A facile synthesis of supported amorphous iron oxide with high performance for Cr(VI) removal from aqueous solution under visible light irradiation

A series of supported iron oxide nanoparticles were prepared by impregnation with Fe(NO₃)₃ supported on TiO_2, followed by low-temperature calcination. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra and BET have been used to characterize the samples. These iron oxide-impregnated TiO₂ were examined for photocatalytic reduction of Cr(VI). The experiments demonstrated that Cr(VI) in aqueous solution was more efficiently reduced using Fe₂O₃/TiO₂ heterogeneous photocatalysts than either pure Fe₂O₃ or TiO₂ under visible light irradiation. All TiO₂ supported samples were somewhat active for visible light photoreduction. With an optimal mole ratio of 0.05-Fe/Ti, the highest rate of Cr(VI) reduction was achieved under the experimental conditions. We also compared the photoreactivity of TiO₂ supported iron oxide samples with that supported on Al₂O₃ and ZrO₂. It can be noted that iron oxide nanoparticles deposited on high surface area supports to increase the solid-liquid contact area renders it considerably more active. Noticeably, iron oxide cluster size and dispersion are important parameters in synthesizing active, supported Iron oxide nanoparticles. In addition, the interaction between iron oxide and TiO₂ was proposed as the source of photoactivity for Cr(VI) reduction.     

Synthesis, characterization and devitrification behaviour of an yttrium containing boroaluminate glass

The glass forming region in the B₂O₃-Al₂O₃-Y₂O₃ composition diagram has been determined by a melting and quenching procedure at temperatures up to 1800°C. Different physical characteristics (density, coefficient of thermal expansion, glass transition and crystallization peak temperatures) have been determined for a 35B₂O₃-40Al₂O₃-25Y₂O₃ glass composition (in mol.%). By using a predictive model and some NMR structural data, different elastic moduli (Young's modulus, bulk modulus, shear modulus and Poisson's ratio) have been calculated. The devitrification behaviour has also been studied. Internal crystallization is the dominant mechanism and a new (Y, Al)BO₃ ternary phase has been characterized by X-ray powder diffraction. The temperature and time nucleation dependence have been determined from DTA experiments as well as the crystallization kinetics (i.e. the Avrami exponent and the activation energy for crystal growth).     

An overview on microwave processing of material: A special emphasis on glass melting

Material processing adopting microwave heating has emerged as an alternative tool owing to faster processing, a cleaner environment, and several other advantages. This review provides a summary of recent reports of microwave synthesis of materials. This study reviews the use of microwave energy for application in several material processing technologies apart from food processing. A special emphasis has been made in the processing of glass adopting microwave energy. Melting of glass comprising SiO₂, P₂O₅, B₂O₃ as the main building block has been discussed. It has been revealed that silica, a microwave transparent material as reported earlier, can be heated under microwave heating directly. Microwave absorption of raw materials and different glass system has been discussed. Dielectric properties, particularly loss tangent or loss factor, are presented for some glass composition. Less evaporation of ingredient and low contamination from the crucible wall are noticed during glass melting using microwave heating. Enhanced iron redox ratio (Fe⁺²/∑Fe) in microwave processing may be considered an advantage in the preparation of heat absorbing filter glass. Small-scale glass melting using the microwave heating has a significant impact on energy and time saving. However, the challenges associated with the upscaling glass melting with microwave heating and future scope have been talked about.     

Crystallization and microstructural behaviour of strontium titanate borosilicate glass ceramics with Bi2O3 addition

Glasses in the system (65 −x) [SrO·TiO₂] − (35) [2SiO₂·B₂O₃] − (x) [Bi₂O₃] wherex = 1, 5, 10 (wt%) prepared by melting in alumina crucible (1375–1575 K), were subjected to different heat treatment schedules followed by DTA studies. Crystallization study showed the formation of Sr₂B₂O₅ as major phase at low temperature (≈950°C) heat treatment. At high temperatures, TiO₂ and SrTiO₃ with or without Sr₂B₂O₅ crystallize out depending on heat treatment. In this paper, the influence of variation in composition, thermal treatment on the nature of crystallizing phases as well as on the resulting microstructures are investigated through XRD, IR and SEM. Uniform crystallization was achieved by suitable addition of Bi₂O₃ and proper heat treatment.     

