Effect of Sm2O3 on microstructure,thermal shock resistance and thermal conductivity of cordierite-mullite-corundum composite ceramics for solar heat transmission pipeline

Cordierite-mullite-corundum composite ceramics for solar heat transmission pipeline were fabricated via pressureless sintering at a low sintering temperature with added Sm₂O₃. The effects of Sm₂O₃ on sintering behaviors, mechanical property, phase transformation, microstructure, thermal shock resistance and thermal conductivity of the composite ceramics were investigated. TEM analysis results demonstrated that Sm³⁺ located in glass and grain boundaries to facilitate the densification via the liquid-phase sintering mechanism and improve bending strength by grain refinement, respectively. Proper addition (3 wt%) of Sm₂O₃ could promote the crystallization of cordierite, and improve thermal shock resistance of the composite ceramics with an increasing rate of 16.70% for bending strength after 30 thermal shock cycles (air cooling from 1100 °C to RT). The composite ceramics possessed a superior thermal shock resistance, where a large amount of particles were formed to suppress crack initiation and propagation during thermal shock. Cordierite-mullite-corundum composite ceramics with proper Sm₂O₃ addition (3 wt%) had a lower thermal conductivity than that of composite ceramics without Sm₂O₃ addition by strengthening the scattering of phonon, which could reduce the heat loss during solar heat transmission process.     

Microstructure and fracture toughness of in-situ nanocomposite coating by thermal spraying of Ti3AlC2/Cu powder

The low fracture toughness of ceramic coatings has always hindered their wide application. In this study, an in-situ nanocomposite coating was prepared by the atmospheric plasma spraying of a 50 wt% Ti₃AlC₂-50 wt% Cu mixed powder. The in-situ nanocomposite coating was found to have an unusual microstructure with a nano-micrometre phase synergistic enhancement, which consisted of submicrometre-thick layers of Cu and nanoparticles of Cu(Al), Ti₄O₅, TiO₂, and Al₂TiO₅. Thus, in the spraying process, Al was delinked out of Ti₃AlC₂, forming a large amount of plastic Cu(Al) with Cu. The delinked channel provided a path for Cu to diffuse into Ti₃AlC₂, which a spatial Cu network structure was formed in the coating. The in-situ nanocomposite coating has high fracture toughness and crack growth resistance by a three-point bending test. This paper reports a new method to prepare a high-fracture-toughness composite ceramic coating.     

Sol-gel synthesis,spark plasma sintering,structural characterization,and thermal conductivity measurement of heavily Nb-doped SrTiO3/TiO2 nanocomposites

Heavily Nb-doped strontium titanate (SrTi_1-xNb_xO₃) nanoparticles and SrTi_1-xNb_xO₃/TiO₂ nanocomposite powders were synthesized by a sol-gel method. Structural characterization of the obtained powders was performed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV–visible spectroscopy. The powders were densified by spark plasma sintering (SPS) method up to 98% of the relative density. Upon composite production, the thermal conductivity of the un-doped samples was effectively decreased for SrTiO₃/TiO₂ nanocpmposite from 12 to 8 W/m.K. On the other hand, thermal conductivity of the Nb-doped SrTi_0.8Nb_0.2O₃/TiO₂ composite was decreased by about 50% down to 3.4 W/m.K in comparison to SrTiO₃/TiO₂ due to the phonon scattering at the point defects originated from both Nb atoms and TiO₂ nanoparticles.     

Fabrication of a TiO2/carbon nanowall heterojunction and its photocatalytic ability

A two-dimensional TiO₂/carbon nanowall composite material was fabricated by growing carbon nanowalls on a Ti sheet with hot filament chemical vapor deposition, followed by metal-organic chemical vapor deposition using titanium isopropoxide as TiO₂ precursor and argon as carrier gas. Scanning electron microscopy showed that TiO₂ was uniformly coated on the entire carbon nanowall and a TiO₂/carbon nanowall composite was obtained. Raman spectroscopy and X-ray diffraction indicated that the crystal phase of the TiO₂ coating was anatase. The asymmetry of the current-voltage plot for the material revealed that a heterojunction was formed between the TiO₂ and the carbon nanowall. As a result of this heterojunction, enhanced separation of photogenerated electrons and holes was confirmed by surface photovoltage and photocurrent measurements. The investigation of photocatalytic ability showed that the TiO₂/carbon nanowall had a higher photocatalytic activity than TiO₂ nanotubes for the degradation of phenol under UV light irradiation.     

