Degradation observations of encapsulated planar CH3NH3PbI3 perovskite solar cells at high temperatures and humidity

The stability of encapsulated planar-structured CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSCs) was investigated under various simulated environmental conditions. The tests were performed under approximately one sun (100 mW cm^-2) illumination, varying temperature (up to 85 °C cell temperature) and humidity (up to 80%). The application of advanced sealing techniques improved the device stability, but all devices showed significant degradation after prolonged aging at high temperature and humidity. The degradation mechanism was studied by post-mortem analysis of the disassembled cells using SEM and XRD. This revealed that the degradation was mainly due to the decomposition of MAPbI3, as a result of reaction with H2O, and the subsequent reaction of hydroiodic acid, formed during MAPbI3 decomposition, with the silver back contact electrode layer.

Atomically thin boron nitride: unique properties and applications

Atomically thin boron nitride (BN) is an important 2D nanomaterial, with many properties distinct from graphene. In this feature article, these unique properties and associated applications, often not feasible with graphene, are outlined. The article starts with characterization and identification of atomically thin BN. It is followed by demonstrating their strong oxidation resistance at high temperatures and applications in protecting metals from oxidation and corrosion. As flat insulators, BN nanosheets are ideal dielectric substrates for surface enhanced Raman spectroscopy (SERS) and electronic devices based on 2D heterostructures. The light emission of BN nanosheets in the deep ultraviolet (DUV) and ultraviolet (UV) regions is also included for its scientific and technological importance. The last part is dedicated to synthesis, characterization, and optical properties of BN nanoribbons, a special form of nanosheets.

Inferring dynamic recrystallization in ferrite using the kinetics of static recrystallization

A general relationship between the kinetics of dynamic and static recrystallization is developed. It is predicted that conventional dynamic recrystallization will occur whenever the deformation time exceeds the adjusted start time for static recrystallization. This approach is verified using data for austenite and lead. It is then applied to current and previous work on ferrite. The model provides support for the contention that conventional dynamic recrystallization occurs in low carbon ferrite if deformation is carried out at high temperatures and low strain rates. In the present work, which was carried out at 700 °C, evidence for dynamic recrystallization was observed for strain rates less than around 0.01 s−1. At higher strain rates, the model predicts a critical strain for the onset of dynamic recrystallization that exceeds the critical strain for the beginning of the recovery steady-state region. While the model allows dynamic recrystallization to begin in this region, the critical strain for its onset is expected to increase rapidly with increasing strain rate and decreasing temperature once steady state has been reached.

A criterion for conventional dynamic recrystallization: Application to magnesium alloys

An analytical approximation for the steady state dynamic recrystallized grain size is combined with a simple nucleation criterion to assess the propensity for dynamic recrystallization. In line with observation, the criterion predicts dynamic recrystallization in 99.9995% pure Al but not in material 99.5% pure. It also agrees with the observation that zone refined ferrite can display dynamic recrystallization at high temperatures and low strain rates but not at lower hot working temperatures. The criterion is applied here to common wrought magnesium alloys to argue that conventional dynamic recrystallization is expected under "normal" hot working conditions.

A comparative study of microstructures and mechanical properties obtained by bar and plate rolling

Microstructures and mechanical properties of a low carbon steel were studied after plate rolling and bar rolling. Plate rolling is characterized as a monotonic compressive loading, while bar rolling is characterized as a cross-compressive loading. A four-pass plate rolling and bar rolling experiment was designed so that the material experiences the same amount of strain at each pass during rolling. The rolling experiment was performed at moderately high temperatures (450, 550 and 650 °C). The microstructures and mechanical properties of the low carbon steel acquired from the two types of rolling experiments were compared. The results revealed that differences of loading path attributed by monotonic loading (plate rolling) and cross loading (bar rolling) significantly influenced the microstructures and mechanical properties such as yield stress, ultimate tensile stress, strain hardening exponent and elongation of the low carbon steel.

