Effect of chloride content of molten nitrate salt on corrosion of A516 carbon steel.

The corrosion behavior of A516 carbon steel was evaluated to determine the effect of the dissolved chloride content in molten binary Solar Salt. Corrosion tests were conducted in a molten salt consisting of a 60-40 weight ratio of NaNO{sub 3} and KNO{sub 3} at 400{sup o}C and 450{sup o}C for up to 800 hours. Chloride concentrations of 0, 0.5 and 1.0 wt.% were investigated to determine the effect on corrosion of this impurity, which can be present in comparable amounts in commercial grades of the constituent salts. Corrosion rates were determined by descaled weight losses, corrosion morphology was examined by metallographic sectioning, and the types of corrosion products were determined by x-ray diffraction. Corrosion proceeded by uniform surface scaling and no pitting or intergranular corrosion was observed. Corrosion rates increased significantly as the concentration of dissolved chloride in the molten salt increased. The adherence of surface scales, and thus their protective properties, was degraded by dissolved chloride, fostering more rapid corrosion. Magnetite was the only corrosion product formed on the carbon steel specimens, regardless of chloride content or temperature

Thermal stability and adhesion of low-emissivity electroplated Au coatings.

We are developing a low-emissivity thermal management coating system to minimize radiative heat losses under a high-vacuum environment. Good adhesion, low outgassing, and good thermal stability of the coating material are essential elements for a long-life, reliable thermal management device. The system of electroplated Au coating on the adhesion-enhancing Wood's Ni strike and 304L substrate was selected due to its low emissivity and low surface chemical reactivity. The physical and chemical properties, interface bonding, thermal aging, and compatibility of the above Au/Ni/304L system were examined extensively. The study shows that the as-plated electroplated Au and Ni samples contain submicron columnar grains, stringers of nanopores, and/or H{sub 2} gas bubbles, as expected. The grain structure of Au and Ni are thermally stable up to 250 C for 63 days. The interface bonding is strong, which can be attributed to good mechanical locking among the Au, the 304L, and the porous Ni strike. However, thermal instability of the nanopore structure (i.e., pore coalescence and coarsening due to vacancy and/or entrapped gaseous phase diffusion) and Ni diffusion were observed. In addition, the study also found that prebaking 304L in the furnace at {ge} 1 x 10{sup -4} Torr promotes surface Cr-oxides on the 304L surface, which reduces the effectiveness of the intended H-removal. The extent of the pore coalescence and coarsening and their effect on the long-term system integrity and outgassing are yet to be understood. Mitigating system outgassing and improving Au adhesion require a further understanding of the process-structure-system performance relationships within the electroplated Au/Ni/304L system

Effect of chloride content of molten nitrate salt on corrosion of A516 carbon steel.

The corrosion behavior of A516 carbon steel was evaluated to determine the effect of the dissolved chloride content in molten binary Solar Salt. Corrosion tests were conducted in a molten salt consisting of a 60-40 weight ratio of NaNO{sub 3} and KNO{sub 3} at 400{sup o}C and 450{sup o}C for up to 800 hours. Chloride concentrations of 0, 0.5 and 1.0 wt.% were investigated to determine the effect on corrosion of this impurity, which can be present in comparable amounts in commercial grades of the constituent salts. Corrosion rates were determined by descaled weight losses, corrosion morphology was examined by metallographic sectioning, and the types of corrosion products were determined by x-ray diffraction. Corrosion proceeded by uniform surface scaling and no pitting or intergranular corrosion was observed. Corrosion rates increased significantly as the concentration of dissolved chloride in the molten salt increased. The adherence of surface scales, and thus their protective properties, was degraded by dissolved chloride, fostering more rapid corrosion. Magnetite was the only corrosion product formed on the carbon steel specimens, regardless of chloride content or temperature

