Search Results (8)

The use of solid waste such as ceramic sludge, ceramic rollers, and magnesite was studied to obtain cheap refractory ceramics at temperatures of 1300 °C based on XRF, XRD SEM, EDX, bending strength, and dielectric properties. The prepared samples were examined. The results showed that the significant crystalline phases formed were mullite, spinel, and corundum. They also showed that mullite hindered the formation of cordierite and enhanced spinel formation. With increased cordierite content, the microstructure varied from fine grained to coarse grained. Bending strength increased with increasing mullite content and bulk density, ranging from 10.80 to 13.50 MPa. Bulk density increased with the increase in mullite content and sintering temperature and ranged from 1.99 to 1.94 g/cm³, while the percentage of porosity and water absorption decreased and ranged from 29.40 to 38.83, respectively. To examine the effect of the produced phases on the dielectric characteristics, the permittivity (ε′), dielectric loss (ε″), and AC conductivity (σ_ac) were measured in the frequency range of 10⁻¹ Hz to 10⁶ Hz. As the concentration of cordierite increased, there was a noticeable drop in ε′ from 35.6 to 8.2 and σ_ac from 10⁻⁸ s/cm to around 10⁻¹¹ s/cm and high values of resistivity from 10⁸ cm/s to about 10¹⁰ cm/s, suggesting that this material might be an excellent insulator. Full article

Ceramics based on zirconium dioxide are very important compounds for dental, implant, and structural material applications. Despite the fact that tetragonally stabilized YSZ has been well studied, the search for new compositions of zirconia-based ceramics is still in progress. The ZrO₂-CeO₂ system is one of the alternatives for YSZ materials, but there is conflicting experimental data on its phase composition and mechanical properties depending on the ratio of components. In this study, we investigated the phase composition, and microstructural, mechanical, and physical properties of (1 − x)∙ZrO₂-x∙CeO₂ (step of x = 0.05) ceramics obtained by the solid-state sintering process from micron-sized powders. For the characterization of samples, XRD, Raman spectroscopy, SEM, the Vickers Microhardness Test, and dielectric spectroscopy were implemented. The results showed that by varying the CeO₂ concentration, it is possible to synthesize stable tetragonal ZrO₂ at room temperature with a high microhardness HV0.05 value of ~1500, low porosity (~2.5%), and a high dielectric constant of 36. The pronounced combined effect of tetragonal phase formation, densification, and grain size reduction on the mechanical and dielectric properties of the experimental samples was investigated. Refined experimental data make it possible to synthesize high-quality zirconia–ceria ceramics for use as refractories, dispersed nuclear fuel, or solid oxide fuel cells. Full article

This paper presents the results of ceramic synthesis in the field of a powerful flux of high-energy electrons on powder mixtures. The synthesis is carried out via the direct exposure of the radiation flux to a mixture with high speed (up to 10 g/s) and efficiency without the use of any methods or means for stimulation. These synthesis qualities provide the opportunity to optimize compositions and conditions in a short time while maintaining the purity of the ceramics. The possibility of synthesizing ceramics from powders of metal oxides and fluorides (MgF₂, BaF₂, WO₃, Ga₂O₃, Al₂O₃, Y₂O₃, ZrO₂, MgO) and complex compounds from their stoichiometric mixtures (Y₃Al₃O₁₂, Y₃Al_xGa_(5-x) O₁₂, MgAl₂O₄, ZnAl₂O₄, MgWO₄, ZnWO₄, Ba_xMg_(2-x) F₄), including activators, is demonstrated. The ceramics synthesized in the field of high-energy electron flux have a structure and luminescence properties similar to those obtained by other methods, such as thermal methods. The results of studying the processes of energy transfer of the electron beam mixture, quantitative assessments of the distribution of absorbed energy, and the dissipation of this energy are presented. The optimal conditions for beam treatment of the mixture during synthesis are determined. It is shown that the efficiency of radiation synthesis of ceramics depends on the particle dispersion of the initial powders. Powders with particle sizes of 1–10 µm, uniform for the synthesis of ceramics of complex compositions, are optimal. A hypothesis is put forward that ionization processes, resulting in the radiolysis of particles and the exchange of elements in the ion–electron plasma, dominate in the formation of new structural phases during radiation synthesis. Full article

