Thermally conductive glue

Many years later in Singapore, we were using a specially formulated thermally conductive glue to fix the overtemperature sensing thermistor smack on to the very plastic body of the TO-220 power transistor. We had empirically ascertained that in this way, the junction temperature and the adjacent temperature as seen by the thermistor were less than 10°C apart, even during an abnormal event. So if, for example, we wanted to have the transistor turned off just before it hit 150°C, we simply needed to set the trip temperature (of the thermistor-based circuit) at about 140°C. In that way, we could also be sure that we wouldn t encounter nuisance tripping on a particularly hot day, when the temperature inside the enclosure would also be much higher. 

The thermal conductance of each glue spot below 150 mK was very low because of the two contact resistances Rc (Kapton-glue and glue-copper), and the power Ph delivered to the copper sample did not flow through the Kapton foil. To be sure of that, however, 1 mm large, 56 xm thick copper ribbon was internally glued around the upper end of the Kapton support. A heater Hk and a thermometer Tk (Fig. 11.6) were fixed on the ribbon and a power Pk was delivered to the Kapton support in such a way that T = Th. 

Since the thermal conductivity of Kapton is linear in T below 150 mK as happens for copper [26], a negligible temperature difference was supposed to be present across the glue spots. In practice, we found an extremely high value of Rc, since the temperature Th was not influenced at all by changes of Tk up to about ten times Th. 

Thanks to all these properties, the dolocarbonate seems promising for different applications, first of all for all the applications of traditional low density mineral fillers. This material could for instance be used as a component in thermal insulating materials like panels or foams, as a filler in mortars or plasters or concretes to decrease their thermal conductivity, as a filler in polymer or rubber compositions to improve their fire and/or mechanical properties, as a filler in paints, papers, cosmetic compositions, as a rheology modifier (viscosifying agent) in mineral slurries, glues, bitumen or asphalts, polymer compositions, as an ad- or absorbant in different applications such as water or flue gas treatment or even in the field of catalysis, as e.g. a catalyst support, or as a carrier for perfumes, aromas, active substances, medicines... 

In metals, the bonding is predominantly metallic, where delocalized electrons provide the glue that holds the positive ion cores together. This delocalization of the bonding electrons has far-reaching ramifications since it is responsible for properties most associated with metals ductility, thermal and electrical conductivity, reflectivity, and other distinctive properties. 

It is possible to enhance the conductivity of polymeric composites by the formation of a core-sheU fillers, where the core could be either conductor or dielectric and the shell is a conductor. This is of practical interest in the technology of the production of glues and varnishes. For example, the conductivity of dielectric Sn02 particles coated with a silver layer (8 vol%) is substantially increased to a = 1 X 10 S m ), versus only o = 2xl0 Sm for a mechanical mixture of Sn02 and 16 vol% of Ag powders. The silver layer was prepared by thermally treating an Ag(I)-containing polymer. 

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