Controlled Size Characterization Process for In-Situ TiB₂ Particles from Al Matrix Composites Using Nanoparticle Size...

The wide size range and high tendency to agglomerate of in-situ TiB₂ particles in reinforced Al matrix composites introduce great difficulties in their size characterization. In order to use a nanoparticle size analyzer (NSA) to obtain the precise size distribution of TiB₂ particles, a controlled size characterization process has been explored. First, the extraction and drying processes for TiB₂ particles were optimized. In the extraction process, alternated applications of magnetic stirring and normal ultrasound treatments were proven to accelerate the dissolution of the Al matrix in HCl solution. Furthermore, freeze-drying was found to minimize the agglomeration tendency among TiB₂ particles, facilitating the acquisition of pure powders. Such powders were quantitatively made into an initial TiB₂ suspension. Second, the chemical and physical dispersion technologies involved in initial TiB₂ suspension were put into focus. Chemically, adding PEI (M.W. 10000) at a ratio of m_PEI/m_TiB2 = 1/30 into the initial suspension can greatly improve the degree of TiB₂ dispersion. Physically, the optimum duration for high-energy ultrasound application to achieve TiB₂ dispersion was 10 min. Overall, the corresponding underlying dispersion mechanisms were discussed in detail. With the combination of these chemical and physical dispersion specifications for TiB₂ suspension, the bimodal size distribution of TiB₂ was able to be characterized by NSA for the first time, and its number-average diameter was 111 ± 6 nm, which was reduced by 59.8% over the initial suspension. Indeed, the small-sized and large-sized peaks of the TiB₂ particles characterized by NSA mostly match the results obtained from transmission electron microscopy and scanning electron microscopy, respectively.