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Advanced Manufacturing (EUA)

New 2D Hematene Material Shows Promise for Solar Fuel Generation

Publicado em 02 julho 2018

Hematene created by a Rice University-led team is the first known 2D non-van der Waals material. The transmission electron image shows a single sheet of hematene. Scale bar equals 0.5 µm. Image courtesy Shyam Sinha and Peter van Aken/Max Planck Institute for Solid State Research, Stuttgart, Germany

An international team of scientists led by Rice University (Houston) researchers has created a new 2D hematene material, an atomically thin form of the common iron oxide known as hematite, which holds potential for 2D magnetism and efficient light-assisted water splitting. In the wake of the team’s recent discovery of a flat form of gallium, the team’s latest discovery is this new 2D material that the researchers said could be a game-changer for solar fuel generation.

Rice materials scientist Pulickel Ajayan and colleagues extracted 3-atom-thick hematene from common iron ore, and the researchers published their findings May 7 in the journal Nature Nanotechnology. An abstract of the paper can be found at http://dx.doi.org/10.1038/s41565-018-0134-y.

Hematene may be an efficient photocatalyst, especially for splitting water into hydrogen and oxygen, and could also serve as an ultrathin magnetic material for spintronic-based devices, according to the Rice researchers. “Two-dimensional magnetism is becoming a very exciting field with recent advances in synthesizing such materials, but the synthesis techniques are complex and the materials’ stability is limited,” Ajayan said. “Here, we have a simple, scalable method, and the hematene structure should be environmentally stable.”

Ajayan’s lab worked with researchers at the University of Houston and in India, Brazil, Germany and elsewhere to exfoliate the material from naturally occurring hematite using a combination of sonication, centrifugation, and vacuum-assisted filtration. Hematite was already known to have photocatalytic properties, but they are not good enough to be useful, the researchers said.

“For a material to be an efficient photocatalyst, it should absorb the visible part of sunlight, generate electrical charges and transport them to the surface of the material to carry out the desired reaction,” said Oomman Varghese, a co-author of the paper and associate professor of physics at the University of Houston. “Hematite absorbs sunlight from ultraviolet to the yellow-orange region, but the charges produced are very short-lived. As a result, they become extinct before they reach the surface.”

Hematene photocatalysis is more efficient because photons generate negative and positive charges within a few atoms of the surface, the researchers said. By pairing the new material with titanium dioxide nanotube arrays, which provide an easy pathway for electrons to leave the hematene, the scientists found they could allow more visible light to be absorbed.

The researchers also discovered that hematene’s magnetic properties differ from those of hematite. While native hematite is antiferromagnetic, tests showed that hematene is ferromagnetic, like a common magnet. In ferromagnets, atoms’ magnetic moments point in the same direction. In antiferromagnets, the moments in adjacent atoms alternate. Unlike carbon and its 2D form, graphene, hematite is a non-van der Waals material, meaning it’s held together by 3D bonding networks rather than non-chemical and comparatively weaker atomic van der Waals interactions.

“Most 2D materials to date have been derived from bulk counterparts that are layered in nature and generally known as van der Waals solids,” noted co-author Professor Anantharaman Malie Madom Ramaswamy Iyer of the Cochin University of Science and Technology, India. “2D materials from bulk precursors having [non-van der Waals] 3D bonding networks are rare, and in this context hematene assumes great significance.”

According to co-author Chandra Sekhar Tiwary, a former postdoctoral researcher at Rice and now an assistant professor at the Indian Institute of Technology, Gandhinagar, the collaborators are exploring other non-van der Waals materials for their 2D potential.

The research was supported by India’s Ministry of Human Resource Development, the US Army Research Office Multidisciplinary Research Institute, the Air Force Office of Scientific Research, the São Paulo Research Foundation, the T.L.L. Temple Foundation, the John J. and Rebecca Moores Endowment, the State of Texas, Shell International Exploration and Production Inc. and the Neutrino Observatory.

