Journal of the Australian Ceramic Society最新文献

How to properly handle the high-level radionuclides cesium(Cs) and strontium(Sr) generated during the nuclear fuel cycle has become a challenging issue. Geopolymer, a novel aluminosilicate inorganic gel material, can be in-situ converted into zeolite and ceramics, exhibiting excellent immobilization capability for radioactive nuclides. This work provides a comprehensive review of the research on the conversion and synthesis methods of geopolymer into zeolite and ceramics, and conducts a detailed analysis of the performance and mechanisms of geopolymers, geopolymer-zeolite composites, and geopolymer ceramics in the immobilization of Cs and Sr. Through a thorough analysis and summary of existing literature, this study presents the optimal conditions for the conversion of geopolymers into zeolite and proposes improved methods for geopolymer ceramic immobilization of Cs. Furthermore, a comparison and analysis are conducted of the applicability, as well as the advantages and disadvantages of these three solidification matrices in immobilizing Cs and Sr. Finally, the challenges and prospects faced by geopolymer and its derivative materials in the immobilization of high-level radionuclides Cs and Sr are discussed.

In this work, to establish the oxidation resistance for graphite in the air atmosphere with temperatures ranging from 700 to 1000 °C, an innovative multi-component, dual-layer coating was developed. The coating consists of two layers with a total thickness of around 250 μm. The first layer was consisted of B₂O₃ with SiO₂ and ZnO, while the second layer included SiC with silicon as an additive. Through scanning electron microscopy (SEM) images and elemental maps, alongside heat treatment experiments at 1000 °C, which resulted in only a 6% weight loss, it was evident that the coating was effectively applied and performed exceptionally well. Moreover, cyclic heat treatment experiments confirmed the coating’s durability and thermal stress resistance, with minimal weight reduction results. Applying these coatings is uncomplicated, and the materials are readily available, ensuring cost-effectiveness.

Graphite material is a kind of conductive material with excellent thermal shock resistance, is an important strategic mineral resources, widely used in iron and steel smelting, aviation, aerospace and other fields. However, the graphite electrode is easy to be oxidized in the air, resulting in a large amount of graphite electrode loss. In this paper, a new impregnation material is used to prepare graphite electrode oxidation resistance coating, by changing the ratio of raw materials, impregnation times, sintering process and other process parameters to prepare samples, and then oxidation resistance experiment to characterize its antioxidant capacity. The optimum technological parameters of graphite electrode coating obtained in this paper are: The content of antioxidant is Si 4.6%, SiC 5.8%, TiO₂ 6.9%, Al₂O₃ 5.4%, H₃BO₃ 3.7%, carboxymethyl cellulose 2.6%, deionized water 70%, hot impregnation twice, after sintering in nitrogen atmosphere at 400 ℃ for 30 min, In the range of 800 ℃~1200 ℃, the weight loss of the graphite samples with anti-oxidation coating is reduced by 7.3%~11.3%. The coating can protect the anti-oxidation of the graphite matrix well.

Hydrogen (H₂), a renewable energy source with a high energy density and a reputation for being environmentally benign, is being lauded for its potential in various future applications. In the present context, the catalytic methanolysis of sodium borohydride (NaBH₄) is of considerable importance due to its provision of a pathway for the efficient production of hydrogen gas (H₂). The main aim of this research attempt was to assess the viability of utilizing refuse defatted sumac seeds as an unusual precursor in microwave-assisted K₂CO₃ activation to produce a biocatalyst.

The primary objective that motivated the synthesis of the biocatalyst was to facilitate the generation of hydrogen via the catalytic methanolysis of NaBH₄. With the aim of developing a biocatalyst characterized by enhanced catalytic performance, we conducted an exhaustive investigation of a wide range of experimental parameters. The activation agent-to-sample ratio (IR), impregnation time, microwave power, and irradiation time were among these parameters.

Significantly enhanced in catalytic activity, the biocatalyst produced under particular conditions achieved a peak hydrogen production efficiency of 10,941 mL min^− 1 g.cat^− 1. In particular, it was determined that the ideal conditions were as follows: 0.5 IR, 24 h of impregnation, 500 W of microwave power, and 10 min of irradiation. This novel strategy not only demonstrates the impressive potential of eco-friendly biocatalysts, but also positions them as a viable alternative material for the sustainable production of hydrogen via NaBH₄ methanolysis.

Three significant parameters contribute to the value and renewability of this study. The first is that waste is used as the primary material; the second is that the activator is less hazardous than other activators; and the third is that microwave activation is a green chemistry technique.

Graphical Abstract

While sustainable material systems have become paramount, recycling unused waste cathode ray tubes (CRTs) glass can possess great potential for radiation protection applications. With this motivation, the present study addressed the utilization of waste CRTs in combination with MoO3 towards a glass composition of xMoO₃—(100-x)CRTs where x typifies 0, 1, 3, and 5 wt%. The glass samples coded Mo0 to Mo5 were synthesized using a traditional melting technique. After successfully preparing the glass series, some sets of characterization analyses were performed to understand physical, structural, optical, and radiation shielding properties. According to the findings, density increased from 2.92 to 2.96 g/cm³ as MoO₃ was introduced into the glass network. Yet more, all glass samples exhibited an amorphous structure irrespective of varying MoO₃ doping rates. On the other hand, FTIR measurements paved the way for highlighting possible vibrational modes, such as Si–O-Si and Si–O, in the structure. According to the optical properties via UV–Vis, the direct E_g values equaled 1.75, 1.69, 1.65, and 1.61 eV for Mo0 to Mo5, respectively, whereas R values ranged from 2.8534 to 2.9281. For investigating mass attenuation coefficients (MAC), the transmission measurements were performed for 30.9–383 keV photon energy ranges using radioactive source of 133-Ba and Ultra-Ge detector. The correctness of the experimental MAC values were checked with EpiXS program and MCNP codes. It is determined that the highest MAC values changing from 0.5951 cm²/g to 0.1022 cm²/g belong to Mo5 glass for 30.9–383 keV. It is also revealed that with the increasing MoO₃ addition, EABF, EBF, HVL and MFP values of the Mo0-Mo5 glasses dropped and MAC, Z_eff and N_el values enhanced. As a result, MoO₃ substitution has improved the material characteristics of CRTs glasses.

