Chemieal Synthesis and Magnetie Properties of Nanocrystalline （La0.67-XGdx）Sr0.33MnO3 Using Amorphous Molecular Alloy as Precursors

A new route to synthesize nanosized crystalline of （La0.67-xGdx）Sr0.33MnO3 （X=0.05, 0.10, 0.15, 0.20） perovskite-type complex oxides at calcination temperature of 600-1000℃ using the amorphous molecular alloy as precursors was reported. The precursor could be completely decomposed into complex oxide at temperature below 500℃ according to the TGA and DTA results. XRD demonstrates that the decomposed species is composed of perovskite-type structure at calcination temperature of 600℃ for 2 h. The particle size that depends on the calcination temperature of the precursor is in a range of 30-120 nm as determined by transmission electron microscopy （TEM）. This method is effective and can be easily quantitatively controlled to synthesize nanosized perovskite-type complex oxides. The magnetic properties of （La0.67 xGdx）Sr0.33MnO3 nanocrystalline were preliminary studied.     

Fabrication, Structures and Properties of Quasi One-dimensional ZnO Toothed- nanostructures

Uniform ZnO toothed-nanobelts and nanocombs were fabricated respectively through pure zinc powder evaporation without catalyst at temperature of 600-650℃. Scanning electron microscopy （SEM） and high-resolution transmission electron microscopy （HRTEM） observations show that such ZnO nanostructures have several types in morphology, and all of them are single crystalline. The experimental results reveal that the growth of the ZnO nanostructures was controlled by vapor-solid mechanism. Room temperature photoluminescence spectra of the toothed-nanobelts show a UV emission at - 390 nm and a broad green emission with 4 subordinate peaks at 455-495 nm.     

Effect of pre-heating temperature on structural and optical properties of sol-gel derived Zn<Subscript>0.8</Subscript>Cd<Subscript>0.2</Subscript>O thin films

Zn_0.8Cd_0.2O thin films prepared using the spin-coating method were investigated. X-ray diffraction, scanning electron microscopy, and UV-Vis spectrophotometry were employed to illustrate the effects of the pre-heating temperature on the crystalline structure, surface morphology and transmission spectra of Zn_0.8Cd_0.2O thin films. When the thin films were pre-heated at 150 °C, polycrystalline ZnO thin films were obtained. When the thin films were pre-heated at temperatures of 200 °C or higher, preferential growth of ZnO nanocrystals along the c-axis was observed. Transmission spectra showed that thin films with high transmission in the visible light range were prepared and effective bandgap energies of these thin films decreased from 3.19 eV to 3.08 eV when the pre-heating temperature increased from 150 °C to 300 °C.     

Decorating multiwalled carbon nanotubes with zinc oxide nanoparticles by thermally decomposing Zn-oleate in an organic medium

Carbon nanotubes decorated with zinc oxide nanoparticles were produced by thermally decomposing a Zn-oleate complex in an octadecene medium. The structure of the ZnO decorating nanotube surfaces was characterized by transmission electron microscopy, scanning electron microscopy and X-ray diffraction. The surfaces were shown to be densely and homogeneously covered by ZnO nanoparticles with a size below 10 nm. The nanoparticles had the wurtzite hexagonal crystal structure and showed good adhesion to the nanotubes. The carbon nanotubes decorated by metal oxide nanoparticles were synthesized at relatively low temperature and non-oxidation environment. Moreover, the large-scale production with low cost can be realized.     

Controlled growth and photoluminescence of highly oriented arrays of ZnO nanocones with different diameters

Large-scale oriented ZnO nanocone arrays were directly grown on zinc substrate through a hydro-thermal reaction of Zn foil with aqueous butylamine solution(3 mol/L) at 100—180 ℃ for 12 h.The syn-thesized products were characterized with X-ray diffraction,Raman spectrum,scanning electron mi-croscopy and transmission electron microscopy.The results showed that the ZnO nanocones were single crystalline with the wurtzite structure and grown along the [0001] direction.The diameter of nanocones is decreased with ...     

