The effect of trace elements on the sintering of an Al-Zn-Mg-Cu alloy

Trace elements can have a significant effect on the processing and properties of aluminium alloys, including sintered alloys. As little as 0.07 wt% (100 ppm) lead, tin or indium promotes sintering in an Al-Zn-Mg-Cu alloy produced from mixed elemental powders. This is a liquid phase sintering system and thin liquid films form uniformly throughout the alloy in the presence of the trace elements, but liquid pools develop in their absence. Analytical transmission electron microscopy indicates that the trace elements are confined to the interparticle and grain boundary regions. The sintering enhancement is attributed to the segregation of the microalloying addition to the liquid-vapour interface. Because the microalloying elements have a low surface tension, they lower the effective surface tension of the liquid. This reduces the wetting angle and extends the spreading of the liquid through the matrix. An improvement in sintering results. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

ENCORE: The effect of nutrient enrichment on coral reefs. Synthesis of results and conclusions

Coral reef degradation resulting from nutrient enrichment of coastal waters is of increasing global concern. Although effects of nutrients on coral reef organisms have been demonstrated in the laboratory, there is little direct evidence of nutrient effects on coral reef biota in situ. The ENCORE experiment investigated responses of coral reef organisms and processes to controlled additions of dissolved inorganic nitrogen (N) and/or phosphorus (P) on an offshore reef(One Tree Island) at the southern end of the Great Barrier Reef, Australia. A multi-disciplinary team assessed a variety of factors focusing on nutrient dynamics and biotic responses. A controlled and replicated experiment was conducted over two years using twelve small patch reefs ponded at low tide by a coral rim. Treatments included three control reefs (no nutrient addition) and three + N reefs (NH4Cl added), three + P reefs (KH2PO4 added), and three + N + P reefs. Nutrients were added as pulses at each low tide (ca twice per day) by remotely operated units. There were two phases of nutrient additions. During the initial, low-loading phase of the experiment nutrient pulses (mean dose = 11.5 muM NH4+; 2.3 muM PO4-3) rapidly declined, reaching near-background levels (mean = 0.9 muM NH4+; 0.5 muM PO4-3) within 2-3 h. A variety of biotic processes, assessed over a year during this initial nutrient loading phase, were not significantly affected, with the exception of coral reproduction, which was affected in all nutrient treatments. In Acropora longicyathus and A. aspera, fewer successfully developed embryos were formed, and in A. longicyathus fertilization rates and lipid levels decreased. In the second, high-loading, phase of ENCORE an increased nutrient dosage (mean dose = 36.2 muM NH4+; 5.1 muM PO4-3 declining to means of 11.3 muM NH4+ and 2.4 muM PO4-3 at the end of low tide) was used for a further year, and a variety of significant biotic responses occurred. Encrusting algae incorporated virtually none of the added nutrients. Organisms containing endosymbiotic zooxanthellae (corals and giant clams) assimilated dissolved nutrients rapidly and were responsive to added nutrients. Coral mortality, not detected during the initial low-loading phase, became evident with increased nutrient dosage, particularly in Pocillopora damicornis. Nitrogen additions stunted coral growth, and phosphorus additions had a variable effect. Coral calcification rate and linear extension increased in the presence of added phosphorus but skeletal density was reduced, making corals more susceptible to breakage. Settlement of all coral larvae was reduced in nitrogen treatments, yet settlement of larvae from brooded species was enhanced in phosphorus treatments. Recruitment of stomatopods, benthic crustaceans living in coral rubble, was reduced in nitrogen and nitrogen plus phosphorus treatments. Grazing rates and reproductive effort of various fish species were not affected by the nutrient treatments. Microbial nitrogen transformations in sediments,were responsive to nutrient loading with nitrogen fixation significantly increased in phosphorus treatments and denitrification increased in all treatments to which nitrogen had been added. Rates of bioerosion and grazing showed no significant effects of added nutrients, ENCORE has shown that reef organisms and processes investigated ill situ were impacted by elevated nutrients. Impacts mere dependent on dose level, whether nitrogen and/or phosphorus mere elevated and were often species-specific. The impacts were generally sub-lethal and subtle and the treated reefs at the end of the experiment mere visually similar to control reefs. Rapid nutrient uptake indicates that nutrient concentrations alone are not adequate to assess nutrient condition of reefs. Sensitive and quantifiable biological indicators need to be developed for coral reef ecosystems. The potential bioindicators identified in ENCORE should be tested in future research on coral reef/nutrient interactions. Synergistic and cumulative effects of elevated nutrients and other environmental parameters, comparative studies of intact vs. disturbed reefs, offshore vs, inshore reefs, or the ability of a nutrient-stressed reef to respond to natural disturbances require elucidation. An expanded understanding of coral reef responses to anthropogenic impacts is necessary, particularly regarding the subtle, sub-lethal effects detected in the ENCORE studies. (C) 2001 Published by Elsevier Science Ltd.

