Conventional and Non-conventional Sintering Techniques of High Purity Alumina Ceramics

The goal of this study is to compare the properties of cold isostatically pressed (CIP) alumina (A2O3) samples sintered by conventional (electrical) and non-conventional (hybrid microwave) techniques. X-ray diffraction was used to determine phase composition of A2O3 samples (raw powder and granules). Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to investigate the thermal behaviour of the Al2O3 powder and granules during the thermal treatment. Compaction of spray dried A2O3 granules into green compact bodies was performed by CIP, followed by sintering of green bodies at 1600 °C in an electrical and hybrid microwave kiln, respectively. Scanning electron microscopy (SEM) was used to analyse morphology of the Al2O3 granules and fracture surface of Al2O3 compacts derived by both sintering techniques. Higher linear shrinkage and densification were obtained for alumina samples sintered in electrical kiln (conventional method), while sintering by faster and more energy efficient hybrid microwave kiln (non-conventional sintering method) yielded alumina samples with finer grain size. Alumina samples sintered by electrical kiln displayed higher relative densities and lower porosities

Showcase of tools for preparing, modifying and describing thin lms for energy conversion devices with special attention on plasma phenomenology

This paper draws attention to the wide range of capacities of the roup, including chemical and physical deposition, modification and processing techniues, and advanced characterisations. In particular, this work demystifies the new plasma discharge method for the synthesis of thin films, which is still under development. Specifically, the coupled spark plasma ablation deposition (SPAD) can be performed at almost ambient conditions in various configurations with respect to several deposition reactors, proving powerful, versatile, green, and easy-to-use nature of the method. Composition-wise, up to 4 element material can be derived combining pure electrodes, however the derived composition can be broader when using alloy electrodes. It is indisputable that SPAD is capable of producing thin films at a significantly reduced cost compared to other methods.which we want to put in use for the constituent layers of the last generation of energy conversion devices. enerally, the SPAD optimisation envelope heavily differs for the case of intended products nanoparticle vs thin film, or metal vs metal oxide, or crystalline vs amorphous. Here, we will provide a more detailed description of the ablation parameters that are necessary to achieve the various crystallinities of nanomaterials. Copper nanoparticles and thin films were derived via SPAD and additionally thermally treated. (Micro)structural and thermal evolution points out to interesting development of the surface morphologies. In addition, the results enabled the correlation between oxygen plasma concentration and order of crystallinity in the thin films

Multinuclear Magnetic Resonance Study on Aluminium Sec-butoxide Chelated with Ethyl Acetoacetate in Various Amounts

Reactive aluminum alkoxide (ASB, aluminium sec-butoxide) was chelated using β-diketone (EAA, ethyl acetoacetate) in order to gain control over rapid hydrolysis in the course of the sol-gel process. Derived chelates were analysed using several NMR spectroscopic techniques: one-dimensional 1H, 13C, 27Al NMR and two-dimensional COSY, HSQC and DOSY. The NMR analysis enabled identification of the formed chelate species, as well as determination of their quantitative relationships. Several complexation products were observed: tris-chelated monomer, Al(EAA)3, bis-chelated dimmer, Al2(OnBu)4(EAA) 2, tris-chelated dimmer, Al2(OnBu)3(EAA)3, tetra-chelated dimmer, Al2(OnBu)2(EAA)4, and monochelated trimer, Al3(OnBu)8(EAA). Of the formed oligomer compounds, this is the first evidence of Al2(OR)3L3 in any alkoxide and β-ketoester or β-diketone combination. Aluminium sec-butoxide and ethyl acetoacetate complexes Al2(OnBu)4(EAA) 2 and Al2(OnBu)2(EAA)4 were also observed for the first time. With the increase of the EAA/ASB ratio the coordination of aluminium shifts towards six, whereas above the EAA/ASB ratio of 2.5 solely six-coordinated aluminium exists. This work is licensed under a Creative Commons Attribution 4.0 International License

