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In this paper, the stability of CaO doped partially stabilised zirconia (CaO-PSZ) prepared by electrofusion method was improved from 88.14% to 95% within one hour using the microwave heating method. The increase of the stability rate was because of the microwave heating method’s advantages, including selective heating and fast heating. Analysis techniques, namely X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy, and scanning electron microscopy (SEM), were used to analysis the influences of the holding time (1–4 h) on the CaO doped PSZ samples at a heating temperature of 1100 °C to understand the fundamental mechanism of the optimisation process. The Raman and XRD spectra were fitted by the Gaussian method to further analysis the effect of holding time on the microstructure evolution of the samples. The fitting results indicated that the sample’s crystal quality and stability were improved after microwave heating, and the optimised holding time is 2h.

In this paper, 3 mol% yttria-doped tetragonal zirconia polycrystal material (3 mol% Y₂O₃–ZrO₂) was prepared using an optimised pressureless sintering process. The phase change and particle size distribution of Y₂O₃–ZrO₂ during sintering were studied, and the effect of sintering temperature on the properties of Y₂O₃–ZrO₂ was analysed. The raw materials and prepared samples were analysed using XRD, Raman spectroscopy, SEM, and Gaussian mathematical fitting. The results show that sintering encourages the transformation of the monoclinic phase into the tetragonal phase, thus improving the crystallinity of the sample. The relative content of the tetragonal phase in the sample increased from 57.43% to 99.80% after sintering at 1200 °C for 1 h. In the range of sintering temperatures studied in this paper (800–1200 °C), the zirconia material sintered at 1000 °C presented the lowest porosity and the best density.

In this work, microwave heating approach was introduced into the preparation process of zirconia materials to overcome the tricky technical defects during the traditional electric arc furnace method. Magnesia-partially stabilised zirconia (MgO-PSZ) with enhanced stability and a uniform microstructure was prepared via microwave heating of a ZrO₂ sample manufactured by the electric arc furnace method. The effects of microwave heating on the phase stability properties, microstructure, and surface morphology of the prepared MgO-PSZ sample were evaluated via X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and Scanning electron microscopy, and the obtained results suggested that the stability rate of the MgO-PSZ sample improved from the initial value of 81.19%–94.82% after microwave heating at 1300 °C for 1 h. As a result of the martensitic conversion of ZrO₂ material, the m-ZrO₂ diffraction peaks were suppressed at the same time. Additionally, a similar changing trend was noticed in the XRD pattern, Raman spectrum, and FT-IR spectrum, indicating a decrease in the m-ZrO₂ phase content in the microwave treated products. Furthermore, the microstructure on the surface of the microwave-sintered MgO-PSZ sample was improved in contrast to the raw MgO-PSZ sample, and became relatively more uniform and smooth. This study determined the optimal microwave heating conditions for the preparation of MgO-PSZ material with enhanced performance, and can provided as a good foundation for developing the further related research on zirconia materials preparing by microwave heating technology.

High-quality vanadium pentoxide powder is an important product of the vanadium industry and was usually prepared from ammonium polyvanadate (APV) using a roasting process combined with a drying pretreatment. Conventional hot air drying is usually used for the drying of APV, the heat transfer of which is from outside to inside thus limited the efficiency of the drying pretreatment. In the present paper, microwave heating was applied as an alternative heating method for the drying of APV because of its advantages including selective heating, high heating efficiency, low energy consumption, and green environmental protection. An experimental comparison between hot air drying and microwave drying is provided, and the results show that microwave drying is more energy-saving and faster. The drying characteristics of APV under the irradiation of microwave energy were investigated. The influences of factors including microwave power, material quality, and initial moisture content on microwave drying were studied. The results show that the microwave power, initial moisture content, and initial mass are positively proportional to the microwave drying efficiency of APV. Additionally, the Page model was robust in describing the kinetics of microwave drying and hot air drying of APV. This study provides fundamental knowledge on the microwave drying process and provides the trial for the industrial applications of microwave heating on the preparation of V₂O₅.

Partially stabilised zirconia has advantages for the applications in the metallurgical processes which have special requirements in corrosion resistance and high-temperature performance. In the present work, controllable microwave heating was used for the uniform thermal field and consequent microstructure improvement to further improve the stability of partially stabilised zirconia, which was 88.14% prepared by electric arc melting. Analyses including X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (Raman) were used to study the effect of temperature change on the phase composition and structure of the samples. After heating at temperatures of 900 °C, 1000 °C, 1100 °C, 1200 °C and 1300 °C for 1h, the stabilities of the heated product were 88.51%, 95.02%, 95.17%, 96.31% and 97.64%, respectively. From the phase transformations based on the experimental results, the discussion indicates that the martensitic transformation temperature of zirconia from m-ZrO₂ to t-ZrO₂ during the heating stage was reduced under the radiation of microwave energy.

