Consolidation of h-BN/Feldspar Composites in Air

2006 ◽  
Vol 11-12 ◽  
pp. 429-432
Author(s):  
Shoichi Kume ◽  
Saruhan Saklar ◽  
Koji Watari
Keyword(s):  
Melting Point ◽  
Boron Nitride ◽  
Bulk Density ◽  
Boron Oxide ◽  
Hexagonal Boron Nitride ◽  
Normal Pressure ◽  
Heating Process ◽  
Pressureless Sintering ◽  
Sintering Aid

Attempts have been made to sinter hexagonal boron nitride (h-BN) by pressureless-sintering in air. In order to achieve this purpose, feldspar has been selected as a sintering aid to produce sintered compacts at a temperature above the melting point of feldspar. Even though h-BN was not wetted by the molten feldspar in nitrogen, the wettability was significantly improved in air. Through the heating process, the h-BN powder disappeared owing to the oxidation of the powder followed by sublimation of the boron oxide. The decomposition of BN was prevented effectively by the presence of molten feldspar in the h-BN/feldspar (30 vol.%) compact. It was shown that h-BN/feldspar composite can be sintered in air under normal pressure, although the bulk density of h-BN/feldspar composites (1.40 to 1.51 g/cm3) was not satisfactory enough.

scholarly journals Evolution of Boron Nitride Structure upon Heating

2017 ◽  
Vol 27 (4) ◽  
pp. 301
Author(s):  
Nguyen Thi Thuy Hang
Keyword(s):  
Boron Nitride ◽  
Hexagonal Boron Nitride ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Heating Process ◽  
Thermodynamic Quantities ◽  
First Order ◽  
Evolution Of Structure ◽  
Lindemann Criterion ◽  
Liquid States

The evolution of structure upon heating of hexagonal boron nitride nanoribbon (h-BNNR) model is studied via molecular dynamics simulation. The temperature is increased from 50K to 5500K in order to observe the change of the structure during heating process. Various thermodynamic quantities related to the change of structure are calculated such as radial distribution functions, Lindemann criterion, the occurrence/growth of liquidlike atoms, the formation of clusters, and ring statistics. The melting point is defined. The phase transition from solid to liquid states exhibits first order behavior.

Microstructural Aspects of the Hot-Pressed Hexagonal Boron Nitride Ceramics with Limited Content of Boron Oxide

2007 ◽  
Vol 554 ◽  
pp. 197-200 ◽  
Author(s):  
B. Ertug ◽  
T. Boyraz ◽  
O. Addemir
Keyword(s):  
Boron Nitride ◽  
Boron Oxide ◽  
Hexagonal Boron Nitride ◽  
Secondary Phase ◽  
Nitrogen Atmosphere ◽  
Microstructural Properties ◽  
Growth Behaviour ◽  
Sintering Additive ◽  
Eds Analysis ◽  
Nitride Ceramics

Hexagonal boron nitride (h-BN) based ceramics have been fabricated by hot-pressing in a nitrogen atmosphere at 1900°C for 60 min. under a pressure of 50 MPa with B2O3 as sintering additive. The phase composition was confirmed by XRD. The microstructural properties of h-BN powders and hot-pressed surfaces were evaluated by SEM-EDS analysis. The formation of the secondary phase was also investigated with particular interest on grain boundaries. The sintered densities were also determined by Archimedes’ method. The maximum relative density was obtained to be about 92 %. The effect of the existence of boron oxide on the boron nitride grain growth behaviour was discussed on the basis of microstructural features.

Pressureless Sintering of Hexagonal Boron Nitride Powders

2007 ◽  
Vol 554 ◽  
pp. 207-212 ◽  
Author(s):  
Nuran Ay ◽  
I. Tore
Keyword(s):  
Boron Nitride ◽  
Hexagonal Boron Nitride ◽  
Maximum Density ◽  
Pressureless Sintering ◽  
Micro Hardness ◽  
Sintering Additives ◽  
Heat Treated ◽  
Density Values ◽  
Mercury Porosimeter ◽  
Hardness Values

Pressureless sintering of hexagonal boron nitride (BN) with and without additives was performed using a powder which was previously nitrided at 900oC and then heat treated at 1400oC. Sintering additives were B2O3 (2, 4, 6 wt %) and Y2O3 (2, 4, 6 wt %) and sintering temperatures was 1900oC. Sintered samples were characterized by XRD, SEM, micro hardness, density and mercury porosimeter measurements. Maximum density values of samples were 1.56 g/cm3 without additives and 1.63 g/cm3 with additives. Hardness values of samples were found to improve with the presence of additives.

Marcus-Hush Theory Revealed by Electron Tunneling Through Hexagonal Boron Nitride

2019 ◽  
Author(s):  
Matěj Velický ◽  
Sheng Hu ◽  
Colin R. Woods ◽  
Peter S. Toth ◽  
Viktor Zólyomi ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Boron Nitride ◽  
Electron Tunneling ◽  
Hexagonal Boron Nitride ◽  
Large Body ◽  
Liquid Solution ◽  
Limiting Current ◽  
Electron Transfer Rate Constant ◽  
Electrochemical Parameters ◽  
Voltammetric Measurements

Marcus-Hush theory of electron transfer is one of the pillars of modern electrochemistry with a large body of supporting experimental evidence presented to date. However, some predictions, such as the electrochemical behavior at microdisk electrodes, remain unverified. Herein, we present a study of electron tunneling across a hexagonal boron nitride barrier between a graphite electrode and redox levels in a liquid solution. This was achieved by the fabrication of microdisk electrodes with a typical diameter of 5 µm. Analysis of voltammetric measurements, using two common redox mediators, yielded several electrochemical parameters, including the electron transfer rate constant, limiting current, and transfer coefficient. They show a significant departure from the Butler-Volmer behavior in a clear manifestation of the Marcus-Hush theory of electron transfer. In addition, our system provides a novel experimental platform, which could be applied to address a number of scientific problems such as identification of reaction mechanisms, surface modification, or long-range electron transfer.

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