treatment). Oxide layer coated Mg alloy was then coated with pure epoxy coating (as top coat). This oxide inner barrier layer protected Mg substrate from 3.5wt % NaCl solution when it passes through from epoxy top layer. Lowest anodic current density and highest charge transfer resistance (1118.124 kΩ cm2) and impedance modulus (│Z│) at low frequency substantiated that the existence of thick epoxy top layer which is integrated (via physical anchoring) with the oxide inner barrier layer could considerably reduce the corrosion rate of magnesium substrate in the chloride containing solutions. Moreover, corrosion mechanism for coated Mg–0.4%Ca alloys was then suggested.

Single NbSi2 and duplex NbSi2/Nb5Si3 coatings were successfully applied on Nb substrates using halide activated pack cementation (HAPC) method at 1100 and 1300°C, respectively. Duplex NbSi2/Nb5Si3 coating with Nb5Si3 inner barrier layer, higher thickness, and lesser micro-cracks considerably decreased the infiltration of simulated body fluid (SBF) solution. This deduction was pertained to the high corrosion potential and lowest corrosion current density for the NbSi2/Nb5Si3 coated Nb alloy in corrosive solution. The Nb5Si3 inner barrier layer can protect the Nb substrate from corrosive solution when it passes through from NbSi2 top layer. Moreover, higher charge transfer resistance (Rct), impedance modulus at a low-frequency ( $$\left| Z \right|$$ ) and phase angle were also observed for the duplex NbSi2/Nb5Si3 coated Nb alloy. On the other hand, in vitro bioactivity test indicated higher capability of apatite formation on the silicide coatings compared to uncoated Nb substrate in SBF solution. In fact, modification of chemical composition and surface morphology of Nb substrate surface can provide suitable nucleation sites for apatite formation and growth in SBF solution.

In this study, hydrophobic silica aerogels were synthesized from rice husk ash-derived sodium silicate through sol-gel processing, solvent exchange, surface modification and ambient pressure drying. By volume, 10% of trimethylchlorosilane (TMCS) in 90% of n-hexane was used as a hydrophobic solution in the surface modification process. The physical and chemical properties of silica aerogels were characterized by density and porosity measurements, scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller theory (BET) and dynamic scanning calorimetry (DSC). The hydrogels prepared were in the form of 2.5 ± 0.5 mm beads and then converted into alcogels through solvent exchange with ethanol for repetition of 3, 6 and 9 days. It is found that the optimal quality of silica aerogels with the BET surface area as high as 668.82 m2/g was obtained from the alcogels of the solvent exchange period of 9 days. Depending on the size of the gel’s block, a longer solvent exchange period will ensure adequate removal of pore water. Post heat treatment on silica aerogels obtained from the 9 days of solvent exchange at 200, 300 and 400 °C for 2 h results in slight decreased of aerogel’s density from 0.048 g/cm3 to 0.039 g/cm3 and the hydrophobicity of the aerogels is decreased above 380 °C as confirmed by DSC analysis.

Cobalt chromium alloys constitutes the base of one important group of biometallic with excellent mechanical properties. However, due to its non-bioactive and non-antimicrobial surface, cobalt chromium alloys are vulnerable to wear corrosive attack and bacterial infection. Hence, coating cobalt chromium alloys surface with superior biomaterials is the best proven techniques. In this work, nanostructure silver adopted titanium dioxide coating was deposited on cobalt chromium alloys using air plasma spray (APS) and high velocity oxy-fuel (HVOF) techniques. Nanostructure TiO2–Ag coating demonstrated superior hardness, wear resistance and lower coefficient of friction when compared to bare CoCr alloys. Reduced plastic deformation detected by microstructural analysis indicate that the interference of nano-structure coating in metallic matrix help lower the wear rate of the sample. Meanwhile, low porosity of the coating produced by HVOF technique shown a better wear resistance result than APS technique. Keywords: Cobalt–chromium alloy, Nanostructure TiO2–Ag coating, Thermal spray coating method, Surface properties, Wear performance

An unsaturated polyester resin was modified with plain and core-shell SiO2 aerogels having mean particles diameter of 2.5±0.5 mm. The core-shell structured particle consists of nanoporous SiO2 aerogel core and polyvinyl alcohol shell fabricated using fluidized bed coating process. Two types of polymer composites were prepared at a 30% (by volume) of plain and core-shell aerogels and the thermal conductivities and viscoelastic behaviors of the composites were compared using hot-disk thermal analyzer and dynamic mechanical analysis. The results in this work reveal better thermal insulation and dynamic mechanical properties of the composite containing core-shell aerogels due to preserved aerogel pores and better filler-matrix interaction.

