Coarse-grained refractory composites based on Nb-Al2O3 and Ta-Al2O3 castables

Zienert, Tilo; Farhani, Mahdi; Dudczig, Steffen; Aneziris, Christos G.

doi:10.1016/j.ceramint.2018.06.116

Cited by 19 publications

(37 citation statements)

References 29 publications

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“…Hereafter, the samples were taken out and dried in air at 120 °C for 24 h, followed by a pressureless sintering regime under argon atmosphere at 1600 °C for 4 h. Heating rates of 3 K/min up to a temperature of 500 °C, and 10 K/min up to the sintering temperature of 1600 °C, were applied. Details of the chemical composition of the raw materials, the castable recipe and the castable technology were reported recently in [39]. Cylinders with a diameter of 15 mm and a height of 25 mm were prepared for the high-temperature mechanical tests from the sintered prism by hollow drilling.…”

Section: Methodsmentioning

confidence: 99%

“…Coarse-grained ceramic refractories are used in favor of fine-grained ceramic materials in high-temperature and metallurgical applications, due to their relatively high resistance to creep, thermal shock and corrosion resistance [34,35,36,37,38]. Furthermore, it was shown by Zienert et al [39] that the shrinkage can be even further reduced by adding high melting refractory metals as fine matrix component. The sum of these promising results regarding the shrinkage behavior in combination with both good resistance to thermal shock, as well as the excellent electrical and thermal properties of these materials, offer the opportunity to selectively design individual parts of large-sized construction components.…”

Section: Introductionmentioning

confidence: 99%

“…The aim of the present paper is to investigate a new generation of coarse-grained refractory composites [39] based on pre-synthesized coarse grains of a ceramic (Al 2 O 3 ) and refractory metals (Nb, Ta). Considering their potential applications as, e.g., electrically controlled heat shields or non-wetting, electrically heatable crucible materials, experimental studies on their mechanical properties at high temperatures (in particular, compressive strength, creep, and stress-relaxation, as well as damage and fracture behavior) are necessary.…”

Section: Introductionmentioning

confidence: 99%

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Mechanical High-Temperature Properties and Damage Behavior of Coarse-Grained Alumina Refractory Metal Composites

et al. 2019

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The present study provides the mechanical properties of a new generation of refractory composites based on coarse-grained Al2O3 ceramic and the refractory metals Nb and Ta. The materials were manufactured by refractory castable technology and subsequently sintered at 1600 °C for 4 h. The mechanical properties and the damage behavior of the coarse-grained refractory composites were investigated at high temperatures between 1300 and 1500 °C. The compressive strength is given as a function of temperature for materials with two different volume fractions of the refractory metals Ta and Nb. It is demonstrated that these refractory composites do not fail in a completely brittle manner in the studied temperature range. The compressive strength for all materials significantly decreases with increasing temperature. Failure occurred due to the formation of cracks along the ceramic/metal interfaces of the coarse-grained Al2O3 particles. In microstructural observations of sintered specimens, the formation of tantalates, as well as niobium oxides, were observed. The lower compressive strength of coarse-grained Nb-Al2O3 refractory composites compared to Ta-Al2O3 is probably attributed to the formation of niobium oxides. The formation of tantalates, however, seems to have no detrimental effect on compressive strength.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mechanical High-Temperature Properties and Damage Behavior of Coarse-Grained Alumina Refractory Metal Composites

et al. 2019

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“…After gelation, the wet green beads were removed from the calcium chloride solution with the aid of a sieve, washed with deioinzed water to remove any solution residues, and, finally, dried at 50

C for 24 h. It was reported that the decomposition of sodium alginate should be completed at approximately 680

C, with three main exothermic peaks [ 20 ]. However, in the case of metal-ceramic composite beads, it was not possible to perform the debinding step up to this temperature, due to the high affinity of Nb to oxygen [ 5 ]. Instead, the following debinding program was chosen: 0.5 K/min heating rate up to 220

