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					12d Advanced Structural Ceramics: Markets and Production Costs




Author’s Name and Affiliation:

Julie M. Schoenung, Ph.D.
Professor
Chemical and Materials Engineering
California State Polytechnic University, Pomona
3801 West Temple Avenue
Pomona, CA 91768
909-869-2622
909-869-6920 (fax)
jmschoenung@csupomona.edu


Address to which to send proofs:

Julie M. Schoenung, Ph.D.
1412 Treasure Lane
Santa Ana, CA 92705
714-838-6653 (Tel; FAX on request)




                                                                 Page 1 of 17
12d     Advanced Structural Ceramics: Markets and Production Costs



Advanced structural ceramics are inorganic, non-metallic materials that can be used for

components that have severe “structural” design constraints. These materials exhibit desirable

properties such as high-temperature strength, high-temperature stability, wear resistance,

chemical inertness and corrosion resistance. Furthermore, they are generally made from

synthetic powders that can be tailored to specific applications and manufacturing methods.

These materials are also referred to as “high-tech” ceramics, “engineering” ceramics, and/or

“technical” ceramics. In contrast, “traditional” ceramics are derived from naturally occurring

minerals and are used for products with less rigid design constraints, such as tile, brick,

refractories, and whitewares (e.g., sanitary ware and consumer products) (Lewis 1991). Yet

another category of ceramic materials are “electronic” ceramics or “functional” ceramics. These

materials exhibit unique “electronic” behavior that allow them to be used for various functions,

such as insulative, capacitive, conductive, resistive, sensor, electro-optic and magnetic functions

(Buchanan 1991). The markets and market forces for “traditional” and for “electronic” ceramics

are different than those for “advanced structural” ceramics and will not be discussed here.



The markets for advanced structural ceramics are diverse, encompassing a wide variety of

applications, desirable properties, and available materials. Advanced structural ceramics are an

enabling technology that must compete with more traditional materials. Thus, superior properties

are not only required, but cost competitiveness is a must. To understand this market, the reader

is presented with a description of the market, including potential and existing applications, and

key market forces. This is followed by a discussion of ceramic processing and production costs.



1. Market Characteristics

1.1 Potential Applications

Advanced structural ceramics are being used or have the potential to be used in a large variety of

applications (Ferber and Tennery 1991, American Ceramic Society 1999). Some of the primary




                                                                                              Page 2 of 17
application areas are listed in Table 1. This is not intended as a complete list, but rather a

sampling of some of the applications with the greatest potential and/or the greatest interest.



As one can see, the number of potential applications is essentially infinite. This is not surprising if

one thinks of the tremendous number of different “structural” products made from traditional

materials (metals, plastics and fused quartz). Thus, the ceramic manufacturer must have the

versatility to produce parts of various shapes and sizes, as well as various quantities. This

capability combined with some of the inherent features of processing advanced structural

ceramics, make these materials inherently expensive. Only under the best set of conditions can

advanced structural ceramics compete with traditional materials. Two examples of existing

markets in which advanced structural ceramics are competing effectively include cutting tool

inserts and mechanical seal rings.



1.2 Existing Markets

In 1986, Rothmann, Clark and Bowen presented an analysis of the costs and potential market for

silicon nitride as a cutting tool insert material (Rothmann et al. 1986). Their work shows that

market penetration would be dependent on the materials being machined and the machine tools

used to do the machining. Certain conditions were necessary for this market to materialize.

Since 1986, silicon nitride has become an established material for use as cutting tool inserts. It

has not, however, completely replaced tradition materials, only supplemented them.



