Thermal stability of nanometric TiC-carbon composites: effects of carbon allotropes and Zr milling impurities

In the ISOL (Isotope Separator OnLine) method a target at high temperatures (up to 2300?°C), is bombarded with high energy protons in order to produce isotopes through nuclear reactions which are simultaneously extracted from the target, ionized and delivered to physics experiments. Due to the enhanced isotope release properties of nanosized porous materials, titanium carbide-carbon porous nanocomposites have been developed at CERN and tested up to 1500?°C. In the interest of the ISOL application, in this study we extended the range of temperatures up to 1800?°C, to test the sintering hindering capabilities of different carbon allotropes. Carbon black was the most effective with the smallest TiC crystallite size: <80?nm at 1800?°C. Additionally, using thermodynamic modelling, ex-situ X-ray powder diffraction and in-situ gas phase analysis, we show that there are interesting additional phase and lattice parameter changes due to the ZrO₂ impurities from the attrition milling.     

Corrosion protection of AA 2024-T3 aluminium alloys using 3, 4-diaminobenzoic acid chelated zirconium-silane hybrid sol-gels

Organic-inorganic polymers formed by hydrolysis/condensation reactions of alkoxide precursors, such as organically modified silanes (Ormosils) are used for several industrial applications such as electronic, optical and protective anticorrosion coatings. Such materials possess superior chemical stability, physical strength and scratch resistance characteristics when compared to organic polymers. Further performance improvement can be achieved through the incorporation of zirconium and titanium based nanoparticles, also formed through from precursors via the sol-gel process. However due to the inherent reactivity differences of the above precursors, they must be hydrolysed separately before being combined for final condensation. Zirconium precursors are commonly chelated using acetic acid or acetyl acetonate prior to hydrolysis, to lower the hydrolysis rate.In this body of work, 3,4-diaminobenzoic acid (DABA) and acetyl acetonate (acac) were compared as chelating ligands for controlling the hydrolysis reactions of zirconium n-propoxide to form nanoparticles within a silane sol matrix. The sols were applied as coatings on aerospace grade aluminium alloy AA 2024-T3 and characterised by physical, spectroscopical, microscopical, electrochemical and calorimetric techniques. The electrochemical properties of the coatings, as characterised by EIS and PDS, correlated with neutral salt spray evaluations confirming that the use of DABA as a chelating ligand significantly improved the coating performance when compared to the traditional diketone ligand. The data indicates the anticorrosion properties of the nitrogen rich chelate have a key role in protecting the alloy through the formation of smaller zirconium nanoparticles, thus improving the polymer network stability.     

The effect of MEVVA ion implantation of Zr on the corrosion behaviour of PVD TiN coatings

The use of TiN coatings as corrosion barriers is limited by the presence of defects such as pin-holes. In this study Zr ions were implanted into PVD deposited TiN coatings at varying doses, to improve the corrosion resistance. The corrosion behaviour was assessed in saline environments using linear polarisation techniques and the corroded surface of the coatings characterised using XPS and SEM. Overall, ion implantation resulted in an increase in the coating’s corrosion resistance. Protection was attributed to closure of existing pin-holes and the formation of various nitrides, oxides and oxynitrides of Ti and Zr.     

γ辐照后TBP—煤油对^95Zr的萃取和保留

研究了用不同浓度HNO_3预平衡和经γ辐照不同剂量后的TBP-煤油对~(95)Zr的萃取行为。测定了0.01mol/1HNO_3,5%Na_2CO_3洗涤后的有机相中~(95)Zr的保留百分率。比较了辐照后的TBP-煤油用碱和水萃洗分离得到的三个组份以及HDBP等7种辐解产物对~(95)Zr的萃取和洗涤后有机相中的保留情况。结果表明~(95)Zr的萃取和洗涤后的保留与溶剂所受的辐照剂量和预平衡酸度均有关系。在辐解产物中,单烷基长链酸性磷酸酯和异羟肟酸对Zr的萃取影响都较严重。前者在碱洗时容易产生乳化,而后者在碱洗后对Zr的保留更为严重。     

Influence of sputtering power on oxygen reduction reaction activity of zirconium oxides prepared by radio frequency reactive sputtering

Zirconium oxides (ZrO_2−x) have been investigated as new cathodes for direct methanol fuel cells without platinum. ZrO_2−x films were prepared using a radio frequency (RF) magnetron sputtering at RF powers from 75 to 175 W. The influence of the RF power on the catalytic activity for the oxygen reduction reaction (ORR) and properties of the ZrO_2−x films were examined. The ORR activity of the ZrO_2−x catalyst increased with the RF power in the range we studied. The onset potential for ORR over ZrO_2−x deposited at 175 W was 0.88 V vs RHE. In addition, the relationship between the ORR activity and the composition, crystallinity, electric conductivity, as well as the ionization potential has been investigated. The zirconium oxide with an oxygen defected state and the higher electric conductivity showed the higher ORR activity, and the electrocatalytic activity for ORR increased with the decreasing in the ionization potential of the ZrO_2−x catalyst.     