The eutectic generation effect and chemical modification of thermal lance cutting of concrete

Thermal lance is one of the methods for concrete cutting/piercing. The burning lance not only provides high temperature to melt the concrete target in the form of lava, but also has a eutectic effect changing the lava melting temperature. The eutectic effects by adding lance material such as FeO, Al₂O₃ and TiO₂ to concrete (SiO₂-CaO) system are discussed. The discussion and concrete piercing experiments both show that, due to eutectic generation effects, aluminum and titanium modified lances are not effective on concrete objects although these lances provide high lance temperature. Iron based lance is the most effective thermal lance due to its eutectic generation effect. Experimental results of cutting improvement by using chemically modified iron lance are presented and the eutectic generation effect in this process is discussed.     

A crystallization conditions study of the Ti‐doped barium hexaferrite powders synthesized with the glass crystallization technique for microwave applications

For microwave applications Titanium doped M‐type hexagonal ferrites have been synthesized by means of glass crystallization technique varying the crystallization parameters and the melt doping concentrations. The chosen melt dopings were x = 5.4 and 7.2 mole‐% TiO₂ with the following basic composition (mole‐%): 40 BaO + 33 B₂O₃ + (27‐x) Fe₂O₃ + x TiO₂. We have studied the dependencies between the magnetic properties, the valence of the iron ions in the glasses and the powders, the formation of new dielectric phases and the microwave absorption. After the Ti⁴⁺ ions substitutions, the magnetocrystalline anisotropy changed, this effect was observed in the static magnetic properties (_JH_C and M_S) measured using a vibration sample magnetometer. Furthermore the Ti⁴⁺ ions preferably occupy mainly the 2a as well as slightly the 2b sites in the lattice of the barium hexaferrite, which are studied using Mössbauer spectroscopy. Besides, the X‐ray diffraction studies proved that the formation of the ferrimagnetic (BaFe_12‐xTi_xO₁₂) and dielectric (BaTi₆O₁₃) phases are dependent on the crystallization parameters. The controlled influencing of lattice sites occupation and of the Fe²⁺ content in the ferrimagnetic phase as well as the controlled formation of the dielectric phase rate during the annealing are possibilities to optimize the microwave absorption of Ti‐doped barium hexaferrite powders synthesized by glass crystallization technique.     

Spectroscopic characterization of alkali borosilicate glasses containing iron ions

Structural properties of alkali borosilicate glasses containing iron ions were investigated using infrared, laser Raman and Mössbauer spectroscopy. Two types of glasses were prepared: SRL-type with the composition 18.5 wt% Na₂O, 10.0 wt% B₂O₃, 52.5 wt% SiO₂, 4.0 wt% Li₂O, 10 wt% TiO₂ and 5.0 wt% CaO, and sodium borosilicate glass with the composition 16.7 wt% Na₂O, 18.7 wt% B₂O₃ and 64.6 wt% SiO₂. Raman spectroscopy showed that orthosilicates are the dominant amorphous phase in the SRL-type of glass. Incorporation of iron in the SRL-type of glass induced polymerization of silicate units and -Si-O-Fe- copolymerization. It was concluded that different amorphous phases are simultaneously present in the SRL-type of glass containing iron ions. Interpretation of the Raman spectra is given. Incorporation of iron ions into the sodium borosilicate glass also affected the corresponding IR spectra. The valence state of iron and its coordination were determined by⁵⁷Fe Mössbauer spectroscopy.     

