Formulation of Clay Refractory Bricks: Influence of the Nature of Chamotte and the Alumina Content in the Clay
Moustapha Sawadogo,
Mohamed Seynou,
Lamine Zerbo,
Brahima Sorgho,
Gisèle Laure Lecomte-Nana,
Philippe Blanchart,
Raguilnaba Ouédraogo
Issue:
Volume 9, Issue 4, December 2020
Pages:
59-67
Received:
22 October 2020
Accepted:
5 November 2020
Published:
23 November 2020
Abstract: Refractory materials from kaolinitic clays and clay chamotte or quartz were studied to increase the refractoriness under load at temperature above 1300°C. Two different clays mined in Burkina Faso were used and chamotte grains were obtained by preliminary firing a local clay. Fired materials at 1350-1400°C present a typical granular composite microstructure where large grains of chamotte or quartz are embedded in the clay matrix phase. Under load at high temperature, the behavior of material is influenced by the nature of the clay matrix phase that progressively melt at high temperature, the type of chamotte or quartz grains, the grain sizes of different phases and the sequence of the thermal transformations during firing. Kinetics of creep under a constant load were characterized against temperature and time. It gives the typical temperatures at fixed creep strains, that’s a well-recognized method for the refractoriness quantification. It’s shown that the kinetic of creep change with the variation of viscosity with temperature of the melted clay matrix phase, that’s related to both the chemical composition and the extend of the micro-composite nature of the heat transformed clays. Results also indicated that values of activation energy for creep are correlated to the refractoriness of materials.
Abstract: Refractory materials from kaolinitic clays and clay chamotte or quartz were studied to increase the refractoriness under load at temperature above 1300°C. Two different clays mined in Burkina Faso were used and chamotte grains were obtained by preliminary firing a local clay. Fired materials at 1350-1400°C present a typical granular composite micro...
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Interactions in Atomic and Ionic Liquids
Issue:
Volume 9, Issue 4, December 2020
Pages:
68-93
Received:
3 February 2020
Accepted:
9 July 2020
Published:
23 November 2020
Abstract: This review seeks to describe, from first principles, the nature of the interaction forces in atomic and ionic liquids. The atoms and molecules made up of dipoles and multipoles interact with van der Waals forces, while the ionic systems are viewed as pseudoions interacting through effective forces depending on the electronic structure and the physical ionic arrangement. The interplay between these two aspects of materials is quite complex and forms the main subject of this review. As it will be shown, the two-component system of interacting electrons and ions can be reduced, in second order perturbation theory, to an effective one-component system made up of pseudoions acting under the influence of two-body, central, screened potentials. These potentials result from a weak interaction between the electrons and the ions, deduced from the pseudopotential theory. Once the interatomic forces are known, the atomic structure and the electronic transport properties can be determined by methods of classical mechanics and quantum mechanics. Besides, a large volume-dependent term in the free energy, independent of the ionic positions, which distinguishes the conducting liquids from the simple isolator liquids like argon, is indispensable for explaining the thermodynamical properties.
Abstract: This review seeks to describe, from first principles, the nature of the interaction forces in atomic and ionic liquids. The atoms and molecules made up of dipoles and multipoles interact with van der Waals forces, while the ionic systems are viewed as pseudoions interacting through effective forces depending on the electronic structure and the phys...
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ZnO and ZnO:Ga Ceramics for Advanced Scintillators
Donats Millers,
Larisa Grigorjeva,
Aleksejs Zolotarjovs,
Faina Muktepavela,
Jurgis Grube,
Agnese Spustaka,
Piotr Rodnyi,
Ivan Venevtsev,
Elena Gorokhova
Issue:
Volume 9, Issue 4, December 2020
Pages:
94-101
Received:
24 November 2020
Accepted:
8 December 2020
Published:
22 December 2020
Abstract: The undoped ZnO reveals narrow luminescence bands located close to fundamental absorption edge, known as near band luminescence (NBL) and defects related wide luminescence band within visible range of spectrum. NBL decay is in sub-nanosecond range and it is promising for fast scintillator development. However, the defects luminescence decay is in microsecond range and it is disturbing for fast scintillators. Dopants strongly change the luminescence properties, mainly the intensity and decay time and that is the cause for intense study of doped ZnO luminescence properties. Thus the study of luminescent properties of undoped ZnO and doped ZnO:Ga ceramics was carried out. The dependence of the radioluminescence intensity on temperature and spectrum of near band edge luminescence were examined. NBL spectra comparison of ZnO and ZnO:Ga ceramics with ZnO:Ga single crystal allowed drawn out that at 300 K the donor-acceptor pair luminescence is dominant. It was suggested that the reabsorption within band edge spectral region could significantly affected the near band luminescence intensity and spectral position at 300 K. The significant impact of gallium on the ZnO luminescence is observed. The decay kinetics of luminescence were studied in picosecond range and the two-stage luminescence decay was found for undoped ZnO. The fastest decay stage time is determined to be within 37 – 57 ps. One stage decay kinetics of NBL was determined for ZnO:Ga ceramic and decay time of 17 ps was estimated.
Abstract: The undoped ZnO reveals narrow luminescence bands located close to fundamental absorption edge, known as near band luminescence (NBL) and defects related wide luminescence band within visible range of spectrum. NBL decay is in sub-nanosecond range and it is promising for fast scintillator development. However, the defects luminescence decay is in m...
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