Synthesis of Al₃BC₃ particulates by carbo-thermal reduction process—Parameter optimization and mechanism analysis

Abstract

The synthesis mechanism of Al 3 BC 3 through carbo-thermal reduction process was investigated and the processing conditions were optimized using Al(OH) 3 B 2 O 3 C as starting materials. The mass change and phase formation of the compacts were analyzed with varying temperature. Excess Al(OH) 3 and B 2 O 3 were required compared to the stoichiometric composition due to the loss of the source materials by vaporization at 1,5001,600°C. At 1,600°C, Al 2 O gas began to actively react with carbon to form Al 4 C 3 on the carbon particles. Al, Al 2 O and B 2 O 3 gases diffused through Al 4 C 3 layer and reacted with carbon at and above 1,650°C to form Al 3 BC 3 . The formation of hexagonal terrace at the surface of synthesized powder indicated that the gases also reacted at the particle surface with carbon which diffused through the carbide layers. The reactions were completed after calcination at 1,725°C for 4 h or at 1,800°C for 1 h. Gas-solid reactions were the major synthesis mechanism. The optimum composition for the synthesis of the ternary compound was Al(OH) 3 :B 2 O 3 :carbon = 0.7:1.4:0.25 by weight.

Low-Temperature Molten Salt Synthesis and the Characterisation of Submicron-Sized Al8B4C7 Powder

“…Thanks to the strong accelerating effect of the NaCl-NaF binary salt discussed above, essentially phase-pure Al 8 B 4 C 7 particles were successfully prepared at 1250 • C. This synthesis temperature was 350-550 • C lower than that required by the conventional synthesis routes [11,[13][14][15][16][17][18][19][20][21], demonstrating the great advantage and feasibility of the MSS technique developed in this work.…”

“…The particles overall were dispersed well, though some were agglomerated together. The average size of the particles was much smaller, and their dispersion was much better than it was when the conventional synthesis techniques were used [15][16][17][18]. The lattice interlayer spacing (one of the insets in Figure 6) was measured as around 0.29 nm, which corresponds to the (111) plane of hexagonal Al8B4C7.…”

“…In this regard, several synthesis methods/techniques have been developed to date, among which the thermal reduction and direct reaction methods have been investigated most extensively. In the former, Al or carbon (C) is often used as a reducing agent [15][16][17][18], so inexpensive and readily available boron-containing oxides can be used as a boron source to replace the much more expensive element boron (B) or B 4 C. However, a high synthesis temperature (1700-1800 • C) is required to complete the formation reaction. Furthermore, some by-products/intermediate phases such as Al 2 O 3 , Al 4 O 4 C and Al 2 OC often remain in the final product powder.…”

“…By using similar raw materials and a higher temperature (1800 • C), Cui et al [17] prepared hexagonal micro-platelets of Al 8 B 4 C 7 containing minor Al 2 OC. On the other hand, Lee et al [18] prepared Al 3 BC 3 via a complex route using Al(OH) 3 , B 2 O 3 and phenolic resin as raw materials. Despite the use of phenolic resin instead of solid C powder, the synthesis temperature still remained as high as 1725 • C.…”

Synthesis of a Fine (Ta0.8,Hf0.2)C Powder from Carbide or Oxide Powder Mixtures

“…The average grain sizes of the synthesized (Ti,W)C powders were >100 nm and 10.4–28.3 nm when using the oxide and carbide raw materials, respectively. Lee et al also reported the growth of Al 3 BC 3 particles up to 20 μm when prepared using Al(OH) 3 ‐B 2 O 3 ‐C as the starting materials while the average particle size was 14.1 μm using Al, B 4 C and C as raw materials . Although several reports indicated that the growth of ternary carbides occurred more strongly during synthesis when using the oxide raw materials than carbides, the reasons have not been clearly identified.…”