Influence of calcination atmosphere on photocatalytic reactivity of K2La2Ti3O10 for water splitting

The layered perovskite type oxide K2La2Ti3O10 powders were prepared under air, Ar and H2 calcination atmospheres by sol-gel method and characterized by X-ray diffractometry, UV-Vis diffuse reflectance and X-ray photoelectron spectroscopy. The influence of the calcination atmosphere on the photocatalytic reactivity of K2La2Ti3O10 for hydrogen production was investigated. The photocatalytic reactivity of K2La2Ti3O10 prepared under air, Ar and H2 atmospheres was compared with that prepared under ultraviolet and visible light radiation using Г as electronic donor. The results show that K2La2Ti3O10 prepared under Ar and H2 atmospheres has higher photocatalytic activity for hydrogen production than that prepared under air atmosphere. The hydrogen production rates under ultraviolet irradiation are 127.5, 81.3 and 57.0 μmol/（L·h） and those under visible light irradiation are 40.2, 30.2 and 16.5 μmol/（L2h） respectively when K2La2Ti3O10 is prepared under Ar, H2 and air atmospheres.     

KCl-Induced Corrosion of a 304-type Austenitic Stainless Steel in O2 and in O2 + H2O Environment: The Influence of Temperature

The oxidation of the 304-type (Fe18Cr10Ni) austenitic stainless steel was investigated in the temperature range 400–600 °C in 5% O₂ and 5% O₂ + 40% H₂O. Exposure time was up to 1 week. Prior to exposure, the polished samples were coated with 0.1 mg/cm² KCl. Uncoated samples were also exposed and used as references. The oxidized samples were analyzed by gravimetry and by ESEM/EDX, XRD, IC and AES. The results show that KCl is strongly corrosive. Corrosion is initiated by the reaction of KCl with the chromia-containing oxide that normally forms a protective layer on the alloy. This reaction produces potassium chromate particles, leaving a chromium-depleted oxide on the alloy surface. At 500 and 600 °C this results in rapid oxidation, resulting in the formation of a thick scale consisting of a mixture of hematite, spinel oxide ((Fe,Cr,Ni)₃O₄) and K₂CrO₄. The thick scale is poorly protective and permeable to e.g. chloride ions. The KCl-induced corrosion of alloy 304L in dry O₂ and in an O₂ + H₂O mixture increases strongly with temperature in the range 400–600 °C. The strong temperature dependence is explained partly by the temperature dependence of the chromate-formation reaction and partly by the ability of the chromium-depleted oxide to protect the alloy at low temperature. At 400 °C, the oxide was still protective after 168 h.     

Yb2O3或Y2O3掺杂Cu-(NiFe2O4-10NiO)惰性阳极的导电性和耐蚀性

在氧分压约为100 Pa的氮气氛下烧结制备了掺杂Y2O3、Yb2O3的10Cu-(NiFe2O4-10NiO)金属陶瓷,并对其进行导电性能测试和10h(Na3A1F6-Al2O3体系中)铝电解实验.采用XRD、SEM和EDS分析稀土氧化物以及其与陶瓷基体反应产物的分布,考查电解实验后材料表层显微结构变化尤其是金属相的流失情况,评价稀土氧化物的添加对金属陶瓷电解初期腐蚀行为的影响.结果表明:掺杂稀土氧化物均使NiO相呈连通迹象,掺杂Yb2O3金属陶瓷晶粒较未掺杂的粗大,其与陶瓷相反应生成物成点线状分布于NiFe2O4相晶界,Y2O3与陶瓷相反应生成物则分布于NiO与NiFe2O4相间;所制备材料具有半导体特征,随着稀土氧化物的掺杂,材料导电性呈下降趋势;掺杂稀土氧化物尤其是Yb2O3有利于提高材料的耐蚀性能.     

