A ground-based electrostatic-aerodynamic levitator for high-temperature containerless processing and property characterization of glasses and ceramics

2002 ◽  
Author(s):  
P.-F. Paradis ◽  
T. Ishikawa ◽  
J. Yu ◽  
S. Yoda
Keyword(s):  
High Temperature ◽  
Containerless Processing ◽  
Property Characterization

Measurements of the Thermal Conductivity of Individual α-Tetragonal Boron Nanoribbons

2011 ◽  
Author(s):  
Juekuan Yang ◽  
Scott W. Waltermire ◽  
Yang Yang ◽  
Deyu Li ◽  
Xiaoxia Wu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Silicon Nanowires ◽  
Complex Structures ◽  
One Dimensional ◽  
Seebeck Coefficients ◽  
Electrical Conductivities ◽  
Mechanical Devices ◽  
Property Characterization

Boron-based materials (i.e., boron and its borides) are mostly semiconductors with complex structures. These structures are characterized by an arrangement of an icosahedral cluster of B12 atoms [1]. The complexity of the crystal structure gives boron-based material a high melting point and low thermal conductivity at high temperature. On the other hand, the Seebeck coefficients and electrical conductivities of most bulk boron-based materials increase as temperature increases. Therefore, bulk boron-based materials are good candidates for high-temperature thermoelectric applications [2]. Due to the unique properties of bulk boron-based materials, one-dimensional nanostructures of boron-based materials have also attracted much attention, and various boron-based nanostructures have been synthesized recently [3]. These boron-based nanostructures are projected to be promising materials for novel nanoelectronic and nanoelectro-mechanical devices, as well as high temperature thermoelectric materials. However, compared to the extensive studies of carbon nanotubes and silicon nanowires, little has been done on the property characterization of boron and boride nanostructures.

scholarly journals Fabrication and Characterization of Quinary High Entropy-Ultra-High Temperature Diborides

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 108-120
Author(s):  
Simone Barbarossa ◽  
Roberto Orrù ◽  
Valeria Cannillo ◽  
Antonio Iacomini ◽  
Sebastiano Garroni ◽  
...  
Keyword(s):  
High Temperature ◽  
Single Phase ◽  
Nominal Composition ◽  
High Entropy ◽  
Chemical Complexity ◽  
Alternative Processing ◽  
Plasma Sintering ◽  
High Temperature Synthesis ◽  
Spark Plasma

Due to their inherent chemical complexity and their refractory nature, the obtainment of highly dense and single-phase high entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5, and 98.2%, respectively) were successfully produced by spark plasma sintering (SPS) using powders prepared by self-propagating high-temperature synthesis (SHS). Although the latter technique did not lead to the complete conversion of initial precursors into the prescribed HE phases, such a goal was fully reached after SPS (1950 °C/20 min/20 MPa). The three HE products showed similar and, in some cases, even better mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values were found for the (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2 and the (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 systems, i.e., 28.1 GPa/538.5 GPa and 28.08 GPa/498.1 GPa, respectively, in spite of the correspondingly higher residual porosities (1.2 and 2.2 vol.%, respectively). In contrast, the third ceramic, not containing tantalum, displayed lower values of these two properties (25.1 GPa/404.5 GPa). However, the corresponding fracture toughness (8.84 MPa m1/2) was relatively higher. This fact can be likely ascribed to the smaller residual porosity (0.3 vol.%) of the sintered material.

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