Solvo-displacement route to ternary compounds Ag–M–S (M=Ga,Cu or Hg)

Ternary compounds AgGaS₂, Cu_0.8Ag_1.2S and Ag₂HgS₂ were prepared at 200 °C via a solvo-displacement route. The products were characterized with X-ray powder diffraction patterns, X-ray photoelectron spectra and transmission electron microscope images. A possible formation mechanism of solvo-displacement reaction was proposed.     

Photocatalytic activities of N-doped nano-titanias and titanium nitride

TiO₂ doped with various loadings of nitrogen was prepared by nitridation of a nano-TiO₂ powder in an ammonia/argon atmosphere at a range of temperatures from 400 to 1100 °C. The nano-TiO₂ starting powder was produced in a continuous hydrothermal flow synthesis (CHFS) process involving reaction between a flow of supercritical water and an aqueous solution of a titanium salt. The structures of the resulting nanocatalysts were investigated using powder X-ray diffraction (XRD) and Raman spectroscopy. Products ranging from N-doped anatase TiO₂ to phase-pure titanium nitride (TiN) were obtained depending on post-synthesis heat-treatment temperature. The results suggest that TiN started forming when the TiO₂ was heat-treated at 800 °C, and that pure phase TiN was obtained at 1000 °C after 5 h nitridation. The amounts and nature of the Ti, O and N at the surface were determined by X-ray photoelectron spectroscopy (XPS). A shift of the band-gap to lower energy and increasing absorption in the visible light region, were observed by increasing the heat-treatment temperature from 400 to 700 °C.     

Solid state synthesis of nano-boehmite-derived CuAlO2 powder and processing of the ceramics

The delafossite CuAlO₂ powder was prepared from the nano-boehmite AlOOH·xH₂O and Cu₂O by the solid state synthesis at 1100 °C in argon. The inherently slow solid state reaction was accelerated by introducing rod-like boehmite nano-particles which fully covered the 1 μm sized Cu₂O particles in the reactant mixture, and decomposition of the nano-boehmite upon calcination. In contrast, the reaction between the Cu₂O and Al₂O₃, introduced as a reference, resulted in mixed phases under the same experimental conditions. Sintering of the nano-boehmite derived CuAlO₂ powder compact at 1100 °C for 2 h in air resulted in the delafossite ceramic with 86% of theoretical density, without any impurities detectable by X-ray diffraction analysis. The analysis of the microstructure by scanning electron microscopy confirmed that the bulk of the sintered sample was delafossite phase with uniformly distributed porosity, with only traces of Cu-rich impurities at the surface.     

Synthesis of nanocrystalline MoSe2 by sonochemical reaction of Se with Mo(CO)6

Nanocrystalline MoSe₂ was prepared by a sonochemical reaction between Mo(CO)₆ and Se in decalin at 273 K in nitrogen atmosphere. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDXS) and thermal analysis (TG and DSC). The XRD patterns showed that the product is amorphous, while annealing at 330 °C yields nanocrystalline MoSe₂. The influence of ultrasound and temperature is discussed.     

Cu2(OH)3Cl microspheres with self-assembled nanostructures through a dissolution regulation reaction and exhibits excellent antibacterial activity

Basic copper chloride (Cu₂(OH)₃Cl) microspheres with different surface nanostructure were synthesized via the dissolution regulation of calcite in CuCl₂ solution. We studied the influence of CuCl₂ concentration, reaction time and reaction temperature on the formation of Cu₂(OH)₃Cl, and the products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The concentration of CuCl₂ has a great influence on the dissolution rate of calcite, dispersed microsphere particles assembled by nano-blocks formed in 20 mM CuCl₂ solution. The surface of Cu₂(OH)₃Cl microsphere change from nano-block to nano-rod with increasing the reaction time from 20 min to 2 h Cu₂(OH)₃Cl microspheres with surface structure changed from nano-sheet, nano-plate to nano-block with the reaction temperature increase from 37 °C to 70 °C. The Cu₂(OH)₃Cl microsphere also displays superior antibacterial properties against S. aureus and E. coli. This work displays a new strategy to synthesize functional materials by the use of dissolution regulation methods.     