Effect of Cu powder addition on thermoelectric properties of Cu/TiO2−x composites

Spark plasma sintering was used to fabricate Cu/TiO_2−x composites by adding Cu powder to nonstoichiometric titanium dioxide, TiO_2−x. The composition and crystal forms of the composites were examined. The thermoelectric properties of the composites were measured and the effects of composite formation on these properties were discussed. The rule of mixture (ROM) of composite and general effective medium theory (GEM) were used to investigate the composite effects of the Cu/TiO_2−x composites. The results revealed that the electrical resistivities of the composites was much lower than that of TiO_2−x. As the added amount of Cu powder increased, the electrical properties of the composites shifted from semiconductor behavior to metallic behavior. The thermoelectric performances of the composites improved as a result of composition formation. The thermoelectric performance can be improved by adjusting the balance among electrical resistivity, thermal conductivity and the Seebeck coefficient, based on the composite effects.     

Electrically conductive composites prepared from 3-methyl thiophene by the FeCl3 oxidation method

Surface conductive polyurethane films from poly(propylene glycol), toluene 2,4-diisocyanate, 3-methyl thiophene and butyltin dilaurate can be successfully prepared by the diffusion-oxidative polymerization method. Various effects of the doping conditions, such as the reaction time, the FeCl₃ concentration, the weight ratio of the 3-methyl thiophene to PU and the temperature on the electrical conductivity and thickness of the conductive layer of the 3-methyl thiophene/PU composite were investigated. Decomposition temperature rises gradually from pure undoped PU to doped composite that indicates blending took place in FeCl₃/ethyl acetate solution. As oxidative reaction time increases, the electrical conductivity of the 3-methyl thiophene doped PU film increases together with the thickness of the coating layer. With increasing FeCl₃ concentration and weight ratio of the 3-methyl thiophene to PU, the thickness of the coating layer decreases, while the electrical conductivity increases. The increase of the thickness of the PU film leads to the rise of the electrical conductivity. The thickness of the coating layer decreases, while the electrical conductivity of the 3-MT doped PU film increases with increasing reaction temperature. As the reaction time and temperature increase, the polar components of the PU film increase resulting into the increase of moisture regain value.     

SiO2 coated platy TiO2 designed for noble UV/IR-shielding materials

SiO₂ coated platy TiO₂ (S-pTi) was prepared as a noble UV/IR(Ultraviolet/Infrared)-shielding material by a modified Stöber method. S-pTi consists of a dense and uniform SiO₂ shell onto platy TiO₂ (pTi) core, and the thickness of SiO₂ shell layer was coated about 8–20 nm by tuning SiO₂ coating amount. The zeta-potential of S-pTi was decreased from −12 to −32 mV with increasing amounts of coated SiO₂, indicating the improvement of dispersibility between the particles. The UV-shielding ability of S-pTi was improved by enhancing UV absorption of the SiO₂ coating layer onto pTi and thus the photocatalytic activity was suppressed effectively. Compared to nanosized TiO₂(nTi), S-pTi showed higher UV absorption at the shorter wavelength and exhibited higher IR reflectance because of high reflective index and the crystal shape and size of pTi to reflect the IR effectively under its wide shielding area. These results can contribute to the prevention of harmful UV and the maintenance of a cool environment from IR heat source as noble UV/IR-shielding materials on the skin.     

