Theory of Sublinear Power Dependence of Microwave Heating in Some Ceramic Materials

1992 ◽  
Vol 269 ◽  
Author(s):  
V. M. Kenkre ◽  
M. Kus ◽  
J. D. Katz
Keyword(s):  
Simple Model ◽  
Grain Boundary ◽  
Microwave Heating ◽  
Microwave Field ◽  
Ceramic Materials ◽  
Absorption Efficiency ◽  
Power Dependence ◽  
Spatial Confinement ◽  
Model Calculations ◽  
Combined Action

ABSTRACTA sublinear dependence of the microwave heating rate on the incident microwave power implying a saturation effect appears to have been observed recently. We present simple model calculations to address this observation on the basis of an idea of spatial confinement of the absorbing charges in grain boundary regions. Two natural lengths exist in this model: the spatial extent of the confining region, and the maximum distance an absorbing charge travels under the combined action of damping and of the oscillating microwave field. We suggest that a mismatch of these lengths results in the observed saturation, more generally, in the observed decrease in absorption efficiency.

Microwave Equipment Considerations for High Temperature Studies in Ceramics

1988 ◽  
Vol 124 ◽  
Author(s):  
Martin Yonnone
Keyword(s):  
High Temperature ◽  
Microwave Heating ◽  
Microwave Field ◽  
Rapid Heating ◽  
Ceramic Materials ◽  
Microwave Energy ◽  
Ceramic Samples ◽  
Scientists And Engineers

The utilization of microwave energy as a source for the heating of ceramic materials is not a recent discovery. Notably, Von Hippel(1) and others including Tinga(2) investigated the microwave heating of ceramic materials in the 50's and 60's. Today, many microwave scientists and engineers are working on the complexities associated with the rapid heating exhibited by ceramic samples in the microwave field.

Model for Anomalous Power Dependence of Microwave Heating in Ceramic Materials

1992 ◽  
Vol 172 (1) ◽  
pp. 337-347 ◽  
Author(s):  
V. M. Kenkre ◽  
M. Kus ◽  
J. D. Katz
Keyword(s):  
Microwave Heating ◽  
Ceramic Materials ◽  
Power Dependence

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

THE ENERGY EFFICIENCY TECHNIQUE OF THERMAL PROCESSING OF GRAIN

2019 ◽  
pp. 176-182
Author(s):  
А. Zykov ◽  
S. Orlova ◽  
L. Ovsiannykova
Keyword(s):  
Energy Efficiency ◽  
Thermal Processing ◽  
Microwave Field ◽  
Low Frequency ◽  
Heat Pipes ◽  
Biologically Active ◽  
Microwave Drying ◽  
Post Harvest ◽  
Combined Action ◽  
Frequency Radiation

The methods of energy efficiency increasing of pre- and post-harvest thermal processing of grain are considered. The effective ways to deliver energy to the grain using heat pipes and microwave field are given. The effect of combined action of microwave and low-frequency radiation on the grain germination is shown. Currently, the intensification of technological processes under the influence of microwave radiation is used in many industrial processes. Microwave equipment is becoming a necessary technological component of large profitable industries. The process of drying is no exception. In recent years, new versions of dryers have been proposed that use combined methods of energy supply, including microwave energy. Microwave dryers for foodstuffs, grains and oilseeds, including those for seed stock, have been created and are beginning to be used, along with drying and disinfection, disinfection of drying products from harmful bacteria, fungi, and mildew. For the implementation of microwave drying of particular importance is the choice of regime parameters of drying, given the fact that the grain is a biologically active object. Microwave drying allows you to provide a powerful flow of energy to the object of drying and to obtain a significant intensification of moisture evaporation. But at the same time there is also an intense heating of the product, which can degrade its quality. The possibility of supplying energy throughout the cross section of the product allows for the evaporation of moisture from the inner layers of the product, which is especially important at the end of drying, when the zone of evaporation of moisture is significantly deeper. Therefore, the highest drying efficiency can be obtained in combined processes that take advantage of various drying methods, such as convective, as well as the use of microwave and low-frequency magnetic fields. The paper presents effective ways to supply energy to the grain using heat pipes and a microwave field. The effect of the combined action of microwave and low-frequency radiation on grain similarity is shown. Ways to improve the energy efficiency of the processes of preseeding and post-harvest heat treatment of grain are considered.

Effects of microwave heating in nanostructured ceramic materials

2010 ◽  
Vol 49 (1-2) ◽  
pp. 31-41 ◽  
Author(s):  
Yu. V. Bykov ◽  
S. V. Egorov ◽  
A. G. Eremeev ◽  
V. V. Kholoptsev ◽  
I. V. Plotnikov ◽  
...  
Keyword(s):  
Microwave Heating ◽  
Ceramic Materials ◽  
Nanostructured Ceramic

Dielectric Characterizations and Microwave Heating Behavior of Zinc Compound in Microwave Field

2017 ◽  
Vol 43 (5) ◽  
pp. 2329-2338 ◽  
Author(s):  
Guo Lin ◽  
Tu Hu ◽  
Chenhui Liu ◽  
Libo Zhang ◽  
Jinhui Peng ◽  
...  
Keyword(s):  
Microwave Heating ◽  
Microwave Field ◽  
Zinc Compound ◽  
Heating Behavior

scholarly journals Model Calculations of Elastic Moduli in Highly Deformed Composites

