Glass long-time stability

The scheme of such a metal-arch capacitance transducer is shown in Fig. 50. The transducer is about 3 mm thick and has a diameter between 6 and 10 mm. The fixed electrode consists of a sputtered tantalum film on a glass substrate, the dielectric is a reactively sputtered tantalum pentoxide film, and the variable electrode consists of phosphor bronze and is either an arch shaped 15 pm thin foil obtained from a metal strip or a spherical dome shaped foil made by sputtering [245]. A maximum capacitance value of 340 pF could be obtained and short time and long time stability s were better than 0.2 pF min 1 and 0.05 pF hour 1 respectively. The sensitivity of such transducers was between 2000 and 8000 pF mm 1. Q factors have been obtained in... 

The glass s >strate is covered by a metallic film (Ag) which serves as a back contact. The heterojunction system is based on a CdS film (between lO and 30 ym thickness) which due to sulfur vacancies is n-type. On the top of the CdS film a Cu S film (x 2) is prepared which due to small deviations from stoichiometry is p-type. A highly transparent grid represents the front contact. The front glass plate through which the incoming radiation penetrates to the junction provides a hermetically sealed encapsulation which is required for long time stability. 

The polyimide is formed by the thermal polycyclocondensation of the poly(amide acid). For this purpose, 5 ml of poly(amide acid) solution are placed on a watch glass (diameter 10 cm) and kept in a vacuum oven at 50 °C for 24 h.The solvent evaporates and at the same time cyclization to the polyimide takes place the resulting film is insoluble in dimethylformamide.The formation of the polyimide can be followed by IR spectroscopy the NH-band at 3250 cm disappears while imide bands appear at 1775 and 720 cm" Once the initial drying process has raised the solid content to 65-75%, the polyimide formation can be accelerated by heating the poly(amide acid) film to 300 °C in a vacuum oven for about 45 min.The polyimide made from pyromellitic dianhydride and 4,4 -oxydianiline exhibits long-term stability in air above 200 °C. 

No long-time experience exists about the stability and leaching of glasses containing the high a-active actinides. 

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