Precipitation hardening of Cu-Fe-Cr alloys - Part II - Microstructural characterisation

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. Promising properties have been measured for the following alloys: Cu-0.7wt%Cr-0.3wt%Fe and Cu-0.7wt%Cr-2.0wt%Fe. This paper reports on the microstructural characterisation of these alloys and discusses the mechanical and electrical properties of these alloys in terms of their microstructure, particularly the formation of precipitates. These alloys have evinced properties that warrant further investigation. Cost modelling has shown that Cu-0.7wt%Cr-0.3wt%Fe is approximately 25% cheaper to produce than commercial Cu-1%Cr. It has also been shown to be more cost efficient on a yield stress and % IACS per dollar basis. The reason for the cost saving is that the Cu-0.7%Cr-0.3%Fe alloy can be made with low carbon ferro-chrome additions as the source of chromium rather than the more expensive Cu-Cr master-alloy. For applications in which cost is one of the primary materials selection criteria, it is envisaged that there would be numerous applications in both cast and wrought form, where the Cu-0.7%Cr-0.3%Fe alloy would be more suitable than Cu-1%Cr. (C) 2001 Kluwer Academic Publishers.

Quaternary Cu-0.7%Cr-0.3%Fe-X alloys

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. The aim of the present work was to increase the electrical conductivity and strength of the Cu-0.7wt%Cr-0.3wt%Fe alloy through selective minor additions (less than or equal to0.15 wt%) of elements expected to promote precipitation of dissolved Fe: Ti, B, P, Ni & Y. Such quaternary alloys with reduced Fe in solid solution would be expected to have properties equivalent to or better than those of the Cu-1%Cr reference alloy (Alloy Z). The investigation showed that none of the trace element additions significantly improved the size of the age hardening response or the peak aged electrical conductivity of Alloy A, although further work is required on the influence of Ti. Additions of P and B were detrimental. Other trace additions had little or no effect apart from causing some slight changes to the precipitation kinetics. The mechanical properties of the Cu-0.7%Cr-0.3%Fe alloy made with less expensive high carbon ferrochrome were found to be inferior to those of the equivalent alloy made with low carbon ferrochrome. (C) 2001 Kluwer Academic Publishers.

Investigations of growth processes in Y-Ba-Cu-O materials by microstructural examination of quenched samples

Y-Ba-Cu-O samples with additions of Y2O3 and CeO2 were quenched during seeded isothermal melt processing and examined by optical microscopy and scanning electron microscopy. Large YBa2Cu3O7-y (Y123) particles in the starting powder were found to form a distinct type of melt during heating, which was unaffected by the Y2O3 or CeO2 additives. This type of melt later formed regions with a low concentration of Y2BaCuO5 (Y211) particles in the Y123 matrix. The maximum growth rate of Y123 that could be sustained in the sample was found to be lower in the melt formed from large Y123 particles, and this may lead to growth accidents and subgrains in some samples.

Precursor scavenging of resistive grain-boundary phase in 8 mol % ytterbia-stabilized zirconia

The grain-boundary conduction of 8 mol % ytterbia-stabilized zirconia (8YbSZ) was improved markedly by precursor scavenging via the two-stage sintering process. The most significant increase in the grain-boundary conductivity was found when the sample, whose conductivity was higher than that via Al2O3-derived scavenging, was heat-treated at 1250degreesC for greater than or equal to 20 h. The formation of a stable Si-containing phase such as ZrSiO4 during the first-stage heat-treatment was suggested as one probable scavenging route from the optimal heat-treatment temperature (HTT), long duration time (>20 h) at HTT, and the stability of the formed phase up to sintering temperatures (1500degrees C). (C) 2002 The Electrochemical Society.

