Bulk anisotropic composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets with (BH)max=45–50MGOe have been synthesized by blending a Nd–Fe–Ga–B powder with an α-Fe or Fe–Co powder followed by hot compaction at 600–700 °C and hot deformation (die upsetting) at 850–950 °C with a height reduction of 71%. The composite Nd13.5Fe80Ga0.5B6∕α-Fe and Nd14Fe79.5Ga0.5B6∕Fe–Co magnets show microstructures consisting of a very large soft phase up to ∼50μm, which is more than 1000 times larger than the upper size limit of the soft phase expected from the existing models of interface exchange coupling.
An effort to increase the impact toughness of Nd–Fe–B sintered magnets by adding small amounts of Al, Nd, Ga, Cu, and Nb was successful. No significant compromise to magnetic properties occurred. Based on this work, a series of sintered Nd–Fe–B magnets with improved toughness was developed, which we call ToughNEO™. Small precipitates, which may contribute to the improvement of toughness, were observed using scanning electron microscope for all samples with improved toughness. Tumbling and drilling tests further verified the improved toughness of these developed ToughNEO™ magnets.
The effect of aromatic type and concentration on the thermal-oxidative stability characteristics of a synthetic paraffinic kerosene (SPK) aviation fuel was performed using batch and flow reactor systems, in combination with detailed chemical fuel analyses. An improved understanding of the impact of aromatic addition will assist in optimizing beneficial operational characteristics of the SPK feedstocks and the development of fully synthetic jet fuels. A primary goal of this study was to elucidate the controlling reaction chemistry and identify the cause for differing stability characteristics for varying types of aromatics. Studies were performed using a SPK comprised primarily of mildly branched iso-and n-paraffins as the base feedstock; limited studies were performed using a highly branched SPK. Commercially available aromatic solvents were used to represent petroleum-derived jet fuel and potential synthetic aromatic blending streams. These solvents were composed of mono-and diaromatic compounds of varying average molecular weight and size. The resulting thermal-oxidative stability characteristics were highly sensitive to the blend composition, with both increasing aromatic size and concentration, resulting in a higher deposition propensity upon stressing. It was determined that oxidation and molecular growth of the aromatic compounds are the probable primary pathways of surface deposit formation for these blends. Larger aromatic compounds (e.g., diaromatic) require fewer successive growth steps to produce insoluble deposit precursors, resulting in significantly higher deposition propensity than lower molecular weight (e.g., monoaromatic) species. Limited testing showed that the impact of aromatic type on deposition is consistent for different SPK compositions, but the deposit magnitude may be affected. ■ INTRODUCTIONThere has been significant interest during recent years in the development and approval of alternative (non-petroleum) aviation fuels. Alternative fuels have the potential to increase the supply and availability of reliable domestic sources while reducing associated cost volatility. Extensive laboratory and fullscale testing have resulted in the approval of synthetic paraffinic-type fuels for use as a blending feedstock (up to 50% by volume) in both commercial and military aviation fuels (per ASTM D1655-11 and MIL-DTL-83133H). This includes synthetic paraffinic kerosene (SPK) produced via Fischer− Tropsch synthesis and hydroprocessed esters and fatty acids (HEFA) derived from plant oils and animal fats. These SPK and HEFA blend stocks are predominantly paraffinic (normal and iso-) in composition and contain minimal aromatic and heteroatomic compounds. The neat paraffinic blend stocks exhibit favorable characteristics, such as excellent thermaloxidative stability and significantly reduced particulate matter (PM) propensity during combustion, which is attributable to the lack of the aromatics and heteroatomic compounds. 1 However, the lack of these compound classes results in fuels with insufficient m...
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