Edward F. Cuddihy

Hygroscopic properties of magnetic recording tape

Relative humidity has been recognized as an important environmental factor in many head-tape interface phenomena such as headwear, friction, staining, and tape shed. Accordingly, the relative humidity is usually specified in many applications of tape use, especially when tape recorders are enclosed in hermetically sealed cases. Normally, the relative humidity is believed regulated by humidification of the fill gas to the specification relative humidity. However, this study demonstrates that the internal relative humidity in a sealed case is completely controlled by the time-dependence of the hygroscopic properties of the pack of magnetic recording tape. Procedures for the humidity conditioning of sealed cases must be established on the basis of the tapes hygroscopic properties, and not on humidification of the fill gas. Without taking the tape into account, the final, stabilized, relative humidity can be significantly different from the specification requirement. Additionally, this same study finds differences in the hygroscopic properties of the same brand of tape, which apparently results from aging, and which may have significance on the long-term humidity-regulating behavior in a sealed case, and on the occurrence of head-tape interface phenomena from the long-term use of the tape. This article presents results on the basic hygroscopic properties of tape, its humidity-regulating behavior in a sealed case, and includes a theoretical commentary on the relative humidity dependence of head-wear by tape.

Soiling Mechanisms and Performance of Anti-Soiling Surface Coatings

Physical examination of surfaces undergoing natural outdoor soiling suggests that soil matter accumulates in up to three distinct layers. The first layer involves strong chemical attachment or strong chemisorption of soil matter on the primary surface. The second layer is physical, consisting of a highly organized arrangement of soil creating a gradation in surface energy from a high associated with the energetic first layer to the lowest possible state on the outer surface of the second layer. The lowest possible surface energy state is dictated by the chemical and physical nature of the regional atmospheric soiling materials. These first two layers are resistant to removal by rain. The third layer constitutes a settling of loose soil matter, accumulating in dry periods and being removed during rainy periods.

Healing of voids in the aluminum metallization of integrated circuit chips

A thermal treatment for healing voids in the aluminum metallization of integrated circuit (IC) chips has been discovered. The aluminum metallization is alloyed with nominally 1 wt.% of silicon. This discovery arose from efforts to cause further growth of preexisting voids in IC RAMs intended for long-term unattended spacecraft applications. The experimental effort was intended to cause further void propagation for the purpose of establishing a time/temperature propagation relationship, but it resulted instead in a healing of the voids. The thermal treatment consisted of heating IC chips with voids in the aluminum/silicon metallization to temperatures in excess of 200 degrees C, followed by quick immersion into liquid nitrogen. The thermal treatment is described, and a theory based on silicon solubility and migration in aluminum is advanced to explain both the formation and the healing of voids in the aluminum metallization of IC chips. >

Gas Diffusion in a Closed-Cell, Polymeric F oam by D irect Measu re of Internal Gas Pressure

which predicts for a foam of constant density a straight line relationship for a plot of In (Df/T) vs 1/T, where T is the absolute temperature. Both Equations 2 and 4 were confirmed (Reference 1 and 2) for foams where diffusion coefficients were measured by a simple technique which monitored the time-dependent weight loss of gas from foams exposed to vacuum. However, there was a concern that diffusion coefficients measured by the weight loss technique were an averaged value, and that D may not be constant throughout the foam, but possibly vary as a function of foam depth and/ or gas pressure. This article presents the results of a study which monitored gas diffusion in a foam by directly measuring the internal gas pressure at vari-

Method for calculating multidimensional electric fields in photovoltaic modules

Abstract A method for evaluating the multidimensional effects of the conductor geometry on the electric field in a photovoltaic module has been developed. The electrical stress intensification at the edges and corners of the solar cells is not predicted by the simple parallel plate model developed previously. The multidimensional electric field was calculated with the finite-element-based NASTRAN thermal analyzer, using the analogy between thermal and electrostatic fields. To evaluate the maximum electric field accurately, the NASTRAN output had to be post-processed; a polynomial was fitted to the predicted values of potential as a function of distance from the cell surface by the method of least squares, and the surface field was calculated from the best-fit polynomial. The accuracy of this method was verified by comparison with an exact solution for a geometry similar to that of typical solar cells. Two sample geometries were analyzed: a square test coupon used in the electrical isolation tests performed earlier and a family of disc-shaped solar cells. These sample analyses demonstrated that this finite element method is a useful design tool for evaluating candidate module encapsulation designs. They also showed geometric limits for which the model incurs numerical difficulties: (1) cells having very sharp edges, (2) cells much thinner than the dielectric pottant layer and (3) cells much thicker than the dielectric pottant layer. (The dielectric pottant layer is the material, usually organic, surrounding the solar cell which serves to isolate the cell mechanically and electrically from the load-bearing member of the total structure.) These limits, some of which occur with advanced thin film device modules, would require larger specially designed computer models.

The Effect of an Oxidative-Caustic Environment on Graft Copolymer Membranes

This paper discusses the accumulated results of a continuing study on the long-term effect of the environment in a Ag-Zn battery on a separator material prepared from thin films of crosslinked polyethylene grafted with poly (potassium acrylate), the acrylate content being usually approximately 40 wt % These materials have been prepared for JPL by Southwest Research Institute, San Antonio, Texas (Ref. l). This type of separator membrane is considered for spacecraft applications because of its relative stability and the ability to withstand heat sterilization at 135°C.