Boron nitride nanotubes : pronounced resistance to oxidation

Boron nitride (BN) nanotubes have the same nanostructure as carbon nanotubes but are found to exhibit significant resistance to oxidation at high temperatures. Our systematic study has revealed that BN nanotubes are stable at 700 °C in air and that some thin nanotubes (diameter less than 20 nm) with perfect multiwalled cylindrical structure can survive up to 900 °C. Thermogravimetric analysis reveals an onset temperature for oxidation of BN nanotubes of 800 °C compared with only 400 °C for carbon nanotubes under the same conditions. This more pronounced resistance of BN nanotubes to oxidation is inherited from the hexagonal BN and also depends on the nanocrystalline structure. This high level of resistance to oxidation allows promising BN nanotube applications at
high temperatures

Urban heat island and its impact on building energy consumption

Urban areas tend to have higher air temperatures than their surroundings as a result of man-made aiterations. This phenomenon is known as the urban heat island (UHI) effect. UHI is considered to he one of the major problems encountered by the human race this century. Solar radiation that is absorbed during the day by buildings is re~emitted after sunset creating high temperatures in urban areas. Also, anthropogenic heat sources such as air conditioners and road traffic add to the rise in temperatures, A number of
studies have indicated that UHI has a significant effect on the energy use of buildings. In mid- and low-latitude cities, heat islands contribute to urban dwellers' summer discomfort and significantly higher air-conditioning loads. This chapter summarizes and reviews the latest research methodologies and findings about the effect of increased temperatures on the energy consumption of buildings. The latest developments in the heat island mitigation strategies are remarkable, However, more attention needs to be
given to the implementation and testing of these strategies in full-scale buildings.

Evaluation of heat stress indices using physiological comparisons in an alumina refinery in a sub-tropical climate

The production of alumina involves the use of a process known as the Bayer process. This method involves the digestion of raw bauxite in sodium hydroxide at temperatures around 250°C. The resultant pregnant liquor then goes through a number of filtering and precipitation processes to obtain the aluminium oxide crystals which are then calcined to obtain the final product. The plant is situated in a sub tropical climate in Northern Australia and this combined with the hot nature of the process results in a potential for heat related illnesses to develop. When assessing a work environment for heat stress a heat stress index is often employed as a guideline and to date the Wet Bulb Globe Temperature (WBGT) has been the recommended index. There have been concerns over the past that the WBGT is not suited to the Northern Australian climate and in fact studies in other countries have suggested this is the case. This study was undertaken in the alumina plant situated in Gladstone Queensland to assess if WBGT was in fact the most suitable index for use or if another was more applicable. To this end three indices, Wet Bulb Globe Temperature (WBGT), Heat Stress Index (HSI) and Required Sweat Rate (SWreq) were compared and assessed using physiological monitoring of heart rate and surrogate core temperature. A number of different jobs and locations around the plant were investigated utilising personal and environmental monitoring equipment. These results were then collated and analysed using a computer program written as part of the study for the manipulation of the environmental data . Physiological assessment was carried out using methods approved by international bodies such as National Institute for Occupational Safety & Health (NIOSH) and International Standards Organisation (ISO) and incorporated the use of a ‘Physiological Factor’ developed to enable the comparison of predicted allowable exposure times and strain on the individual. Results indicated that of the three indices tested, Required Sweat Rate was found to be the most suitable for the climate and in the environment of interest. The WBGT system was suitable in areas in the moderate temperature range (ie 28 to 32°C) but had some deficiencies above this temperature or where the relative humidity exceeded approximately 80%. It was however suitable as a first estimate or first line indicator. HSI over-estimated the physiological strain in situations of high temperatures, low air flows and exaggerated the benefit of artificial air flows on the worker in certain environments ie. fans.

