Thermodynamic study and methanothermal temperature-programmed reaction synthesis of molybdenum carbide

Nanostructured molybdenum carbide （Mo2C） was successfully prepared from molybdenum trioxide （MoO3） using methanothermal temperature-programmed reaction. Thermodynamic analysis indicated that in presence of methane, the formation of Mo2C from MoO3 occurs through the path of MoO3 → MoO2→ Mo2C. The carburized MoO3 was characterized using X-ray diffraction （XRD）, CHNS/O analysis, Brunauer-Emmett-Teller （BET） analysis, and field-emission scanning electron microscopy （FESEM）. At final carburization temperatures of 700 and 800℃ and at methane contents ranging from 5vol% to 20vol%, Mo2C was the only solid product observed in the XRD patterns. The re- suits indicated that the effect of methane content on the formation of the carbide phase is substantial compared with the effect of carburization time. Elemental analysis showed that at a final temperature of 700℃, the carbon content of carburized MoO3 is very close to the theoretical carbon mass percentage in Mo2C. At higher carburization temperatures, excess carbon was deposited onto the surface of Mo2C. High-surface-area Mo2C was obtained at extremely low heating rates; this high-surface-area material is a potential electrocatalyst.

Preparation of nano-sized cerium and titanium pyrophosphates via solid-state reaction at room temperature

Nano-sized cerium-titanium pyrophosphates Ce1-xTixP2O7 （with x = 0, 0.2, 0.5, 0.7, 0.9, and 1.0） were obtained by grinding a mixture of Ce（SO4）2·4H2O, Ti（SO4）2, and Na4P2O7·10H2O in the presence of surfactant PEG-400 at room temperature, washing the mixture with water to remove soluble inorganic salts, and drying at 100℃. The products and their calcined samples were characterized using ultraviolet-visible spectroscopy （UV-vis）, thermogravimetry and differential thermal analyses （TG/DTA）, X-ray powder diffraction （XRD）, and transmission electron microscopy （TEM）. The results show that nano-sized Ce1-xTixP2O7 behave as an excellent UV-shielding material. Thereinto, the CeP2O7 has the most excellent UV-shielding effect, and the amorphous state of Ce0.8Ti0.2P2O7 can keep at a higher temperature than CeP2O7. Therefore, the stabilization of the amorphous state of the cerium pyrophosphates was carded out by doping titanium. This stabilization is a significant improvement, which enables to apply these amorphous pyrophosphates not only to cosmetics and paints, but also plastics and films.

High Temperature Chemical Reaction of La_2O_3 in H_3BO_3-C System

The high temperature chemical reaction process of La2O3 in H3BO3-C system was studied by means of XRD and TG-DTA.The results showed that dehydration reaction of H3BO3 occurred in the temperature range of 82～390 ℃;La2O3 and B2O3 reacted to form LaB3O6,LaBO3,and B4C in the temperature range of 836～1400℃;at 1450 ℃,B4C and LaBO3 further reacted to form LaB4,and partial LaB4 and B reacted to form LaB6;at 1500 ℃,LaB4 and B reacting into LaB6 was the main reaction,and the content of LaB6 increased with prolonging time.

Doping effect of cations(Zr^(4+),Al^(3+),and Si^(4+)) on MnO_x/CeO_2 nano-rod catalyst for NH_3-SCR reaction at low temperature

