Development of carbonaceous tin-based solder composite achieving unprecedented joint performance

Weight reduction and improved strength are two common engineering goals in the joining sector to benefit transport, aerospace, and nuclear industries amongst others. Here, in this paper, we show that the suitable addition of carbon nanomaterials to a tin-based solder material matrix (C-Solder® supplied by Cametics Ltd.) results in two-fold strength of soldered composite joints. Single-lap shear joint experiments were conducted on soldered aluminium alloy (6082 T6) substrates. The soldering material was reinforced in different mix ratios by carbon black, graphene, and single-walled carbon nanotubes (SWCNT) and benchmarked against the pristine C-solder®. The material characterisation was performed using Vickers micro-indentation, differential scanning calorimetry and nano-indentation, whereas functional testing involved mechanical shear tests using single-lap aluminium soldered joints and creep tests. The hardness was observed to improve in all cases except for the 0.01 wt.% graphene reinforced solders, with 5% and 4% improvements in 0.05 carbon black and SWCNT reinforced solders, respectively. The maximum creep indentation was noted to improve for all solder categories with maximum 11% and 8% improvements in 0.05 wt.% carbon black and SWCNT reinforced ones. In general, the 0.05 wt.% nanomaterial reinforced solders promoted progressive cohesion failure in the joints as opposed to instantaneous fully de-bonded failure observed in pristine soldered joints, which suggests potential application in high-performance structures where no service load induced adhesion failure is permissible (e.g. aerospace assemblies). The novel innovation developed here will pave the way to achieving high-performance solder joining without carrying out extensive surface preparations.

The Polarisation Behaviour of Silver in Potassium Hydroxide Solution at Elevated Temperatures

<p>The Polarisation behaviour of silver in 1 mol kg-1 KOH solution over the temperature range 295-478 K was studied using cyclic voltammetry, potentiostatic, galvanostatic and a.c. impedance techniques. Thermodynamic data for the silver/water system at temperatures up to 573 K is presented in the form of potential-pH diagrams which assist in the interpretation of results at elevated temperatures. The cyclic voltammograms and galvanostatic charging curves indicate the principal changes to be the appearance of additional peaks and arrests, respectively, as the temperature is increased, followed by their disappearance at higher temperatures. The data obtained from cyclic voltammetry and also potentiostatic polarisation are analysed in terms of previously-derived relations for limiting rate control, in particular that due to diffusion. The impedance data are examined using equivalent circuit models from which it is shown that surface roughness of the electrodes has a significant effect on the reaction kinetics over the temperature range studied. It is proposed that substantial changes in the electrochemistry of silver at 478 K are associated with extensive surface roughness that a change in the kinetics of growth of the Ag2O multilayer takes place at elevated temperatures with the rate of nucleation of Ag2O growth centres becoming more important in relation to the rate of solid-state diffusion.</p>

The Polarisation Behaviour of Silver in Potassium Hydroxide Solution at Elevated Temperatures

<p>The Polarisation behaviour of silver in 1 mol kg-1 KOH solution over the temperature range 295-478 K was studied using cyclic voltammetry, potentiostatic, galvanostatic and a.c. impedance techniques. Thermodynamic data for the silver/water system at temperatures up to 573 K is presented in the form of potential-pH diagrams which assist in the interpretation of results at elevated temperatures. The cyclic voltammograms and galvanostatic charging curves indicate the principal changes to be the appearance of additional peaks and arrests, respectively, as the temperature is increased, followed by their disappearance at higher temperatures. The data obtained from cyclic voltammetry and also potentiostatic polarisation are analysed in terms of previously-derived relations for limiting rate control, in particular that due to diffusion. The impedance data are examined using equivalent circuit models from which it is shown that surface roughness of the electrodes has a significant effect on the reaction kinetics over the temperature range studied. It is proposed that substantial changes in the electrochemistry of silver at 478 K are associated with extensive surface roughness that a change in the kinetics of growth of the Ag2O multilayer takes place at elevated temperatures with the rate of nucleation of Ag2O growth centres becoming more important in relation to the rate of solid-state diffusion.</p>

Deciphering complex groundwater age distributions and recharge processes in a tropical and fractured volcanic aquifer system