Tech Papers from SME Journals and Manufacturing Letters

These summaries, excerpts, and web links are from recent papers published in the SME Journal of Manufacturing Systems, Journal of Manufacturing Processes, and Manufacturing Letters, which are printed by Elsevier Ltd. and used here with permission.

Part Data Integration in the Shop Floor Digital Twin

In the paper “Part data integration in the Shop Floor Digital Twin: Mobile and cloud technologies to enable a manufacturing execution system,” authors Pedro Daniel Urbina Coronado, Roby Lynn, Wafa Louhichi, Mahmoud Parto, Ethan Wescoat and Thomas Kurfess of the George E. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, cover the advantages of mobile and cloud computing in smart factory environments. Their paper is published online in the Journal of Manufacturing Systems and is available at doi.org/10.1016/j.jmsy.2018.02.002.

The availability of data from a manufacturing operation can be used to enable an increase in capability, adaptability, and awareness of the process. In current cyber/physical systems, data are collected from pieces of manufacturing equipment and used to drive useful change and affect production output. The data gathered typically describe the operating state of the equipment, such as a machine tool, and can be provided using standard protocols. One such protocol, known as MTConnect, is becoming increasingly popular to collect data from machine tools. Other useful data can be collected from production personnel using a Manufacturing Execution System (MES) to monitor process output, consumable usage, and operator productivity. However, MTConnect data and MES data usually reside in separate systems that may be proprietary and expensive.

This paper describes the development and implementation of a new MES, powered by Android devices and cloud computing tools, that combines MTConnect data with production data collected from operators; the proposed MES is particularly suitable for small manufacturing enterprises, as it is low-cost and easily implementable. A case study using the MES to track a production run of titanium parts is presented, and data from the MES are correlated with MTConnect data from a machine tool. This work is integral to realizing a complete digital model of the shop floor, known as the Shop Floor Digital Twin, that can be used for production control and optimization.

Planning Process Parameters for Direct Metal Deposition

Schematic of the DMD fabrication of a functionally graded part. Image courtesy Elsevier Ltd.

The paper “Planning the process parameters for the direct metal deposition of functionally graded parts based on mathematical models,” by authors Jingyuan Yan and Georges M. Fadel of the Department of Mechanical Engineering at Clemson University, Clemson, SC, and Ilenia Battiato of the Department of Energy Resources Engineering of Stanford University, Stanford, CA, discusses the many factors involved in developing DMD processes. Published in Volume 31 of the January 2018 issue of the Journal of Manufacturing Processes, the paper is available online at doi.org/10.1016/j.jmapro.2017.11.001.

In recent years, the need for functionally graded material (FGM) parts has surfaced with the development of material science and additive manufacturing techniques. The Direct Metal Deposition (DMD) process, a metal-based additive manufacturing technique, can locally deposit dissimilar metal powders to produce FGM parts. Yet inappropriate mixing ratio of materials without considering the influence of dilution and overlapping effects among layers and tracks and the variation of material properties can result in inaccurate material composition in the fabricated parts when compared to the desired compositions.

Within such a context, this paper proposes a design method that links the process parameters to the desired composition of the part based on mathematical models. The proposed scheme is illustrated through a case study of fabricating an iron-nickel FGM part with three-dimensional composition variation. Using the proposed method, the process parameters can be planned prior to the manufacturing process, and the material distribution deviation from the desired one can be reduced.

The fast-growing metal-based additive manufacturing is being applied in increasingly diverse industry fields. The promising technologies include powder bed methods such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM), and direct energy deposition methods such as Direct Metal Deposition (DMD) and Laser Engineered Net Shaping (LENS). The powder bed methods are preferred for their ability to fabricate beam or shell structures that need support during the process, whereas the direct energy deposition methods can deposit and melt powders where and when needed. Because of this, the potential of DMD will grow significantly with the ability to design and fabricate functionally graded materials (FGM).