Influence of boehmite intermediate layer as covalent linker on synthesis of LTA zeolite coatings

The incorporation of nanostructured materials, such as LTA-type zeolite on the silicon wafers, opens a very interesting door to the use of these materials within silicon based microfabrication technologies. This work studies the deposition and intergrowth of defect-free LTA-type zeolite layer onto 3-inch Silicon wafers with a layer of SiO2 subjected to pretreatment. The main disadvantage associated with zeolite layer synthesis are crack the formation of cracks and difficulty of obtaining a uniform layer. By modifying the supports with boehmite, a substantial improvement was observed in terms of layer continuity and crystal intergrowth in comparrison to coatings prepared on cationic polymer, poly (diallyldimethylammonium chloride). An LTA- type zeolite layer was synthesized in a range of 350 to 1300 nm via hydrothermal ex-situ method at 363 K for 12 h. Tetramethylammonium hydroxide (TMAOH) was used as a template, and aluminum isopropoxide and colloidal silica were used as Al and Si sources, respectively

Nanoporous PBI Membranes by Track-Etching for High Temperature PEMFC

This article describes for the first time the preparation of conducting track-etched PBI membranes 25 mm thick with pore diameter values varying from 15 nm to 50 nm and overall porosity up to 10%. The TGA, DSC and FTIR characterization results for the so obtained nanoporous membranes reveal the chemical modification of PBI upon irradiation along the track walls. A clear conduction outperforming is shown by phosphoric acid doped track-etched PBI in comparison with dense PBI counterparts. This behavior could be explained by the effective contribution of additional pathways for proton transport involving shorter benzimidazole fragments, cross-linked PBI nanodomains and free amphoteric phosphoric acid molecules settled on the pore walls

Helium contamination through polymeric walls

The concentration of impurities in helium gas is an important parameter for a recovery and liquefaction plant. A low level of impurities is necessary to maintain an optimum liquefaction rate in any kind of liquefier. The main origin of the impurities is the air contamination that enters into the helium mainstream at some point in the recovery cycle. In this work we have: i) identified the main sources for impurities in an experimental helium recovery plant, ii) quantified the contamination rate and iii) proposed a mitigation strategy. An analysis of the He impurities composition reveals a nitrogen/oxygen ratio different to the one existing in air. This observation is in accordance with the permeability values for nitrogen and oxygen through the polymer materials used in the plant. Experimental on line measurements for oxygen content in the He mainstream with sensitivity below 1 ppm, have been performed after recirculation through metal and polymeric pipelines, respectively, to validate our hypothesis. In addition, the dependence of the impurities concentration with the He retention time in the recovery gas bag has been evaluated. Finally some operational recommendations are given for practical applications

Purification of recovered helium with low level of impurities: evaluation of two different methods

Helium gas coming from low temperature experimental systems is recovered to avoid losses of this scarce gas on Earth. Once this helium gas has been recovered and before its liquefaction, the impurities contained should be removed. It is possible to achieve a low level of impurities by using the proper materials and procedures on the road to helium recovery. A comparison of two different methods applied for the purification of recovered helium with low level of impurities is reported in this paper. One method is the use of liquid nitrogen traps and the other one is the application of a purification system based on getter materials. The cleaning efficiency has been probed experimentally for both methods through the analysis of the purified He gas. The evaluation covers the life time between regenerations, the everyday care as well as the long term, the energy consumption, the initial investment besides the cost of maintenance of both methods