Groundwater recharge in highly-fractured volcanic aquifers remains poorly understood in the humid tropics, whereby rapid demographic growth and unregulated land use change are resulting in extensive surface water pollution and a large dependency on groundwater extraction. Here we present a multi-tracer approach including δO-δH, H/He, and noble gases within the most prominent multi-aquifer system of central Costa Rica, with the objective to assess dominant groundwater recharge characteristics and age distributions. We sampled wells and large springs across an elevation gradient from 868 to 2,421 m asl. Our results suggest relatively young apparent ages ranging from 0.0±3.2 up to 76.6±9.9 years. Helium isotopes R/RA (0.99 to 5.4) indicate a dominant signal from the upper mantle across the aquifer. Potential recharge elevations ranged from ~1,400 to 2,650 m asl, with recharge temperatures varying from ~11°C to 19°C with a mean value of 14.5±1.9°C. Recharge estimates ranged from 129±78 to 1,605±196 mm/yr with a mean value of 642±117 mm/yr, representing 20.1±4.0% of the total mean annual rainfall as effective recharge. The shallow unconfined aquifer is characterised by young and rapidly infiltrating waters, whereas the deeper aquifer units have relatively older waters. These results are intended to guide the delineation and mapping of critical recharge areas in mountain headwaters to enhance water security and sustainability in the most important headwater dependent systems of Costa Rica.

Development and testing of carbonaceous tin-based solder composites achieving unprecedented joint performance

Weight reduction and improved strength are two common engineering goals in the joining sector to benefit various engineering sectors ranging from transport, aerospace, nuclear to many others. Here, in this paper, we show that the suitable addition of carbon nanomaterials to a tin-based solder material matrix (C-Solder® supplied by Cametics Ltd.) results in two fold strength of soldered composite joints. Single-lap shear joint experiments were conducted on soldered aluminium alloy (6082 T6) substrates. The soldering material was reinforced in different mix ratios (0.01 wt% and 0.05 wt%) by carbon black, graphene and single-walled carbon nanotubes. and benchmarked against the pristine C-solder®. The material characterisation was performed using Vickers micro-indentation, differential scanning calorimetry and nano-indentation whereas functional testing involved mechanical shear tests using single-lap aluminium soldered joints and creep tests. The 0.05 wt.% nanomaterials reinforced solders promoted progressive cohesion failure in the joints as opposed to instantaneous fully disbond failure observed in pristine soldered joints, which suggests potential application in high performance structures where no service load induced adhesion failure is permissible (e.g., aerospace assemblies). The novel innovation developed here will pave the way to achieving low-cost high-performance solder joining without carrying out extensive surface preparations.

Comparative studies on the microstructure and corrosion behaviour of forged and SLM processed 316L stainless steel

The corrosion behaviour of forged and SLM (Selective Laser Melting) processed 316L samples was investigated in a 3.5% NaCl solution at neutral and light acidic pH. The influence of the oxygen concentration in the testing solution on the corrosion resistance of the alloy was also proved. This made it possible to qualitatively evaluate the influence of the additive manufacturing process on the microstructure of the 316L alloy in comparison to that of the forged steel. Therefore, the logarithmic polarisation curves generated during the electrochemical investigations were compared, especially in respect to the corrosion potential respectively corrosion current density. The results showed that the corrosion resistance of the 3D-printed samples was inferior to that of the forged 316L. Instead of the pitting corrosion that often appears during exposure of the forged material to chloride containing media, the SLM processed material exhibited rather an extensive surface attack. The microscopic examination of the samples revealed large differences in porosity between the microstructures obtained by means of the two manufacturing methods, whereby the 3D-printed samples exhibited a larger number of voids.

Huts and stone arrangements at Hilary Creek, western Queensland: Recent fieldwork at an Australian Aboriginal site complex

This paper reports on an Aboriginal site complex, incorporating hut structures, ceremonial stone arrangements, an extensive surface artefact assemblage of lithics and mussel shell, and a silcrete quarry, located along Hilary Creek, a tributary of the Georgina River in western Queensland, Australia. At least two phases of occupation are indicated. The most recent huts have their collapsed organic superstructure still present, while those of a presumably earlier phase are distinguished as bare, circular patches of earth which are conspicuous amongst the ubiquitous gibber, with or without stone bases, and lacking any collapsed superstructure. Immediately adjacent to the huts and also a few hundred metres away are clusters of small stone arrangements, and about 2 km to the southwest, along the same creekline, is another series of larger, more substantial stone arrangements; these features speak to the importance of the general Hilary Creek area for ceremonial purposes. Radiocarbon dating reveals use of the Hilary Creek complex dates to at least 300 years ago; the absence of any European materials suggests it was likely not used, or only used very sporadically, after the 1870s when pastoralists arrived in the area, and when traditional lifeways were devastated by colonial violence.