1989 ◽  
Vol 10 (2) ◽  
pp. 153-164 ◽  
Author(s):  
H. J. Bunge
Keyword(s):  
Plastic Deformation ◽  
Simple Model ◽  
Elastic Moduli ◽  
Opposite Sign ◽  
Internal Stresses ◽  
Minor Importance ◽  
High Increase ◽  
Two Phase ◽  
Linear Elasticity Theory ◽  
Model Calculations

Young's modulus of heavily deformed two-phase composites shows an unusually high increase after plastic deformation. It is assumed that this is due to two reasons, i.e. texture changes and changes of the moduli of the constitutive phases on the basis of non-linear elasticity theory and internal stresses of opposite sign in the phases. Expressions of the two contributions are given on the basis of simple model assumptions. It is estimated that the changes of shape and arrangement of the phases and shape and arrangement of the crystallites in the phases are only of minor importance.

Microwave Processing of Silicon Nitride

1990 ◽  
Vol 189 ◽  
Author(s):  
T. N. Tiegs ◽  
J. O. Kiggans ◽  
H. D. Kimrey
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Microwave Heating ◽  
Grain Growth ◽  
Microwave Power ◽  
Microwave Sintering ◽  
Microwave Processing ◽  
Microwave Furnace

ABSTRACTMicrowave sintering of Si3N4—based materials showed improved densification as compared to samples heated conventionally under similar conditions. Accelerated nitridation of Si in the microwave furnace to produce Si3N4 was also observed. Dense Si3N4, annealed by microwave heating, exhibited enhanced grain growth; however preferential coupling of the microwave power to the grain—boundary phases in the present experiments resulted in their degradation.

Thermal Runaway of the BaCO3 + Fe2O3 Homogenous Mixture and Mechanical Alloys at the Microwave Heating

2013 ◽  
Vol 837 ◽  
pp. 185-189 ◽  
Author(s):  
I. Danut Savu ◽  
Sorin Vasile Savu ◽  
Gabriel Constantin Benga
Keyword(s):  
Electrical Properties ◽  
Heat Source ◽  
Microwave Heating ◽  
Structural Changes ◽  
Critical Phenomenon ◽  
Ceramic Materials ◽  
Heating Time ◽  
Thermal Runaway ◽  
Heating Process ◽  
Active System

Microwave heating represents a modern technique to sintering the composites materials. The microwaves absorbance property of the materials is depending by the electrical permittivity of the materials. Researchers showed that the ceramic materials are suitable for sintering using microwave heating. The most important advantage of that sintering procedure is the reduced sintering time and temperatures. However, during the heating process these properties are changing and a pattern of the heating process cannot be established. The penetration depth of microwaves into materials depends on the electrical properties of them, and gives rise to a heat source. The electromagnetic wave absorption is responsible for the macro and micro structural changes in the materials morphology, and consequently for their electrical properties. Thermal runaway is one phenomenon which should be avoided during the microwave processing of the materials. The microwave heating consists in direct introduction of the energy in the volume of the material. If the absorbance properties of the material are increasing with temperature, than a critical phenomenon, called thermal runaway, appears during the heating process. This paper aims to study the thermal runaway of the BaCO3 + Fe2O3 homogenous mixture and mechanical alloy in a mono-mode applicator, when the heat source is a microwave generator at 2,45 Ghz. A special mono-mode chamber has been designed with dimensions 140 x 140 x 70 mm and an active system for rotating the samples, in order to record the values of the temperature and to assure a uniform exposure of the samples to the high frequency electromagnetic field. The materials used in experiments were homogenous mixture of BaCO3 + Fe2O3 which have been milled in a planetary ball mill for 5 and 20 hours. The experimental procedure consists in establishing the levels of the temperatures during the microwave heating process when the thermal runaway appears. These experiments have been done for fixed levels of microwave injected power from 0 1250 W. Numerical simulation for different heating conditions (microwave power, heating time, position of the samples inside the chamber) has been performed in order to elaborate a predictable mathematical model for continuous microwave heating and avoiding the thermal runaway of the homogenous mixture.

Simulation of the Effects of Boundary Energy on Microstructure Evolution in Nanocomposite Ceramic Tool Material

2010 ◽  
Vol 44-47 ◽  
pp. 2443-2447
Author(s):  
Hong Mei Cheng ◽  
Chuan Zhen Huang ◽  
Han Lian Liu ◽  
Bin Zou ◽  
Hong Tao Zhu ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Boundary Energy ◽  
Tool Material ◽  
Ceramic Materials ◽  
Nano Particles ◽  
Grain Boundary Energy ◽  
Two Phase ◽  
Interfacial Energies ◽  
Pinning Effect ◽  
Simulation Results

A Monte Carlo Potts′ model with different ratios of grain boundary energy is proposed for the sintering process of two-phase nanocomposite ceramic materials. The grain growth process is successfully investigated, and the effect of grain boundary energy on the microstructure is discussed. The simulation results show that the competition between grain boundary and interfacial energies can affect the pinning effect of nano-particles, lead to various microstructure. The simulation results are in accordance with the experiments.

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