Thursday, November 30, 2023

Ceramic coatings offer protection that lasts much longer than traditional paint and coating options. However, it is important to remember that ceramic coatings are locked into place semi-permanently when they cure.

As such, it is important to make sure that the surface is ready to receive the coating before locking it in place. Prepping a surface often takes hours and dollars, and is the most important part of the process.

Thermal Shock Test

The thermal shock test is a common and important method to test the performance of coatings. It involves placing the samples into a heat chamber and changing its temperature. The accelerated thermal stress is applied to the coating and the temperature change is measured over time. It is used to ensure that the coating can withstand the high temperatures and rapid temperature changes in boilers.

This testing is done using a special thermal shock chamber that can reach extremely high temperatures in a short period of time. The chamber is also capable of cooling down the surface of the sample quickly, which helps it maintain its shape and prevent damage to the ceramic coating. The test also determines the strength of the coating against cracking and spalling.

Before the thermal shock test, the sample is cleaned thoroughly with a solvent to remove any impurities that might interfere with the results. Then, the sample is placed in a muffle furnace and exposed to high temperature for 5 minutes. It is then removed and quickly put back into normal temperature water. The test continues until the area of the coating rupture reaches 5%.

The results of the thermal shock test show that the ceramic coating is able to withstand these extreme temperature changes. The test also shows that the coating is compatible with the constant changes in temperature that occur within a boiler system.

In addition, the tests showed that the ceramic coating has excellent antiscaling and antifouling properties. The ceramic surface has a lower liquid-bridge force and smaller adhesion area, which means that the coating will have less fouling in a shorter amount of time than a stainless steel surface. The coating is also much less likely to crack or spall, which is a benefit for the long-term stability of the system.

The testing of the ceramic coating has shown that it is able to withstand the harsh conditions found in power plants. It is a good option for power plants that use fossil fuels because it will reduce the emission of gases. This will help them meet environmental standards. The ceramic material is also easier to clean than other materials. This makes it a great choice for power plants that have to meet strict emissions requirements.

Microscratch Test

The ceramic can be applied to Boiler Coating in real waste incineration power plants to alleviate the fouling problem and improve energy efficiency. To achieve this goal, we developed a low-cost ceramic coating with high thermal shock resistance by the slurry spray method, using mica powder and sodium silicate water glass as binder. A macro- and micromorphology analysis of the coating was carried out, and mechanical properties tests were performed to judge its practical application.

We also analyzed the performance of the ceramic coating under a high-temperature and high-shock environment through various experimental methods, including thermal shock test, microscratch test, mechanical properties testing, and high-temperature wettability experiment. The results showed that the ceramic coating can resist high-temperature oxidation and corrosion, and it has superior machinability. In addition, the microscratch test and adsorption tests confirmed that the coated surface can be devoid of the adsorption of fly ash and molten flue gas. The high-temperature wettability experiment also demonstrated that the ceramic coating has a lower liquid-bridge force and smaller adhesion area, as well as a shorter fouling cycle for molten corrosive fouling.

Microscratch test is a commonly used test for thin films and coatings, in which the material is scratched by a stylus under a load. The resulting frictional responses can be studied and correlated to the observed failure modes under the microscope. The technique is particularly useful for analyzing the cracking dynamics and causality in complex systems. Traditionally, the critical scratch load was determined by the energy release rate (E) of the system under test, based on the formula below:

However, this method is only applicable to brittle materials that crack at a specific energy. The use of an acoustic emission (AE) sensor allows for more accurate measurement of the cracking energy, and it can be compared to a traditional stress-energy density curve to obtain the critical scratch load.

AE is an electroacoustic signal produced by the vibration of the coating or film during fracture. It provides an indirect measurement of the tensile stress in the substrate and coating, and it is highly sensitive to the local damage mechanisms, such as fracturing, shear, and bending. In addition, AE can provide an early warning of the formation and growth of cracks that can eventually lead to the failure of the material.