Thermoelectric properties and thermal stability of metal-doped cuprous sulfide thermoelectrics

Mn doping and S-evaporation are strategies used to improve the thermoelectric properties and thermal stability of cuprous sulfide thermoelectric materials. Cu_1.8S and Mn-alloyed Cu_1.8S powders were prepared via ball milling, and different samples were obtained via current-assisted sintering at different times. It was found that Mn and S-evaporation optimized the carrier concentration and thus improved the figure of merit (ZT) of the samples. The introduction of pore defects induced by S-evaporation also improved the ZT. The maximum ZT of the optimized sample reached 0.89 at 500 °C. Mn in the samples reacted with oxygen to form an oxide film on the surface of the block, which inhibited the kinetic process of Cu_1.8S decomposition and improved the thermal stability of the samples. However, the reaction between Mn and oxygen led to a continuous loss of metal cations in the material, resulting in changes in the thermoelectric properties.     

Design of core-shell structured YSZ@Cu cermet powders with thermal conductivity anisotropy by electroless deposition

Core-shell structured cermet powders with thermal conductivity anisotropy have been brought into focus because they have a great potential application as the horizontal thermal diffusion layer material in multilayer thermal protective coating (TPC). In this contribution, core-shell structured YSZ@Cu cermet powders were fabricated by electroless deposition (ED) of Cu on yttria-stabilised zirconia (YSZ) powder. The surface of YSZ powder was uniformly coated with a thin Cu shell of approximately 2 μm. Through X-ray photoelectron spectra (XPS) analysis, it was found that trace CuO and Cu₂O oxides formed on the surface of Cu shell. Results of thermal spraying adaptability analysis show the flowability of core-shell structured YSZ@Cu cermet powder improved to 56.8 s/50 g, which conforms better to the basic requirements of thermal spraying material. By differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests, the YSZ@Cu powder had good thermal stability. In particular, between 25 and 500 °C, the anisotropy thermal conductivity rose higher than 1.8 and it remained stable at approximately 1.6 with temperature as high as 900 °C. All these features promise it a high-performance thermal conductivity anisotropy material.     

Low temperature synthesis of nano Ti(C,N) by novel mechanical and thermal activation method

This paper presents a novel mechanical and thermal activation assisted carbothermal reduction (CR) method for synthesising Ti(C,N) powder at lower temperatures. Nano Ti(C,N) powder with approximately 30?nm grain size was synthesised by mixing powders of titanium, anatase, and carbon black. The starting powders were first milled for 10 to 40?h under N₂/Ar atmosphere, and then vacuum heat treated for 1?h at 800 to 1050°C. Consequently, nano Ti(C,N) powder with approximately 30?nm grain size was synthesised. X-ray diffraction analysis shows that Ti(C,N) is partially formed during mechanical milling, and the remaining reactants react completely below 1050°C. However, when the unmilled starting powders are heat treated at 1050°C under N₂ for 1?h, large amounts of reactants remain. Thermogravimetry and differential scanning calorimetry analysis shows that the CR reaction of activated TiO₂ occurs at a lower temperature under N₂ than under Ar or vacuum.     

Crystal structure, thermal flexibility and structural transformations of tin umbite and copper exchanged tin umbite prepared from clear solution

For the first time tin silicate with umbite structure K₂SnSi₃O₉·H₂O (AV-6) has been prepared from clear solution using SnCl₂ as a source of tin. In situ high temperature powder X-ray diffraction study of AV-6 and its copper ion exchanged form K_0.98Cu_0.51SnSi₃O₉·2H₂O (Cu-AV-6) has been performed. Rietveld refinement revealed that the ion exchange with copper alters the initial orthorhombic structure into monoclinic one. In this way the temperature stable framework of AV-6 has been transformed into thermally flexible material that can be contracted at 200 °C and preserved at ambient conditions. At higher temperatures (300–700 °C) the structure gradually amorphisize and at 750 °C it transforms into nanosized cassiterite type solid. We also study the structural reversibility and the influence of the dehydration process on the dimensions of the both structures.     