Crystallization, microstructure development and dielectric behaviour of glass ceramics in the system [SrO · TiO2]-[2SiO2 · B2O3]-La2O3

Various glasses in the system (65 – x)[SrO · TiO₂]-(35)[2SiO₂ · B₂2O₃]-(x)La₂O₃, where x = 1,5,10 (wt%) were prepared by melting in alumina crucible (1375–1575 K). Heat treatment schedules were selected from DTA plots of respective glasses. X-ray diffraction studies of glass ceramic samples containing different concentrations of La₂O₃ revealed the formation of Sr₂B₂O₅, Sr₃Ti₂O₇ and TiO₂ (rutile) phases. The addition of La₂O₃ results in the development of well formed, elongated crystallites of different phases. Results of the dielectric behaviour demonstrate higher values of dielectric constant for some of the glass ceramic samples. This can be ascribed to the relaxation polarization at the crystal-glass interface due to conductivity differences between crystalline and glassy phases.     

Effects of TiO2 coating on microstructure and mechanical properties of magnesium matrix composite reinforced with Mg2B2O5w

The interface between the reinforcement and the matrix is very important for metal matrix composites. The effects of TiO₂ coating on microstructure and mechanical properties of Mg₂B₂O₅w-reinforced AZ91D magnesium matrix composite fabricated by squeeze casting technique were studied. The results indicate the flexural strength and flexural modulus of Mg₂B₂O₅w/TiO₂/AZ91D composite is 40% and 35% up on that of Mg₂B₂O₅w/AZ91D composite. The reason is that the MgO interfacial product resulting from the reaction between the TiO₂ coating and the liquid Mg can enhance the interfacial bonding strength and increase the load transfer from the matrix to the reinforcement, which leads to higher mechanical properties of Mg₂B₂O₅w/TiO₂/AZ91D composite.     

Thermodynamic Properties of FeNb<Subscript>2</Subscript>O<Subscript>6</Subscript> and FeTa<Subscript>2</Subscript>O<Subscript>6</Subscript>

Empirical calculational approaches have been used to evaluate the enthalpy, entropy, heat capacity, and melting point of iron(II) niobate and iron(II) tantalate and the coefficients A, B, and C in an equation for the temperature dependence of their heat capacity. The melting point of FeTa₂O₆ has been experimentally determined to be 1891 ± 5 K. The calculated heat capacity (C°_p (298.15 K)) of iron tantalate and the Gibbs energies of formation of FeN₂O₆ and FeTa₂O₆ have been compared to previously reported data.     

The relationship between phase composition and conditions of sintering seawater derived magnesium oxide

This study has focused on the favourable effect of the TiO₂ addition (1, 2 and 5 wt%) on the reduction of B₂O₃ content during activated sintering of magnesium oxide from seawater at temperatures of 1400, 1500 and 1700°C for the duration of 1, 2 and 4 h. A mathematical model of dependence between the B₂O₃ mass fraction in the sintered sample, the temperature of isothermal sintering, the isothermal sintering time and the mass fraction of TiO₂ added have been proposed. Magnesium oxide was obtained from seawater by substoichiometric precipitation, with the addition of 80% of dolomite lime as the precipitation agent. New phases formed in magnesium oxide samples were examined by the XRD and SEM/EDS analysis. The results indicate that during activated sintering of seawater-derived magnesium oxide with a TiO₂ addition, reactions of formation of Ca₂B₂O₅, CaTiO₃ and Mg₂TiO₄ took place simultaneously. The thermodynamics analysis of experimental results, based on the Onsager reciprocity relations (symmetry relations), was applied and phenomenological coefficients were calculated to describe the interference of these three irreversible processes.     

Wear behavior of TiB<Subscript>2</Subscript> inoculated 20Cr–3Mo–4C high chromium white cast irons

FeTi, B₂O₃, Al, and FeW particulates, approximately 40–60 μm in size, were mixed in stoichiometric ratio and sintered at 1,200 °C. The sintered particulates were added as 5 wt% to molten high chromium white cast iron over 50 C-deg above the melting temperature, and stirred at 1,000 rpm. The samples were investigated in three groups: (1) high Cr white cast iron inoculated by the particulates sintered from Al–FeTi–B₂O₃ particulates; (2) high Cr white cast iron inoculated by the sintered particulates derived from Al–FeTi, B₂O₃, and FeW particulates; and (3) specimens of the second group that were subsequently homogenized. The microhardness of ceramic particulates was measured as 2,800–3,400 HV₁₀. The effect of sintered particulate volume fraction on the abrasive wear resistance of the high chromium white cast iron was determined. The wear resistance and hardness of the composites improved significantly as a result of particulate inoculation. The application of the homogenization heat treatment to the inoculated samples produced a microstructure having homogeneously distributed particulates.     

