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The high hot strength of MgO–Cr2O3 refractory is often ascribed to its intimate aggregate/matrix bonding. For a fundamental comparison with it, ∼2 mm aggregates of MgO and Al2O3 were separately embedded in ZnAl2O4 and MgAl2O4 matrices, sintered at 1600°C, and examined. It was found that similarity of thermal expansion coefficient (TEC) between the aggregate and the matrix is critical to achieve good bonding and this is more important than the extent of interdiffusion. The TEC mismatch of ≥5.7 × 10−6 K−1 caused significant undesirable debonding in MgO aggregate/MgAl2O4 matrix sample and MgO/ZnAl2O4 despite >736 μm Zn2+ diffusion depth in the latter. Direct bonding, as inferred from a thicker interfacial reaction layer and a greater shift of the aggregate/matrix interface before and after firing, was better in MgAl2O4/ZnAl2O4 combination, followed by tabular Al2O3/ZnAl2O4 and Al2O3/MgAl2O4. Powder X‐ray diffraction indicated that the volatilization of ZnAl2O4 at 1600°C in air was negligible compared to MgO–Cr2O3. [ABSTRACT FROM AUTHOR]

Zinc aluminates form a niche class of ceramics, which are useful in various applications, including photoelectronic devices, catalysts, and high efficacy optical materials. Selecting appropriate starting precursors is the key impertive to control synthetic parameters in ceramics syntheses for the improvement of phase purity and corresponding physicochemical properties. The current study reports the successful preparation of high crystallinity and purity of ZnAl 2 O 4 via thermal decomposition of the metal complex precursor using triethanolamine (TEA) as the additive and chelating agent. The effects of calcination temperatures and the existence of TEA on the formation of the desired ZnAl 2 O 4 and the suppression of ZnO impurity are thoroughly investigated. Herein, the correlation between the in-depth analysis of the thermal decomposition profile of the mixed metal-TEA precursor and the characteristic features of the obtained ZnAl 2 O 4 product are highlighted. The variation of optical bandgap energy of the derived materials by controlling the structural defects via a variation of synthetic parameters is explored. The obtained results show strong evidence that the ZnAl 2 O 4 powders derived from the thermal decomposition of the mixed metal-TEA precursor are superior in terms of crystallinity, phase purity, and optical properties to those without using the TEA chelating agent. [ABSTRACT FROM AUTHOR]

Optically transparent samples of ceramic materials based on the magnesium aluminate and zinc aluminate spinels of density close to the theoretically attainable one have been obtained, and their heat conductivity was measured in the temperature range 50–300 K. It is shown that the heat conductivities of these ceramic materials at room temperature are close and fall within the range 17–18 W/(m·K). At a cryogenic temperature (T = 50 K), the heat conductivity of the ceramic materials based on the zinc aluminate spinel (180 W/(m·K)) is much higher than the heat conductivity of the ceramic materials based on the magnesium aluminate spinel (122 W/(m·K)). The absolute heat conductivities of the ceramic materials based on the indicated spinels are dependent on the sintering additives used in their production. [ABSTRACT FROM AUTHOR]