Photocatalytic oxidative desulfurization of dibenzothiophene catalyzed by amorphous TiO2 in ionic liquid

Three types of TiO₂ were synthesized by a hydrolysis and calcination method. The catalysts were characterized by X-ray powder diffraction (XRD), diffuse reflectance spectrum (DRS), Raman spectra, and X-ray photoelectron spectroscopy (XPS). The XRD and Raman spectra indicated that amorphous TiO₂ was successfully obtained at 100 °C. The results indicated that amorphous TiO₂ achieved the highest efficiency of desulfurization. The photocatalytic oxidation of dibenzothiophene (DBT), benzothiophene (BT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and dodecanethiol (RSH) in model oil was studied at room temperature (30 °C) with three catalysts. The system contained amorphous TiO₂, H₂O₂, and [Bmim]BF₄ ionic liquid, ultraviolet (UV), which played vitally important roles in the photocatalytic oxidative desulfurization. Especially, the molar ratio of H₂O₂ and sulfur (O/S) was only 2: 1, which corresponded to the stoichiometric reaction. The sulfur removal of DBT-containing model oil with amorphous TiO₂ could reach 96.6%, which was apparently superior to a system with anatase TiO₂ (23.6%) or with anatase — rutile TiO₂ (18.2%). The system could be recycled seven times without a signicant decrease in photocatalytic activity.     

Kinetic model applicable to synthesis of (Cu0·25 N0·25 Zn0·5 )Fe2O4 ferrite

Abstract

A study was undertaken of the reaction whereby (Cu_0·25 Ni_0·25 Zn_0·5 )Fe₂O₄ ferrite is obtained from the corresponding oxides. The effect of synthesis temperature on the ferrite formation rate was determined by means of high temperature X-ray diffractometry (HT-XRD). An empirical model for the reaction was developed based on the hypothesis that diffusion through the product layer is the rate controlling process step. The proposed model was found to satisfactorily reproduce the amount of ferrite that formed as a function of time and temperature (750–1000°C).     

Polymerisation von Vinylchlorid bei Atmosphärendruck 1. Polymerisationssysteme zur Herstellung von U-PVC

A method for polymerization of vinylchloride (VC) at atmospheric pressure is described, in which the gaseous monomer is polymerized with K₂S₂O₈ as an initiator at 45°C to 60°C. The amount of the polymer formed (so-called U-PVC) as a function of the reaction time depends on the rate of monomer flow. The reaction rate increases with higher initiator concentration as well as with increasing temperature. It is also possible to initiate the polymerization with the redox-system K₂S₂O₈/Na₂SO₃/Cu²⁺ within the range of 0°C to 20°C. By means of transmission electronmicroscopic (TEM) investigations the particle size and particle size distribution as a function of polymerization time and temperature was determined.     

Comparative Study of the Physico-Chemical Properties of Nanocrystalline CuO–ZnO–Al2O3 Prepared from Different Precursors: Hydrogen Production by Vaporeforming of Bioethanol

The physico-chemical and catalytic properties of CuO–ZnO–Al₂O₃, synthesised by sol–gel process (SG), impregnation method (IMP) and a combination of both preparative procedures (ISG), were comparatively studied. Samples were characterised with thermogravimetric-differential thermal analysis (TG–DTA), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) techniques and oxygen chemisorption. XPS study was not consistent with the bulk findings and revealed the presence of Cu²⁺, Cu⁺ and/or Cu⁰ species at the catalysts surface. Surface analysis revealed also that copper enrichment occurred mainly at the surface of SG and IMP solids. The reducibility of the mixed oxides catalysts was always modified with respect to that of pure copper oxides phases and the reduction of CuO was markedly affected by the presence of ZnO–Al₂O₃. Temperature programmed reduction (H₂-TPR) analysis showed that the temperature corresponding to maximum reduction rate of copper oxide was ca. 256 °C for IMP sample and ca. 296 °C for both SG and ISG solids. These latter showing a high resistance to reduction suggest a strong interaction of copper species with ZnO–Al₂O₃, limiting thus copper particles sintering. CuO particle size was found to be ca. 20 nm for both SG and ISG solids and ca. 40 nm for IMP catalysts. Besides, at 300 °C SG and ISG samples showed superior amount of reversible O₂ uptake with respect to IMP solids. Catalytic activity of CuO–ZnO–Al₂O₃ was measured with bio-ethanol steam reforming reaction. SG catalysts exhibited both high selectivity to hydrogen and high stability with time on stream than IMP and ISG catalysts. This was attributed both to the particles size of copper species, their amount on the catalytic surface and to their strong interaction with ZnO–Al₂O₃.     

