The thermogravimetric techniques and differential thermal analysis have been employed in this work to analyze the macro-reactions mechanism of the silicon delay composition. Quantum chemical calculation has been performed to study the microscopic mechanism of the main reaction (Pb 3 O 4 + Si) at the density functional theory BPW91/6−311++G(d, p) level of theory with the SDD implicit solvent model. Our results have shown that in the silicon delay composition, the strongest reaction exothermic peak is originated from the reaction between Pb 3 O 4 cluster and Si. For the microscopic reaction process of Pb 3 O 4 and Si containing two reaction pathways, we found that they proceeded in this manner, Pb 3 O 4 + Si → SiO + 3PbO and SiO + Pb 3 O 4 → SiO 2 + 3PbO, with a total of four reaction channels. In addition, we have determined the reaction sites by making use of the charge distribution from natural bonding orbital analysis and the HOMO–LUMO gap of the reactants.
To improve the storage stability and delay accuracy of boron series delayed composition, in this study, the reaction thermokinetic characteristics and microscopic reaction mechanism of B-Pb 3 O 4 delay composition were systematically analysed. Synchronous thermal analysis and differential scanning calorimetry were used to evaluate the thermodynamic properties of the delay composition. The kinetic parameters were calculated based upon Ozawa method. The macroscopic and microscopic reaction characteristics of Pb 3 O 4 -B were studied via X-ray photoelectron spectroscopy and density functional theory calculation. The reaction path and reaction site were determined by analysing the HOMO–LUMO orbit of reactants. The results showed that there are two reaction sites in the reaction process of lead tetraoxide and boron, which are Pb6 (Pb5) and Pb7 (Pb4) sites, respectively. The poor storage stability was mainly due to the reaction energy barrier of Pb 3 O 4 cluster and B being low, which are prone to chemical reactions in storage. The microscopic reaction mechanism of lead trioxide and boron mainly consists of five steps: Pb 3 O 4 + B → BO + 3PbO, (2) BO + Pb 3 O 4 → BO 2 + 3PbO, (3) B + PbO → BO + Pb, (4) BO + BO → B 2 O 2 , and (5) BO + BO 2 → B 2 O 3 , respectively.
Understanding the growth behaviors of nanomaterials during liquid-phase synthesis will be beneficial in designing and applying many functional nanodevices. However, the growth pathways regarding the nanocrystal facet development remain largely unknown as direct observation is lacking. Herein, the in situ study of Pb3O4 nanocrystals’ growth is reported by using the liquid cell transmission electron microscopy with high spatial and temporal resolution. The findings indicate that Pb3O4 nanocrystals’ growth follows distinct trajectories with shape evolution when the growth pathways are varied. Three growth pathways are observed, including the monomer growth of Pb3O4 nanocrystals, the coalescence growth of four stationary Pb3O4 nanocrystals, and the oriented attachment growth of Pb3O4 nanocrystal pairs and multiple randomly dispersed Pb3O4 nanocrystals. It is the first observation that Pb3O4 nanocrystals with a regular quadrilateral shape are formed, in which nanocrystal facets preferentially grow along the [002] direction of Pb3O4. Theoretical analysis confirms in this study that the surface energy and physical driving force play key roles in the growth of nanocrystals in a liquid. Such understanding of the growth pathways and quantification of formation kinetics are important for the design of hierarchical nanomaterials and the control of nanocrystal self-assembly for functional devices.
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