Nanosized CeO₂–ZrO₂ powders prepared by atmospheric pressure pyrolysis were used as raw materials to prepare CeO₂–ZrO₂ ceramics using microwave sintering. The samples were characterised using bulk density measurements, X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FT-IR), Raman, and scanning electron microscopy (SEM). The purpose was to determine the optimised microwave sintering process for CeO₂–ZrO₂ ceramics and reveal the corresponding mechanism. The results show that with a CeO₂ addition content above 5 mol%, the tetragonal phase peak appeared obviously in the sample. The results show that the tetragonal phase peak appears when the CeO₂ content is more than 5 mol%. The dopants, namely CeO₂, have reduced the solid solution’s phase transformation temperature with the assistance of microwave heating. Additionally, the grain size of the CeO₂–ZrO₂ ceramics has shown a negative relationship with Ce content at a temperature of 900 °C. The reason is that the rapid sintering due to microwave sintering and the oxygen vacancies generated by CeO₂ can effectively inhibit grain growth. The regulation mechanism on microwave sintering of CeO₂–ZrO₂ ceramic was clarified, and the technical prototype of controlled prepared CeO₂–ZrO₂ ceramics by microwave sintering was constructed.

The effects of microwave power and sample quality on microwave drying kinetics and characteristics of zirconia were studied. It is found that by increasing the microwave power and decreasing the sample mass, the surface diffusion coefficient (Deff) appears to an upward tendency. The corresponding value Deff at a sample mass of 10, 20, 30, and 40g are 1.849E-14, 2.443E-14, 3.210E-14, and 3.278E-14 m²/s, respectively. The corresponding value Deff at a microwave power of 300, 400, 500, 600, and 700W are 1.270E-14, 1.784E-14, 2.619E-14, 3.392E-14, and 4.497E-14 m²/s, respectively. Besides, the materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR) to evaluate the changes of materials before and after drying. The results show that microwave accelerates the drying of zirconia and increases its dispersibility. The heat conduction direction of microwave drying is the same as that of moisture diffusion, which avoids being affected by heat inertia and heat transfer loss. The drying process is fast and efficient, and the microwave directly penetrates the product, avoiding the disadvantage of slow evaporation caused by the temperature gradient.

Partially stabilised zirconia (PSZ) ceramics have attracted much interest because of their outstanding properties. In this study, fused ZrO₂ was treated as a raw resource for the synthesis of CaO-PSZ ceramic materials through a facile sintering process. The crystal structure and thermomechanical properties of the synthesised CaO-PSZ ceramic samples were determined using XRD and SEM. The results revealed that various process parameters had different effects on the zirconia stability rate, including the temperature changing rate during the heating and cooling stages and the temperature and isothermal time during the quenching treatment; this was primarily a result of the thermodynamic characteristics of the martensitic conversion of ZrO₂ ceramics. Secondly, the martensitic conversion process was revealed by XRD patterns, expressed as the partial conversion of c-ZrO₂ to m-ZrO₂. Meanwhile, SEM-EDAX analysis highlighted the precipitation behaviour of the CaO stabiliser and the successful preparation of CaO-PSZ ceramics by sintering, represented by the gathering phenomenon of the acicular grains and particles, as the findings matched the stability rate analysis. This study can supply a sound reference for the synthesis of CaO-PSZ ceramics from fused ZrO₂.

Partially stabilized zirconia (PSZ) ceramics play a significant role as fundamental ceramics and refractory materials. In this work, a CaO-PSZ ceramics material was synthesized from fused ZrO₂ by microwave sintering. The stability properties and structural characteristics of the products were characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated that in a microwave field, the duration and sintering temperature presented similar influence trends for the stability properties of ZrO₂ ceramics materials, which the finding was assigned to the phase transformation of ZrO₂ with temperature change. In addition, following the microwave treatment of the fused zirconia sample at 1450 °C for 2.0 h, a cubic and monoclinic mixed phase was formed. These outcomes corresponded to the results from the SEM and energy dispersive X-ray (EDAX) analysis, demonstrating the successful preparation of the CaO-PSZ ceramics. The toughness of the ceramics was improved, which could be attributed to the formation of CaO-stabilizer-precipitated acicular crystals. The theoretical fundamentals and the practical cases presented in this paper are beneficial for the application of the microwave sintering technology in the synthesis of CaO-PSZ ceramics.