Magnetoresistive study of the antiferromagnetic-weak ferromagnetic transition in single-crystal La₂CuO₄+δ

Resistive measurements were made to study the magnetic field-induced antiferromagnetic (AF)—weak ferromagnetic (WF) transition in the La₂CuO₄ single crystal. The magnetic field (dc or pulsed) was applied normally to the CuO₂ layers. The transition manifested itself in a drastic decrease of the resistance in critical fields of 5–7 T. The study is the first to display the effect of the AF–WF transition on the conductivity of the La₂CuO₄ single crystal in the direction parallel to the CuO₂ layers. The results provide support for the three-dimensional nature of the hopping conduction of this layered oxide

Дослідження електронної структури графенових нанолистів методом рентгенівської фотоелектронної спектроскопії

Investigations of graphene nanosheets and oxidized graphene nanosheets were carried out using X-ray photoelectron spectroscopy. Scanning and transmission electron microscopy investigations were used in addition to X-ray photoelectron spectroscopy. It was found that functional carboxyl and epoxide groups were removed from samples due to argon bombardment in studies of oxidized graphene nanosheets with X-ray photoelectron spectroscopy. Thus the ОKα-band was not revealed in oxidized graphene nanosheets owing to oxygen removal due to electron bombardment with the use of. ultra-soft X-ray emission spectroscopy. Дослідження графенових нанолистів та окислених графенових нанолистів, було проведене методом рентгенівської фотоелектронної спектроскопії (РФС). На додаток до рентгенівської фотоелектронної спектроскопії зразки досліджували методами скануючої та просвічуючуючщї мікроскопії. Встановлено, що аргонне бомбардування усуває функціональні карбоксильні та епоксидні групи зі зразків. Відсутність емісійних ОKα-смуг в ОГНЛ та ГНЛ пов’язана з видаленням зі зразка кисню в результаті електронного бомбардування при дослідженні зразка методом ультрам‘якої рентгенівської емісійної спектроскопії

Lubricant pyrolysis during sintering of powder metallurgy compacts

The chemistry surrounding the pyrolysis of N,N′-ethylenebisstearimide (EBS) compacted with iron powder is described for the first time. Heat treatment is carried out in a 5 vol pct hydrogen atmosphere (balance nitrogen) over the 100 °C to 850 °C range. The exhaust from the furnace is monitored by Fourier transform infrared and dispersive ultraviolet absorption spectroscopy; condensable materials are analyzed by gas chromatography/mass spectrometry (GC/MS). A wide range of analytes emitted from the preceding process were characterized. The aliphatic CH stretch in the 3000 to 2700 cm⁻¹ range and the asymmetric CO stretch in gaseous CO₂ at 2350 cm⁻¹ are excellent indicators of the extent of delubrication. A bimodal CO emission phase is observed in the temperature window between delubrication and sintering. Three major large molecule reaction products, along with five minor compounds, are identified by GC/MS. A preliminary reaction mechanism is inferred based on product analysis and known organic chemistry. It appears that hydrolysis of EBS competes with γ-H abstraction yielding an N-vinyl amide and stearamide, which undergoes further reaction. Hydrolysis affords stearic acid, which decarboxylates to heptadecane, and 2-heptadecyl-4,5-dihydroimidazole via ring closure of the corresponding amino-amide