Improved Materials Selection Research Articles

Selection and Optimization of Piezoelectric Polyvinylidene Fluoride Polymers for Adaptive Optics in Space Environments

Various piezoelectric polymers based on polyvinylidene fluoride (PVDF) are of interest for large aperture space-based telescopes. Dimensional adjustments of adaptive polymer films depend on charge deposition and require a detailed understanding of the piezoelectric material responses which are expected to deteriorate owing to strong vacuum UV, γ -, X-ray, energetic particles and atomic oxygen exposure. We have investigated the degradation of PVDF and its copolymers under various stress environments detrimental to reliable operation in space. Initial radiation aging studies have shown complex material changes with lowered Curie temperatures, complex material changes with lowered melting points, morphological transformations and significant crosslinking, but little influence on piezoelectric d33 constants. Complex aging processes have also been observed in accelerated temperature environments inducing annealing phenomena and cyclic stresses. The results suggest that poling and chain orientation are negatively affected by radiation and temperature exposure. A framework for dealing with these complex material qualification issues and overall system survivability predictions in low earth orbit conditions has been established. It allows for improved material selection, feedback for manufacturing and processing, material optimization/stabilization strategies and provides guidance on any alternative materials.

Calcium carbonate efflorescence on Portland cement and building materials

Whitish deposits of calcium carbonate, CaCO3, frequently develop on Portland cement concrete and on masonry units, including brick and tile, which have been bonded with Portland cement. These surface deposits are termed efflorescence and are most frequently encountered in new or recent construction. While efflorescence is not normally damaging, except possibly to decorative coatings, it is aesthetically undesirable. The origin of efflorescence is explained and a physicochemical model is developed to explain and quantify the key features of its formation. Calculations and experiments highlight the important role of soluble alkalis in the formation of efflorescence. Mechanistic interpretations and calculations suggest ways in which efflorescence can be mitigated by interrupting one or more steps of the process in conjunction with improved materials selection.

Needs and technical prerequisites of an improved supply of donor material for penetrating keratoplasty

The supply of donor material for keratoplasty is still considered a problem in many clinics. Preservation of donor tissue makes it possible to improve material selection. As far as the grafting of typed corneas is concerned, corneal organ culture offers a valuable time interval for planning the operation. In these preservation techniques the transplanted tissue is trephined from the endothelial side. With an optimal trephining technique the number of viable endothelial cells transplanted can be increased.