Final Voids Research Articles

The influences of Ag nanoparticles on voids growth and solderability about Sn3.0Ag0.5Cu/Cu solder joint

Although Sn3.0Ag0.5Cu solder (SAC305) has higher reliability, there are a large number of harmful voids in solder joints. Larger voids can reduce thermal conductivity of solder joints. However, as a microstructure growth inhibitor, the influences of Ag nanoparticles on voids growth are not clear at present. Herein, we prove that Ag nanoparticles can increase SAC305 solderability, but promote voids growth. Ag nanoparticles and SAC305 solder paste were mixed by mechanical stirring for 0.5 h. Next, SAC305-xAgP (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 wt%) was obtained. The results indicated that solder solderability was improved increasingly with Ag nanoparticles addition. The lower the amount of nanoparticles added, the greater the final loss. After being aged at 100 °C for 150 h, the voids stopped growing. Due to the violent reaction between Ag nanoparticles and flux, the final voids growth rate became faster, and the average voids size changed from 14.34% to 24.91%.

The final voids: the ambiguity of emptiness in Australian coal mine rehabilitation

AbstractIn the Australian coal mining region of the Hunter Valley, a political contest is taking shape around the mine final voids, the large holes that are left in the ground after mining has finished. This article describes an effort led by the coal lobby to fill the voids with imaginative and hopeful futures, described as a process of techno‐speculative deferral. In contrast, local environmentalists (Indigenous and non‐Indigenous) are drawing on dispossession and ongoing extractivism to craft an affective politics of loss around these spaces. The article considers the particular issues around the mine final voids as metonyms of the Anthropocene in order to caution against approaches which celebrate the hopefulness of ruins. Instead, the void's negativity presents an alternative analytical starting point for a politics of the Anthropocene, one which derives from Indigenous dispossession and expands to counter ongoing ruination.

Voids in cosmological simulations over cosmic time

We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids evolution is traced by matching voids between successive snapshots (by analogy to halo merger trees). We apply the new method to a cosmological simulation of a standard LambdaCDM cosmological model and study evolution of basic properties of typical voids (with effective radii between 6Mpc/h and 20Mpc/h at redshift z=0) such as volumes, shapes, matter density distributions and relative alignments. The final voids at low redshifts appear to retain a significant part of the configuration acquired in initial conditions. Shapes of voids evolve in a collective way which barely modifies the overall distribution of the axial ratios. The evolution appears to have a weak impact on mutual alignments of voids implying that the present state is in large part set up by the primordial density field. We present evolution of dark matter density profiles computed on iso-density surfaces which comply with the actual shapes of voids. Unlike spherical density profiles, this approach enables us to demonstrate development of theoretically predicted bucket-like shape of the final density profiles indicating a wide flat core and a sharp transition to high-density void walls.

Study of carbonate sedimentary rocks as engineered dry fills

During feasibility studies for the planned 75 km long Arabian Canal project, Dubai, United Arab Emirates, the reuse of a variety of calcareous sedimentary rocks was investigated so as to inform the specification for bulk earthworks operations associated with plot development adjoining the canal route. Laboratory and field testing were undertaken through a series of large-scale earthwork compaction trials. The practicalities were investigated of compacting weak rocks at natural moisture content, taking into account that in situ moisture contents are typically dry of the optimum. With such large earthworks volumes, maximum thickness of fill layer, high productivity and consistent compaction were key considerations. Fundamental parameters controlling compaction were assessed, such as particle density, grading, and applied compactive effort, degree of saturation and final air voids, along with the performance of the fills. The results enabled the specification for the bulk earthworks to be developed making use of permissible air voids, and so permitting maximum potential for reuse of all fill types without the addition of water.

Cover Picture: Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals (Adv. Funct. Mater. 11/2006)

AbstractHollow nanocrystals have been synthesized through a mechanism analogous to the Kirkendall Effect. When a cobalt nanocrystal reacts with sulfur in solution, the outward diffusion of cobalt atoms is faster than the inward diffusion of sulfur atoms through the sulfide shell. The dominating outward diffusion of cobalt cations produces vacancies that can condense into a single void in the center of the nanocrystal at high temperatures. This process provides a general route to the synthesis of hollow nanostructures of a large number of compounds and is described in the Full Paper by A. P. Alivisatos and co‐workers on p. 1389.Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature‐dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell‐size statistics and transmission electron microscopy images of as‐grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system.

Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals

AbstractFormation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature‐dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell‐size statistics and transmission electron microscopy images of as‐grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system.

Aquatic invertebrates in final void water bodies at an open‐cut coal mine in central Queensland

Abstract We describe the diversity of aquatic invertebrates colonising water‐filled final voids produced by an open‐cut coal mine near Moura, central Queensland. Ten disused pits that had been filled with water from <1 year to 22 years prior to the survey and three nearby ‘natural’ water bodies were sampled in December 1998 and again in March 1999. All invertebrates collected were identified to family with the exception of oligochaetes, cladocerans, ostracods and copepods, which were identified to these coarser taxonomic levels. Sixty‐two taxa were recorded from >20 000 individuals. The greatest familial richness was displayed by the Insecta (33 families) followed by the mites (Acari) with 12 families. While natural water bodies held the greatest diversity, several mine pits were almost as rich in families. Classification analyses showed that natural sites tended to cluster together, but the groupings did not clearly exclude pit sites. Mining pits that supported higher diversity tended to be older and had lower salinity (<2000 µS/cm); however, salinity in all water bodies varied with rainfall conditions. We conclude that ponds formed in final voids at this mine have the potential to provide habitat for many invertebrate taxa typical of lentic inland water bodies in central Queensland.

Metal-ceramic interfaces: Sources and sinks for mass transfer

The closure of interface voids during metal-ceramic diffusion bonding studied for a number of metal foils joined to TZP zirconia. In the case of bonds to large grained Cu and Ni foils the final voids to close on the interface are found to rest on grain boundaries in the metal foil where they intersect the metal-ceramic interface. Bonds made to foils of smaller grain sized Fe and Ni do not show this behaviour. When the final interface voids occur at the intersections of metal grain boundaries with the metal-ceramic interface, voids are also seen to nucleate on grain boundaries within the metal foil away from the interface. These observations suggest that the metal-ceramic interface does not act as an efficient vacancy sink during interface formation. Possible mass transfer routes are proposed to allow vacancies to sink on metal grain boundaries within the foil during interface void closure. The nucleation of voids within the metal foil during diffusion bonding is possibly caused by interactions of creep and diffusional mass transfer during bonding.

DENSITY OF ASPHALT CONCRETE - HOW MUCH IS NEEDED?

Density is one of the most important parameters in construction of asphalt mixtures. A mixture that is properly designed and compacted will contain the optimum amount of air voids. Because density of an asphalt mixture varies throughout its life, the voids must be low enough initially to prevent permeability of air and water and high enough after a few years of traffic to prevent rutting caused by plastic flow. There are three primary methods of specifying density: (a) percent of control strip, (b) percent of laboratory density, and (c) percent of theoretical maximum density (TMD). If used correctly, all three methods can result in satisfactory compaction. The initial in-place air voids must be below approximately 8% and are determined by comparing bulk density and TMD. The final in-place air voids, which must be above approximately 3%, are estimated by comparing the bulk density of laboratory-compacted samples and the TMD. The two methods that have been used to measure bulk density of asphalt mixture are physical measurements of cores and use of the nuclear gauge. The nuclear gauge is fast and nondestructive but is not as accurate as the core method.