Cylindrical moldings of 20 and 40 mm diameter were injection molded with the application of modulated hold pressure using a well-characterized alumina-polypropylene suspension. The effect of frequency on sprue solidification was explored. For the smaller moldings, very little extension to sprue solidification time was obtained with pressures up to 140 MPa, and this is attributed to the low reciprocating volume flow. For the larger moldings, pressures of 98 MPa were sufficient to produce moldings with neither voids nor cracks, and the sprue solidification time corresponded to the time needed for solidification of the molding. The use of higher pressures resulted in internal residual stresses which were qualitatively detected by the defomation on annealing of polished diametral sections.

Despite the extremely low density and the hence low weight of aerogel materials, the applicability of these materials to reflective applications has had little attention due to the high porosities exhibited by the materials. This high porosity yields an intrinsically rough but uniform surface topology for aerogel of density in the low hundreds of milligrams per cubic centimeter and a fractal surface geometry for lower density aerogel (densities of the order of tens of milligrams per cubic centimeter). This paper presents new results of aerogel materials used as ultra-light substrates for reflective coatings by way of surface machining, polishing, and planarization prior to metallization, and the optical characterization thereof.

When an appropriate mixture of a low-softening borosilicate glass (BSG) and a high-softening high silica glass (HSG) is sintered at temperatures ranging from 800 to 1000 °C, a crystalline phase, identified as cristobalite by XRD, is known to precipitate out of the initial amorphous binary mixture of glasses as the sintering continues. The precipitation of cristobalite is found to originate in HSG, and is controlled by the transport of alkali ions (e.g., K+, Na+, and Li+) from BSG to HSG.1 In this paper, we report that when a small amount of alumina is present as a dopant in the above binary mixture of BSG and HSG, the cristobalite formation is completely prevented at the sintering temperatures investigated. The above result is attributed to a strong affinity between Al+3 from alumina and alkali ions from BSG, which diverts the diffusion of alkali ions from HSG to alumina, thus forming a K+ and Al+3-rich reaction layer adjacent to the alumina particles far too rapidly compared to that of cristobalite formation.

An infinite cylinder model was used to predict the optical transmission of transparent composites containing unidirectionally aligned glass fibers. The parameters used in the model are the volume content and diameter of the glass fibers, the refractive index of the fiber and matrix, the nonwet fiber content, the thickness of the composite, and the temperature coefficient of the refractive index of the matrix. The transmission calculated from the model agreed well with the measured temperature-dependent transmission of a composite from 20 to 70 °C for thin specimen (<1.0 mm) containing fiber less than 10 vol. %. The model showed that a small amount of nonwet fiber (0.7% of fiber content) could cause a substantial reduction in the maximum transmission. The content of nonwet fibers should be as small as possible for making a highly transparent composite.

A simple model which is able to account for the distribution of matrix crack spacings as a function of applied stress in unidirectional fiber-reinforced brittle materials has been used to generate stress-strain curves for such materials up to the maximum stress level at which transverse matrix cracking can occur when a tensile stress is applied parallel to the length of the fibers. The results give an insight into how to tackle the experimental problem of determining accurately the level of first-matrix-cracking stress in such materials.

Polyimide Kapton and spin-cast polyamic acid (PAA) on sapphire have been implanted with 1 MeV Ar ions to a dose of 4.7 × 1015 cm−2 at ambient temperature. The properties of both pristine and implanted surfaces were characterized by a depth-sensing low-load indentation technique. Experiments were carried out to investigate the effects of substrate, indentation rate, relaxation, and indentation technique. The results showed that (1) hardness was depth-dependent and decreased with increasing indentation depth, (2) measurements of the ion beam hardened surface with the untreated material as a substrate underestimated the hardness while measurements over the sapphire substrate overestimated it, (3) the effects of loading/unloading rates were apparent in the load displacement results, and (4) hardness values measured using the force modulation technique showed very little depth dependence. The hardness value at 100 nm depth is used for comparison purposes since the hardness value at this depth was almost independent of substrate, indentation rate, and indentation method. The hardness of Kapton, which was measured using the techniques described herein, was increased by over 30 times after Ar implantation, from 0.43 to 13 GPa at 100 nm indentation depth. A similar increase in hardness was also observed for polyamic acid. This result suggests that spin-cast PAA film may have potential technological applications for protective coatings where hardness and wear resistance are required.

Several polymers with high temperature and high performance properties have been modified by ion implantation. Ions of As and Xe with energies of 50 keV and 180 keV have been implanted in the dose range of 1015 to 1017 ions/cm2. Electrical conductivities of these originally insulating polymers have been greatly enhanced after the ion implantation. Structural and compositional changes that accompanied these electrical enhancements were observed using infrared (IR) and Raman spectroscopies, scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS), and elastic recoil detection analysis (ERDA) methods. Our high resolution data reveal a two-component conductivity that depends on both one-dimensional variable range hopping (VRH) and three-dimensional VRH. For lightly damaged samples (e.g., 1015 ions/cm2) the 1-D VRH is dominant while for highly damaged samples (e.g., 1017 ions/cm2) the 3-D VRH dominates.