Borosilicate Glass-Ceramics Containing Zirconolite and Powellite for RE- and Mo-Rich Nuclear Waste Immobilization

In order to increase the loading of rare earth- and molybdenum-rich high-level waste in the waste forms, zirconolite- and powellite-based multi-phase borosilicate glass-ceramics were synthesized via an in-situ heat treatment method. The effects of the CTZ (CaO, TiO2 and ZrO2) content on the crystallization, microstructure and aqueous durability of the multi-phase borosilicate glass-ceramics were studied. The results indicate that the increase of CTZ content can promote crystallization. The glass-ceramics presented even structures when the CTZ content was ≥ 40 wt%. For the glass-ceramic with 40 wt% CTZ, only zirconolite and powellite crystals were detected and powellite crystals were mainly distributed around zirconolite, whereas for the glass-ceramics with 50 wt% CTZ, perovskite was detected. Furthermore, the leaching rates of Na, Ca, Mo and Nd were in the ×10−3, ×10−4, ×10−3 and ×10−5 g·m−2·d·−1 orders of magnitude on the 28th leaching day, respectively.

The Effect of ZrO2 as Different Components of Ni-Based Catalysts for CO2 Reforming of Methane and Combined Steam and CO2 Reforming of Methane on Catalytic Performance with Coke Formation

The role of ZrO2 as different components in Ni-based catalysts for CO2 reforming of methane (CRM) has been investigated. The 10 wt.% Ni supported catalysts were prepared with ZrO2 as a support using a co-impregnation method. As a promoter (1 wt.% ZrO2) and a coactive component (10 wt.% ZrO2), the catalysts with ZrO2 were synthesized using a co-impregnation method. To evaluate the effect of the interaction, the Ni catalyst with ZrO2 as a coactive component was prepared by a sequential impregnation method. The results revealed that the activity, the selectivity, and the anti-coking ability of the catalyst depend upon the ZrO2 content, the Ni-ZrO2 interaction, basicity, and oxygen mobility of each catalyst resulting in different Ni dispersion and oxygen transfer pathway from ZrO2 to Ni. According to the characterization and catalytic activation results, the Ni catalyst with low ZrO2 content (as a promoter) presented highest selectivity toward CO owning to the high number of weak and moderate basic sites that enhance the CO2 activation-dissociation. The lowest activity (CH4 conversion ≈ 40% and CO2 conversion ≈ 39%) with the relatively high quantity of total coke formation (the weight loss of the spent catalyst in TGA curve ≈ 22%) of the Ni catalyst with ZrO2 as a support is ascribed to the lowest Ni dispersion due to the poor Ni-ZrO2 interaction and less oxygen transfer from ZrO2 to the deposited carbon on the Ni surface. The effect of a poor Ni-ZrO2 interaction on the catalytic activity was deducted by decreasing ZrO2 content to 10 wt.% (as a coactive component) and 1 wt.% (as a promoter). Although Ni catalysts with 1 wt.% and 10 wt.% ZrO2 provided similar oxygen mobility, the lack of oxygen transfer to coke during CRM process on the Ni surface was still indicated by the growth of carbon filament when the catalyst was prepared by co-impregnation method. When the catalyst was prepared by a sequential impregnation, the intimate interaction of Ni and ZrO2 for oxygen transfer was successfully developed through a ZrO2-Al2O3 composite. The interaction in this catalyst enhanced the catalytic activity (CH4 conversion ≈ 54% and CO2 conversion ≈ 50%) and the oxygen transport for carbon oxidation (the weight loss of the spent catalyst in TGA curve ≈ 7%) for CRM process. The Ni supported catalysts with ZrO2 as a promoter prepared by co-impregnation and with ZrO2 as a coactive component prepared by a sequential impregnation were tested in combined steam and CO2 reforming of methane (CSCRM). The results revealed that the ZrO2 promoter provided a greater carbon resistance (coke = 1.213 mmol·g−1) with the subtraction of CH4 and CO2 activities (CH4 conversion ≈ 28% and CO2 conversion ≈ %) due to the loss of active sites to the H2O activation-dissociation. Thus, the H2O activation-dissociation was promoted more efficiently on the basic sites than on the vacancy sites in CSCRM.

A Study of Osmosis Rate Through Several Proton Conducting Polymer Composite Membranes

Carbon dioxide is typically considered to be a byproduct of various industrial processes that should not be released into the environment due to its nature as a harmful greenhouse gas. One of the more promising ways to dispose of it in an economical and environmentally friendly way is by using it as a raw material in electrochemical synthesis reactors. An important part of such reactors is an ion exchange membrane. In this study the influence of ZrO2 content in SPEEK – ZrO2 composite membranes on rate of osmosis trough them was investigated, with the goal of evaluating ZrO2 as an additive for making ion exchange membranes with fine-tuned osmotic permeability.

