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Chemical synthesis of crystalline and nanoscale cobalt-iron metal boride powders was studied using hydrous metal chlorides and NaBH4. The effects of precursor concentration and optimized synthesis conditions on the phase formation, microstructure, and magnetic properties were investigated. After applying a reaction of CoCl2 center dot 6H(2)O-FeCl3 center dot 6H(2)O-NaBH4 at 850 degrees C, (CoFe)B-2, (CoFe)B, Co2B, Fe3B, and Fe0.71Co0.29 boride phases were obtained from different synthesis conditions applied under autogenic pressure or Ar flow atmosphere. Oxychloride impurities were the reason for the reduced magnetization values. The highest saturation magnetization of 183 emu/g belongs to obtained nanoparticles containing (CoFe)B-2 and (CoFe)B pure phases. High temperature magnetic measurements marked synthesized powders as soft magnetic materials up to 795 K while no T-c was reached for the obtained phases.

Due to promising mechanical and chemical properties, transition metal borides have attracted attention, and numerous studies have investigated various combinations of transition elements in hopes of acquiring a final product with desired properties combined. In this study, novel low-temperature approach was adopted for the synthesis of cobalt-titanium-boron based crystalline powders. The method was based on the single-step direct reaction of CoCl2(s), TiCl4(l) and NaBH4(s) in a sealed reactor under autogenic pressure. After the reaction of the precursors at 850 degrees C by using the molar ratios of metal chlorides to NaBH4 as 1:3, CoB and TiB2 phases were formed in-situ. The subsequent annealing process at 1100 degrees C achieved a full conversion of metal chlorides to CoB-TiB2 composite nanostructures. It was concluded that the binary forms of the borides tend to form as separate phases, which is illustrated in the SEM/EDS analyses with different morphologies. Amorphous boron layer surrounded TiB2 particles with an average particle size of 60 nm, whereas the CoB particles formed agglomerates with an average size of 450 nm. The use of synthesized composite powders as reinforcement in metal matrices resulted in enhanced hardness (506 HV) and compressive strength (1682 MPa) of the Ti6Al4V bulk samples. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Tungsten matrix composites reinforced with TiB2and Y2O3 particles were fabricated by milling underambient/cryogenic conditions and Ni activated sintering. Powder blendsconstituting the W - 1 wt. % Ni - 2 wt. % TiB2 - 1 wt. % Y2O3composition were mechanically milled for 12 h under ambient condition or cryomilledfor 10 min or sequentially milled under ambient and cryogenic conditions.Milling was carried out in a high-energy ball mill under ambient conditionwhereas cryogenic milling was conducted in externally circulated liquidnitrogen. Milled powders were compacted using a hydraulic press and the pelletswere sintered at 1400°C for 1 h under Ar / H2 gas flowingconditions. The effects of different milling types on the microstructural andmechanical properties of the sintered composites were investigated. Aftersintering, in addition to dominant W phase, small amounts of WB and NiW phaseswere detected in all sintered samples. The application of cryomilling aftermilling at ambient condition provided the disappearance of the clustered TiB2and Y2O3 particles in the sintered sample: They werelocated at the grain boundaries of W1Ni matrix and homogeneously distributedthrough the microstructure. Sequentially milled and sintered composite had thehighest relative density (95.77 %) and the highest microhardness (7.23 GPa)values among the samples. Nano-indentation tests showed that there was animprovement in the hardness and elastic modulus of W matrix phase, whichyielded the values of 8.9 and 373.7 GPa, respectively., Bu çalışmada, Ni ile aktive edilerek sinterlenen tungsten esaslımatrisin TiB2 ve Y2O3 partikülleri ile takviyeedilmesiyle, tungsten esaslı kompozit malzeme üretimi gerçekleştirilmiştir. W -% 1 ağ. Ni - % 2 ağ. TiB2 - % 1 ağ. Y2O3kompozisyonundan oluşan toz harmanları, normal koşullarda 12 sa mekanik olaraköğütülerek ya da 10 dk kriyojenik ortamda öğütülerek ya da normal ve kriyojenikşartlarda ardışık olarak öğütülerek hazırlanmıştır. Normal şartlarda öğütmeyüksek enerjili bir değirmende uygulanırken; kriyojenik şartlarda öğütme sıvı azotile dışarıdan çevrelenen bir sistemde yapılmıştır. Öğütülmüş tozlar hidrolikpres kullanılarak preslenmiş ve pekiştirilen bünyeler Ar/H2 gazaltışartlarında 1400°C’de 1 sa sinterlenmiştir. Farklı öğütme koşullarınınsinterlenen kompozit malzemelerin mikroyapısı ve özellikleri üzerindeki etkisiincelenmiştir. Sinterlenme sonrasında, baskın W fazına ek olarak düşük mikardaWB ve NiW fazları oluşumu gözlemlenmiştir. Normal şartlarda öğütme sonrasıuygulanan kriyojenik öğütme, sinter malzemelerin mikroyapısındaki TiB2ve Y2O3 partiküllerin topaklanmasının yok olmasına nedenolmuştur: Partiküllerin W1Ni matrisinin tane sınırlarında ve homojen olarakmikroyapıda dağılması sağlanmıştır. Ardışık olarak öğütülmüş ve sinterlenmişkompozitler, numuneler arasında en yüksek rölatif yoğunluk (% 95,77) vemikrosertlik değerlerini (7,23 GPa) sunmuştur. Nano-indentasyon testlerisayesinde, W matris fazının sertlik ve elastisite modül değerlerinin sırasıyla8,9 ve 373,7 GPa değerlerine kadar iyileştirildiği kanıtlanmıştır.

Although there isa wide variety of superconducting materials, only a few of them are suitablefor practical applications. Nowadays, low temperature superconductors such asNbTi and Nb3Sn are widely used. However, after discovery of MgB2with its considerably high critical temperature which has a simple crystalstructure and cheap raw materials used in its production, renewed interestshave emerged for employing MgB2 in commercial application as well.This study reportson the effects of production techniques on the superconducting properties ofmagnesium diboride and includes an introduction to MgB2, its crystaland electronic structure and basics of superconducting properties. The productiontechniques would be explained as well as the probable problems during processand the way for optimizing superconducting property of MgB2. Furthermore,the improvement of superconducting properties by oxygen reduction, dopingelements as well as introducing of defects are covered. Finally, effects ofstarting materials and studies done by our research team in this regard arementioned.

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In this study, 8 mol% yttria-stabilized zirconia (8YSZ), ceria-, and scandia-doped YSZ powders were synthesized by the reverse microemulsion method. The powders were calcined at 1000 degrees C and sintered at 1450 degrees C. The crystalline properties and microstructure of the samples were characterized by X-ray diffraction and SEM methods, respectively. Oxygen ionic conductivities of the samples were measured by electrochemical impedance spectroscopy in the temperature range 250-375 degrees C. Grain interior and grain boundary resistivities were also calculated. Particle sizes of YSZ and Sc-doped YSZ were found to be < 100 nm, while that of Ce-doped YSZ was 120-150 nm. Approximately 1 mu m grains were observed after sintering of YSZ at 1450 degrees C. Particularly, the grain boundary and also the grain interior resistivities decreased with 3% scandia-doped YSZ. It was observed that the total conductivity of 3YSZ was higher than that of 3% ceria-doped YSZ.