Oxidative dehydrogenation of 1 -butene to butadiene on α-Fe2O3/ZnAl2O4 and ZnFexAl2-xO4 catalysts

The oxidative dehydrogenation of 1-butene to butadiene was studied over a series of catalysts of iron impregnated on ZnAl₂O₄ used as a support and also Fe coprecipitated with zinc and aluminum in order to obtain ZnFe_xAl_2-xO₄ type catalysts. Results were compared with bulk -Fe₂O₃, ZnAl₂O₄ and ZnFe₂O₄. X-ray diffraction (XRD) and Mössbauer spectroscopy suggest that in the impregnated catalysts, Fe ions are in strong interaction with the support. These samples have higher butadiene selectivity than coprecipitated ZnFe_xAl_2-xO₄ catalysts, in which iron is incorporated into the ZnAl₂O₄ spinel network. Results suggest also that iron content has a greater effect on butadiene selectivity than the zinc aluminate-iron oxide interaction.     

Modified Semi‐Coke‐Supported Cerium Oxide‐Doped Zinc Ferrites for the Removal of H2S from Coal Gas

Cerium oxide‐doped ZnFe₂O₄ sorbents supported on modified semi‐coke (MSC) were prepared to improve the desulfurization efficiency of zinc ferrites. The sulfidation tests of the ZnFe₂O₄/MSC sorbents with and without Ce were carried out using a fixed‐bed reactor at 450 °C. The effect of the CeO₂/ZnFe₂O₄ molar ratio of the sorbents on the sulfur capacity was studied. The characteristics of the sorbents were analyzed by X‐ray diffraction, N₂ adsorption, scanning electron microscopy and X‐ray photoelectron spectroscopy. The results showed that cerium oxide could greatly improve the desulfurization reactivity of the ZnFe₂O₄/MSC sorbents. The molar ratio of Ce to Zn and Fe influences the desulfurization reactivity, and a good sulfur capacity of the sorbent can be obtained with a Ce/Zn/Fe ratio of 4:4:1. It was also found that the addition of CeO₂ could enlarge the surface area and the pore volume, thus improving the dispersion of active components. Ce doping results in an increment of the oxygen adsorbed on the sorbent surface, which facilitates the adsorption of H₂S. The Ce ions could act as carriers of the oxidation and reduction reactions and the oxygen transfer could be accelerated during the desulfurization process of coal gas.     

Origin of Violet‐Blue Emission in Ti‐Doped Gahnite

ZnAl₂O₄ doped with Ti⁴⁺ (2%) was synthesized by the hydrothermal method at 220°C at pressure of 25 bars. An average grain size of the as‐prepared sample was 3 nm, the samples with biggest grain size were obtained after annealing at 300°C, 500°C, 600°C, 700°C, and 900°C, diameter of the latter was about 33 nm. IR spectroscopy indicated that ZnAl₂O₄ was partially inverted. The degree of the inversion decreases with increase in the annealing temperature but increases with increasing Ti⁴⁺ content. Absorption and emission spectra as well as emission decay profiles were recorded at 300 and 77 K. The observed spectra are due to charge‐transfer O^2??Ti⁴⁺ transitions. Color of the emission depends on the nanocrystal size and with increase in its diameter changes from violet to blue, accordingly the absorption bands exhibit redshift. The calculations based on Density Functional Theory confirmed the experimental results. 3d electrons of titanium ions form the bottom of the ZnAl₂O₄:Ti⁴⁺ conduction band, oxygen, aluminum or zinc vacancies create additional levels in the gahnite energy band gap. It was also found that in ZnAl₂O₄ aluminum or zinc vacancy induces magnetism with relatively high magnetic moment close to 1 μ_B per vacancy.     

Synthesis of ternary zinc spinel oxides and their application in the photodegradation of organic pollutant

Ternary zinc spinel oxides such as Zn₂SnO₄, ZnAl₂O₄ and ZnFe₂O₄ were synthesized and characterized, and their activities in the photodegradation of phenol molecules were investigated. Zn₂SnO₄, ZnAl₂O₄ and ZnFe₂O₄ powders were synthesized by hydrothermal, metal–chitosan complexation and solvothermal routes, respectively. The face-centered cubic spinel structure of each material was confirmed by powder X-ray diffractometry (XRD) and its porous structure by N₂ adsorption–desorption isotherms. The characterization of spinels was complemented with Fourier transform infrared spectroscopy (FTIR) and X-rays fluorescence (XRF), revealing the formation of spinel structures with high purity. The photocatalytic activity in the degradation of phenol was observed only with Zn₂SnO₄ oxide. Mineralization degree of phenol molecules by Zn₂SnO₄ photocatalyst determined by total organic carbon analysis (TOC) reached 80% at 360 min under sunlight.     

