Dark blue nano tungsten oxide for heat insulation coating can be prepared by using a regular type ammonium paratungstate (APT with regular crystal form) or a common type ammonium paratungstate (APT with common crystal form). Some researchers have compared the impurity elements of the two types of crystalline ammonium paratungstate with the national standard GB/T10116-2007 APT-1 standard requirements.
They found that both APTs effectively controlled the content of impurity elements, especially the control of Cl ions, which is not specified in the national standard. The Cl ions in the two samples of APT reached a higher technical level. While it must be said that some small domestic manufacturers of ammonium paratungstate ignoring the presence of Cl ions, which may cause corrosion to the equipment. These manufacturers do not deal with Cl ions in APT to reduce the production cost. They said that the national standard is not specified for Cl ions. And therefore, There are cases that the Cl ions content of some ammonium paratungstate samples is larger than 10×10-6, and even beyond the scope of the analytical device.
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