Boron has a promising application in the field of propellants due to its high calorific value. However, the difficulty of ignition and the poor combustion efficiency of boron (B) have severely ...limited its efficient application. In response to this issue, this paper proposes to improve the ignition and combustion performance of micron-sized boron by the Polyvinylidene Fluoride (PVDF) coating. The effect of PVDF content on the B combustion performance was systematically studied using a Thermogravimetry-Differential Scanning Calorimetry (TG-DSC), a Transmission Electron Microscope (TEM), an X-Ray Diffractometer (XRD), a laser Particle Size Analyzer (PSA), and a high-speed camera. The results show that PVDF can significantly reduce the initial oxidation temperature of B powder and increase its reaction heat. When the PVDF content is 23wt%, the reaction heat and the combustion intensity of B powder reach the maximum and are significantly higher than those of the uncoated B powder. Moreover, the fluorination reaction that occurs during the combustion process not only can effectively shorten the combustion time of B powder, but also has a positive effect on its flame intensity and propagation speed, and it significantly reduces B particle agglomeration, which improves the combustion efficiency significantly. This study lays the foundation for the application of PVDF modified B in B-based solid propellants.
In this work, a technique was proposed to prepare UO2 from UO3 by the two processes of fluorination reaction of UO3 with NH4HF2 and electrochemical reduction of UO22+ for the recycle uranium. The ...feasibility of fluorination reaction was firstly confirmed using thermodynamic calculation; then, the products were analyzed using XRD, Raman and fluorescence to be UO2F2. The fluorination mechanism was inferred to be UO3(s) + NH4HF2 → (NH4)3UO2F5→ NH4(UO2)2F5 → UO2F2. The redox behavior of UO22+ on W electrode was investigated by cyclic voltammetry and square wave voltammetry, which indicated that UO22+ was reduced to UO2via a two-step single electron transfer with diffusion-controlled. The diffusion coefficient of UO22+ was calculated to be 6.22 × 10−5 cm2/s. The disproportionation reaction of UO2+ was observed, and the relationship between the disproportionation reaction and scan rate was discussed. Moreover, the electrochemical fabrication of UO2 was conducted by electrolysis at −0.8 V, and the product was analyzed by XRD, SEM and EDS to be UO2. ICP-AES results showed that the extraction efficiency of UO2 could reach 98.53%.
UO3 obtained by high-temperature oxidation of spent fuel is first fluorinated to produce UO2F2, and then UO2F2 is electrochemically reduced to the oxide fuel UO2 in LiCl-KCl molten salt. Display omitted
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•We simulated the fluorination of the silicon nitride surface by HF and CHxF4−x.•For CHxF4−x, the formation of SiF* and SiNHCHxF3−x* is exothermic.•Only CH3F showed lower activation ...energy for the formation of SiF* than SiNHCH3*.•For the SiF* formation, CH3F showed the lowest activation energy on silicon nitride.•For the SiF* formation, HF showed the lowest activation energy on silicon oxide.
Gaseous fluorine-containing molecules are crucial for controlled etching in semiconductor industries. This work presents the first-principle density functional theory (DFT) study on the modification of silicon nitride surface by fluorine-containing gases such as HF, CF4, CHF3, CH2F2, and CH3F. The reactions were modeled and simulated by assuming that the silicon nitride surface was exposed to a single fluorine-containing molecule to form different resulting surface groups and byproducts. For all fluorine-containing molecules, the SiF* formation was expected to be spontaneous. For the CHxF4−x (x = 0 to 3) molecules, the formation of SiNHCHxF3−x* was also predicted as an exothermic reaction. In the case of CH3F only, the activation energy (EA) for the SiF* formation was 0.98 eV, which is significantly lower than 2.03 eV for the SiNHCH3* formation. For the other CHxF4−x molecules, the activation energies for the formation of SiNHCHxF3−x* and SiF* were approximately the same. For the SiF* formation, CH3F showed the lowest EA value on the silicon nitride surface, whereas HF showed the lowest EA value on the silicon oxide surface. The selective fluorination of silicon nitride with CH3F was explained using the absence of fluorine in the CH3 after the dissociation of a fluorine atom and the basicity of the silicon nitride surface. These findings imply that with a good selection of a fluorine-containing gas, SiF* can be selectively produced on a specific surface.
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An expedient and mild strategy for the synthesis of unconventional 2-(dimethylamino)-3,3-difluorochroman-4-one derivatives from o-hydroxyarylenaminones and Selectfluor was developed ...at room temperature under catalyst-free conditions. This method showed excellent chemoselectivity and great functional groups tolerance.
We conducted research aimed at developing a novel method for synthesis of MgF2 hollow nanoparticles that is simpler than the conventional synthetic method. First, Mg(OH)2 raw material nanoparticles ...were contact with hydrofluoric acid vapor in a gas-solid reactor at 473 K. As a result, the surfaces of the Mg(OH)2 nanoparticles were fluorinated to obtain Mg(OH)2-MgF2 core-shell particles. Next, the MgF2 hollow nanoparticles were synthesized by soaking the core-shell particles in 1.0 mol/L hydrochloric acid to dissolve only the Mg(OH)2 core portion. We have succeeded in developing a method for synthesizing MgF2 hollow nanoparticles with different MgF2 shell thicknesses by controlling the surface fluorination reaction period of Mg(OH)2 raw material nanoparticles.
A novel synthesis method of 1,1-dichlorooctafluorocyclopentane and 1,2-dichlorooctafluorocyclopentane through the reaction of 1,2-dichlorohexafluorocyclopentene, anhydrous hydrogen fluoride (AHF) and ...chlorine were reported. The new catalyst ZFZCC containing Fe(+3), Zr(+4), Co(+2), Zn(+2) and Cu(+2) were prepared and the mechanism was discussed.
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•A novel method of preparing dichlorooctafluorocyclopentane was reported.•A series of single- and multi-component catalysts was prepared by improving components and methods.•The co-precipitated catalyst containing Fe(+3), Zr(+4), Co(+2), Zn(+2) and Cu(+2) showed the highest catalytic activity.•The catalytic reaction mechanism was put forward.
A novel method was used for preparing 1,1-dichlorooctafluorocyclopentane and 1,2-dichlorooctafluorocyclopentane through the reaction of 1,2-dichlorohexafluorocyclopentene, anhydrous hydrogen fluoride, and chlorine. A series of single- and multi-component catalysts were prepared by means of impregnation and coprecipitation, respectively. The catalyst containing Fe(III), Zr(IV), Co(II), Zn(II) and Cu(II) showed the highest catalytic activity among these catalysts. Moreover, the main reaction routes and catalytic mechanism were investigated through experiments and theoretical analysis. Given the environmental and economic benefits, this method has a great application potential in industrial production.
![[Technical Report] Analysis...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0435-4036/small "[Technical Report] Analysis of multiple sulfur isotopes using a Curie-point Pyrolyzer and an automated sample preparation system")
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