Volume 5  Number 11                            Dennis R. Dinger                                1 September 2007

Updates

"... for Ceramists" Series Books

          Spanish Language Books

For those of you who speak Spanish as your primary language, a downloadable PDF version of Rheology for Ceramists in Spanish is currently in progress.  Reología para Ceramistas is currently being edited to be made available as soon as possible.  Best estimate at this time is that it will be available sometime this fall.  The PDF file will be set up so it can be printed on your printer if you prefer a hard copy.  Depending on the reception this version receives, I will then consider translating the Particle Calculations book as well.  I will also then consider translating it into Portuguese.  Any thoughts, comments, and/or suggestions will be appreciated.

          English Language Books

The paperback version of Characterization Techniques for Ceramists is 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.  Purchase a 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.

          Requests for Multiple Copies

I have had several recent inquiries about the purchase of multiple copies of these books.  Here are my two suggestions:  

          (1)  If you purchase downloadable versions, purchase the required number of copies (please be honest about the number) from the Books and Downloads page of this website.  Then download a single copy and distribute it (or print it and distribute it) to the people for whom you purchased the copies. ... or ... 

          (2) Purchase the required number of paperback copies from the Books and Downloads page of this websiteand distribute them to your people.  My books are priced $19.95, $24.95, and $29.95 with this in mind.  You won't find many other good ceramics books in this price range.  Most others start at $80 to $100 each and prices rise from there.  For example, our PPC book (when it was available) was $195 per copy.  (I had no input when that price was set.  During one phone conversation, after they made sure I was sitting down, they simply told me the price.)          

The E-zine

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.

This month's article is another in a series discussing PPC, its applications, and mind set.

PPC & ISO Standards

Introduction

One of the first characteristics we noticed about PPC was that it was an excellent methodology to use when it became necessary to document to meet ISO standards.  We will discuss this briefly below.

Which Comes First, the PPC or the ISO Standards?

The ISO standards and the documentation required is supposed to help companies, not only to describe procedures to take in case something goes wrong but, to work their way through all kinds of problems in a standardized, routine manner.  Our experience with PPC and ISO shows that when PPC is in place, it is relatively straight forward to document the procedures to be followed as properties change and/or as problems occur.

On the other hand, if PPC is not in place, then one must try to solve each identified potential problem as one writes the ISO documentation.  This could lead to a non-coordinated set of solutions for each potential situation, rather than one large coordinated solution for process control throughout the whole plant.

The answer to this question, therefore, is that it helps when PPC comes first.

A Coordinated Solution Set for Process Control with PPC

We have already discussed this point in previous articles, but it bears repetition.  To implement PPC is to define very tight specifications -- generic specifications -- that describe the body and satisfy the process requirements.  It may not be critical that one uses Dinger #5 clay and Smith #3 kaolin, but it may be critical that the body always has a certain particle size distribution (PSD) and a certain specific surface area (SSA).  The methylene blue index (MBI) of Dinger #5 may vary from batch to batch (actually, from shovel full to shovel full) but when the MBI of the batch is always controlled to 4.0-4.1, you can expect to have excellent body forming properties.  The alkali contents of the feldspars may vary from batch to batch, but when the %Na is 2.0-2.1 and the %K is 1.5-1.6, the body may fire well.  

In these cases, there is excellent reason to define the body to contain:
                the particular PSD (specified at several points),
                the particular SSA,
                MBI = 4.0-4.1,
                %Na = 2.0-2.1,
                %K = 1.5-1.6,
                etc.

You can see that these requirements are generic in the sense that they aren't based on a set % of several different named raw materials, but they focus specifically on the particular properties of interest.  It doesn't matter which named materials are used if the PSD and SSA meet the desired specifications at the same time as the MBI, %Na, %K, and all other parameters are met.  When the PPC formulation is properly specified, it is impossible to meet specs and achieve a refractory body rather than a whiteware body.  In a technical ceramic plant, it is impossible to produce a high alumina body that meets the specifications for a barium titanate body.  When the PPC formulation is properly specified, a whitewares plant will always produce a whiteware body, a refractory plant will always produce a refractory body, a technical ceramic plant will always produce the desired technical ceramic body, etc., without fear that the fundamental body type can change far and wide from day to day.  

