| Energetic aluminum has been widely used in the solid rocket propellants because of the abundant reserves,high reactivity and big heat releases.Much energy would be released by the redox reaction of oxidants and reductants when Al was considered as a reductant.Nano-Al will have wider application prospect because of the higher reactivity and faster energy release compared with the traditional micro-Al.But because of the smaller size,the severe dieseling phenomenon will happen with the nano-Al by the contact with oxygen.Therefore,in order to reserve and subsequent using,we need to stabilize the aluminum powders through the surface treatment.Meanwhile,in order to keep the energy at high temperature,the nano-Al which was stabilized also needs to keep higher active aluminum contents.The solvent-free coating method was used to treat the surface of nano-Al briefly with the commercial aluminum powders which was seen as the primary materials.The monolayer coating on the surface of the nano-Al powders was achieved by a reaction between the silane and the hydroxyl group with the using of dimethyldimethoxysilane?DMODMS?.The studies have shown that the hydrophobicity of surface was significantly improved after coating,and the contact angle can reach to 125.86°.In order to meet the compatibility of propellant components,the surface hydrophobicity and hydrophily of the stabilized nano-Al were adjusted by using trimethylchlorosilane?CTMS?.The contact angles of nano Al gradually became to 26.94°with the increasement of trimethylchlorosilane.After the DMODMS and CTMS were introduced,the low-temperature heat release of N-Al-2.5D-0.3C was 3763.64 J·g-1 compared with 3961.43J·g-1 of uncoated nano-Al at about 560?.The active aluminum content of the uncoated aluminum with oxidation film decreased to 70.48 mass%,while the active aluminum content of coated N-Al-2.5D decreased to 74.63 mass%which was higher than uncoated aluminum in humid environment.These results fully demonstrated that the coated samples not only have improved stability in humid conditions,but also have no significant deline in the energy releasement compared with the uncoated samples.Based on the above research,the corresponding reaction mechanism and adjustable hydrophobicity were explored.And micron aluminum powders were also used to support the above conclusions.The non-oxidized nano-aluminum powder which was made by our laboratory was realized by the method of solvent-free phase coating,and it cannot be directly exposed to the air due to its high reactivity.After being coated with DMODMS,the product can be stable in air with the contact angle of 121.15°.With the continuous introduction of CTMS,the contact angle was gradually reduced to 51.80°.Thus the method will also change the surface wettability.After 14 days in a humid environment,the reduction rate of active aluminum content of Al?M?-2.5D-0.2C with 10.37%was lower than that of Al?M?-2.5D-0.3C with 10.96%.And with the increasement of CTMS,the mass gain of the sample at800°C can reach to 118.4 mass%,which is about 3 mass%loss compared with the coated samples with DMODMS.Thus the protection effect against vapor is realized.The solvent-free phase coating method has a simple process,a short processing time,and does not require an excessively high temperature.The use of much organic solvents is also avoided.And it would be easier to industrialize. |
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