Formation of cubic C-BN by crystallization of nano-amorphous solid at atmosphere

1998 ◽  
Vol 13 (7) ◽  
pp. 1753-1756 ◽  
Author(s):  
Bin Yao ◽  
L. Liu ◽  
W. H. Su
Keyword(s):  
Solid Solution ◽  
Grain Size ◽  
High Pressure ◽  
Boron Nitride ◽  
Amorphous Carbon ◽  
Solid Solutions ◽  
Room Temperature ◽  
Amorphous Solid ◽  
High Energy ◽  
High Pressure And Temperature

An amorphous carbon-boron nitride (C-BN) solid was prepared by ball milling the mixture of graphite and hexagonal BN powders for a period of 120 h. After annealing the amorphous C-BN solid for 1 h at atmosphere in the temperature range from 800 to 900 K and then quenching it to room temperature, a small amount of cubic C-BN solid solutions with diamond-like structure, which belong to a high energy phase and can only be synthesized previously under high pressure and temperature (30 GPa, 2000 K), were observed in the annealed amorphous C-BN solid. The lattice constant of the cubic C-BN solid solution was 0.3587 nm, and its grain size was in the range of 10 to 50 nm.

scholarly journals Transformation of Ammonium Azide at High Pressure and Temperature

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4102
Author(s):  
Guozhao Zhang ◽  
Haiwa Zhang ◽  
Sandra Ninet ◽  
Hongyang Zhu ◽  
Keevin Beneut ◽  
...  
Keyword(s):  
High Pressure ◽  
Room Temperature ◽  
High Energy ◽  
High Energy Density ◽  
X Ray Diffraction ◽  
Polymeric Compound ◽  
High Pressure And Temperature ◽  
Polynitrogen Compounds ◽  
Vibrational Features ◽  
Solid Ammonia

The compression of ammonium azide (AA) has been considered to be a promising route for producing high energy-density polynitrogen compounds. So far though, there is no experimental evidence that pure AA can be transformed into polynitrogen materials under high pressure at room temperature. We report here on high pressure (P) and temperature (T) experiments on AA embedded in N2 and on pure AA in the range 0–30 GPa, 300–700 K. The decomposition of AA into N2 and NH3 was observed in liquid N2 around 15 GPa–700 K. For pressures above 20 GPa, our results show that AA in N2 transforms into a new crystalline compound and solid ammonia when heated above 620 K. This compound is stable at room temperature and on decompression down to at least 7.0 GPa. Pure AA also transforms into a new compound at similar P–T conditions, but the product is different. The newly observed phases are studied by Raman spectroscopy and X-ray diffraction and compared to nitrogen and hydronitrogen compounds that have been predicted in the literature. While there is no exact match with any of them, similar vibrational features are found between the product that was obtained in AA + N2 with a polymeric compound of N9H formula.

scholarly journals ELECTRIC CONDUCTIVITY AT ROOM TEMPERATURE IN LINATANBO SYNTHESIZED AT A HIGH PRESSURE

2020 ◽  
pp. 61-72
Author(s):  
Вадим Викторович Ефремов ◽  
Михаил Николаевич Палатников ◽  
Ольга Борисовна Щербина
Keyword(s):  
Solid Solution ◽  
Electrical Conductivity ◽  
Dielectric Constant ◽  
High Pressure ◽  
Room Temperature ◽  
Activation Enthalpy ◽  
Relaxation Times ◽  
Charge Carriers ◽  
High Electrical Conductivity ◽  
High Pressure And Temperature

Методом импеданс спектроскопии в области температур 290 - 460 К исследован сегнетоэлектрический твердый раствор LiNaTaNbO со структурой перовскита, синтезированный в условиях высокого давления и температуры. Определены значения статических удельных проводимостей, наиболее вероятные времена релаксации в зависимости от температуры, энтальпии активации носителей заряда и реальная часть диэлектрической проницаемости. Обнаружено, что при комнатной температуре LiNaTaNbO обладает высокой электропроводностью, близкой к суперионной. Обсуждаются возможные механизмы обнаруженных явлений. A ferroelectric solid solution LiNaTaNbO with a perovskite structure, synthesized under the high pressure and temperature conditions, has been studied by impedance spectroscopy in the temperature range 290 - 460 K. The values of static conductivity, the most probable relaxation times as functions of temperature, the activation enthalpy of charge carriers, and the real part of the dielectric constant have been determined. It was found that at room temperature LiNaTaNbO has a high electrical conductivity, close to the superionic one. Possible mechanisms of the discovered phenomenon are discussed.

