Microwave Synthesis and Sintering of Piezoceramics
Development and Technology Demonstration of Microwave Synthesis and Sintering of Piezoceramic Elements for Ultrasonic Pulsed Oscillators and Receivers
Tech Area / Field
3 Approved without Funding
National Academy of Sciences of the Republic of Belarus / Institute of Radiation Physics and Chemistry Problems, Belarus, Minsk, Sosny
- National Academy of Sciences of the Republic of Belarus / Institute of Technical Acoustics, Belarus, Vitebsk
- Tohoku University / Institute of Fluid Science (IFS), Japan, Sendai\nNational Research Council / Institute of Science and Technology for Ceramics, Italy, Faenza\nMichigan Technological University / Institute of Materials Processing, USA, MI, Houghton\nLoughborough University, UK, Loughborough\nFerroperm Piezoceramics A/S, Denmark, Kvistgard\nVirginia Polytechnic Institute and State University, USA, VA, Blacksburg
Project summaryThe main goal of the project is meant for investigation of the mechanisms underlying the effect of a microwave field on synthesis and sintering of piezoceramic materials in a reactor, for developing the technology of synthesis and sintering of piezoelectric ceramics, preparing specimens of piezoelectric elements and for using them to create a demonstration plant for radiating and receiving ultrashort ultrasonic pulses.
State of the Art in the Field of Sintering of Ceramics.
At the present time, the thermal technique of heating is the basic one in production of articles from ceramic materials. The main disadvantages of this technique are the long duration of the process, high specific consumption of electricity, disturbance of the stoichiometric composition of the material and the high percentage of spoilage. For example, if in the process of ceramic firing there occurs an escape of lead, which is the basic component of piezoelectric elements, this upsets the stable operation of the instrumentation used in radioengineering and impairs the environment. Therefore, the search for non-traditional techniques of ceramic firing and their development represent a very urgent problem.
One of the alternative techniques is the use of microwave (MW) energy for synthesizing and sintering ceramic materials. On the credit side of this method are the high heating rate, sharp shortening of the process and reduction of the specific energy consumption, the possibility of sintering materials of prescribed stoichiometric composition and obtaining highly homogeneous fine-grain ceramics with maximum electrophysical parameters, reduction in spoilage and in emission of harmful substances into the atmosphere (lead monoxide). The most essential feature of microwave firing is the possibility of sintering materials having volatile and metastable components.
In recent years, in a number of countries investigation touching upon the effect of MW radiation on ceramic materials have been undertaken in order to develop the technology of rapid sintering of ceramic articles (8th International Conference on Microwave and High Frequency Heating, Bayreuth, Germany, 2001.). The main object of investigations is the process of ceramic firing, with the process of synthesis having been studied considerably less thorough (Seong Seo Park, Eun Hee Huang, Byoung Chan Kim, Hee Chan Park. Synthesis of hydrated alluminium sulfate from kaolin by microwave extraction. J. Amer. Ceram. Soc. 2000. Vol. 83, No. 6, P.1341-1345.), with the process of synthesizing piezoceramic materials virtually left intact. The works on the physics of sintering are based in the main on stationary models of the process, in which structural and chemical changes of grains are taken into account by analyzing the macroscopic properties of materials (Yu. V. Bykov, K. I. Rybakov and V. E. Semenov. High-temperature microwave processing of materials. J. Phys. D: Appl. Phys. 2001, No. 34, P.55–75.).
At the same time, it has been established by the authors of the project that in the process of microwave synthesis of a number of ceramic materials (ferroelectrics, ferrites, high-temperature superconductors) the kinetics of solid-phase synthesis differs substantially from the well-known notions, with this difference being manifested to the greatest extent in synthesis of ceramic materials involving volatile (lead monoxide) or metastable components. The results obtained indicate that the kinetics of microwave synthesis does not lend itself to the description by the equations of the Yander type of kinetics, etc. The growth of the new phase nuclei cannot be represented as a purely diffusion process.