In 1987, Rothmann, Schoenung and Clark presented an analysis of the costs and potential

markets for four advanced structural ceramic components: cutting tool inserts, turbocharger

rotors, automotive valve guides, and mechanical seal rings (Rothmann et al. 1987). Their work

shows that cost reduction and improved reliability would be necessary for significant use of

advanced structural ceramics in these applications. Today, for advanced structural ceramics, the

cutting tool market is small but stable. The turbocharger rotor market exists only in Japan in part

because of the small number of turbocharger rotors used in the US. The automotive valve guide




                                                                                            Page 3 of 17
market (and internal combustion engine components market in general) does not exist. And the

mechanical seal ring market is small but real.



A few more words are warranted about the mechanical seal ring market. In the Rothmann et al.

(1987) analysis, the focus is on seal rings to be used in chemical pumps. Today, the market for

ceramic rings is in auxiliary power units for aircraft. It should be noted that because of the

extreme wear resistance of the ceramic part, the lifetime of the seal ring is nearly infinite, thus

eliminating the market for replacement parts. This “one-time” installation type of market is

common among the wear applications that ceramics could be used in and should be recognized

as a limiting factor in the total market potential for these components.



1.3 Market Barriers

For the vast majority of the applications identified above, the use of ceramics would result only

from technology push, not from market pull. For the applications where there is sufficient market

pull, penetration has been painfully slow because of three key limitations to advanced structural

ceramics: reliability, cost effectiveness, and user education (or “bias”). For ceramics to penetrate

potential markets, each of these issues must be addressed in a manner specific to the

application. Furthermore, the ceramic supplier must expect strong competition from the

traditional material supplier. Thus, for success, it is key for the ceramic supplier to identify

applications where traditional materials really do not work (e.g., cutting tool inserts), or do not

work very well (e.g., hip implants), or are limiting technology development (e.g., in silicon device

manufacturing). In addition, ceramic suppliers need to educate their users to eliminate bias.

While traditional ceramics are brittle and exhibit low fracture toughness, advanced structural

ceramics exhibit far superior properties (Richerson, 1992, p. 186-7). Ceramic suppliers also need

to either find applications that are not reliability sensitive (e.g., the expected lifetime of a missile is

far shorter than that of an automobile) or maximize reliability through process development.

Finally, suppliers of advanced structural ceramics must recognize that their products must be

cost-competitive with traditional alternatives and should therefore strive to minimize cost.




                                                                                                Page 4 of 17
The cost of producing ceramic components is a function of the complex processing required.

Thus, processing is discussed first, before the discussion on production costs.



2. Processing of Advanced Structural Ceramics

The processing required to form and finish a structural ceramic part is complex, and requires

numerous process steps (Rahaman 1995, Richerson 1992). A basic process flow diagram is

presented in Figure 1. The process begins with micron-size powder mixed with additives to

facilitate forming and/or sintering. This mixture is then formed into a shape using processes such

as cold isostatic pressing, uniaxial pressing, injection molding, gelcasting, extrusion and slip

casting. The shape that is produced depends on the shape forming technique and the complexity

of the tooling used. If the part is formed to a near-net-shape, green machining or bisque

machining is generally not required. If the part is formed to a “blank”, it can be green machined or

bisque machined after preliminary heat treatments such as drying, binder burnout, and bisque

firing/presintering. This level of machining can be done with conventional tooling because the

part is still rather soft. Heat treating for densification is then required. This is called sintering, and

is the step in which the powder compact is converted into a dense, pore-free solid, as a result of

atomic diffusion. Significant shrinkage occurs in this step. Sintering is sometimes done in an

atmospheric furnace, sometimes in a gas pressure furnace, and sometimes in a hot isostatic

press. After sintering, the part generally requires some final machining, depending on the

dimensional and surface tolerances. Final machining requires diamond tooling because of the

hardness of the dense ceramic part. After machining the part is inspected for flaws using dye

penetrant and radiography techniques, for dimensions using coordinate measuring machines,

and for strength (if necessary) using proof testing. In general, because of the small production

quantities for advanced ceramic parts, all inspection steps are completed on each part. No

sampling is done.




