Using PXRD to Investigate the Crystallization of Highly Concentrated Emulsions of NH4NO3

The process of crystallization of highly concentrated emulsions of ammonium nitrate can be studied using powder X-ray diffraction. The dispersed particles comprise a supercooled aqueous solution of the ammonium nitrate salt and are dispersed in a paraffin-based oil. This results in a thermodynamically unstable system that ‘ages’ with time resulting in changes in rheological properties and its phase composition where the collapse of the supercooled aqueous solution forms the crystallized salt. The crystallization processes of these emulsions are kinetically slow and can take up to a few months to crystallize completely. The general approach to this type of analysis is to determine the change in crystalline diffraction peak intensities relative to the halo due to the amorphous content. However, there are a number of problems associated with this method which are addressed by using Rietveld refinement methods which can take into account factors such as preferred orientation, crystallite size variations and mixtures of solid phases. The study showed that the ammonium nitrate emulsions kept at room temperature slowly crystallize predominantly to the room temperature solid ammonium nitrate phase IV. However, depending on the formulations used some samples showed crystallization to the high temperature ammonium nitrate phase II before changing to phase IV. The crystallization change could be modelled by the well-known JMAK kinetic relationship.Keywords:  Ammonium nitrate emulsion, crystallinity, X-ray diffractio

The Use of an Experimental Design Approach to Investigate the Interactions of Additives used in the Making of the Negative Plate in Lead-acid Batteries

When a conventional starting, lighting and ignition (SLI) lead acid battery is exposed to a high rate partial state of charge (HRPSoC) cycling, it would experience a build-up of irreversible PbSO4 on the negative plate, resulting in capacity loss and electrode damage. The addition of certain graphites to the negative paste mix has proven to be successful in reducing this effect. This study looked at using statistical design of experimental (DoE) principles to observe interactions between two graphite types and a nanocarbon together with other additives, such as BaSO4 and Vanisperse, to a negative paste mixture. The response factors considered were in relation to their effect on the battery’s cold cranking ability (CCA) at –18 °C, the HRPSoC and its active material utilization. Typical flooded nominal 8 Ah test cells were assembled in a reverse ratio build,with three positive and two negative plates, with three types of added carbons (flake graphite, natural graphite and nanocarbon) added to the negative paste mixture at a two-level design. The study showed the usefulness of a statistical DoE approach in the effective use of additives that are included to the negative plate paste mixture, where there are interactions between the amounts of added carbon, BaSO4 and Vanisperse, with respect to the responses of CCA and HRPSoC, that do not necessarily act independently – based on their amounts – on the performance of the active material. The study also showed that there are correlations between certain response factors, such as the number of achievable cycles within a HRPSoC test sequence, and the type of added carbon.Keywords: Pb-acid battery, Pb-plate, graphite, expanders, design of experimen

Electrochemical Oxidation of Phenol using a Flow-through Micro-porous Lead Dioxide/Lead Cell

The electrochemical oxidation of phenol to benzoquinone followed by the reduction to hydroquinone and catechol was demonstrated by constructing a three-dimensional porous micro-flow cell from lead dioxideand lead. The electrodes were made by using the principles of curing and formation of lead oxide material that are common in the construction of the electrodes used in lead-acid batteries. This resulted in highly porous electrodes that can allow the reactant solution to flow through them in series, without the risk of having the products being oxidized again at the anode that usually occurs in a simple undivided cell. In this study, a 50 mM solution of phenol in a 60 % acetonitrile and water mixture was used that contained 2 % sulphuric acid. The reactantsolution would flow through the anode porous material oxidizing the phenol to benzoquinone. The benzoquinone in solution would then flow through the cathode porous material and reduce to catechol and hydroquinone. The study showed that almost all of the phenol could be converted in one continuous flow process in using a relatively low cost electrochemical micro-flow cell that can be easily scaled up to accommodate larger volumes and concentrations by using electrode manufacturing principles used in the lead-acid battery industry.Keywords: Phenol, hydroquinone, catechol, lead dioxide, micro-flow cel

The TATA-binding protein regulates maternal mRNA degradation and differential zygotic transcription in zebrafish

Early steps of embryo development are directed by maternal gene products and trace levels of zygotic gene activity in vertebrates. A major activation of zygotic transcription occurs together with degradation of maternal mRNAs during the midblastula transition in several vertebrate systems. How these processes are regulated in preparation for the onset of differentiation in the vertebrate embryo is mostly unknown. Here, we studied the function of TATA-binding protein (TBP) by knock down and DNA microarray analysis of gene expression in early embryo development. We show that a subset of polymerase II-transcribed genes with ontogenic stage-dependent regulation requires TBP for their zygotic activation. TBP is also required for limiting the activation of genes during development. We reveal that TBP plays an important role in the degradation of a specific subset of maternal mRNAs during late blastulation/early gastrulation, which involves targets of the miR-430 pathway. Hence, TBP acts as a specific regulator of the key processes underlying the transition from maternal to zygotic regulation of embryogenesis. These results implicate core promoter recognition as an additional level of differential gene regulation during development