Microstructural evolutions of nickel-aluminide nanocomposites during powder synthesis and thermal spray processes

The synthesis and microstructural evolutions of the NiAl-15 wt% (Al₂O₃–13% TiO₂) nanocomposite powders were studied. These nanocomposite powders are used as feedstock materials for thermal spray applications. These powders were prepared using high and low-energy mechanical milling of the Ni, Al powders and Al₂O₃–13% TiO₂ nanoparticle mixtures. High and low-energy ball-milled nanocomposite powders were also sprayed by means of high-velocity oxy fuel (HVOF) and air plasma spraying (APS) techniques respectively. The results showed that the formation of the NiAl intermetallic phase was noticed after 8 h of high-energy ball milling with nanometric grain sizes but in a low-energy ball mill, the powder particles contained only α-Ni solid solution with no trace of the intermetallic phase after 25 h of milling. The crystallite sizes in HVOF coating were in the nanometric range and the coating and feedstock powders showed the same phases. However, under the APS conditions, the coating was composed of the NiAl intermetallic phase in the α-Ni solid solution matrix. In both of the nanocomposite coatings, reinforcing nanoparticles (Al₂O₃–13% TiO₂) were located at the grain boundaries of the coatings and pinned the boundaries, therefore, the grain growth was prohibited during the thermal spraying processes.     

Cu2O-Au nanocomposites with novel structures and remarkable chemisorption capacity and photocatalytic activity

The decomposition of CuH nanoparticles in aqueous solution has been successfully developed as a novel method for the preparation of Cu₂O nanoparticles. In particular, we found that the decomposition of CuH nanoparticles in aqueous solution could be catalyzed by Au colloids, forming Cu₂O-Au nanocomposites. The composition and structure of the resulting Cu₂O-Au nanocomposites have been characterized in detail by inductively coupled plasma atomic emission spectroscopy, powder X-ray diffraction, N₂ adsorption-desorption isotherms, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Their visible-light-driven photocatalytic activity toward various dye molecules has also been investigated. Depending on the Au:Cu ratio, Cu₂O-Au nanocomposites exhibit different novel nanostructures including a beautiful flower-like nanostructure that consists of polycrystalline Cu₂O, amorphous Cu₂O and Au colloids. We propose that the rapidly-generated bubbles of H₂ during the course of the catalytic decomposition reaction drive the simultaneously-formed Cu₂O to form amorphous curved thin foils and might also act as a template to assemble curved thin foils of amorphous Cu₂O, polycrystalline Cu₂O and Au colloids into uniform nanostructures. A Cu₂O-Au nanocomposite with a Cu:Au ratio of 40 exhibits remarkable chemisorption capacity and visible-light-driven photocatalytic activity towards methyl orange and acid orange 7 and is a promising chemisorption-photocatalysis integrated catalyst. The catalytic decomposition of the metal hydride might open up a new approach for the fabrication of other metal/metal oxide nanocomposites with novel nanostructures and properties.      

An investigation of thermal decomposition of β-FeOOH nanowire arrays assembled in AAO templates

β-FeOOH nanowire arrays were assembled into porous anodized aluminum oxide (AAO) templates by electrochemical deposition in the mixture solution of FeCl₃ and (NH₄)₂C₂O₄. In order to obtain well-crystallized α-Fe₂O₃ and other iron oxides nanowires, β-FeOOH nanowire arrays with amorphous crystal structure were heat-treated at different temperatures from 200 to 600 °C. The decomposition products were characterized by DTA, XRD, FTIR, and Mössbauer spectroscopy. When heat-treated at 200 °C, only 65% of β-FeOOH decomposed, whereas, when the temperature was up to 300 °C, it was completely decomposed and formed poorly crystallized β-Fe₂O₃. This transition temperature is higher than the 200 °C obtained on other β-FeOOH materials. However, when heated above 300 °C, the main products are characterized as poorly crystallized α-Fe₂O₃ nanowires, whereas, well-crystallized α-Fe₂O₃ nanowire arrays can be formed when the temperature was up to 600 °C, and this temperature is also higher compared with those temperatures observed on other β-FeOOH materials. From Mössbauer results, the α-Fe₂O₃ nanowires were composed of fine particles in which 66% of the particles are superparamagnetic.     

