Molten Salt Synthesis of Magnesium Aluminate (MgAl₂O₄) Spinel on Ti₃AlC₂ Substrate

Abstract

A MgAl2O4 (MA) spinel layer was synthesized on Ti3AlC2 substrate through the molten salt synthesis (MSS) method. The Ti3AlC2 substrate was immersed in MgCl2·6H2O powders and treated at 800°, 850°, and 900°C for 4 h in air. A continuous and 10‐μm‐thick MgAl2O4 layer was obtained at 900°C, by which the surface hardness of Ti3AlC2 can be effectively improved. The combined scanning electron microscopy observations and crystal morphology simulation further revealed that the as‐formed MgAl2O4 presents tetragonal bipyramids morphology with (400)‐orientation.

Microsized Red Luminescent MgAl2O4:Mn4+ Single-Crystal Phosphor Grown in Molten Salt for White LEDs

“…Among all the MgAl 2 O 4 :Mn 4+ phosphors obtained, the crystallites shown in Figure 2d draw our interest since the unique tetragonal bipyramids morphology indicates a singlecrystal-like nature of the grains which may contain less luminescence-quenching defects. Zhang et al 25 reported the formation of a MgAl 2 O 4 layer with a similar morphology by immersing Ti 3 AlC 2 into the MgCl 2 (melting temperature, 712 °C) at 800−900 °C. The molten MgCl 2 provides an unstrained environment for MgAl 2 O 4 crystal growth and its {111} planes with the lowest growth rate retained, resulting in the formation of a tetragonal bipyramids morphology.…”

“…For the cubic structure of MgAl 2 O 4 (space group Fd3̅ m), the densities of lattice points of the {111} plane are the highest among all the planes and, thus, has the lowest growth rate when receiving the same amount of growth units. 25 The growth units can sufficiently select the growing sites on the crystalline surface according to its crystal structure, under the approximate-equilibrium condition given in the unstrained molten-salt environment for crystal growth. The surface that grows at the lowest rate will be of the highest morphological importance in the shape formation of final crystals.…”

“…The measured interplanar d-spacing is 0.202 nm (Figure 4d), corresponding to the (400) plane of MgAl 2 O 4 , in agreement with the values in the standard data (JCPDS 47- 0254). Zhang et al 25 have simulated the crystal morphologies of the (400)-oriented MgAl 2 O 4 with different relative growth rates on {111} and {400} faces, which are schematically reillustrated in Figure S4. For MgAl 2 O 4 in a cubic system, the densities of lattice points of the {111} plane are the highest among all planes, which corresponds to the lowest growth rate when receiving the same amount of growth units.…”

“…The molten MgCl 2 provides an unstrained environment for MgAl 2 O 4 crystal growth and its {111} planes with the lowest growth rate retained, resulting in the formation of a tetragonal bipyramids morphology. For the cubic structure of MgAl 2 O 4 (space group Fd 3̅ m ), the densities of lattice points of the {111} plane are the highest among all the planes and, thus, has the lowest growth rate when receiving the same amount of growth units . The growth units can sufficiently select the growing sites on the crystalline surface according to its crystal structure, under the approximate-equilibrium condition given in the unstrained molten-salt environment for crystal growth.…”

Synthesis and characterization of MgAl2O4 micro-rods by a molten salt method

“…Therefore, MSS has attracted the interest of materials scientists for synthesis of ceramic powders with varying morphologies as well as complex stoichiometry. Recently this technique has been used to synthesize MgAl 2 O 4 spinel [6][7][8][9][10][11][12][13][14].…”