Selective heavy metals removal from waters by amorphous zirconium phosphate: behavior and mechanism

Selective removal of heavy metals from water has been of considerable concern for several decades. In the present study, the amorphous zirconium phosphate (ZrP) was synthesized and characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron micrography (SEM), thermogravimetric analysis (TGA) as well as pH-titration experiments. Uptake of heavy metals including lead, cadmium, and zinc onto ZrP was studied by using a polystyrene sulfonic-acid exchanger D-001 as a reference sorbent and Ca(2+) as a competing cation due to its ubiquity in natural or industrial waters. The results indicated that the uptake of heavy metals onto ZrP is essentially an ion-exchange process and dependent upon solution pH. In comparison with D-001, ZrP exhibited more favorable sorption of heavy metals particularly in terms of high selectivity, as indicated by the distribution coefficients of ZrP even several orders higher than D-001 towards heavy metals when calcium ion coexisted at a high level in solution. The Fourier transform-infrared (FT-IR) spectroscopic investigation indicated that the uptake of calcium, cadmium, and zinc ions onto ZrP is only driven by the electrostatic interaction, while that of lead ion is possibly dependent upon the inner-sphere complex formation with ZrP. XPS results further elucidated that ZrP displays different sorption affinity towards heavy metals in the same order as selectivity sequence of Pb(2+)>Zn(2+) approximately Cd(2+)>Ca(2+), which can be explained by hard and soft acids and bases (HASB) theory. Moreover, uptake of heavy metals onto ZrP approached to equilibrium quickly and the used ZrP could be readily regenerated for reuse by the dilute HCl solution. Thus, all the results suggest that amorphous ZrP has excellent potential as a sorption material for water treatment.     

Structural characterization of bulk ZrTiO4 and its potential for thermal shock applications

Zirconium titanate, ZrTiO₄, is a well known compound in the field of electroceramics. Furthermore, it shows a large potential as structural material for thermal shock resistance applications, since it presents crystallographic anisotropy in thermal expansion. However, there is no information in the current literature about its thermomechanical behaviour. In this work, single phase zirconium titanate bulk materials have been prepared from well dispersed ZrO₂ and TiO₂ mixed suspensions, combining reaction and conventional sintering processes. The crystal structures of ZrTiO₄ have been studied by the Rietveld method for bulk samples. The structural evolution upon the cooling rate has been unravel, as the b-axis strongly decreases for slow cooled samples when compared to quenched materials. For the first time apparent Young's modulus (≈130 GPa) and Vickers hardness (≈8 GPa) values of a fully dense single phase zirconium titanate material have been evaluated and its potential for thermal shock applications has been analysed in comparison with other thermal shock resistant materials.     

Evaluation of the corrosion resistance of new ZrTi alloys by experiment and simulation with an adaptive instance-based regression model

The aim of this study is to investigate the electrochemical behaviour of ZrTi alloys in artificial saliva for different pH and NaF content, with albumin protein addition. The corrosion resistance of the alloys was quantitatively evaluated by polarization resistance, estimated with EIS method. SEM analysis was additionally used to observe the corrosion effects on the surface of alloys. A simulation study based on an adaptive regression model, AKNN, designed for experiments with insufficient or missing data, was performed. Accurate results were obtained in evaluating the influence of the working conditions on the corrosion resistance of the alloys.     

Perforation corrosion of automotive materials: comparison between laboratory and field exposures

Abstract

Two of the most important testing parameters, the wet/dry ratio and the temperature, were varied in order to study their influence on the extent of perforation corrosion of automobile materials. The results are compared with results from field exposures performed at the marine site of Bohus Malmön (Sweden) and with results from mobile exposure. In situ measurements of the galvanic current and the electrochemical impedance of the confined surface were used to determine the degree of macrowetness and the corrosion rate respectively. From the results it is shown that both the drying time and the temperature are important factors when designing cyclic corrosion tests for perforation corrosion of auto motive materials.     

The influence of experimental conditions on the morphology and phase composition of Nb-doped ZrO2 films prepared by spark anodization

This paper reports the morphological and microstructural characterization of Nb-doped ZrO₂ films obtained by anodic doping in conditions of spark electrolytic breakdown. The oxide films were prepared by galvanostatic anodization of metallic Zr in oxalic acid solution containing ammonium oxaloniobate, NH₄H₂[NbO(C₂O₄)₃]⋅3H₂O using Nb(V) ions as the precursor dopant. The characterization was performed by SEM and XRD. A factorial design was used to optimize the experiments and study the influence of experimental variables on morphology and phase composition. The results demonstrated that the dopant concentration is the most important factor that affected the analyzed responses. A significant influence of this variable was observed on the pore average diameter and on the percentage of the stabilized tetragonal phase. The temperature also affected the phase composition, however no effect was observed on the morphological response.