Thermally stable Zr4+, Al3+, and Si4+ cations were incorporated into the lattice of CeO2 nano‐rods (i.e., CeO2‐NR) in order to improve the specific surface area. The undoped and Zr4+, Al3+, and Si4+ doped nano‐rods were used as supports to prepare MnOx/CeO2‐NR, MnOx/CZ‐NR, MnOx/CA‐NR, and MnOx/CS‐NR catalysts, respectively. The prepared supports and catalysts were comprehensively characterized by transmission electron microscopy (TEM), high‐resolution TEM, X‐ray diffraction, Raman and N2‐physisorption analyses, hydrogen temperature‐programmed reduction, ammonia temperature‐programmed desorption, in situ diffuse reflectance infrared Fourier‐transform spectroscopic analysis of the NH3 adsorption, and X‐ray photoelectron spectroscopy. Moreover, the catalytic performance and H2O+SO2 tolerance of these samples were evaluated through NH3‐selective catalytic reduction (NH3‐SCR) in the absence or presence of H2O and SO2. The obtained results show that the MnOx/CS‐NR catalyst exhibits the highest NOx conversion and the lowest N2O concentration, which result from the largest number of oxygen vacancies and acid sites, the highest Mn4+ content, and the lowest redox ability. The MnOx/CS‐NR catalyst also presents excellent resistance to H2O and SO2. All of these phenomena suggest that Si4+ is the optimal dopant for the MnOx/CeO2‐NR catalyst.

Morphology Tuning of Mono-disperse Silver Nanoparticles by Reaction Temperature Adjustment

Mono-disperse silver nanoparticles with tunable morphologies have been fabricated by reducing AgNO3 in the presence of N-dimethylformamide （DMF） and larger molecular weight poly （vinylpyrrolidone） （PVP）. By adjusting the reaction temperature, the conversion of the morphology can be easily and effectively controlled. The crystal structures and growth mechanism of mono-disperse silver nanoparticles were studied by using TEM, HR-TEM, FFT, XRD and UV-Vis spectra data. The results show that the morphologies of nanoparticles with spherical shape can be adjusted to a truncated triangle/hexagon along with the change of reaction temperature from 80 to 120 ℃. It is found that the shape transformation from sphere to mmcated triangle is caused by the difference in surface energy and the selective adsorption of PVP on silver atom.

Effects of Pouring Temperature on Interfacial Reaction between Ti-47-5Al-2-5V-1Cr Alloy and Mold during Centrifugal Casting

Pouring temperature and time are the most important influencing factors on interfacial reaction during the centrifugal casting. When cast at high temperatures, the crucible becomes brittle and prone to cracking, and shows a low stability. In this paper, we studied the centrifugal casting of Ti-47.5-Al-2.5V-1Cr alloy, and explored the effects of pouring temperature on the interfacial reaction. Castings at 1 600, 1 650, and 1 700 ℃ were obtained by controlling the other parameters constant in the experiments. The microstructure, elemental distribution, thickness of the reaction layer and phase composition of the castings at the interface were studied. The results show that the thickness at the interfacial reaction layer is increased by raising the pouring temperature. The elements in the mold and the matrix were double-diffused and reacted at the interface during the casting process, and formed solid solutions with the precipitation of many new phases such as AlOand TiO. The roughness of interface structure and layer thickness of reaction increase with the rise of temperature, and the interfacial reaction is more intense. There is a minimum layer thickness of the reaction layer that is 80 μm when the temperature is 1 600 ℃.

Acting mechanism of F,K,and Na in the solid phase sintering reaction of the Baiyunebo iron ore

The effect of F,K,and Na on the solid phase reaction of the Baiyunebo iron ore was investigated by differential thermal analysis （DTA） and X-ray diffraction（XRD）.It has been identified that alkaline elements K and Na in the Baiyunebo ore instigate the formation of low melting point compounds Na2SiO3 and Na2O·Fe2O3 and the generation of molten state in the solid phase sintering.Element F in the Baiyunebo ore facilitates the formation of cuspidine compound 3CaO·2SiO2·CaF2 in the solid phase reaction.The cuspidine compound is kept in solid as one of the final products through the entire sintering process due to its high melting point.In the sintering process,CaF2and SiO2 react with CaO first and form 3CaO·2SiO2·CaF2 and 3CaO·2SiO2,so the formation of ferrites,Na2O·Fe2O3,and 2CaO·Fe2O3 is inhibited.