Notice in this example:  Rheological properties and the forming properties to which they correspond are functions primarily of PSD and SSA.  Plastic properties correspond primarily to SSA and MBI.  Firing properties correspond primarily to %Na and %K.  

There are quite a few other properties that need to be specified to produce this actual body, but the few specs in this example give the idea.  Also, if it's a whiteware body, each of these specifications will be possible by varying a fixed number of ingredient materials.  Only those ingredients normally used in a whiteware body are candidates to produce these characteristics for a whiteware body.  No silicon carbide or barium titanate ingredients are allowed.  Conversely, for a silicon carbide body, or a barium titanate body, only appropriate raw materials for those body types become candidates for those bodies.

          Example #1 -- A Superconducting Oxide

I have used this example before, but here it is again.  One of our students was trying to tape cast superconducting oxide powders.  This was in the 1990s when everyone was searching for the Nobel prize winning composition for the best high temperature superconductor.  This student wanted to tape cast his powders in preparation for a methodology to form the prize winning composition when it was identified.

He couldn't tape cast successfully at 60% solids.  He had his powders and he had commercial solvents for the liquid fraction for the tape casting process.  He followed the routine recipe and it didn't work.  I told him to change the PSD.  He said he only had one PSD available from the supplier.  So, he milled that one powder to a broad range of PSDs in a ball mill.  He milled for something like 1 hr, 2 hr, 4 hr, 8 hr, 16hr, 24 hr, and 48 hr.  I don't remember the specific times he used, and they are not important anyway.  The point is that he had a wide range of PSDs available to him with his original powder being both the feed powder for milling and the coarsest available powder.  

With the milling completed, we calculated the best packing PSD of these 8 distributions using the packing program.  With this new composition recipe in hand, he went back to the lab.  Note:  This new composition was still 100% of the original powder.  The PSD had been changed, but the composition was the same.  He then came back and reported two things:  (1) He could tape cast successfully at 75% solids, and (2) he lost his superconducting properties.  Point #1 showed him that he could tape cast successfully if he could produce a different PSD.  Point #2 showed him that he had contaminated his materials when he milled them in the ball mill.  Point #2 also meant that he needed to go back to the supplier with Point #1 to make the case that he could tape cast successfully if he had a different PSD and if they (the supplier) could supply him with different particle size powders that were not contaminated.  

          Example #2 -- Finer Feldspars

This example deals with feldspars, but it is broadly applicable to other powders as well.  Studies have shown that by milling feldspars (or by using finer feldspars from the same supplier) firing temperatures can be reduced.  In some cases, firing temperatures can be reduced by more than 100^oC by reducing feldspar particle size.  

This may be a simple solution to a firing problem -- decrease the size of the feldspars (i.e., change the feldspar PSD) -- but forming properties, in general, are functions of the PSD of the body.  If your body is not firing properly and you simply substitute some finer feldspars for some coarser feldspars in the batch formulation, you may change the firing behavior, but you will also change the rheology and thereby, the forming behavior, because you are changing the PSD of the whole body.  In the PPC formulation above, if you still match the %Na and %K with the new finer feldspars, it will be necessary to adjust the overall PSD of the body to still hit the desired PSD and SSA specs.  

If the PPC formulation is a good one, making changes to the feldspar PSD will require adjustments to %s and/or sizes of other body ingredients -- and it will all be accomplished within that given formulation.  In a traditional body composition, changing the PSD of the feldspar will not require changes to any other body ingredients.  A good process engineer may realize that other adjustments need be made, but the requirement won't show up in the traditional body composition.  If the traditional composition calls for 30% Feldspar #16 from Company A, it would be easy to change this to 20% Feldspar #16 from Company A plus 10% of the finer Feldspar #4 also from Company A.  That should certainly lower firing requirements but it will also change forming properties as discussed.  The traditional body composition will not indicate any other adjustments are needed.  