Structure and electrochemical properties of LiMn2O4

LiMn2O4, a cathode material of lithium ion battery, was prepared by the citric acid complexing method using lithium acetate and manganese acetate as raw materials. The type of atom location confused degree, the confused degree and judgement method in LiMn2O4 were analyzed. The effect of sintering temperature on structure and electrochemical properties of LiMn2O4 was also investigated. The results show that the atom location confused degree increases with the decrease of the X-ray diffraction peak intensity ratio of LiMn2O4, Ⅰ111/Ⅰ311. The type of atom location confused degree depends on the variation tendency of Ⅰ111/Ⅰ311 and Ⅰ311/Ⅰ400 value. If the variation tendency is the same, it belongs to the 16c type location confusion, however, if the variation tendency is contrary, it belongs to the anti-spinel type location confusion. When the sintering temperature is low, it is apt to produce the anti-spinel location confusion in LiMn2O4. With the increase of sintering temperature, the confused degree with the anti-spinel type gradually reduces, however, the confused degree with 16c type increases to some extent. When the atom location confusion with the anti-spinel type appears in LiMn2O4, both the initial discharging capacity and cycling properties of LiMn2O4 reduce. However, the atom location confusion with 16c type does not affect the charge and discharge properties of LiMn2O4.     

Effect of Ni content on corrosion behavior of Ni/（10NiO-90NiFe2O4） cermet inert anode

Ni/（10NiO-90NiFe2O4） cermet inert anodes with metal Ni content of 0, 5, 10, 15 and 20 （mass fraction, %） were prepared and their corrosion behavior in Na3AlF6-Al2O3 melts was investigated in laboratory electrolysis tests. The results indicate that the content of metal Ni in anodes has little effect on the steady-state concentration of impurities Ni and Fe in electrolyte and the values range in （114-173）×10^-6 and （287-385）×10^-6, but the content of impurities in the metal aluminum manifolds. There is preferential corrosion for metal Ni in NiO-NiFe2O4 based cermet anodes. Considering the corrosion resistance and electrical conductivity, the cermet containing 5%Ni （mass fraction） behaves best among NiO-NiFe2O4 based cermet anodes studied, and should be further studied.     

Synthesis and characterization of CoFe2O4 nanoparticles

The reverse microemulsion composition consisting of 37.0% cyclohexane, 26.0% surfactant （TX-10 and AEO9）, 13.0% n-pentanol and 24.0% aqueous phase was investigated and chosen for the preparation of cobalt ferrite nanoparticles. Then silicon dioxide was coated onto the surface of the magnetite nanoparticles. The two kinds of nanoparticles were characterized by means of X-ray diffractometry（XRD）, scanning electron microscopy （SEM）, infrared spectroscopy （IR）, and energy dispersion spectrometry （SEM-EDS）. The SEM results indicate that both nanoparticles have narrow size distribution, less agglomeration and are in the size range of 10 -60 nm. XRD patterns show that there is not any peak detected except for the peaks of CoFe2O4, and imply that the coated silicon dioxide is amorphous. IR absorption spectra of the samples show the characteristic bands of Si—O—Si group and Fe—O group. SEM-EDS indicates that the molar ratio of Fe to Si is 96.11 ： 3.89. These results prove that a thin film of SiO2 is coated on the surface of the magnetite nanoparticles. And the characterization of cobalt ferrite nanoparticles prepared by conventional precipitation method are compared.     

Synthesis and character of spinel LiMn2O4

1　INTRODUCTIONTheincreasingconcernsonportableelectricele mentsdemandmoreandmoreelectrochemicalener gy .Countriesallovertheworldhaveputlargequan tityofmanuallabors ,materialresourcesandfinancialresourcesonbasicresearchanddevelopmentonnewtypeofrechargeablebatteries[1,2 ] .However ,thisnewtypeofbatteriesisbasedonstudyinganddevel opingperfectperformanceofmaterials ,especiallyonmaterialsofthelithiumbatteries.LixMn2 O4 cathodematerialshavebeenwidelystudiedoverthelasttwodecadesasapotentialcand…     

Crystallization and properties of some CaO-Al2O3-SiO2 system glass-ceramics with Y2O3 addition

The crystallization behavior and mechanical properties of CaO-Al2O3-SiO2 （CAS） system glass-ceramics with addition of Y2O3 were investigated. The optimal sintering temperatures of all heat-treated glasses were altered and the crystallization was accelerated with Y2O3 addition, and only wollastonite as a main crystalline phase was precipitated. The volume fraction of crystalline phase and density were increased with Y2O3 addition. The results suggest that the CAS glass-ceramics would get the lowest sintering temperature and optimal microstructure with the addition of Y2O3 by 3.25 %. The bending strength has a maximum due to the oriented and interlocked wollastonite crystal, which causes crack divert or blunts to limit the further development of the flaw size and increases the surface energy of fracture.     

