Alumina - 7.5 wt% yttria-stabilized zirconia (YSZ) ceramic composites were sintered using 24 GHz microwave heating at rates of 10 - 200 degrees C/min with zero isothermal hold. The starting powders were nanophase i-Al2O3 and YSZ prepared by a laser evaporation method. The final densities of the sintered samples were up to 97.5 % of the theoretical value. The samples exhibited rapid densification until transformation to the alpha-Al2O3 phase. The temperature of the densification rate peak (and hence of the phase transformation) decreased consistently with increasing microwave electromagnetic field intensity (varied by using different susceptor materials). The densification peak temperature difference between microwave and conventional sintering experiments exceeded 200 degrees C.

Samples of alumina - 3 % yttria-stabilized zirconia (YSZ) composites were sintered in rapid processing regimes using 24 GHz microwave heating at rates of up to 200 degrees C/min and zero hold time. The final relative density was 96-99 % for the samples containing 1.5 and 7.5 wt % YSZ and 98-99 % for the samples containing 13 wt % YSZ. The microwave sintering kinetics were compared for the processes carried out by direct and susceptor-assisted microwave heating. Under direct microwave heating, the effect of an intense microwave electromagnetic field with an estimated absorbed power density of up to 130 W/cm(3) resulted in a shift of the shrinkage curves by about 100( degrees )C towards lower temperatures compared to the case of susceptor-assisted heating. The grain size of the samples sintered by direct microwave heating decreased with an increasing heating rate. The mechanical properties were slightly higher for the materials sintered under susceptor-assisted microwave heating. The samples containing 13 wt % YSZ exhibited a microhardness of about 20 GPa and a fracture toughness of about 7 MPa m (1/2) .

Using the method of sintering by microwave heating at a rate of 10–100°C/min to a temperature of 1250 °C without isothermal hold, we obtain ceramic samples with the composition Ba0.75Sr0.25TiO3. The experiments are performed on a gyrotron complex for the high-temperature microwave treatment of materials, which is operated at a frequency of 24 GHz with a maximum power of 5 kW. The features of the formation of a solid solution in the sintered samples are analyzed. The dependence of the intensity of recrystallization growth of grains on the microwave-heating rate during the sintering is demonstrated. The permittivity of the samples obtained by microwave sintering with heating rates of 10 and 30 °C/min amount to 3600–4400 in the frequency range 25Hz–3MHz at room temperature.

Rapid microwave sintering processes with heating rates of up to 300 degrees C/min and zero isothermal hold have been implemented using a 5 kW 24 GHz gyrotron system for high-temperature microwave processing of materials. ZnO-based varistor ceramics, BaTiO3/SrTiO3 dielectric ceramics and Gd:CeO2 ceramics for solid electrolyte applications have been sintered to densities of up to 96% of the theoretical value. Using in situ optical dilatometry, correlation between the development of thermal instability under intense volumetric microwave heating and the early onset of densification has been revealed. The influence of the absorbed microwave power on densification and grain growth has been studied by comparing direct and susceptor-assisted microwave heating processes. The possibility of tailoring the microstructure and functional properties of the obtained materials by choosing optimal regimes of rapid microwave sintering is discussed.

ZnO samples with an addition of 0, 0.035, 0.1, and 0.35 mol.% Bi2O3 were microwave sintered at heating rates 10 and 50 degrees C/min to a maximum temperature of 1200 degrees C with zero hold time. The densification curves obtained by optical dilatometry have been studied in their dependence on the dopant concentration and the heating rate. Direct volumetric absorption of microwave radiation resulted in a 50-60 degrees C shift of the densification curves toward low temperatures compared to susceptor-assisted heating. An analysis of the effect of the volumetrically absorbed microwave power on the formation of grain-boundary phases that facilitate densification is presented.

