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Synthesis of high-silica ZSM-5 in microgravity

Abstract High-silica ZSM-5 crystals were grown in the microgravity environment (10 −3 –10 −6 g) of the space shuttle from precursor solutions held unmixed until activation on orbit. The flight crystals grown from untreated (not heat-treated) silica gel grade 12 had the intergrown disk morphology and were larger than the spherulitic aggregates of small elementary crystals observed for the terrestrial/control samples. The flight and the terrestrial/control crystals grown from silica gel grade 12 heat-treated at 973 K prior to synthesis had similar intergrown disk morphologies. The similar morphologies of the flight crystals grown from untreated silica gel and the terrestrial/control crystals grown from heat-treated silica gel imply that the nucleation rate of ZSM-5 was reduced in microgravity. The results of isomerization of 2,4,4-trimethyl-1-pentene (2,4,4-TMP-1) to 2,4,4-trimethyl-2-pentene on crystals grown from untreated silica gel showed that the flight crystals exhibited a lower external surface activity than the terrestrial/control crystals with an identical total external surface area (∼0.6% conversion of 2,4,4-TMP-1 after 3 h on flight versus ∼1.3% conversion on the terrestrial crystals). This indicated that the flight crystals had a lower surface roughness than their terrestrial controls. An atomic force microscopy examination of the crystal surfaces confirmed these results. In contrast, both the flight and the terrestrial/control crystals grown from heat-treated silica gel had similar surface topographies and roughness.

Zeolite crystal growth in microgravity

The interest in zeolites is due to their extensive commercial uses as molecular sieves in highly selective catalysts, adsorbents, ion exchangers, and separators. These properties enabled the development of a large number of chemical and petrochemical processes. Zeolites are crystalline aluminosilicates. Independent control of product composition, morphology and the control of defect concentrations during crystallization of zeolites from reactive aluminosilicate gels are difficult. Modifications in synthesis conditions aimed at modifying crystal size and shape also effect the chemistry of the reactions and the nucleation and growth in the gel. It is hypothesized that with the control of the nucleation event, varying defect concentrations and size can be obtained in the microgravity environment on the space shuttle. Experimental results from previous flight samples (STS‐50, STS‐57) and their terrestrial counterparts indicated that crystal size is increased around 25 percent for zeolite A and 50 percent for ...

Zeolite Crystal Growth in Space

The growth of large, uniform zeolite crystals in high yield in space can have a major impact on the chemical process industry. Large zeolite crystals will be used to improve basic understanding of adsorption and catalytic mechanisms, and to make zeolite membranes. To grow large zeolites in microgravity, it is necessary to control the nucleation event and fluid motion, and to enhance nutrient transfer. Data is presented that suggests nucleation can be controlled using chemical compounds (e.g., Triethanolamine, for zeolite A), while not adversely effecting growth rate. A three-zone furnace has been designed to perform multiple syntheses concurrently. The operating range of the furnace is 295 K to 473 K. Teflon-lined autoclaves (10 ml liquid volume) have been designed to minimize contamination, reduce wall nucleation, and control mixing of pre-gel solutions on orbit. Zeolite synthesis experiments will be performed on USML-1 in 1992.

Investigating the nucleation and growth of zeolite crystals in space

The extensive use of zeolites and their impact on the world’s economy has resulted in many efforts to characterize their structure and improve the knowledge base for nucleation and growth of these crystals. The zeolite crystal growth (ZCG) experiment on USML-2 aimed to enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, and Silicalite were grown during the 16-day USML-2 mission. The solutions where the nucleation event was controlled yielded larger and more uniform crystals of better morphology and purity than their terrestrial/control counterparts.

MEASUREMENT OF THE RESIDUAL ADSORPTION CAPACITY OF CHARCOAL FILTERS UNDER CONDITIONS OF VARIABLE HUMIDITY

Abstract High surface area charcoals are used to remove noxious vapor from gas streams. Recently our laboratory has developed a simple and reliable method to determine a filters residual adsorption capacity under dry and humid conditions. Work has been performed on ASC whetlerite saturated to various extents with an “irreversible” adsorbed adsorbate (dimethyl methylphosphonate). Data are presented which illustrate how the retention time of a 1 ml(NTP) pulse of methane can be used to quantify the fraction of unoccupied adsorption sites for a strong adsorbent when a filter is saturated with water or dry. In addition, data are presented which suggest that with some charcoals the retention time of methane can be used to determine a filters residual absorption capacity regardless of its previous water loading history.

A low temperature furnace for solution crystal growth on the International Space Station

The Zeolite Crystal Growth Furnace Unit (ZCG-FU) is the first module in an integrated payload designed for low temperature crystal growth in solutions on the International Space Station (ISS). This payload is scheduled to fly on the ISS flight 7A.1 in an EXPRESS rack. Its name originated from early shuttle flight experiments limited to the growth of zeolite crystals but has since grown to include other materials of significant commercial interest using the solution method of crystal growth. Zeolites, ferroelectrics, piezeoelectrics and silver halides are some of the materials considered. The ZCG-FU experiment consists of a furnace unit and its electronic control system, and mechanically complex, crystal growth autoclaves suitable for use with a particular furnace and solution. The ZCG facility is being designed to grow into four independent furnaces controlled by IZECS (Improved Zeolite Electronic Control System). IZECS provides monitoring of critical parameters, data logging, safety monitoring, air-to-gr...

The Center for Advanced Microgravity Materials Processing-A partnership between NASA, Northeastern University and industry

CAMMP (the Center for Advanced Microgravity Materials Processing) is a NASA-sponsored Commercial Space Center (CSC) establish in 1997 at Northeastern University as a partnership between NASA, academics and industry. It is one of 16 NASA CSCs at major universities nationwide and is exclusively focussed on materials science. Its mission is to stimulate innovations in materials technology and to develop commercial products through knowledge gained from microgravity research. Materials Synthesis experiments conducted under microgravity conditions permit control over the fluid dynamics and associated heat and mass transfer phenomena that govern crystal growth. Crystals with fewer defects, with narrow size distribution, and with controlled morphologies can be obtained. One key outcome of CAMMP’s research is the development of a nucleation and growth database for the intelligent design of solution synthesis and crystal growth experiments. This database supports a wide range of materials interests including, but ...