Salt-assisted Low Temperature Solid State Synthesis of High Surface Area CoFe_2O_4 Nanoparticles

A novel salt-assisted low temperature solid state method using CoCl2.6H2O, FeCl3.6H2O and NaOH as precursor and using NaCI as a dispersant to synthesize high surface area CoFe2O4 nanoparticles, has been investigated. The effects of the molar ratio of added salt and calcination temperature on the characteristics of the products were investigated by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, vibrating sample magnetometer （VSM） and Brunauer, Emmett and Teller （BET） surface area analysis. Results showed that the introduction of leachable inert inorganic salt as a hard agglomeration inhibitor in the mixture precursor led to the formation of high dispersive CoFe2O4 nanoparticles; and the increase in specific surface area from 28.28 to 73.97 m^2/g, and the saturation magnetization is 84.6 emu/g.

Temperature-dependent Hydrothermal Synthesis of Two Distinct Three-dimensional Copper Complexes

Two distinct copper coordination polymers, namely [Cu^Ⅱ2（2,5-pydc）2（bpp）2]·H2O（1） and Cu2^ⅠCu^Ⅱ（2,5-pydc）2（bpp）2（2）（2,5-pydc = pyridine-2,5-dicarboxylic acid, bpp = 1,3-bi（4-pyridyl）propane）, have been successfully synthesized through hydrothermal conditions under different temperatures. Single-crystal X-ray structural analysis revealed that both complexes 1 and 2 are 3D frameworks. Complex 1 is an 8-connected 2-fold interpenetrating network based on [Cu（2,5-pydc）]4 molecular building block（MBB）, and also can be simplified as a 4-connected net if the Cu（Ⅱ） ion is regarded as an independent node, whereas 2 shows a（4,4）-connected non-interpenetrated framework which contains mixed valence Cu（Ⅰ/Ⅱ） centers. The results demonstrate that temperature plays a significant role in the final structures of the complexes.

Ultrasonic-Assisted Synthesis of Monodisperse Ag Nanoparticles and Their Applications in Surface Enhanced Raman Scattering and Fluorescence Enhancement

Monodisperse Ag nanoparticles with diameters of about 3.4 nm were synthesized by a facile ultrasonic synthetic route at room temperature with the reduction of borane-tert-butylamine in the presence of oleylamine （OAm） and oleic acid （OA）. The reaction parameters of time, the molar ratios of OAm to OA were studied, and it was found that these parameters played important roles in the morphology and size of the products. Meanwhile, surface enhanced Raman spectrum （SERS） property suggested the Ag nanoparticles exhibited high SERS effect on the model molecule Rhodamine 6G. And also, two-photon fluorescence images showed that the silver nanoparticles had high performances in fluorescence enhancement.

Preparation and gas sensing properties for acetone of amorphous Ag modified NiFe_2O_4 sensor

Nickel ferrite nano-powders were prepared by microwave radiating low-temperature solid-state reaction method, and then modified with Ag by dipping method. The crystal structure and morphology of the samples were characterized by means of X-ray diffraction（XRD）, scanning electron microscopy （SEM） and X-ray photoelectron spectroscopy （XPS）. The gas sensing properties of the samples were also investigated. The results reveal that the Ag, as amorphous structure, can efficiently prevent the reuniting and growing-up of nanosized NiFe2O4 grains, and 1.5% Ag modified NiFe2O4 sensor has a better sensitivity, up to 43, for acetone gas than 1.5%Ag mixed NiFe2O4 sensor prepared by low-temperature solid-state reaction, at an optimal working voltage of 4.5 V. The quick response time （1 s） and fast recovery time （～10 s） are the main characteristics of this sensor.

Yttrium aluminum garnet (Y_3A_(l5)O_(12)) nanopowders synthesized by the chemical method

The homogeneously dispersed, less agglomerated YAG nanopowders are synthesized by the citrate-gel method followed by low-temperature self-propagating combustion reaction, using Y2O3, Al(NO3)3?9H2O and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and the hard ag-glomerates brought by the chemical precipitation method. The powders are characterized by TG-DTA, XRD, FT-IR and TEM respectively. The experiments show that the forming temperature of YAG crystal phase is 850°C and the pseudo-YAG crystalline appears during the calcination and transforms to pure YAG at 1050°C. The powders with sizes less than 50 nm are observed by TEM micrography, which is consistent with the result calculated by Scherrer's formula. The powders consist of single grains.