Rearing juvenile Australian native percichthyid fish in fertilised earthen ponds

The post-larvae and fry of Australian native species, including those of species belonging to the family Percichthyidae, are routinely reared to a fingerling size (35-55 mm in length) in fertilised earthen fry rearing ponds. The juveniles of Murray cod (Maccullochella peelii peelii\ trout cod (Maccullochella macquariensis) and Macquarie perch (Macquaria australasicd) (Percichthyidae) are grown in fry rearing ponds at the Marine and Freshwater Resources Institute, Snobs Creek (Vie. Australia) for production of fingerlings for stock enhancement and aquaculture purposes. However, no detailed studies have been undertaken of the productivity of these ponds and factors that influence fish production. An ecologically based study was undertaken to increase the knowledge of pond ecology and dynamics, particularly in relation to the rearing of juvenile Murray cod, trout cod and Macquarie perch in ponds. Over nine consecutive seasons commencing in 1991, water chemistry, plankton, macrobenthos (2 seasons only) and fish were monitored and studied in five ponds located at Snobs Creek. A total of 80 pond fillings were undertaken during the study period. Additional data collected from another 24 pond fillings undertaken at Snobs Creek collected prior to this study were included in some analyses. Water chemistry parameters monitored in the ponds included, temperature, dissolved oxygen pH, ammonia, nitrite, nitrate, orthophosphate and alkalinity. Water chemistry varied spatially (within and between ponds) and temporally (diurnally, daily and seasonally). Liming of ponds increased the total alkalinity to levels that were considered to be suitable for enhancing plankton communities and fish production. Water quality within the ponds for the most part was suitable for the rearing of juvenile Murray cod, trout cod and Macquarie perch, as reflected in overall production (growth, survival and yield) from the ponds. However, at times some parameters reached levels which may have stressed fish and reduced growth and survival, in particular, low dissolved oxygen concentrations (minimum 1.18 mg/L), high temperatures (maximum 34°C), high pH (maximum 10.38) and high unionised ammonia (maximum 0.58 mg/L). Species belonging to 37 phytoplankton, 45 zooplankton and 17 chironomid taxa were identified from the ponds during the study. In addition, an extensive checklist of aquatic flora and fauna, recorded from aquaculture ponds in south-eastern Australia, was compiled. However, plankton and benthos samples were usually numerically dominated by a few species only. Rotifers (especially Filinia, Brachionus, Polyarthra, and Asplanchnd), cladocerans (Moina and Daphnid) and copepods (Mesocyclops and Boeckelld) were most abundant and common in the plankton, while chironomids (Chironomus, Polypedilum, and Prodadius) and oligochaetes were most common and abundant in the benthos. Both abundance and species composition of the plankton and macrobenthos varied spatially (within and between ponds) and temporally (diurnally, daily and seasonally). Chlorophyll a concentrations, which ranged from 1.8 to 184 \ig/L (mean 29.37 ng/L), initially peaked within two weeks of filling and fertilising the ponds. Zooplankton peaked in abundance 2-4 weeks after filling the ponds. The maximum zooplankton density recorded in the ponds was 6,621 ind./L (mean 721 ind./L). Typically, amongst the zooplankton, rotifers were first to develop high densities (2nd-3rd week after filling), followed by cladocerans (2nd-4th week after filling) then copepods (2nd-5th week after filling). Chironomid abundance on average peaked later (during the 5th week after filling). The maximum chironomid density recorded in the ponds was 27,470 ind./m2 (mean 4,379 ind./m2). Length-weight, age-weight and age-length relationships were determined for juvenile Murray cod, trout cod and Macquarie perch reared in ponds. These relationships were most similar for Murray cod and trout cod, which are more closely related phylogenetically and similar morphologically than Macquarie perch. Growth of fish was negatively correlated with both size at stocking and stocking biomass. Stocking density experiments showed that, at higher densities, growth offish was significantly reduced, but survival was not affected. The diets of juvenile Murray cod trout cod and Macquarie perch reared in fry ponds were similar. The cladocerans Moina and Daphnia, adult calanoid and cyclopoid copepods and the chironomids, Chironomus, Polypedilum and Procladius were the most commonly occurring and abundant prey. Selection for rotifers and copepod nauplii was strongly negative for all three species of fish. Size range of prey consumed was positively correlated with fish size for trout cod and Macquarie perch, but not for Murray cod. Diet composition changed as the fish grew. Early after stocking the fish into the ponds, Moina was generally the more common prey consumed, while in latter weeks, copepods and chironomids became more abundant and common in the diet. On a dry weight basis, chironomid larvae were the most important component in the diets of these fish species. Selective feeding by fish on larger planktonic species such as adult copepods and cladocerans, may have influenced the plankton community structure as proposed by the trophic cascade or top -down hypothesis. The proximate composition and energy content of Murray cod, trout cod and Macquarie perch, reared in the ponds did not vary significantly between the species, and few significant changes were observed as the fish grew. These results suggested that the nutrient requirements of these species might not vary over the size range of fish examined. Significant differences in the proximate composition of prey were observed between species, size of species and time of season. The energy content of prey (cladocerans, copepods and chironomids) on a pond basis, was closely related to the abundance of these taxa in the ponds. Data collected from all pond fillings during the present study, along with historical data from pond fillings undertaken prior to this study, were combined in a data matrix and analysed for interactions between pairs of parameters. In particular, interactions between selected water chemistry parameters, zooplankton and chironomid abundance indicators were analysed to identify key factors that influence fish production (growth, survival, condition and yield). Significant correlations were detected between fish production indicators and several water chemistry and biota (zooplankton and chironomids) parameters. However, these were not consistent across all three species of fish. These results indicated that the interactions between water chemistry, biota and fish were complex, and that combinations of these parameters, along with other factors not included in the present study, may influence fish production in these ponds. The present study, showed that more stringent monitoring of fry rearing ponds, especially water quality, zooplankton and benthos communities and fish, combined with an associated increase in understanding of the pond ecosystem, can lead to substantial improvements in pond productivity and associated fish production. In the present study this has resulted in a general increase in fish survival rates, which became less variable or more predictable in nature. The value of such knowledge can provide managers with a more predicative capacity to estimate production of ponds in support of stock enhancement programs and provision of juvenile for aquaculture grow-out.

