Heat resistance in paints and coatings

A heat-resistant coating is a specialized coating designed to protect surfaces from the effects of high temperatures. These coatings have:
 

• high melting point,
• excellent thermal stability, and
• resistance to oxidation and corrosion

High-temperature resistant paint can tolerate temperatures up to 600 °C¹.

 

Methods of application

Several methods can be used to apply heat-resistant coatings:
 

• Thermal spraying: A high-velocity process that melts and sprays coating material onto the substrate.
• Plasma spraying: A similar process to thermal spraying but uses a plasma jet to heat and propel the coating material.
• Electrostatic spraying: A process that uses electrostatic forces to apply the coating material to the substrate.
• Dip coating: The substrate is immersed in a tank of coating material.
• Brush or roller application: Suitable for smaller-scale applications and touch-ups.
   

Figure 1: Application Methods of Heat-resistant Coatings

Key considerations for selecting heat-resistant coatings

The choice of heat-resistant coating can significantly impact the performance of a component or system. By carefully selecting the appropriate heat-resistant coating, it is possible to significantly improve the performance, durability, and lifespan of components exposed to high temperatures. Factors to consider when selecting a heat-resistant coating include:
 

• Maximum operating temperature: The coating must be able to withstand the highest expected temperatures.
• Chemical resistance: The coating should be resistant to any chemicals or substances that may come in contact with the surface.
• Abrasion resistance: If the surface is subject to mechanical wear, the coating should be able to resist abrasion.
• Adhesion: The coating must adhere well to the underlying substrate to ensure its effectiveness.
• Cost: The cost of the coating and the application process should be considered.
• Substrate preparation: Proper surface preparation is essential for optimal adhesion and performance of the coating.
• Coating thickness: The thickness of the coating should be sufficient to provide adequate protection.
• Curing process: The coating must be cured properly to achieve its desired properties.
• Post-application treatment: Some coatings may require additional treatments, such as heat treatment or post-firing.
  
   

Heat-resistant powder coatings

The key difference between powder coatings and paint is that the former is applied in its solid form and does not emit volatile organic compounds (VOCs). Heat-resistant coatings are specialized, protective finishes that can withstand heightened temperatures. These coatings ensure the surfaces maintain their appearance and integrity in most temperatures and environmental conditions. Heat-resistant coatings form a formidable barrier when used as a dry powder and cured in baking.

 

Types of heat-resistant powder coatings²

Heat-resistant coatings can resist high temperatures in various applications by incorporating heat-resistant silicone resins. There are several types of heat-resistant powder coatings, each of them has an optimal application, discussed below:
 

• Silicone-based coatings: Offer great heat resistance. These work well in industrial machinery and automotive exhaust system applications.
• Polyester powders: Super durable polyester powders withstand demanding environments and harsh climates. It improves finishing due to ultraviolet light (UV) and corrosion resistance.
• Epoxy coatings: Offer good abrasion and impact resistance. This type is seen in industrial applications, electrical components, and petrochemical facility applications.
• Fluoropolymers: Offer excellent weatherability and chemical and abrasion resistance. They are used in the architectural sector and non-stick cook or bakeware.
• Ceramic coatings: Offer extreme temperature resistance. They find use as a thermal insulator in automotive, industrial, and aerospace industries.
• Phenolic coatings: Provide good heat resistance and chemical resistance. They are often used in industrial applications.
• Alkyd-based coatings: While not as heat-resistant as other options, alkyd-based coatings can offer decent performance at moderate temperatures.

Thermal barrier coatings (TBCs) are a specialized type of heat-resistant coating designed to provide a barrier between a high-temperature environment and the underlying substrate. They are commonly used in applications where components are exposed to extremely high temperatures, such as gas turbine engines and jet engines.

The TBC needs to perform several different functions. It needs to protect the alloy against heat and oxidation. Furthermore, it needs to 'stick' to the alloy and have a similar coefficient of thermal expansion, so the coating doesn't fall off when the turbine is heated or cooled.

Figure 2 shows the anatomy of a TBC which consists of the following four layers:
 

1. Topcoat: It acts as a thermal barrier and is usually made of yttria-stabilized zirconia.
2. Bond coat: Its depth varies from 75 to 150 mm and it is essential to dictate the spallation failure of TBC. The NiCrAlY or NiCoCrAlY are used as the bond coat and it is coated using the plasma spray technique, electron beam technique, or physical vapor deposition method.
3. Substrate: The substrates are in the combination of nickel, nickel-iron, nickel-cobalt and so on.
4. Thermally grown oxide (TGO): The intermediate oxide scale to a thickness of 10 to 20 mm below the topcoat exposed to elevated temperature is called the TGO.