Shape-controlled synthesis of CaSnO3 micro crystals via a precursor route

Well-crystallized CaSnO₃ micro crystals were successfully synthesized by a simple precursor method. Detailed investigation revealed that the product morphology was predestined by the precursor's morphology. By carefully choosing the experimental conditions, CaSnO₃ micro crystals with cubic and eight-horn shape could be selectively prepared. Thermolgravimetric analysis (TGA) and powder X-ray diffraction (XRD) analysis helped greatly in identifying the stage of the phase transformation. The morphologies have been characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). On the basis of the experiment results, a possible mechanism of the morphology control was also proposed.     

Enhanced antibacterial activity and mechanism studies of Ag/Bi2O3 nanocomposites

In this work, sphere-like Ag/Bi₂O₃ nanocomposites with the average size of ca. 170?nm were successfully synthesized by simple deposition-precipitation method. The antibacterial activities of as-prepared Ag/Bi₂O₃ nanocomposites were evaluated by minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and colony counting methods. It was found that Ag/Bi₂O₃ nanocomposites displayed greatly improved antibacterial ability against common pathogenic Gram-positive and Gram-negative bacteria in comparison with single-component Bi₂O₃ nanospheres. More importantly, Ag/Bi₂O₃ nanocomposites exhibited remarkably outstanding antibacterial activities against clinical drug-resistant bacteria. The antibacterial activity of Ag/Bi₂O₃ nanocomposite increased with the increase of Ag content and 15?wt% Ag/Bi₂O₃ nanocomposites showed the highest antibacterial activity. Furthermore, a plausible antibacterial mechanism of Ag/Bi₂O₃ nanocomposite was proposed. It was believed that the enhanced generation of H₂O₂ could lead to the membrane leakage of cytosol and the inactivation of respiratory chain dehydrogenaes, which was possibly responsible for the enhanced antibacterial activities of nanocomposites.     

Structural characterization, thermal and mechanical properties of polyurethane/CoAl layered double hydroxide nanocomposites prepared via in situ polymerization

Dodecyl sulfate (DS), one kind of sulfate anion, was intercalated in the interlayer space between CoAl layered double hydroxide (CoAl-LDH) layers, and then polyurethane (PU) based nanocomposites were prepared by in situ intercalation polymerization with different amounts of the organo-modified CoAl-LDH. An exfoliated dispersion of CoAl-LDH layers in PU matrix was verified by the disappearance of the (0 0 3) reflection of the XRD results when the LDH loading was less than 2.0 wt%. Tensile testing indicated that excellent mechanical properties of PU/LDH nanocomposites were achieved. The weak alkaline catalysis of DS to polyurethane chains, combined with the dehydration and structural degradation of the LDH below 300 °C, accounted for the process of proceeded degradation as shown in TGA results. The real-time FTIR revealed that the as-prepared nanocomposites had a slower thermo-oxidative rate than neat PU from 160 °C to 340 °C, probably due to the barrier effect of LDH layers. These results suggested potential applications of CoAl-LDH as a promising flame retardant in PUs.     