Investigation of the displacement reaction in mixed AIN + TiO2 powders

Micrometre-size AIN + TiO₂ powders in the molar ratio 2/1.5 were mixed, cold-pressed and heat-treated to 1400-1800 K in an AIN + N₂ = 1 atm buffer environment. Coarse AIN particles in fine TiO₂ powder, and TiO₂ single-crystal chips in fine AIN powder were also processed similarly. From X-ray diffraction and direct microstructural observations it is described and discussed that to a first approximation the overall reaction proceeds in three major steps: (i) reduction of TiO₂ to Ti₄O₇ or Ti₃O₅ with concurrent Al₂O₃ dissolution, (ii) formation of Ak _x Ti _y O₅ phases of either monoclinic or orthorhombic structure depending chiefly on the initial TiO₂ particle size, (iii) decomposition of such mixed oxide into Al₂O₃+ TiN. Simultaneously with these steps, the progressive oxidation of AIN to Al₂O₃ takes place at a rate which does not limit the overall reaction kinetics. Evidence is also provided that the reaction takes place in part via the transport of gaseous AI- and Ti-containing species, which calls for further investigation to be reported in the companion paper.     

Oxide fibres and their composites with nickel and molybdenum matrices produced by internal crystallization

Complex oxide 2Al₂O₃·MgO·3CaO and a triple oxide eutectic TiO₂-MgO-CaO, both with relatively low melting points, were used to reinforce a nickel matrix by the internal crystalization method. Strength properties of the fibres were measured by testing composites with nickel as well as molybdenum matrices. It is shown that the fibre strength depended strongly on both the initial melt composition of the fibre material and the fabrication regimes.     

The effect of processing parameters in the carbothermal synthesis of titanium diboride powder

The mechanism of the carbothermal method for synthesizing titanium diboride (TiB₂) powder has been studied. Mixtures of TiO₂, H₃BO₃ and carbon were heated in an argon atmosphere at 1000–1600 °C. The effect of the molar ratio and holding time on the phase evolution was studied by X-ray diffraction. The products were also characterized by scanning electron microscopy observations and particle size measurements.For a composition with a molar ratio of TiO₂:H₃BO₃:C = 1:2.4:5 heated for 1 h, the simultaneous presence of TiC and TiB₂ phases at 1100 °C and the transformation of TiO₂ to Ti₂O₃ at 1200 °C and higher confirms that TiB₂ synthesis is based on a TiC formation mechanism, in which TiC may be formed from a reaction between TiO₂ or Ti₂O₃ and carbon. Then TiC may react with liquid B₂O₃ and/or gaseous B₂O₂ to form the TiB₂ phase. The reaction is completed at 1500 °C. Also by increasing the molar ratio of boric acid to 3, the impurities decreased considerably and pressing of the material had an obvious effect on decreasing the impurities, due to an increase of the surface contact of particles, which causes an effective inhibition of boron escape from the reaction chamber. Under these experimental conditions, a relatively narrow size distribution of TiB₂ particles was produced. When the reaction time increased to 1.5–2 h, grain growth of particles occurred. Therefore, a wider distribution of particle size was obtained.     

Acid-base reactions in fused alkali borate + TiO2 mixtures

The nature of the titanium-containing phases which crystallize from solutions of TiO₂ in fused alkali metal borates, varies with the alkali cation, the mole ratio of alkali oxide to B₂O₃, and the initial concentration of TiO₂. Recrystallization of TiO₂ rather than crystallization of complex titanates, is enhanced by the presence in solution of small cations, by a high proportion of B₂O₃ relative to alkali oxide, and by higher concentrations of TiO₂.The crystallization of complex titanates is correlated with the formation of borate groups containing non-bridging oxygens whose existence has been suggested by previous workers.     

