Preparation And Property Investigation Of Doped Vanadium Dioxide Ultrafine Powder

Vanadium dioxide (VO2) is one kind of metallic oxide with thermochromism property at phase transition temperature of 68℃. It can alter infrared transmittance by transforming crystal structure reversibly when phase transition occurs, that characteristic is applicable to prepare intelligent temperature-control films. At present, the research about relevant issues is focused on preparation of VO2 inorganic films though Sputtering, CVD, sol-gel, and so on. However, these methods need expensive instrument and raw material, besides the area of the films is limited, so that they are not suitable for large-scale production.It was reported that ultrafine powder of VO2 is capable of lessening the stress caused by the phase transition and to make light transmittance improved. The hybrid films made by adding the fine particle of VO2 to the polymer are able to overcome defects in VO2 inorganic films, which have infinite potential in application. Yet, there is seldom research on that field, because it's lacking in mass production of VO2 ultrafine powder which possess the function of phase transition at low temperature, as well as the powder surface modification technique.In this dissertation, the VO2 was doped effectively to low the phase transition temperature via sol-gel method, combining with the azeotropic distillation procedure thermochromism VO2 micro powder were successfully synthesized, simultaneously we had tried to modify the powder in order to improve the compatibility between the inorganic particles and polymer. The primary contents, methods and results are as follows:1. Research on the VO2 phase transition properties doped by some different dopants. In this experiment, Vanadium pentoxide(V2O5) was doped by dopant through the elevated temperature fusion process, the result doped VO2 powder were achieved after reduced V2O5 by ammonia. By selecting different tungsten compounds as tungsten dopant, the performance of doped VO2 were characterized by means of XRD,DSC,XPS,SEM and so on, it was found that the powder doped by sodiumtungstate(Na2WO4) showed the best effect, the phase transition temperature of VO2 is decreased by 32℃with only lat.% Na2WO4 doped. Sodium molybdate (Na2MoO4) was chosed as molybdenum dopant, the phase transition temperature is reduced by 20℃with lat.% Na2MoO4 doped.2. Effect of azeotropic distillation on the phase transition behavior and powder morphology of doped VO2 powder had been investigated. The doped VO2 powder which has small size and good distribution was successfully prepared by an improved azeotropic distillation processing, which prevented the formations of agglomeration. With comparison, the reduced rate of phase transition temperature of VO2 doped by Na2WO4 or Na2MoO4 prepared by azeotropic distillation method were lower than the rate of which without azeotropic distillation, however, the enthalpy value has increased the more than doubled. On the other hand, the V2O5 nanorods were formed through changing calcination temperature growth from the nanocrystalline phase created after azeotropic distillation.3. Preliminary studies on VO2 powder surface modification method. Two different ways were used for VO2 powder surface modification:(1)Inorganic/organic surface treatment. First, the particle was coated by silica via hydrolysis of tetraethoxy silane(TEOS), and then modified by silane coupling agent. (2) Poly (acryloyl chloride) and poly (ethylene glycol) was covalently grafted onto the surface.