Volume 3 Number 6 Dennis R. Dinger 1 April 2005
An Update
The PAPERBACK BOOKS are HERE!!! The paperback version of Characterization Techniques for Ceramists is now available on the Books and Downloads page at the web site! Retail price is $29.95 plus shipping and handling. The book has 256 pages and it covers 34 different characterization techniques that are commonly used by ceramists. Spread the word! Order your copy NOW!
The book sets on the web site have also been revised to include this new book. A 3-book set of paperbacks, including one each of Particle Calculations for Ceramists, Rheology for Ceramists, and Characterization Techniques for Ceramists, is now available for $64.85 plus shipping and handling. This is a $10 saving off the total retail price of the 3 paperback books. A 3-book set of downloads is also available for $52.85. This, too, represents a $10 saving off the total retail price of the 3 downloadable books.
The E-Book version of Characterization Techniques for Ceramists is available for downloading at the Books and Downloads page of the website for $24.95. The download is a 2.889 Mb self-extracting Zip® file for the Windows® environment which unzips to the 2.998 Mb book in PDF file format. Those of you who order the downloadable book will want to know that the PDF book is formatted to print on 5.5" X 8.5" paper (i.e., 8.5" X 11" sheets cut in half.)
The other two books, Rheology for Ceramists and Particle Calculations for Ceramists, continue to be available for purchase as downloadable E-books and as paperback books at the Books and Downloads page of the web site.
As always, if this is the first issue of the Ceramic Processing E-zine that you've seen, you can add your name to the mailing list by clicking HERE. All back issues can be accessed from the Publications page at the web site. For those of you whose e-mail programs don't properly show the figures in these E-zines, go to the Publications page of the web site using your web browser to open any and all issues. All figures should open properly when issues are accessed from the web site. Questions, suggestions, and/or requests for topics to be covered in future issues of this e-zine can be sent to QuestionsandComments@DingerCeramics.com .
If you have friends, business associates, etc., who are ceramists, materials engineers, or any other type of engineer or technician, and they are interested in receiving this e-zine, please forward this issue to them and encourage them to sign up. Or simply point them to the Dinger Ceramics web site. Also -- whether you are a new or continuing reader -- please send suggestions for topics you'd like to see addressed in future issues of this E-zine.
Remember: Dr. Dinger is available for on-site consulting for a daily fee plus traveling expenses. He can also teach a variety of ceramic processing short courses at your site. If interested, please inquire.
This article is the fourth in the series on particle size analysis techniques.
Particle Size Analysis Using Photon Correlation Techniques
One of the newest techniques for measuring particle size distributions is the photon correlation technique which can measure well down into the sub-micron region.
Instrument Capabilities
Photon correlation instruments can measure particle sizes from single-digit micron sizes down to about 1 nm (i.e., ~10 Angstroms.) Particle sizes in sample slurries and suspensions can be analyzed at production solids contents without the requirement to produce highly diluted samples, and without requiring repeated sampling, dilution, sampling, dilution, etc., of samples.
How Does Photon Correlation Work?
This technique makes use of the same phenomenon that allows one to decide from the sound of a train, truck, car, or airplane to determine whether it is approaching or departing from your location. In this case, the frequencies of laser light reflected from particles in the sample cell are shifted by the vibrational motion of the particles. Sub-micron sized particles vibrate at frequencies inversely related to their sizes: Larger particles vibrate at lower frequencies, smaller ones vibrate at higher frequencies. The vibrational motion of colloidally sized particles affects the frequencies of back-scattered laser light.
The complexity of the technique is that it can measure many, many particles in a single analysis. The processor speeds and memory sizes of today's computers are employed to sort out the results from the backscattered signals to calculate the distribution of particle sizes that caused the sample's total signal envelope. Fortunately, today's powerful computers are available and capable of handling these analyses.
Fortunately also for all of you engineers and technicians who are cringing at the thought that maybe, I will next present a physics lesson ... Never fear!! The instrument manufacturers have taken care of all the details and incorporated them into the instrument software. You don't need to know the physics, or the exact equations, or the derivations of those equations to successfully use one of these instruments --- you only need to know how to run it, that it works well on sub-micron particles, and that instrument manufacturers have taken care of all of the details. Even if you did understand it perfectly, it would do you little good because the instrument manufacturers don't give you control over their software.
Size Range Capabilities
Photon correlation techniques do not work well on particles much larger than 1 micrometer, but they do work well on particles well down into the sub-micron range. In fact, this technique can measure almost all sub-micron sizes of consequence in ceramic bodies. What particles of consequence can be identified that are less than 10 Angstroms in size? Less than 10 Angstroms defines the size range where it is debatable whether independent crystals of any material can be identified. Surely crystals are forming in those size ranges, but at what size can such a crystal be identified as a particle of a particular substance?
With this in mind, I suggest the following: The photon correlation method effectively covers the sub-micron size range that cannot be measured by other particle size analysis techniques.
Another supporting point should be made: Particles in the finest reaches of the sub-micron size range seldom travel individually. That is, they readily cling to one another to form larger 'particles' or flocs. So, few (if any) particles in this size range will actually be independent of one another and available to be measured. This is another reason for the suggestion that the photon correlation technique effectively covers the finest size ranges that the other techniques cannot.
For years we dealt with particle size analyzers that were incapable of measuring sub-micron particle sizes. Now, we have instruments practically all such particles. To go even further than the statement above, I submit that for all practical purposes, with today's instruments we can now measure all particle sizes of consequence to ceramic processing behaviors.
