Abstract
To address the various shortcomings of a high material cost, energy-intensive temperature conditions and ultra-low efficiency of the conventional boro/carbothermal reduction method for the industrial preparation of ZrB2-SiC powders, a novel molten-salt and microwave-modified boro/carbothermal reduction method (MSM-BCTR) was developed to synthesize ZrB2-SiC powders. As a result, phase pure ZrB2-SiC powders can be obtained by firing low-cost zircon (ZrSiO4), amorphous carbon (C), and boron carbide (B4C) at a reduced temperature of 1200 °C for only 20 min. Such processing conditions are remarkably milder than not only that required for conventional boro/carbothermal reduction method to prepare phase pure ZrB2 or ZrB2-SiC powders (firing temperature of above 1500 °C and dwelling time of at least several hours), but also that even with costly active metals (e.g., Mg and Al). More importantly, the as-obtained ZrB2 particles had a single crystalline nature and well-defined plate-like morphology, which is believed to be favorable for enhancing the mechanical properties, especially toughness of their bulk counterpart. The achievement of a highly-efficient preparation of such high-quality ZrB2-SiC powders at a reduced temperature should be mainly attributed to the specific molten-salt and microwave-modified boro/carbothermal reduction method.
Highlights
IntroductionThe industrial production of ZrB2 -SiC powders mainly employs the boro/carbothermal reduction (BCTR) approach, with ZrO2 and SiO2 as Zr and Si as precursors [6,7,8,9]
Materials 2018, 11, 1811 temperature (1500–1700 ◦ C) and long soaking time as well as a high agglomeration degree, low purity, and poor sinterability of powder product. These shortcomings of the conventional boro/carbothermal reduction (BCTR) method are due to the following two reasons: (1) the poor reactivity of commercial ZrO2 and SiO2 raw materials, resulting in the inefficiency of synthetic process; and (2) the intrinsic requirements for strict temperature conditions and a long soaking time, and phase pure ZrB2 -SiC powders with a well-defined morphology and textured structure are difficult to prepare by the conventional BCTR method
For the sample (MB-1) prepared at 1100 ◦ C, all the visible diffraction peaks belonged to ZrSiO4, implying the decomposition of zircon (Reaction (1)) had not yet occurred
Summary
The industrial production of ZrB2 -SiC powders mainly employs the boro/carbothermal reduction (BCTR) approach, with ZrO2 and SiO2 as Zr and Si as precursors [6,7,8,9] This method suffers from several significant disadvantages, such as the requirement of a high processing. Materials 2018, 11, 1811 temperature (1500–1700 ◦ C) and long soaking time (at least several hours) as well as a high agglomeration degree, low purity, and poor sinterability of powder product Speaking, these shortcomings of the conventional BCTR method are due to the following two reasons: (1) the poor reactivity of commercial ZrO2 and SiO2 raw materials, resulting in the inefficiency of synthetic process; and (2) the intrinsic requirements for strict temperature conditions and a long soaking time, and phase pure ZrB2 -SiC powders with a well-defined morphology and textured structure are difficult to prepare by the conventional BCTR method. A modification of the conventional method by an advanced synthetic technique, and using high-activity and low-price raw materials to prepare
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