Source lei small knowledge | what are the surface modification methods of quartz powder?
The surface modification of quartz powder can be divided into two types according to different uses: first, coating modification to improve the mechanical properties of quartz sand, such as resin coated fine casting sand, oil well filter sand, etc., which is characterized in that the coating itself contains only one layer of covering layer, and no chemical bond is generated between the coating and minerals; The second is to improve the compatibility of quartz powder with resin or polymer base materials, such as rubber and plastic fillers, it is characterized by chemical adsorption between the surface modifier or covering agent and the mineral particles.
surface coating modification
Shell casting sand is a technology used in the foundry industry to produce high-finish products that do not require mechanical finishing. This technology can be used in large-scale production, because it can produce high-quality casting surface, but also has the characteristics of high production speed and good reproducibility. In order to obtain a smooth processing surface, the casting film is made of fine sand particles coated with phenolic resin or furan resin. This coated sand is poured into a hot template, and when the temperature is around 200°C, the resin softens and bonds with the sand grains. After the shell or molded article has cooled and hardened, the mold is removed for re-casting. The surface coating of the sand is generally round, which can reduce the amount of resin.
Different coatings can be made into various grades of coated resin sand. This resin sand can not only obtain high melt film casting speed, but also can maintain the mold and mold core production to obtain high anti-roll shell and anti-cracking performance.
The processing method of resin coated sand can be divided into two kinds of hot method and cold method. The quartz sand shall be rinsed, scrubbed and dried prior to coating.
Cold method coated sand is prepared at room temperature. First mix the powder resin with sand, then add the solvent (industrial alcohol, acetone or furfural), and then continue to mix and grind until the solvent volatilizes, after drying, the product is obtained after crushing and sieving. However, the modified method has a large amount of organic solvent and is only used for small production.
Thermal coating is the heating of sand for coating. The quartz sand is first heated to 120~160°C, and then mixed with resin in a sand mixer (the amount of resin acid is 2 ~ 5% of the amount of quartz sand). At this time, resin sand is softened by hot frying, coated on the surface of sand particles, and becomes sticky with the decrease of temperature. At this time, urotropine is added to distribute on the surface of sand particles, and the sand is quenched (urotropine is used as a catalyst to solidify the resin during shell mold formation), calcium stearate is added (to prevent caking), mixed, sand is produced, then crushed, sieved and cooled to obtain the product. This method has good effect and is suitable for mass production. However, the process is more complex and requires special sand mixing equipment.
The modified sand coated with furan resin is used for oil well drilling. In the second stage of oil production, the sand is pumped to the downhole production area to expand the fracture and increase production. The coating cures at well temperature conditions, and the sand remains in the fractures to form a solids filter, which screens out debris from the recovered oil.
surface chemical modification
Quartz powder used for rubber and plastic fillers must make its surface compatible with the polymer base material in order to obtain the best performance and the best processability of the filling material, which requires surface chemical modification of the quartz powder surface.
Silane coupling agents are mainly used for surface chemical modification of quartz powder, and various silanes used include amino, epoxy, trimethyl, methyl and vinyl silanes. Silane coupling agent-RO functional group hydrolysis to produce silanol group, this group can be combined with SiO2 chemical adsorption or with the surface of the original silanol group as a whole, into a homogeneous system. In this way, the water on the surface of SiO2 is removed, and the silicon ether bond is formed with the oxygen atom, so that the organic functional group-R' of the high molecular polymer with good affinity carried by the other end of the coupling agent is firmly covered on the surface of the quartz powder to form a reactive coating film. The organic functional group-R' can reduce the surface energy of quartz, improve the wettability with the polymer base material, and improve the compatibility of quartz powder with the polymer base material. In addition, this new interface can also improve the rheological properties of the filling system.
The main factors affecting the effect of surface chemical modification of quartz powder are: the variety, dosage, usage, treatment time, treatment temperature and PH value of silane coupling agent.
Surface modification process is divided into two kinds
Wet mixing method:The use of appropriate dilution and additives and silane coupling agent forced to mix into a treatment solution, the quartz powder to soak, and then remove the moisture.
Dry mix legal:Add a small amount of diluent and silane to form a treatment agent. Under the conditions of high-speed stirring, dispersion and certain temperature, the treatment agent is added to the quartz powder in the form of spray, and the material is treated after a certain period of time. This method does not require further dehydration and drying.
Method, surface, modification, quartz powder, chemistry, silane, casting, resin, conduct, coupling agent
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