Cubic Boron Nitride as a New Semiconductor for Optoelectronics: Luminescence Properties and Potentialities

1989 ◽  
Vol 162 ◽  
Author(s):  
Koh Era ◽  
Osamu Mishima
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Boron Nitride ◽  
Room Temperature ◽  
Cubic Boron Nitride ◽  
Visible Region ◽  
Vibrational Structure ◽  
Luminescence Properties ◽  
Optoelectronic Applications ◽  
P Type

ABSTRACTIn cubic boron nitride made by high pressure and high temperature technique in our institute, we have found three luminescence bands in the ultraviolet and the short visible region at room temperature by cathode-ray excitation. They are: a band having vibrational structure and ascribable to undoped state of the crystal, a band ascribable to p-type doping and a band ascribable to n-type doping. Discussion is made on differences between the injection luminescence and the cathodoluminescence. Potentialities and difficulties in realizing the potentialities of cBN for optoelectronic applications are discussed.

scholarly journals Ge0.57Ti0.43O2: a new high-pressure material with rutile-type crystal structure

2018 ◽  
Vol 74 (7) ◽  
pp. 1010-1012 ◽  
Author(s):  
Emil Stoyanov ◽  
Kurt Leinenweber ◽  
Thomas L. Groy ◽  
Abds-Sami Malik
Keyword(s):  
Crystal Structure ◽  
Solid Solution ◽  
High Pressure ◽  
Single Crystals ◽  
Structure Type ◽  
Site Symmetry ◽  
Rutile Structure ◽  
High Pressure And Temperature ◽  
Atom Position ◽  
Type Crystal

Single crystals of a GeO2–TiO2 solid solution with the corresponding composition Ge0.57Ti0.43O2 (germanium titanium tetraoxide) were obtained by devitrification of germania-titania glass at high pressure and temperature. The new compound crystallizes in the rutile structure type (space group P42/mnm), where Ge and Ti share the same position M (site symmetry m.mm), with occupancy values of 0.57 (3) and 0.43 (3), respectively, and one O-atom position (m.2m). The M site is in a sixfold O-atom coordination and, as in the original TiO2 rutile structure, an elongation of the O—M—O bonds along the c-axis direction of the coordination polyhedron and deviation of the angles from 90° lead to a decrease in the coordination symmetry from octahedral to tetragonal. The Ge and Ti atoms are fully disordered in the structure, which indicates that the rutile structure is surprisingly pliant given the differing sizes of the two cations.

scholarly journals Production of alumo-matrix composite material modified by nanostructured cubic boron nitride

2018 ◽  
Vol 63 (3) ◽  
pp. 271-279
Author(s):  
P. A. Vityaz ◽  
V. T. Senyut ◽  
M. L. Kheifetz ◽  
A. G. Kolmakov
Keyword(s):  
High Pressure ◽  
Aluminum Alloy ◽  
Boron Nitride ◽  
Cubic Boron Nitride ◽  
Aluminum Matrix ◽  
Treatment Temperature ◽  
Chemical Affinity ◽  
High Temperature Annealing ◽  
High Pressure And Temperature ◽  
Primary Particles

The structure and microhardness of an aluminum alloy with additives of nanostructured cubic boron nitride (cBN) after treatment under high pressure and temperature are investigated. А nanostructured powder of cBN with primary particles within 50–200 nm is used as a filler. A preliminary chemical-thermal modifying of the nanostructured cBN, which consists in its high-temperature annealing in the temperature range of 750–950 °C in a medium of aluminum-contai ning compounds, is carried out to increase the chemical affinity of the nanostructured cBN to the aluminum matrix. It is shown that the modifying of nanostructured cBN with aluminum increases the strength of the additives retention in the aluminum matrix. At the same time the increase in the concentration of BN additives from 1.5 to 5 wt.% as well as the increase in the treatment temperature at a fixed pressure promotes the increase in the microhardness of the material by a factor of 1.5 to 2 as compared with the base aluminum alloy without the addition of a modifier. An increase in the cBN concentration to 5 % by weight results in an increase in the fraction of smaller particle conglomerates (1–5 μm) in the material and in a decrease in the size of large inclusions to 10–20 μm. In this case, the distribution of BN particles in the aluminum matrix is more uniform in comparison with a material with a cBN content of 1.5 wt.%. In the material with the growth of temperature up to 1000 °С, cBN in aggregates is recrystallized with the formation of single-crystal (polycrystalline) particles with the size of 1–10 μm  with faceting specific for cBN micron particles.

