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BELL SYSTEM TECHNICAL JOURNAL 



temperatures and about 30°C at high temperatures in response to the design 

 trend towards operation of the units at higher temperatures. The units 

 employing this compound may, if desired, be repeatedly heated and cooled 

 rapidly between — 50°C and +100°C without damage. 



Use of the impregnating compound not only improves mechanical stability 

 but prevents ingress or absorption of moisture. Increase of humidity 

 would subject the unit not only to changes in electrical properties such as 

 variation in the radio frequency impedance, but also to serious corrosion, 

 for the galvanic couple at the junction would support rapid corrosion of the 

 metal point. In fact, with condensed moisture present in unfilled units 

 corrosion can be observed in 48 hours. For this reason alone, the develop- 

 ment of a satisfactory filling compound was an important step in the suc- 

 cessful utilization of the units by the Armed Services under diverse and 

 drastic field conditions. 



Table I 

 Shelf Aging Data on Silicon Crystal Rectifiers of the Ceramic Cartridge Design 



The large improvement in stability achieved in the present device as 

 compared with the older crystal detectors may be attributed to the design 

 of the contact spring, correct alignment of parts in manufacture and to 

 the practice of filling the cavity in the unit with the gel developed for this 

 purpose. Considering the apparently delicate construction of the device, 

 the stability to mechanical or thermal shock achieved by these means is 

 little short of spectacular. Standard tests consist of drojiping the unit 

 three feet to a wood surface, immersing in water, and of ra])idly lieating 

 from —40 to 7()°C None of these tests im])airs the quality of the unit. 

 Similarly the unit will withstand storage for long periods of time under 

 adverse conditions. Table I summarizes the results of tests on units 

 which were stored for approximately one year under arctic ( — 40°), tropical 

 (114°F — 95% relative humidity), and temi)erate conditions. Though 

 minor changes in the electrical characteristics were noted in the accelerated 

 tropical test, none of the units was inoperative after this drastic treatment. 



