(124b) Dominant Role of Chemical Diffusion and Reaction in Shaping Particles

Chemical diffusion and reaction are generally involved in the formation of materials. These two processes are coupled together and play a role in the structure evolution of materials. Although the individual role of diffusion and reaction has been investigated, it is still unclear how these two factors work together to determine the materials structure and what is the mechanism behind. Firstly we used different approaches to regulate the diffusion and reaction rates in the synthesis of silver particles [1-3]. The role of diffusion and reaction in shaping particles was generalized. At a diffusion limitation, small silver particles were obtained and big polyhedral particles were formed at a reaction limitation. In the middle range of diffusion and reaction, dendritic structures were largely produced, which is independent on the preparation methods. In the following, the control on diffusion and reaction has been extended to synthesize other materials and the similar results were obtained [4,5], which further confirms the general role of diffusion and reaction in shaping materials. The Damkoehler number was employed to quantify the relative change of diffusion and reaction[6]. It was found that the morphology of materials is dependent on the relative strength of diffusion and reaction. Since the diffusion and reaction determine the chemical distribution around the growth front of materials, the local chemical gradient was proposed to be the mechanism of diffusion and reaction controlling materials structures, which was verified by measuring the local chemical distribution by laser interference as well as by conducting phase field simulation. Currently the crystallographic characters have been included in the diffusion and reaction model. The interface fields (concentration gradient) and surface energy (crystallography) were considered at the same time in crystallization. The compromise of their competition may lead to the diversity and complexity of materials structures, which is accorded with the concept of mesoscience.

References

[1] Chemical Engineering Science 138, 457, 2015.

[2] Scientific Reports 5, 14942, 2015.

[3] IEC Research 55, 8319-8326, 2016.

[4] Crystal Growth & Design 13, 1820-1825, 2013.

[5] CrystEngComm 19, 72-79, 2017.

[6] Crystal Growth & Design 16, 2850−2859, 2016.