Effect of water on behaviour of Na2B4O7·5H2O and Na2B4O7 in HCl-CH3OH medium

The reactivity of Na₂B₄O₇·5H₂O and Na₂B₄O₇ in non-aqueous HCl-CH₃OH solvent system was investigated. The effects of H₂O, CH₃OH/B mole ratio and reaction time on the reaction at room temperature were examined. Experimental results show that when Na₂B₄O₇·5H₂O and Na₂B₄O₇ are the reactants, the dissolved B₂O₃ contents are observed to be 98.2% and 99%, respectively, in 5 min at the CH₃OH/B mole ratio of 4. The decrease of water in the reaction medium was observed to increase the crystallization of NaCl in the order of Na₂B₄O₇2B₄O₇·5H₂O. It was also observed that the boron solution obtained after the reaction could be hydrolyzed by the addition of H₃BO₃. The results show that HCl-CH₃OH system is a more effective solvent compared to H₂SO₄-CH₃OH both in the reactivity and the shortened reaction time.     

Hydrothermal conversion of Ti-containing minerals in system of Na_2O–Al_2O_3–SiO_2–CaO–TiO_2–H_2O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution.Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na_2O–Al_2O_3–Si O_2–Ca O–Ti O_2–H_2O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to Al_4Ti_2 SiO_(12) at low temperatures(60–120 °C), which is similar to anatase in crystal structure. As the temperature continues to rise, Al4Ti2 Si O12decomposes gradually and converts to Ca_3 Ti Si_2(Al_2Si_(0.5)Ti_(0.5)O_(14) at 200 °C. When the temperature reaches 260 °C, Ca Ti O_3 forms as the most stable titanate species for its hexagonal closest packing with O_2-and Ca_2?. The findings enhance the understanding of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.     

Study on hot corrosion behavior of Yb2Zr2O7 ceramic against Na2SO4 + V2O5 molten salts at temperatures of 900–1200 °C in air

Yb₂Zr₂O₇ ceramic powders synthesized by chemical‐coprecipitation and calcination method were pressureless‐sintered at 1700 °C for 10 h in air to fabricate dense bulk materials. Hot corrosion studies were performed on Yb₂Zr₂O₇ against Na₂SO₄ and Na₂SO₄ + V₂O₅ (molar ratio = 1:1) molten salts in a temperature range of 900–1200 °C for 8 h in air, respectively. Chemical reactions were investigated using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The Yb₂Zr₂O₇ ceramic was severely corroded by Na₂SO₄ + V₂O₅ molten salt, however, no chemical reaction was found between individual Na₂SO₄ and Yb₂Zr₂O₇. Yb₂Zr₂O₇ reacted with Na₂SO₄ + V₂O₅ molten salt to form YbVO₄ and m‐ZrO₂. The thickness of hot corrosion scales formed at different temperatures was investigated to evaluate hot corrosion behavior based on fluxing mechanism. The introduction of vanadium into sulfate led to subsequent formation of NaVO₃, which was acidic enough to dissolve Yb₂Zr₂O₇ by acidic fluxing.     

