Tape casting applications

Mistier, R.E. (1995) The principles of tape casting and tape casting applications, in Ceramic Processing (eds R.A. Terpstra, P.P.A.C. Pexand A.H. deVries), Chapman Hall, London, UK, Chapter 5. 

Ferroelectric ceramics (such as barium titanate, lead zircanate titanate) Sensors and actuators, electronic memory, optical applications Tape casting, sputtering, pressing, templated grain growth Improved dielectric and piezoelectric properties... 

Common consolidation methods include variations on pressing powders, plastic forming, slip casting and tape casting. The choice of which method to use for a given application is very dependent upon the shape, size and required dimensional tolerances of the final product, available capital outlay and desired productivity. Each of these methods is examined in turn below, followed by sintering, which turns the consolidated powders into a monolithic body with mechanical integrity. 

Tape casting is a well known method for making thin, flat and dense ceramics [13-15]. This technique is limited by the thickness (a few millimetres) of the films obtained. The most important applications are in the electronics industry. Simon et al. [16] have described the preparation of flat ceramic membranes. This type of geometry is receiving interest because of the possibility of obtaining a high module compactness (compactness is defined by the ratio of membrane surface area to module volume). 

MAJOR APPLICATIONS Fiber, slit tape, cast and biaxially oriented film, containers and closures, automotive interior trim, appliance housings and components, component in elastomeric blends with polyethylene and olefinic rubbers. 

Tape casting is used to make flat ceramic sheets having a thickness up to about 1mm. The process was developed during the 1940s for capacitor dielectrics. The production of ceramic capacitors is still one of the most important applications of tape casting. 

In the next chapter we will review some of the many applications of tape casting for the manufacture of a wide variety of products. The list is not meant to be all-inclusive. It is meant to show the diverse nature of the products and where they are used. 

As we mentioned in the Foreword, the uses for tape casting as a fabrication tool have advanced well beyond the scope envisioned by the pioneers in the field some 50 years ago. In this chapter we will review some of the standard applications as well as some uses that are only beginning to be recognized as potential applications for this unique fabrication technology Almost everyone involved with ceramic processing knows that thin, flat sheets can be produced using this technique, but how many ceramists appreciate the fact that 1.2 x 2.5 m (4 x 8 ft.) sheets that are 0.5 to 0.76 mm (0.020 to 0.030 in.) thick are produced by tape casting for use in the manufacture of molten carbonate fuel cells These are some of the diverse applications that we will discuss in the sections that follow. 

Thin sheets of piezoelectric materials are used in sensors, buzzers, and actuators. In addition to the conventional vibrators, pressure and acceleration sensors are now also being manufactured from these materials. Lead zirconate titanate (PZT) is one of the most common materials used for these applications. The trend is to produce thinner and thinner and smaller and smaller parts. Therefore tape casting has become the manufacturing route of choice. One of the basic applications of piezoelectric ceramics is as a gas igniter where a spark is generated by the piezoelectric under an applied mechanical stress. Microphone discs are also prepared from thin... 

A special class of materials that is also ferroelectric are electrooptic ceramics. Materials such as lanthanum-modified lead zirconate titanate (PLZT) produce excellent electrooptic devices. These polycrystalline ceramics exhibit voltage-variable behavior—that is, they can be switched from optically transparent to opaque by the application of voltage. Most of these devices, which are used for shutters, modulators, and displays, are processed by hot pressing to full density. Experiments in many laboratories are being carried out to tape-cast these materials into thin sheets. The main problem encountered to date has been the ability to sinter to full density. The use of nanosized powders has helped in this regard. The ability to tape-cast large sheets could open a wide variety of applications for these materials. 

Many different types of sensors have also been fabricated by tape casting. One of the most widely used sensors is the oxygen sensor used in automotive and other applications. These sensors are based upon solid-state conductivity of the ceramic elements at elevated temperatures. Most are fabricated from stabilized zirconia, which is the electrolyte in the device. The zirconia is a solid ionic conductor that transforms oxygen partial pressure or activity gradients into an electrical signal, which can then be further processed to perform control activities such as carburation or ignition modification. The... 

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