Efficient photocatalytic degradation of methylene blue over BiVO4/TiO2 nanocomposites

BiVO₄/TiO₂ nanocomposites were successfully synthesized by coupling the modified sol-gel method with hydrothermal method. The samples were physically characterized X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer, Emmett and Teller (BET)-specific surface area, UV–vis diffuse reflectance spectrophotometry, zeta potential, and photoluminescence techniques. The BiVO₄/TiO₂ nanocomposites exhibited good photocatalytic activity in degradation of methylene blue under simulated solar light irradiation. The photodegradation of methylene blue demonstrated that 0.5BiVO₄/0.5TiO₂ photocatalyst exhibited much enhanced photoactivity than pure BiVO₄ and TiO₂. Based on the obtained results, the as-prepare BiVO₄/ TiO₂ nanocomposite possessed great adsorptivity of methylene blue, extended light adsorption range, and efficient charge separation properties. Overall, this work could provide new insights into the fabrication of a BiVO₄/TiO₂ composite as high performance photocatalyst and promise as a solar light photocatalyst for dye wastewater treatment.     

Preparation and characterization of Cr2O3-TiO2-Al2O3-V2O5 green pigment

Green pigments with high near infrared reflectance based on a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition have been synthesized. Cr₂O₃ was used as the host component and mixtures of TiO₂, Al₂O₃ and V₂O₅ were used as the guest components. TiO₂, Al₂O₃, and V₂O₅ were mixed into 39 different compositions. The spectral reflectance and the distribution of pigment powder were determined using a spectrophotometer and a scanning electron microscope, respectively. It was found that a pigment powder sample S9 with a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition of 80, 4, 14 and 2 wt%, respectively, gives a maximum near infrared solar reflectance of 82.8% compared with 49.0% for pure Cr₂O₃. The dispersion of pigment powders in a ceramic glaze was also studied. The results show that the pigment powder sample S9 is suitable for use as a coating material for ceramic-based roofs.     

Dopant‐induced microstructural,optical, and electrical properties of TiO2/PVA composite

The optical, electrical, and microstructurtal properties of pure and TiO₂/Poly(vinyl alcohol) (PVA) composite polymer films were carried out using FTIR, XRD, UV‐Visible, DC electrical conductivity, and Positron annihilation lifetime spectroscopy (PALS) techniques. The FTIR study reveals that the Ti⁺ ions of TiO₂ interacts with the OH groups of PVA via intra/inter molecular hydrogen bonding and forms charge transfer complex (CTC). These formed CTC will affect the optical property of the composite film, which is reflected from UV‐Visible study. Using the observed UV–Visible spectra, optical energy band gap is estimated and its value decreases with increasing dopant concentration. The positron annihilation studies show that the considerable effect on free volume related microstructure of the PVA due to doping and complex formation. These microstructural modifications are also enhances PVA crystallinity which is reflected from XRD studies. It is also observed that the TiO₂ particle forms cluster within the PVA due to the aggregation of particles and these particle cluster size increases with dopant concentration. These microstructural variations due to doping affects the DC electrical conductivity and its variations are understood based on the intra chain one‐dimensional interpolaron hopping conduction mechanism. POLYM. COMPOS. 37:987–997, 2016. © 2014 Society of Plastics Engineers     

Angular absorptance and thermal degradation analysis of TiB2/Ti(B,N)/SiON/SiO2 multilayer solar absorber coating

Multilayer solar selective absorber coatings have been developed in the last few decades. The thermal stability in terms of microstructure gives an insightful understanding of the optical properties of such coatings. In this context, we extensively utilized transmission electron microscopy (TEM) analysis to establish the thermal stability of TiB₂/Ti(B,N)/SiON/SiO₂ coating, under thermal cycling/continuous heating to 500°C in vacuum for 250 h. In particular, this work reports the variation in the solar absorptance of TiB₂/Ti(B,N)/SiON/SiO₂ coating with different angles of incidence of the solar radiation. Extensive analysis using the TEM technique reveals the presence of oxide interlayers that act as diffusion barrier layers to enhance the thermal stability of the coating. Computational simulation using SCOUT software validates the measured reflectance spectrum of the developed multilayer coating. The minor changes in absorptance and emissivity after heat treatment in vacuum at 500°C, together with high solar absorptance over a broad angular variation, establish the potential application of TiB₂/Ti(B,N)/SiON/SiO₂ as a selective coating in concentrated solar power systems.     

