Richard Ball

The detection and measurement of impact damage in thick carbon fibre reinforced laminates by transient thermography

Transient thermography (TT) images of impact damaged 3.44, 8.66 and 13.76 mm thick composites, from the impact face and rear face, are compared with the corresponding ultrasonic c-scan (UCS) images. Comparisons of apparent delamination area and size were made using novel image analysis techniques. The defect image sizes were also compared with crack lengths obtained from a selected number of specimens that were sectioned. For all composite thicknesses, the UCS damage area was proportional to the impact energy. The damage area obtained by TT from the front faces of the specimens did not correlate to the UCS damage areas although there was a correlation for the rear face damage on 3.44 and 6.88 mm thick specimens. Crack lengths obtained from sectioning showed that UCS damage length was equal to the maximum crack length and back and front sub surface cracks corresponded to back and front TT images.

Cosensitization of dye sensitized solar cells with a thiocyanate free Ru dye and a metal free dye containing thienylfluorene conjugation

A stepwise approach has been applied for the cosensitization of a thiocyanate free Ru sensitizer (SPS-01) with a metal free dye containing thienylfluorene conjugation (JD1) for dye sensitized solar cells (DSSCs). The cosensitized SPS-01 + JD1 based DSSC showed a significant enhancement in both the open circuit voltage (Voc) and the short circuit current (Jsc) relative to the individual single dye based DSSCs. The DSSC based on the SPS-01 + JD1 system yielded a Jsc of 15.38 mA cm−2, a Voc of 0.72 V, a fill factor (FF) of 0.76 and a power conversion efficiency (PCE) of 8.30%. This performance was superior to that of the DSSCs sensitized with the individual dyes SPS-01 (PCE = 5.98%) or JD1 (PCE = 4.76%) fabricated under the same conditions. Results show that the JD1 dye effectively overcomes the competitive light absorption by I3−/I− and also prevents dye aggregation and reduces the charge recombination. To understand the effects of the charge recombination of the injected electrons with I3− in the electrolyte, the dark current–voltage characteristics and electrochemical impedance spectra of the DSSCs sensitized with the SPS-01 and SPS-01+JD1 systems were measured. It was observed that the recombination of the electrons in the conduction band with I3− in the electrolyte in the DSSC sensitized with SPS-01 +JD1 was significantly reduced relative to the DSSC based on SPS-01.

Ocean warming, more than acidification, reduces shell strength in a commercial shellfish species during food limitation.

Ocean surface pH levels are predicted to fall by 0.3–0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2–4°C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH –0.4 pH units) and warming (ambient temperature +4°C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4–6 h day−1). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO3 saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited.

Failure mechanisms in valve regulated lead/acid batteries for cyclic applications

Valve regulated lead/acid (VRLA) batteries are used in a variety of different applications, one of which is cycling. Cycle life testing of a batch of 40 Ah VRLA batteries showed a large variation in the cycles to failure ranging from 10 to 133 cycles. Further testing and the destructive examination of these batteries provided information on the likely causes of failure. Results from monitoring reduction in cell voltage during a final discharge/charge cycle, scanning electron microscopy (SEM), BET surface area analysis, X-ray diffraction, interfacial analysis and electron probe analysis, were used to identify the failure mechanisms occurring within the batch. Batteries that failed after a low number of cycles, 10 and 28, were believed to have done so due to sulphation of the positive plate. Thick corrosion layers were shown to be the cause of failure in the batteries that sustained high numbers of cycles, 92 and 133. Results suggested that batteries failing at intermediate numbers of cycles, 42, 49, 65 and 73, failed due to degradation of the cells simultaneously and a single failure mechanism could not be identified.

Dithienylthienothiadiazole-based organic dye containing two cyanoacrylic acid anchoring units for dye-sensitized solar cells

A new dithienylthienothiadiazole-based organic dye (D) was synthesized by a seven-step synthetic route for use as a sensitizer in dye sensitized solar cells (DSSCs). The dye contains a dithienylthienothiadiazole central unit and two cyanoacrylic acid anchoring side groups. Optical and electrochemical properties of D were evaluated. In addition, density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were carried out. A favorable electronic excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) indicated that the dye can be used as a sensitizer for DSSC applications. The photovoltaic properties of laboratory scale optimized DSSCs sensitized with D showed a power conversion efficiency (PCE) of 4.22%, which was further improved to 5.47% upon the addition of chenodeoxylic acid (CDCA) as a coadsorbant.

