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High-Silica Glasses and Coatings

#A-955


Development of High-Silica Glasses and High-Temperature Coatings Based Thereon for the Oxidation Protection Used in Technics of High Temperatures

Tech Area / Field

  • MAT-CER/Ceramics/Materials
  • CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
  • MAN-COM/CAD and CAM/Manufacturing Technology

Status
3 Approved without Funding

Registration date
28.10.2002

Leading Institute
Institute of Electronic Materials, Armenia, Yerevan

Supporting institutes

  • NIIGrafit, Russia, Moscow

Collaborators

  • Université de Claude Bernard-Lyon 1 / Laboratoire de Physico - Chimie des Materiaux Luminescents, France, Lyon\nFriedrich-Schiller-Universität Jena / Otto-Schott-Institute für Glaschemie, Germany, Jena\nEngineering Glass-Ceramic-QM, Germany, Jena\nCorning Inc., USA, NY, Corning\nSamsung Electro-Mechanics, Korea, Suwon\nTechnische Universität Ilmenau / Fakultat fur Maschinenbau, Germany, Ilmenau\nAuburn University / Materials Research and Education Center, USA, AL, Auburn\nFederal Institute for Materials Research and Testing, Germany, Berlin\nInstituto Superior Técnico, Portugal, Lisbon\nWerkstoffzentrum Rheinbach GmbH, Germany, Rheinbach\nUniversity of Aveiro, Portugal, Aveiro\nJSJ Jodeit GmbH, Germany, Jena-Maua

Project summary

The 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 garnissage furnace of direct heating” 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 linear expansion (LETC) of (18-20)10-7K-1 and a temperature of deformation start (Tds) of (800±10) °C, 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 1,500 °C.

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, “wiping-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 2,000 °C and Tds about 1,050 °C. And the electrical garnissage furnace of direct heating (EGFDH) developed on the invention level (Patent #956) is capable to attain temperatures up to 2,400 °C, 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 1,050 °C 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 1,100 to 1,150 °C;


– As the crystalline fillers in the coatings to use high-melting (melting point of at least 2,000 °C) 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 1,700-1,800 °C;
– 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 glass compositions in the basic EGFDH, determination of structural, power and methodological changes necessary in the basic installation for melting and producing novel glass compositions;
– Introducing the necessary changes into EGFDH, melting and obtaining pilot lots of glasses, determination of their main physical-chemical properties, testing the best ones in heat-resistant compositions;
– On the basis of preliminary investigations and testing in 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)·10-7K-1LETC and (1,100-1,150) °C 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 1,700 to 1,800 °C;
– 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:

(A) Glasses.

– 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 LETCs;
– In other fields of science and technology for obtaining heat-resistant composites of various purposes, readily sintering ceramics, glass-solders having LETC of (-10+30)·10-7 and soldering temperature of (1,200-1,300) °C, etc.

(B) Heat-resistant compositions.

– As the antioxidant protection coatings of calorific intensive parts used in different regions of high temperature technics.


– 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 meets 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 International Community of Scientists, favors solving international and national economic problems.

Teams of scientists of AOZ SPEMS and SUE “NIIGrafit” 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, South Korea, and Norway for cooperation, and also propose to carry out joint seminars and scientific investigations.


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