Low‐melting sulfate glasses as additives to semirigid PVC and their flame retardant and smoke suppressant properties

The role of low‐melting sulfate glasses (LMSG) as additives on the flame retardant and smoke suppressant properties of semirigid poly(vinyl chloride) (PVC), as well as the mechanism for flame retardancy and smoke suppression, were studied through the Limiting Oxygen Index (LOI) test. Smoke Density Rating (SDR) test, DTA‐TG, and SEM. The results show that the LMSG have good smoke suppressant properties. When the PVC compound contains 40 parts of LMSG, the SDR value will be reduced by about 45%. The Cu²⁺, Zn²⁺, Mn²⁺, and Ni²⁺ sulfates, as well as MoO₃, cause PVC to crosslink and form char, and the melt can protect not only the char formed during combustion and thermal degradation, but also undecomposed polymer. That is the main mechanism for flame retardation and smoke suppression when the additives melt. The mechanical properties of the PVC compounds containing different levels of LMSG were also studied.     

Synthesis of Ni2+‐doped ZnAl2O4/ZnO Composite Phosphor Film with Largely Enhanced Polychromatic Emission via a Single‐Source Precursor

Ni²⁺‐doped ZnAl₂O₄/ZnO composite films were successfully fabricated on single crystal silicon substrates through a single‐source precursor route, which mainly involved slurry coating of Ni–Zn–Al‐layered double hydroxide precursor followed by calcination at elevated temperatures. Material characterization has been presented using a combination of X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectra, Raman spectra, UV–vis diffuse reflectance spectra, and fluorescence spectroscopy measurements. The results showed that Ni²⁺ ions could be uniformly doped in the two‐phase ZnO and ZnAl₂O₄ lattices. A broadened and intense polychromatic emission peak covering the whole visible region was obtained over 4.3 mol% Ni²⁺‐doped ZnAl₂O₄/ZnO composite film, which was attributed to the presence of an appropriate number of luminescent Ni²⁺centers in the ZnO and ZnAl₂O₄ double host matrix, thus largely enhancing the related transition. We believe that such unique ZnAl₂O₄/ZnO films can open up a new opportunity for advanced applications of composite phosphors.     

Recent developments in zinc-based two-cation oxide spinels: From synthesis to applications

Zinc stannate (Zn₂SnO₄), zinc ferrite (ZnFe₂O₄), zinc antimonate (ZnSb₂O₄) and zinc aluminate (ZnAl₂O₄) are examples of zinc-based two-cation oxide spinel semiconductors (ZTCOSSs) that have been investigated and employed in many applications. These include applications in solar cells, photocatalysts, batteries, supercapacitors, thermoelectrics and sensors. Zinc-based two-cation oxide spinel semiconductors have peculiar properties that include low electrical resistivity and unique optics. Also, ZTCOSSs permit multiple redox reactions and exhibit magnetic properties depending on the cations. ZTCOSS has the advantages of better optical, electrical and chemical properties over the zinc oxide spinel semiconductor. In this review, the concept of zinc-based two-cation spinel oxides, fabrication techniques and their properties are discussed. Applications of zinc-based two-cation oxide spinel semiconductors are explored and the performance compared with that of single oxides spinel semiconductors.     

In Situ crystallization to zinc aluminate films with controlled surface microstructure and anticorrosion performance

Spinel‐type zinc aluminate (ZnAl₂O₄) thin films with controlled surface microstructure on aluminum substrates were fabricated via a facile and effective in situ crystallization method without using any templates or surfactants. The surface microstructure of ZnAl₂O₄ films could be significantly controlled by varying the experimental conditions including concentration of reactants, crystallization temperature, and crystallization time. After surface modification, the specific topography of ZnAl₂O₄ films was beneficial to obtain surface hydrophobic or superhydrophobic properties. More importantly, compared to nanoparticle‐ and nanosword‐assembled ZnAl₂O₄ films, nanorod‐assembled ZnAl₂O₄ film provided a more effective barrier to aggressive species for aluminum substrates in a wide range of pH values; very low corrosion current density of the order of ～10^?19 A cm^?12 could be achieved. A new contribution to the development of advanced coating system with ZnAl₂O₄ film materials that can be used in practical application for corrosion protection of aluminum materials is provided. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Phosphorus‐containing silica gel‐coated ammonium polyphosphate: Preparation,characterization, and its effect on the flame retardancy of rigid polyurethane foam