Fabrication of High Nano-ZnO Assembled Cotton Fabric with UV Blocking Property

In order to fabricate a novel ZnO/cotton composite, a high proportion of ZnO nanoparticles were assembled in cotton fibers, and the as-obtained cotton fabric can possess better UV blocking property compared with common ZnO/cotton composite. Firstly, the cotton fibers were pre-treated by hydrogen peroxide solution(H_2 O_2) and sodium hydroxide(NaOH), urea(CON_2 H_4). Secondly, the fabric was fabricated via in situ deposition. The effects of concentration of treatment liquid, ammonia-smoking time and curing temperature on the tensile property of the fabric, UV blocking property and water-washing durability test of as-obtained cotton fabrics were investigated. Thirdly, the as-obtained cotton sample was characterized by X-ray diffraction(XRD) and field emission scanning electron microscopy(FESEM). It was shown that ZnO nanoparticles were assembled between cotton fibers, the surface and inside of the lumen and the mesopores of cotton fibers, while the content of nano-ZnO assembled in fabric can reach 15.63 wt%. It is proved that the finished fabric can obtain a very excellent UV blocking property, under the condition of zinc ion in concentration of 15 wt%, ammonia-smoking time for 10 min, curing temperature at 150 ℃ for 2 min.     

Controlled synthesis of CuO nanoparticles by TritonX-100-based microemulsions

CuO nanoparticles were synthesized by using microreactors made of Triton X-100/n-hextnol/cyclohexane/water W/O microemulsion system. Basic synthesis parameters were determined. The results of thermo gravimetric/differential thermal analysis(TG/DTA) of the precursor products indicated that the proper calcination temperature was about 500 ℃. The nanoparticles were characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM) and UV-visible spectra. It was indicated that the grain size was highly dependent on the ratio of water to surfactant(R). With the R value increasing, the particles size became larger.     

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100°C–800°C and 900°C conditions. After the fracture failure, the microstructure, oxide film, and precipitated phases were analyzed using optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In both atmospheres, increasing the maximum temperature from 800°C to 900°C results in lower strength and fatigue life and higher elongation and grain size. At the same maximum temperature, the thermal fatigue life of the specimen is lower in the synthetic exhaust gas than in the air. Both the higher maximum temperature and the synthetic exhaust gas facilitate fatigue failure. The failure mechanism is discussed according to the grain size, thermal stress, high-temperature oxidation rate, and the precipitation of secondary phases. Some precipitated carbides play an important role in the rapid fatigue failure of specimens in the synthetic exhaust gas.

     

Preparation of Rod-like Aluminum Doped Zinc Oxide Powders by Sol-gel Technique Using Metal Chlorides and Acetylacetone Precursors

Al-doped ZnO(AZO) powders were prepared by using metal chloride precursors and the sol-gel technique. IR peaks observed at 1590 cm-1 and 1620 cm~(-1) indicated the formation of metal chelate as a consequence of the addition of acetylacetone to the metal chloride solution. TG-DSC analysis of the AZO gels confirmed the formation of metal chelate as evidenced by the development of several weight loss peaks accompanied by the introduction of new endothermic peaks. The resulting AZO gels were annealed at 500, 600, and 800 ℃ to study the effect of annealing temperature. XRD and SEM results showed that crystallization of AZO gels takes place around 600 ℃. Hexagonal wurtzite structure was identified as the main phase for all the samples. In addition, small shift of the XRD(002) peak coupled with XPS results from the AZO powders confirmed the successful doping of the ZnO powders. Micron sized rod-like AZO powders were uniform in dimension and morphology and remained stable even at 800 ℃.     

Coprecipitation preparation and voltage sensitive characteristics of doped ZnO varistor

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Effects of annealing on microstructure, mechanical and electrical properties of AlCrCuFeMnTi high entropy alloy

The multi-component A1CrCuFeMnTi high entropy alloy was prepared using a vacuum arc melting process. Serial annealing processes were subsequently performed at 590 ℃, 750 ℃, 955 ℃ and 1 100 ℃ respectively with a holding time of 4 h at each temperature. The effects of annealing on microstructure, mechanical and electrical properties of as-cast alloy were investigated by using differential thermal analysis （DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that two C14 hexagonal structures remain unchanged after annealing the as-cast A1CrCuFeMnTi alloy specimens being heated to 1 100℃. Both annealed and as-cast microstructures show typical cast-dendrite morphology and similar elemental segregation. The hardness of alloys declines as the annealing temperature increases while the strength of as-cast alloy improves obviously by the annealing treatment. The electrical conductivities of annealed and as-cast alloys are influenced by the distribution of interdendrite re~ions which is rich in Cu element.     

