Research on the composition of UV curing modified compounds for 3D printing based on HyperChem simulation

The precursor conversion method provides the possibility of 3D printing ceramic materials, and the resin system with polysilazane as the precursor is expected to prepare high-performance ceramic materials for aviation. In this paper, the UV curing reaction system of polysilazane for 3D printing is taken as the research object, and hyperchem8.0 software is used as the research means. The model construction, chemical bond energy calculation, reaction enthalpy calculation and other modules in the software are used to simulate and predict the reaction process and mechanism of UV curing, which provides a theoretical basis for the selection and optimization of the subsequent UV curing reaction system for 3D printing.

Surface Reactivity of Carbonaceous Nanoparticles: The Importance of Surface Pocket

The surface reactivity of carbonaceous nanoparticles is revealed from the barrier height and reaction enthalpy of hydrogen abstraction reaction by H radicals computed at the M06-2X/6–311g(d,p)//B3LYP/6-311G(d,p) level of theory. Small polycyclic aromatic hydrocarbon (PAH) clusters are selected as the model system of carbonaceous nanoparticles. The PAHs considered are naphthalene, pyrene, coronene, ovalene and circumcoronene. Cluster sizes range from dimer to tetramer with a parallel or crossed configuration. All results show similar values as that of monomers, but naphthalene dimers with a crossed configuration yield a lower barrier height and reaction enthalpy by ∼2 kcal/mol. A minor size dependence is noticed in the series of naphthalene clusters where a larger cluster exhibits a smaller barrier height. Larger homogeneous PAH clusters in a size range of 1.1–1.9 nm are later generated to mimic nascent soot surface. It is found that the barrier height decreases with the increase in particle size, and the averaged values are ∼2 kcal/mol lower than that of monomers. More importantly, a larger particle shows a wider spread in barrier heights, and low barrier heights are seen in the surface shallow regions (e.g., surface pockets). The lowest barrier height of ∼8.5 kcal/mol is observed at a C-H site locating in a surface pocket. A set of model systems are built to reveal the underlying mechanism of reduction in barrier height. It is shown that the reduction is caused by local interactions between the neighboring atoms and the local curvature. Further analysis on the average localized ionization potential shows that larger particles have higher reactivity, further supporting our findings from the barrier height of hydrogen abstraction reactions. Therefore, it is concluded that the surface reactivity depends on the particle size and the most reactive sites always locate at the surface pockets.

Effect of Pyrolysis Reactions on Coal and Biomass Gasification Process

Thermodynamic analysis of a gasification process was conducted assuming that it is composed of two successive stages, namely: pyrolysis reaction followed by a stage of gasification reaction. This approach allows formulation the models of selected gasification processes dominating in industrial applications namely: Shell (coal), SES (coal), and DFB (dual fluid bed, biomass) gasification. It was shown that the enthalpy of fuel formation is essential for the correctness of computed results. The specific computational formula for a wide range of fuels enthalpy of formation was developed. The following categories were evaluated in terms of energy balance: total reaction enthalpy of gasification process, enthalpy of pyrolysis reaction, enthalpy of gasification reaction, heat demand for pyrolysis reaction, and heat demand for gasification reactions. The discussion of heat demand for particular stages of gasification related to the various processes was performed concluding the importance of the pyrolysis stage.

Evaluation of the Pr + O → PrO+ + e− chemi-ionization reaction enthalpy and praseodymium oxide, carbide, dioxide, and carbonyl cation bond energies

Guided ion beam tandem mass spectrometry was used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal praseodymium cation (Pr+) with O2, CO2, and CO and reactions of PrO+ with CO, O2, and Xe.

Thermodynamic Efficiency of Water Vapor/Solid Chemical Sorption Heat Storage for Buildings: Theoretical Limits and Integration Considerations

The theoretical limits of water sorbate-based chemical sorption heat storage are investigated in this study. First, a classification of thermochemical heat storage is proposed based on bonding typology. Then, thermodynamics of chemical solid/gas sorption is introduced. The analysis of the reaction enthalpy from the literature indicates that this value is only slightly varying for one mole of water. Using this observation, and with the help of thermodynamic considerations, it is possible to derive conclusions on energy efficiency of closed and open heat storage systems. Whatever the salt, the main results are (1) the energy required for evaporation of water is, at least, 65% of the available energy of reaction, and (2) the maximum theoretical energy efficiency of the system, defined as the ratio of the heat released to the building over the heat provided to the storage, is about 1.8. Considering the data from literature, it is also possible to show that perfectly working prototypes have an energy efficiency about 49%. Based on those results, it is possible to imagine that for the best available material, a perfect thermochemical heat storage system would correspond to 12 times water with a temperature difference about 50 °C. Such solution is definitely competitive, provided that some difficult issues are solved—issues that are discussed throughout this paper.

Characterization of reaction enthalpy and kinetics in a microscale flow platform

We report an isothermal flow calorimeter for characterization of reaction enthalpy and kinetics.