Ordering and stability in conducting polypyrrole

X-ray diffraction (XRD) was employed to characterize electrochemically synthesized polypyrrole (PPy) films with 1,5-naphthalene disulfonate (1,5-NDS) counterions treated with simple acid and base. Results show that the as-synthesized film is amorphous with short-range ordering in the polymer backbone. This ordering is soon lost after thermal ageing at 150°C for 60 days and there is evidence of counterion degradation. Base treatment of the PPy/1,5-NDS films has similar effects leading to a complete loss of ordering in the polymer backbone and dedoping of the polymer. Acid treatment at high temperatures increases the ordering of the polymer backbone and results in the development of a secondary interdopant peak confirming that ion exchange has occurred. Conductivity of the PPy was also increased substantially. The enhanced ordering was maintained even after thermal ageing. Room-temperature acid treatment also results in improved ordering of the polymer as well as the counterion but the increase in conductivity is only marginal and most of the ordering is soon lost after thermal ageing. Increase in ordering of the polymer structure seems to lead to better conductivity, although not necessarily improved thermal stability.

Mechanisms governing the enhanced thermal stability of acid and base treated polypyrrole

One of the major problems associated with the use of polypyrrole (PPy) in a practical engineering application is its poor thermal stability at elevated temperatures, especially in the presence of oxygen and moisture. Several authors have shown that enhanced stability can be achieved through treatment with simple acids and bases. This paper presents a summary of the possible structural changes which occur as a result of these treatments and those that appear to be related to enhanced conductivity stability. A slight increase in conductivity (10–20%) is observed for acid treated PPy films which is found to be the result of protonation of the pyrrole structure. This effect is dramatically enhanced by treatment at high temperatures where an increase in conductivity of >84% can be achieved. Base treatment of the PPy films results in the deprotonation of the pyrrole structure leading to the loss of conductivity (>40%). Preliminary X-ray Photoelectron Spectroscopy (XPS) results indicate that both acid and base treatment resulted in the elimination of reactive sites for oxygen. Long term thermal ageing of these treated films were conducted at 150 °C in air. The conductivity decay behaviour was found to follow multiple first order chemical reaction kinetics.

