Zn Aluminum Research Articles

Structural and dielectric properties of Cerium doped Magnesium-Zinc Aluminate spinel nano-crystallites for high frequency applications

The Ce3+ doped Mg–Zn Aluminate spinel nano size crystals with compositional formula of Mg0.5Zn0.5CexAl2-xO4 (x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) were synthesized by sol gel auto-combustion method followed by annealing at 800 °C for 3 h. The X-ray diffractometric (XRD) analysis confirmed space group FD3m and spinel structure of Ce3+ doped Mg–Zn Aluminates with crystallite size between 10 and 28 nm. Generally, an increasing trend in particles size and other structural parameters were observed at higher concentration of Ce3+ content. Transmission Electron Microscopy (TEM) was utilized to study the morphology and size of the Ce doped MG-Zn Aluminates that were consistent with XRD results. Furrier transforms infrared spectroscopy (FTIR) has been employed to reveal the absorption bands for the octahedral and tetrahedral sides observed in between 400 and 1000 cm−1. All samples were pelletized to study the dielectric properties like dielectric constant, impedance, electric modulus and tangent loss. Impedance spectroscopy was employed at room temperature in the applied frequency ranging from 1 MHz to 3 GHz. A consistent behavior in dielectric constant and dielectric loss was observed for the intermediate range of applied frequencies. The concentration at x = 0.10 was found to exhibit the most stable dielectric constant and dielectric loss behavior at high frequencies. The effect of doping concentration on grain and grain boundaries, the polarization phenomena and conductivity mechanism has been discussed. It is found that AC conductivity for all doping concentration is low at lower frequencies range from 1 MHz to 300 MHz while a peak is observed at higher frequency around 2.5 GHz. The valuable responses of dielectric constant and dielectric lost at higher frequency range show that Mg0.5Zn0.5CexAl2-xO4 can be used in high frequency devices.

Study of Adaptation Processes in Tribofilms during Friction of Antifriction Aluminum Alloys for Journal Bearings

This paper provides results on the tribological behavior of experimental Al–Sn–Pb–Si–Cu–Mg–Zn aluminum alloys and describes the adaptation phenomena that reduce wear intensity during friction with steel. The main focus is on tribofilm formation, which plays an important role in friction energy dissipation. The alloys were tested in a rig imitating a journal-bearing shaft couple, and the friction surfaces were studied by the scanning electron microscopy, energy-dispersive analysis and X-ray photoelectron spectroscopytechniques. Based on the analysis, a conclusion on processes and tribochemical reactions was made. Compared to the initial state, eight new compounds were found on the friction surface. In the most wear-resistant alloy, magnesium precipitated from a solid solution with the subsequent oxidation. The same process was detected for zinc in the least wear-resistant alloy due to its low magnesium content. Furthermore, CuSn3 and PbS compounds, which require >600 °C temperature to compose, were found in tribofilms, indicating that the rubbing body lost thermodynamic equilibrium during friction. The revealed processes are non-spontaneous and decrease the wear intensity of the alloys, as they are accompanied by negative entropy production and dissipation of friction energy. Stepwise depth XPS analysis also showed the functional levels of the tribofilms.

Using the method of correlation of digital images for plotting stress–strain curves in true coordinates

This article describes the features of determining strain curves in true stress–true strain coordinates, using samples of circular cross section from Al–Cu–Mg–Zn aluminum alloy. The calculation and experimental methods of determining true stresses and strains were compared Calculation methods based on the condition of volume constancy may not reflect actual regularities of deformation at the stage of strain localization in the considered material. Nevertheless, the use of systems of digital image correlation (DIC) allows measurements of both the geometrical sizes of deformed sample and strain fields on its surface to be performed, including on the sample neck. It was demonstrated that the measurement error of the sample diameter by the coordinate field was 0.02 mm at the instance of destruction. In order to improve the measurement precision, an increase in the recording frequency in proportion to increase in strain rate was proposed, as well as measuring the surface coordinates from both sides of the sample. It is also possible to supplement the strain curves obtained by DIC optical systems with the measurements of true fracture stress, and the true fracture strain determined by calculations on the destructed sample. The presented methods of analysis of plastic flow by direct measurement of field displacements and strains allow actual regularities between true stresses and strains at the interval of irregular plastic strain to be established. This cannot be achieved by analytical conversion of conventional curve. The obtained hardening coefficients and strain curves can be used for simulation and design of machinery structures and parts.