Forsterite (Mg₂SiO₄) materials have been used in the industrial applications of refractory materials, bone grafting materials, and microwave dielectric materials. In order to avoid the formation of the secondary phase of MgO or MgSiO₃, spray pyrolysis with the precursors of magnesium nitrate hydrate and tetraethyl orthosilicate has been applied to synthesized Mg₂SiO₄ powders. In this study, three typical morphologies of smooth solid sphere, rough hollow sphere, and concaved hollow sphere were observed using scanning electron microscopy and transmission electron microscopy. The experimental results suggested that morphology and particle size distribution are strongly influenced by the calcination temperature. Finally, the corresponding powder formation mechanisms were proposed and discussed. Full article

As solar energy is a low-cost and clean energy source, there has been a great deal of interest in how to harvest it. To absorb solar energy efficiently, we designed a broadband metamaterial absorber based on the principle of Fabry–Pérot (FP) cavities and surface plasmon resonance (SPR). We propose a broadband perfect absorber consisting of a four-layer structure of silica–tungsten–silica–titanium (SiO₂–W–SiO₂–Ti) for the incident light wavelength range of 300–2500 nm. The structure achieves perfect absorption of incident light in the wavelength range of 351.8–2465.0 nm (absorption > 90%), with an average absorption of 96.3%. The advantage of our proposed structure is that it combines the characteristics of both high and broadband absorption, and has high overall absorption efficiency for solar radiation. It is also independent of polarization and insensitive to incident angle. We investigated how absorption was affected by different structures, materials, geometric parameters, and refractive indices for different dielectric materials, and we explored the reasons for high absorption. This structure is refractory and ultrathin, and it offers a good tradeoff between bandwidth and absorption. It therefore has premium application prospects and value. Full article

Random surface roughness and surface distortions occur inevitably because of various material processing and fabrication techniques. Tailoring and smoothing the surface roughness can be especially challenging for thermomechanically stable materials, including refractory metals, such as tungsten (W), and polar dielectrics, such as silicon carbide (SiC). The spectral reflectivity and emissivity of surfaces are significantly impacted by surface roughness effects. In this paper, we numerically investigated the surface roughness effects on the spectral reflectivity and emissivity of thermomechanically stable materials. Based on our results, we determined that surface roughness effects are strongly impacted by the correlation length of the Gaussian surface. In addition, our results indicate that surface roughness effects are stronger for the materials at the epsilon-near-zero region. Surface roughness effects are stronger between the visible and infrared spectral region for W and around the wavelength of 12 $\mathsf{\mu }$ m for SiC, where plasma frequency and polar resonance frequency are located. Full article

Excellent characteristics and promising application prospects promote the rapid development of metamaterials. We have numerically proposed and demonstrated a novel subwavelength broadband metamaterial perfect absorber (BMPA) based on diamond dielectric arrays. The proposed absorber is composed of an ultra-thin two-layer structure covering the dielectric periodic array on a metal substrate. The materials of dielectric silicon (Si) and gold (Au) substrate are discussed in detail. In addition, different dielectric and refractory materials are also applied to achieve broadband absorption, which will make the proposed absorber greatly broaden the application field. A perfect absorption window (i.e., absorption rate exceeding 90%) can be obtained from near-ultraviolet to the visible range. The average absorption rate of 93.3% is achieved in the visible range. The results of multipole decomposition show that broadband absorption is mainly caused by electromagnetic dipole resonance and lattice resonance in a periodic array of Si. The proposed absorber can be extended freely by adjusting the structural parameters. The polarization-independent and incident angle insensitivity are proved. The proposed absorber may well be used in light energy acquisition, as well as for the scalability of optoelectronic and sensing devices. Full article

Microwave energy can be advantageously used for materials processing as it provides high heating rates and homogeneous temperature field distribution. These features are partly due to the large microwave penetration depth into dielectric materials which is, at room temperature, a few centimeters in most dielectric materials. However, up to now, this technology is not widely spread for high-temperature material processing applications (>1200 °C), because its reproducibly and ability to sinter large size samples (>30 cm³) still needs to be improved. In this context, this paper describes both an empirically designed 915 MHz single-mode cavity made from SiC susceptors and refractory thermal insulation, and the 3D modeling of the process in order to improve our understanding of it. Different susceptors geometries and coupling slit position were numerically tested in order to better understand how these parameters impact the field homogeneity and the process stability. It was found that positioning the largest surface of the susceptors parallel to the electrical field allows a very uniform and hybrid heating of the material, while avoiding plasma or thermal instabilities. This was correlated to the 3D modeling results. Finally, thanks to a fully-automatized system this apparatus was used to sinter large size (~30 cm³) low-loss dielectric alumina samples. The sintered materials were subsequently characterized in terms of density, grain size distribution, and homogeneity. The reproducibility was also discussed, demonstrating the process efficiency and reliability. Full article