Structure-solubility relationship and thermal decomposition of furosemide

Furosemide, a high ceiling diuretic, decomposes on heating and is very sparingly soluble in water. The aim of this study was to identify the thermal decomposition product(s) of furosemide and to calculate the activation energy needed for this reaction. This was done to gain a better understanding of the unusually low water solubility of this drug. The main thermal decomposition product was identified by nuclear magnetic resonance (NMR), mass spectrometry (MS), and infrared (IR) analysis as 4-chloro-5-sulfamoylanthranilic acid (saluamine), and the activation energy, calculated from thermogravimetric analysis (TGA) measurements, for this reaction was 47.7 (±1.93) kcal/mol. The experimentally measured activation energy was well below the normal 59 ± 4 kcal/mol needed for the cleavage of the C-N bond to form saluamine. This could possibly be explained by the weakening of the C-N bond through the I-effect of the furane ring and the delocalization of the electrons of the aniline nitrogen in the chlorosulfamoyl benzoic acid entity of furosemide. This decomposition of furosemide indicates the breaking of intramolecular bonds before those of intermolecular bonds (separation of individual furosemide molecules). Strong inter- and intramolecular bonds are a probable cause for the poor water solubility of furosemide because, when some of the inter- and intramolecular bonds that form part of the hydrogen bond network disappeared, as in the structurally related decomposition product saluamine, the aqueous solubility increased.     

VOC2O4·H2O热分解制备纳米VO2粉体及相变特性

提出了一种采用草酸氧钒(VOC2O4·H2O)热分解制备纳米VO2的方法.通过热分析(TG-DSC)、XRD和TEM手段,分析了草酸氧钒前驱体的热分解过程,纳米VO2的结构和形貌,测定了纳米VO2粉体的电阻-温度曲线.实验结果表明VOC2O4·H2O热分解开始温度为343℃,在380℃,真空度为20～50Pa的条件下,热分解获得VO2的平均尺寸为22nm,相变温度为69℃.     

An investigation of the synthesis,consolidation and mechanical behaviour of Al 6061 nanocomposites reinforced by TiC via mechanical alloying

Nanostructured Al 6061–x wt.% TiC (x = 0.5, 1.0, 1.5 and 2.0 wt.%) composites were synthesised by mechanical alloying with a milling time of 30 h. The milled powders were consolidated by cold uniaxial compaction followed by sintering at various temperatures (723, 798 and 873 K). The uniform distribution and dispersion of TiC particles in the Al 6061 matrix was confirmed by characterising these nanocomposite powders by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The mechanical properties, specifically the green compressive strength and hardness, were tested. A maximum hardness of 1180 MPa was obtained for the Al 6061–2 wt.% TiC nanocomposite sintered at 873 K, which was approximately four times higher than that of the Al 6061 microcrystalline material. A maximum green compressive strength of 233 MPa was obtained when 2 wt.% TiC was added. The effect of reinforcement on the densification was studied and reported in terms of the relative density, sinterability, green compressive strength, compressibility and Vickers hardness of the nanocomposites. The compressibility curves of the developed nanocomposite powders were also plotted and investigated using the Heckel, Panelli and Ambrosio Filho and Ge equations.     

Synthesis of TiO2 nanotubes coupled with CdS nanoparticles and production of hydrogen by photocatalytic water decomposition

The CdS/TiO₂NTs composite was prepared by a simple two-step chemical solution routes to directly transfer trititanate nanotubes to TiO₂NTs and simultaneously coupled with CdS nanoparticles. The results of XRD, TEM, Diffuse reflectance UV-Visible absorption spectra revealed that the CdS nanoparticles were homogeneously embedded on the surface of TiO₂NTs and the absorption spectrum of TiO₂NTs was extended to visible region. The activity of hydrogen production by photocatalytic water decomposition for the CdS/TiO₂NTs composite was examined under visible light irradiation (λ > 400 nm) and the quantity of H₂ evolution was ca. 1708 μL/g for 6 h.     