From Lab to Technical CO2 Hydrogenation Catalysts: Understanding PdZn Decomposition.

The valorization of CO2 to produce high-value chemicals, such as methanol and hydrocarbons, represents key technology in the future net-zero society. Herein, we report further investigation of a PdZn/ZrO2 + SAPO-34 catalyst for conversion of CO2 and H2 into propane, already presented in a previous work. The focus of this contribution is on the scale up of this catalyst. In particular, we explored the effect of mixing (1:1 mass ratio) and shaping the two catalyst functions into tablets and extrudates using an alumina binder. Their catalytic performance was correlated with structural and spectroscopic characteristics using methods such as FT-IR and X-ray absorption spectroscopy. The two scaled-up bifunctional catalysts demonstrated worse performance than a 1:1 mass physical mixture of the two individual components. Indeed, we demonstrated that the preparation negatively affects the element distribution. The physical mixture is featured by the presence of a PdZn alloy, as demonstrated by our previous work on this sample and high hydrocarbon selectivity among products. For both tablets and extrudates, the characterization showed Zn migration to produce Zn aluminates from the alumina binder phase upon reduction. Moreover, the extrudates showed a remarkable higher amount of Zn aluminates before the activation rather than the tablets. Comparing tablets and extrudates with the physical mixture, no PdZn alloy was observed after activation and only the extrudates showed the presence of metallic Pd. Due to the Zn migration, SAPO-34 poisoning and subsequent deactivation of the catalyst could not be excluded. These findings corroborated the catalytic results: Zn aluminate formation and Pd0 separation could be responsible for the decrease of the catalytic activity of the extrudates, featured by high methane selectivity and unconverted methanol, while tablets displayed reduced methanol conversion to hydrocarbons mainly attributed to the partial deactivation of the SAPO-34.

Cation exchange in Ni–Cu–Zn aluminate spinels revealed by EXAFS

Nanocrystalline Ni–Cu–Zn aluminate powders (Ni1-xCuxAl2O4, Cu1-xZnxAl2O4, and Zn1-xNixAl2O4) with different divalent ion concentrations (0 ​≤ ​x ​≤ ​1) were successfully synthesized by the sol-gel auto combustion method using diethanolamine (DEA) as a novel fuel. The structural, morphological, and the local atomic structures of each calcined sample were investigated by XRD, TEM, and synchrotron EXAFS measurements. The XRD results confirmed the formation of single-phase spinel structure with Fd-3m space group of all samples. When XRD Rietveld refinement and Williamson-Hall analysis were applied to the XRD data, the exact crystallite size and structural parameters were obtained. The EXAFS spectra showed the main translocation trends in the trivalent (Al3+) and divalent (Ni2+, Cu2+, Zn2+) ions between the tetrahedral (A) and octahedral (B) sublattices. Furthermore, the degree of inversion in these spinel aluminates is completely dissimilar and identified as 0.493–0.499 for Ni1-xCuxAl2O4, 0.254–0.498 for Cu1-xZnxAl2O4 and 0.093–0.453 for Zn1-xNixAl2O4 series, as indicated by the multiple-edge curve-fitting analysis of Ni, Cu, and Zn K-edge EXAFS spectra. These values comprise essential data for comprehension of numerous relevant properties.

Investigation on structural, optical, and electrical properties for sintered Mg–Zn aluminate systems

In the present work, the insulating MgAl2O4 and a semiconducting ZnAl2O4 were mixed as Zn0.5Mg0.5Al2O4 compound, which is synthesized by chemical co-precipitation method. We have investigated the structural, optical, and electrical properties for Zn0.5Mg0.5Al2O4 at different sintering temperatures. By X-ray diffraction (XRD) data analysis, the phase identification and intermediate phase formation were confirmed through the appearance of the superlattice peak at 2θ = 49.1° for (331) plane. The particle sizes of sintered samples were examined through high-resolution transmission electron microscopy (HRTEM) analyses. The weight percentages of Zn, Mg, Al, and O ions in the samples were obtained from EDX analysis. The cation distribution in the sintered Zn0.5Mg0.5Al2O4 samples was analyzed using solid-state nuclear magnetic resonance (SS-NMR) spectra. In addition, the UV absorbance spectra reveal an inter-bandgap region for the Zn0.5Mg0.5Al2O4 system. The optical bandgap was found to be a blue shift as observed from absorbance spectra on sintering. The frequency dependence impedance spectra and AC conductivity expose the contribution of grain, grain boundaries, and electrode–sample interface effects very clearly. The frequency dispersive nature of the dielectric constant and tan δ was measured and analyzed. The disparity observed due to the sintering of the sample was discussed and reported.

