Widok Tom 68 Nr 3 (2016)

MATERIA£Y CERAMICZNE /CERAMIC MATERIALS/, 68, 3, (2016) 1984

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MATERIA£Y CERAMICZNE /CERAMIC MATERIAS/, 68, 3, (2016) ISSN 1505-1269

COMPLEXITY IN BORIDES: EXOTIC SOLIDS OR USEFUL MATERIALS?

Barbara Albert

Technische Universität Darmstadt, Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Germany e-mail: albert@ac.chemie.tu-darmstadt.de

Metal borides [1] are inorganic solids that often show refractory properties, like super-hardness [2] and very high-melting points. They may also prove to be exciting concerning their electronic structure, as shown for super-conducting magnesium diboride, MgB₂ [3], or samarium hexaboride - SmB₆ [4], which was recently found to be a topological insulator. New inve-stigations on nanoscale and bulk mono-, di- tetra-, and hexaborides will be presented. Examples are MnB₄, crystallizing similar to hypothetical tetragonal diamond but exhibiting an unexpected Peierls distortion [5, 6], solid solutions of (M,M’)B₆ with good thermoelectric properties [7], and nanoscale metal borides that can be (ferro)magnetic [8]. Synthesis, characte-rization, structures, and properties will be discussed.

References

[1] Albert, B., Hillebrecht, H.: Angew. Chem. Int. Ed., 48, (2009), 8640-8668.

[2] Mohammadi, R., Lech, A. T., Xie, M., Weaver, B. E., Yeung, M. T., Tolbert, S. H., Kaner, R. B.: PNAS, 108, (2011), 10958-10962. [3] Nagamatsu, J., Nakagawa, N., Muranaka, T., Zenitani, Y., Akimitsu, J.: Nature, 410, (2001) 63-64.

[4] Kim, D. J., Xia, J., Fisk, Z.: Nature Materials, 13, (2014), 466-470.

[5] Knappschneider, A., Litterscheid, C., George, N. C., Brgoch, J., Wagner, N., Beck, J., Kurzman, J. A., Seshadri, R., Albert, B.: Angew.

Chem., 126, (2014), 1710-1714, Int. Ed. Engl., 53, (2014), 1684-1688.

[6] Knappschneider, A., Litterscheid, C., Brgoch, J., George, C., Henke, S., Cheetham, A. K., Hu, J. G., Seshadri, R., Albert, B.: Chem.

Eur. J., 21, (2015), 8177-8181.

[7] Gürsoy, M., Takeda, M., Albert, B.: J. Solid State Chem., 221, (2015), 191-195. [8] Rades, S., Kraemer, S., Seshadri, R., Albert, B.: Chem. Mater., 26, (2014), 1549-1552.

Keywords: Borides, Structure, Superconductivity, Superhardness, Synthesis

A REVIEW ON THE ELECTROSTATIC AND STERIC STABILIZATION OF OXIDES,

BORIDES AND CARBIDES IN AQUEOUS MEDIA

Thomas Graule

1

_{*, Maciej Wozniak}

1,2

_{, Dariusz Kata}

2

1 EMPA Swiss Laboratories for Materials Science and Technology, Laboratory for High Performance Ceramics, Düben-dorf; Switzerland 2_{AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Ceramics and} Refractories, Kraków, Poland *e-mail: thomas.graule@empa.ch The efficient stabilization of ceramic based nanopowders is a prerequisite for the achievement of highly reliable ceramic materials. Agglomeration or re-agglomeration due to Van der Waals forces can be avoided using different concepts to increase the separation barrier by electrostatic or steric means. Concepts for the stabilization of oxide based ceramic po-wders applying anion and cation type surfactants can be easily transferred to stabilization of carbides and borides, basing on the fact that the relevant particle surfaces are covered by an hydroxide layer. We present here studies in order to have a basic understanding of the mechanism of steric stabilization in aqueous media [1-2]. Another approach is based on mini-mizing the Van der Waals attraction by a proper selection of the dispersion medium [3]. After giving an extensive review on

Abstracts of Workshop on Extraordinary Boride

Ceramics for Advanced Engineering Applications,

MATERIA£Y CERAMICZNE /CERAMIC MATERIALS/, 68, 3, 2016)

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the aspects of steric stabilization, we present here additionally new concepts to apply cationic comb copolymers as a pro-mising alternative in case of the stabilization of titania and silica. The effectiveness of the anionic and cationic dispersants is evaluated on the basis of adsorption, zeta potential measurements, rheology and particle size measurements [4-5]. References [1] De Hazan, Y., Reuter, T., Werner, D., Clasen, R., Graule, T.: Interaction and dispersion stability of aluminium oxide colloid particles in electroless nickel coatings, J. Colloid Interf. Sci., 323, (2008), 293-300.