A phosphorus‐containing silica gel was synthesized via a reaction between phenyl dichlorophosphate, poly(ether polyol), and γ‐aminopropyltriethoxysilane. Ammonium polyphosphate (APP) was modified by the synthesized phosphorus‐containing silica gel (MAPP) and then incorporated into the rigid polyurethane foam (PU). Results showed that APP had a smaller particle size, lower initial decomposition temperature, better heat resistance at high temperature, and better compatibility with PU matrix after the modification. The cone calorimeter test results showed that the incorporation of MAPP obviously reduced the values including peak of heat release rate, total heat release, average effective heat of combustion, and total smoke release, and increased the char yield of PU composite comparing with APP. The improved flame retardancy of PU/MAPP composite was attributed to the quenching effect of PO· and PO₂· free radicals released by MAPP in the early stage and the improved thermal stability of phosphorus‐ and silicon‐containing char layer formed in the later stage. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46334.     

Flame‐retardant action of red phosphorus/magnesium oxide and red phosphorus/iron oxide compositions in recycled PET

Red phosphorus was combined with metallic oxides Fe₂O₃ and MgO to improve the fire properties of recycled PET. Both Fe₂O₃ and MgO act as co‐synergist agents at a total loading of 5 wt%. The analysis by diffraction X of the char formed during combustion shows that transformation of Fe₂O₃ to Fe₃O₄ occurs. Fe₂O₃ favours the oxidation and improves the effectiveness of red phosphorus. It is suggested that MgO interacts with acidic end groups of PET and forms a thermal stable residue. The thermal decomposition of recycled PET containing red phosphorus combined with Fe and Mg oxides was studied by thermal analysis and leads to an increase in char formation. While the incorporation of Fe₂O₃ in this ternary blend maintains the mechanical properties of PET, the reactivity of MgO leads to a brittle material. The use of reinforcements (talc and glass fibres) to mechanically stabilize the char formed during combustion of ternary blend with Fe₂O₃ entails a further decrease in heat release rate, nevertheless impact resistance of the material decreases dramatically. Copyright © 2005 John Wiley & Sons, Ltd.     

Preparation,structural, and electrical studies of polyaniline/ZnFe2O4 nanocomposites

Polyaniline/ZnFe₂O₄ nanocomposites were synthesized by a simple and inexpensive one‐step in situ polymerization method in the presence of ZnFe₂O₄ nanoparticles. The structural, morphological, and electrical properties of the samples were characterized by wide angle X‐ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). WAXD and SEM revealed the formation of polyaniline/ZnFe₂O₄ nanocomposites. Infrared spectroscopy indicated that there was some interaction between the ZnFe₂O₄ nanoparticles and polyaniline. The dc electrical conductivity measurements were carried in the temperature range of 80 to 300 K. With increase in the doping concentration of ZnFe₂O₄, the conductivity of the nanocomposites found to be decreasing from 5.15 to 0.92 Scm⁻¹ and the temperature dependent resistivity follows ln ρ(T) ∼ T^−1/2 behavior. The nanocomposites (80 wt % of ZnFe₂O₄) show a more negative magnetoresistance compared with that of pure polyaniline (PANI). These results suggest that the interaction between the polymer matrix PANI and zinc nanoparticles take place in these nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanochemical synthesis of zinc ferrite from zinc oxide and α-Fe2O3

Mechanochemical synthesis of zinc ferrite (ZnFe₂O₄) from a powder mixture of zinc oxide (ZnO) and hematite (α-Fe₂O₃) by room temperature grinding using a planetary ball mill was investigated. The grinding enables us to obtain the amorphous mixture of the starting materials. Most of ZnO reacts with α-Fe₂O₃ to convert into insoluble amorphous zinc and iron compounds within 2h-grinding. Prolonged grinding enhances the crystallization of ZnFe₂O₄ from the amorphous compounds. ZnFe₂O₄ crystallized by the grinding for 3 h or more consists of nanocrystalline particles with high specific surface area.     