 

Figure 2: Schematic Illustration of TBCs for Turbine Blades³

Thermal barrier coatings vs. heat-resistant coatings

TBCs are a specialized type of heat-resistant coating designed for extreme temperatures. Whereas, heat-resistant coatings are designed to protect surfaces from oxidation, corrosion, and other forms of degradation at high temperatures. The key differences are summarized below⁴.
 

Applications of thermal barrier coatings⁴

High-temperature applications require materials and coatings that can withstand extreme heat without degradation. Heat-resistant coatings, including TBCs, are crucial for these applications. Common high-temperature application solutions include⁴:
 

• Ceramic coatings: These coatings offer excellent thermal insulation and resistance to oxidation.
• Metal alloys: High-temperature alloys, such as nickel-based superalloys, can withstand extreme heat and pressure.
• Composite materials: Advanced composite materials, such as ceramic matrix composites, can provide superior thermal and mechanical properties.
• Gas turbine engines: Protecting turbine blades and vanes from high temperatures and reducing thermal stress.
• Rocket engines: Shielding components from intense heat generated during combustion.
• Power plant equipment: Protecting boiler tubes and other components from high temperatures and corrosion.
• Industrial furnaces: Lining furnaces to improve energy efficiency and reduce heat loss.
• Automotive components: Coating engine components to enhance performance and durability.
• Industrial furnaces and ovens: Protecting furnace linings and components from high temperatures.
• Exhaust systems: Protecting exhaust pipes and mufflers from corrosion and heat damage.
• Engine components: Coating pistons, cylinder heads, and other engine parts to improve heat resistance and performance.
• Aerospace components: Protecting aircraft parts from extreme temperatures during flight.
• Chemical processing equipment: Coating equipment exposed to high temperatures and corrosive chemicals.

Want to know more about thermal barrier coating materials for high temperatures? Get more information here. 

 

Fire-resistant coatings vs. heat-resistant coatings

Both heat-resistant and fire-resistant coatings can protect surfaces from heat, however, they serve different purposes:
 

Ceramic coatings vs. metal-based heat-resistant coatings

Ceramic coatings generally offer superior heat resistance. However, they may be more brittle than metal-based coatings⁵. The best choice between ceramic and metal-based heat-resistant coatings depends on the specific application requirements. This includes temperature, thermal shock resistance, mechanical properties, cost, and application methods. Their key differences are listed below.
 

High-temperature paints vs. heat-resistant coatings

Both high-temperature paints and heat-resistant coatings are designed to protect surfaces from high temperatures. However, they have distinct characteristics and applications. Key differences are summarized here⁶.
 

Thermal insulation coatings vs. heat-resistant coatings

While both can protect from heat, thermal insulation coatings are primarily designed to reduce heat transfer, either from a hot surface to a cooler environment or vice versa. They create a barrier that hinders the flow of heat, often through a combination of low thermal conductivity materials and air pockets. Heat-resistant coatings focus on protecting the surface from high temperatures. They form a protective layer that resists oxidation, corrosion, and other forms of degradation at high temperatures.
 

Epoxy coatings vs. heat-resistant coatings

Epoxy coatings are generally not as heat-resistant as specialized heat-resistant coatings. The choice between the two depends on the specific application requirements and the level of heat resistance needed. For applications requiring extreme heat resistance, a heat-resistant coating is the best choice. For applications where corrosion and chemical resistance are the primary concerns, an epoxy coating may be more suitable. Their differences are summarized below⁷.
 

Silicone-based coatings vs. ceramic-based heat-resistant coatings⁹

Both silicone-based and ceramic-based coatings are effective at protecting surfaces from high temperatures. The choice between the two depends on the specific application requirements. This includes the temperature range, chemical exposure, mechanical stress, and desired level of protection.
 

Liquid coatings vs. powder coatings for heat resistance¹⁰

Liquid and powder coatings are two primary methods used to apply heat-resistant coatings. The choice between the two types of coatings depends on various factors, including:
 

• the desired level of heat resistance,
• the complexity of the substrate, and
• the environmental considerations

For applications demanding extreme heat resistance and durability, powder coatings are often the preferred choice. However, for complex shapes or smaller-scale applications, liquid coatings may be more suitable.
 

High-temperature varnishes vs. heat-resistant coatings¹¹

While high-temperature varnishes can protect surfaces from heat damage and discoloration. They are not as durable or heat-resistant as specialized heat-resistant coatings. Heat-resistant coatings and high-temperature varnishes are designed to protect surfaces from high temperatures, but they serve different purposes.
 

Refractory coatings vs. heat-resistant coatings¹²
 

Heat-resistant coatings for metals vs. plastics

The choice of heat-resistant coating depends on various factors, including the desired level of:
 

• heat resistance,
• chemical resistance,
• mechanical properties, and
• applications

Consulting with a coatings expert can help select the most appropriate coating for your needs. When selecting a heat-resistant coating, the substrate material is a crucial factor.