Preparation and characterization of copper-nickel bulk nanocrystals

Copper-nickel nanoparticle was directly prepared by flow-levitation method(FL) and sintered by vacuum sintering of powder(VSP) method. Several characterizations, such as transmission electron microscopy(TEM), scanning electron microscopy(SEM), X-ray diffraction(XRD), differential thermal analysis(DTA), and energy-dispersive X-ray spectroscopy(EDX) were used to investigate the prepared nanostructures. The results of the study show that FL method could prepare high purity Cu-Ni nanocrystals of uniform spheres with size distribution between 20 and 90 nm. After sintering the bulk nanocrystalline copper-nickel has obvious thermal stability and the surface Webster hardness increases with the rising sintering temperature. At the temperature of 900 ℃, the specimen shows higher surface Webster hardness, which is about two times of traditional materials. When the sintering temperature arrives at 1 000 ℃ the relative density of bulk nanocrystals can reach 97.86 percent. In this paper, the variation tendency of porosity, phase and particles size of bulk along with the changing of sintering temperature have been studied.     

Synthesis of carbon nanotubes using Cu-Cr-O as catalyst by chemical vapor deposition

A novel powder catalyst Cu-Cr-O applied to the synthesis of carbon nanotubes(CNTs) was developed, which was prepared via ammonia precipitation method. Techniques of thermo-gravimetric/ differential scanning calorimeter(TG-DSC), X-ray diffraction(XRD) as well as scanning electron microscopy(SEM) and transmission electron microscopy(TEM) have been employed to characterize the thermal decomposition procedure, crystal phase and micro structural morphologies of the as-synthesized materials, respectively. The results show that carbon nanotubes are successfully synthesized using Cu-Cr-O as catalyst when the precursors are calcined at 400, 500, 600, and 700 ℃. The results indicate that the calcination of the Cu-Cr-O catalyst at 600 ℃ is an effective method to get MWCNT with few nano-tube defects or amorphous carbons.     

Synthesis of n-alkane mixture microcapsule and its application in low-temperature protective fabric

We investigated synthesis and characterization of melamine-urea-formaldehyde(MUF) microcapsules containing n-alkane mixture as phase change core material for thermal energy storage and low-temperature protection. The phase change microcapsules(microPCMs) were prepared by an in situ polymerization using sodium dodecyl sulfate(SDS) and polyvinyl alcohol(PVA) as emulsifiers. Surface morphology, particle size, chemical structure, and thermal properties of microPCMs were, respectively, characterized by using scanning electron microscopy(SEM), field emission scanning electron microscopy(FESEM), Fourier transform infrared spectroscopy(FT-IR), differential scanning calorimetry(DSC), and thermal gravimetric analysis(TGA). Low-temperature resistance performances were measured at-15,-30,-45, and-60 ℃ after microPCMs were coated on a cotton fabric by foaming technology. The results showed that spherical microPCMs had 4.4 μm diameter and 100 nm wall thickness. The melting and freezing temperatures and the latent heats of the microPCMs were determined as 28.9 and 29.6 ℃ as well as 110.0 and 115.7 J/g, respectively. Encapsulation of n-alkane mixture achieved 84.9 %. TGA analysis indicated that the microPCMs had good chemical stability below 250 ℃. The results showed that the microencapsulated n-alkane mixture had good energy storage potential. After the addition of 10 % microPCMs, low-temperature resistance duration was prolonged by 126.9%, 145.5%, 128.6%, and 87.5% in environment of-15,-30,-45 and-60 ℃, respectively as compared to pure fabric. Based on the results, phase change microcapsule plays an effective role in lowtemperature protection field for the human body.     