Enhancement of corrosion resistance of a high Zn-yttrium aluminum alloy

The corrosion resistance of a high Zn (11 wt%) aluminum alloy was found to be significantly improved by 45% when doped with Y (solid solution limit 1.4 wt %), while the hardness of the material is only reduced by 3.5%. Although corrosion is frequently observed in the grain boundaries of high Zn aluminum alloys, it is not observed in the grain boundary of the Y-included alloys under current approach, in spite of the increased volume of grain boundary phases. The content of Mg and Zn decreased in the grain boundary precipitates as the Y content increases, leading to an increase of the corrosion potential of these grain boundary phases. The calculated atomic binding energies, diffusion energies and surface energies suggested that Y substitution has improved the binding forces between alloy elements Mg, Cu, Zn and Al, but has a different effect on Cr. The precipitates in grain boundaries appear to have converted from the Al-based solid solution into a more stable intermetallic compound of MgZn2-type.

Post-annealing effect on transparent Mg-Zn aluminate solid solutions fabricated by spark plasma sintering

In MgAl2O4 (Mg aluminate) fabricated by pressure sintering, carbon contamination, oxygen vacancy, and other defects exist and cannot be completely removed even after post-annealing. ZnAl2O4 (Zn aluminate) has the same crystallographic structure as Mg aluminate and excellent light transmission by post-annealing. In this study, the transmission of (Mg1-XZnX)Al2O4 spinel, which is a solid solution between Mg aluminate and Zn aluminate, was investigated. After post-annealing, the transmission of (Mg1-XZnX)Al2O4 spinel was higher than Zn aluminate and Mg aluminate, which means that the absorption center disappeared. Besides, the real in-line transmission is improved by up to 30% by post-annealing, which is related to the driving force to increase the configurational entropy and form a more stable solid solution phase. In solid solution spinel, as the Zn content increases, the optical properties can be improved by post-annealing, but the mechanical properties are slightly decreased.

Microstructural characterization of dental zinc phosphate cements using combined small angle neutron scattering and microfocus X-ray computed tomography

ObjectiveTo characterize the microstructure of two zinc phosphate cement formulations in order to investigate the role of liquid/solid ratio and composition of powder component, on the developed porosity and, consequently, on compressive strength. MethodsX-ray powder diffraction with the Rietveld method was used to study the phase composition of zinc oxide powder and cements. Powder component and cement microstructure were investigated with scanning electron microscopy. Small angle neutron scattering (SANS) and microfocus X-ray computed tomography (XmCT) were together employed to characterize porosity and microstructure of dental cements. Compressive strength tests were performed to evaluate their mechanical performance. ResultsThe beneficial effects obtained by the addition of Al, Mg and B to modulate powder reactivity were mitigated by the crystallization of a Zn aluminate phase not involved in the cement setting reaction. Both cements showed spherical pores with a bimodal distribution at the micro/nano-scale. Pores, containing a low density gel-like phase, developed through segregation of liquid during setting. Increasing liquid/solid ratio from 0.378 to 0.571, increased both SANS and XmCT-derived specific surface area (by 56% and 22%, respectively), porosity (XmCT-derived porosity increased from 3.8% to 5.2%), the relative fraction of large pores ≥50μm, decreased compressive strength from 50±3MPa to 39±3MPa, and favored microstructural and compositional inhomogeneities. SignificanceExplain aspects of powder design affecting the setting reaction and, in turn, cement performance, to help in optimizing cement formulation. The mechanism behind development of porosity and specific surface area explains mechanical performance, and processes such as erosion and fluoride release/uptake.

