Being moisture-resistance is very important for Dry chemical extinguishing agent such as ABC dry Chemical powder ,BC type fire extinguishing ageni ,BC dry chemical. Below is abstracted from research article:
* Hydrophobic components
Silicone oil and hydrophobic white carbon make up the hydrophobic component of a thousand powder fire extinguishing agent like ABC chemical powder, which together form a superimposed water repellent field around the particles of the fire extinguishing agent, and cooperate to maintain the water repellent and moisture resistance of the dry powder.
1. Silicone oil
Silicone oil: linear polysiloxane, divided according to the group connected to the main chain silicon atom side groups, the silicone oil used for dry powder fire extinguishing agent is methyl silicone oil, ethyl silicone oil, methyl hydrogen silicone oil, ethyl hydrogen silicone oil Etc., among which methyl hydrogen silicone oil (202) is most commonly used. In the hydrogen-containing silicone oil, the ratio of the number of side chain ethyl, methyl and silicon atoms is less than 2, when R / Si = 2, since the side group has no hydrogen atoms, the intermolecular force of the linear polysiloxane is weak, and the hydrolysis The cross-linking reaction is slow, and it takes a long time for the silicone oil to solidify. As a result, although the dry powder has polymerized for a long time, it still feels sticky. When 2/3 <R / Si <2, where H / R = 0.9 / 1.0-1.1, due to active hydrogen atoms, there is an intermolecular hydrogen bond, the molecules are easily accessible to each other, which facilitates crosslinking. The polymer has good mechanical properties after curing. If the H content is too high, the crosslinking is dense, the polymer is brittle, and it is easily damaged by mechanical agitation; if the H content is too low, the polymer does not cure well and becomes soft, which affects the dry powder's performance and water repellency.
After linear silicone oil is cross-linked and polymerized to form a three-dimensional network structure, the cross-linking reaction requires the following conditions: the presence of water and catalyst. The catalyst is usually Lewis protonic acid, such as activated clay, which is a porous high specific surface powder made of bentonite by sulfuric acid treatment. In the presence of a catalyst, the linear silicone oil is diluted and hydrolyzed and cross-linked to the surface of the particles of the fire extinguishing agent under high-speed stirring. The catalytic reaction is homogeneous. After curing, a silicone oil film is formed on the surface of the powder particles, in which the hydrophobic group CH: facing outward, because the methyl electron cloud is distributed in a cylindrical shape, the three-dimensional space is large, so the molecular spacing is large, the methyl cohesive density is small, and the water repellency Strong. The silicone oil film covers the surface of the particles. Due to its strong water repellency, CH3, the liquid film cannot form a film during the formation process. The water film does not wet the surface of the particles well, but shrinks into a spherical shape. The contact area between the particle and the particle surface is reduced, the precipitated crystal connection is weak, and the tendency of agglomeration is significantly weakened, thus giving the dry powder water repellency
It is best to use a thinner to dilute the silicone oil during polymerization, so that the spiral structure of the silicone oil can be irregularly curled, showing molecular polarity, which is beneficial to spread on the surface of the fire-extinguishing particles for the next cross-linking reaction.
2. Hydrophobic silica
Hydrophobic white carbon black is made of white carbon black by hydrophobization treatment of silicone oil. There are alcohol hydroxyl groups on the surface of white carbon black, which are dehydrogenated with hydrogen-containing silicone oil to be bonded. In addition, the adsorbed water in the pores of white carbon black also undergoes dehydrogenation reaction with hydrogen-containing silicone oil, and the physical adsorption of silicone oil polymer on the surface of white carbon black is the main one.
After the addition of hydrophobic white carbon black, due to the extremely fine particle size (above 1000 mesh), it is fully dispersed between the particles and further supplements the areas that are not covered by the silicone oil. The hydrophobic white carbon black between particles not only plays a role of physical separation, but also mainly repels the liquid film of adjacent particles, making them difficult to connect and reducing the tendency of agglomeration. Hydrophobic white carbon black and silicone oil make up for each other in water repellency, and together form a superposed water repellent field.