What effects do particle size distributions in the finest reaches of the submicron range have on ceramic processing? There are tons of specific questions like this that can and should be asked. For years, we suggested answers based on our best estimates and on specific surface area measurements. That was the best we could do. But now, with photon correlation instruments, we can begin to address these questions with specific experiments, specific studies, and actual experimental results.
Solids Content Capabilities
Since this technique analyzes back-scattered signals from incident laser beams, and since transparent sample cell walls don't affect analysis results, suspensions at production solids contents can be analyzed using this technique. Sample sizes can therefore be relatively small (a few cubic centimeters). The combination of these two features, plus relatively short analysis times, make this a very handy technique.
Overall Benefit
On the coal slurry project at Alfred University years ago, and on almost all ceramic processing research projects since then, we always wanted to (but couldn't) analyze the size distributions of the colloidal fractions in our slips and slurries. In those days, photon correlation instruments were not available. So we combined sieve analyses, sedimentation analyses, and different laser scattering analyses to cover the range from boulders (~1/4") down to sub-micron particles.
The majority of surface area in our slips and slurries was contributed by the sub-micron fractions which we could not measure (or which we could not accurately or effectively measure) with our particle size analyzers. Measured surface areas and surface areas calculated from measured particle size distributions never agreed. The discrepancies were always attributed to non-spherical particle shapes, agglomerates, and especially to the finest colloidal fractions which we could not analyze and therefore could not include in surface area calculations.
It appears that we can now combine sieve analyses, sedimentation, laser scattering, and/or electrical resistance particle size distribution results with photon correlation results to begin to answer all of these questions.
New Questions to be Studied and Answered
The ability to measure the sizes of effectively all particles and molecules in the colloidal size range now raises all sorts of new questions for ceramic process engineers to answer. For example, just exactly what is being measured in each of these fine size ranges? What particles are we now measuring that we were not measuring before? And of greatest importance, how much do particle size distribution variations in this size range contribute to the rheology of slip and to processing properties? With this new experimental capability, research to answer such questions can now be addressed and results will soon be appearing.
This is a GREAT advance in particle size analysis technology!
The answers to these new questions will be left to current and future generations of ceramic engineers to study, understand, apply, and explain to others.
The Main Advantages of Photon Correlation Techniques
In summary, note once again the main advantages of the photon correlation technique:
(1) Photon correlation instruments effectively cover the remaining size range of particles (the sub-micron range down to ~1nm) that traditionally has not been measurable by other common particle size analysis techniques.
(2) Not only can samples be small, but they don't require dilution.
(3) Short analysis times are possible.
.... Some Feedback is Requested, Please ....
As you know, there are now three books in the
... for Ceramists series:
Particle Calculations for Ceramists
Rheology for Ceramists
Characterization
Techniques for Ceramists
As guidance for further topics, I request your feedback:
What other topics would you like to see covered
by new books in the
...
for Ceramists series?
For example, I have considered writing a book entitled Phase Equilibria for Ceramists (or a similar title like that.) I am of the opinion that current phase equilibria books don't go into sufficient detail to explain how to apply (i.e., how to make practical application of) the information in phase diagrams. After all, this is phase "equilibria" and these are phase "equilibrium" diagrams that we're talking about. Put this together with the fact that most current ceramic production processes are far removed from the phase equilibrium results depicted in phase diagrams and you can see the problem. Some diagrams were prepared using firing durations greater than a year (put the samples into kilns, turn them on, and forget about them for months and months), yet today we routinely fire our products in as short times as possible (some wares in as little as ~30 minutes cold to cold.) Do equilibrium diagrams even apply to such cases? Well .... YES they do! But HOW? Lots can be said from an applications point-of-view to explain the usefulness of phase diagrams to today's ceramic and materials engineers, as well as to all other engineers who routinely perform thermal processing.
The average ceramic engineer DOES NOT need to know how to create a phase diagram, or how to calculate one from fundamental, theoretical thermodynamics, but the average ceramic engineer (as well as the average materials and metallurgical engineers) DOES need to know how to read, interpret, and apply the information in phase diagrams to his/her process.
With Phase Equilibria as one possible topic, what other topics would you like to see in this series? What other topics are needed in this series? Technicians, Engineers, Managers, Presidents, Production Supervisors --- here's your chance to speak up and give me some feedback! What's needed? When you hire new ceramists, or materials engineers, or metallurgists, what practical topics (covered by one or more good reference books on their bookshelf) could help bring them up to speed quickly in their new positions? What practical topics should they be studying during their ceramic educations? Unit operations? Applied mathematics? Spreadsheet applications? Computer programming? Heat Transfer? Combustion? Engineering economics? Mechanical properties? Something else? Remember, these will all be aimed specifically at practicing ceramists -- but they will also be useful for materials engineers, metallurgical engineers, chemical engineers, etc.
I perceive a real need out there for this type of books -- handy, reasonably-priced, easily readable, practical explanations of necessary engineering topics. The "Why the need?" question is a separate subject. I'm not sure you want to get me started down that path! Articles addressing this question would be more editorial commentary than practical engineering helps (But as an Emeritus Professor, I have definite opinions about current educational trends.) If you'd like me to address that topic in future E-zine articles, let me know -- and I'll consider it.
But in the meanwhile, please help by e-mailing your thoughts, suggestions, and/or recommendations for other topics in the ... for Ceramists series.
Thanks.
Miscellany
Suggested topics for future issues of this E-zine .... Please continue to send your ideas or questions for future topics. Thanks. Until next time ...
Thanks for signing up to receive Ceramic
Processing E-zine
To unsubscribe, click the "Remove Me" link below.
Copyright © 2005 Dennis R Dinger
103 Augusta Rd, Clemson, SC 29631 (864) 654-5731
All Rights Reserved.
All Rights Reserved.