It should be expected that fine feldspar particles will behave differently during forming operations than equally fine clay particles, but the PPC formulation at least defines the need for further adjustments when a compositional change like this occurs.  The traditional composition will not define any such need. 

With a properly specified PPC formulation in place and PPC implemented in the plant, the requirements necessary to adjust for decreasing feldspar particle sizes or an insufficient supply of different PSDs to meet the PSD specification are automatically accommodated by the PPC formulation.

A Non-Coordinated Solution for Meeting ISO Specifications

It is possible to put together procedures which solve a long list of problems without having any coordination between them.  In the example above, one might suggest that to change the firing temperature of a body, one must either change the nature, amount, or PSD of the feldspar components in a body.  In a technical ceramic, one would change the nature, amount, or PSD of the fluxing materials in the body composition.  In either or both cases, however, it could be a relatively complex task to define all possible property variations and corrective procedures that must follow such changes.

For example, hanging from a normal feldspar to nepheline syenite can produce lower firing temperatures.  But nepheline syenite is the material that we use to do dilatancy demonstrations.  Just add water to fine nepheline syenite and Voilá!  Instant severe dilatancy!  This is a good material to use as a flux, but if its PSD is fine and narrow, it can produce forming difficulties.

Changing from 20% to 30% of the same feldspar in a body will also produce lower firing temperatures.  This too will produce forming problems because now there's 10% less of all other ingredients in the body.  Reducing the clays and kaolins by 10% will change plastic properties.  Reducing other non-plastics will change other body properties or ware properties.

Changing the PSD of a single feldspar will also produce lower firing temperatures.  As noted above, this will change the overall PSD of the body which will change its rheology and forming properties as well.  It will also change SSA and it may change % alkalis.

All three of these changes will alter the SSA of the body which will change the need for additives.  Since most additives act on particle surfaces, changes in body SSA will change the required amounts of additives that should be used.  Increasing the SSA by 10% will normally require 10% more additive if the goal is to maintain constant additive coverage on each unit area of surface.  To not increase or decrease additive concentrations as SSA changes is to vary the coverage and effectiveness of those additives on particle surfaces.  

Changing PSDs of a body also changes packing capabilities of the body, which changes the solids content required to hit a particular viscosity in the absence of additive chemicals.  Changing body PSD without also adjusting solids content will cause different rheologies (shear-thinning vs dilatant) to occur when additives produce desired body viscosities.  

Any one change in a body should be expected to have several different effects on processing performance and/or ware properties.  If ISO requirements call for documentation that explains how all such variations will be handled, it is possible to have a large list of procedures that are simply not coordinated solutions to problems.  Non-coordinated procedures could lead one to run in circles.

PPC Should Come First.  ISO Documentation Should Follow.

You should all know by now that I am biased, of course, towards PPC.  Implementation of PPC in a plant requires engineers to solve a variety of body and process problems leading to a proper and rigorous PPC formulation for each body.  Each process engineer needs to know in great detail how each property and each specification in a PPC formulation affects the body, forming properties, drying properties, firing properties, and ware properties.  PPC necessarily forces this exceptional amount of detailed body and product knowledge.

A good PPC formulation then should handle all possible variations.  All possible occurrences of Murphy's Law (when something can go wrong, it will) should then be handled by the proper PPC formulation.  With such a rigorous knowledge of a process and an equally rigorous PPC Body Formulation, it should be relatively easy to produce documentation of coordinated procedures for ISO requirements.  

An attitude that might emerge from a traditional body composition and ISO documentation requirements is that the engineers will do whatever it is they normally do when a problem occurs -- regardless what the ISO documentation says.  PPC requires a daily mentality that does not allow this type of thinking.  

