The chemical property of aluminum powder
The appearance of aluminum powder is granular and it is silvery grey. It can react with oxygen in the air to generate Al2O3 in the room temperature. It can be easily reacted or oxidized when encounters with acids, alkalis, salts, water, rain, snow and high air temperature. It is a kind of metal powder which is chemically active, flammable, explosive and easily oxidized.
The particle size shape of aluminum powder
Different production process of aluminum powder for sale can make it produce three kinds of particle size shape: 1.Spherical shape; 2. Raindrop shape (Nonspherical); 3.Flaky shape. Spherical aluminum powder, raindrop-shaped aluminium powders are known collectively as particulate aluminum powder of which the activated aluminum content is more than 98%, while the content of active flake aluminium powder is more than 85%. The apparent density of granular aluminum powder is 1-1.3 and the apparent density of aluminum flake powder is between 0.16 and 0.6. The specific gravity of granular aluminum powder is similar to that of the magnesia and their particle size is closely. Also the particle velocity is same and the mixture is equal in the production mixed. So it is not easy to cause the state of segregation. As a result, the aluminum powder used in the magnesia-carbon bricks is raindrop-shaped aluminium powders or spherical aluminum powder.
The usage of aluminium powder in magnesia carbon brick
The main effect of aluminium powder added in magnesia carbon brick is antioxidant. The presence of carbon in magnesia carbon brick is to prevent the slag erosion in magnesia carbon brick. But the brick itself has the characteristic of oxidizable. When the carbon in the magnesia carbon brick is oxidized, the erosion resistance of brick is sharply declined. This will speed up the damage of magnesia-carbon brick and reduce service life of the brick. In order to prevent the oxidation of carbon, we should add aluminium powder to protect the carbon of magnesium-carbon brick. The reaction mechanism is as follows:
a. When the magnesium carbon brick is heated, the active metal aluminium in brick firstly reacts with carbon and generates high melting point carbide. Thus will reunite the carbon and generates Al4C3 and Al2O3. Al4C3 wraps and melts in the surface of MgO, preventing the penetration and erosion of slag. It will improve the corrosion resistance, slag resistance and peeling resistance of magnesium-carbon brick.
b. When magnesia-carbon bricks are at high temperature condition, the activated aluminum is oxidized and generates high melting oxides of Al2O3. It’s a phase change process for metal to be transformed into non-metal. In this process, the volume of AL2O3 which is generated by oxidization is expanded, thus will dense the pores of brick, increase the density of brick, and then forms a ceramic body which improves the removal resistance of magnesia-carbon bricks in high temperature condition.
The safe handling of aluminium powder
Before the forming of Magnesia carbon brick, we should mix the various raw materials and add aluminium powder. Due to the flammable and explosive of aluminium powder, it will be explored when encountering with open fire at room temperature under normal oxygen content in the air, and dust density is 35-301 g/m3. In the mixing process of magnesia carbon brick, the dust density generated by the joining aluminium powder amount is within the explosive range. And as the oxygen content of mixers in the air is enough, when it comes to the high-speed movement of magnesia in the mixer collide to produce a spark, then the aluminum powder in the mixers will be in deflagration and cause the accident. To ensure production safety in production of mixing, we should therefore complete the following work:
a. The particle size of aluminium powder should not be too small as the superfine aluminium powder will be suspended easily in the air and the dust generated by it will be easily to reach the explosion zone. Meanwhile the superfine aluminum powder and magnesium will be fricted and collided with each other, thus will destroy the oxide film in the surface of aluminum particle, speed up the oxidization rate of aluminum powder, greatly reduces the activity of aluminum powder and impact the antioxidative effect of aluminum powder in magnesia carbon brick. Therefore the particle size distribution of aluminum powder is important.
b. The aluminum powder should be premixed artificially before entering into the mixers. To artificially mix the aluminum powder and the magnesia which has similar particle size in proportion and make them attached together. In the process of mixing, aluminium powder should not be an independent formation of dust. The aluminium powder dust density should be controlled within the safe density. At the same time, the bending phenomenon of the aluminum powder in the mixing process should not be occurred.
c. The machine should be started after the premixed aluminum powder is put in the mixer. There is enough oxygen in the operation of the mixer and it also will generate the open fires. If we put the aluminum powder at this moment, the airflow in the mixer will suspend it. It will cause explosive accident as the dust density now is within the explosion range. Therefore the mixer should be in closing condition when the aluminum powder is poured.
d. The static occurred in the running of mixers should be eliminated timely. If the static is not eliminated, it will cause discharging phenomenon easily and will detonate the aluminium powder. Therefore we should set up static grounding device for the mixers.
e. When the mixer is working, the operators should operate it in long distance so as not to cause harm when the accident occurred. In short, although the antioxidant effect of aluminium powder in the magnesia carbon brick is very important, the safety problem in use should not be ignored.