Mechanical Property Test

A critical requirement for materials used in high-temperature applications is their ability to withstand mechanical and corrosive load. This is why we at Innovative Test Solutions use a wide range of materials testing frames that can handle loads from ounces to 1,000 pounds. Our frames are available with different rated load cells to accommodate your unique needs and provide the data needed to verify the strength and durability of the ceramic coatings you are using in your power plants.

The physical properties of the ceramic material must also be tested to ensure they can hold up under the extreme heat and pressure conditions found in a power plant or aircraft engine. This includes the strength, hardness, and modulus of elasticity. For this, we utilize a multi-point bend test that can simulate the loading conditions found in the boiler of a power plant. The specimens are placed in a muffle furnace to simulate the high-temperature environment of a power plant, where the flue gas temperature can reach up to 900 degC. This testing method is designed to determine the bend strength of the ceramic coating and the sintering condition of the ceramic material, which helps to verify that the resulting ceramic material can meet the demands of the power industry.

A key property of ceramic coatings is their toughness, which requires a strong bonding between the ceramic and metal substrate. However, if this bond is weak, the ceramic material may deform and break down during use in high-temperature environments. This is due to the fact that the oxidation of the metal-ceramic interface can lead to stress transfer problems and loss of mechanical properties.

In order to prevent this, the sintering process of ceramic materials must be optimized to ensure that the resulting ceramic has sufficient toughness. The sintering of non-oxide ceramic composites can be improved by the addition of carbon or nitrogen in the sintering process. This helps to improve the bonding between the HA matrix and the carbon or nitrogen-rich fibers, allowing for effective stress transfer between the two.

A ceramic coating can be applied to the interior and exterior of any aircraft or helicopter to reduce corrosion, icing, and maintenance expenses. This type of coating is also ideal for protecting water tanks, portable containers, and other air vessels to protect them from corrosive chemicals and ice buildup. The ceramic coating will not only protect the vessel from damage but will also keep it insulated, which can save energy and money by blocking out sun radiation.

High-Temperature Wetability Experiment

The ceramic coating is able to maintain its integrity when it contacts molten metal at high temperatures. This is important, as the coating can prevent slag formation by preventing the liquid bridge that would normally be formed between the steel and the molten bottom layer. Additionally, the ceramic coating can reduce heat checking by minimizing thermal expansion differences between the coating and the metal surface.

A wettability experiment was used to evaluate the ability of the ceramic coating to withstand high-temperature conditions. In this test, a drop of metal was placed on a binderless ceramic substrate and the formation and evolution of the drop were recorded with a camera adapted to the equipment. The resulting images were used to estimate the contact angle of the metal on the ceramic substrate.

An alloy composed of Fe15Ni10Cr and a Ti(C, N) ceramic substrate was used in the tests. An additional 1 wt% of C was added to the alloy in order to lower the solidus and liquidus temperatures, avoid oxidation, and facilitate the sintering of the alloy. After processing, the assembly was characterised by FESEM and EDX. EDX mapping confirmed the presence of inclusions corresponding to aluminium oxides, which led to poor wettability and porosity of the metal bulk.

During the wettability tests, no drop was actually formed on the ceramic surface, but the morphology of the metal bulk did change as the temperature rose. This allowed for a transversal cut of the assembly to be made, which was evaluated by means of FESEM and EDX. The results showed that, despite the inability to form a droplet, the ceramic-metal interaction was good, as evidenced by carbide reprecipitation in the metal region and binder diffusion into the substrate.

Lastly, the ceramic coating was subjected to a thermal shock test to assess its ability to withstand high-temperature fluctuations. To do this, the test specimen was heated in a muffle furnace to a high temperature, then quickly taken out and put into water at normal temperature. The test was repeated until the coating rupture area reached 5%. The results showed that the ceramic coating was able to withstand this type of thermal shock, which is an important characteristic for boiler systems where high temperatures are commonly encountered.


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