Sol-gel synthesis and characterization of ZnAl2O4 powders for transparent ceramics

The sol-gel synthesis of ZnAl₂O₄ ceramic powders from alkoxide and acetate sources of metals, as well as the microstucture and the hardness of the hot-pressed ZnAl₂O₄ specimens were considered. ZnAl₂O₄ powders were prepared by the hydrolysis of an alcohol solution of aluminium isopropoxide using an aqueous solution of zinc acetate followed by heat treatment. The thermal evolution of the ZnAl₂O₄ precursor was investigated. The effect of calcination temperature on the morphology and the specific surface area of ZnAl₂O₄ powders were also studied. The sintering of the resultant powders to the high transparent ceramic using a hot pressing with 1?wt% ZnF₂, as a sintering additive was successfully demonstrated. The in-line transmittance of ZnAl₂O₄ ceramics (1?mm thickness) achieved 80% in the visible region and 85% at 5?µm; Vickers hardness was 11.6?GPa.     

Fire performance of charring closed‐cell polymeric insulation materials: Polyisocyanurate and phenolic foam

Results are presented from 2 series of ad hoc experimental programmes using the cone calorimeter to investigate the burning behaviour of charring closed‐cell polymeric insulation materials, specifically polyisocyanurate (PIR) and phenolic (PF) foams. These insulation materials are widely used in the construction industry due to their relatively low thermal conductivity. However, they are combustible in nature; therefore, their fire performance needs to be carefully studied, and characterisation of their thermal degradation and burning behaviour is required in support of performance‐based approaches for fire safety design. The first series of experiments was used to examine the flaming and smouldering of the char from PIR and PF. The peak heat release rate per unit area was within the range of 120 to 170 kW/m² for PIR and 80 to 140 kW/m² for PF. The effective heat of combustion during flaming was within the range of 13 to 16 kJ/g for PIR and around 16 kJ/g for PF, while the CO/CO₂ ratio was within 0.05 to 0.10 for PIR and 0.025 to 0.05 for PF. The second experimental programme served to map the thermal degradation processes of pyrolysis and oxidation in relation to temperature measurements within the solid phase under constant levels of nominal irradiation. Both programmes showed that surface regression due to smouldering was more significant for PF than PIR under the same heat exposure conditions, essentially because of the different degree of overlap in pyrolysis and oxidation reactions. The smouldering of the char was found to self‐extinguish after removal of the external heat source.     

Studies on Fourier transform infrared spectroscopy,scanning electron microscope,and direct current conductivity of polyaniline doped zinc ferrite

In situ polymerization of aniline was carried out in the presence of zinc ferrite to synthesize polyaniline/ZnFe₂O₄ composites (PANI/ZnFe₂O₄) by chemical oxidation method. The composites have been synthesized with various compositions (10, 20, 30, 40, and 50 wt %) of zinc ferrite in PANI. From the Fourier transform infrared spectroscopy (FTIR) studies on polyaniline/ZnFe₂O₄ composites, the peak at 1140 cm⁻¹ is considered to be measure of the degree of electron delocalization. The surface morphology of these composites was studied with scanning electron micrograph (SEM). The dc conductivity has been studied in the temperature range from 40–160°C and supports the one‐dimensional variable range hopping (1DVRH) model proposed by Mott. The results obtained for these composites are of scientific and technological interest. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fabrication and Characterization of Glass‐Ceramic Fiber‐Containing Cr3 + ‐Doped ZnAl2O4 Nanocrystals

Glass‐ceramic fibers containing Cr³⁺‐doped ZnAl₂O₄ nanocrystals were fabricated by the melt‐in‐tube method and successive heat treatment. The obtained fibers were characterized by electro‐probe micro‐analyzer, X‐ray diffraction, Raman spectrum and high‐resolution transmission electron microscopy. In our process, fibers were precursor at the drawing temperature where the fiber core glass was melted while the clad was softened. No obvious element interdiffusion between the core and the clad section or crystallization was observed in precursor fiber. After heat treatment, ZnAl₂O₄ nanocrystals with diameters ranging from 1.0 to 6.3 nm were precipitated in the fiber core. In comparison to precursor fiber, the glass‐ceramic fiber exhibits broadband emission from Cr³⁺ when excited at 532 nm, making Cr³⁺‐doped glass‐ceramic fiber a promising material for broadband tunable fiber laser. Furthermore, the melt‐in‐tube method demonstrated here may open a new gate toward the fabrication of novel glass‐ceramic fibers.     

