Specialty ceramic cements are directly relevant to our lives, but we rarely notice their presence. The important physical characteristics of these cements include the capacity to deal with temperature changes varying from ambient temperature up to 3000°F (1650°C) and higher, depending on the specific case.
Each material has a different coefficient of thermal expansion. Selecting the cement with the proper coefficient of thermal expansion (i.e., one that is similar to that of the other material in the application) is important to avoid cracks and failures.
Some ceramic cements are insulators; they are selected not only for their temperature resistance, but also for their ability to insulate and protect parts from damage due to extreme high temperatures, like in thermocouples used to check the quality of molten iron and other molten ores. Some ceramic cements are also chemical resistant, making them appropriate for service in acidic or alkaline environments. In other words, they are not only able to withstand the temperature changes and aggressive environments, but they can also be used as insulators or in contact with dissimilar materials. In addition, ceramic cements are able to isolate parts of an application from the surroundings. The combination of all of these properties helps the pieces and parts to do their jobs.
Nearly all ceramic cements are made of inorganic materials, which presents a small problem: porosity. Some ceramic cements are never going to be able to protect the part in full from water and humidity penetration. This is characteristic of inorganic ceramic cements. In many cases, the addition of a primer helps to delay or prevent this kind of penetration.
Some of these cements are made by mixing the cement with water, which is required for the material to cure. In the curing process, it is crucial to eliminate all the excess water (also known as water of convenience) used to hydrate the cement and initiate the curing process. After the cement has cured and reached its peak, that water of convenience needs to be removed before the part is put in service to avoid cracking, steaming or even short-circuiting the part (if it is transmitting electricity).
Some ceramic cements need to be fast curing to comply with manufacturers’ demands to be able to assemble and pack the parts in order to send to consumers as soon as possible. Others need to be oven baked to cure properly, letting all the water used in the mixing of the cement reach a complete cure to avoid problems when the parts are put into service.
When selecting the proper cement, keep in mind that some ceramic cements might have a bad reaction when in contact with certain metals and other parts. To select the proper ceramic cement for your application, the ceramic supplier should be provided with the following details:
• What the application is
• Degree of electrical resistance required
• Temperature range the cement will withstand
• Thermal shock resistance required
• How fast the temperature goes from one extreme to the other
• Frequency of those temperature changes
• Desired thermal conductivity
• Allowed degree of thermal expansion
• What materials will be in contact with the cement
• Whether volume stability is required
• Whether moisture absorption will be a problem
• Dispensing methods
• Required pot life
• Whether a predetermined set time exists
• Whether a force cure is needed
Keeping it Together
Ceramic cements can be applied in many different ways: potting, casting, sealing, encapsulating, bonding and coating. They help to keep the different components that form a particular part isolated, insulated and protected. They help to keep all the pieces together, bonding metals to ceramics and to glass, to avoid the de-bonding of the components.
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Where Are Ceramic Cements Used?
In Your Garage
Every breaker in your garage’s electric panel is assembled using a specialty ceramic cement able to keep the calibration of the breaker in the right position. All of the international assemblers of those products use this kind of cement.
In Your Kitchen
In your kitchen, gas ranges with electric starters are all made with a special ceramic cement that can take the heat generated to ignite the gas for you to fry an egg or boil water. By pushing a button or turning a knob on your gas range, a spark jumps from the edge of the burner into the path from where the gas is coming to ignite the gas and provide flame for the burner.
When you choose to toast a bagel for breakfast, all the resistors located in the toaster are assembled using a specialty ceramic cement able to withstand the high temperature required to toast your bagel to perfection.
Like many families, you probably have a set of silverware that was passed down through the generations. Many people believe these antique pieces are made entirely of silver, but the truth is that all of them are assembled using a special ceramic cement to give weight and balance to the piece of silverware and make it affordable to everyone.
In Your Car
Every light bulb on your dashboard is assembled with a specialty cement able to take the cycling of the temperature from the moment you start your car until you turn it off.
At the Mall
Did you ever see store window displays that are illuminated by tiny little light bulbs (halogen lamps)? Those lamps are assembled using a ceramic cement that is able to handle not only the high temperature, but also the electrical conductivity necessary to keep the lamps lit.