scholarly journals Key Role of Precursor Nature in Phase Composition of Supported Molybdenum Carbides and Nitrides

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 415 ◽  
Author(s):  
Zdeněk Tišler ◽  
Romana Velvarská ◽  
Lenka Skuhrovcová ◽  
Lenka Pelíšková ◽  
Uliana Akhmetzyanova
Keyword(s):  
Phase Composition ◽  
Final Phase ◽  
Ammonium Heptamolybdate ◽  
Synthesis Conditions ◽  
Temperature Conditions ◽  
Good Dispersion ◽  
Molybdenum Carbides ◽  
Molybdenum Nitrides ◽  
Different Temperatures

In this work, we studied the effect of molybdenum precursors and the synthesis conditions on the final phase composition of bulk and supported molybdenum carbides and nitrides. Ammonium heptamolybdate, its mixture with hexamethylenetetramine, and their complex were used as the precursors at different temperatures. It was investigated that the synthesis of the target molybdenum nitrides strongly depended on the structure of the precursor and temperature conditions, while the synthesis of carbide samples always led to the target phase composition. Unlike the carbide samples, where the α-Mo2C phase was predominant, the mixture of β-Mo2N, MoO2 with a small amount of metal molybdenum was generally formed during the nitridation. All supported samples showed a very good dispersion of the carbide or nitride phases.

scholarly journals MICROWAVE-HYDROTHERMAL HEXAMETHYLENETETRAMINE-MEDIATED SYNTHESIS OF NANOCRYSTALLINE MnO2

2018 ◽  
Vol 13 (2) ◽  
pp. 56-63
Author(s):  
O. M. Gaytko ◽  
A. E. Baranchikov ◽  
V. K. Ivanov
Keyword(s):  
Phase Composition ◽  
Manganese Dioxide ◽  
Single Phase ◽  
Ph Value ◽  
Temperature Synthesis ◽  
Synthesis Conditions ◽  
Microwave Hydrothermal ◽  
Polymorphic Modifications ◽  
Synthesis Duration

The article considers a non-conventional approach to the synthesis of various polymorphic modifications of manganese dioxide. The approach consists in hydrothermal microwave processing of a reaction mixture containing potassium permanganate and hexamethylenetetramine. We emphasize the relevance of the work due to such MnO2 properties as catalytic and photocatalytic activity, its application in accumulators, supercondensers and biochemistry. We report on the first detailed study on the role of temperature, synthesis duration and pH value on the phase composition and morphology of nanocrystalline MnO2. We show that the phase composition of manganese dioxide is largely determined not only by temperature, synthesis duration and pH value, but also by the acid added to the reaction mixture (nitric or sulphuric). In particular, the presence of sulfuric acid apparently results in α-MnO2 stabilization. It is noted that the type of the acid used in the course of the synthesis, as well as other synthesis conditions exercise no significant influence neither on the shape nor on the size of α-, γ- and δ-MnO2 particles. In contrast, the morphology of β-MnO2 turned out to be extremely sensitive to the synthesis conditions. Long (24 h) hydrothermal processing of reaction mixtures at рН 0.5-1 results in the formation of single-phase pyrolusite. The microstructure of the latter is determined by the reaction mixture composition.

scholarly journals Modeling of magneto-conductivity of bismuth selenide: a topological insulator

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Yogesh Kumar ◽  
Rabia Sultana ◽  
Prince Sharma ◽  
V. P. S. Awana
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Single Crystal ◽  
Single Crystals ◽  
X Ray Diffraction ◽  
Field Range ◽  
X Ray ◽  
Bulk Carriers ◽  
Different Temperatures

AbstractWe report the magneto-conductivity analysis of Bi2Se3 single crystal at different temperatures in a magnetic field range of ± 14 T. The single crystals are grown by the self-flux method and characterized through X-ray diffraction, Scanning Electron Microscopy, and Raman Spectroscopy. The single crystals show magnetoresistance (MR%) of around 380% at a magnetic field of 14 T and a temperature of 5 K. The Hikami–Larkin–Nagaoka (HLN) equation has been used to fit the magneto-conductivity (MC) data. However, the HLN fitted curve deviates at higher magnetic fields above 1 T, suggesting that the role of surface-driven conductivity suppresses with an increasing magnetic field. This article proposes a speculative model comprising of surface-driven HLN and added quantum diffusive and bulk carriers-driven classical terms. The model successfully explains the MC of the Bi2Se3 single crystal at various temperatures (5–200 K) and applied magnetic fields (up to 14 T).

scholarly journals Microstructure and magnetic properties of Nd-Fe-B-(Re, Ti) alloys

Nukleonika ◽  
2015 ◽  
Vol 60 (1) ◽  
pp. 29-33
Author(s):  
Mariusz Hasiak
Keyword(s):  
Magnetic Properties ◽  
Phase Composition ◽  
Volume Fraction ◽  
Magnetic Characteristics ◽  
Ti Alloys ◽  
Wide Range ◽  
Magnetically Hard ◽  
Ti Addition ◽  
Microstructure And Magnetic Properties