                                                                                               Page 5 of 17
Figure 1 shows seven steps in the process flow diagram. Actual process sequences tend to have

multiple steps for each “step” shown in this Figure, which can lead to processes with twenty steps

or more. The fact that there are so many steps has several implications: capital is required for

each step, process development time for optimization of properties is required for each step, and

parts rejected must be accounted for at each step. Each of these affects the cost of producing

advanced structural ceramics. The cost is also effected by the choice of shape forming

technique, the quality and price of the raw materials, and the segmentation of the market.



3. Production Costs

3.1 Costs of Capital

Several factors affect the cost of the capital equipment required to produce advanced structural

ceramics. Some of these are process driven; others are market driven. The numerous process

steps mentioned above are one factor that is process driven. Another factor is the nature of the

process, especially the sintering, final machining, and inspection steps. Sintering requires

extreme temperatures, and sometimes pressures, under controlled atmospheres. The process

must be highly controlled to control densification, shrinkage, and, ultimately, properties. Final

machining requires diamond tooling and rigid fixtures. Inspection often includes radiography, with

the task of finding micron-sized flaws.



The market-driven factors that affect the cost of capital equipment include the total size of the

market for advanced structural ceramics (i.e., small) and the size of the markets for any one

product (i.e., also small). Because the total market is very small, there are only a few suppliers

worldwide. Thus, the equipment they need tend not to be off-the-shelf items. They are unique

and require significant develop time and financial investment by both the ceramic supplier and the

original equipment manufacturer. Because the markets for any one product are small, there is no

need to have facilities dedicated to producing that product. Instead, production facilities must be

flexible enough to produce a large range of different products, while at the same time maximizing

the utilization of capital.




                                                                                           Page 6 of 17
3.2 Process Development

Because of the numerous process steps required to produce advanced structural ceramics, it is

quite a task to optimize each step and the combined total process, so as to optimize properties.

Not only is it a task to optimize each step for a change from one part to a different part, but each

change in one process step affects the optimal parameters for the other process steps. For

instance, if a new binder is used, the materials preparation might be different, the shape forming

parameters will probably be different, and the heat treating conditions will definitely be different.

Thus, for just one change (one change that could, say, significantly enhance properties), several

other changes will need to be made. This dominoe effect in process development is a major

issue limiting the ultimate commercialization of advanced structural ceramics. For years, the

federal governments around the world, and some private industries, supported these process

development costs through a variety of funding initiatives. Many of these funding sources no

longer exist. Process development costs can only be supported by high value-added markets

where there is tremendous market pull. For advanced structural ceramics to move into the

markets that could result from technology push, the process development costs must be

significantly reduced.



3.3 Reject Rate

Related to process development is reject rate. The goal of process development is to minimize

reject rate, throughout the process. Several studies have shown that the primary factor that

controls the cost of producing advanced structural ceramics is reject rate (Rothmann et al. 1986,

Schoenung et al. 1997, Schoenung 1999). These studies reinforce that there is little that can be

done to change the cost of capital and the cost of materials. Furthermore, although within the

control of the ceramic supplier, changes in shape forming technique also have little effect on the

total cost (Schoenung et al. 1997). Changes in shape forming technique have more effect on the

reject rate and process development costs. Thus, ceramic suppliers should carefully evaluate the

cost tradeoff between the costs of reject parts and the cost of process development.




                                                                                            Page 7 of 17
There are two reasons why reject rate has such a significant influence on production costs. First,

there are many steps in the process. If the reject rate at each step in a twenty-step process is

one percent, the cumulative reject rate is 82%. This means that in order to produce 100 “good”

parts, the facility must have sufficient capital, labor, and materials at the early steps in the

process to make 122 parts. If the reject rates for any of process steps are greater than one

percent (which is quite possible given the amount of process development required), one can

imagine the exponential effect on the cumulative reject rate and the resultant excess costs for

capital, labor and materials.



