Alcoa (United States)

In preparation for Issue 2, the Journal’s editorial board reached out to its network of organizers to invite short statements on their current work. We asked that these reflections address the guiding questions for this issue, including how their work intersects with social movements, unions or electoral politics, their experiences of working in and against authoritarianism, and their efforts to defend or promote democracy. The following statements from colleagues across three continents offer insights from diverse organizing networks and roles: an organizer turned local official in Hungary; a director of Faith in Action affiliates for Central America; an immigration organizer for the African diaspora in Detroit, and a lead organizer for Berlin, representing one of the largest German organizing networks.

Abstract The term alumina hydrates or hydrated aluminas is used in industry and commerce to designate aluminum hydroxides. These compounds are true hydroxides and do not contain water of hydration. The most well‐defined crystalline forms are the trihydroxides, Al(OH) 3 : gibbsite, bayerite, and nordstrandite. In addition, two aluminum oxide–hydroxides, AlO(OH), boehmite and diaspore, have been clearly defined. The terms gelatinous alumina or alumina gel cover a range of products in which colloidal hydrated alumina is the predominant solid phase. Structural order varies from x‐ray indifferent (amorphous) to some degree of crystallinity. Apart from the crystalline forms, aluminum hydroxide often forms a gel. Gel products have considerable technical use. Aluminum hydroxides are technically the most widely used members of the alumina chemicals family. The most important source of aluminum hydroxides is the bauxite refining plant (Bayer process) for alumina production. Several commercial grades of aluminum hydroxide are produced. Hydroxide grades can be surface‐treated to modify dispersion behavior and rheological properties. Aluminum hydroxides are minimally absorbed by the body. Death upon ingestion occurs from intestinal blockage rather than systemic aluminum toxicity. In recognition of the possible adverse effects of long‐term exposure to alumina dusts, threshold limit values have been established by the ACGIH. Aluminum hydroxide and aluminum hydroxide oxide are reported in EPA TSCA inventory.

PFC emissions from aluminum smelting are characterized by two mechanisms, high-voltage generation (HV-PFCs) and low-voltage generation (LV-PFCs). HV-PFCs are emissions produced when a cell is undergoing an anode effect, typically >8 V. Modern cell technology has enabled pre-bake smelters to achieve low anode effect rates and durations, thereby lowering their HV-PFC emissions. LV-PFCs are the emissions produced when the cell voltage is below 8 V. Lacking a clear process signal to act upon, LV-PFCs can be difficult to treat. To tackle this issue, Alcoa has conducted sampling on individual electrolysis cells, during which continuous process and emissions data, as well as periodic bath samples, were collected. In the sampled cells, a variety of conditions were observed where LV-PFCs were generated. Understanding what was occurring at the cell level allowed for the identification of opportunities for process improvement, both for the reduction of LV-PFC emissions and cell performance.KeywordsLow-voltage PFCProcess improvementEmission measurements

Mechanically passive exoskeletons may be a practical and affordable solution to meet a growing clinical need for continuous, home-based movement assistance. We designed, fabricated, and preliminarily evaluated the performance of a wearable, passive, cam-driven shoulder exoskeleton (WPCSE) prototype. The novel feature of the WPCSE is a modular spring-cam-wheel module, which generates an assistive force that can be customized to compensate for any proportion of the shoulder elevation moment due to gravity. We performed a benchtop experiment to validate the mechanical output of the WPCSE against our theoretical model. We also conducted a pilot biomechanics study (eight able-bodied subjects) to quantify the effect of a WPCSE prototype on muscle activity and shoulder kinematics during three shoulder movements. The shoulder elevation moment produced by the spring-cam-wheel module alone closely matched the desired theoretical moment. However, when measured from the full WPCSE prototype, the moment was lower (up to 30%) during positive shoulder elevation and higher (up to 120%) during negative shoulder elevation compared to the theoretical moment, due primarily to friction. Even so, a WPCSE prototype, compensating for about 25% of the shoulder elevation moment due to gravity, showed a trend of reducing root-mean-square electromyogram magnitudes of several muscles crossing the shoulder during shoulder elevation and horizontal adduction/abduction movements. Our results also showed that the WPCSE did not constrain or impede shoulder movements during the tested movements. The results provide proof-of-concept evidence that our WPCSE can potentially assist shoulder movements against gravity.

Producing aluminum alloys in the Hall-Héroult cells can be an economical alternative to meet ever-increasing light-weight alloy applications. Alcoa has carried out comprehensive studies over the past years using the Hall cells to produce aluminum–silicon, aluminum–scandium, and aluminum–rare earth alloys. The studies were performed in 300 A lab scale cells with multiple electrolysis campaigns for each alloy with kilo scale of alloys produced. For the Al–Si, over 7.0% Si foundry alloy was produced by feeding the Hall cell with alumina–sand mixture. For the Al–Sc, a master alloy of 3.5% Sc was produced by introducing scandium oxide and alumina. For Al–Re, 8.5% Re alloy was obtained by feeding rare earth oxides and alumina. This paper summarizes our lab scale studies for each of the Al alloy systems. Electrolysis operating conditions and key parameters were obtained which are considered a critical step toward commercial application in producing such alloys in the Hall-Héroult cells.KeywordsElectrolytic depositionHall-Héroult cellsAluminum alloysAluminum–silicon foundry alloyAluminum–scandium alloyAluminum–rare earth alloy

Thepresent work focuses on the gasification of a single carbon-anodeparticle with CO2, using a detailed reaction-transportmodel based on the reaction intrinsic kinetics and transport of gaseousspecies. The model includes the mass conservation equations for thegas components and solid carbon particles, resulting in a set of nonlinearpartial differential equations, being solved using numerical techniques.The model may predict the gas generation rate, the gas compositions,and the carbon consumption rate during the gasification of a carbonparticle. Five kinetic models were compared to describe the gasificationbehavior of carbon particles. It was found that the random pore model(RPM) provided the best description of the reactivity of anode particles.The model also predicted the particle shrinkage during the gasificationprocess. The model was validated using experimental results obtainedwith different particle size ranges, being gasified with CO2 at 1233 K. The experiments were performed in a thermogravimetricanalyzer (TGA). Good agreement between the model results and the experimentaldata showed that this approach could quantify with success the gasificationkinetics and the gas distribution within the anode particle. In addition,the Langmuir–Hinshelwood (L–H) model is used in orderto capture the inhibition effect of carbon monoxide on the gasificationreaction. The effectiveness factor and Thiele modulus simulated forvarious particle sizes helped assess the evolution of the relativedominance of diffusion and chemical reactions during the gasificationprocess.