Fly ash is used in functional coatings!

The application research of fly ash in coatings mainly focuses on two ways of using its composition and as a coating filler

By surface modification and functional design of fly ash powder, it is possible to expand the application range of fly ash, slow down the pressure on the demand for functional fillers in the coating industry, increase the added value of fly ash utilization, and improve the resource utilization of powder by enterprises.

1 Coatings using fly ash

1.

Fly ash contains aluminosilicate, which can be used as a raw material for ceramic coatings in some studies

The application of fly ash in ceramic coatings has the advantages of cheap raw materials and easy availability.

1.

Geopolymer is an inorganic polymer with a three-dimensional cross-linked aluminosilicate structure.

The coating prepared by using the components in the fly ash to participate in the reaction has higher requirements on the composition of the fly ash, which facilitates the formation of the corresponding network structure in the reaction and obtains the coating with the expected performance

2 Coatings that use fly ash as a filler

Fly ash can directly act as a filler in some paints that do not require high color, and most of them directly utilize its own physical and chemical properties

2.
1 Casting coating

In the production process of castings, the casting coating is applied on the surface of the cavity or core of the mold to improve the resistance of the mold to erosion by molten metal, the fire resistance and chemical stability of the surface of the mold, and the anti-sticky sand of the molten metal.
It is an indispensable auxiliary material for casting
.
The key to the application of fly ash in casting coatings is how to maintain its suspension so that it can be evenly coated on the cavity wall of the mold
.
In order to improve the suspension of fly ash in casting coatings, fly ash casting coatings prepared with ethyl cellulose (EC) can meet the application requirements of casting coatings, and have the advantages of high suspension rate and good use effect
.

Redispersible powders can also be used to improve the suspension of fly ash in casting coatings, and at the same time increase the density, wear resistance and crack resistance of the coatings of the fly ash casting coatings
.

2.
2 Thermal insulation coating

The thermal insulation coating adopts materials with low thermal conductivity, which not only prevents the transmission of indoor and outdoor temperature, reduces the temperature in the building, but also prevents the internal temperature of the building from dissipating and plays a role of heat preservation
.
The fillers of thermal insulation coatings usually choose materials with lower thermal conductivity
.
Fly ash, especially floating beads, is porous, and its thermal conductivity is low.
After modified and foamed, a thermal insulation material with excellent performance can be obtained
.
The application of fly ash float beads in the coating can reduce the thermal conductivity of the composite coating, so that the coating has the effect of heat preservation, and can be used in architectural exterior wall coatings
.
Due to the insufficient whiteness of fly ash, there are also reports using titanium dioxide to coat fly ash to prepare exterior wall thermal insulation coatings
.

2.
3 Fireproof coating

Because of its low thermal conductivity, fly ash can act as a filler in fire-resistant coatings, reducing the heat transfer rate
.
For example, fly ash can be used as a filler in steel structure fire-retardant coatings to change the thermal conductivity of the fire-retardant coating
.
The combination of fly ash and epoxy resin can also be used to obtain fireproof coatings with excellent performance
.
In the wood fire-retardant coating, the amount of fly ash added can be changed to obtain a wood fire-retardant coating with better smoke density and flame retardant properties
.

Through simple surface treatment of fly ash, it acts as a filler in different resins and compounded to obtain coatings for various purposes
.
This method is a way to use a large amount of fly ash, and in casting, fireproof coatings, etc.
, when the color requirements are not high, fly ash may be directly used as a filler in large amounts
.

3 Modified fly ash acts as a coating for functional fillers

Functional fly ash fillers can be obtained through surface modification and functional design of fly ash, which can be added to various coatings to obtain coatings with different functionalities
.

3.
1 Fly ash hydrophobic coating

Using the hydrochloric acid precipitation method, a coating layer of nano-SiO2 particles is uniformly precipitated on the surface of the fly ash glass beads to prepare composite particles with a core-shell structure to realize the functional design of fly ash
.
The fly ash microbead composite material prepared by this method can have a wide range of applications in super-hydrophobicity, self-cleaning, photocatalysis, and heat insulation
.
After simple hydrophobic modification of fly ash with stearic acid, the compound polyacrylate can be prepared to obtain a hydrophobic coating.
By adjusting the pigment volume concentration of the coating, a contact angle of up to 120° can be obtained
.
This type of method is to obtain hydrophobic fly ash by modifying the surface of fly ash, and then apply it to paint to obtain a hydrophobic coating
.

3.
2 Fly ash photocatalytic coating

Anatase TiO2 nano layer is formed on the surface of fly ash microbeads to obtain fly ash with photocatalytic effect
.
By controlling the concentration of the reactants, the ratio of the reaction, the external conditions of the reaction, etc.
, the crystal shape of the nanomaterials coated on the surface of the microbeads can be changed, and the photocatalytic performance of the coating can be improved
.
Experiments show that the TiO2/fly ash composite material coating thus prepared has a degradation rate of more than 90% under ultraviolet light, and has high photocatalytic activity
.
Sulfur-doped TiO2 coated fly ash also has a good photocatalytic effect
.
The fly ash prepared by coating TiO2 on fly ash float beads has good photocatalytic degradation characteristics
.
What plays a role in this process is the TiO2 coated on the fly ash carrier
.

3.
3 Fly ash humidity control coating

In some environments where indoor humidity needs to be controlled, such as libraries, wooden ancient buildings, etc.
, the humidity in the environment has an important influence on the storage life of the items
.
The method of using air-conditioning dehumidification or air humidifier can maintain the humidity in the indoor air, but such a method consumes a large amount of electric power.
In recent years, passive, energy-saving and environmentally friendly humidity control coatings can also be applied to this occasion
.
Through the compounding of modified fly ash and hydrophilic polymer, a humidity-controlling material with excellent humidity-controlling performance is obtained.
At the same time, the compounding of hydrophilic modified fly ash and styrene-acrylic emulsion can be prepared with humidity-controlling performance.
For interior wall coatings, research has found that when the pigment volume concentration of fly ash in the coating is close to the critical pigment volume concentration, the humidity control effect is the best
.
The modified fly ash with humidity control performance is used as a filler to obtain an interior wall functional coating with humidity control performance
.

3.
4 Fly ash anti-formaldehyde paint

Utilizing the porosity and physical adsorption of fly ash, fly ash that adsorbs formaldehyde can be obtained through modification
.
Combined with the formaldehyde trapping agent designed to modify the fly ash and then loaded, the duality of comprehensive physical adsorption and chemical adsorption has obtained the fly ash functional material that first adsorbs and then eliminates formaldehyde, and uses this as a filler to prepare a formaldehyde elimination function For interior wall coatings, the concentration of formaldehyde per unit volume can be reduced to 0.
03 mg/m3 in the test, which is lower than the national standard value of 0.
08 mg/m3
.

In general, the functional fly ash powder is obtained by the method of surface treatment and interface loading.
The role of fly ash is a carrier, and its functionality is determined by the functional materials coated or loaded on the interface.

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