Advanced ceramics, also known as engineered or technical ceramics, differ from traditional ceramics in that they are designed to withstand harsh environments. These specialized ceramics are used in a variety of applications because of their superior resistance to corrosion, erosion and wear; electrical and thermal insulation at high temperatures; and, high heat resistance.
Advanced ceramics are used in many industries, such as electronics (semiconductors), industrial, aeronautics, automotive, dental/medical, filtration, electrical engineering and more, to overcome a variety of challenges. Quite a few of these are really being driven by the ‘big data’ society as it expands and starts to move to the internet of things, i.e. artificial intelligence (AI), smart devices, smart grids and houses and eventually the smart city, etc. The issue is that the ceramics industry is finding it difficult to keep up with the speed of change and the requirements for higher tolerances of their ceramic products. For instance, aerospace requires ceramics with higher thermal stability as they begin to look at swapping metal turbine blades for ceramics; electronics are seeing a massive growth in semiconductor innovation and efficiencies as they look to enhance thermal, mechanical, and also electrical stability; of course this has really been driven by the growth in memory and devices, and displays (LCD and OLED) as these devices become larger, flexible and thinner.
The current big drivers for advanced ceramics manufacturers are increasing speed and reducing cost to provide a more efficient process. However, it is the journey to higher tolerances and reduced waste that is the most important driver and probably one of their key aims. This is somewhat related to achieving more uniform properties while trying to minimize cracks or pores within the green body of the ceramic as it is formed in the mold before finally drying in a kiln. These issues could be affected using additives, binders and thickeners in a positive manner; therefore most ceramic manufacturers are looking actively at and for new processes/materials to help manufacture the higher tolerance advanced ceramics.
At a high level, dispersants are used in ceramic formulations to wet and disperse fine powders in media (like water), and for rheology control. Dispersants can help to decrease viscosity and help achieve a narrow particle size distribution by reducing agglomeration.
Lubrizol has extensive experience with dispersants for both water-based and solvent-based ink and coating systems, with a full product line that provides excellent compatibility with a wide range of solvents, resins and other formulation components. We’re now using the experience gained in dispersing inorganic particles in solvents and water for paints, plastics and inks to develop dispersants for application in the advanced ceramics market.
Several years ago, Lubrizol began looking at using dispersants in decorative ceramics. While this application was changing from traditional analog printing to a digital printing system, this created good potential for using Lubrizol dispersants to create better products. We have more recently built on this early work to validate how high-end dispersants can bring value to advanced ceramics. Hyperdispersants have been designed to have excellent adsorption to the surfaces of different ceramic particles such as aluminum oxide, zirconium oxide, silicon nitride and barium titanate, and also have good compatibility with the solvent medium being used whether that is water, solvent or a plastic.
A Focus on the Process
Today, Lubrizol has identified opportunities and an understanding of the market needs, which has led us to focus on the process and testing of dispersants in ceramic manufacturing. In that time, we have developed several high performance hyperdispersants to meet different requirements for the various manufacturing processes employed in the advanced ceramics market, such as in slip casting, tape casting, spray drying granules, extrusion, injection molding and dry press. We’ve learned that beyond the end use, the process of making the ceramic is extremely important and a labor-intensive process. The choice of dispersant can impact on several parameters in the processing of a ceramic part, but the key properties are to produce consistent pastes/slurries with low viscosity and enable de-aeration of the slurry, thus reducing any batch variations and improving flow and fill into the molds to reduce gaps or defects.
In the case where water is used as a medium, the hyperdispersant can maintain optimum rheology of the ceramic system in the mold as it becomes dry. Even as the water is drained away through the mold walls, the hyperdispersant can prevent sedimentation and allow the ceramic particles to move around each other to form a denser ‘wet’ green body. Thus, improving green body density with hyperdispersants leads to fewer defects and reduces shrinkage of the ceramic part during removal (burning/debinding step) of the organic additives and before final firing to sinter the remaining particles together to form the final ceramic piece. Ultimately, by reducing defects in the final piece, breakages and waste can be minimized.
Although the strength of the final product from the kiln is what ceramic producers worry most about, many final product failures result from cracking/distortion/defects at the green body stage. Therefore, the choice of dispersant can also impact on the performance of the final ceramic piece and the green body strength is an important factor to control especially as ceramic manufacturers try to meet higher tolerances in new advanced ceramic parts whether they are for larger pieces or made by new disruptive technology such as 3D printing.
Advanced ceramics is a growing market and dispersants are critical components when formulating ceramic slurries and pastes. Contact us to learn more about our range of dispersants that can be incorporated into ceramic formulations and how we can collaborate to benefit the processing and performance of your final ceramic parts.