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Cadmium-substituted ZnAl 2 O 4 (Cd x Zn (1- x) Al 2 O 4 , where x = 0, 0.1, 0.3, and 0.5) nanoparticles were synthesized by the microwave combustion process. The XRD analysis confirmed the cubic system. The crystallite size of Cd2+ doped ZnAl 2 O 4 isin the range between 20.82 and 15.12 nm. Fourier transform infrared (FT-IR) spectra are displayed the stretching frequencies. The energy gap values decrease from 4.15 to 2.67 eV with increasing doping concentrations of Cd2+, which is due to the formation of sub-bands and is calculated by the Kubelka-Munk function. HR-SEM pictures showed the features of nanoclusters grain boundaries. The elemental mixing of Zn2+/Cd2+, Al3+andO2− was confirmed by EDX analysis. Magnetic properties reveal that the undoped ZnAl 2 O 4 has diamagnetism and Cd2+ doped ZnAl 2 O 4 system has superparamagnetic behaviour. The nonlinear index of refraction (10−8 cm2/W), nonlinear absorption coefficient (10−4 cm/W) and the 3rd order nonlinear susceptibility (10−6 esu) are found out by Z-scan experiments. The obtained results of optical limiting analysis confirm that these materials are viable candidates for devices like optical power limiters and optical switches. • The Cd x Zn (1- x) Al 2 O 4 (x = 0, 0.1, 0.3, and 0.5) composites were prepared via microwave strategy. • Optical, thermal, and magnetic properties of Cd x Zn (1- x) Al 2 O 4 composites were studied. • Third-order nonlinear parameters for prepared composites were obtained via Z-scan experiments. • Low limiting threshold values make these composites suitable for optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this paper, zinc aluminate (ZnAlO) nanoparticles were obtained by a new synthesis method, thermal decomposition of Zn(II) and Al(III) carboxylates mixture. Complex combinations were obtained in the redox reaction between Zn(NO)·6HO, Al(NO)·9HO, and 1,3-propanediol at ~130 °C. The mechanism of Zn(II) and Al(III) carboxylates formation and decomposition was observed by thermal analysis and Fourier transform infrared spectroscopy. Zn(II) carboxylate, Al(III) carboxylate, and Zn(II) and Al(III) carboxylates mixture were annealed at different temperatures. Metal oxides synthesized from carboxylates precursors in single metal systems crystallized very well at 400 °C (ZnO) and weak at 800 °C (AlO), as shown by X-ray powder diffractometry. Homogenous mixture of Zn(II) and Al(III) carboxylates heated at 400 °C has led to a mixture of amorphous ZnO and AlO, which reacted forming at 600 °C well-crystallized ZnAlO, with mean crystallites size of 14.2 nm. The decomposition of carboxylates precursors is an appropriate method to obtain ZnAlO spinel as well-crystallized single phase at low temperatures. [ABSTRACT FROM AUTHOR]

Zinc aluminate (ZnAl2O4) nanopowders were synthesized by co-precipitation method using zinc chloride and aluminum chloride as starting precursors. The calcination temperature which was a crucial preparation factor was varied and its influence on relevant physical properties of the product was investigated. Structural properties of synthesized nanoparticles were investigated by X-ray diffraction, X-ray absorption spectroscopy, scanning electron microscope, and Raman spectroscopy. The results suggest that that ZnAl2O4 in spinel structure with high crystallinity can be obtained after calcination beyond specific temperature affirmed by XRD results. Raman result indicates the correlated chemical bonding relating to the formation of ZnAl2O4 structure. Meanwhile, the Zn K-edge X-ray absorption near-edge structure (XANES) spectra of these samples with different calcination temperature obtained from the synchrotron X-ray absorption spectroscopy measurement show the existence of accurate oxidation state for zinc ion (Zn2+) in the spinel crystal structure. Moreover, it is revealed that the calcination temperature has significant effect on the local environment of the zinc absorbing atoms through the interesting change of white line appearance. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Highlights: [•] Large surface area ZnAl2O4 powder was prepared using a new combustion technique. [•] Basically, this new technique relies on using zinc acetate instead of zinc nitrate. [•] The nanocrystalline (6nm) ZnAl2O4 powder had a specific surface area of 127m2/g. [•] The addition of NH4NO3 increased even more the specific surface area to 201m2/g. [•] At the same time, the average crystallite size of ZnAl2O4 decreased to 2nm. [Copyright &y& Elsevier]

Highlights: [•] Pt, PtSn and PtGe catalysts were studied in the n-decane dehydrogenation. [•] The support ZnAl2O4 was prepared by coprecipitation and mechanochemical synthesis (MS). [•] Its catalytic performances depended on the nature of the second metal. [•] PtSn catalysts showed better catalytic performance than the PtGe catalysts. [•] Catalysts prepared with ZnAl2O4 MS were more stable. [ABSTRACT FROM AUTHOR]

Abstract: The transesterification of soybean oil with methanol to biodiesel using lanthanum doped zinc aluminate with spinel structure as catalyst is studied. The catalyst was characterized by X-ray diffraction (XRD), N2 adsorption/desorption, temperature programmed desorption of CO2 (CO2-TPD) and infrared spectroscopy of CO2 adsorption (CO2-IR). The results of CO2-IR show that the basic sites of La doped zinc aluminate are surface isolated O2− anions and OH− groups. The results of CO2-TPD show that the total amount of basic sties of the catalyst improves with the increase of the La doping amount until which is to 18.5wt%. Doping La also enlarges the pore volume and diameter of zinc aluminate. It gets the largest pore volume (0.30cm3 g−1) and pore diameter (7.9nm) when doped with 5.5wt% La. Zinc aluminate doped with 5.5wt% La (5.5% La/ZnAl2O4) exhibits the highest activity, with which the biodiesel yield exceeds 95% at 160°C, 2.0MPa and 0.9h−1. Furthermore, the transesterification reaction of about 500h in a fixed-bed reactor was carried out over 5.5% La/ZnAl2O4 catalyst. No deactivation and leaching of catalyst components were happened on the catalyst in reaction. [Copyright &y& Elsevier]

