Thirty two boehmites, synthesized at temperatures ranging from room temperature to 300°C, were examined by scanning electron microscopy, transmission electron microscopy, electron diffraction, X-ray powder diffraction, differential thermal analysis, and infrared spectroscopy. The results show that boehmite exhibits a continuous gradation in crystallite size ranging from single octahedral layers or a few unit cells to about 65 unit cells in the y-direction. This conclusion suggests that the term pseudoboehmite is inappropriate for finely crystalline boehmite. Finely crystalline boehmite contains more sorbed water than coarsely crystalline boehmite; this water is commonly intercalated between octahedral layers, usually randomly but sometimes regularly. The regularly interstratified boehmite gives rise to a diffuse “long spacing” X-ray diffraction reflection. Calculated 020 X-ray diffraction peaks approximate closely those observed experimentally when a range of crystallite sizes is taken into account.

The crystal structure of a synthetic boehmite sample has been refined to an R of 0.047 in the space group Amam from X-ray powder diffraction data. Inclusion of hydrogen atoms and/or refinement in the space group A21am gave poorer results. Cell dimensions were determined as a = 3.6936 (± 0.0003), b = 12.214 (± 0.001), c = 2.8679 (± 0.0003) Å. All Al-O(OH) distances lie between 1.88 and 1.91 Å. Shared octahedral edges are 2.51–2.52 Å, and unshared octahedral edges are 2.86–2.87 Å, in excellent agreement with those for layered silicates. The O-H … O distance between contiguous octahedral sheets is 2.71 Å. The computed X-ray pattern matches closely with the experimental pattern, indicating the degree to which the crystal structure has been determined.

Time discounting – the degree to which individuals value current more than future resources – is an important component of natural resource conservation. As a response to climate change impacts in island communities, such as sea level rise, discounting the future can be a rational response due to increased stress on natural resources and uncertainty about whether future generations will have the same access to the same resources. By incorporating systematic responses of discount rates into models of resource conservation, realistic expectations of future human responses to climate change and associated resource stress may be developed. This paper illustrates the importance of time discounting through a theoretical agent-based model of resource use in island communities. A discount rate change can dramatically change projections about future migration and community-based conservation efforts. Our simulation results show that an increase in discount rates due to a credible information shock about future climate change impacts is likely to speed resource depletion. The negative impacts of climate change are therefore likely to be underestimated if changes in discount rates and emerging migration patterns are not taken into account.

The current work provides an overview of the state-of-the-art in polymer and metal additive manufacturing and provides a progress report on the science and technology behind gradient metal alloys produced through laser deposition. The research discusses a road map for creating gradient metals using additive manufacturing, demonstrates basic science results obtainable through the methodology, shows examples of prototype gradient hardware, and suggests that Compositionally Graded Metals is an emerging field of metallurgy research.

In this study, compact Charpy impact testing was used to investigate the effect of processing history and dendrite morphology of bulk metallic glass matrix composites (BMGMCs) on impact toughness. Composite samples were fabricated via suction casting and semisolid forging, and the results were compared with crystalline alloys in the same geometry. A strong dependence on processing was observed, with samples exhibiting up to a 30-fold increase in impact toughness depending on processing and microstructure. Provided that attention is paid to processing techniques, BMGMCs are shown to have properties that equal or surpass some conventionally used crystalline alloys. These properties invite further exploration of these materials in structural applications.

A major drawback in using bulk metallic glasses (BMGs) as structural materials is their extremely poor fatigue performance. One way to alleviate this problem is through the composite route, in which second phases are introduced into the glass to arrest crack growth. In this paper, the fatigue crack growth behavior of in situ reinforced BMGs with crystalline dendrites, which are tailored to impart significant ductility and toughness to the BMG, was investigated. Three composites, all with equal volume fraction of dendrite phases, were examined to assess the influence of chemical composition on the near-threshold fatigue crack growth characteristics. While the ductility is enhanced at the cost of yield strength vis-à-vis that of the fully amorphous BMG, the threshold stress intensity factor range for fatigue crack initiation in composites was found to be enhanced by more than 100%. Crack blunting and trapping by the dendritic phases and constraining of the shear bands within the interdendritic regions are the micromechanisms responsible for this enhanced fatigue crack growth resistance.