Abstract The microstructure and magnetic properties of nanocomposite hard magnetic Nd-Fe-B-(Re, Ti) materials with different Nd and Fe contents are studied. The role of Re and Ti addition in phase composition and volume fraction of the Nd-Fe-B phase is determined. All samples are annealed at the same temperature of 993 K for 10 min. Mössbauer spectroscopy shows that the addition of 4 at.% of Re to the Nd8Fe78B14 alloy leads to creation of an ineligible amount of the magnetically hard Nd2Fe14B phase. Moreover, the microstructure and magnetic characteristics recorded in a wide range of temperatures for the Nd8Fe79−xB13Mx (x = 4; M = Re or Ti) alloys are also analyzed.

scholarly journals Role of temperature in the numerical analysis of CaO under high pressure

2010 ◽  
Vol 8 (1) ◽  
pp. 126-133 ◽  
Author(s):  
Purvee Bhardwaj ◽  
Sadhna Singh
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Numerical Analysis ◽  
Thermodynamic Properties ◽  
Elastic Constants ◽  
Volume Change ◽  
Thermodynamical Properties ◽  
Phase Transition Pressure ◽  
Different Temperatures

AbstractIn this paper we focus on the elastic and thermodynamic properties of the B1 phase of CaO by using the modified TBP model, including the role of temperature. We have successfully obtained the phase transition pressure and volume change at different temperatures. In addition elastic constants and bulk modulus of B1 phase of CaO at different temperatures are discussed. Our results are comparable with the previous ones at high temperatures and pressures. The thermodynamical properties of the B1 phase of CaO are also predicted.

scholarly journals Conidia sporulation of Pyricularia oryzae in segments of wheat plants under six different temperatures

2020 ◽  
Vol 50 (4) ◽  
Author(s):  
Marcos Kovaleski ◽  
João Leodato Nunes Maciel ◽  
Gustavo Bilibio dos Santos ◽  
Alieze Nascimento da Silva ◽  
Carolina Cardoso Deuner
Keyword(s):  
High Temperature ◽  
Petri Dish ◽  
Pyricularia Oryzae ◽  
Causal Agent ◽  
Temperature Conditions ◽  
Wheat Blast ◽  
Conidia Production ◽  
Different Temperatures

ABSTRACT: Wheat blast is known for developing itself more intensely under relatively high temperature conditions but many aspects related to its epidemiology remain unknown. The objective of this research was to evaluate the sporulative capacity of Pyricularia oryzae Triticum (Pot), the causal agent of wheat blast, in tissues of wheat plants under different temperatures degrees. Wheat plants of the cultivar Anahuac 75, susceptible to blast, were inoculated in the stage of flowering with conidial suspensions (105 conidia/mL) of the Pot isolates Py 12.1.209 and Py 12.1.132. Seven days after the inoculation, plants were cut in the following segments: leaves, stems and rachis (with blast severity ranging from 40 to 60%). Groups of each one of the three plant segments with the lesions were disposed in Petri-dish moist chambers, that were submitted to six different temperature treatments (18, 21, 24, 27, 30 and 33 °C). The most appropriate model that related the conidia production with temperature was identified in the evaluations conducted with stems. The established equations allowed identifying that the highest production of conidia of Pot occurs between 24 and 27 °C.

scholarly journals The role of frost cracking in local denudation of steep Alpine rockwalls over millennia (Eiger, Switzerland)

2020 ◽  
Vol 8 (3) ◽  
pp. 637-659
Author(s):  
David Mair ◽  
Alessandro Lechmann ◽  
Romain Delunel ◽  
Serdar Yeşilyurt ◽  
Dmitry Tikhomirov ◽  
...  
Keyword(s):  
Swiss Alps ◽  
Rock Fall ◽  
Temperature Changes ◽  
Rock Face ◽  
Temperature Conditions ◽  
Denudation Rates ◽  
Reconstructed Temperature ◽  
Cryogenic Processes

Abstract. Denudation of steep rockwalls is driven by rock fall processes of various sizes and magnitudes. Rockwalls are sensitive to temperature changes mainly because thermo-cryogenic processes weaken bedrock through fracturing, which can precondition the occurrence of rock fall. However, it is still unclear how the fracturing of rock together with cryogenic processes impacts the denudation processes operating on steep rockwalls. In this study, we link data on long-term rockwall denudation rates at the Eiger (Central Swiss Alps) with the local bedrock fabric and the reconstructed temperature conditions at these sites, which depend on the insolation pattern. We then estimate the probability of bedrock for failure through the employment of a theoretical frost cracking model. The results show that the denudation rates are low in the upper part of the NW rockwall, but they are high both in the lower part of the NW rockwall and on the SE face, despite similar bedrock fabric conditions. The frost cracking model predicts a large difference in cracking intensity from ice segregation where the inferred efficiency is low in the upper part of the NW rockwall but relatively large on the lower section of the NW wall and on the SE rock face of the Eiger. We explain this pattern by the differences in insolation and temperature conditions at these sites. Throughout the last millennium, temperatures in bedrock have been very similar to the present. These data thus suggest the occurrence of large contrasts in microclimate between the NW and SE walls of the Eiger, conditioned by differences in insolation. We use these contrasts to explain the relatively low denudation rates in the upper part of the NW rockwall and the rapid denudation in the SW face and in the lower part of the NW rock face where frost cracking is more efficient.

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