Aluminium Metal powder or paste
Aluminium powder, which is commonly used as a reaction agent in AAC Plants, is a fine granular powder made up of Aluminium Metal.
Process of Manufacture:
The aluminium powder is usually manufactured in many forms such as flaky particles, granulated powder (atomised aluminium) etc.
There are different processes one can use for the production of aluminium powder.
The metal is melted in furnaces, and the temperature is maintained around 720 to 760 C.
Atomised Aluminium is produced by blasting the stream of molten Aluminium into small articles by air jet.
For this purpose, an atomiser is employed which consists of a straight tube with lower end dipped in molten metal and upper end terminating as a little orifice.
A jet of hot air under pressure is passed through armular opening near the top which impinges on a stream of molten Aluminium drawn by suction through the orifice.
This results in the formation of small particles of Aluminium.
These particles are drawn by suction, through a collecting duct placed above the nozzle and eventually into a cyclone collecting system.
The particle size are often controlled to some extent by varying nozzle opening atmospheric pressure , etc.
The different sizes of Aluminium powders are segregated by sieving.
Then packing is done in required quantities and as per the customer requirement.
Collection Chamber → Dust Collector
Coarse Powder Fine Powder
Role of Aluminium Powder in AAC
Aluminium acts as pore (cellular structure) forming material and the density of AAC Block is controlled by the input of aluminium.
After pouring of aluminium suspension into the alkaline mixture hydrogen gas is developed.
When aluminium is added (usually at about 0.3% to 0.7% by dry weight of cement) to the mixing ingredients, it reacts with hydroxide of calcium or alkali which liberates hydrogen gas (3H2) and forms bubbles.
The rate at which the air bubbles form is critical to the final product of aerated block.
2 Al + 3Ca (OH)2 + 6 H2O ------> 3 Cao.Al2O3.6H2O + 3H2
Steam water or condensed hot water from autoclave also contributes to the gas development in the reaction.
A lot of pores are formed and the cake is rised until the mould is filled.
This process is influenced by the viscosity of the mixture and the temperature development in the mixture.
According to the intended AAC density class different types of aluminium powder or paste with different particle sizes have to be used, which will be discussed later in other post.
Value of active aluminium content in Metal powder – approx.. 95%
Value of active aluminium content in Metal Paste – approx.. 80%
Care should be taken in storage life of the aluminium. Please confirm with the supplier regarding the same.