Abstract: The transesterification of waste frying oil (WFO) with methanol and ethanol was studied in a batch reactor using a zinc aluminate catalyst prepared by the combustion reaction method. The reaction runs were carried out for 2hours, using alcohol:oil molar ratio of 40:1, temperature range of 60–200°C, catalyst ratio of 1–10% wt., under 700rpm stirring. The catalyst was characterized by XRD, EDX, TG, FTIR, N2 physisorption, NH3- and CO2-TPD. The catalyst showed a normal spinel structure and acid character (Lewis acid), in spite of the presence of both strong acid and base sites. Methyl and ethyl esters yields higher than 95% were obtained at 150 and 200°C and the catalyst was recovered and reused in 3 reaction cycles, without significant loss of activity. [Copyright &y& Elsevier]

Two aluminate spinel materials (ZnAlO and NiAlO) were synthesized by the citrate precursor method. The citrate precursors consisting of coprecipitated citrates of Zn or Ni and aluminum were first subjected to thermal analysis (TG-DSC) for determining the optimum temperature for annealing. Two step decomposition was observed incorporating dehydration and formation of the aluminate. The second step gives an endo peak (−2937 J/g) at 356 °C in the DSC curve of the coprecipitated nickel(II) citrate-aluminum citrate gel in O atmosphere. Kinetic/mechanistic analysis of the TG data has also been carried out and values of E, Δ S, Δ G, and A were approximated. On the basis of the findings, 450 °C has been chosen for annealing of the gels. Annealing has also been done at 650 °C for 1 h in muffle furnace in an attempt to obtain nanometric particles of aluminates (MAlO) {M = Ni, Zn} and to find out their magnetic properties which could render them useful for chemical sensing applications, etc. The TG-DSC curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N atmosphere. NiAlO and ZnAlO spinels (particle size 17 and 34 nm, respectively) are obtained in pure crystalline phase at 650 °C. ZnAlO prepared this way shows coercivity values of 470 and 58.37 G and NiAlO, 107 and 23.24 G when annealed at 450 and 650 °C, respectively. ZnAlO prepared by a polymer precursor method and annealed at 1000 °C, has earlier been reported to have coercivity value of 469 G. Thus, the citrate precursor method is good for the synthesis of ZnAlO, producing single phase nanocrystalline powder of high quality and crystallinity. The value of magnetization was found to be small in the present case for the NiAlO spinel obtained at 450 °C. [ABSTRACT FROM AUTHOR]

Abstract: Zinc aluminate (ZnAl2O4) nanoparticles with an average particle size of about 8nm were easily prepared by the co-precipitation method using aqueous ammonia solution as the precipitating agent. This nanosized spinel-type oxide was characterized by TGA, XRD, FT-IR, TEM, and surface area measurement and used as the heterogeneous catalyst for the acetylation reaction. Efficient acetylation of various amines, alcohols and phenols was carried out over ZnAl2O4 nanoparticles using acetic anhydride and/or acetyl chloride as the acetylating agents at room temperature without the use of a solvent. The method is highly selective, allowing the alcoholic hydroxyl group to be protected while the phenolic hydroxyl group remains intact, and the amine group can be acetylated in the presence of the hydroxyl group. This method is fast and has a high yield. It is also clean, safe, cost effective, compatible with substrates that have other functional groups and very suitable for practical organic synthesis. In addition, the catalyst can be reused without significant loss of activity. Indeed, the catalytic activity of the ZnAl2O4 nanoparticles is higher than that of bulk ZnAl2O4. [Copyright &y& Elsevier]

Abstract: Copper-containing ZnAl2O4 catalysts have been properly prepared by the glycothermal method, with copper loaded within the mixed oxide structure (catalyst Zn0.95Cu0.05Al2O4) or impregnated in the previously prepared support ZnAl2O4 (catalyst 5%Cu/ZnAl2O4). The samples were characterised by XRD, HRTEM, SEM-EDAX, N2 adsorption at −196°C, FT-IR, and H2-TPR, and the catalytic combustion of soot under NOx/O2 was tested. The mixed oxides, with confirmed spinel structure, consist of nanoparticles with around 5–12nm. The impregnated catalyst is more active for soot combustion than both the bare support and the substituted catalyst, which is attributed to the proper reducibility of copper that catalyses the NO oxidation to NO2. This catalyst is also highly selective towards CO2 formation as soot combustion product. [Copyright &y& Elsevier]