The excellent photocatalytic activity of novel Cs3PW12O40/WO3 composite toward the degradation of rhodamine B

In this paper, a simple one-pot thermal decomposition method was successfully used to synthesize a novel Cs₃PW₁₂O₄₀/WO₃ composite for the first time. The synthesized composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), FTIR, diffuse reflectance spectroscopy (DRS) and N₂ adsorption-desorption techniques. The photocatalytic activity to degrade RhB molecules over Cs₃PW₁₂O₄₀/WO₃ composite was evaluated under xenon light irradiation. The results indicated the complete degradation of RhB molecules over Cs₃PW₁₂O₄₀/WO₃ composite after 30?min irradiation. However, the photocatalytic degradation of RhB over WO₃ and Cs₃PW₁₂O₄₀ after 80?min light irradiation are nearly 52%, and 68%, respectively. The enhanced photocatalytic activity of Cs₃PW₁₂O₄₀/WO₃ composite compared with WO₃, and Cs₃PW₁₂O₄₀ was ascribed to the strong interaction between WO₃ and Cs₃PW₁₂O₄₀, which effectively reduces the recombination of photogenerated electron-hole pairs. Based on experimental results, the possible mechanism of photocatalytic reactions on the Cs₃PW₁₂O₄₀/WO₃ composite photocatalyst was investigated, and the hydroxyl radical (OH) and superoxide radical (O₂^?) were determined as the main active species in the photocatalytic degradation of RhB over Cs₃PW₁₂O₄₀/WO₃ composite.     

Study of thermal decomposition of methyl ethyl ketone peroxide using DSC and simulation

Methyl ethyl ketone peroxide (MEKPO) is a typical organic peroxide with thermally unstable nature that has been broadly employed in the manufacturing process of acrylic resins, as a hardening agent for fiberglass-reinforced plastics, and as a curing agent for unsaturated polyester resins. The aim of this study was to identify the characteristics of MEKPO 31 wt.% while mixing with contaminants, such as H(2)SO(4), HCl, and NaCl under runaway conditions. To acquire the thermal runaway data, DSC and a simulation were used for thermal analysis. The results showed that the thermal decomposition of MEKPO and MEKPO+H(2)SO(4) follows two stages. The first one can be modeled by using an empirical nth order rate equation. The second stage can be modeled as autocatalytic. MEKPO+HCl and MEKPO+NaCl included two independent autocatalytic reactions. The decomposition of MEKPO in the presence of Cl- ions (added in MEKPO either in the form of HCl or NaCl) follows a significantly different path, an earlier decomposition "onset" temperature, higher amount of generated thermal power and smaller temperature of no return (T(NR)) and time to maximum rate (TMR) values. Simulations based on experimental data indicated that the effect of H(2)SO(4) was the most dangerous contaminant on MEKPO 31 wt.%. However, the impact of Cl ions was also important. It is therefore recommended that the means of fire fighting employed for this substance to be free of Cl-.     

Improved photocatalytic activity of zeolite- and silica-incorporated TiO2 film

Porous TiO2 film was prepared by sol-gel method from TiO2 sol containing polyvinylpyrolidone (PVP). Photocatalytic activity of the film was evaluated by the elimination rate of ethylene. Several adsorbents including zeolite and silica powders were incorporated into the TiO2 film. All the adsorbents enhanced the activity. The optimum adsorbent content was 0.005-0.01 g/ml of the coating sol solution. Silica provided better activity than zeolite. At high humidity and in dry air the activity decreased.     

Facile synthesis and characterization of novel nanocomposites of titanate nanotubes and rutile nanocrystals

The nanocomposites of one-dimensional (1D) titanate nanotubes and 0D rutile nanocrystals were fabricated by hydrothermal treatment of bulky rutile TiO₂ powders in a 10 M NaOH solution without using any templates and catalysts. The as-prepared samples were characterized with transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, Fourier transform infrared spectroscopy (FTIR), UV–visible spectrophotometry (UV–vis), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that many small rutile nanocrystal particles of about 5 nm could uniformly attach to the outer surface and in the inner of the titanate nanotubes, forming an interesting and novel nanocomposite structure. Adjusting reaction time could control the amount of rutile nanoparticles in the nanocomposites. With increasing reaction time, the specific surface areas, porosity, pore volume, UV absorption and band gap energies of the nanocomposites gradually increased due to the fact that rutile particles were steadily turned into the tubular nanocomposites, finally completely formed titanate nanotubes.     

