SURFACE HEATER ELEMENTS ON PLATES OF VACUUM THICK CERAMICS
Bohos R. Aprahamian1, Meline O. Aprahamian2
1 Nicola Vaptzarov Naval Academy, Dept. of Electrical Eng., Vassil Drumev str. 73, 9026 Varna, Bulgaria, e-mail: email@example.com
2 Technical University of Varna, Dept. of Mathematics, Studentska str. 1, 9010 Varna, Bulgaria, e-mail: firstname.lastname@example.org
Prototypes of surface heater elements for mean temperature heating are developed. The heaters are formed upon electroinsulated plates of vacuum thick alumina ceramics by magnetron sputtering or screenprinting of a resistive layer. Various compositions of resistive layer are investigated, including amorphous metal alloys. Electrical, thermal mechanical and climatic research of the heaters is made. Some prototypes with various compositions of amorphous metal layers are applied as sensors for hot – wire anemometer.
Foil heater elements have recently been widely applied in comercial and household heaters for low temperature heating. At present heater elements with insulating substrates of polyvinylchloride, polyester, polyamid, mecanite, silicon, enamelled metal , etc. are mainly used.
Having experience in developing and implementation of foil heater elements in production we faced the problem of developing surface heater elements for heating in the range of 300 – 600 oC. These were to be formed on dielectric substrate of a certain class of heat resistance. Having analized a lot of dielectrics avaible we found Al2O3 ceramics to be the most suitable one. It is widely used in microelectronics and in hybrid integrated circuits in particular. This material was prefered because of its advantageous properties, such as:
– It does not contain volatile components and thermal dissociation of oxides in the ceramics composition occurs at temperatures higher than those necessary for processing technology.
– Gas permeability is negligible. Practicaly no polluting substances are released in processing and high – grade conducting layers can be obtained.
– It has high volume resistance which practicaly remains constant in the process of wear and is slightly affected by temperature. It has high electric resistance and perfect insulating properties.
– It has high heat conductivity, much higher than that of standart insulating materials.
– It is inert to effects of various chemicals and highly resistant to humidity, fog, mist, etc.
– It has good contractability in all directions and appearance which practicaly does not change with ageing. Elements with a size of some fractions of milimeter up to some hundred milimeters can be made.
– Ceramics composition is mainly Al2O3, which is cheap and avaible.