Abstract: Epitaxially ordered zinc aluminate domains with sub-micron dimensions are formed on bare c-sapphire substrates using a vapour phase method (with vapour generated by carbothermal reduction of ZnO) at various temperatures and growth durations. A zinc aluminate (ZnAl2O4) layer is formed by reaction of the source materials (Zn and O) with the substrate. We observe crystallites with a well-defined epitaxial relationship on the sapphire substrate in addition to polycrystalline material. The epitaxially oriented deposit displays the form of characteristically twinned (singly or multiply) grains of sub-micron dimensions with three variants, consistent with the c-sapphire substrate symmetry. Scanning electron microscopy and transmission electron microscopy studies show that the formation of these grains is associated with the presence of extended defects in the sapphire substrate. Epitaxially ordered grains formed at higher temperatures show a change in the nature of the twin boundaries and epitaxial relations as a function of growth time, attributed to the effects of annealing during growth. [Copyright &y& Elsevier]

Abstract: Self-organized ZnAl2O4 nanostructures with the appearance (in SEM) of high aspect ratio horizontal nanowires are grown on uncatalysed -sapphire by vapour phase transport. The nanostructures grow as three equivalent crystallographic variants on -sapphire. Raman and cathodoluminescence spectroscopy confirm that the nanostructures are not ZnO and TEM shows that they are the cubic spinel, zinc aluminate, ZnAl2O4, formed by the reaction of Zn and O with the sapphire substrate. [Copyright &y& Elsevier]

Abstract: Nanosized zinc aluminate spinel has been obtained by the thermal decomposition of Zn–Al gel prepared by sol–gel technique using oxalic acid as a chelating agent. Stirring an enthanol solution of zinc nitrate, aluminium nitrate and oxalic acid yields a gel precursor, followed by calcination of the resulting gel at different temperatures. Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) have been used to study the thermal behaviour of the precursor. Powder X-ray diffraction (XRD) show that the sample obtained by heating the precursor at 700 °C for 5 h is single-phase cubic material having the spinel-type structure, which can be confirmed by Infrared spectra (IR). The particle size of 15–20 nm has been measured by transmission electron microscopy (TEM). The specific surface area determined by BET surface area measurement was found to be 58 m2 g−1. [Copyright &y& Elsevier]

Abstract: Microwave assisted hydrothermal method, where the advantages of both microwave and hydrothermal method are being made use of, is proposed for preparing nanosized (mean particle size 2.4 nm with a narrow size distribution) zinc aluminate ZnAl2O4 with a spinel structure of interesting properties including high specific surface area (220 m2/g), microporosity and narrow pore size distribution. The precursors for microwave–hydrothermal synthesis were aluminium hydroxy nitrate having the empirical formula Al2(OH)6−x (NO3) x , wherein x was equal or close to 1, and hydrated zinc acetate. The proposed synthesis, in contrast to other methods, is very rapid and does not require a high temperature heating to obtain the spinel phase. The samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), scanning electron microscopy (SEM) with EDS analysis, differential thermal analysis-thermal gravimetric (DTA-TG), and textural analysis (surface area and porosity). The potential application of such obtained ZnAl2O4 as convenient material for the preparation of thermal stable thin films coatings on different planar substrates is also reported. [Copyright &y& Elsevier]

A new mesoporous Zn1-xMxAl2O4 photocatalyst was prepared using the metal-chitosan complexation method with different degrees of Zn2+ cation substitution with cobalt and nickel ions (M = Co2+ and Ni2+). Characterization using X-ray diffraction (XRD), Infrared absorption spectrometry (FTIR), energy dispersion spectroscopy (EDS), diffuse reflectance spectrometry (DRS), scanning electron miscoscopy (SEM), transmission electron miscroscopy (TEM), N2 adsorption- desorption isotherms using the Barrett-Joyner-Halenda (BJH) method, thermogravimetric analysis (TG) and differential thermal analysis (DTA) confirmed the formation of the spinel phase and high purity for all samples. N2 adsorption/desorption and size pore distribution confirmed the high surface area. The photocatalytic activity of Zn1-xMxAl2O4 and the effect of replacing Zn2+ ions with Ni2+ and Co2+ on the degradation of rhodamine B under ultraviolet light were studied in detail. The sample containing 0.1 mol of cobalt had the highest removal rate reaching 83%, favored by surface area and material bandgap (109 m2 g−1 and 2.19 eV, respectively). [ABSTRACT FROM AUTHOR]