Gd:CeO2 ceramic samples with a density of up to 96% of the theoretical value have been obtained by rapid 24 GHz microwave sintering with heating rates of up to 300 degrees C/min and zero hold time. It has been found that a higher absorbed microwave power density lowers the densification onset temperature by up to 150 degrees C. The grain size in the final materials decreased with an increase in the heating rate at a lower power density (a few W/cm(3)) but increased at a higher power density (similar to 40 W/cm(3)). The ionic conductivity of the sintered materials depended on the microwave heating rate; samples sintered at 30 - 100 degrees C/min had an ionic conductivity of approximately 0.5 S/m at a temperature of 560 degrees C.

24 GHz microwave sintering of BaTiO3 ceramics has been studied under rapid heating at a rate of up to 300 degrees C/min to a maximum temperature of 1150-1300 degrees C with no isothermal hold. Under direct volumetric microwave heating the temperature difference measured between the center and periphery of the samples was 200-300 degrees C, and the estimated volumetrically absorbed power density was about 40 W/cm(3). The use of a SiC susceptor made it possible to reduce the required microwave power and equalize the temperature distribution, but in this case densification started at a higher temperature. Evidence of recrystallization-induced microstructure transformation propagating outward from the core of the sample is presented. The possiblity of implementing control over the microstructure and functional properties by choosing the parameters of the microwave sintering regime is discussed.

Rapid microwave sintering of different oxide ceramics with heating rates up to 300 °C/min and zero hold time has been implemented using a 24 GHz gyrotron-based system for high-temperature processing of materials. The design of the system, principle of operation, and process control are described. Particular attention is given to the design of thermal insulation assemblies and the implementation of temperature measurement in an environment with intense electromagnetic fields. A description of an optical system for dilatometry and temperature measurement is presented. The interrelation between the automatically regulated output power of the gyrotron and the microwave power absorbed volumetrically in the sample is analyzed on the basis of energy balance considerations. The analysis is illustrated by considering examples of rapid sintering processes with ZnO-based and BaTiO3 ceramic samples making use of direct and susceptor-assisted microwave heating. It is demonstrated that an increase in the volumetrically absorbed power leads to the development of a controlled thermal instability, which results in a lower temperature of the densification onset.

Using hydroxyapatite as an example, first results of research on a new additive method of manufacturing ceramic products are presented. The method consists of repeated sequential application of suspension layers with high content of powder material and their rapid 24 GHz microwave sintering. The stability of aqueous suspensions of hydroxyapatite powder with submicron particle size depending on the pH of the dispersion medium and dispersants was studied. Suspensions with a high value of the solid load mass and a fluidity sufficient to ensure the continuity of layers applied by the doctor blade method were obtained. By the method of layer-by-layer microwave sintering with a heating rate of up to 30°C/min and a maximum temperature of up to 1330°C, ceramic samples with a closed system of micron-sized pores and a density of up to 92% of the theoretical value were obtained.

IPSC line RCPCMi004-8 was generated from skin fibroblasts collected from a male patient with spinocerebellar ataxia 17. The patient has expanded trinucleotide CAG repeats in the TBP (TATA-binding protein) gene on chromosome 6q27. The reprogramming of fibroblasts was performed with Sendai viruses containing Oct-4, Sox-2, Klf-4, and c-Myc. Pluripotency was confirmed by immunofluorescence, RT-PCR, and the formation of embryoid bodies. The RCPCMi008-A cell line carries the same trinucleotide CAG repeats in the TBP gene. The RCPCMi008-A cell line can be used to model Spinocerebellar ataxia in vitro.