Effect of silver growth temperature on the contacts between Ag and ZnO thin films

Highly c-axis oriented ZnO thin films were deposited on Si substrates by the pulsed laser deposition (PLD) method. At different growth temperatures, 200 nm silver films as the contact metal were deposited on the ZnO thin films. The growth temperatures have great influence on the crystal quality of Ag films. Current-voltage characteristics were measured at room temperature. The Schottky contacts between Ag and ZnO thin films were successfully obtained when silver electrodes were deposited at 150°C and 200°C. Ohmic contacts were formed while the growth temperatures were lower than 150°C or higher than 200°C. After analysis, the forming of Ag/ZnO Schottky contacts was shown to be dependent on the appearance of the p-type inversion layer at the interface between Ag and ZnO layers.     

Synthesis of refractory cordierite from calcined bauxite, talcum and quartz

A cordierite was synthesized from calcined bauxite, talcum, and quartz. The properties and microstructure of the cordierite sintered samples were characterized by Archimedes’ method, thermal dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), and so on. The experimental results showed that calcined bauxite could broaden the range of synthesizing temperature from 1300 °C to 1420 °C and get pure cordierite. The bulk density and linear thermal expansion coeffi cient of the sample synthesized at 1420 °C for 2 h were 1.97 g·cm^?3 and 2.1×10^?6 °C^?1, respectively. The XRD analysis showed that the major crystalline phase was α-cordierite with almost no glassy matters, the SEM images illustrated a small vent hole and the size were 5–100 μm, the well-grown hexagonal and granular cordierite grains had the sizes distributed among 0.1–8 μm, and providing high mechanical strength and lower linear thermal expansion coeffi cient.     

Au modified ZnO nanowires for ethanol gas sensing

We demonstrated the application of sensors for ethanol gas detection.The ZnO nanowires based sensors with interdigital electrodes were fabricated,and a platform was constructed to test the properties of the sensors.To acquire better response and shorter response/recovery time,the ZnO nanowires were modified with Au.The ethanol gas sensing performance of the pure sensors and those modified with Au nanoparticles were investigated for comparison,and the optimal test temperature of 350℃ was obtained.We found that the response/recovery time for the modified sensor towards 500 ppm of the ethanol gas was reduced by 1.35 and1.42 times compared with the pure sensors,and the sensitivities towards 500 and 10 ppm of the ethanol gas were also increased by 3.18 and 1.35 times,respectively.These proved the enhancement of the Au nanoparticles in the ZnO nanowires based sensors for ethanol gas sensing.     

Low temperature synthesis of SiCN nanostructures

Silicon carbon nitride (SiCN) nanowires, nanorods and nanotubes have gained much attention due to their excellent field emission and photoluminescence properties. These nanostructures were usually grown using catalysts at high temperature (800―1000℃). In this paper, synthesis of SiCN nanostruc-tures at a temperature less than 500℃ is reported. Various kinds of SiCN nanostructures were synthe-sized using microwave plasma chemical vapor deposition method. Gas mixtures of CH4, H2 and N2 were used as precursors and Si chips were inserted in the sample holder at symmetrical positions around the specimen as additional Si sources. Metallic gallium was used as the liquid medium in a mechanism similar to vapor-liquid-solid. Morphologies of the resultant were characterized by field emission scan-ning electron microscopy. Energy dispersive spectrometry and X-ray photoelectron spectroscopy were used to characterize their compositions and bonding states.     

Controlled growth of ZnO nanorods by polymer template and their photoluminescence properties

A large amount of one-dimensional ZnO nanorods with diameters in 15―50 nm aligned in radial cluster were successfully synthesized by polar polymer polyvinyl alcohol (PVA) as soft-template. The growth of ZnO nanorods was controlled by changing annealing temperature. The evolution of the morphology and microstructure was investigated by scanning electron microscope, transmission electron micro- scope and X-ray diffraction. It is shown that ZnO nanorods tend to be uniform and the crystallization is gradually i...     

Influences of heat treatments on crystallization in SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-K<Subscript>2</Subscript>O-F glass-ceramics

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO2-Al2O3-MgO-K2O-F glass ceramics samples.The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques.The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 ℃ for 3 h.The phase separation can accelerate the precip...