Clathrate hydrates for production of potable water

Clathrate hydrates are crystalline inclusion compounds of water and a guest molecule that can form at temperatures above the freezing point of water. Such inclusion compounds exclude dissolved solutes, e.g., sodium chloride present in the aqueous phase, and thereby provide a basis for desalination. Clathrate hydrate formation experiments were performed using several guest molecules, including R141b (CFClH), a commercial refrigerant, and ethylene. Ethylene, a gaseous hydrate guest, readily formed hydrates with saline water at up to 5°C and 20 atm. of pressure. Hydrates of R141b, in the liquid state, were formed at temperatures from 2°C to 6°C and atmospheric pressure from deionized water and 2% - 7% NaCl solutions. Significant reductions in saline content were obtained with both forming agents in a batch reactor without additional separation equipment. Samples of the R141b hydrates were characterized by cold-stage x-ray diffraction and Raman spectroscopy and determined to be structure II. Proof-of-concept experiments were performed to demonstrate a novel technique of desalination using R141b as the hydrate forming agent and an inert secondary fluid

Thermal stability and adhesion of low-emissivity electroplated Au coatings.

We are developing a low-emissivity thermal management coating system to minimize radiative heat losses under a high-vacuum environment. Good adhesion, low outgassing, and good thermal stability of the coating material are essential elements for a long-life, reliable thermal management device. The system of electroplated Au coating on the adhesion-enhancing Wood's Ni strike and 304L substrate was selected due to its low emissivity and low surface chemical reactivity. The physical and chemical properties, interface bonding, thermal aging, and compatibility of the above Au/Ni/304L system were examined extensively. The study shows that the as-plated electroplated Au and Ni samples contain submicron columnar grains, stringers of nanopores, and/or H{sub 2} gas bubbles, as expected. The grain structure of Au and Ni are thermally stable up to 250 C for 63 days. The interface bonding is strong, which can be attributed to good mechanical locking among the Au, the 304L, and the porous Ni strike. However, thermal instability of the nanopore structure (i.e., pore coalescence and coarsening due to vacancy and/or entrapped gaseous phase diffusion) and Ni diffusion were observed. In addition, the study also found that prebaking 304L in the furnace at {ge} 1 x 10{sup -4} Torr promotes surface Cr-oxides on the 304L surface, which reduces the effectiveness of the intended H-removal. The extent of the pore coalescence and coarsening and their effect on the long-term system integrity and outgassing are yet to be understood. Mitigating system outgassing and improving Au adhesion require a further understanding of the process-structure-system performance relationships within the electroplated Au/Ni/304L system

Scalable Synthesis of Nanoporous Palladium Powders

Nanoporous palladium powders are synthesized on milligram to gram scales by chemical reduction of tetrachloro complexes by ascorbate in a concentrated aqueous surfactant at temperatures between −20 and 30 °C. Particle diameters are approximately 50 nm, and each particle is perforated by 3 nm pores, as determined by electron tomography. These materials are of potential value for storage of hydrogen isotopes and electrical charge; producing them at large scales in a safe and efficient manner will help realize this. A slightly modified procedure also results in nanoporous platinum

Thermally Stable Nanoporous Palladium Alloy Powders by Hydrogen Reduction in Surfactant Templates

Nanometer-scale pores in metals used for hydrogen storage are expected to facilitate mass transport in the materials – in particular, the release of helium decay products when tritium is stored. Scalable methods for production of bulk powders of nanoporous metals typically use chemical reducing agents that can leave impurities in the product. Hydrogen gas can be used as the reducing agent in such procedures. This not only improves purity, but also expands the range of accessible pore and particle sizes and particle compositions. Powders of nanoporous palladium and its alloys with rhodium are synthesized by chemical reduction of chloride complexes by hydrogen in a concentrated nonionic aqueous surfactant at room temperature. Particle diameters are typically several micrometers and each particle is perforated by 2–3 nm pores, as determined by electron microscopy and nitrogen porosimetry. Alloys show major improvement in thermal stability and pore regularity compared to pure palladium. In addition to facilitating heavier isotope storage, the high surface areas of these materials may allow development of metal hydride batteries with high power density