As the world becomes increasingly aware of the devastating effects of climate change, the need for sustainable building materials that are both durable and environmentally friendly increases. Geopolymer and alkali-activated materials formed by a chemical reaction between an alkaline activator solution and an aluminosilicate source have gained popularity in recent years. The alkaline activator solution dissolves the aluminosilicate source, which then undergoes a polycondensation reaction to form a three-dimensional geopolymeric gel network. The development of this network ensures the strength and durability of the material. Today, this phenomenon of durability has been studied in detail to enable the development of superior construction materials, taking into account degradation mechanisms such as carbonation, leaching, shrinkage, fire, freezing and thawing, and exposure to aggressive environments (chlorides, acids, and sulphates). Although there are many unsolved problems in their engineering applications, slag-based alkali-activated materials appear to be more advantageous and are promising as alternative materials to ordinary Portland cement. First of all, it should not be ignored that the cure sensitivity is high in these systems due to compressive strength losses of up to 69%. Loss of strength of alkali-activated materials is considered an important indicator of degradation. In binary precursors, the presence of fly ash in slag can result in an improvement of over 10% in compressive strength of the binary-based alkali-activated materials after undergoing carbonation. The binary systems can provide superior resistance to many degradation mechanisms, especially exposure to high-temperature. The partial presence of class F fly ash in the slag-based precursor can overcome the poor ability of alkali-activated materials to withstand high temperatures. Due to the desired pore structure, alkali-activated materials may not be damaged even after 300 freeze–thaw cycles. Their superior permeability compared to cementitious counterparts can extend service life against chloride corrosion by more than 20 times. While traditional (ordinary Portland cement-based) concrete remains the most widely used material in construction, geopolymer concrete’s superior performance makes it an increasingly emerging option for sustainable and long-lasting infrastructure.

In this article, the dielectric properties of a Li₄Ti₅O₁₂ (LTO) ceramic at the radio frequency (RF) and microwave (MW) regions were evaluated. X-ray diffraction showed that LTO was obtained without the presence of spurious and/or secondary phases. Complex impedance spectroscopy (CIS) analysis was conducted, whereas an activation energy (E_a) of 0.88 eV was observed. The temperature capacitance coefficient (TCC) was also calculated and demonstrated that LTO could be employed as a Class 1 ceramic capacitor. In the MW region, LTO presented ε’_r = 25.4, tan δ = 5.7 × 10^–4, and τ_f = -14.5 ppmºC⁻¹, values that are interesting for devices that operate in the MW region. Numerical simulation demonstrated values of a realized gain of 4.78 dBi, a bandwidth of 227 MHz, and a radiation efficiency of 98%. Moreover, LTO was evaluated as a temperature sensor operating in the MW region and demonstrated a sensitivity of -0.06 MHz ºC⁻¹. The values presented demonstrate that LTO could be employed in devices that operate in RF and MW regions.

With the acceleration of industrialization, environmental issues have received great attention from governments and societies around the world. Utilizing solid wastes containing valuable heavy metals and exploring their role and application in materials is one of the focal issues of environmental protection in recent years. In this paper, in order to explore the effect of Mn content on the crystallization of CaO-MgO-Al₂O₃-SiO₂ glass–ceramics, glass–ceramics with different content of MnO₂ were prepared by sintering method and the effect of MnO₂ doping on the crystalline properties, glass stability and heavy metal fixation properties of the stainless steel slag glass–ceramics was investigated by differential scanning calorimetry (DSC), Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM). The analysis using crystallization kinetics showed that surface crystallization dominated the whole crystallization process in the range of 0% to 10% MnO₂ content. The peak glass crystallization and depolymerisation temperatures of the glass–ceramics increased gradually with increasing MnO₂ content, and the main crystallization mode of the samples was one-dimensional crystallization. The main crystalline phase of the resulting glass–ceramics was transformed from diopside to spinel, with a crystallization temperature of 860℃. Heavy metals solidified in the spinel phase. This study shows that heavy metals can be effectively immobilized in glass–ceramics. In summary, the use of solid waste to prepare final products with good environmental performance provides a feasible way to utilize solid waste resources.

Face–centered cubic–Bi₂O₃ (δ–phase) material is a better ion conductor when compared to other types of solid electrolytes that have been declared in the literature due to its anion–defective crystal configuration, and hence it can be a promising solid electrolyte choice for intermediate temperature SOFC applications. In this research, Er–Ho–Tb co–doped Bi₂O₃ compounds were successfully synthesized by the solid–state reaction method and characterized using the XRD, TG & DTA, FPPT, and FE–SEM techniques. Apart from sample 4Er4Ho4Tb, each sample became stable with a cubic δ–phase at room temperature, according to XRD patterns. The DTA curves revealed no exothermic or endothermic peaks, implying a phase change in the constant heating cycle. The conductivity of Ho–rich compositions was higher than that of others, confirming the impact of cation polarizability on conductivity. In addition, at 700 °C, the sample 4Er8Ho4Tb with 1:2:1 content ratios had the highest conductivity of 0.29 S/cm. The porosity on the grain boundaries increased with doping, leading to higher grain boundary resistance, which could be responsible for the conductivity drop.