Effects of casting and heat treatment processes on the thermal conductivity of an Al-Si-Cu-Fe-Zn alloy

In this study, the effects of casting processes and heat treatments on the thermal conductivity of an Al-10wt% Si-0.6wt% Cu-0.9wt% Fe-0.7wt% Zn aluminum alloy were studied. Both gravity- and die-casting processes were used. The porosity in die castings was controlled by varying the injection pressure and plunger velocity. The porosity, microstructures, and thermal and electrical conductivities of the die castings were characterized. The thermal conductivity of gravity-cast material achieved 143.4Wm−1K−1, whereas those of die-cast materials ranged from 110.8 to 126.8 Wm−1K−1. The die-cast aluminum alloys demonstrated considerably finer interconnecting precipitates than did the gravity castings. The closely spaced precipitates acted as barriers for thermal conduction, leading to reduced thermal conductivity. Die-casting pressures and velocities were controlled to form die castings with up to 3.73% porosity, which led to a 12.6% decrease in thermal conductivity. The die-cast Al alloys were then subject to solutionization (T4) and aging treatments (T6). The silicon precipitates were spheroidized, thus widening the paths for heat conduction. The thermal conductivity was greatly enhanced, increasing from 126.8Wm−1K−1 in the die-cast condition to 151.6Wm−1K−1 after 550°C solutionizing and 4h of aging at 200°C. The thermal conductivity of the gravity-cast materials remained unchanged after the same heat treatments. Improving the thermal conductivity of die castings through proper heat treatments is crucial for aluminum alloys in rigorous heat-dissipating applications.

Study on Cooling Curve Behavior During Solidification and Investigation of Impact Strength and Hardness of Recycled Al–Zn Aluminum Alloy

An ingot of recycled aluminum is usually used as a raw material to produce casting pans in small industries is used as a base material to produce samples of impact toughness and hardness in this study. The cast samples are produced by gravity casting using a metal mold. The pouring temperature is 760 °C (1400 °F), and the mold temperature is 220 °C (428 °F). The impact test specimens followed ASTM 23 standards for V-notch. The cooling curve during solidification is observed through a curve generated by data input. The impact toughness is tested by the Charpy method, and the hardness value is obtained by Brinell method. The impact toughness and hardness values of Al–Zn cast alloy are 7 J/cm2 and 38.43 BHN, respectively.

Intermediate members of the lime-monteponite solid solutions (Ca1−xCdxO, x = 0.36–0.55): Discovery in natural occurrence

Lime-monteponite solid solutions [(Ca,Cd)O ss] with 58.5–73.3 wt% CdO were discovered as an accessory phase in medium-temperature combustion metamorphic (CM) spurrite-fluorellestadite/fluorapatite marbles from central Jordan. The type locality is situated in the northern part of the Siwaqa complex (Tulul Al Hammam area), the largest area of the “Mottled Zone” Formation in the Dead Sea region. The marbles were derived from bitumen-rich calcareous marine sediments of the Muwaqqar Chalk Marl Formation, which have high Cd, Zn, U, and Ni enrichments and contain Cd-rich wurtzite and sphalerite. Oxidative sintering of these sediments at 800–850 °C gave rise to unusual oxide accessories: lime-monteponite solid solutions, Cd-bearing Ca and Zn aluminate—tululite, zincite, and Zn-, Ni-, and Cu-rich periclase. Cadmium incorporation into different oxides was controlled by steric factors, while Cd [6] → Ca [6] was the principal isomorphic substitution. The intermediate members (Ca 0.645 Cd 0.355 )O–(Ca 0.453 Cd 0.547 )O with a halite-type structure have a cadmium incorporation ratio (K Cd = Cd mineral /Cd rock ) of about 843 and are the main sites for cadmium in CM marbles. In supergene environments, at low water/rock ratios, (Ca 1−x Cd x )(OH) 2 ss ( x ≤ 0.5) constitute the main secondary phase after (Ca,Cd)O ss. At higher water/rock ratios and in the presence of Cl − and F − in the solutions, calcium, and cadmium precipitated as separate phases {fluorite (CaF 2 ) and basic cadmium chloride [Cd(OH) 2−x Cl x )]}. A part of cadmium becomes retained in calcium silicate hydrates. The common occurrence of anhydrous (Ca,Cd)O grains in natural rocks, only partly altered to (Ca,Cd)-hydroxide after at least 100 ka exposure to weather and climate, proves that both phases are effective long-term Cd immobilizers.