At the present time, quartz is the basic material used in manufacturing the elements of radiators and detectors of ultrashort ultrasonic pulses. This is not conducive to creating small-size elements of pulse devices with high specific characteristics. This shortcoming can be obviated by replacing quartz with piezoceramics. At the same time, since lead is the main component of piezoceramics, stringent requirements are imposed on piezoceramic sources of ultrasound as regards the stoichiometric composition, homogeneity of grains, and the grain size. It is very difficult to observe these stringent requirements with the aid of traditional means of synthesis and sintering of materials. For this reason, further development of the technology of microwave synthesis and sintering of piezoceramics seems to be a promising trend.
Thus, the study of the solid-phase synthesis and sintering of piezoceramics using a non-traditional technique of heating material and a unique procedure of investigation, the development of new materials for piezoelectric elements, and the creation, on their basis, of devices for radiation and detection of ultrashort ultrasonic pulses is an urgent problem of both scientific and practical importance.
Impact of Project on the Progress in this Field.
The results of the project may exert a substantional influence on the progress in the development of investigations relating to the region of interaction of variable electromagnetic fields with a material at high temperatures. The results of investigation of the microwave solid-phase synthesis and sintering of piezoceramic materials under strongly nonequilibrium conditions in the case of external nonstationary effect that will be carried out following a unique procedure will make it possible to refine the generally known concepts of the kinetics of solid-phase processes and the available models. The knowledge of the mechanisms of these processes will allow one to predict the physical properties of finished articles and their electromechanical parameters, in particular, the possibility of generating ultrashort pulses with a length of several microseconds.
The technology of microwave synthesis and sintering of piezoceramic elements will to better maintain the physical properties of products and their electromechanical parameters. This will allow one to come on closer to the solution of the problem of creating piezoceramic materials with specified characteristics.
Competence of the Project Team.
Participating in the project are the Joint Institute for Power and Nuclear Research of the National Academy of Sciences of the Republic of Belarus (JIPNR NASB) and the Institute of Technical Acoustics of the National Academy of Sciences of the Republic of Belarus (ITA NASB). The team members have gained experience in the development of high-power laser installations, nuclear power plants for military forces, in the development of the systems and facilities for tracking target missiles in antimissile systems, and also in radioelectronic equipment for missiles and missile materials. All the team members are experienced research workers in the field associated with the topic of the project. Among their there are 2 doctors of sciences and 4 candidates of sciences.
For a long time, the JIPNR NASB has been engaged in studying thermal treatment of various materials by a MW electromagnetic field. Various-purpose experimental equipment have been created for high-temperature (heating, melting, sintering) and low temperature (drying, sterilization) heating of materials.
In recent years, the ITA NASB staff members have been concerned in the main with the development of the elements of hydroacoustic systems of radiation and detection of ultrasound. The Institute has been engaged for a long time in investigation aimed at the development of materials and technologies for the production of the elements of electronic engineering with the use of high-frequency and super-high-frequency electromagnetic fields.
The staff member of both Institutes will cooperate in solving the problems posed by the project.
In solving three problems posed by the project the following results are to be obtained:
1. A microwave reactor will be developed intended for investigating the processes of synthesis and sintering of piezoceramics, the mechanisms determining different stages of the given processes under nonequilibrium and nonstationary conditions will be investigated experimentally, and a mathematical model of the process will be developed.
2. The technology of the MW synthesis and sintering of piezoceramic materials will be developed, piezoceramic materials will be developed and synthesized that would have short relaxation times for pulse radiators and detectors. Piezoceramic elements will be produced to demonstrate the possibilities of microwave synthesis.
3. An installation will be created for radiation and detection of ultrashort ultrasonic pulses to demonstrate the advantages of the use of new piezoelectric elements for the need of medicine, hydroacoustics and flaw detection.
The ultimate purpose of the project is to develop the technology of microwave synthesis and sintering of piezoceramics that can also be used for thermal treatment of other materials, production of piezoelectric elements, and for creation, on their basis, of new experimental facilities intended for radiation and detection of ultrashort ultrasonic pulses.
It is planned to file an application for a patent to protect the technology of microwave synthesis and sintering of piezoceramics.
