Firebreaks for prescribed burning

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Preparation of Radiation-grafted Powders for use as Anion Exchange Ionomers in Alkaline Polymer Electrolyte Fuel Cells

A novel alkaline exchange ionomer (AEI) was prepared from the radiation-grafting of vinylbenzyl chloride (VBC) onto poly(ethylene-co-tetrafluoroethylene) [ETFE] powders with powder particle sizes of less than 100 μm diameter. Quaternisation of the VBC grafted ETFE powders with trimethylamine resulted in AEIs that were chemically the same as the ETFE-based radiation-grafted alkaline anion exchange membranes (AAEM) that had been previously developed for use in low temperature alkaline polymer electrolyte fuel cells (APEFC). The integration of the AEI powders into the catalyst layers (CL) of both electrodes resulted in a H2/O2 fuel cell peak power density of 240 mW cm−2 at 50 °C (compared to 180 mW cm−2 with a benchmark membrane electrode assembly containing identical components apart from the use of a previous generation AEI). This result is promising considering the wholly un-optimised nature of the AEI inclusion into the catalyst layers

Integrated motor drives: state of the art and future trends

With increased need for high power density, high efficiency and high temperature capabilities in Aerospace and Automotive applications, Integrated Motor Drives (IMD) offers a potential solution. However, close physical integration of the converter and the machine may also lead to an increase in components temperature. This requires careful mechanical, structural and thermal analysis; and design of the IMD system. This paper reviews existing IMD technologies and their thermal effects on the IMD system. The effects of the power electronics (PE) position on the IMD system and its respective thermal management concepts are also investigated. The challenges faced in designing and manufacturing of an IMD along with the mechanical and structural impacts of close physical integration is also discussed and potential solutions are provided. Potential converter topologies for an IMD like the Matrix converter, 2-level Bridge, 3-level NPC and Multiphase full bridge converters are also reviewed. Wide band gap devices like SiC and GaN and their packaging in power modules for IMDs are also discussed. Power modules components and packaging technologies are also presented

Radiation-grafted anion-exchange membranes: the switch from low- to high-density polyethylene leads to remarkably enhanced fuel cell performance

Herein we detail the development of a new high-density polyethylene-(HDPE)-based radiation-grafted anion-exchange membrane (RG-AEM) that achieves a surprisingly high peak power density and a low in situ degradation rate (with configurations tailored to each). We also show that this new AEM can be successfully paired with an exemplar non-Pt-group cathode. Broader context: A primary motivation for the development of anion-exchange membrane (AEM) fuel cells (AEMFCs) is the broader range of sustainable, non-precious-metal catalysts that are feasible; if costs are lowered enough, AEMFCs would be deployable in a range of stationary power sectors (e.g. back-up and off-grid). However, as the performance of AEMFCs typically drop when Pt-based electrodes are replaced with non-Pt types, it is essential that the highest performing polyelectrolytes are developed, both membranes and ionomers (the latter incorporated to impart ionic conductivity in the electrodes). The findings with the high conductivity AEM reported herein will also be of interest to developers of AEMs for metal–air and redox-flow batteries, electrolysers (both H2O → H2 and CO2 → high-value chemicals and fuels), and salinity gradient power.</p

Reliability Study Of Au-In Transient Liquid Phase Bonding For Sic Power Semiconductor Packaging

Transient liquid phase (TLP) bonding is a promising advanced die-attach technique for wide-bandgap power semiconductor and high-temperature packaging. TLP bonding advances modern soldering techniques by raising the melting point to over 500°C without detrimental high-lead materials. The bond also has greater reliability and rigidity due in part to a bonding temperature of 200°C that drastically lowers the peak bond stresses. Furthermore, the thermal conductivity is fractionally increased 67 % while the bond thickness is substantially reduced, lowering the thermal resistance by an order of magnitude or more. It is observed that Au-In TLP bonds exude excellent electrical reliability against thermal cycling degradation if designed properly as experimentally confirmed in this work. © 2011 IEEE

Comparison of Au-In Transient Liquid Phase Bonding Designs for SiC Power Semiconductor Device Packaging

