Douglas P. Hart

Building on established work on aluminum-water reactions for hydrogen production, this study investigates the reactivity of activated aluminum in aqueous ammonia. Unlike pure water, ammonium hydroxide introduces a dual role in its reaction with aluminum as both solvent and gas promoter, enabling the generation of more potential energy per unit volume of solvent, a crucial feature for compact, energy-dense-seeking applications, such as underwater devices. Experimental results quantify the benefits of using ammonia solution at varied hydrostatic pressures in a buoyancy engine. The reaction mechanism is discussed in terms of the intermolecular interactions between activated aluminum and ammonia molecules within both aqueous and ionic solutions.

A buoyancy engine design is presented that utilizes an aluminum/oil fuel paste which is reacted with a 30% ammonia solution to produce ammonia and hydrogen gases, aluminum oxyhydroxide (boehmite) and steam. Buoyancy is achieved by using the generated gases to inflate two bladders; one for primary buoyancy control and the other for vehicle moment control. Although the use of a compressible gas for buoyancy is highly inefficient, the aluminum fuel used by this system is more than forty times as energy dense as lithium batteries, resulting in a three-fold reduction in overall weight and volume compared to conventional hydraulic buoyancy engines. Moreover, since the fuel paste is incompressible and reacts with the ammonia solution on contact, the engine can be entirely housed within a small flooded hull section while remaining mechanically simple and robust.

Presented is an evaluation of the carbon footprint and costs associated with hydrogen production via the aluminum-water reaction (AWR), identifying an optimized scenario that achieves 1.45 kgCO 2 equiv per kg of hydrogen produced. U.S.-based data are used to compare results with conventional production methods and to assess hydrogen use in fuel-cell passenger vehicles. In the optimized scenario, major contributors include the use of recycled aluminum (0.38 kgCO 2 equiv), aluminum processing (0.45 kgCO 2 equiv), and alloy activator recovery (0.57 kgCO 2 equiv). A cost analysis estimates hydrogen production at $9.2/kg when using scrap aluminum, alloy recovery, and recycling thermal energy, aligning with current green hydrogen prices. Reselling reaction byproducts such as boehmite could generate revenue 5.6 times greater than input costs, enhancing economic feasibility. The cradle-to-grave assessment suggests that aluminum fuel, as an energy carrier for hydrogen distribution and fuel cell vehicle applications, offers a low-emission and economically viable pathway for clean energy deployment.

When activated, aluminum reacts with water to generate hydrogen gas, heat, and aluminum oxyhydroxide, a non-toxic and valuable commodity. This process serves as an efficient and cost-effective means of producing and transporting both hydrogen and thermal energy. The study presented here focuses on recovering a gallium-indium eutectic utilized as a surface coating to induce aluminum’s reactivity in water. The findings indicate that the addition of very low concentrations (0.02 M) of imidazole to seawater leads to rapid reactions being completed in under 10 min, enabling the retrieval and reuse of over 90% of the relatively costly gallium-indium eutectic and producing 99% of the anticipated hydrogen output based on the aluminum’s mass. Additionally, conducting the reaction at elevated temperatures ensures the swift and complete reaction of aluminum in saltwater.

This paper explores maneuvering strategies for range-based cooperative localization between submerged marine elements without access to the sea surface. The undersea environment presents significant challenges to effective communication and navigation due to the rapid attenuation of electromagnetic signals. Acoustics presents a viable option for communication at the cost of reduced bandwidth and transmission speeds compared to standard communication and navigation signals on land. Range-based techniques utilizing a single transducer offer advantages over an array of transducers in cost and complexity. Still, they must overcome the need for bearing information through iterative range measurements converging on a reliable localization estimate. This task becomes more difficult in a cooperative navigation setting due to the assumption that elements within such a scheme are in constant relative motion. For our analysis, we assume two undersea vehicles communicate via acoustic modems to cooperatively navigate to a known target location. A ’leader’ vehicle equipped with superior navigation sensors supports a ’follower’ vehicle less equipped for self-localization. This work analyzes multiple maneuvering strategies for their impact on cooperative localization estimates, energy consumption, and how they translate to real-world environments and vehicle dynamics.

The ocean is vast, complex, and increasingly threatened by human activities. There is an urgent need to find complementary ways to gather extensive information and promote the comprehensive understanding and management of the ocean. In addition, as coastal populations grow, these regions are becoming more vulnerable to hazardous natural events. The global network of subsea cables provides an opportunity to support a holistic ocean observation system, in particular, to anticipate and provide warning about hazards and to prepare responses to catastrophic events. Large-scale and widespread ocean monitoring may also enable the oversight and tracing of global phenomena that have local impacts.