Combustion Synthesis of NbB2–Spinel MgAl2O4 Composites from MgO-Added Thermite-Based Reactants with Excess Boron

Abstract

The formation of NbB2–MgAl2O4 composites from the MgO-added thermite-based reaction systems was investigated by self-propagating high-temperature synthesis (SHS). Two thermite mixtures, Nb2O5/B2O3/Al and Nb2O5/Al, were, respectively, adopted in Reactions (1) and (2). The XRD analysis confirmed the combination of Al2O3 with MgO to form MgAl2O4 during the SHS process and that excess boron of 30 atom.% was required to yield NbB2–MgAl2O4 composites with negligible NbB and Nb3B4. The microstructure of the composite reveals that rod-shaped MgAl2O4 crystals are closely interlocked and granular NbB2 are embedded in or scattered over MgAl2O4. With the addition of MgAl2O4, the fracture toughness (KIC) of 4.37–4.82 MPa m1/2 was obtained for the composites. The activation energies Ea = 219.5 ± 16 and 167.9 ± 13 kJ/mol for Reactions (1) and (2) were determined from combustion wave kinetics.

Enhancing the thermal shock and corrosion resistance of low‐carbon Al2O3–C refractories: The role of h‐BN composite powder

“…Therefore, samples with the addition of h‐BN composite powder showed enhanced resistance to slag corrosion compared to samples without it. Additionally, both in situ formed spinel and AlN whiskers demonstrated excellent resistance against slag corrosion 47,48 . It should be noted that sample BM‐1.0 has a lower porosity compared to sample BM‐0, which is beneficial for improving slag corrosion resistance.…”

“…Additionally, both in situ formed spinel and AlN whiskers demonstrated excellent resistance against slag corrosion. 47,48 It should be noted that sample BM-1.0 has a lower porosity compared to sample BM-0, which is beneficial for improving slag corrosion resistance. Furthermore, by adding the h-BN composite powder, the size of the pores in the refractory would be reduced, as the introduced h-BN would fill and partition macropores.…”

Aluminothermic synthesis of ceramics from the hercynite-alumina system, using mill scale and aluminum chips

“…Synthetic spinels can be generated as by-products of various industrial processes, such as iron spinels associated with aluminothermic process slag [4], or spinel-type compounds present in steelmaking powders generated during steel production processes [5,6]. The synthetic formation of metallic oxides with spinel-type crystal structure generally occurs in association with high-temperature processes involving mixtures of aluminum or its oxides with different precursors such as metallic oxides or metallurgical process slags [7][8][9].…”

Self-Propagating High-Temperature Synthesis of Magnesium Aluminate Spinel Using Mg–Al Alloy

“…The SHS of MgAl 2 O 4 usually uses Al 2 O 3 /Mg or MgO/Al as a raw material. − As a result, the particle size of synthesized MgAl 2 O 4 is influenced by the raw material. MgAl 2 O 4 is generated during the oxidation of Mg–Al alloys, and at the same time, the oxidation layer of Mg–Al alloys breaks down during the oxidation process .…”