Effects of Technological Parameters on Carbothermal Reduction and Nitridation of Zircon

Carbothermal reduction and nitridation （CRN） of zircon （ ZrSiO4 ） permits obtaining diffbrent composites of oxides and nitrides such as ZrO2 -Si2N2O and ZrN - Si3N4. The effects tf technological parameters （ carbon source, reaction temperature, and carbon con.tent ） on the reaction rate and product phase composition of CRN of zircon were investigated by TGA and XRD. The resuhs show that： （1） carbon source is an important factor for a rapid reaction, and actiwtted carbon is chosen as the carbon source considering the expect products and reaction rate ; （ 2 ） reaction tetnperature has vital effect on reaction rate and product. In, case of carbon content above 20% , the zircon phase and m-ZrO2 phase decrease with increasing temperature, while the ZF7N8O4 phase increases firstly and then decreases, and the ZrN phase increases continually; （3） different carbon contents result in different reaction products. The higher the carbon content, the lower the starting temperature for the CRN of zircon.

Synthesis of aluminum nitride in a coke – calcium reduction bed using nitrogen in air

An experimental study on the heating of a mixture of aluminum and lithium hydroxide （LiOH） powders in a reductive bed under air atmosphere is reported. The formation of aluminum nitride （A1N） during this process was the focus of this study. The formation of A1N was achieved using LiOH as an additive and heating the sample in a resistance furnace in a specially designed double crucible within a bed of a mixture of coke and filamentous calcium. The temperature range of the reaction was between 700℃ and 1100℃. The optimum temperature of 1100℃ and the optimum LiOH amount （Swt%） required to achieve maximum yield were determined by powder X-ray diffraction （XRD） analysis. Scanning electron microscopy （SEM） micrographs clearly indicated the transformation of grain structures from rods （700℃） to cauliflower shapes （1100℃）.

Effect of carboxymethyl cellulose on dissolution kinetics of carboxymethyl cellulose-sodium carbonate two-component tablet

Sodium carbonate and carboxymethyl cellulose powders are compressed into two-component tablets with three mass ratios,97%:3%,95%:5% and 93%:7%.The dissolution tests for two-component tablets and reference pure sodium carbonate tablets are carried out at various temperatures.The dissolution process of each tablet is measured by electrical conductivity tracking method and the concentration of dissolved sodium carbonate is quanti fied with calibrated conductivity-concentration converting equation of sodium carbonate.The quanti fied dissolution data is fitted with both surface reaction model and diffusion layer model and the results clearly show that surface reaction model is suggested as the appropriate dissolution model for all measured tablets.Therefore,it is determined that carboxymethyl cellulose is a stable element to remain the dissolution mechanism of tablet unchanged.The dissolution rate constant quanti fied with surface reaction model presents that carboxymethyl cellulose-sodium carbonate two-component tablets obtain signi ficant higher dissolution rate constant than pure sodium carbonate tablet and higher proportion of carboxymethyl cellulose leads to apparent higher dissolution rate constant.The results prove for the usage of carboxymethyl cellulose in most practical applications at a relative low-level,the effect of carboxymethyl cellulose is effective and positive for two-component tablet to enhance the dissolution process and improve dissolution rate constant and this effect is speculated coming from its dynamic physical transforming process in water including dilation and conglutination.

Modified room temperature solid-state synthesis of yttria-stabilized zirconia(YSZ) nano-powders for solid oxide fuel cells

High-performance solid oxide fuel cell(SOFC) is in urgent need of high-quality electrolyte powders with high reactivity and chemical uniformity.Here,8 mol% Y_(2)O_(3) doped ZrO_(2)(YSZ) nano-powders were synthesized by an improved solid-state reaction method at ambient temperature,and were applied to the fabrication of SOFC electrolytes.YSZ nano-powders show average grain sizes of ^(2)0 nm and high dispersibility,which is comparable with or even better than some other chemical methods.Benefitting from their high reactivity,dense YSZ electrolytes(relative density of 97.9%) can be obtained at a relatively low sintering temperature of 1400℃.The optimized electrical conductivity reaches up to a high value of0.034 S/cm at 800 0C in air.The anode supported single cell with the construction of Ni-YSZ/YSZ/Sm_(0.2)Ce_(0.8)O_(2-δ)(SDC)/La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ)(LSCF) exhibits the peak power density of 0.827 W/cm^(2) at800℃ while taking wet H_(2) as fuels and ambient air as oxidants.

