Investigation of the surface morphology of ASD-4 powder, modified by V2O5
Abstract
The changes in the surface layer of aluminum particles treated with V2O5 • nH2O hydrogel were studied by ellipsometry and raster electron microscopy methods. It was shown that at 0.8 wt.% content of metallic vanadium in the modified powder, the particle surface layer has a well developed relief, and a high degree of impregnation is achieved. The values of the thickness of this layer measured by different methods were compared, and the obtained deviations were analyzed.
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Introduction
The use of vanadium oxides for improving the combustion of metal powders has been studied for many years [1-4]. Due to vanadium polyvalence, a large amount of oxides and other compounds formed during its oxidation makes this metal a good oxygen carrier to the reaction zone. Being the most demanded material in this field, vanadium oxide (V) in itself is a strong oxidant and has a melting point close to aluminum, which promotes its use as an additive reducing the ignition temperature and increasing the speed and heat of combustion of powder aluminum. In the liquid state, vanadium pentoxide, due to a low surface tension [5], penetrates into the pores and cracks of the oxide film on the surface of aluminum particles [1, 6, 7], promoting active oxidation of aluminum with simultaneous formation of AlVO4. The application of V2O5 · nH2O gel on the surface of aluminum powders of the ASD-4 type [8] significantly increases their specific surface, without changing the shape of the metallic particles, which positively affects their rheological properties [6]. We have established that the aluminum powders modified with V2O5 · nH2O, Na2V12O31 · nH2O, LiV12O31 · nH2O, Na2MoV11O31 · nH2O and 6V2O5 · B2O3 · nH2O had twice as large specific surface area as the initial ASD-4, a high storage stability and, according to thermogravimetric data, a high oxidation efficiency in air [6, 7]. It is known [2, 9, 10] that during dehydration of gels the obtained xerogels have a quasi-two-dimensional (2D) layered structure that is easily intercalated at room temperature by metal ions, molecules of organic solvents, organometallic complexes and other compounds. However, the characteristics of the modified powder surface, the geometric parameters of the oxide and modifying layers, the structure and stability of the modified layer remain unknown. Thus, the main aim of the present work is a more detailed study of the morphology, thickness of the oxide and modifying layers in the initial and modified particles of aluminum powder, as well as the stability of the modified layer during heating to the temperature close to the aluminum melting point.
Conclusion
Using ellipsometry, microscopy and elemental analysis, it was shown that the samples, obtained by impregnation of aluminum powder with vanadium-containing hydrogel, after drying and calcination at 623 K in air represent a system, in which the deposited gel forms a nanosize layer impregnated with V2O5 ∙ nH2O on the particle surface. If the content of metallic vanadium in the modified powder is 0.8 wt. %, the surface layer is characterized by a highly developed relief with good adhesion due to the chemical bonding of the modifier with the surface of aluminum particles owing to the intercalation of aluminum ions in the xerogel structure.
The work was carried out in accordance with the state assignment and R&D plans of the Institute of Solid State Chemistry of the Urals Branch of the Russian Academy of Sciences (No. AAA-A16-116122810219-4).