Yang Shi,Zhangyi Huang,Jingjing Chen,Mao Deng,Mingyu Su,Jianqi Qi,Jun Wang,Haomin Wang
High-density (∼99.34%), fine-grained (∼685 nm) ZnO ceramic was successfully fabricated by the high-pressure cold sintering. The influences of solvent (liquid phase) fraction and the applied pressure on densification in this process have been carefully studied. The excess solvent can result in grain refinement, but impedes the densification of ceramic. Significantly, the role of pressure is unlike that in the traditional pressure-assisted sintering, which can improve the densification and inhibit grain growth. There is a critical pressure (∼1 GPa) that can be associated with the transition of recrystallization from heterogeneous nucleation to homogeneous nucleation . When the pressure is lower than this critical value, the applied pressure can improve densification, but cannot inhibit grain growth. Above the critical value, the densification is dramatically weakened and many small crystals in the interstitial space between grains can be found.
Step ladder-structured nitrocellulose (LNC) is a novel energetic binder prepared by chemically modifying nitrocellulose (NC) with the introduction of flexible polyethylene glycol (PEG-400) chain segments, with a regular structure and good performance of bonding. The step ladder-structured addresses critical limitations of NC-based propellants, including low-temperature brittleness and high sensitivity, while enhancing process safety. Although the structural, thermal, and other properties of LNC have been investigated in our previous research, there is a lack of systematic studies on the rheological properties during solution and gelatinization. The study of the relationship between the structural features and rheological properties of LNC is a key factor in guiding its gelatinization and improving the properties of LNC-based propellants. Steady-state rheology flow experiments revealed that LNC exhibited shear thinning in different solutions, which decreased with increasing concentration. It has desirable solubility and dispersion in N, N-dimethylformamide (DMF) solvent. The effect of solvents on the entanglement or orientation of LNC molecular chains may be reduced. These results can be quantitatively demonstrated using the Herschel-Bulkley model. Dynamic viscoelastic studies identified a critical point of concentration-frequency of 2.5 rad/s. This particular frequency point is a turning point in the law of the effect of concentration on the loss factor (tan δ ). For gelatinized systems, increasing the solvent content reduces the temperature sensitivity of the gelatinized materials. The viscosity-temperature correlation based on the Arrhenius equation allowed the optimization of the solvent content through the derived equilibrium relationship. These structure-rheological performance relationships establish basic guidelines for the precision gelatinization of LNC-based propellant, provide theoretical support for the replacement of conventional NC by LNC, and guide the gelatinization process to improve the performance of gun propellants.
危险品化学品经营许可证（带存储）