[2] De Hazan, Y., Heinecke, J., Weber, A., Graule, T.: High Solids Loading Ceramic colloidal Dispersions in UV Curable Media via Comb polyelectrolyte Surfactans, J. Colloid Interf. Sci., 337, (2009), 66-74.

[3] Wozniak, M., de Hazan, Y., Graule, T., Kata, D.: Rheology of UV curable colloidal silica dispersions for rapid prototyping applications,

J. Eur. Cer. Soc., 31, (2011), 2221-2229.

[4] Klimkevicius, V., Graule, T., Makuska, R.: Effect of structure of cationic comb copolymers on their adsorption and stabilization of titania nanoparticles, Langmuir, 31, (2015), 2074-2083.

[5] Klimkevicius, V., Makuska, R., Graule, T.: Rheology of Titania Based Ceramic Nanodispersions Stabilized by Cationic Comb Copol-ymers; Applied Rheology, accepted January 2016

Keywords: Borides, Carbides, Electrostatic stabilization, Oxides, Steric stabilization

BORIDE PARTICLE DISPERSED HARD METAL

Kiyotaka Matsuura

Hokkaido University, Faculty of Engineering, Sapporo, Hokkaido, Japan, e-mail: matsuura@eng.hokudai.ac.jp FeAl-TiB₂ composites have been combustion synthesized from mixtures of Fe, Al, Ti and B powders. When the powder mixture was heated in vacuum, a sudden and rapid temperature rise was observed near the melting point of Al, indicating that the combustion synthesis reactions between Al liquid and the powders of other elements occurred. X-ray diffraction analyses and electron probe microanalyses revealed that the combustion-synthesized sample consisted of only FeAl and TiB₂. Metallographic investigations, using a scanning electron microscope, revealed that fine TiB₂ particles were dispersed in the FeAl matrix phase with a lot of pores. The porosity was dramatically reduced by using pseudo-isostatic pressure during the combustion synthesis reactions. The average TiB₂ particle size increased from 1 μm to 7 μm and the average Vickers hardness of the composites increased from 800 to 1600, as the volume fraction of the TiB₂ phase was increased from 0.3 to 0.8 by controlling the powder mixture composition. This method has been applied to the fabrication of some other ceramic particle dispersed hard metal or intermetallic matrix composites such as Fe-TiC and FeAl-TiC systems.

Keywords: FeAl-TiB₂ composites, Combustion synthesis, Final microstructure, Mechanical properties,

COMBUSTION SYNTHESIS AND PROPERTIES OF BORIDES

AND RELATED CERAMIC MATERIALS

Dariusz Kata

1

_{*, Paweł Rutkowski}

1

_{, Jerzy Lis}

1

_{, Nina Orlovskaya}

2

1_{AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Ceramics and} Refractories, Kraków, Poland, 2_{Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, Florida, US} *e-mail: kata@agh.edu.pl Self-propagating high-temperature synthesis (SHS) can be used to produce quality boron-rich solid solutions. However, this is conditioned upon a correct identification of process mechanisms giving the control over the course of reaction, which in effect enables obtaining repeatable products. The presentation describes a part of author’s long-term investigation on combustion synthesis of ceramic functional materials, e.g., borides. The stability of ReB₂-type hexagonal OsB₂ powder at high temperatures in the presence of oxygen has been studied by thermogravimetry, differential scanning calorimetry, SEM, EDS, high-temperature scanning transmission electron microscopy, and XRD. The results of the study revealed that OsB₂ ceramics interacts readily with oxygen which is present in a reducing atmosphere, especially at high temperatures, and produces boric acid, which decomposes on the surface of the powder resulting in the formation of boron vacancies in the hexagonal OsB₂ lattice as well as changes in the stoichiometry of the compound.