Plasma electrolytic oxidation (PEO) was developed as a bond coat for air plasma sprayed (APS) nanostructure ZrO2 as top coat to enhance the corrosion resistance and antibacterial activity of Mg alloy. Corrosion behavior and antibacterial activities of coated and uncoated samples were assessed by electrochemical tests and agar diffusion method toward Escherichia coli (E. coli) bacterial pathogens, respectively. The lowest corrosion current density and the highest charge transfer resistance, phase angle and impedance modulus were observed for PEO/nano-ZrO2 coated sample compared with those of PEO coated and bare Mg alloys. Nano-ZrO2 top coat which has completely sealed PEO bond coat is able to considerably delay aggressive ions transportation towards Mg alloy surface and significantly enhances corrosion resistance of Mg alloy in simulated body fluid (SBF) solution. Moreover, higher antibacterial activity was also observed in PEO/nano-ZrO2 coating against bacterial strains than that of the PEO coated and bare Mg alloys. This observation was attributed to the presence of ZrO2 nanoparticles which decelerate E. coli growth as a result of E. coli membranes.

This work proposes a process for the fabrication of a silica aerogel (SA)–polyvinyl alcohol (PVA) core–shell structure using the fluidized bed method. First, nearly spherical hydrophobic SA particles with a diameter between 0.5 mm and 3.0 mm were prepared from rice husk ash via a sodium silicate route and ambient-pressure drying. Subsequently, a specific batch size of the SA particles was suspended in a heated air stream and sprayed with aqueous PVA using a bottom nozzle via the fluidized bed process. Coating of an individual SA particle is possible for large particle sizes and hydrophobization of the SA surface prevents penetration of PVA into its pores. The core–shell structured material showed a combination of high thermal insulation and good mechanical stability, rendering it suitable for use as filler in polymer resin, paints, and coatings. The core–shell structured material had an average density of 0.09 g cm−3 with well-preserved SA pores. The average shell volume fraction was 2.5%; the shell thickness varied below 50 μm, and was mostly approximately 20 ± 5 μm. Thermal analysis using transient plane hot-disk method and thermogravimetric analysis showed that the SA–PVA/core–shell structure exhibited lower thermal conductivity (0.035 W/mK) and higher thermal stability than uncoated SA.

Rice husk is rich in amorphous silica which has found various applications as a filler in rubbers and plastics. In the research described here silica was extracted from rice husk ash in the form of...

Plasma electrolytic oxidation (PEO) coatings in the aluminate-silicate-based mixture electrolyte solution with different duty cycles were successfully applied on Mg alloy. The corrosion behavior of the samples was evaluated by water contact angle test, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion tests. Hydrophobic PEO coating could be obtained by adjusting the duty cycle of the applied electric signal. This coating considerably diminished the Mg dissolution and could enhance the impedance values of Mg alloy in 3.5 wt % NaCl solution. However, the surface of other PEO coated samples showed more hydrophilic properties compared to that of the uncoated sample. Dense structure of the modified PEO multiphase (including Mg2SiO4, MgO and MgAl2O4 phases) coating and also its appropriate thickness provided an effective barrier to remarkably delay corrosive solution penetration into the PEO coating. This phenomenon led to major decrease in anodic current density of alloy in chloride solution.

Atmospheric plasma spraying was carried out to deposit a bilayered NiCrAlY/nTiO2-CNT composite coating. Initially, NiCrAlY, as an under-layer with a thickness of around 100 µm, was deposited. Afterwards, nanostructured TiO2 (nTiO2), as an over-layer with a thickness of 135 μm, was deposited with and without the incorporation of carbon nanotubes (CNTs) on the Mg alloy surface. In contrast to NiCrAlY and NiCrAlY/nTiO2, the NiCrAlY/nTiO2-CNT nanocomposite coating displayed a higher bonding strength. The wear behaviour of the coatings was examined by the pin-on-disc test and the results revealed that the incorporation of CNTs into the nTiO2 coating considerably enhanced the tribological behaviour of Mg alloy due to the CNT’s bridging mechanism.

The thermal-mechanical properties of unsaturated polyester (UP) composite were enhanced by the dispersion of silica aerogel (SA) with preserved pores. Low-cost SA was prepared from rice hus...

Thermal degradation of the composite blend consisting unsaturated polyester resin, alumina trihydrate and silica aerogel was studied using thermal gravimetric analysis. Composite filled with silica aerogel show lower density and slightly improve the thermal stability of the pure polymer. The addition of alumina trihydrate slows down the degradation of the polymer due to the release of bond water while the combination of silica aerogel and alumina trihydrate in polyester matrix does not interrupt the function of alumina trihydrate due to inert properties of silica aerogel.