Transient liquid phase (TLP) bonding is an advanced die-attach technique for wide-bandgap power semiconductor and high-temperature packaging. TLP bonding advances current soldering techniques by raising the melting point to over 500 °C without detrimental high-lead materials. The bond also has greater reliability and rigidity due in part to a bonding temperature of 200 °C that drastically lowers the peak bond stresses. Furthermore, the thermal conductivity is increased 67 % while the bond thickness is substantially reduced, lowering the thermal resistance by an order of magnitude. This work provides an in-depth examination of the TLP fabrication methodology utilizing mechanical and thermal experimental characterization data along with thermal reliability results

The First High-Performing Commercial PGM-free Cathodes for Anion Exchange Membrane Fuel Cells

To reduce the cost of fuel cell stacks and systems, it is important to create commercial catalysts that are free of platinum group metals (PGMs). To do this, such catalysts must have very high activity, but also have the correct microstructure to facilitate the transport of reactants and products. Here, we show a high-performing commercial oxygen reduction catalyst that was specifically developed for operation in alkaline media and is demonstrated in the cathode of operating anion-exchange membrane fuel cells (AEMFCs). With H2/O2 reacting gases, AEMFCs made with Fe–N–C cathodes achieved a peak power density exceeding 2 W cm−2 (>1 W cm−2 with H2/air) and operated with very good voltage durability for more than 150 h. These AEMFCs also realized an iR-corrected current density at 0.9 V of 100 mA cm−2. Finally, in a second configuration, Fe–N–C cathodes paired with low-loading PtRu/C anodes (0.125 mg PtRu per cm2, 0.08 mg Pt per cm2) demonstrated a specific power of 10.4 W per mg PGM (16.25 W per mg Pt)

Thermo-Mechanical Characterization Of Au-In Transient Liquid Phase Bonding Die-Attach

Semiconductor die-attach techniques are critically important in the implementation of high-temperature wide-bandgap power devices. In this paper, thermal and mechanical characteristics of Au-In transient liquid phase (TLP) die-attach are examined for SiC devices. Samples with SiC diodes TLP-bonded to copper-metalized silicon nitride substrates are made using several different values for such fabrication properties as gold and indium thickness, Au/In ratio, and bonding pressure. The samples are then characterized for die-attach voiding, shear strength, and thermal impedance. It is found that the Au-In TLP-bonded samples offer a high average shear strength of 22.0 kgf and a low average thermal impedance of 0.35 K/W from the device junction through the substrate. It is also discovered that some of the fabrication properties have a greater influence on the bond characteristics than others. Overall, TLP bonding remains promising for high-temperature power electronic die-attach. © 2011-2012 IEEE

Importance of balancing membrane and electrode water in anion exchange membrane fuel cells

Anion exchange membrane fuel cells (AEMFCs) offer several potential advantages over proton exchange membrane fuel cells (PEMFCs), most notably to overcome the cost barrier that has slowed the growth and large scale implementation of fuel cells for transportation. However, limitations in performance have held back AEMFCs, specifically in the areas of stability, carbonation, and maximum achievable current and power densities. In order for AEMFCs to contend with PEMFCs for market viability, it is necessary to realize a competitive cell performance. This work demonstrates a new benchmark for a H2/O2 AEMFC with a peak power density of 1.4 W cm−2 at 60 °C. This was accomplished by taking a more precise look at balancing necessary membrane hydration while preventing electrode flooding, which somewhat surprisingly can occur both at the anode and the cathode. Specifically, radiation-grafted ETFE-based anion exchange membranes and anion exchange ionomer powder, functionalized with benchmark benzyltrimethylammonium groups, were utilized to examine the effects of the following parameters on AEMFC performance: feed gas flow rate, the use of hydrophobic vs. hydrophilic gas diffusion layers, and gas feed dew points

Reliability Characterization Of Au-In Transient Liquid Phase Bonding Through Electrical Resistivity Measurement

Transient liquid phase (TLP) die-attach bonding is an attractive technique for high-temperature semiconductor device packaging. In this paper, the material reliability of gold-indium (Au-In) TLP bonding is investigated utilizing electrical resistivity measurement as an indicator of material diffusion. Samples were fabricated featuring a TLP reaction, representative of TLP die-attach, by depositing TLP materials on glass substrates with various Au-In compositions, but with identical barrier layers, and were then used for reliability investigation. The samples were annealed at 200 °C and then stressed with thermal cycling. Samples containing high indium content in the TLP bond are shown to have poor reliability due to material diffusion through barrier layers, whereas the samples containing sufficient gold content proved reliable through electrical resistivity measurement, energy-dispersive X-ray spectroscopy, focused ion beam, and scanning electron microscope characterization