The second reason reject rates are so significant is that most rejects are not identified until the

inspection steps that occur near the end of the process. As a result, there is significant value

added to the part before it is determined to be defective. Ideally, quality control steps throughout

the process could redistribute the rejects and reduce costs. Unfortunately, detection of defects

that limit performance can only be done after sintering, which is quite late in the process.

Inspection prior to sintering can only look for gross defects such as impurities in the raw material

and parts that distort during forming or heat treatment.



What are “defects that limit performance”? For advanced structural ceramics, both internal and

surface flaws can limit performance. Internal flaws include pores and impurities. Surface flaws

include scratches such as those that can be introduced during final machining. There are two

reasons why flaws in ceramics must be controlled more so than in metals. First, ceramics exhibit

lower fracture toughness values than do traditional materials. Second, ceramics fail

catastrophically (crack propagation is rapid), which means the probability of failure must be

evaluated using Weibull statistics (Richerson 1992, Barsoum 1997).



Consider an example to illustrate the significance of flaws in ceramics versus those in metals.

Assume the metal has a fracture toughness (KIC) value of 1.0. An advanced structural ceramic




                                                                                              Page 8 of 17
has a relative KIC value of approximately 0.1. Using the Griffith equation to describe the

relationship between fracture toughness and critical flaw size (Barsoum 1997), and normalizing

the values to 1.0 for the metal, the critical flaw size for the ceramic is 0.01 – two orders of

magnitude smaller than that of the metal! The critical flaw in the metal is typically in the millimeter

size range, which is easy to detect using conventional inspection equipment such as dye

penetrant. The critical flaw in the ceramic will be in the tens-of-microns range, which is difficult to

detect even with sophisticated, costly inspection equipment such as radiography. As a result,

both the cost of inspection and the number of rejected parts are greater for ceramics than they

are for traditional metals.



3.4 Shape Forming

Shape forming is the sequence of steps that convert the raw materials from powder-plus-

additives into a component. The component at this stage cannot yet be used because it consists

only of powder that is held together with an organic binder. The component, said to be in the

“green” state, does have enough strength to be handled.



There are two reasons why the choice of shape forming steps affect cost. First, there are several

available shape forming methods, including uniaxial pressing, cold isostatic pressing, gelcasting,

injection molding, slip casting, and extrusion, each with its own characteristic process parameters

and costs. Second, not all of the choices result in a component of the same shape. Some

forming techniques produce blanks, while others produce near-net-shape parts. For the blanks,

some green machining is generally needed. The choice between near-net-shape and blank-plus-

machining must be made taking into consideration both part complexity and cost. Near-net-

shape processes require high-cost tooling, which is easiest to justify for large production volumes

but may be necessary for complex parts such as rotors. Blank-plus-machining is generally the

first choice for prototype parts, but also can be the best choice for low production volumes or for

parts that would require too much process development if made with near-net-shape techniques.

Schoenung et al. (1997) present a representative analysis of the cost tradeoffs between different




                                                                                             Page 9 of 17
forming techniques. The results are component specific, but reinforce that the effect of changing

shape forming method is far less significant than the effect of changes in reject rate.



3.5 Raw Materials

The raw materials used to make advanced structural ceramics include oxides (e.g., Al2O3 and

ZrO2), carbides (e.g., SiC and B4C), nitrides (e.g., Si3N4 and AlN), and borides (e.g., TiB2). These

raw materials are generally synthetic (i.e., man-made) and are highly engineered to have the best

combination of properties that will result in fully-dense, strong, tough, high-quality ceramic parts

(Rothmann et al. 1985). These raw materials are used in powder form, with average particle

sizes of one micron or less, preferably submicron.



The nature of these raw materials effect cost in a variety of ways. The powders themselves are

expensive. This is so because of their engineered quality and because worldwide supply is quite

limited (note that demand is also limited). The powders also contribute to process development

costs. The powders from two suppliers are not exactly alike and do not respond to processing in

exactly the same way. Thus, they cannot be interchanged or mixed, which is a significant

limitation and a significant difference from the raw materials used by producers of traditional

materials such as metals and plastics.



