High-Temperature Interactions of Metal Oxides and a PVDF Binder

Abstract

Interactions between energetic material relevant nanoscale metal oxides (SiO 2 , TiO 2 , MgO, Al 2 O 3 , CuO, Bi 2 O 3 ) and poly(vinylidene fluoride) (PVDF) at high temperature were investigated by temperature-jump/time-of-flight mass spectrometry (T-jump/TOFMS) and thermogravimetric-differential scanning calorimetry (TGA-DSC). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology of the compositions, while X-ray diffraction (XRD) was utilized to analyze the condensed phase crystalline species at temperatures of interest. The exergonicity and exothermicity of HF gas with hydroxyl-terminated metal oxide surfaces make HF the likely fluorine-bearing moiety and primary mode of the fluorinating reactions, where terminal OH − configurations are replaced by F − in the formation of a stronger metal−fluorine bond. However, not all compositions produce corresponding stable metal fluoride. The results show that while some of the investigated metal oxide−PVDF compositions enhance PVDF decomposition and release HF in larger quantities than PVDF, others release HF in smaller quantities than PVDF and even retard PVDF decomposition. The former compositions demonstrate exothermic, multistep mass loss modes prior to neat PVDF mass loss, and the relative intensity of HF gas increases as the temperature of the release point decreases, implying a correlation between HF release and the progression of exothermic behavior. An interplay dynamic where surface interactions both lower the onset of HF release and engage exothermically with HF gas subsequently is proposed.

Catalytic Cleavage of the Dative Bond of Ammonia Borane by Polymeric Carbonyl Groups for Enhanced Energy Generation

“…Temperature jump probes coupled with a time-of-flight mass spectrometer (T-jump TOFMS) have been used to perform in situ time and temperature-resolved analysis of the gas phase species released on the decomposition of AB, polymers, and AB in polymer matrices at high heating rates of ∼10 5 K/s. Details about the mass spectrometer can be found in several of our previous publications. ,,, For the measurements, either AB powder was drop-casted from dispersion in hexane or the dissolved polymer or AB/polymer are drop-casted as films directly from their solutions, on a ∼75 μm Pt wire, which is resistively heated to ∼1500 K with a ∼3 ms voltage pulse, which maintains an average heating rate of ∼10 5 K/s. For the Flynn–Wall–Ozawa activation energy measurements, the heating rate was varied by adjusting the pulse width.…”

“…Details about the mass spectrometer can be found in several of our previous publications. 32,45,67,68 For the measurements, either AB powder was dropcasted from dispersion in hexane or the dissolved polymer or AB/ polymer are drop-casted as films directly from their solutions, on a ∼75 μm Pt wire, which is resistively heated to ∼1500 K with a ∼3 ms voltage pulse, which maintains an average heating rate of ∼10 5 K/s. For the Flynn−Wall−Ozawa activation energy measurements, the heating rate was varied by adjusting the pulse width.…”

In-Situ Thermochemical Shock-Induced Stress at the Metal/Oxide Interface Enhances Reactivity of Aluminum Nanoparticles

“…Details about the mass spectrometer can be found in several of our previous publications. 3,48,49 For this measurement, a thin Pt wire (∼75 μm) is used as the sample holder, on which thin layers of solid nanopowder samples are coated by drop-casting through micropipets. During the measurement, the Pt wire is resistively heated to ∼1500 K by applying a voltage pulse of width ∼3 ms, which leads to an average heating rate of ∼10 5 K/s.…”

“…Temperature jump time-of-flight mass spectrometry (T-jump TOFMS) was used for in-situ time- and temperature-resolved identification of the gas phase species released during the preignition and combustion reactions. Details about the mass spectrometer can be found in several of our previous publications. ,, For this measurement, a thin Pt wire (∼75 μm) is used as the sample holder, on which thin layers of solid nanopowder samples are coated by drop-casting through micropipets. During the measurement, the Pt wire is resistively heated to ∼1500 K by applying a voltage pulse of width ∼3 ms, which leads to an average heating rate of ∼10 5 K/s.…”

Residual Li2O degrades PVdF during the preparation of NMC811 slurries for Li-ion batteries

“…1 Consequently, a surface reaction between the more basic LiOH and PVdF is frequently suggested in the literature as a possible cause of the widely observed slurry gelation. 1–6 Such a phenomenon was indeed found to occur more likely for high Ni compositions—more affected by the formation of lithiated surface species—than during the preparation of electrodes based on NMCs with lower Ni content. According to this explanation, the PVdF would undergo dehydrofluorination following the simplified reaction (CH 2 –CF 2 ) n + LiOH → (CHCF) n + LiF + H 2 O proposed by G.J.…”