Enhancing the thermal stability of S/Se based thermoelectric materials using self-generated oxide films

This study focuses on the thermal stability of Cu_1.8S materials. During the ball milling process, metal powder is added to the milled Cu_1.8S powder, and then the obtained powder is sintered using current assisted sintering to obtain dense blocks. The aim is to enable the added metal elements to spontaneously grow an oxide film on the surface of the material block at high temperature, achieving protection of the material matrix. The thermal stability of materials is evaluated by utilizing changes in room temperature phase composition before and after high-temperature heat treatment, changes in material electrical conductivity during high-temperature processes, and cyclic electrical transmission performance testing. By observing the surface oxide film state of the material after high-temperature treatment, the commonalities and differences in the effects of different element additions on the thermal stability of the material were analyzed. The effects of different metal elements on material hardness and electrical transmission performance were evaluated. It is found that adding metal powder can effectively improve the thermal stability of Cu_1.8S, improve material hardness, and regulate the electrical transmission performance of the material. The characteristics of the oxide film formed by the spontaneous growth of metal elements and oxygen on the surface of the material substrate determine the effectiveness of the oxide film in protecting the material from high temperatures. The pure Cu_1.8S bulk can only maintain stability at 300 ^oC, and the addition of Cr, Al, 316L, Fe, and Mn powder respectively increased the stable temperature of the material to 400, 400, 450, 450, 500 ^oC. Adding metal elements to the material matrix to grow an oxide film on the surface of the material to prevent high-temperature oxidation or decomposition is an effective way to improve the thermal stability of S/Se compounds.     

Facile synthesis of LaAlO3 and Eu(II)-doped LaAlO3 powders by a solid-state reaction

Lanthanum aluminate (LaAlO₃) powder was prepared by a solid-state reaction between lanthanum(III) carbonate fluoride (LaFCO₃) and alumina (Al₂O₃) powders at elevated temperatures, and characterized by powder X-ray diffraction (XRD), ²⁷Al magic-angle spinning nuclear magnetic resonance spectroscopy, and scanning electron microscopy. The formation temperature (1000 °C) of LaAlO₃ was much lower than that in other solid-state reactions. The Eu(II)-doped LaAlO₃ powder was prepared by calcination of a mixture of Eu(III)-doped LaFCO₃ and Al₂O₃ in a nitrogen atmosphere and characterized by powder XRD, and photoluminescence and X-ray photoelectron spectroscopy. The intensity of blue emission due to Eu(II) ions in the LaAlO₃ powder increased with increasing calcination temperature up to 1200 °C but decreased with further increases in temperature. The origin of the Eu(II) ions was explained by the thermal decomposition of EuF₃.     

Effect of heat treatment on the synthesis of hydroxyapatite from Indian clam seashell by hydrothermal method

Hydroxyapatite (HA) powder has been successfully synthesized from low-cost Indian clam seashells by using hydrothermal method. The mixture of tri-calcium phosphate [Ca₃(PO₄)₂], heat-treated ball-milled clam seashell, and demineralized water are heat-treated at several temperatures (700 °C, 800 °C, 900 °C, 1000 °C, and 1100 °C) for various time periods (1 h, 2 h, and 3 h) to perform the hydrothermal reactions. The phases and microstructure of the solid-state reaction products are analyzed through X-ray diffraction (XRD) method and field emission scanning electron microscopy (FESEM) respectively. The crystallite size of all the synthesized powders is calculated by using Scherrer's model. Mainly HA phase is obtained in all the different reaction products. However, these HAs are found to be non-stoichiometric in nature. As per the literature, non-stoichiometric HA is a more biologically active material compared to the stoichiometric one. Almost pure HA is formed with any selected reaction temperature applied for 2 h time duration. The crystallinity and Ca/P ratio of the synthesized pure HA are estimated by using standard model and energy-dispersive X-ray spectroscopy (EDS) analysis, respectively. The highest amount of near stoichiometric crystalline HA has been obtained at 900 °C of reaction temperature applied for 2 h time duration. With raising reaction temperature, the grain size of pure HA is found to be increased. Needle/rod shaped nano grains are noticed to form at lower reaction temperature whereas; beyond 1000 ^oC of temperature globular/spherical shaped grains are also observed to form. At 3 h reaction time agglomeration of grains is found to occur in all the synthesized powders.     