3.6 Market Segmentation

As discussed earlier under Market Characterization, the market for advanced structural ceramics

is highly segmented. A typical market projection for any given component is in the range of tens-

of-thousands per year. Even the automotive engine market, which at first thought would appear

to be quite large, has significant segmentation in engine models and configurations (Schoenung

1989). This segmentation, again, leads to a market for any one specific part that is quite small.



This market segmentation and limited production quantities has significant ramifications on the

costs of production, as shown in the work on mechanical seal rings by Rothmann et al. (1987).




                                                                                          Page 10 of 17
Production volume affects the general level of capital investment, the choice of shape forming

technique, the level of automation, and, ultimately, reject rate. Furthermore, low production

volumes necessitate flexible manufacturing, instead of a dedicated facility, which implies that

there is limited potential to take advantage of economies of scale to reduce cost. Instead, costs

will be minimized with respect to production volume and product mix only when the physical plant

is non-dedicated and is utilized one hundred percent, except for maintenance required downtime.

This is an optimistic assumption. In reality, for at least the near term, the product mix of ceramic

parts will be significant and will lead to less than optimal costs.



4. Summary

Advanced structural ceramic materials such as silicon nitride and silicon carbide exhibit properties

far superior to traditional ceramics and metals. Thus, they offer significant potential to improve

the performance/lifetime of other engineering systems such as engines, aircraft, heat exchangers,

manufacturing equipment, medical devices and military devices. Unfortunately, the processing

required to convert these materials into usable components is complex and requires significant

process development for each component and each new raw material. Appropriate shape

forming techniques must be chosen, and unique capital equipment and tooling must be

purchased. In addition, advanced structural ceramics are two orders of magnitude more sensitive

to flaws than are metals. As a result, reject rates are typically higher, inspection costs are higher,

and processing steps are less robust than those for metals. All of these factors combined cause

advanced structural ceramics to be expensive. Thus, the rate at which these materials have

penetrated into the potential markets has been slow, and will continue to be so, unless there is a

major breakthrough in the industry.




                                                                                          Page 11 of 17
Bibliography



American Ceramic Society 1999, Ceramic Fact Sheets, Online at www.acers.org.



Barsoum, M. 1997 Fundamentals of Ceramics, McGraw-Hill, New York.



Buchanan, R.C., 1991 Electrical/Electronic Applications for Advanced Ceramics. In: Engineered

Materials Handbook Ceramics and Glasses, Vol. 4. ASM International, Section 15.



Ferber, M.K. and Tennery, V.J., 1991 Structural Applications for Technical, Engineering, and

Advanced Ceramics. In: Engineered Materials Handbook Ceramics and Glasses, Vol. 4. ASM

International, Section 13.



Lewis, G., 1991 Applications for Traditional Ceramics. In: Engineered Materials Handbook

Ceramics and Glasses, Vol. 4. ASM International, Section 12.



Rahaman, M.N. 1995 Ceramic Processing and Sintering. Marcel Dekker, Inc. New York, NY.



Richerson, D.W. 1992 Modern Ceramic Engineering: Properties, Processing and Use in Design,
 nd
2 Ed. Marcel Dekker, Inc. New York, NY.



Rothmann, E., Stitt, J., and Bowen, H.K. 1985 A Look at Ceramic Powder Production Processes

– Old and New. Ceramic Industry, May, 24-29.



Rothmann, E.P., Clark, J.P., Bowen, H.K., 1986 Ceramic Cutting Tools: A Production Cost Model

and an Analysis of Potential Demand. Advanced Ceramic Materials 1, No. 4, 325-31.




                                                                                      Page 12 of 17
Rothmann, E.P., Schoenung, J.M., Clark, J.M., 1987 Markets for advanced structural ceramics.