Tensile fracture and thermal conductivity characterization of toughened epoxy/CNT nanocomposites

Rubber toughened epoxy/CNT nanocomposites were manufactured at different weight percents between 0 and 1% of multiwall carbon nanotube (MWNT) using a high intensity ultrasonic liquid processor with a titanium probe. Mechanical properties of manufactured dog bone samples were measured in tension and the results indicated a maximum of 23% increase in the elastic modulus at 0.6% by weight of MWNT. However, the fracture strength showed a maximum decrease of about 11% as a function of increasing MWNT loading. Scanning Electron Microscopy (SEM) images from the neat samples revealed a distinct circular pit at the top left edge of the specimen with an overall tearing deformation causing the fracture paths. Comparatively, all nanocomposite samples on an average seemed to show a prominent brittle fracture with little or no evidence of circular pit formation. The amount of tearing deformation seemed to be enhanced in the nanocomposite specimens as compare to the neat ones. Finally, Transmission Electron Microscopy images indicated that different states of dispersion exist in all of the nanocomposite samples. The data showed that agglomeration of nanotubes increases as a function of weight percent. In addition to mechanical property characterization, thermal conductivity of all the samples was determined as a function of temperature between 30 °C and 100 °C using the 3ω method. The tested samples showed an almost 16% increase in thermal conductivity. The minimal enhancement in thermal conductivity has been analyzed from the standpoint of the Effective Medium Theory. Interfacial thermal resistances exhibit no order of magnitude changes explaining the conductivity results.     

Silica coating onto graphene for improving thermal conductivity and electrical insulation of graphene/polydimethylsiloxane nanocomposites

Graphene possess extremely high thermal conductivity, and they have been regarded as prominent candidates to be used in thermal management of electronic devices. However, addition of graphene inevitably causes dramatic decrease in electrical insulation, which is generally unacceptable for thermal interface materials(TIMs) in real electronic industry. Developing graphene-based nanocomposites with high thermal conductivity and satisfactory electrical insulation is still a challenging issue. In this study,we developed a novel hybrid nanocomposite by incorporating silica-coated graphene nanoplatelets(Silica@GNPs) with polydimethylsiloxane(PDMS) matrix. The obtained Silica@GNP/PDMS composites showed satisfactory electrical insulation(electrical resistivity of over 10~(13)Ωcm) and high thermal conductivity of 0.497 W m-1K-1, increasing by 155% compared with that of neat PDMS, even higher than that of GNP/PDMS composites. Such high thermal conductivity and satisfactory electrical insulation is mainly attributed to the insulating silica-coating, good compatibility between components, strong interfacial bonding, uniform dispersion, and high-efficiency heat transport pathways. There is great potential for the Silica@GNP/PDMS composites to be used as high-performance TIMs in electronic industry.     

Enhanced visible light photocatalytic activity of CeO2/alumina nanocomposite: Synthesized via facile mixing-calcination method for dye degradation

In this present study, an effort has been made to novel CeO₂/alumina nanocomposite photocatalyst was fabricated through mixing-calcination method. The XRD, IR, SEM, TEM, EDX and XPS results designated that these synthesized materials are formed effectively. The photocatalytic results for the degradation of dye solution indicate that the most dynamic ratio is CeO₂:Al₂O₃ (2.5:1) under visible light irradiation. The photocatalytic degradation was made under dark and in the presence of light to establish the photocatalytic efficiency of the synthesized photocatalyst. The improved performance of CeO₂/alumina nanocomposite is attributed to the separation efficiency of photo-induced charge carriers and it inhibit charge recombination. The major active species are determined by radical scavengers trapping experiments were revealed that superoxide radical (O₂^?) and hydroxyl radical (OH) are playing a vital role in the degradation of dye solution. The stability of catalyst was confirmed by consecutive runs of CeO₂/alumina nanocomposite.