Preparation of Magnesia Partially Stabilized Zirconia Nanomaterials from Zirconium Hydroxide and Magnesium Carbonate Precursors Using PEG as a Template

Stabilized zirconia is a promising material due to its great physical and chemical properties, and thermal stability. In this work, MgO was used as a stabilizer in ZrO2 to obtain Magnesia Partially Stabilized Zirconia (MSZ) nanomaterials assisted with PEG as a template through conventional mixing process. Zirconium hydroxides prepared from local zircon and MgCO3 were used as MSZ precursors. Meanwhile, the stabilizer concentration was varied from 1 to 4 wt% of ZrO2. The effect of the stabilizer concentration and the calcination temperature to the crystallinity and the morphological properties of the MSZ nanoparticles were studied using X-ray diffraction and scanning and transmission electron microscopy. The ZrO2 content in the zirconium hydroxides precursors is accounting 89.52 wt% of the total and exhibits the dominant m-phase at 1000 °C. Meanwhile, the tetragonal and the monoclinic phases were formed in all MSZ samples at a temperature of 800–1000 °C. The as-synthesized MSZ samples show typical FT-IR spectra, consisting of the metal–oxygen bonds at below 500 cm−1 and the organic functional groups ranging at 1000–3000 cm−1. The ZrO2 morphologies exhibit spherical-like shapes with elongated agglomeration at 800 °C. In addition, the average particle sizes of the final product ranges from 20 to 50 nm. At a sintering temperature of 1500 °C, MSZ samples show the monoclinic phase of ZrO2 and densities in the range of 3.95–4.14 g/cm3.

Effect of Zirconium Oxide Reinforcement on Microstructural, Electrochemical and Mechanical Properties of TiNi Alloy Produced Via Powder Metallurgy Route

Equiatomic TiNi alloy composites, reinforced with 0, 5, 10 and 15 vol. % ZrO2, were synthesized using conventional sintering approach. Equiatomic TiNi pre-alloyed powder and ZrO2 powder were mixed in planetary ball mill for 6 hours followed by cold compaction and pressure-less sintering, respectively. The sintered density was found to vary inversely with the addition of ZrO2 content. The X-Ray diffraction spectra have shown the formation of multiple-phases which were resulted from the decomposition of the B19'and B2 phases of the equiatomic TiNi alloy due to the addition of ZrO2 and higher diffusion rate of Ni than that of Ti in the alloy composite. An increase in hardness was noted due to the addition of ZrO2, measured by micro and nanoindentation techniques. Potentiodynamic polarization scan revealed a 10% decrease in the corrosion rate of the composite containing 10 vol. % ZrO2. Electrochemical impedance spectroscopy results indicated an increase in passive layer resistance (Rcoat) due to the increase in charge transfer resistance (Rct) caused by the reduced leaching of ions from the surface.

Zirconia–Alumina Composites Obtained by Centrifugal Slip Casting as Attractive Sustainable Material for Application in Construction

This paper focuses on the possibility of adapting the centrifugal slip casting method to obtain zirconia–alumina composite materials in the form of finished tube-shaped products. These types of products, due to their unique properties, can be utilised, for example, in the transport of aggressive substances, even in extreme temperatures or corrosive conditions. The study reports on the two series of zirconia–alumina composites differing in the content of ZrO2—2.5 and 25 vol%. The fabricated and sintered materials were characterised using scanning electron microscopy (SEM), X-ray diffraction (XRD) and stereological analysis. Moreover, a life cycle assessment (LCA) was provided in accordance with the requirements of the ISO 14044 and EN 15805 standards. The obtained data clearly show that the centrifugal slip casting method allows obtaining samples with high density and extremely uniform distribution of the ZrO2 phase in the alumina matrix. The stereological analysis results proved also that the addition of ZrO2 is effective in reducing the growth of Al2O3 grains during the sintering process. The phase analysis carried out by means of XRD showed that during the sintering process, in the case of composites with a lower ZrO2 content (2.5 vol%), the monoclinic to tetragonal transformation of ZrO2 was total, while for samples containing 25 vol% ZrO2, the monoclinic phase remained in a small amount in the final product.

Some Aspects of the Geochemistry and Natural Radioactivity of the Azov Deposit Ores

The analysis of the Azov deposit of zirconium-rare earth ores as the object capable on qualitative and quantitative parameters to become key for creation and modernization of rare earth subsectors of the industry of Ukraine is carried out. On the basis of the generalized characteristics of zirconium-rare earth mineralization, conclusions were drawn regarding the nature of the increased radioactivity at the Azov deposit, which is mainly due to the presence of certain minerals in the ores. The actual radioactive minerals were found only as inclusions in zircon and do not make a significant contribution to the natural radioactivity of ores. It has been established that the radioactivity is uranium-thorium due to the inclusion of these elements in the composition of the aforementioned minerals. The results of the radiation-hygienic assessment of core samples from the deposit are presented. According to the existing standards, the enclosing rocks of the supra-ore and under-ore strata can be used in all types of construction without restrictions. The ores of the deposit are assigned to the third class in terms of the level of effective specific activity. It was found that there is a significant direct relationship between gamma activity and the total REE content in the field. There is also a correlation between the content of U and Th, the dose rate of γ-radiation and the content of the total REE. It was shown that there is no relationship between these indicators and the ZrO2 content. Analysis of the gamma-ray logs showed the possibility of confidently drawing the boundaries of the ore intervals and fixing the inter-ore intervals. The main stages of the technological process of integrated development, enrichment, processing and storage of enrichment tailings, slags and sludge, which ensure the minimum impact of production on the environment and human health, have been determined.