Theoretical development and validation of a Sharp Front model of the dewatering of a slurry by an absorbent substrate

The absorption of water from a slurry into an absorbent substrate is analysed using Sharp Front theory. The analysis describes the relationship between the sorptivity S of the substrate, the desorptivity R of the slurry and the transfer sorptivity A between slurry and substrate, and leads to the relationship 1/A2 = 1/R2 + 1/S2. Experimental data are presented which validate this equation for the practically important case of the absorption of water from soft mortar mixes by fired clay bricks. A unique feature of the experimental work is the measurement of the desorptivity of the mortars at a pressure equal to the wetting front capillary pressure of the clay brick substrate. Analysis of the experimental data also enables, for the first time, the calculation of the capillary potential at the slurry/substrate interface. The analysis has relevance to many aspects of ceramic and mineral processing, industrial filtration and construction engineering.

Efficient dye-sensitized solar cells based on cosensitized metal free organic dyes with complementary absorption spectra

Dye sensitized solar cells (DSSCs) were fabricated using two metal-free organic dyes, TA-St-CA and D, with complementary absorption bands in the visible and near infrared regions. The power conversion efficiency (PCE) of the cosensitized DSSC (6.26%) was improved when compared to DSSCs based on individual dyes TA-St-CA (4.98%) or D (4.22%). The PCE was further enhanced up to 7.19% when deoxycholic acid (DCA) was added to the mixed dye solution as a coadsorbant. The enhancement of PCE observed in the cosensitized DSSC by addition of DCA was attributed to both suppression of dye aggregation and prevention of the backward electron transfer from the conduction band of TiO2.

Effect of Deoxycholic Acid on the Performance of Liquid Electrolyte Dye-Sensitized Solar Cells Using a Perylene Monoimide Derivative

The effect of coadsorption with deoxycholic acid (DCA) on the performance of dye-sensitized solar cell based on perylene monoimide derivative (PCA) as sensitizer and liquid electrolyte had been investigated. The current-voltage characteristics under illumination and incident photon to current efficiency (IPCE) spectra of the DSSCs showed that the coadsorption of DCA with the PCA dye results in a significant improvement in short circuit photocurrent and slight increase in the open circuit photovoltage, which lead to an overall power conversion efficiency. The enhancement of short circuit current was attributed to the increased electron injection efficiency from the excited state of PCA into the conduction band of TiO2 and charge collection efficiency. The current-voltage characteristics in dark indicates a positive shift in the conduction which also supports the enhancement in the photocurrent. The coadsorption with DCA suppressed charge recombination as indicated from the electrochemical impedance spectra and thus improved the open circuit photovoltage.

The oxidative corrosion of carbide inclusions at the surface of uranium metal during exposure to water vapour

The reaction between uranium and water vapour has been well investigated, however discrepancies exist between the described kinetic laws, pressure dependence of the reaction rate constant and activation energies. Here this problem is looked at by examining the influence of impurities in the form of carbide inclusions on the reaction. Samples of uranium containing 600 ppm carbon were analysed during and after exposure to water vapour at 19 mbar pressure, in an environmental scanning electron microscope (ESEM) system. After water exposure, samples were analysed using secondary ion mass spectrometry (SIMS), focused ion beam (FIB) imaging and sectioning and transmission electron microscopy (TEM) with X-ray diffraction (micro-XRD). The results of the current study indicate that carbide particles on the surface of uranium readily react with water vapour to form voluminous UO(3) · xH(2)O growths at rates significantly faster than that of the metal. The observation may also have implications for previous experimental studies of uranium-water interactions, where the presence of differing levels of undetected carbide may partly account for the discrepancies observed between datasets.

Characterisation of separator papers for use in valve regulated lead/acid batteries

Separator papers are an essential component of a valve regulated lead/acid (VRLA) battery. In addition to separating the positive and negative electrodes, they provide a constant pressure on the active materials thereby reducing the rate of degradation during cycling. Dendrites formed from the negative active material are also less likely to cause short circuits in batteries where a separator is employed. The level to which a separator will influence the performance of a VRLA battery it strongly dependent on its properties. This paper describes the results from a series of tests used to characterise the properties of separators most influential to battery performance. These properties include, the macroscopic structure, permittivity and wicking rates. During the operational life of a VRLA battery the volume of electrolyte will decrease, due mainly to the electrolysis of water during overcharging. The consequence of this process is a variation of acid saturation during the life of the battery, which will have a direct influence on the compressive and diffusive properties of the separator. Compressive and diffusive characteristics were therefore measured over a range of saturation levels. Characterisation was conducted on three separator types. Types A and B were 100% glass but had slightly different structures and type C contained 8% polyester fibres mixed with glass.