Silica aerogels with a surface area as high as 773 m2 g−1 and a density of 0.077 g cm−3 were produced from rice husk via sol–gel process and ambient pressure drying. A particulate composite materia...

One of the key issues in the DMFC framework is methanol crossover. Surface modification is a promising approach to problem solving. A SPEEK/cloisite nanocomposite membrane exfoliated by electrospun is developed in this research. The membrane is prepared by immersing electrospun SPEEK/cloisite fibers mats in the SPEEK polymer matrix, which is half-solidated. The research addresses the effect of exfoliated morphology on the productivity of membranes. Compared to other sampling membranes like Nafion® 117, SP/e-spunCL15 with a completely exfoliated configuration has the best efficiency with a current density of 7.73 mAcm−2 and a power density of 1.18 mWcm−2. Improved morphological, dimensional change properties and performance assign a well dispersed cloisite15A induced by the electrospinning technique to the membranes more effective for direct methanol fuel cell applications.

Nanotechnology provides innovative approaches and prospects for maintaining renewable resources and future ecosystems. Nanofibrous morphological materials are desirable in solving various energy and environmental problems. Electrospinning can effectively generate nanofibers, which is a simple and inexpensive technique. Three-dimensional (3D), highly compressible and robust aerogels derived from 1D electrospun polymer nanofibers will have wide technical implications for areas ranging from bioengineering, electrical devices and energy storage; however, aerogels derived from these electrospun polymer nanofibers have proved too challenging to develop. In this review, new strategies for the development of 3D structured aerogels with a hierarchical cellular structure and super elasticity for fibrous, isotropically bonded elastic reconstructed 1D electrospun polymer nanofibers were reported by combining electrospun nanofibers and various fibrous freeze-shaping techniques. The contents of this review article are arranged in the following way. The first section will present aerogel manufacturing technology with a focus on how the electrospinning technology can be used to make a significant impact as aerogel reinforcement. The analysis of nanocellulose-derived aerogels and chitins will then be addressed with a focus on nanofiber network aerogels and potential properties in energy storage. The applications of the electrospun nanofibers and electrospun carbon nanofibers aerogels will be defined after that. There will be examples of energy converters, secondary battery electrodes, and supercapacitors made of lightweight carbon nanofiber aerogels. Finally, it will raise opportunities for potential research.

Titania nanoparticles were utilized as suspension in alkaline aluminate electrolyte to form nanocomposite coatings on magnesium alloy containing 1 wt% calcium by plasma electrolytic oxidation process. Microhardness, wettability, potentiodynamic polarization, wettability, electrochemical impedance spectroscopy (EIS), and immersion tests were performed in 3.5% NaCl solution to study corrosion behavior of the coated samples in reference to the uncoated Mg alloy. The coating with 4 g/L concentration of nanoparticles showed the highest microhardness, lowest hydrophilic properties and highest corrosion resistance. This coating substantially diminishes the Mg dissolution in the in 3.5% NaCl solution and increases the charge transfer resistance of the Mg alloy. Although higher concentrations of nanoparticles enhanced the defect density in the coating, they resulted in lower corrosion resistance. © 2016 Elsevier B.V.

Bone defects are very challenging in orthopedic practice. The ideal bone grafts should provide mechanical support and enhance the bone healing. Biodegradable magnesium (Mg)–based alloys demonstrate good biocompatibility and osteoconductive properties, which are promising biomaterials for bone substitutes. However, the high rate of their biodegradation in human body environment is still challenging. For this scope, synthesis Mg-based composites with bioceramic additives such as HA and titania (TiO2) is a routine to solve this problem. The aim of this study was to evaluate the effect of addition TiO2 nanopowders on the corrosion behavior and mechanical properties of Mg/HA-based nanocomposites fabricated using a milling-pressing-sintering technique for medical applications. The microstructure of Mg/HA/TiO2 nanocomposites, in vitro degradation and biological properties including in vitro cytocompatibility were investigated. The corrosion resistance of Mg/HA-based nanocomposites was significantly improved by addition 15 wt% of TiO2 and decrease HA amount to 5 wt% this was inferred from the lower corrosion current; 4.8 µA/cm2 versus 285.3 µA/cm2 for the Mg/27.5 wt%HA, the higher corrosion potential; −1255.7 versus −1487.3 mVSCE, the larger polarization resistance; 11.86 versus 0.25 kΩ cm2 and the significantly lower corrosion rate; 0.1 versus 4.28 mm/yr. Compressive failure strain significantly increased from 1.7% in Mg/27.5HA to 8.1% in Mg/5HA/15TiO2 (wt%). The Mg/5HA/15TiO2 (wt%) nanocomposite possessed high corrosion resistance, cytocompatibility and mechanical properties and can be considered as a promising material for implant applications.

