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Due to an increasing number of electric vehicles, battery pack endurance over the cell lifetime is an important issue of public interest, because it determines to a large degree the value of the vehicle. The exact state of health of a battery is still a major challenge for analysis, especially since the individual ageing factors are not well understood and depend on the cell chemistry and design. In this analysis, X-ray computer tomographic (CT) images of new and aged battery electrodes are compared to determine structural changes over lifetime. The X-ray CT images with sub-micrometer resolution show the internal pore structure of the electrodes and allow the identification of the morphology of the materials. Organic residues and depositions responsible for reduced porosity in aged anodes are quantified and visualized. Furthermore, particle cracking and current collector corrosion is detected on the cathode side. All these are ageing effects, which might influence the cell capacity and impedance. A quantitative analysis of the lithium distribution completes the interpretation of the ageing study confirming that the degradation can be attributed to the loss of cyclable lithium which is bound in the particle surface layer of the anode.

One of the open questions in understanding the reactivity of nanometric metal/metal oxide particulate composites is the relative role of gas–solid vs. condensed state reactions. This work is an investigation of several nano-Al based thermites subjected to very rapid heating rates. The ignition temperature of thermites, as measured by the onset of optical emission, was measured using a rapidly heated Pt wire. Generally, ignition was seen to occur above the melting temperature of aluminum. The exception was Al/Bi2O3 which ignited slightly below this point. Samples were also rapidly heated in situ within electron microscopes to provide direct imaging before and after heating. The sintering of aggregated and/or agglomerated particles into characteristically larger structures was experimentally observed in all cases, and the fuel and oxidizer were found to be in surface contact suggesting that a condensed-phase reactive sintering mechanism had occurred. High resolution image sequences of thermites ignited on the Pt wire were collected using a real time phase contrast imaging technique at the Advanced Photon Source of Argonne National Lab. The results suggest that reactive sintering occurs on a fast timescale, and relatively early in the reaction, leading to rapid melting and coalescence of aggregated particles. This dramatically changes the initial size and morphology of the constituents before the remainder of the material burns. The results question the idea that a decrease in particle size will necessarily lead to an enhancement in reactivity, since large amounts of sintering occurs early in the reaction, and alters the morphology. It is suggested that improvements in reactivity can be achieved by designing architectures to improve the interfacial contact upon sintering, as well as by selecting oxidizers based on their ability to liberate and transport oxygen in the condensed phase, while producing volatile species to assist in convective energy transport.

Polycythemia has marked effects on blood flow through large arteries, but there has been little study of microvascular flow properties, particularly in the hypertensive state. We have previously shown that skin blood flow in the rat had properties very similar to those in man. We used laser Doppler techniques to determine the effect of erythropoietin-induced polycythemia on skin blood flow in 12 Spontaneously Hypertensive Rats (SHR) as compared with 12 normotensive Wistar-Kyoto (WKY) rats. We contrasted flow values at the back and base of tail, nutritively (NUTR) perfused skin sites, with those at the plantar surface of the paw, a site with substantial arteriovenous anastomotic (AVA) perfusion. Erythropoietin treatment produced a substantially greater hematocrit response in the SHR rats, rising from 47 ± 1 to 64 ± 1, than in the WKY animals, who showed an increase from 46 ± 1 to 55 ± 1. Blood pressure was higher in the EPO-treated WKY and SHR rats: 157 ± 4 mm Hg as compared to 148 ± 2 mmg Hg in the WKY animals and 228 ± 4 mm Hg as compared to 201 ± 3 mm Hg, respectively (both p < 0.03). Erythropoietin treatment had very little effect on basal skin blood flow in either WKY or SHR rats. However, there was significantly lower heat-stimulated flow at the plantar surface of the paw in the EPO treated rats (WKY: 27.3 ± 1.9 ml/min/100 gm vs 35.5 ± 1.5 ml/min/100 gm in the untreated state; p < 0.02; SHR: 32.7 ± 2.6 ml/min/100 gm vs 45.4 ± 2.3 ml/min/100 gm in the untreated state; p < 0.01). In contrast, there was little difference at the back or tail. We conclude that erythropoietin-induced polycythemia affects flow in AVA rather than NUTR microvessels. Although raised vascular pressure has produced microvascular flow in our previous studies, the rise in pressure associated with high hematocrit appears to result from an increase in microvascular resistance, decreasing flow. Our study helps clarify clinical observations on the hemodynamic consequences of hematocrit elevation.