Samples of ZnO + Bi2O3 + Sb2O3 varistor ceramics were microwave sintered using gyrotron systems operating at a frequency of 24 GHz. The microwave power was automatically regulated to implement heating at a constant heating rate of 10-130 degrees C/min up to a temperature of 1100-1300 degrees C with no isothermal hold. The final sintered density of the samples was 95-96 % of the theoretical value. Manifestations of the thermal instability associated with the liquid phase formation were observed at a temperature of about 600 degrees C. The estimated volumetrically absorbed power density at the onset of instability was >= 20 W/cm(3), and the temperature difference measured between the center and periphery of the samples reached 200 degrees C. Correlation has been revealed between the thermal instability occurrence and the shift of densification curves towards lower temperatures. A mechanism underlying enhanced densification in electromagnetic field-assisted sintering processes is suggested.

according This paper reports recent results on the use of millimeter-wave and sub-terahertz electromagnetic radiation in the implementation of additive fabrication methods of ceramic products. GPa inside the individual layers. No delamination of the layered structure was observed after indentation.

We demonstrate the possibility to use focused beams of millimeter-wave radiation to heat ceramic materials locally with the purpose of manufacturing sintered products on the basis of such materials by additive methods. The results of experiments on layer-by-layer sintering of ceramic hydroxiapatite samples heated by a gyrotron facility operating at a frequency of 24 GHz are presented.

The paper presents gyrotron-based system (developed by IAP RAS jointly with GYCOM Ltd.) for ECR plasma heating in the new T-15MD tokamak which is under construction in National Research Center "Kurchatov Institute". The first of a series (8 units) of microwave setups of a megawatt power level was developed and successfully tested. The setup includes a gyrotron, set of power supplies, a microwave radiation transmission line, and a fast protection system. 1 MW/82.6 GHz generation regime during 30 second pulse with an efficiency of 57% was experimentally demonstrated.

Hydroxyapatite powder compacts have been sintered to a relative density of about 95% using rapid 24 GHz microwave heating at rates 10-100 degrees C/min to 1300 degrees C with zero hold time. An optical system based on an infrared camera has been developed to measure shrinkage and temperature distributions over the surface of the samples. Ultra-rapid localized consolidation of hydroxyapatite powder, with application prospects in additive manufacturing, has been achieved using heating by a focused beam of 263 GHz millimeter-wave radiation. (C) 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the III All-Russian Conference (with International Participation) "Hot Topics of Solid State Chemistry: From New Ideas to New Materials".

Compacted alumina samples with an addition of 1.0 and 2.5 wt % carbon nanotubes (CNT) have been microwave sintered at heating rates 50 and 100 degrees C/min to a maximum temperature of 1550-1600 degrees C with zero hold time. The densification kinetics has been studied using optical dilatometry. No noticeable influence of CNT on the development of thermal instability during rapid microwave sintering of alumina has been detected. The relative densities of the samples containing 1.0 and 2.5 wt % CNT sintered at a maximum temperature of 1550 degrees C and zero hold time were 93.8 and 87.5%, respectively. Microwave sintering with a repeated development of thermal instability has resulted in an increase in the final density to 95.0%.

As part of the creation of a unique T-15MD tokamak with a magnetic field of 2 T and an aspect ratio of 2.2, the first one of a series (8 pieces) of microwave setups of a megawatt power level for electron–cyclotron plasma heating and current drive was developed and successfully tested. The setup includes a gyrotron, power supplies, a microwave radiation transmission line, and a fast (response time is no more than 10 μs) gyrotron emergency protection system. The generation regime was experimentally demonstrated with the parameters 1 MW/30 s/82.6 GHz for an efficiency of 57%.

Gyrotrons for plasma fusion installations operated at frequencies 40-170 GHz with an output power up to 1 MW are presented. Some novel ideas are proposed to enhance gyrotron output energy, efficiency, frequency spectrum. In the collaboration between the Institute of Applied Physics and industrial company GYCOM Ltd the series of gyrotrons for plasma installations has been realized. The brightest examples are 170 GHz gyrotrons for ITER, long-pulse 140 GHz gyrotrons developed for EAST and KSTAR installations, 82.6 GHz for T-15MD tokamak, 28 GHz and 45 GHz complex for modern electron cyclotron resonance ion sources (ECRIS) facilities. Some steps were done in development of 230-700 GHz gyrotrons for future plasma installations and for plasma diagnostics.