Resources Policy June, 123-41.



Schoenung, J.M., 1989 Markets for Advanced Ceramics in Internal Combustion Engines.

Materials and Society 13, No.3, 233-46.



Schoenung, J.M., Masseth, R., Santos, M., Tuazon, H., Draskovich, B., and Mascarin, A., 1997

Economic Analysis of Alternative Fabrication Approaches for Advanced Structural Silicon Nitride

Components. In: Sohn, H.Y., Evans, J.W., and Apelian, D. (eds.) Proceedings of The Julian

Szekely Memorial Symposium on Materials Processing, The Minerals, Metals & Materials

Society, 631-51.



Schoenung, J.M. 1999 Cost Modeling and Analysis for Advanced Structural Silicon Nitride

Turbomachinery Ceramics. Ceramic Engineering and Science Proceedings, in press.



Schoenung, J.M., Kraft, E., and Ashkin, D., 1999 Advanced Silicon Nitride Components: A Cost

Analysis. Ceramic Engineering and Science Proceedings, in press.




                                                                                     Page 13 of 17
Author’s Name and Affiliation:


Julie M. Schoenung, Ph.D.
Professor
Chemical and Materials Engineering
California State Polytechnic University, Pomona
3801 West Temple Avenue
Pomona, CA 91768
909-869-2622
909-869-6920 (fax)
jmschoenung@csupomona.edu




                                                  Page 14 of 17
Table 1.
Potential Uses for Advanced Structural Ceramic Components.
Components for use in:                     Example Components                          Valuable Properties
Adiabatic Diesel Engines             Liners for the Combustion Chamber             Low Thermally Conductivity
                                            Cam Roller Followers                        Wear Resistance

Advanced Gas Turbine Engines              Rotors, Stators, Shrouds                 High Temperature Strength

Automotive Engines                          Valves, Valve Guides                        Wear Resistance
                                            Turbocharger Rotors                            Low Inertia

Aerospace Systems                   Seal Rings in the Auxiliary Power Unit              Wear Resistance

Heat Exchangers                                      Tubes             High Temperature Strength, Chemical Inertness

Manufacturing of Silicon-Based Electronic Devices
                                       Plasma Etch Domes and Rings           High Corrosion and Erosion Resistance
                                     Chemical Vapor Deposition Domes         High Corrosion and Erosion Resistance

Medical Products                     Balls and Sockets For Hip Implants       Wear Resistance, Chemical Inertness
                                               Dental Implants                  Biologically Compatible, Reactive

Metal Machining                             Cutting Tools Inserts             Wear Resistance, Chemical Inertness

Military Devices Such As Missiles            Rotors and Nozzles              Light Weight, High Temperature Strength
                                                    Bearings                            Wear Resistance




                                                                                                             Page 15 of 17
Figure 1. Simplified, representative process flow diagram for the production of advanced
structural ceramic components.




                                                                                     Page 16 of 17
                                             Receiving
                            (includes quality control on raw materials)
                                                    |
                                                    V
                                       Materials Preparation
                          (includes mixing, milling, seiving, spray drying)
                                                    |
                                                    V
                                           Shape Forming
              (includes mold fill, hold time @ temperature or pressure, part removal)
                                                    |
                                                    V
                                     Green/Bisque Machining
                          (could require multiple types of machine tools)
                                                    |
                                                    V
                                    Heat Treating & Densification
         (includes drying, binder burnout, sintering, hot isostatic pressing, recrystallization)
                                                    |
                                                    V
                                          Final Machining
                          (could require multiple types of machine tools)
                                                    |
                                                    V
                                     Inspection & Quality Control
           (includes dye penetrant, radiography, dimensions & tolerances, proof testing)


Figure 1. Simplified, representative process flow diagram for the production of advanced
structural ceramic components.




                                                                                           Page 17 of 17

				
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