Thursday, 16 August 2012

Thermochromic glass (IV)

I would like to finish the article at the address 
""The morphology of the undoped and W-doped VO2 nanopowders is characterized by SEM as shown in Figure 1. It is observed in Figures 1(a) to 1(g) that the tungsten dopant concentration almost has no effect on the morphology of the nanoparticles, and the particle sizes are about 20–60 nm. The experimental results also indicate that particles will be congregated with the increase of annealing time. Especially, the particles with 2 at% W-doped are relatively uniform, and the size is about 25 nm, which is in favor of the practice application on thermochromic window coatings. As is known, small and uniform particles are relatively easy to disperse in solvent and obtain homogeneous coating. [..]
TEM images of the undoped VO2 and 2 at % W-doped VO2 nanopowders are shown in Figures 4(a) and 4(c). The morphologies and sizes of the as-obtained samples are consistent with those of SEM images in Figures 1(a) and 1(e). Figures 4(b) and 4(d) show the lattice-resolved HRTEM images.[..] ""
 -) What is the difference between TEM, SEM and HRTEM?
Here is the answer difference-between-tem-and-sem/
or here on Wikipedia: High-resolution_transmission_electron_microscopy 
""When the phase transition of VO2 occurs, it exhibits a noticeable endothermal or exothermal profile in the DSC curve. Figure 5(a) shows the typical DSC curves of undoped and 2 at% W-doped VO2 nanopowders. With 2 at% W-doped sample, Mott phase transition arises at around 44°C and 34.5°C for the heating and cooling cycles, compared to 71°C and 58°C for the undoped VO2, respectively. The phase transition can be modified under the different factors such as defect density or lattice change . The appearance of endothermal and exothermal peaks during the heating and cooling process confirms the first-order transition between monoclinic VO2 (M) and tetragonal rutile VO2 (R) . To be vital for the practical thermochromic effect applications, the phase transition temperature of W-doped must be approaching to room temperature. In this case, the phase transition temperature could be reduced to 35°C with 3 at% W-doped in Figure 5(b).""

For the full discussion please see the cited article.

Lihua Chen, Chunming Huang, Gang Xu, et al., “Synthesis of Thermochromic W-Doped VO2 (M/R) Nanopowders by a Simple Solution-Based Process,” Journal of Nanomaterials, vol. 2012, Article ID 491051, 8 pages, 2012. doi:10.1155/2012/491051

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