Photoactive behavior of polyacrylonitrile fibers based on silver and zirconium co‐doped titania nanocomposites: Synthesis,characterization, and comparative study of solid‐phase photocatalytic self‐cleaning

Silver and zirconium co‐doped and mono‐doped titania nanocomposites were synthesized and deposited onto polyacrylonitrile fibers via sol–gel dip‐coating method. The resulted coated‐fibers were characterized by X‐ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, diffuse reflectance spectroscopy, thermogravimetric analysis, and BET surface area measurement. Photocatalytic activity of the TiO₂‐coated and TiO₂‐doped coated fibers were determined by photomineralization of methylene blue and Eosin Y under UV–vis light. The progress of photodegradation of dyes was monitored by diffuse reflectance spectroscopy. The XRD results of samples indicate that the TiO₂, Ag‐TiO₂, Zr‐TiO₂, and Ag‐Zr‐TiO₂ consist of anatase phase. All samples demonstrated photo‐assisted self‐cleaning properties when exposed to UV–vis irradiation. Evaluated by decomposing dyes, photocatalytic activity of Ag–Zr co‐doped TiO₂ coated fiber was obviously higher than that of pure TiO₂ and mono‐doped TiO₂. Our results showed that the synergistic action between the silver and zirconium species in the Ag‐Zr TiO₂ nanocomposite is due to both the structural and electronic properties of the photoactive anatase phase. These results clearly indicate that modification of semiconductor photocatalyst by co‐doping process is an effective method for increasing the photocatalytic activity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

UV‐curable coatings with nano‐TiO2

Nano‐TiO₂ particles were first milled into butyl acetate or trimethylolpropane triacrylate (TMPTA) to obtain TSB and TST slurries, then embedded into epoxy acrylate to obtain UV‐curable coating. The influence of nano‐TiO₂ particles on the photopolymerization kinetics, tack free time, thermal and optical properties of UV‐curable coatings was investigated. It was found that TST‐based coating had a decreasing but TSB‐based coating had an increasing UV cured rate in comparison with the pristine epoxy acrylate. Nevertheless, the TST‐based coating occupied shorter tack free time, good thermal property and UV absorbance than their corresponding TSB‐based coating. POLYM. ENG. SCI. 46:1402–1410, 2006. © 2006 Society of Plastics Engineers.     

Bismuth oxide cocatalyst and copper oxide sensitizer in Cu2O/TiO2/Bi2O3 ternary photocatalyst for efficient hydrogen production under solar light irradiation

A novel Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite was prepared, in which copper oxide improves the visible light absorption of TiO₂ and bismuth oxide improves electron–hole separation. The ternary composite exhibited extended absorption in the visible region, as determined by UV–Vis diffuse reflectance spectroscopy. High-resolution transmission electron microscopy images showed close contact among the individual semiconductor oxides in the ternary Cu₂O/TiO₂/Bi₂O₃ nanocomposite. Improved charge carrier separation and transport were observed in the Cu₂O/TiO₂/Bi₂O₃ ternary composite using electrochemical impedance spectroscopy and photocurrent analysis. TiO₂ modified with bismuth and copper oxides showed exceptional photocatalytic activity for hydrogen production under natural solar light. With optimum bismuth and copper oxide loadings, the Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite exhibited an H₂ production (3678 μmol/h) 35 times higher than that of bare TiO₂ (105?μmol/h). The synergistic effect of improved visible absorption and minimal recombination was responsible for the enhanced performance of the as-synthesized ternary nanocomposite.     

The effect of UV irradiation on the electrospun PCL/TiO2 composites fibers

The effect of UV irradiation and micro‐ and nano‐TiO₂ as well as titanate nanotubes (TiNT) on the phase morphology and thermal properties of the electrospun PCL composite fibers was investigated. Polycaprolactone (PCL)/TiO₂ (micro‐ and nano‐TiO₂ as well as titanate nanotubes) composite fibers were prepared by electrospinning a polymer solution. The PCL and PCL/TiO₂ composite fibers were exposed to UV light at irradiation times of 5 and 10 days. After UV irradiation the crystallinity of the electrospun PCL/TiNTcomposite fibers increased because of the large specific surface area of TiNT. The thermal stability of the PCL/TiNT electrospun composite fibers increased due to the formation of crosslinking structure after UV irradiation. The SEM analysis suggests that after UV radiation the fibers showed high degree of degradation due to the high number of fibers breakages and fibers surface voids. The results of FTIR spectroscopy confirmed that the TiO₂ particles enhance the degradation process because of their photocatalytic activity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43539.     