Columnar to equiaxed transition of eutectic in hypoeutectic aluminium-silicon alloys

Directional solidification of unmodified and strontium modified binary, high-purity aluminium-7 wt% silicon and commercial A356 alloys has been carried out to investigate the mechanism of eutectic solidification. The microstructure of the eutectic growth inter-face was investigated with optical microscopy and Electron Backscattering Diffraction (EBSD). In the commercial alloys, the eutectic solidification inter-face extends in the growth direction and creates a eutectic mushy zone. A planar eutectic growth front is observed in the high-purity alloys. The eutectic aluminium has mainly the same crystallographic orientation as the dendrites in the unmodified alloys and the strontium modified high-purity alloy. A more complex eutectic grain structure is found in the strontium modified commercial alloy. A mechanism involving constitutional undercooling and a columnar to equiaxed transition explains the differences between pure and commercial alloys. It is probably caused by the segregation of iron and magnesium and the activation of nucleants in the commercial alloy. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Characteristic zirconium-rich coring structures in Mg-Zr alloys

The most characteristic feature of the microstructure of a magnesium alloy that contains more than a few tenths per cent soluble zirconium is the zirconium-rich cores that exist in most grains. The morphology, distribution and composition of cores observed in a Mg-0.56%Zr alloy and the small particles present in them were investigated. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Tree yield and fruit minerals concentrations influence 'Hass' avocado fruit quality

To investigate the variation in quality of 'Hass' avocado fruit within an orchard, fruit were harvested at commercial maturity from 15 'Hass' trees of similar appearance, growing in three adjacent rows on the same soil type, and receiving similar management. Fruit were harvested at commercial maturity, and either ripened at 22 degreesC or stored at 2 or 7 degreesC for 3 or 5 weeks and then ripened. Significant positive correlations (based, on the mean for each datum tree) were noted between fruit flesh calcium (Ca) and magnesium (Mg) concentrations and the (Ca + Mg)/potassium ratio, and the number of days for the fruit to reach the eating ripe stage (DTR). Negative correlations were also observed between these minerals and anthracnose and mesocarp discolouration (MD) severity. Negative correlations were observed between fruit potassium (K) and phosphorus (P) concentrations and DTR. Fruit from trees with high fruit yield were generally smaller, with lower anthracnose and MD severity, ripened more slowly, and had higher flesh Ca concentrations. It is likely that cultural practices that maintain moderate to high fruit yield and reduce variation in yield will improve avocado fruit quality and reduce variability in quality. Since the main differences between adjacent trees in this trial were the seedling rootstocks of unknown origin, it is suggested that rootstocks can have a significant impact on avocado yield and fruit quality. (C) 2002 Elsevier Science B.V. All rights reserved.

Novel composites of TiO2 (anatase) and silicate nanoparticles

Thermally stable composite nanostructures of titanium dioxide (anatase) and silicate nanoparticles were prepared from Laponite clay and a sol of titanium hydrate in the presence of poly(ethylene oxide) (PEO) surfactants. Laponite is a synthetic clay that readily disperses in water and exists as exfoliated silicate layers of about 1-nm thick in transparent dispersions of high pH. The acidic sol solution reacts with the clay platelets and leaches out most of the magnesium in the clay, while the sol particles hydrolyze further due to the high pH of the clay dispersion. As a result, larger precursors of TiO2 nanoparticles form and condense on the fragmentized pieces of the leached silicate. Introducing PEO surfactants into the synthesis can significantly increase the porosity and surface area of the composite solids. The TiO2 exists as anatase nanoparticles that are separated by silicate fragments and voids such that they are accessible to organic molecules. The size of the anatase particle can be tailored by manipulating the experimental parameters at various synthesis stages. Therefore, we can design and engineer composite nanostructures to achieve better performance. The composite solids exhibit superior properties as photocatalysts for the degradation of Rhodamine 6G in aqueous solution.

Modelling the activated sludge flocculation process combining laser light diffraction particle sizing and population balance modelling (PBM)

A technique based on laser light diffraction is shown to be successful in collecting on-line experimental data. Time series of floc size distributions (FSD) under different shear rates (G) and calcium additions were collected. The steady state mass mean diameter decreased with increasing shear rate G and increased when calcium additions exceeded 8 mg/l. A so-called population balance model (PBM) was used to describe the experimental data, This kind of model describes both aggregation and breakage through birth and death terms. A discretised PBM was used since analytical solutions of the integro-partial differential equations are non-existing. Despite the complexity of the model, only 2 parameters need to be estimated: the aggregation rate and the breakage rate. The model seems, however, to lack flexibility. Also, the description of the floc size distribution (FSD) in time is not accurate.