Comparison of color and optical absorbance properties of divalent ion substituted Cu and Zn aluminate spinel oxides synthesized by combustion method towards pigment application

Present work focussed on the synthesis of inorganic pigments based on spinel oxides of the formula Zn1−xMxAl2O4 (x = 0–0.5, M = Ni, Mn) and Cu1−xMnxAl2O4 (x = 0–0.7). Characterization of the resulting compounds was carried out by Powder X-ray diffraction, Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy. The optical absorption results and color parameters delineate the impact of the host structures viz, inverse and normal spinel: Mn2+ substitution in copper aluminate show a broad absorption band in the NIR region (1000–1800 nm) whereas, the corresponding zinc analogues do not exhibit such absorption. The oxides are found to be highly stable towards acid and base treatment which demonstrates the suitability of the materials for pigment application.

Cu/ZnO/Al2O3 catalysts for oxidative steam reforming of methanol: The role of Cu and the dispersing oxide matrix

Cu/ZnO/Al2O3 catalysts (5–45 Cu at.%) derived from layered double hydroxide (LDH) precursors were studied for oxidative steam reforming of methanol (OSRM). The precursors were prepared by homogeneous precipitation with urea. The catalysts were obtained by thermal decomposition of the precursors and subsequent reduction in H2 stream. XRD, SEM, N2 adsorption, TPR and NH3 TPD techniques were employed for characterization. Catalytic activity tests were carried out in a fixed bed flow reactor at T=200–400°C, H2O/CH3OH/O2 molar ratios=1.1/1/0.12 (CH3OH concentration=17.8%), GHSV=6×104h−1. Tests of simple steam reforming (SRM), partial oxidation (POM) and CH3OH decomposition (DEC) were also carried out. TPR measurements showed that redox properties depended on the composition of the samples and on the nature of the phases present in the precursors. The area of metallic Cu, measured by N2O passivation method, was correlated to Cu content. The size of Cu particles was smaller than 10nm for Cu content up to 18at.%. NH3 TPD measurements showed acid sites with a wide strength distribution, the strongest ones being mainly related to Al2O3 or Zn aluminate. Catalytic activity was influenced by the chemical composition: kinetic constants for OSRM varied unevenly with Cu surface area, while those for SRM increased with Cu surface area. A reaction mechanism agreeing with OSRM, SRM and DEC data was hypothesized. The mechanism involved an oxidation-reduction cycle of Cu and also the participation of the oxide matrix.

Studies on Eu doped Ba and Zn aluminate phosphors prepared by combustion synthesis

BaAl2O4:Eu2+ and ZnAl2O4:Eu3+ phosphors were prepared by urea combustion route. The formation of crystalline aluminates was confirmed by X-ray diffraction. The X-band EPR spectra of BaAl2O4:Eu2+ showed the presence of Eu2+ ions, while in the case of ZnAl2O4:Eu3+, no signal attributable to Eu2+ was observed. The broad band UV excited luminescence of BaAl2O4:Eu2+ was observed at the blue region (λmax=439nm) due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion, whereas ZnAl2O4:Eu3+ gave an emission at 613nm attributed to 5D0–7F2 transition of Eu3+ ions.

Structure modelling and cation partitioning of spinel solid solutions at high T , P conditions

This paper presents evaluation of cation distributions from diffraction data collected at high T, P, and is an extension of the spinel structure modelling procedure by Lavina et al. (2002). Optimised cation-to-oxygen distances are modified for thermal expansion and compressibility at T and P of interest following Hazen and Prewitt (1977) and Hazen and Yang (1999). The procedure is applied to literature data concerning hercynite, spinel s.s., Zn aluminate, Zn ferrite, magnetite and the (Fe3O4)1− x (MgAl2O4) x join. Calculated cation distribution is strongly affected by standard deviations in cell parameters and oxygen coordinates. The underestimated values often reported in the literature for powder profile refinements may strongly affect the cation distribution; however, if standard deviations are increased to physically realistic values, consistent results are obtained. For P up to 10 GPa, reasonable evaluations of cation distribution are obtained for spinel s.s., Zn aluminate and magnetite, whereas for Zn ferrite they are limited to 1.8 GPa. For P beyond 10 GPa, compressibility cannot be assumed to be linear; the relationship between cell parameter and pressure is well-defined, but the inaccuracy of oxygen coordinate prevents simple modelling of bond distances with pressure.