Effect of deformation temperature and degree on tensile properties of the extruded 2024Al/Al18B4O33w composite with extrusion – forging multistage hot deformation

The effect of extrusion – forging multistage hot deformation on tensile properties of the 2024Al/Al₁₈B₄O₃₃w composites is investigated. The extruded 2024Al/Al₁₈B₄O₃₃w composites are used as blanks. The tensile properties of the extruded 2024Al/Al₁₈B₄O₃₃w composite followed by secondary deformation are studied. The effects of holding temperature and deformation degree on tensile properties of the extruded composite are discussed. The results show that due to the reduction in stress concentration and dislocations, ultimate tensile strength of the extruded 2024Al/Al₁₈B₄O₃₃w composite held at 400 °C for 1 h is lower than that of the extruded composite without holding. Increasing holding temperature from 300 °C to 450 °C, ultimate tensile strength of the extruded 2024Al/Al₁₈B₄O₃₃w composite increases firstly and then decreases. The extruded 2024Al/Al₁₈B₄O₃₃w composite held at 400 °C for 1 h followed by secondary forging with the larger length to width ratio of 4 : 1 has the ultimate tensile strength of 456.1 MPa, higher than that of the extruded 2024Al/Al₁₈B₄O₃₃w composite without secondary forging.     

Influence of Sm2O3 on the crystallization and luminescence properties of boroaluminosilicate glasses

Sm₂O₃-doped SiO₂-B₂O₃-Al₂O₃-BaO glasses were prepared by melting method in order to study the influence of Sm₂O₃ on the crystallization behavior and luminescence properties. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy were used to characterize the rare earth glasses and the crystalline phases after heat-treatment. The course of phase separation and devitrification of the glasses were also investigated. The results show that the thermal stability of the glasses decreases with the increase of content of Sm₂O₃. The crystalline phase changed from SmAl_2.07(B₄O₁₀)O_0.6 to SmBO₃. Divalent Sm²⁺ ions were detected in the crystallization product after heat-treatment. The valence transformation from Sm³⁺ to Sm²⁺ in the crystal suggests the samarium atoms entering the barium sites. The charge carried in vacancy defect induced by the substitution led to the partial reduction process. The reduction of Sm³⁺ ions was promoted by the increasing of Sm₂O₃ content or the extending of heat-treated holding time in boroaluminosilicate glass.     

熔制保温时间对CAMS系矿渣微晶玻璃结构与性能的影响

以白云鄂博二次选后尾矿、高炉渣和粉煤灰为主要原料,采用熔融法制得CaO-Al_2O_3-MgO-SiO_2(CAMS)系微晶玻璃,利用DSC、XRD、SEM、EDS、Raman、红外光谱及理化性能测试手段,研究了熔制过程中不同保温时间对微晶玻璃结构与性能的影响。结果表明:随着熔制保温时间的延长,矿渣玻璃熔液中氟的挥发及对氧化铝坩埚的侵蚀导致基础玻璃中氟含量降低而Al2O3含量升高,基础玻璃析晶温度呈先上升后下降的趋势,微晶玻璃主晶相为透辉石,晶粒出现先细化后粗化的趋势,第二相萤石相随着保温时间的延长逐渐消失,最终导致微晶玻璃结构及理化性能发生改变。当玻璃熔制保温时间为5h时,制备的微晶玻璃综合性能最优,其密度、抗折强度、显微硬度及耐酸碱性分别为3.09g/cm3、201 MPa、7 021 MPa、97.78%和98.83%。     

Effect of TiO2 on properties of magnesium oxide obtained from seawater

The effect has been examined of TiO₂ on B₂O₃ content in sintered magnesium oxide samples obtained by precipitation of magnesium hydroxide in seawater with 80 or 120% of the stoichiometrical quantity of the precipitation agent, i.e. the effect of TiO₂ on product properties has been examined. Coefficients were calculated for dependent reactions of Ca₂B₂O₅ and CaTiO₃ formation.