High-Silicon Glasses and Coatings
Development of Coverings for High-Temperature (up to 1800 C) Protection of Construction Materials
Tech Area / Field
- CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
3 Approved without Funding
Institute of Electronic Materials, Armenia, Yerevan
- EMonument, Belgium, Brugge\nCNRS / Université de Rennes 1, France, Rennes\nPeripheral Support INC, USA, CA, Rancho Dominguez\nUniversity of Science and Technology, Poland, Krakov\nUniversity of Montreal, Canada, QC, Montreal\nCorning Inc., USA, NY, Corning\nBAM, Germany, Berlin
Project summaryThe present Project is a continuation of the ISTC Project A-189 “Development of compositions, investigation of physical-chemical properties, and development of the technology for electric melting of high-silica glasses in an electric direct-heating scull furnace” and is aimed at developing heat-resistant compositions intended for thermal and chemical protection of structural members, parts and blocks of various purposes made of carbon or oxygen-free ceramic materials.
On the basis of molybdenum disilicide and developed by us borosilicate glass having a coefficient of thermal expansion (CTE) of (18-20)10-7K-1 and a temperature of deformation start (Tds) of (800±10)ºC, there has been previously developed and successfully used in various spheres of the modern technology the protective coating M-46 which is stable in a high-velocity air flow up to 1500ºC. In particular, it has been successfully used in the high-temperature thermal protection system of the reusable spaceship “Buran”.
The coating employment under different conditions has shown that its temperature stability and service life are mainly limited by molybdenum disilicide oxidation and intensive evaporation at high temperatures of boron oxide the content whereof in the glass under question is 17 mas %. Besides, in view of the glass low Tds, “washing-off” of the coating occurs under the action of hot and high-velocity gas streams. Therefore for the further increase of reliability, service life or operating temperature it was recommended to use high-melting compounds more resistant to air oxygen oxidation (instead of MoSi2) and glass having a low B2O3 content and the highest Tds.
Within the ISTC Project A-189 framework, in a low-borate range of the Al2O3-B2O3-SiO2 system (B2O3<5 mas.%) there have been developed compositions and synthesis technology for glasses of the melting temperature over 2000ºC and Tds about 1050ºC. And the electric direct-heating scull furnace (EDHSF) developed on the invention level (Patent №956) is capable to attain temperatures up to 2400ºC, and the arising intensive convective flows in the glass melt make it possible to effect therein melting of actually any type of high-melting glass.
There has been experimentally proved the principal opportunity of further increasing physical-chemical and performance indices of the high-temperature coatings, based on the glass of 1050ºC Tds and high-melting oxide fillers.
The present Project is drawn up on the basis of the investigations results in terms whereof for increasing the coating operating temperature it is necessary:
- To develop and use in protective ceramic coatings as the binder a high-silica glass (HSG) with as low as possible content of boron oxide and other highly volatile components (such as R2O) and Tds of 1100 to 1150ºC;
- As the crystalline fillers in the coatings to use high-melting (melting point of at least 2000ºC), oxide (Al2O3, ZrO2, HfO2, MgO, etc) and/or oxygen-free (hafnium and zirconium borides, some high-melting carbides) ceramic materials exhibiting high stability, low volatility and inoxidizability up to 1700-1800ºC;
- When synthesizing the protective compositions, to use special additives and technological steps to ensure the thermal and chemical compatibility of constituting components there between and with the materials to be protected, high uniformity and gas impermeability of the coating, the required wettability and bonding strength with respect to the surface being coated.
For that purpose the following works will be performed in the course of the Project execution:
- Prediction of HSG compositions and melting technologies to meet the Project requirements;
- Laboratory melting and investigation of the predicted glass compositions, the selection of the most promising ones;
- Experimental melting of the selected compositions in the basic EDHSF, determination of structural, power and methodological changes necessary in the basic installation for melting and producing novel glass compositions;
- Introducing the necessary changes into EDHSF, melting and obtaining pilot lots of glasses, determination of their main physicochemical properties, testing the best ones in heat-resistant compositions;
- On the basis of preliminary investigations and testing of the compositions and coatings, the selection of the most promising glass compositions, crystalline fillers, additives and technological approaches and synthesis conditions, which meet the Project requirements;
- Specification of the technological conditions, melting and obtaining a supply lot of the most promising glass, determination of its main parameters;
- Preparation (acquisition, milling, fractionation, appropriate chemical and thermal treatments) of crystalline fillers, special additives and glass, obtaining and testing of high-temperature coatings on carbon and ceramic materials.
The following results will be obtained:
- The composition and melting technology for glass of (10-20)x10-7K-1CTE and (1100-1150)ºC Tds.
- The composition and synthesis technology for glass-ceramic composites for the protection of graphite and ceramic structural members, parts and blocks of various purposes against the action of high-velocity streams of air and other gases at temperatures of 1700 to 1800ºC;
- Supply lots of the developed glass and compositions for testing at organizations being interested;
- Recommendations as concerns the application of the obtained results and the most perspective trends for the future search.
The materials obtained under the Project may be useful:
- In the laser technology as gradating and main glasses for the pump lamps productions;
- In the electrical engineering as high-melting bulbs, cylinders, tubes and other members in the production of high-power lighting and heating lamps;
- In the electronics, power engineering, machine-building, and vacuum technology as a thermostable glass-soldering material to join parts made of glass, ceramics, and sitalls having suitable CTEs;
- In other fields of science and technology for obtaining heat-resistant composites of various purposes, readily sintering ceramics, glass-solders having CTE of (-10+30)x10-7 and soldering temperature of (1200-1300)ºC, etc.
(B) Heat-resistant compositions
- In the aerospace technology, in systems of high-temperature thermal protection as protective coatings to work at high operating temperatures of the parts in air and other oxygen-containing atmospheres;
- In aircraft combustion engines, when creating novel apparatuses and spaceships;
- In metallurgy for oxidation protection of surfaces of crucibles for smelting non-ferrous and noble metals in air.
All the above-mentioned factors define the practical value and expediency of the Project realization
The theoretical value of the work resides in the enrichment of experimental data pool in the field of synthesis of high-melting glasses, glass-solders, and glass compositions, protection of ceramic materials against high-velocity gas streams, etc.
The Project entirely meet the ISTC purposes and requirements and is mainly aimed at the reorientation of scientific teams, previously engaged in creating materials for special engineering, to solve peaceful problems and is consistent with their integration into the World Community of Scientists, favors solving international and national economic problems.
Teams of scientists of AOZ SPEMS for a long time have been engaged in developing HSGs and high-temperature composite coatings, which were used as structural materials for creating novel types of armaments.
The Project authors invite scientific teams, research organizations, and private experts from the European Community countries, USA, Japan, Korea, and Norway for cooperation.
We also propose to carry out joint seminars and scientific investigations.
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.