Another attitude that might emerge from a traditional body composition and ISO documentation is the "black box" mentality.  "Anyone can do this job because all of the solutions are documented."  I have seen this happen.  A statistician was hired for an engineering job because "everything" that needed to be known about the process was in the documentation -- so the statistitian brought new skills (his statistics) to the job that the average engineer could not duplicate.  It didn't work.  No offense to anyone, but statistical process control is no match for a well-trained, excellent process engineer.  It can help an excellent engineer be better, but it can't substitute for the engineering know-how.

A Perfect Body Formulation???

There is no such thing as a perfectly specified body formulation.  Your best engineers won't produce a perfect body formulation;  I couldn't produce a perfect body formulation;  nobody can.  There are simply too many possible variables that can affect each system.  

On the coal slurry project, we were using an instrument that plotted results on a sheet of paper but which also sent the signals out ports on the back of the instrument to the computer.  The lab computer was programmed to collect the data as it was also plotted on the graph paper in the instrument.  We (I) had to smooth this data in the computer before it could be used.  The graph paper contained a line of data.  The computer collected a bazillion points of data that corresponded to the line.  Every time I put code into the smoothing routine to handle one type of error, another error reared its ugly head.  The data was supposed to go from 100% to 0% without every increasing within that range.  Sometimes the data started at 100%, increased to 105%, then decreased to -5%, before finally reaching 0%.  It wasn't supposed to do that.  I wrote code to handle it.  Then, the normal background noise caused local increases which were handled in the code.  Air bubbles caused major increases midway through the analysis.  Those were handled by another set of routines.  All sorts of other problems occurred following these.  They occurred one by one as each larger problem was eliminated.  But the number of potential problems appeared to be endless.  

How did we ultimately solve this problem?  You'll laugh but I'll tell you.  We didn't monitor that instrument with the computer.  We only collected data on the graph paper.  When we wanted to input it into the computer, we used a french curve and a pencil to smooth the data by eye.  Then, we digitized the pencil line using a reticle (instead of a pen) on the plotter.  We allowed each operator's eye to do the smoothing.  It worked really well.  We had a simple routine that allowed the operator to line up the paper in the plotter, define 100%, 0%, max X value, and min X value, and then the plotter went to several X points between the limits and requested the operator to show the Y value by putting the reticle on the pencil line.  

It is possible to solve this problem within the computer, but at the time, the results seemed endlessly far away.  The smoothing routine always needed more code, and more tweaking.  A good body formulation will be like this.  One must be constantly adjusting and tweaking the formulation to improve it -- and on the days when the computer can't calculate a solution -- someone (the process engineer) needs to step forward and make a command decision.  

Body formulations are always like this.  There will always be a property or a specification that was overlooked.  There will always be important variables that we don't recognize as important.  There will always be minor variables that we don't recognize as variables at all.  How many of you have problems that come and go with the phases of the moon or the alignment of the planets?  Those are actually caused by variables that are changing in ways we don't recognize, or by variables that aren't recognized as process variables.

For these reasons, there is no such thing as a perfect body formulation.  They will always need some tweaking.  And when the computer program (Solver or the local Simplex routine) that calculates today's composition that meets the body formulation can't produce the desired body properties from the available raw material ingredients, the process engineer will always be necessary to make some last minute decisions.  

Conclusions

With PPC implimented in a plant, it is fairly easy to produce the ISO documentation of the procedures that will be followed when problems occur.  Such procedures should be well-coordinated due to the PPC requirements.  If implemented properly, the very nature of the PPC process will handle most such problems.  

Without PPC, it can be difficult to document a set of coordinated procedures that will be followed when problems occur.  It is NOT impossible.  It appears, however, to be more difficult to do this when traditional body recipes and traditional control processes are followed.

No body formulation will ever be perfect.  One or several process engineers will always be needed to make the important decisions when problems occur. Don't worry -- your jobs are secure -- even with PPC!