In situ synthesis of ZrB2–ZrC–SiC ultra-high-temperature nanocomposites by a sol–gel process

ABSTRACT

ZrB₂–ZrC–SiC is one of the ultra-high-temperature ceramic composites with excellent properties. In this research, high-purity ZrB₂–ZrC–SiC nanopowders were synthesised using a carbothermal reduction reaction at a relatively low temperature (1370°C) from cost-effective zirconium(IV) chloride by a sol–gel method. The effect of heat treatment temperature on the synthesis of ZrB₂–ZrC–SiC composite powder was studied. X-ray diffractometry results showed that the phases ZrB₂, β-SiC and ZrC were synthesised at 1370°C. The mean crystallite sizes for each of the phases were calculated using the Scherrer method. The specific surface area for the sample calcined at 1370°C was 81.479?m²?g^?1. SEM observation revealed that the particles had a size lower than 250?nm. Backscattered electron image and map analysis with scanning electron microscopy showed that a suitable phase homogeneity was achieved, as confirmed by energy-dispersive X-ray spectroscopy.     

Rate of formation of C3S in the system CaOSiO2Al2O3Fe2O3MgO with addition of CaF2

The influence of CaF₂ on the kinetics of the reaction C+C₂S → C₃S in five-component diffusion sandwiches (CaOSiO₂Al₂O₃Fe₂O₃MgO) was determined in the temperature interval 1350°C to 1500°C. With the addition of 0.5% CaF₂ to the reacting system the rate of reaction increased by a factor of 2.4 at a reaction temperature of 1350°C, and a factor of 1.2 at 1500°C. Addition of 1% CaF₂ raised the reaction rate 2.8 times at 1350°C and 1.7 times at 1500°C. The effect of CaF₂ on the rate of C₃S formation may be attributed to the fact that the C₃S primary field is much wider in the CSCaF₂ system than in the CSAF system.     

Ultrasonic-assisted preparation of AlON from alumina/carbon core-shell nanoparticle

An aluminium oxynitride (AlON) powder was synthesized by carbothermal reduction nitridation (CRN) method. For this purpose, first Al₂O₃/C core-shell nanoparticles were prepared by the pyrolysis of Al₂O₃/polyacrylonitrile (PAN) nanocomposite precursor at 800?°C for 2?h in an argon atmosphere. Alumina/PAN precursor was prepared by ultrasonic method at room temperature. Then, by two-step thermal treatment of Al₂O₃/C core-shell nanoparticles at 1500–1600?°C for 2?h, followed by subsequent heating at 1750?°C for 1?h in N₂ flow, AlON powder was synthesized. The sample was investigated via Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and CHNS elemental analysis.     

Mechanochemical synthesis of alumina–zirconia nanocomposite powder

Abstract

The alumina–zirconia nanocomposite powder has been synthesised by mechanical activation of a dry powder mixture of AlCl₃, ZrCl₄ and CaO. Mechanical milling of the above raw materials with the conditions adopted in this study resulted in the formation of a mixture consisting of crystalline CaO and amorphous aluminium and zirconium chlorides phases. There was no sign of chemical reaction occurring during milling stage as evidenced by X-ray diffraction (XRD) studies. Subsequent heat treatment of the milled powder at 350°C resulted in the occurrence of displacement reaction and the formation of ZrO₂ and Al₂O₃ particles within a water soluble CaCl₂ matrix. The effect of higher temperature calcination on the phase development in this powder mixture was followed by XRD analysis. Scanning electron microscopy and differential thermal analysis were also used in the characterisation of the powders. Perhaps the most important observation in this study was the formation of α-Al₂O₃ phase at a very low temperature of 400°C.