Electrical Conductivity and Phase Transitions in Ferroelectric Solid Solutions Li0.17Na0.83ТауNb1-уO3 (y = 0 – 0.5) in High Pressure

2020 ◽  
Vol 310 ◽  
pp. 6-13
Author(s):  
Vadim V. Efremov ◽  
Mikhail N. Palatnikov ◽  
Yuriy V. Radyush ◽  
Olga B. Shcherbina
Keyword(s):  
Solid Solution ◽  
Electrical Conductivity ◽  
High Pressure ◽  
Phase Transitions ◽  
Solid Solutions ◽  
Synthesis Method ◽  
Ferroelectric Ceramic ◽  
Synthesis Temperature ◽  
Structure Phase ◽  
Ceramic Solid Solution

Ferroelectric ceramic solid solutions LixNa1-xTayNb1-yO3 (х = 0.17; у = 0 – 0.5) with the perovskite structure have been obtained by the thermobaric synthesis method. Particularities of their microstructure, elastic properties, electrical conductivity and permittivity have been researched. It has been established that an increase in the thermobaric synthesis temperature leads to a decrease in the Young’s modulus value. Specific static conductivity values have been determined; charge carrier activation enthalpies На have been calculated. The Curie temperature of the samples has been determined to decrease with an increase in tantalum content. A Ferroelectric ceramic solid solution Li0.17Na0.83Ta0.1Nb0.9O3 was shown to undergo four structure phase transitions in the temperature range 300-820 К. A Li0.17Na0.83Ta0.1Nb0.9O3 has been shown to be a high temperature superionic. Possible mechanisms of the detected phenomena are discussed.

scholarly journals Estimation of the combustion products from the cylinder of the petrol engine and its relation to "knock"

1935 ◽  
Vol 234 (744) ◽  
pp. 433-521 ◽  
Keyword(s):  
High Pressure ◽  
Experimental Evidence ◽  
Combustion Products ◽  
High Energy ◽  
High Pressure And Temperature ◽  
Engine Cylinder ◽  
Engine Knock ◽  
Slow Combustion ◽  
Set Up ◽  
Exhaust Valves

As a result of a variety of experiments it was suggested in 1928 that engine “knock” “appears to be due to inequality in the condition of the charge (in the engine cylinder) set up, particularly in regions of high pressure and temperature as in the neighbourhood of hot exhaust valves. This inequality provides regions of high energy containing molecules in high energy states where reaction can spread more quickly.” This view was a little vague, and was arrived at from indirect experimental evidence. It was with a view to obtaining more precise evidence that knock was occasioned in the flame as the result of processes of slow combustion occurring in the gaseous charge prior to its arrival that the present work was undertaken. Callendar and those working with him had simultaneously arrived at the conclusion that “knock” was occasioned in much the same manner, but they adopted the more definite view that peroxides of the hydrocarbons were formed and stored in the gas, and then suddenly detonated, so igniting a whole region of the gas simultaneously. This view had also been advanced by Moureu and Dufraisse.

Spinel solid solutions in the systems MgAl2O4–ZnAl2O4 and MgAl2O4–Mg2TiO4

1997 ◽  
Vol 12 (10) ◽  
pp. 2584-2588 ◽  
Author(s):  
M. A. Petrova ◽  
G. A. Mikirticheva ◽  
A. S. Novikova ◽  
V. F. Popova
Keyword(s):  
Solid Solution ◽  
Phase Diagrams ◽  
Melting Temperature ◽  
Solid Solutions ◽  
Spinel Structure ◽  
Room Temperature ◽  
Binary Systems ◽  
Continuous Series ◽  
X Ray ◽  
Spinel Solid Solutions

Phase relations in two binary systems MgAl2O4–ZnAl2O4 and MgAl2O4–Mg2TiO4 have been studied and phase diagrams for them have been constructed. Based on the data of x-ray phase and crystal-optical analyses, the formation of a continuous series of solid solutions with spinel structure between the terminal members of the systems studied has been established. In the MgAl2O4–ZnAl2O4 system the solid solution is stable in the range from room temperature to melting temperature. In the MgAl2O4–Mg2TiO4 system the solid solution decomposes below 1380 °C, yielding the formation of limited regions of homogeneity on the basis of MgAlM2O4 and Mg2+2δ Ti1–δO4. Decomposition of the solid solution is accompanied by crystallization of MgTiO3.

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