Rapid formation of an ice doline on Amery Ice Shelf, East Antarctica

&lt;p&gt;Surface meltwater accumulating on Antarctica&amp;#8217;s floating ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to enhanced ice discharge from the continent. Surface melting in Antarctica is predicted to increase significantly during coming decades, but the implications for ice shelf stability are unknown. We are still learning how meltwater forms, flows and alters the surface, and that rapid water-driven changes are not limited to summer. The southern Amery Ice Shelf in East Antarctica already has an extensive surface meltwater system and provides us with an opportunity to study melt processes in detail. We present high-resolution satellite data (imagery, ICESat-2 altimetry and elevation models from WorldView stereo-photogrammetry) revealing an abrupt change extending across ~60 km&lt;sup&gt;2&lt;/sup&gt; of the ice shelf surface in June 2019 (midwinter). We interpret this as drainage of an englacial lake through to the ocean below in less than three days. This left an uneven depression in the ice shelf surface, 11 km&lt;sup&gt;2&lt;/sup&gt; in area and as much as 80 m deep, with a bed of fractured ice: an &amp;#8220;ice doline&amp;#8221;. The englacial lake had lain beneath the perennially ice-covered portion of a 20 km&lt;sup&gt;2&lt;/sup&gt; meltwater lake. The reduced mass loading on the floating ice shelf after the drainage event resulted in flexure, with uplift of up to 36 m around the former lake. Applying an elastic flexural model to the uplift profiles suggests the loss of 0.75&amp;#160;km&lt;sup&gt;3 &lt;/sup&gt;of water to the ocean. In summer 2020, we observed meltwater accumulating in a new lake basin created by the flexure. ICESat-2 observations profiled a new narrow meltwater channel (20&amp;#160;m wide and 3&amp;#160;m deep), rapidly incised inside the doline as meltwater spilled over from the new lake and started refilling the depression. This study demonstrates how high-resolution geodetic measurements from ICESat-2 and WorldView can explore critical fine-scale ice shelf processes. The insights gained will greatly improve our ability to model these processes, ultimately improving the accuracy of our projections.&lt;/p&gt;

Temperate Oligocene surface ocean conditions offshore Cape Adare, Ross Sea, Antarctica

Antarctic continental ice masses fluctuated considerably in size during the elevated atmospheric CO2 concentrations (~ 600–800 ppm) of the Oligocene “coolhouse”. To evaluate the role of ocean conditions to the Oligocene ice sheet variability requires understanding of past ocean conditions around the ice sheet. While warm ocean conditions have been reconstructed for the Oligocene Wilkes Land region, questions arise on the geographical extent of that warmth. Currently, we lack data on surface ocean conditions from circum-Antarctic locations, and ice-proximal to ice-distal temperature gradients are poorly documented. In this study, we reconstruct past surface ocean conditions from glaciomarine sediments recovered from the Deep Sea Drilling Project (DSDP) Site 274, offshore the Ross Sea continental margin. This site offshore Cape Adare is ideally located to characterise the Oligocene regional surface ocean conditions, as it is situated between the colder, ice-proximal Ross Sea continental shelf, and the warm-temperate Wilkes Land Margin in the Oligocene. We improve the existing age model of DSDP Site 274 using integrated bio- and magnetostratigraphy. Subsequently, we analyse dinoflagellate cyst assemblages and lipid biomarkers (TEX86) to reconstruct surface paleoceanographic conditions during the Oligocene (33.7–25.4 Ma). Both TEX86-based sea surface temperature (SST) and microplankton results show temperate (10–17 °C ± 5.2 °C) surface ocean conditions at Site 274 throughout the Oligocene. Increasingly similar oceanographic conditions between offshore Wilkes Land margin and Cape Adare developed towards the late Oligocene (26.5–25.4 Ma), likely in consequence of the widening of the Tasmanian Gateway, which resulted in more interconnected ocean basins and frontal systems. To maintain marine terminations of terrestrial ice sheets in a proto-Ross Sea with as warm offshore SST as our data suggests, requires a strong ice flux fed by intensive precipitation during colder orbital states in the Antarctic hinterland, but with extensive surface melt of terrestrial ice during warmer orbital states.