Bingge Zhao

Formation of amorphous structure in Sn3.5Ag droplet by in situ fast scanning calorimetry controllable quenching

Attributing to sensitive fast scanning calorimetry, combined with focused ion beam and high resolution transmission electron microscopy, we observed the solidification structure of single Sn3.5Ag droplet quenched at controllable rate. Amorphous layers in nanometer adjacent to some Ag3Sn crystals were directly detected. Based on solid state amorphization, a nano diffusion couple between primary formed β-Sn matrix and Ag3Sn intermetallic was put forward. Quenched at 15 000 K/s, the concentration gradient in this diffusion area was up to 109 m−1, which could seriously suppress the growth and further homogeneous nucleation of Ag3Sn, leading to the formation of amorphous structure.

Size control and its mechanism of SnAg nanoparticles

Abstract Sn3.5Ag (mass fraction, %) nanoparticles were synthesized by an improved chemical reduction method at room temperature. 1,10-phenanthroline and sodium borohydride were selected as the surfactant and reducing agent, respectively. It was found that no obvious oxidation of the synthesized nanoparticles was traced by X-ray diffraction. In addition, the results show that the density of primary particles decreases with decreasing the addition rate of the reducing agent. Moreover, the slight particle agglomeration and slow secondary particle growth can result in small-sized nanoparticles. Meanwhile, the effect of surfactant concentration on the particle size can effectively be controlled when the reducing agent is added into the precursor at an appropriate rate. In summary, the capping effect caused by the surfactant molecules coordinating with the nanoclusters will restrict the growth of the nanoparticles. The larger the mass ratio of the surfactant to the precursor is, the smaller the particle size is.

Investigating the formation process of sn-based lead-free nanoparticles with a chemical reduction method

Nanoparticles of a promising lead-free solder alloy (Sn3.5Ag (wt.%, SnAg) and Sn3.0Ag0.5Cu (wt.%, SAC)) were synthesized through a chemical reduction method by using anhydrous ethanol and 1,10-phenanthroline as the solvent and surfactant, respectively. To illustrate the formation process of Sn-Ag alloy based nanoparticles during the reaction, X-ray diffraction (XRD) was used to investigate the phases of the samples in relation to the reaction time. Different nucleation and growth mechanisms were compared on the formation process of the synthesized nanoparticles. The XRD results revealed different reaction process compared with other researchers. There weremany contributing factors to the difference in the examples found in the literature, with themain focus on the formation mechanism of crystal nuclei, the solubility and ionizability of metal salts in the solvent, the solid solubility of Cu in Ag nuclei, and the role of surfactant on the growth process. This study will help define the parameters necessary for the control of both the composition and size of the nanoparticles.

Rapid solidification behavior of nano-sized Sn droplets embedded in the Al matrix by nanocalorimetry

Al-10Sn (wt.%) melt-spun ribbons with nano-sized Sn droplets (20–400 nm in diameter) embedded in the Al matrix and bulk Sn distributed at Al grain boundaries were prepared. Differential fast scanning calorimetry (DFSC) based on nanocalorimetry and thin film technique was successfully applied to investigate the rapid solidification behavior of the embedded nano-sized Sn droplets at cooling rates ranging from 103 to 104 K s−1. Two broad exothermic peaks were observed in the DFSC curves. They were ascribed to the solidification of nano-sized Sn droplets with various catalytic activity factors f(θ). The cooling rate dependence of undercooling of nano-sized Sn droplets has been studied experimentally. The two series of undercooling which correspond to the two exothermic peaks increase slightly with the increases of cooling rate. Furthermore, a theoretical description of the experimental DFSC curves based on classical heterogeneous nucleation theory is developed. It is performed advancing a previously developed approach by assuming a smooth dependence of the droplet mass fraction on contact angle, m(θ), with a double Gaussian distribution during the nucleation process. This modified theoretical model is believed to be relevant also for other related rapid solidification processes.

Beating Homogeneous Nucleation and Tuning Atomic Ordering in Glass-Forming Metals by Nanocalorimetry

In this paper, the amorphous Ce68Al10Cu20Co2 (atom %) alloy was in situ prepared by nanocalorimetry. The high cooling and heating rates accessible with this technique facilitate the suppression of crystallization on cooling and the identification of homogeneous nucleation. Different from the generally accepted notion that metallic glasses form just by avoiding crystallization, the role of nucleation and growth in the crystallization behavior of amorphous alloys is specified, allowing an access to the ideal metallic glass free of nuclei. Local atomic configurations are fundamentally significant to unravel the glass forming ability (GFA) and phase transitions in metallic glasses. For this reason, isothermal annealing near Tg from 0.001 s to 25,000 s following quenching becomes the strategy to tune local atomic configurations and facilitate an amorphous alloy, a mixed glassy-nanocrystalline state, and a crystalline sample successively. On the basis of the evolution of crystallization enthalpy and overall latent heat on reheating, we quantify the underlying mechanism for the isothermal nucleation and crystallization of amorphous alloys. With Johnson-Mehl-Avrami method, it is demonstrated that the coexistence of homogeneous and heterogeneous nucleation contributes to the isothermal crystallization of glass. Heterogeneous rather than homogeneous nucleation dominates the isothermal crystallization of the undercooled liquid. For the mixed glassy-nanocrystalline structure, an extraordinary kinetic stability of the residual glass is validated, which is ascribed to the denser packed interface between amorphous phase and ordered nanocrystals. Tailoring the amorphous structure by nanocalorimetry permits new insights into unraveling GFA and the mechanism that correlates local atomic configurations and phase transitions in metallic glasses.

Role of reactant concentration in size control of SnAgCu nanoparticles

Abstract Attributing to the melting temperature depressing resulted from the size effect of nanoparticles, the SnAgCu alloy system can be a promising candidate to replace the traditional toxic SnPb solder in the field of electronic packaging. Chemical reduction method was used to fabricate the Sn3.0Ag0.5Cu (SAC) (mass fraction, %) alloy nanoparticles. Sodium borohydride and 1,10-phenanthroline were chosen as the reducing agent and surfactant respectively. In addition, the morphology of the synthesized nanoparticles was investigated by field emission scanning electron microscopy (FE-SEM), and the size distribution of the as-prepared particles was obtained from the image analysis. It was found that the particle size increased with increasing the reactant concentration. Finally, theoretical analysis was employed to illustrate the influence of reactant concentration on the particle size.

Solidification behavior of indium droplets embedded in aluminum by differential fast scanning calorimetry

Indium droplets embedded in aluminum matrix were successfully prepared by melt spinning technique. The results showed that an amount of nano-sized indium droplets were embedded inside aluminum grains, while micro-sized indium droplets were distributed along aluminum grain boundaries. The nano-sized indium droplets exhibited an orientation relationship with the aluminum matrix of

Influence of Magnetic Field on Dealloying of Al-15Fe Ribbons and Formation of Fe3O4 Octahedra

(\bar{1}01)_{\text{In}} ||(\bar{1}1\bar{1})_{\text{Al}}