A.W.C. van den Berg

Molecular-dynamics analysis of the diffusion of molecular hydrogen in all-silica sodalite

In order to investigate the technical feasibility of crystalline porous silicates as hydrogen storage materials, the self-diffusion of molecular hydrogen in all-silica sodalite is modeled using large-scale classical molecular-dynamics simulations employing full lattice flexibility. In the temperature range of 700-1200 K, the diffusion coefficient is found to range from 1.610(-10) to 1.810(-9) m(2)/s. The energy barrier for hydrogen diffusion is determined from the simulations allowing the application of transition state theory, which, together with the finding that the pre-exponential factor in the Arrhenius-type equation for the hopping rate is temperature-independent, enables extrapolation of our results to lower temperatures. Estimates based on mass penetration theory calculations indicate a promising hydrogen uptake rate at 573 K.

Effect of cation distribution on self-diffusion of molecular hydrogen in Na3Al3Si3O12 sodalite: a molecular dynamics study.

The diffusion of hydrogen in sodium aluminum sodalite (NaAlSi-SOD) is modeled using classical molecular dynamics, allowing for full flexibility of the host framework, in the temperature range 800-1200 K. From these simulations, the self-diffusion coefficient is determined as a function of temperature and the hydrogen uptake at low equilibrium hydrogen concentration is estimated at 573 K. The influence of the cation distribution over the framework on the hydrogen self-diffusion is investigated by comparing results employing a low energy fully ordered cation distribution with those obtained using a less ordered distribution. The cation distribution is found to have a surprisingly large influence on the diffusion, which appears to be due to the difference in framework flexibility for different cation distributions, the occurrence of correlated hopping in case of the ordered distribution, and the different nature of the diffusion processes in both systems. Compared to our previously reported calculations on all silica sodalite (all-Si-SOD), the hydrogen diffusion coefficient of sodium aluminum sodalite is higher in the case of the ordered distribution and lower in case of the disordered distribution. The hydrogen uptake rates of all-Si-SOD and NaSiAl-SOD are comparable at high temperatures (approximately 1000 K) and lower for all-Si-SOD at lower temperatures (approximately 400 K).

Bandwidth Analysis for Reusing Functional Interconnect as Test Access Mechanism

Test data travels through a System-on-Chip (SOC) from the chip pins to the module-under-test and vice versa via a Test Access Mechanism (TAM). Conventionally, a TAM is implemented with dedicated wires. However, also existing functional interconnect, such as a bus or Network-on-Chip (NOC), can be reused as TAM. This will reduce the overall design effort and the silicon area. For a given module, its test set, and maximal bandwidth that the functional interconnect can offer between ATE and module-under-test, our approach designs a test wrapper for the module-under-test such that the test length is minimized. Unfortunately, it is unavoidable that with the test data also unused (idle) bits are transported. This paper presents a TAM bandwidth utilization analysis and techniques for idle bits reduction, to minimize the test length. We classify the idle bits into four types which explain the reason for bandwidth under-utilization and pinpoint design improvement opportunities. Experimental results show an average bandwidth utilization of 80%, while the remaining 20% is consumed by the idle bits.

Self-diffusion of molecular hydrogen in clathrasils compared: Dodecasil 3C versus sodalite

The self-diffusion coefficient of molecular hydrogen through the all-silica microporous dodecasil 3C structure is calculated by means of molecular-dynamics (MD) calculations, allowing for full framework flexibility, in order to assess the materials feasibility as a hydrogen storage medium. The hydrogen uptake rate into dodecasil 3C is compared to that previously calculated for sodalite and it is found that the latter performs significantly better. The reason for this variation in performance is found to lie in intrinsic topological differences between each framework type. This is explicitly demonstrated by means of a simplified version of transition state theory helping to succinctly rationalize the MD data.

Quality enhancement of NaA zeolite membranes

Abstract UV-irradiation of a TiO2 support prior to synthesis enhances the zeolite 4A crystallization rate hereon by decreasing the induction time and increasing the number of nuclei. As a result, well-attached NaA membranes with a zeolite-layer, thickness of 3.5 μm are formed. These membranes separate H2O from a binary EtOH mixture with high selectivities up to 54000. The H2O/H2, H2O/CH4, and H2O/CO separation factors are as high as 309, 615, and 244 at 303, K and 72, 323, and 30 at 373 K, respectively. The permselectivities of He/N2 and, H2/N2 are 3.6 and 4.6, respectively, higher than those of the Knudsen diffusion. Furthermore, the fluxes of the permeating gases and vapours are considerably higher than reported in the literature [1,2]. These high selectivities with high fluxes indicate the high quality of the zeolite 4A membranes synthesized on UV-irradiated TiO2 supports.

Hydrogen storage and diffusion in 6-ring clathrasils

Abstract In this paper the influence of geometry of five different 6-ring clathrasils on the diffusion rate of hydrogen through these material is investigated in order to determine the most suitable clathrasil for the storage of hydrogen at ambient temperature and pressure by means of encapsulation. The diffusion is estimated via transition state theory and the energy barries are calculated by means of energy minimisations using empirical force fields. A special aspect herewith is that the zeolite framework is modelled in a fully flexible fashion. The calculations show that sodalite (SOD) has the highest hydrogen diffusion rate. SOD also has the highest available void space. A rough estimation for the maximum hydrogen storage capacity in all silica sodalite is 2.5 wt%.