The cubic zirconium tungstate is one of the hotspots in the research of negative thermal expansion materials, with its widest range of negative expansion effect, high negative expansion coefficient and isotropy and other advantages, it can be combined with positive expansion into the specific materials with zero or low expansion, and thus to be used in the some devices which is used under extreme temperature conditions field of aerospace. The preparation methods of zirconium tungstate are solid phase sintering, sol-gel, combustion, chemical coprecipitation and microwave method ect., however, the zirconium tungstate particles or whiskers prepared by these methods are irregular, and can not be used in some specific fields, such as aerospace.

 

There is an invention disclosed a method for preparing nanoscale zirconium tungstate hollow sphere by hydrothermal synthesis method from the raw materials of ammonium metatungstate (AMT) and zirconium oxychloride, with the steps as following:

1. Respectively weight the right amount of ammonium metatungstate and zirconium oxychloride according to the stoichiometric ratio of zirconium tungstate (ZrW₂O₈), respectively, and prepare zirconium oxychloride aqueous solution and ammonium metatungstate aqueous solution respectively;

2. Add zirconium oxychloride aqueous solution into ammonium metatungstate aqueous solution under the condition of stirring, then preheat the mixture at  the temperature of 60～70℃ with stirring continuous;

3. Add hydrochloric acid solution with continuously stirring, and then heat the solution to 80~100℃, then we get the zirconium tungstate precursor suspension after keeping the temperature for a proper time;

4. The zirconium tungstate precursor suspension is carried out a hydrothermal reaction at a temperature of 170~190℃, followed by cooling, collecting the precipitate and washing to remove chloride ions (Cl^- ), drying, calcining at 800~1000℃, and finally to obtain nanoscale zirconium tungstate hollow sphere.

 

In this method of preparing zirconium tungstate by using AMT as raw material, due to the hydrothermal synthesis method can truly realize synthesizing zirconium tungstate powder at a low temperature, cut down the synthesis time of the precursor and control the direction of crystal growth; thus, the prepared nanoscale zirconium tungstate hollow sphere has the benefits of uniform particle size, good negative expansion performance and low density ect., and to have great potential for applying in aerospace field.

Arsenic doped ammonium metatungstate (AMT) is generated by adding ammonium metatungstate into the nitric acid solution of elemental arsenic and stirring, drying and grinding, the excellent raw material for preparing nano tungsten powder. Nano tungsten powder is the tungsten powder which the particle size is fine to nanoscale, at present, the traditional method for manufacturing nano tungsten powder is tungsten oxide reduction method, wherein the reducing agent maybe hydrogen or carbon; with the appearing of nano materials, the manufacture methods of nano tungsten powder are emerging constantly, such as high-energy ball milling, gas evaporation, plasma, self-propagating high-temperature reduction and molten salt electrolysis method.

 

There is a study to take ammonium metatungstate as raw material, and through doping process to get arsenic doped ammonium metatungstate to finally get nano tungsten powder, with the producing process like the following:

1. Preparation of arsenic doped ammonium metatungstate precursor composite powder

Add a certain amount of elemental arsenic into the nitric acid with a certain concentration, then add ammonium metatungstate into the nitric acid solution of elemental arsenic after the As is completely dissolved with the arsenic content being controlled; electric mix the raw materials, then dry them in a oven under 70~90°C for 8~10 hours, and then, grind to get arsenic doped ammonium metatungstate precursor compound powder.

2. Arsenic doped ammonium metatungstate calcination to prepare yellow tungsten trioxide powder

Put the prepared arsenic doped ammonium metatungstate precursor compound powder in a box type resistance furnace at the temperature of 580~620°C to carry out calcination in air atmosphere for 2~3 hours, then we get yellow tungsten trioxide powder.

3. Tungsten trioxide reduction to generate nano tungsten powder

Put the yellow tungsten trioxide powder in a tube furnace to get reduction by inletting hydrogen, under the reduction temperature of 780~820°C with the heating rate of 5°C/min, and the heat preservation time of 3~4 hours, to finally manufacture nano tungsten powder

 

The nano tungsten powder get by arsenic doped ammonium metatungstate has the advantages of good dispersion, and uniform particle size distribution, thus to effectively promote the development and application of nano-crystal WC-Co alloy.