Combustion Synthesis of Boride-Based Electrode Materials for Magnetohydrodynamic (MHD) Direct Power Extraction [electronic resource]

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Ngôn ngữ: eng

Ký hiệu phân loại: 621.312 Generation, modification, storage

Thông tin xuất bản: Washington, D.C. : Oak Ridge, Tenn. : United States. Office of the Assistant Secretary of Energy for Fossil Energy ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2019

Mô tả vật lý: Medium: ED : , digital, PDF file.

Bộ sưu tập: Metadata

ID: 255739

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The goal of the present project was to develop an advanced, low-cost manufacturing technique for fabrication of boride-based ultrahigh-temperature ceramics (UHTCs) that possess all the required properties to function as sustainable electrodes in magnetohydrodynamic (MHD) direct power extraction applications. Specifically, the project investigated use of mechanical activation-assisted self-propagating high-temperature synthesis (MASHS) followed by pressureless sintering for the fabrication of ceramic materials based on ZrB
2
and HfB
2
from inexpensive raw materials ZrO
2
, HfO
2
, and B
2
O
3
, with Mg as a reactant and NaCl or MgO as an inert diluent.

Thermodynamic calculations were conducted for combustion of ZrO
2
/B
2
O
3
/Mg and HfO
2
/B
2
O
3
/Mg mixtures with MgO and NaCl additives. In the experiments, the mixture ingredients were milled in a planetary mill, compacted into pellets, and ignited in an argon environment. MgO and NaCl were removed from the combustion products by acid leaching. The reaction mechanisms in these mixtures were studied using thermogravimetric analysis and differential scanning calorimetry. Pressureless sintering in an induction furnace was explored for purification and densification of the obtained products.

It has been shown that mechanical activation of ZrO
2
/B
2
O
3
/Mg and HfO
2
/B
2
O
3
/Mg mixtures decreases the ignition temperature and enables a self-sustained combustion. The addition of excess Mg increased the oxide-to-boride conversion degree. MgO additive was not effective for milling and for increasing the conversion degree. In contrast, NaCl additive effectively decreased sticking of the material to the grinding media. Combustion of mixtures containing NaCl produced nanoscale particles of ZrB
2
, which is beneficial for sintering. Thermoanalytical studies clarified the reaction mechanisms during magnesiothermic MASHS of ZrB
2
. The pressureless sintering experiments demonstrated that milling, pressing, and adding boron carbide are needed for enhancing the sinterability of ZrB
2
.

1. 30 direct energy conversion
2. 36 materials science
3. Borides
4. Combustion synthesis
5. Mechanical activation
6. Mhd
7. Shs
8. Ultra-high temperature ceramics (uhtc)

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