Effect of NiO content on corrosion behaviour of Ni-xNiO-NiFe2O4 cermets in Na3AlF6-Al2O3 melts

5Ni-xNiO-NiFe2O4 cermets with different NiO contents were prepared and the corrosion behaviour in Na3AlF6-Al2O3 melts was investigated in laboratory electrolysis tests. The results indicate that adding NiO is unfavorable to the densifieation of NiFe2O4-xNiO ceramics, while small Ni doping can greatly improve the sintering property. The electrolysis tests show that excess NiO is beneficial to the reduction of Fe while has little effects on that of Ni in the bath; the steady-state concentrations of Ni, Fe are below the corresponding solubilities of NiFe2O4-xNiO, implying that corrosion mechanism changes while electrifying. Post-electrolysis examination of anodes shows that Ni metal leaches at the anode surface, yet the substrate ceramic prevents the penetration of bath and the further loss of metal phase.     

Discontinuous dissolution of a frozen matrix liquid phase in Ba(Zn1/3Nb2/3)O3 ceramics

Grain-boundary migration during the dissolution of a liquid phase in Ba(Zn_1/3Nb_2/3)O₃ (BZN) ceramics has been investigated. When the BZN specimens sintered at 1550°C are further heat-treated at lower temperatures, the liquid phase formed during sintering is dissolved discontinuously and grain boundaries migrate. With the increase of heat-treatment temperature, grain-boundary migration becomes much less pronounced. These results are consistent with the coherency strain energy model proposed for the driving force for diffusion-induced grain boundary migration (DIGM).     

Fabrication of transparent YAG ceramics by traditional solid-state-reaction method

Transparent polycrystalline YAG ceramics were fabricated by solid-state reaction method using commercial ultrafine yttria andα-Al2O3 powders.The starting materials were milled and calcined at 1 400℃,and sintered into transparent YAG ceramics at 1 750℃in the vacuum for 4 h.Neither the starting materials as-milled or those calcined into YAG phase at 1 500℃can be sintered into transparent ceramics.Wide grain boundaries emerge in the YAG ceramics sintered at 1 850℃for 4 h,at the edge of which YAG phases decompose into perovskite YAlO3(YAP)andα-Al2O3.     

Microstructure, dielectric and ferroelectric properties of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (NBTB) and 0.05BiFeO3-0.95NBTB ceramics: Effect of sintering atmosphere

0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (NBTB) and 0.05BiFeO₃-0.95NBTB (BF-doped NBTB) lead-free ceramics were prepared by solid state reaction method. The ceramics were sintered at 1180 °C for 2 h in O₂ and N₂. All ceramics exhibited a single phase of perovskite structure. Relative amount of tetragonal phase was related to the sintering atmospheres. Both grain size and shape were influenced by the sintering atmospheres. Sintering the ceramics in N₂ weakened their dielectric anomalies corresponding to the transition from ferroelectric phase to the so-called “intermediate phase”. When the NBTB and BF-doped NBTB ceramics were sintered in N₂, their maximum dielectric constant and the degree of diffuseness of the transition from the “intermediate phase” to paraelectric phase increased, but their Curie temperatures decreased. The difference in dielectric properties of the ceramics sintered in different atmospheres was closely related to the difference in oxygen vacancy concentration. The correlation between ferroelectric properties and sintering atmospheres is associated with a competing effect among oxygen vacancy concentration, A-site vacancy concentration and percentage of tetragonal phase.     

Microstructure and electrical properties of Lu2O3-doped ZnO-Bi2O3-based varistor ceramics

Lu2O3-doped ZnO-Bi2O3-based varistor ceramics samples were prepared by a conventional mixed oxide route and sintered at temperatures in the range of 900-1 000°C,and the microstructures of the varistor ceramics samples were characterized by X-ray diffractometry(XRD)and scanning electron microscopy(SEM);at the same time,the electrical properties and V-I characteristics of the varistor ceramics samples were investigated by a DC parameter instrument for varistors.The results show that the ZnO-Bi2O3-based varistor ceramics with 0.3%Lu2O3(molar fraction)sintered at 950°C exhibit comparatively ideal comprehensive electrical properties.The XRD analysis of the samples shows the presence of ZnO,Bi-rich,spinel Zn7Sb2O12 and Lu2O3-based phases.     

