Advanced ceramics, also known as engineered or technical ceramics, are inorganic, nonmetallic, basic crystalline materials of rigorously controlled composition and manufactured with detailed regulation from highly refined and/or characterized raw materials giving precisely specified attributes such as superior corrosion, erosion and wear resistance, toughness, high thermal and electrical insulation, and high temperature resistance.
They are designed to be used in harsh environments and are used in a variety of application and industries including electronics (semiconductors), industrial, aeronautics, automotive, dental/medical, filtration, electrical engineering and more for their superior properties.
Advanced Ceramics are produced using highly refined and purified powders that need to be dispersed into specific media to be processes by traditional (spray drying, slip and tape casting, injection, extrusion) or more disruptive technologies like additive manufacturing.
Dispersants are used in advanced ceramic formulations to wet and disperse the fine powders in different media (like water, solvents, and waxes), and for rheology control.
The dispersion and stabilization of ceramic particles within a liquid medium is often problematic as the nature of the ceramic solid surface can vary widely with their chemical type. Good wetting and stabilization, whether that is electrostatic, steric, or electrosteric will only occur when the polymeric dispersant is firmly anchored to a pigment surface and the polymeric tail has good solubility in the solvent medium used and has sufficient chain length (MW) to counteract the attractive forces between solid particles. Lubrizol dispersants are designed to contain anchor groups which adsorb strongly onto the ceramic particle surface and are attached to a polymer chain which is designed to be compatible with the ceramic slurry media and optimized to give superior slurry dispersion stability.
Dispersants can help to decrease viscosity of the ceramic slurries and help achieve a narrow particle size distribution by reducing agglomeration. Beyond this, the process of making the advanced 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, optimal flow 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 of ceramic molding or extrusion processes, the dispersant will coat the individual ceramic particles completely in order to achieve optimal flow properties during the molding stage and provide a consistent and reduced shrinkage of the molded green body during firing.
In the case where water is used as a medium, the dispersant 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 dispersant 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 additive manufacturing.
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. 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’re now using the experience gained in dispersing inorganic particles in solvents and water for paints, inks, plastics, and decorative ceramics to develop dispersants for application in the advanced ceramics market.
We have more recently built on this early work to validate how dispersants can bring value to the ceramic industry. 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.
These dispersants are now available under a new Solsperse™ AC Hyperdispersants product line, a range of polymeric dispersants tailored for the most demanding ceramic applications and to the more complex formulations. Solpserse AC 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 to have good compatibility with the solvent medium being used whether that is water, solvent, UV monomers or a plastic. Using Solsperse AC Hyperdispersants can not only help to improve the performance of slurries and dispersions, but can also impact the quality of final products and overall manufacturing costs.
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.
Get help with product recommendations, formulation questions, application issues, and more from a Lubrizol expert on Additives for Advanced Ceramics.