Deformation and frictional heating in relation to wear in sheet metal stamping

In the automotive industry, press production rates often need to be reduced in order to minimize tool wear issues and successfully stamp advanced high strength steels. This indicates that heating affects may be important. This paper examines friction and deformational heating at the die radius during sheet metal stamping, using finite element analysis. The results show that high temperatures, of up to 130°C, can occur at the die radius surface. Such behavior has not been previously reported in the literature, for what is expected to be ‘cold’ sheet metal stamping conditions. It will be shown that the temperature rise is due to the increased contact stresses and increased plastic work, associated with stamping AHSS. Consequently, new insights into the local contact conditions in sheet metal stamping were obtained. The outcomes of this work may impact the wear models and tests employed for future tool wear analyses in sheet metal stamping.

Enhanced oxygen permeation through perovskite hollow fibre membranes by methane activation

Hollow fibre membranes of mixed conducting perovskite La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) were prepared via the combined phase inversion and sintering technique. The fibres were tested for air separation with a home-made reactor under the oxygen partial pressure gradient generated by the air/He streams. Some fibres were in situ activated by introducing methane in the He sweeping gas at high temperatures. The activated membranes with new morphology were created by transforming the inner densified surface layer to a porous structure. Compared to the original membranes, the activated gave appreciable higher oxygen fluxes. At 800 °C, the oxygen fluxes were increased by a factor of 10 after activation was carried out at 1000 °C for 1 h.

Possible electrical double-layer contribution to the equilibrium thickness of intergranular Glass films in polycrystalline ceramics

The plausibility of the entropic repulsion of electrical double layers acting to stabilize an equilibrium thickness of intergranular glass films in polycrystalline ceramics is explored. Estimates of the screening length, surface potential, and surface charge required to provide a repulsive force sufficiently large to balance the attractive van der Waals and capillary forces for observable thicknesses of intergranular film are calculated and do not appear to be beyond possibility. However, it has yet to be established whether crystalline particles in a liquid-phase sintering medium possess an electrical double layer at high temperatures. If they do, such a surface charge layer may well have important consequences not only for liquid-phase sintering but also for high-frequency electrical properties and microwave sintering of ceramics containing a liquid phase.

Mechanisms for climate-induced mortality of fish populations in whole-lake experiments

The effects of climate change on plant and animal populations are widespread and documented for many species in many areas of the world. However, projections of climate impacts will require a better mechanistic understanding of ecological and behavioral responses to climate change and climate variation. For vertebrate animals, there is an absence of whole-system manipulative experiments that express natural variation in predator and prey behaviors. Here we investigate the effect of elevated water temperature on the physiology, behavior, growth, and survival of fish populations in a multiple whole-lake experiment, by using 17 lake-years of data collected over 2 years with differing average temperatures. We found that elevated temperatures in excess of the optimum reduced the scope for growth through reduced maximum consumption and increased metabolism in young rainbow trout, Oncorhynchus mykiss. Increased metabolism at high temperatures resulted in increased feeding activity (consumption) by individuals to compensate and maintain growth rates similar to that observed at cooler (optimum) temperatures. However, greater feeding activity rates resulted in greater vulnerability to predators that reduced survival to only half that of the cooler year. Our work therefore identifies temperature-dependent physiology and compensatory feeding behavior as proximate mechanisms for substantial climate-induced mortality in fish populations at the scale of entire populations and waterbodies.