Fabrication and photocatalytic properties of novel ZnO/ZnAl2O4 nanocomposite with ZnAl2O4 dispersed inside ZnO network

Novel ZnO/ZnAl₂O₄ nanocomposites with ZnAl₂O₄ nanoparticles homogeneously dispersed inside a network of ZnO are fabricated by thermal treatment of a single‐source precursor of ZnAl‐layered double hydroxides (ZnAl‐LDHs) at 800°C. The effects of the Zn/Al molar ratio of the LDH precursors on the structure, composition, morphology, textural as well as UV‐absorbing properties and photocatalytic activities of the nanocomposites are investigated in detail. The results show that the ZnO/ZnAl₂O₄ nanocomposites derived from the ZnAl‐LDHs precursors have superior photocatalytic performances to either single phase ZnO or similar ZnO/ZnAl₂O₄ samples fabricated by chemical coprecipitation or physical mixing method. The heterojunction nanostructure and the strong coupling between the ZnO and ZnAl₂O₄ phase derived from ZnAl‐LDHs precursors are proposed to contribute the efficient spatial separation between the photo‐generated electrons and holes, which can concomitantly improve the photocatalytic activities. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Synergistic effect of metal oxides on the flame retardancy and thermal degradation of novel intumescent flame‐retardant thermoplastic polyurethanes

The synergistic effects of some metal oxides on novel intumescent flame retardant (IFR)–thermoplastic polyurethane (TPU) composites were evaluated by limiting oxygen index (LOI), vertical burning test (UL‐94), thermogravimetric analysis (TGA), cone calorimetry, and scanning electron microscopy. The experimental data indicated that the metal oxides enhanced the LOI value and restricted the dropping of the composites. The IFR–TPU composites passed the UL‐94 V‐0 rating test (1.6 mm) in the presence of magnesium oxide (MgO) and ferric oxide (Fe₂O₃) at 35 wt % IFR loading, whereas only the MgO‐containing IFR–TPU composite reached a UL‐94 V‐0 rating at 30 wt % IFR loading. The TGA results show that the metal oxides had different effects on the process of thermal degradation of the IFR–TPU compositions. MgO easily reacted with polyphosphoric acid generated by the decomposition of ammonium polyphosphate (APP) to produce magnesium phosphate. MgO and Fe₂O₃ showed low flammability and smoke emission due to peak heat release rate, peak smoke production rate, total heat release, and total smoke production (TSP). However, zinc oxide brought an increase in the smoke production rate and TSP values. Among the metal oxides, MgO provided an impressive promotion on the LOI value. The alkaline metal oxide MgO more easily reacted with APP in IFRs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and physical characteristics of ZnAl2O4 nanocrystalline and ZnAl2O4/Eu core-shell structure via hydrothermal route

Nanocrystalline zinc aluminate (ZnAl₂O₄) particles with a spinel structure were prepared by hydrolyzing a mixture of aluminum chloride hexahydrate and zinc chloride in deionized water. It was found that pH value and reaction temperature play critical roles in the formation of nano-sized ZnAl₂O₄. Depending on pH values in the precursor solution, ZnAl layered double hydroxide (ZnAl-LDH), ZnO, boehmite or gibbsite could be formed. At pH 7 and T>120 °C, the nanocrystalline ZnAl₂O₄ particles with average particle size of ∼5 nm are easily synthesized through ZnAl layered double hydroxide (ZnAl-LDH). After surface treatment with R-OH by using the cationic surfactant CTAB, the ZnAl₂O₄/Eu core-shell structure can be developed. The ZnAl₂O₄/Eu core-shell structure can show both emissions from ⁵D₀ to ⁷F₂ sensitivity energy level and ⁵D₂ to ⁷F₀ depth energy level.     

Reaction between zinc oxide and chamotte refractories

Conclusions As a result of chemical reaction between chamotte and zinc oxide, zinc aluminate ZnAl₂O₄ and zinc silicate Zn₂SiO₄ are formed.The mullite is not chemically resistant under the action of zinc oxide. Even at 900°C mullite reacts with zinc oxide, forming ZnAl₂O₄ and SiO₂.In accordance with the quantity of melt formed in the refractory under the action of zinc oxide, high-alumina products should be more resistant to the action of vapors and oxides of zinc at elevated temperatures than chamotte and semiacid refractories.Translated from Ogneupory, No. 7, pp. 36–39, July, 1971.