Methods of Improving Alumina Ceramics Strength
Tech Area / Field
8 Project completed
Senior Project Manager
Yakusheva A A
VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- University of British Columbia, Canada, BC, Vancouver
Project summaryCeramics technology is based on using initial powder materials, their dispersion, compactization and caking in the process of which, a structure is formed with a complex of physical and mechanical properties and operation characteristics.
Currently, four main technological processes of fabrication of products out of fine technological ceramics have been developed:
- Process of cold pressing and subsequent caking permits to obtain relatively cheap ceramic products. But such materials have porosity, which decreases their strength.
- Hot-pressed materials have less residual porosity and hence higher level of mechanical properties. But hot pressing differs from caking by higher energy capacity and necessity of applying expensive pressing tools.
- Hot isostatic pressing permits to obtain high-density products of complicated from, whose configuration is designed from conditions of their maximum structural strength. The products produced by method of hot isostatic pressing have different density and uniformity of distribution of structural components. However, realization of method of hot isostatic pressing is related to using complicated and expensive thermal equipment, in which it is necessary to maintain pressure of gas medium of more than 100 МPа.
- Hot casting of slip under pressure, which uses liquid suspensions with high yield permits to decrease sufficiently the pressure of molding.
Analysis of material science and technological solutions revealed the main factors that determine the progress on the problems of ceramic materials strength.
These factors are: using high-dispersion initial components; high quality of mixing and of mechanical and chemical activation of powder; optimization of compactization conditions providing high density and uniform density of ceramic blanks; optimization of caking regime providing fine-grain and practically pore-free material.
Practical use of these factors permits to obtain high-strength ceramic materials and products out of them. But taking into account high sensitivity of ceramics to defects of structure, internal stresses and sufficient dissipation of strength over the volume of ceramic product, fabrication of large products complicated by configuration with high strength and reliability is a problem, which cannot be resolved completely by using expensive technologies, equipment and tools.
New studies are to be directed to the development of materials and technologies that do not require suing expensive, low-efficiency equipment of high pressure.
Advantage of the technology of molding by method of hot casting of dross under pressure is the possibility to fabricate products of the most complicated configuration. But hot casting does not permit to achieve the level of properties, which provide pressing under high pressure.
The goal of proposed project is to develop methods of improving the strength of alumo-oxide ceramics obtained by method of hot casting of dross.
In order to achieve the goal, the following tasks are to be resolved:
- To develop scientific foundations for volume modification and obtaining pore-free alumo-oxide ceramics having internal structure, uniform density, improved strength, decreased dissipation of strength values.
- To develop scientific foundations for surface modification and improvement of strength of products out of alumo-oxide ceramics by method of synthesis of heat-resistant and strong films, neutralizing dissipation of strength, on the surface of ceramics.
New knowledge obtained as the result of the project performance will serve the basis for the development of effective methods of making high-strength ceramics with the help of volume and surface modification.
Competence of the project participants corresponds to the project task: great experience of experts in the frames of the ISTC project #1320 (from January1, 2000 to December 31, 2002) on the development of new technologies of fabrication of glass-titanium and glass-aluminum connectors, including ceramic elements.
The proposed project is related to applied studies.
- Methodical foundations will be developed for improving the strength of alumo-oxide ceramics as the result of volume modification. It is expected to improve bending strength (σb) by a factor of 2 as the result of using water solutions of salts, which release ZrО2 under thermal dissociation.
- Methodical foundations will be developed for improving the strength of alumo-oxide ceramics as the result of surface modification. It is expected to improve bending strength by a factor of 2(σb) by a factor of 1,5 as the result of using water solutions of salts, which release Al2О3, MgО, СаО, lithium and potassium borates under thermal dissociation and which form strong, heat resistant films on ceramics surface under high-temperature synthesis, These films have various, regulated chemical composition and properties.
- Determination will be done of optimum thermo-dynamic parameters of obtaining products out of high-strength alumo-oxide ceramics.
- Complex studies will be done of physical and mechanical properties of ceramics.
Application of the results will be solution of the problems of fabrication of the products of complicated configurations out of high-strength alumo-oxide ceramics by hot casting of dross without expensive, energy-consumption equipment.
Realization of proposed Project perfectly meets the ISTC Goals and Objectives:
- VNIITF specialists, whose work is related to the development of weapon of mass destruction, will have unique opportunities to redirect their talents and experience to solving tasks of civil activity.
- The Project is devoted to resolving current problems of material science that is why the Project will facilitate the involvement of Russian scientists into international scientific community.
- It will be possible to use the results in many areas, for example, in electronics, instrument and machine building.
- One of the goals of the Project is to minimize the cost price of the products, i.e. the Project helps to transfer to market economy meeting civil needs.
The scope of activities is 6597 person*days and is determined by the necessity to resolve the main tasks of the Project.
Role of foreign collaborators consists of the consultation at the stage of the Project preparation, exchange of information on theoretical and experimental studies of actual processes, comments to reports, participation in technical verification of the Project activities, conducting joint workshops.
Originality of the technical approach and methodology of the Project.
1. Up-to-date technologies use age hardening of alumo-oxide ceramics by zirconium dioxide in solid phase. Initial components are grinded, mixed and caked using expensive, energy-consumption equipment.
In this Project, ceramics strength improvement is done at the cost of applying zirconium dioxide, which is released under thermal dissociation of water solutions of salts. Zirconium dioxide is formed in highly dispersed state and is uniformly distributed in ceramics volume.
2.Up-to-date technologies provide expensive surface processing of ceramic products with the aim to eliminate surface defects and to improve ceramics strength.
In this Project, ceramics strength improvement is done by synthesis of strong, heat resistant films neutralizing negative influence of surface defects.
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.