Mineral uptake in tobacco leaf discs during different developmental stages of shoot organogenesis

Relationships between mineral uptake and tobacco shoot organogenesis were investigated during three morphogenic phases: phase 1, days 0-10, pre-meristem formation; phase 2, days 10-20, meristem initiation and formation; and phase 3, days 20-35, growth and differentiation of induced meristems into leafy shoots. The mineral content of both shoot-forming (SF) and non-shoot-forming (NSF) media was examined over the 35-day culture period. Both SF and NSF explants rapidly consumed iron during phase 1. Nitrate uptake in SF explants was high and independent of explant growth during phases 1 and 2, but greatest and strongly correlated with growth during phase 3. Phosphorus uptake was highest in SF explants during phases 2 and 3, and correlated with explant growth. Uptake of potassium, calcium and sulphur was strongly associated with explant growth during phase 3 whereas magnesium uptake was only poorly correlated with growth. Results from this study indicate that particular minerals may have an important role in regulating development as well as generally supporting growth.

Rootstocks influence 'Hass' avocado fruit quality and fruit minerals

To determine the potential for rootstocks to improve avocado quality, 'Hass' fruit from trees on seedling 'Velvick' (SV), clonal 'Velvick' (CV) or clonal 'Duke 7' (CD) rootstocks were harvested in 1999 and 2000, ripened at 20 C immediately after harvest (non-stored) or stored at 5 C for four weeks (stored), and then fruit quality and mineral concentrations determined. In 2000, non-stored CV fruit had lower severity of body rots (5% of flesh volume affected, caused mainly by Colletotrichum gloeosporioides) than CD fruit (20%), while body rots severity in stored CV fruit was 20% compared with 38% in stored CD fruit. Stored CV fruit had less severe diffuse discoloration (3% and 9% in 1999 and 2000, respectively) than CD fruit (7% and 20%, respectively). Stored CV fruit also had less severe vascular browning (19%) than CD fruit (33%) in 2000. In both seasons, CV fruit had 15-19% higher flesh calcium concentrations, 17-22% higher flesh boron concentrations, and 14-15% lower flesh nitrogen concentrations than CD fruit. In 2000, CV fruit also had 27% more skin calcium and 14% less skin nitrogen than CD fruit. There were no effects of rootstock on yield, canopy volume, measured length of non-suberized roots, average fruit weight, fruit length: width ratio, skin thickness, dry matter, proportion of the fruit skin purple-black when ripe, or seed mass: fruit weight ratio. These results suggest that there is potential to improve 'Hass' avocado quality through rootstock selection, and that tree and fruit mineral concentrations have a role in this relationship.

Purification and characterisation of functional early pregnancy factor expressed in Sf9 insect cells and in Escherichia coli

Early pregnancy factor (EPF) is a secreted protein with growth regulatory and immunomodulatory properties. It is an extracellular form of the mitochondrial matrix protein chaperonin 10 (Cpn10), a molecular chaperone. An understanding of the mechanism of action of EPF and an exploration of therapeutic potential has been limited by availability of purified material. The present study was undertaken to develop a simple high-yielding procedure for preparation of material for structure/function studies, which could be scaled up for therapeutic application. Human EPF was expressed in Sf9 insect cells by baculovirus infection and in Escherichia coli using a heat inducible vector. A modified molecule with an additional N-terminal alanine was also expressed in E coli. The soluble protein was purified from cell lysates via anion exchange (negative-binding mode), cation exchange, and hydrophobic interaction chromatography, yielding similar to42 and 36 mg EPF from 300 ml bacterial and I L Sf9 cultures, respectively. The preparations were highly purified ( greater than or equal to99% purity on SDS-PAGE for the bacterial products and greater than or equal to97% for that of insect cells) and had the expected mass and heptameric structure under native conditions, as determined by mass spectrometry and gel permeation chromatography, respectively. All recombinant preparations exhibited activity in the EPF bioassay, the rosette inhibition test, with similar potency both to each other and to the native molecule. In two in vivo assays of immuno suppressive activity, the delayed-type hypersensitivity reaction and experimental autoimmune encephalomyelitis, the insect cell and modified bacterial products, both with N-terminal additions (acetylation or amino acid), exhibited similar levels of suppressive activity, but the bacterial product with no N-terminal modification had no effect in either assay. Studies by others have shown that N-terminal addition is not necessary for Cpn10 activity. By defining techniques for facile production of molecules with and without immunosuppressive properties, the present studies make it possible to explore mechanisms underlying the distinction between EPF and Cpn10 activity. (C) 2003 Elsevier Inc. All rights reserved.