C, 30 min dwell time at 220

C, then 0.1 K/min up to 275

C and 0.5 K/min to 300

C. The furnace was then left to cool freely.…”

Section: Methodsmentioning

confidence: 99%

“…In a recent work, Zienert et al reported for the first time the production of coarse-grained refractory composites consisting of refractory metals and refractory ceramic materials [ 5 ]. Refractory metals with a melting point above 2000

C, namely Nb and Ta, were chosen and combined with alumina.…”

Section: Introductionmentioning

confidence: 99%

Metal-Ceramic Beads Based on Niobium and Alumina Produced by Alginate Gelation

et al. 2021

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Full metal-ceramic composite beads containing different amounts of niobium and alumina, particularly 100 vol% alumina, 100 vol% niobium, and 95/5 vol% niobium/alumina, were produced by the alginate gelation process. The suspension for bead fabrication contained sodium alginate as gelling agent and was added dropwise into a calcium chloride solution to trigger the consolidation process. After debinding in air, sintering of the composite beads was performed under inert atmosphere. Samples in green and sintered state were analyzed by digital light microscopy and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Investigations by mercury intrusion porosimetry revealed that pure alumina beads featured smaller pores compared to composite beads, although the open porosities were comparable. The fracture strength was evaluated on single beads. Contrary to the pure alumina, the composite beads showed a clear plastic deformation. Pure niobium beads showed a ductile behavior with very large deformations. XRD analyses revealed the presence of calcium hexaluminate and beta-alumina as minor phases in the alumina beads, while the composite ones contained about 25 wt% of impurities. The impurities comprised NbO arising from the oxidation, and -Nb2C, from the reaction with the residual sodium alginate.

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Field‐Assisted Sintering of Nb–Al₂O₃ Composite Materials and Investigation of Electrical Conductivity

et al. 2022

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Field‐assisted sintering technique (FAST) is used for the preparation of Nb–Al2O3 composite materials. The electrical conductivity is investigated depending on the particle size of the used starting powders and under varying volume contents of the refractory metal in the starting powder mixture. The percolation threshold is investigated and found to be influenced not only by the metal fraction but also by the particle size of the alumina used for sample preparation. For the fine‐ and coarse‐grained alumina, a percolation threshold of 17.5 and 10 vol% Nb is estimated, respectively. Furthermore, the microstructure is investigated to gain a basic understanding of the dependency between microstructural features and the resulting material properties on the macroscopic scale. Also, the influence of the sintering process and the resulting microstructure–properties relationship is considered. It could be shown that the electrical properties are anisotropic because of anisotropy effects caused by the FAST process.

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Coarse-grained refractory composites based on Nb-Al2O3 and Ta-Al2O3 castables

Cited by 19 publications

References 29 publications

Mechanical High-Temperature Properties and Damage Behavior of Coarse-Grained Alumina Refractory Metal Composites

Mechanical High-Temperature Properties and Damage Behavior of Coarse-Grained Alumina Refractory Metal Composites

Metal-Ceramic Beads Based on Niobium and Alumina Produced by Alginate Gelation

Field‐Assisted Sintering of Nb–Al₂O₃ Composite Materials and Investigation of Electrical Conductivity

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Coarse-grained refractory composites based on Nb-Al2O3 and Ta-Al2O3 castables

Cited by 19 publications

References 29 publications

Mechanical High-Temperature Properties and Damage Behavior of Coarse-Grained Alumina Refractory Metal Composites

Mechanical High-Temperature Properties and Damage Behavior of Coarse-Grained Alumina Refractory Metal Composites

Metal-Ceramic Beads Based on Niobium and Alumina Produced by Alginate Gelation

Field‐Assisted Sintering of Nb–Al2O3 Composite Materials and Investigation of Electrical Conductivity

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Field‐Assisted Sintering of Nb–Al₂O₃ Composite Materials and Investigation of Electrical Conductivity