Evolution of cracks within an Al2O3–40 wt%TiO2/NiCoCrAl gradient coating

In this paper, an Al₂O₃–40?wt%TiO₂/NiCoCrAl gradient coating is deposited by atmospheric plasma spraying (APS). The microstructure and element distribution of the coating are studied by scanning electron microscopy (SEM) and electron probe X-ray microanalysis (EPMA). The crack propagation behaviour in the coating under applied and thermal stress is analysed through a three-point bending test and a thermal shock test, respectively. Two rapid propagation processes of the cracks can be found during the three-point bending test, which lead to two peaks in the load-displacement curves of the gradient coating. The gradual change in the composition also has an effect on the crack propagation process within the coating. Non-directional propagation paths of cracks and the formation of oxides can be observed in the gradient region under the effect of thermal stress, which lead to the spallation failure of the coating.     

The optical properties of PVA/TiO2 composite nanofibers

The electrospun nanofibers emerge several advantages because of extremely high specific surface area and small pore size. This work studies the effect of PVA nanofibers diameter and nano‐sized TiO₂ on optical properties as reflectivity of light and color of a nanostructure assembly consisting polyvinyl alcohol and titanium dioxide (PVA/TiO₂) composite nanofibers prepared by electrospinning technique. The PVA/TiO₂ composite spinning solution was prepared through incorporation of TiO₂ nanoparticles as inorganic optical filler in polyvinyl alcohol (PVA) solution as an organic substrate using the ultrasonication method. The morphological and optical properties of collected composites nanofibers were highlighted using scanning electron microscopy (SEM) and reflective spectrophotometer (RS). The reflectance spectra indicated the less reflectance and lightness of composite with higher nanofiber diameter. Also, the reflectance and lightness of nanofibers decreased with increasing nano‐TiO₂ concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Curing and combustion properties of a PU‐coating system with UV‐reactive phosphazene

A UV‐curable polyurethane (PU)‐coating system containing phosphorus is formulated by the combination of photoinitiator, PU acrylate oligomer, and UV‐reactive phosphazene monomer. PU acrylate oligomer is prepared by the addition of 2‐hydroxyethylmethacrylate (HEMA) to NCO‐terminated PU prepolymer. UV‐reactive phosphazene monomer is derived from the HEMA substitution reaction to hexachlorocyclotriphosphazene (NPCl₂)₃. The curing reaction of this PU‐coating system is carried out by UV irradiation. The resultant UV‐cured PU‐coated films demonstrated better performance properties than those of original UV‐cured PU acrylate (UV‐PU) without UV‐reactive phosphazene monomer. Furthermore, their thermal properties are investigated by a thermogravimetric analyzer and a dynamic mechanical thermal analyzer, respectively. The combustion behaviors of these UV‐cured PU‐coated films are evaluated by the measurements of a limiting oxygen index and a cone calorimeter. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1980–1991, 2002     

Improved adhesion of TiO2‐based multilayer coating on HDPE and characterization of photocatalysis

Multilayered photocatalytic TiO₂‐based coating was prepared by spin coating on a high‐density polyethylene (HDPE) substrate. The multilayered coating consisted of a polyurethane (PU) barrier layer and two layers of TiO₂ nanoparticles bound with PU. The adhesion between the HDPE substrate and protective PU coating was enhanced by oxygen plasma treatment of the substrate. The improved adhesion contributed to the photocatalytic degradation of palmitic acid. Long‐term activity of the photocatalytic coating in degradation of palmitic acid under UV illumination was followed by FTIR‐ATR. The catalytic activity of the coating was maintained in three identical cycles where palmitic acid was added and UV‐irradiated for 6 h. According to FTIR measurements, the palmitic acid was almost completely decomposed after 6 h, but gas chromatography (GC) analysis showed total decomposition to require 12 h UV illumination (∼ 97% of palmitic acid decomposed in 12 h). Study of the degradation of palmitic acid by GC as a function of time indicated that the degradation kinetics was pseudofirst order, and the rate constant obtained was 0.31 h⁻¹. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011