Study of ceramic products and processing techniques in space

An analysis of the solidification kinetics of beta alumina in a zero-gravity environment was carried out, using computer-simulation techniques, in order to assess the feasibility of producing high-quality single crystals of this material in space. The two coupled transport processes included were movement of the solid-liquid interface and diffusion of sodium atoms in the melt. Results of the simulation indicate that appreciable crystal-growth rates can be attained in space. Considerations were also made of the advantages offered by high-quality single crystals of beta alumina for use as a solid electrolyte; these clearly indicate that space-grown materials are superior in many respects to analogous terrestrially-grown crystals. Likewise, economic considerations, based on the rapidly expanding technological applications for beta alumina and related fast ionic conductors, reveal that the many superior qualities of space-grown material justify the added expense and experimental detail associated with space processing

Study of growth of single crystal ribbon in space

The technical feasibility is studied of growing single-crystal silicon ribbon in the space environment. Procedures are described for calculating the electromagnetic fields produced in a silicon ribbon by an rf shaping coil. The forces on the ribbon and the degree of shaping to be expected are determined. The expected steady-state temperature distribution in the ribbon is calculated in the one-dimensional approximation. Calculations on simplified models indicate, that lack of flatness of the shaped ribbon and excessive heating of the melt by the eddy currents induced by the shaping fields may pose problems. An analysis of the relative effects of various kinds of forces other than electromagnetic showed that in the space environment capillarity forces would dominate, and that the shape of the melt is thus principally determined by the shape of any solids with which it comes in contact. This suggests that ribbon may be produced simply by drawing between parallel wires. A concept is developed for a process of off-angle growth, in which the ribbon is pulled at an angle to the solidification front. Such a process promises to offer increased growth rate, better homogeneity, and thinner ribbon

Investigation of immiscible systems and potential applications

The droplet coalescence kinetics at 0 g and 1 g were considered for two systems which contained liquid droplets in a host liquid. One of these (Al-In) typified a system containing a liquid phase miscibility gap and the order (oil-water) a mixture of two essentially insoluble liquids. A number of coalescence mechanisms potentially prominent at low g in this system were analyzed and explanations are presented for the observed unusual stability of the emulsion. Ground base experiments were conducted on the coalescence of In droplets in and Al-In alloy during cooling through the miscibility gap at different cooling rates. These were in qualitative agreement with the computer simulation. Potential applications for systems with liquid phase miscibility gaps were explored. Possibilities included superconductors, electrical contact materials, superplastic materials, catalysts, magnetic materials, and others. The role of space processing in their production was also analyzed

Oxidation of Zr-2.5 Nb Nuclear Reactor Pressure Tubes A New Model

The corrosion and associated deuterium (D) uptake of Zr alloy nuclear reactor pressure tubes have been studied for over 40 years. Zircaloy tubes exhibit rapid D ingress after a period of in-reactor exposure, and have been replaced with tubes fabricated from the more resistant Zr-2.5 wt % Nb alloy. Recently, however, a small percentage of Zr-2.5 Nb tubes have been found to contain high D contents. There is currently no clear understanding of the mechanism for this increased D uptake, and concern exists that an increasing number of high-D tubes will develop with time. A new model for Zr-2.5 Nb corrosion is presented in this paper. The rate of corrosion is shown to be dependent on the rate of transformation of the protective inner oxide layer (closer to the metal) to a porous outer layer. The mechanism of this transformation is not known and should be the subject of future investigations. It is assumed in the model that zirconia chemically dissolves into the solution at the pore bottom. The rate of this dissolution reaction depends on the local pH, which increases if there is a buildup of deuteroxyl ions generated in the cathodic part of the Zr corrosion reaction. A mathematical description of this model, containing several parameters with unknown values, is presented. Assigning certain values to these parameters results in predictions of oxide formation (and thus D buildup) that correspond well with observations.Support of this work by the Atomic Energy Control Board under AECB project no. 2.349.1 is gratefully acknowledged

Storage and Release of Soluble Hexavalent Chromium from Chromate Conversion Coatings on Al Alloys Kinetics of Release

The release of chromate ions from chromate conversion coatings (CCCs) on Al alloys was studied, and the effect of aging of CCCs on the chromate release kinetics was investigated. Chromate release from CCCs into aqueous solutions was monitored by measuring the change in the chromate concentration in solution using UV-visible spectroscopy. Heat-treatment of the CCC greatly reduced the chromate release rate. The chromate release rate also decreased with increasing aging time at room temperature. A diffusion-control model was proposed based on the notion that the CCC in an aqueous solution is a porous, two-phase structure consisting of a solid phase with adsorbed Cr(VI) species that is in local Langmuir-type equilibrium with an interpenetrating solution phase. This model results in a concentration gradient of soluble Cr(VI) in the solution phase of the CCC as chromate is released. The concentration and diffusion coefficients of soluble Cr(VI) in CCC were estimated. The estimated diffusion coefficient tended to decrease with aging time, suggesting that the CCC is modified with aging time.This work was supported under Air Force Office of Scientific Research Multidisciplinary University Research Initiative contract no. F49620-96-1-0479

Acute Resistance Exercise Induces Sestrin2 Phosphorylation and p62 Dephosphorylation in Human Skeletal Muscle

Sestrins (1, 2, 3) are a family of stress-inducible proteins capable of attenuating oxidative stress, regulating metabolism, and stimulating autophagy. Sequestosome1 (p62) is also a stress-inducible multifunctional protein acting as a signaling hub for oxidative stress and selective autophagy. It is unclear whether Sestrin and p62Ser403 are regulated acutely or chronically by resistance exercise (RE) or training (RT) in human skeletal muscle. Therefore, the acute and chronic effects of RE on Sestrin and p62 in human skeletal muscle were examined through two studies. In Study 1, nine active men (22.1 ± 2.2 years) performed a bout of single-leg strength exercises and muscle biopsies were collected before, 2, 24, and 48 h after exercise. In Study 2, 10 active men (21.3 ± 1.9 years) strength trained for 12 weeks (2 days per week) and biopsies were collected pre- and post-training. Acutely, 2 h postexercise, phosphorylation of p62Ser403 was downregulated, while there was a mobility shift of Sestrin2, indicative of increased phosphorylation. Forty-eight hours postexercise, the protein expression of both Sestrin1 and total p62 increased. Chronic exercise had no impact on the gene or protein expression of Sestrin2/3 or p62, but Sestrin1 protein was upregulated. These findings demonstrated an inverse relationship between Sestrin2 and p62 phosphorylation after a single bout of RE, indicating they are transiently regulated. Contrarily, 12 weeks of RT increased protein expression of Sestrin1, suggesting that despite the strong sequence homology of the Sestrin family, they are differentially regulated in response to acute RE and chronic RT

Novel n-3 Docosapentaneoic Acid-Derived Pro-resolving Mediators Are Vasculoprotective and Mediate the Actions of Statins in Controlling Inflammation

“This is a post-peer-review, pre-copyedit version of a chapter published in Advances in Experimental Medicine and Biology book series (AEMB, volume 1161). The final publication is available athttps://doi.org/10.1007/978-3-030-21735-8_7