Low density silica aerogel beads were synthesized from rice husk ash via sodium silicate route. The gel beads were prepared by the ball dropping method and dried at ambient pressure after surface modification (silylation) with trimethylchlorosilane (TMCS) solution. The characteristics of porous structure of silica aerogel beads were measured by Brunauer-Emmett-Teller (BET) nitrogen adsorption and desorption method. The silica aerogel beads showed a specific surface area as high as 773 m2/g. They also displayed water-repellant effect (hydrophobic) due to silylation as revealed by Fourier transform infrared spectroscopy (FTIR).

Aluminum trihydroxide (ATH) is an eco-friendly and economical additive used in polymers as a flame retardant (FR), but its low thermal stability has become an important issue that is critical in determining the fire protection and thermal stability of the composites. The present study was an attempt to enhance the thermal stability of ATH to some extent by combining it with nano-porous silica known as silica aerogel (SA) as a hybrid FR filler in unsaturated polyester resin (UPR). Ultra-low density SA (0.07 g/cm3) in the form of fine particles was extracted from renewable resources (i.e. rice husk), through a sol-gel process, surface modification and dried at atmospheric pressure. From our findings, it is found that the addition of the hybrid filler into UPR results in interesting properties such as lightweight, flame retardancy and enhanced thermal stability whose properties cannot be gained by composites with single filler. From thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and gas analysis using Fourier transform infrared spectroscopy (FTIR); it is evident that doping the ATH with SA helps to improve the thermal stability via synergistic effect, by extending the ATH decomposition process over a wider temperature range. As a result, the UPR filled with SA/ATH hybrid demonstrates higher thermal stability when compared to the composites filled with only ATH or SA. Furthermore, the SA/ATH hybrid also provides sufficient flame retardancy in UPR as evaluate by ASTM D635-14 (UL–94) horizontal burning test. For mechanical properties, a sharp increase in tensile strength was observed for UPR filled with ATH or SA while the addition of SA/ATH hybrid filler only slightly increases the tensile properties of UPR due to particle agglomerations and porosities.

The protection of the human muscle-skeletal system from the rapid degradation needs high corrosion resistance biocompatible scaffold materials. Based on this factor, this paper reports the surface morphology, structure and corrosion resistive traits of some multi-walled carbon nanotubes (MWCNTs) coated porous Ti-30 at.%-Ta shape memory alloys (hereafter coded as MWCNT-TTSMAs). The electrophoretic deposition (EPD) technique at various applied voltages was used to coat these alloys with MWCNTs. The structures and morphologies of the prepared samples were characterized at room temperature using the X-ray Diffraction (XRD), energy dispersive spectroscopy (EDS), Raman spectroscopy, Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM) and Transmission Electron Microscope (TEM) measurements. In addition, the corrosion resistance of the coated alloys was assessed via electrochemical impedance spectroscopy (EIS) in the simulated body fluid (SBF) solution. The thickness (increased from 10.05 to 25.93 μm), surface roughness (increased from 1.38 to 1.95 μm) and homogeneity of the coating was significantly affected by the increase in the applied voltages (0 to 50 V). The corrosion rate of the optimum coated specimens was 10 fold lower (0.0966 mm/year) compared to the uncoated one (0.9403 mm/year). The hydrophilic nature of the proposed MWCNT-TTSMAs affirmed their osseointegration potential to support the cell attachments. The mean water contact angle (WCA) of the coated samples indicated a hydrophilic surface with a value of 22° ± 6 compared to the uncoated sample that exhibited a hydrophobic surface with the WCA value of 96°. Thus, the surface of the MWCNTs tends to be hydrophilic, resulting in an improved surface wettability. Antibacterial activity test exhibited that TTSMAs presented minimal inhibition area toward Escherichia coli (E. coli), in contrast, using the MWCNT has shown an improvement in antibacterial performance.

Nanostructured composite ceramic coatings consisting of Al2O3–13%TiO2 and Al2O3–13%TiO2/TiO2 on NiCoCrAlYTa-coated Mg alloys were sprayed using the atmospheric plasma spraying method. The composition and microstructure of the coated samples were investigated by XRD and FESEM equipped with EDS. Corrosion and wear behaviours of the coated samples were also evaluated. The results showed that Al2O3–13%TiO2/TiO2 coating is able to reduce the anodic dissolution of the Mg alloy in chloride solutions compared to other samples. The surface of the Al2O3–13%TiO2/TiO2 coating with the lowest wear rate exhibited a typical mild wear mode with narrow wear tracks along with very few small transferred particles. This observation was mainly related to the dense structure of the TiO2 coating, which could reduce severe spalling within the splats during the wear test.