Published on March 16th, 2018 | By: Faye Oney0
Learn five factors that control suspension rheology in ACerS short coursePublished on March 16th, 2018 | By: Faye Oney
[Image above] Carty teaches a class at Alfred University. Credit: William Carty
If you work in the manufacturing industry, you already know that failures can happen even under the strictest of conditions. A solid understanding of the variables that play a part in suspension properties can significantly make a difference in the time and money it takes to correct problems.
How do you know what variables control suspension? What tools do you have at your disposal to decipher defect causes? Where do you even begin to troubleshoot problems associated with raw material variations?
William Carty, John F. McMahon Professor & Chair of Ceramic Engineering at Alfred University will provide those answers in the short course “Dispersion and Rheology Control for Improved Ceramic Processing” May 3, 2018, at Ceramics Expo in Cleveland, Ohio.
Carty will discuss five factors that control suspension rheology, which include:
- Powder characterization and the role of powder properties;
- Stabilization mechanisms (electrostatic, electosteric, and steric stabilization) to provide background for evaluating behavior and troubleshooting;
- Aqueous processing and ionic strength;
- Ceramic forming techniques from a perspective that ties all slurry forming techniques together; and
- Defect generation.
Carty explained to me what he’ll cover in the day-long course during a recent phone interview.
Is there anything else you’ll include in the course that’s not listed here?
We’ll talk about how to measure rheology in suspensions. How you measure it makes a difference, and we’ve developed good procedures for it. Most people measure from low rate to high rate—we measure from high rate to low rate, and that gives us much better data.
Who will benefit most from taking your course?
Ceramic engineers are the ideal audience, as they possess a knowledge of materials in general. Other engineering disciplines, such as materials science, mechanical, and chemical, would also benefit, as the course will provide an alternative context for powder processing that is not an obvious extension of the knowledge base in other disciplines. Technicians, managers, and researchers would also benefit from the course.
What are some of the more significant breakthroughs or achievements related to the topic of rheology that you’ve had in your career?
I’ve done a lot of work understanding clay rheology—the rheology of clay particles, especially in understanding the role of dispersants and polymeric additives. The other breakthrough is defining five factors that control suspensions. For example, there’s not just one factor that controls what’s going on. When you start changing things in a suspension, it can be difficult to decipher cause and effect. You might change the amount of dispersant you’re using, but you might also change water content. Both of those things contribute to the suspension’s behavior.
In the classes you teach, what are some of the most common questions your students ask about rheology?
What’s going to be on the final exam?!
No, seriously, one common question is, what causes changes in viscosity over time? It’s aging. Viscosity is constant with time—it goes up with time and it goes down with time. Then, what are the changes that cause viscosity to go up or down? That’s where we go back to the five factors.
And what about changes in raw material properties? What changes in the raw materials result with changes in viscosity? Is there cause and effect? Can I measure a material coming in the door to anticipate a problem/change in behavior?
You encourage participants to bring examples of problems or defects for discussion. What are some of the more interesting discussions you’ve had around this topic?
Typically, people bring their observations and scenarios to class, rather than physical samples.
You have a process window. You know you need a certain viscosity in order to get behavior you want—for example spray drying performance, an extrusion problem, etc. The jobs people do in the factories involve turning a bunch of knobs. You can increase dispersant level, add water to a system, change pH, add powder, or remove water from the system. You’re led to believe that turning a knob a certain way will get you a specific result. And when you add dispersant, viscosity goes up or down. The question is why?
Will you be sharing any case studies regarding successes or failures?
Most of the course is based on and done with examples of data where we went into a factory and corrected a problem. Some companies call us with problems—for instance, they have 20,000 lbs. of suspension, and viscosity goes up. They want to know what are their options.
Or “two months ago the suspension was behaving one way, and now it’s changed. What happened?”
Both of these situations are identical. Someone tells you what’s happening [with their suspension]. It actually takes 10 minutes to decipher the problem. You have to go back and figure out what has actually changed to figure out what the problem is. You have to ask questions to determine that, such as,
- Was it a new raw material shipment?
- Was there a change in the weather?
- Did the water come from a well?
- Is there a lot more salt from a rough winter?
Questions like that. That’s the advantage of understanding the five factors. It allows you to eliminate the variables and causes of the problem. Also, it’s great if attendees bring in actual questions/suspension issues they’re currently experiencing.
What are the most important ideas or concepts from the course you want attendees to leave with?
This list of five factors helps you decipher contributions from different variables. The important concept is to recognize that the flow behavior of a suspension is linked to those five factors. And those factors do not behave independently, but are interactive. If you can eliminate them as variables, then you can focus on the variables that are important.
Carty will address attendees’ questions and current problems during the course. Click here to register for “Dispersion and Rheology Control for Improved Ceramic Processing” and receive a special rate before March 29, 2018. After registering, email your current problems, questions, and actual scenarios for discussion in the course.
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