In future, the scientific knowledge and the experience gained will make it possible to undertake the development of high-temperature piezoceramic materials using the methods of microwave synthesis without disturbing the stoichiometric composition of a specimen. The promising materials are to be used in developing probes for chemical high-temperature reactors, for example, for internal combustion engines that would not fail at a temperature not less than 1,000 °C (at the present time the probes withstand the maximum temperature of 450-500 °C).
Application of Project Results.
The technology of microwave synthesis and sintering of piezoceramics can be used for producing materials with specified properties. To demonstrate the possibilities of the technology developed and the commercial potential of the project it is contemplated to create a facility for radiation and detection of ultrasonic pulses. The facility will rest on the block principle of construction for maximum unification of units and devices. The construction of the demonstrative facility will make it possible, without substantial expenditures, to convert it into models of the devices widely used in engineering (sonars, echo sounders, flaw detectors).
A microwave reactor intended for high-temperature synthesis and sintering of piezoceramics may also be of self-sustained interest.
Project Meets ISTC Goals and Objectives.
– The project gives the possibility for its participants who have experience in developments for the army of directing their abilities to peaceful activity in the field of material science and ultrasonic diagnostics in the interests of public health.
– The project offers for its authors, who earlier were engaged in defense studies, the prospect of solving current fundamental problems of material science and interaction of a microwave field with substance and also applied problems dealing with the development of environmentally pure technology of synthesis and firing of piezoceramics and creation of efficient ultrasonic radiating devices.
– The fulfilment of this project will aid in integration of the project participants into international scientific community studying the problems of material science and ultrasonic probing.
– The works on the project support the going-over of the project participants to market economy due to the possibility of creating the technology which is of commercial importance.
Scope of Activities.
Project duration is 36 months. The total labor input into the project is 251 man/months. The project involves three interconnected tasks, tackled successively:
1. Investigation of the mechanisms of microwave synthesis and sintering of piezoceramic materials.
2. Development of piezoceramic materials and production of test specimens of piezoelectric elements.
3. Creation of a demonstrative facility intended for radiation and detection of ultrashort ultrasonic pulses.
Role of Foreign Collaborators.
– Discussion of the project results.
– Correction of the plan of the works.
– Preparation of joint patents for an invention and publications.
Technical Approach and Methodology.
On the basis of the experience, gained by the project team in design and operation of MW equipment, in the investigation of the kinetics of microwave synthesis of a number of materials and technologies of the production of the elements of electronic engineering, the following technical approach and the methodology of investigations is suggested.
The technical implementation of the project presupposes creation of a microwave reactor for synthesizing and sintering piezoceramics which would ensure high uniformity in warming-up of specimens and efficient use of the supplied MW energy. The use of the computer technology of processing information and the possibility of controlling the power of the MW generator depending on the temperature of the specimen in the zone of firing will make it possible to create a highly automated experimental facility.
To investigate nonequilibrium processes in microwave synthesis and sintering of piezoceramic materials it is suggested to use the method of fast optical spectroscopy. This will make it possible to rapidly scan the radiation spectrum of the heated specimen and determine the degree of conversion of the components in synthesizing piezoceramic material. The proposed methodology will make it possible to investigate materials at high temperatures directly in the process of firing in contrast to the available techniques. This method will aid in creating a kinetic model of the process which also could be used in analysis of the traditional methods of the firing of ceramics. The model will rest on the description of the kinetics of synthesis and sintering on the basis of the Focker-Planck kinetic equations.
In the first stage of investigations dealing with the selection of the materials most suitable for synthesis of piezoceramics the well-studied materials will be used, for example, barium titanate, as the most studied representative of ferroelectrics and lead-barium zirconate-titanate which is the typical material of piezoelectric ceramics. After firing, the piezoceramic materials that have the best electromechanical properties will be used for creating experimental specimens of piezoelectric elements and a demonstrative facility intended for radiating and detecting ultrashort pulses. The facility will be constructed on the block principle. The construction of the facility will make it possible, without great expenditures, to convert it into models of the devices widely used in engineering (sonars, echo sounders, nondestructive testing units).
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