Comparison of Erosion Rate of Slip Cast Monolithic and Composite Ceramics

In this paper, the solid particle erosion wear of slip cast monolithic alumina (Al2O3) and alumina–zirconia (Al2O3– ZrO2) composite ceramics was investigated. Three groups of samples were prepared: (i) monolithic alumina (Al2O3); (ii) composite alumina–zirconia (Al2O3–ZrO2) containing 99 wt. % Al2O3 and 1 wt. % ZrO2 and (iii) composite alumina–zirconia (Al2O3–ZrO2) containing 90 wt. % Al2O3 and 10 wt. % ZrO2. X-ray diffraction and scanning electron microscopy (SEM) were used to investigate the phase composition, the crystallite size, and the morphology of the sintered monolithic and composite ceramic samples. The erosive wear behaviour was studied under different impact angles (30°, 60°, 90°) of silicon carbide (SiC) particles as erodent. Erosion mechanisms of all prepared ceramic samples were evaluated by measuring the surface roughness parameters (Ra, Rz, and Rmax) and the erosion rate. The obtained results showed that the tribological properties of the monolithic Al2O3 can be improved with the addition of ZrO2. It was found that the erosion resistance increases with the increasing amount of ZrO2 in the composite Al2O3– ZrO2 ceramics. It was found that ZrO2 grains are homogenously distributed in the alumina matrix, zirconia grain size is smaller than alumina grains, and that the alumina grain size is reduced by the addition of zirconia

Structural and Electrical Characterization of Pure and Al-Doped ZnO Nanorods

Pure and Al-doped (3 at.%) ZnO nanorods were prepared by two-step synthesis. In the first step, ZnO thin films were deposited on silicon wafers by spin coating ; then, ZnO nanorods (NR) and Al- doped ZnO NR were grown using a chemical bath method. The structural properties of zincite nanorods were determined by X-ray diffraction (XRD) and corroborated well with the morphologic properties obtained by field-emission gun scanning electron microscopy (FEG SEM) with energy- dispersive X-ray spectroscopy (EDS). Morphology results revealed a minute change in the nanorod geometry upon doping, which was also visible by Kelvin probe force microscopy (KPFM). KPFM also showed preliminary electrical properties. Detailed electrical characterization of pure and Al-doped ZnO NR was conducted by temperature-dependent current–voltage (I–V) measurements on Au/(Al)ZnO NR/n-Si junctions. It was shown that Al doping increases the conductivity of ZnO NR by an order of magnitude. The I–V characteristics of pure and Al-doped ZnO NR followed the ohmic regime for lower voltages, whereas, for the higher voltages, significant changes in electric conduction mechanisms were detected and ascribed to Al- doping. In conclusion, for future applications, one should consider the possible influence of the geometry change of (Al)ZnO NRs on their overall electric transport properties

Sol-gel Synthesis and Characterization of Lithium and Cerium Codoped Perovskite

Perovskites are an important group of ceramic materials with a structural formula ABO3 and wide array of potential applications in electronics, superconductors, catalysis, etc. CaTiO3, by which the whole group was named for, is particularly significant due to its use in catalysis, but its photocatalytic activity is limited by a large band gap value (~3.5 eV). A possible solution is the substitution of A and B cations with foreign cations which causes the alteration of properties, including photocatalytic efficiency. The aim of this work was the sol-gel synthesis of lithium and cerium codoped CaTiO3, characterization of the prepared gel and ceramics obtained by its thermal treatment. Samples of codoped perovskite, Ca1-xLixCexTiO3, where x = 0, 0.01, 0.02, 0.03 and 0.04, were prepared and characterized using powder X–ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), differential thermal and thermo- gravimetric analysis (DTA-TGA), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Photocatalytic activity was evaluated through the study of methylene blue photocatalytic degradation. XRD analysis showed that the prepared samples consisted of calcium nitrate and titanium chelate. In accordance with the established thermal evolution path, all samples were thermally treated at 500 °C for 2 hours. Beside perovskite, Ca2Ti2O6 appeared as a secondary phase in all thermally treated samples. SEM analysis of thermally treated samples showed the presence of agglomerates of irregular morphology and the decrease of primary particles size with the increase of dopants concentration. The sample with x=0.04 showed an increased photocatalytic activity