Synthesis of Si3N4 Powder Using Sawdust as Carbon Source

Si3N4 powder was synthesized by carbothermal re- duction nitridation reaction using sawdust as carbon source and introducing SiO2 by silica sol immersion. Effects of SiO2 content of silica sol, molding pressure, reaction temperature, reaction duration, and N2 flow rate on phase compositions and microstructure of result- ants were studied. The results show that using 7. 5 mass% SiO2 containing silica sol immersed sawdust as raw materials, the prepared Si3N4 powder is featured with high α-Si3N4 content, few impurities, etc. in the conditions of 1 450 ℃ of reaction temperature, 9 h of reaction duration, 400 mL ·min- 1 of N2 flow rate and 10 MPa of molding pressure.

Coating Nano-Hematite on (Y, Gd)BO_3∶Eu ^(3+) Phosphors by A Facile Method

(Y, Gd)BO_3∶Eu 3+ particles coated with nano-hematite were prepared by a facile method, for example (humid) solid phase reaction at room temperature. The resulted hematite-coated (Y,Gd)BO_3∶Eu 3+ particles were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and photoluminescence spectra (PL). The SEM and EDS analyses indicate that the particles are coated with a very thin layer of iron oxide. XPS results further confirmed that the coating was hematite, and the coating thickness was in nanometer range. XRD patterns showed that either the hematite coating was too thin or the content of hematite was too small, so that the XRD cannot detect it. The emission spectra illustrate that the peak near 580 nm disappears due to the coating of iron oxide, and when the coating is very thin, the ratio of 5D_0→7F_2 to 5D_0→7F_1 of coated particles is higher than that of uncoated ones, which indicates that the color purity of the phosphor is increased by coating nano-hematite.

Degradative solvent extraction of subbituminous coal with deep eutectic solvent and effect of reaction conditions on products

A degradative solvent extraction method for upgrading low-rank coal was performed at 200-350◦C for 90 min to obtain a substance dissolved in the solvent at room temperature(Soluble).Because the resulting mixture exhibited a high carbon content without ash,it could be readily used as a fuel.Furthermore,deep eutectic solvents(DESs)have attracted attention for improving the Soluble yield and decreasing the oxygen content in Soluble.DES is known to cleave oxygen-containing functional groups in biomass and is considered effective for deoxidizing low-rank coal.Herein,DES was prepared by mixing choline chloride,FeCl3⋅6H2O,and Adaro subbituminous coal(AD)and then added to 1-methylnaphthalene(1-MN)in a non-polar solvent,followed by degradative solvent extraction in the range of 200-350◦C.The effects of reaction temperature and added DES amount on the product yield and the composition were evaluated.As the reaction temperature and amount of DES added increased,the Soluble yield and carbon content increased.It was also found that the thermal decomposition temperature and oxygen content decreased with the increasing DES amounts.This decrease indicates that DES promotes the deoxygenation and decomposition of AD and increases the soluble yield of the fuel source.

Influence of temperature on metal-organic frameworks

Reaction temperature is one of the key parameters in the synthesis of metal-organic frameworks （MOFs）. Though there is no convergence with regard to the various experimental parameters, reaction temperature has been found to have remarkable influence on the formation and structure of MOFs, especially toward the control of topology and dimensionality of the MOF structures. Theoretically, the reaction temperature affects directly the reaction energy barrier in reaction thermodynamics and the reaction rate in the reaction kinetics. This review aims to show the influence of reaction temperature on crystal growth/assembly, structural modulation and transformation of MOFs, and to provide primary information and insights into the design and assernblv of desired MOFs.