Tungsten Oxide

In the process of hydrogen reduction of tungsten oxide , the effect of the reduction is not only the metal elements, there are some trace elements, such as rare earth elements. The effects of trace elements are related not only to quantity, but also to the shape and location of individual elements and the entry stage, for example, the elements that form fine grain particles at grain boundaries are different from the same elements in solid solutions. They are soluble in the bonding phase and different from the tungsten carbide grains. Some scholars believe that the addition of lanthanum or yttrium (La) (Y) in hydrogen reduction of tungsten oxide, can play a similar role to that of Al. In the process of research, scholars used the doping method of wet mixing and flow drying to prepare the blue tungsten powder, and push the boat by reverse hydrogen, the decomposition process is performed in two stages, namely at 500 °C, 850 °C, 900 °C, 950 °C, 1000 °C temperature point five

Blue tungsten oxide is one of the most important raw materials for the manufacture of tungsten powder. In China, there are three main methods for preparation of the blue tungsten oxide: APT closed calcination method, APT mild hydric reduction method and intrinsic reduction method. And the APT closed calcination method is the most used method. APT closed calcination method always keeps the furnace system with positive pressure in the heating process, preventing the air from entering the furnace. By this way, ammonia from APT pyrolysis splits into hydrogen and nitrogen. And in the weak reductive atmosphere, the blue tungsten oxide is produced. The entire process is confined in a rotary calciner. The usage and control of rotary calciner need cautious operation, as it is the main carrier of APT closed calcination process. Rotary hearth furnace is a rotary calciner with high automation, of which the ring-shaped bottom can be rotated. Generally it is divided into two sections to con

Blue tungsten oxide is one of the most important raw materials for the manufacture of tungsten powder. Compared with yellow tungsten oxide, blue tungsten oxide with its high activity, large surface area, easy doping, original crystalline shape is seen as an upgraded version of the Yellow tungsten oxide. Blue tungsten oxide is one of the most important raw materials for the manufacture of tungsten powder. In China, there are three main methods for preparation of the blue tungsten oxide: APT closed calcination method, APT mild hydric reduction method and intrinsic reduction method. And the APT mild hydric reduction method is the most used method. The whole preparation process reacts in a multi-tube furnace of which the heating zone is divided into three parts. In the furnace tube, the heated APT•5H2O installed on the heat resistant boat is decomposed. Feeding a small amount of hydrogen into the furnace tube can keep the reducing atmosphere. Decomposed gas product and waste

Blue tungsten oxide is one of the most important raw materials for the manufacture of tungsten powder. Compared with yellow tungsten oxide, blue tungsten oxide with its high activity, large surface area, easy doping, original crystalline shape is seen as an upgraded version of the Yellow tungsten oxide and used. There are three main methods for preparation of the blue tungsten oxide: APT closed calcination method, APT mild hydric reduction method and intrinsic reduction method. And the APT closed calcination method is the most used method. In APT closed calcinations, ammonia escaping by thermal decomposition or a small amount of introduced ammonia gas is used as reducing agent. Characteristics of this method: thermal decomposition temperature fluctuates between 550℃-700℃, high yield and stable quality. Phase composition of blue tungsten oxide is 70% W 20 O 58  and 30%WO 3 . APT closed calcination method always keeps the furnace system with positive pressure in the heating process

Blue tungsten oxide is one of the important raw materials for making tungsten powder.  Compared with yellow tungsten oxide, blue tungsten oxide is easy to be doped because of its good activity and large specific surface. It can maintain its original crystalline shape and has been widely used as an upgraded version of yellow tungsten oxide.  There are three main methods for the blue tungsten oxide  preparation . APT closed calcination method, APT hydrogen mild reduction method, internal reduction. Internal reduction method was proposed by scholars in Fudan University in 1981.  Internal reduction method by means of an internal component of the tungsten compound to make reduction of W. Intrinsic reduced tungstate was synthesized with APT as raw material (Intramo - lecularly Reduching Tunnstate). It has thermal decomposition in an inert atmosphere, blue tungsten oxide with simple phase composition, large specific surface and high purity has been obtained.  The distinguish

The performance of tungsten oxide materials will directly affect the reduction behavior of tungsten powder and the final product performance. Therefore, on which material is most suitable for the production of ultrafine tungsten powder has been the subject of much attention in material science workers. Blue tungsten oxide and purple tungsten oxide is the main raw material for production of ultrafine tungsten powder, blue tungsten oxide originated in the last century 70's, mainly WO 2.90 , W 20 O 58  and ammonium tungsten bronze (ATB) mixture. Purple Tungsten oxide is a kind of tungsten oxide product developed in recent years in China. Its phase composition is WO 2.72  or W 18 O 49 . Blue tungsten oxide is present through hydrogen reduction of raw materials prepared by tungsten powder is the most widely used, as long as the conditions of low temperature, dry hydrogen, high hydrogen flow, thin material layer, producing ultrafine tungsten powder method can restore th

Tungsten oxide hydrogen reduction process is generally carried out in a multiple tube furnace, in the tubular reduction furnace, the most used in China are the thirteen tube reduction furnace and the four tube reduction furnace. Four tube reduction furnace is commonly used as a tungsten oxide hydrogen reduction unit, the furnace shell is welded by ordinary steel plates, and the four tubes are placed at the same level on the same hearth. Compared with the old four tube muffle furnace up and down the structure, the temperature uniformity is much better. The automation level of the four tube reduction furnace is higher than the thirteen tube reduction furnace, and it is easier to realize mechanization and electrification, in addition, the capacity of the four tube reduction furnace is large, but the unit energy consumption is lower than the thirteen tube reduction furnace. The furnace temperature of the four tube reduction furnace is between 600 °C and 1000 °C centigrade,

In the process of hydrogen reduction of tungsten oxide , the vapor pressure of tungsten oxide increases obviously when there is water vapor at high temperature. This increase in vapor pressure is due to the reaction of various tungsten oxides with water vapor to form a volatile hydrated tungsten oxide. In the W - O - H system, the hydrated tungsten oxide is much more volatile than other volatile tungsten compounds. Most scholars at home and abroad believe that it is the volatile hydrated tungsten oxide that causes the chemical vapor transfer (CVT) process of tungsten. Moreover, the CVT process runs through the whole stage of the reduction of tungsten oxide and hydrogen. It has a decisive influence on the physical and chemical properties of tungsten powder. In the CVT process, tungsten and its oxides are contacted with water vapor to produce hydrated tungsten oxide , which is volatilized to the gas phase and undergoes a homogeneous reduction reaction with H 2 . The reduce