Hot corrosion of a novel (Ni,Co)O/(Ni,Co)Fe2O4 composite coating thermally converted from an electrodeposited Ni–Co–Fe2O3 composite coating

Ni–Co–Fe₂O₃ composite coatings were successfully developed by sediment co-deposition. In order to improve their hot corrosion resistance, a pre-oxidation treatment was conducted at 1000 °C for 6 h. The corrosion behaviour of the oxidised composite coating was investigated at 960 °C in an atmosphere consisting of a mixture of Na₃AlF₆–AlF₃–CaF molten salts and air. They exhibited good hot corrosion resistance due to not only the pre-formed oxide scale with (Ni,Co)O and (Ni,Co)Fe₂O₄ phases after pre-oxidation, but also the formation of (Ni,Co,Fe)Al₂O₄ phases in the outer layer and a well-distributed NiFe₂O₄-enriched phase along the grain boundaries in the subscale area during the corrosion process.     

Effect of BaO addition on electric conductivity of xCu/10NiO-NiFe2O4 cermets

The effects of BaO addition on the phase composition, relative density and electric conductivity of xCu/10NiO-NiFe2O4 （x=5, 10） eermets were studied, which were prepared with cold isostatic pressing-sintering process. The results show that the relative densities of 5Cu/10NiO-NiFe2O4 cermet doped with 1% BaO （mass fraction） and 10Cu/10NiO-NiFe2O4 cermet doped with 1% BaO sintered at 1 473 K in nitrogen atmosphere, are increased by about 9.86% and 9.75% compared with the undoped BaO cermets, respectively. And the electric conductivities 22.79 S/cm of 5Cu/10NiO-NiFe2O4 cermets adding 1% BaO and 23.10 S/cm of 10Cu/10NiO-NiFe2O4 cermets adding 1% BaO are obtained, which are 2.21 times and 1.47 times of those of undoped samples, respectively. Moreover, the 10Cu/10NiO-NiFe2O4 cermets doped with 1% BaO have a maximum σ0 of 58.91 S/cm and electric conductivity of 23.10 S/cm at 1 233 K. Maybe low melting-point phases of BaFe2O4 and Ba2Fe2O5 have an excellent electric conductivity in xCu/10NiO-NiFe2O4 （x=5, 10） cermets at 1 233 K.     

Electrical and magnetic properties of magnesium ferrite ceramics doped with Bi2O3

The effects of concentration of Bi₂O₃ and sintering temperature on DC resistivity, complex relative permittivity and permeability of MgFe_1.98O₄ ferrite ceramics were studied. The objective of the study was to develop magneto-dielectric materials, with almost equal values of permeability and permittivity, as well as low magnetic and dielectric loss tangent, for the design of antennas with reduced physical dimensions. It was found that the poor densification and slow grain growth rate of MgFe_1.98O₄ can be greatly improved by the addition of Bi₂O₃, because liquid phase sintering was facilitated by the formation of a liquid phase layer due to the low melting point of Bi₂O₃. It was found that 3% Bi₂O₃ can result in fully sintered MgFe_1.98O₄ ceramics. The DC resistivities of the MgFe_1.98O₄ ceramics were increased as a result of the addition of Bi₂O₃, except for 0.5%. The exceptionally low resistivities of the 0.5% samples were explained by a ‘cleaning’ effect of the small amount of liquid phase at the samples’ grain boundaries. The electrical and magnetic properties of the MgFe_1.98O₄ ceramics exhibited a strong dependence on the concentration of Bi₂O₃. The 0.5% samples were found to have the highest dielectric loss tangents, which can be understood similarly to the DC resistivity results. The 2–3% Bi₂O₃ is required to attain low dielectric loss MgFe_1.98O₄ ceramics for antenna application. Low concentration of Bi₂O₃ increased the static permeability of the MgFe_1.98O₄ ceramics owing to the improved densification and grain growth, while too high a concentration led to decreased permeability owing to the incorporation of the non-magnetic component (Bi₂O₃) and retarded grain growth. However, the addition of Bi₂O₃ alone is not able to produce magneto-dielectric materials based on MgFe_1.98O₄ ceramics, and further work is necessary to modify the permeability using cobalt (Co).