Features of High Shear Compaction™
Many of the technical benefits can only be achieved with HSC™. Following are the key technical benefits made possible by the HSC™ process that improve quality, increase yields, and lower the manufacturing costs for all types of ceramic tapes including dense tape, ceramic thick tape, and ceramic porous tape.
Water based binders – HSC™ is best suited to utilize water-based binder systems . This removes the need to monitor solvent usage and other EPA restrictions. The use of water-based binder eliminates the explosion hazards associated with solvent systems . The equipment is easily cleaned which reduces downtime. Much less protective equipment is needed for employee safety.
Uniform density – Dense tapes made with the HSC™ process have uniform density throughout all dimensions. This is because the particles and binder distribution is uniform and homogeneous. This is a critical factor since the lack of tape homogeneity always leads to differential shrinkage and camber problems. With tape casting the powders and binders tend to segregate during drying, this problem is eliminated with HSC™; therefore the tapes will fire flat.
Ceramic thick tape – The HSC™ process is capable of producing thick ceramic tapes. The minimum thickness is about 125 microns, but thicker tapes are easily produced in a single layer. This eliminates the need to cast multiple layers and laminate them to form a thick substrate.
Uniform thickness – The HSC™ process offers extreme thickness control. Tolerances of +/- 5 microns are typical even with thick tapes. The final thickness of the ceramic thick tape is not determined until the last step in the process. The thickness is monitored and automatically adjusted so that it remains constant.
Flexible tape – HSC™ tapes can be stiff or flexible, but are never brittle. The unique binders that have been developed allow even dense tapes to remain flexible unlike most cast tape binder systems.
Post forming – Tapes made with HSC™ can easily be post-formed. The binders used are thermoplastic and will flow when heated. Thick ceramic tapes can be placed in a die and formed into complex shapes.
Porous Tape – Fugitive pore former powders such as methyl methacrylate can be mixed with inorganic powders and well dispersed. Upon burn-out and sintering, pores are created in the solid ceramic structure. Pore size and total porosity can be controlled by adjusting the size and volume fraction of the pore former in the ceramic body.
Reduced scrap – The HSC™ tape webbing can be recycled without the need to be reconstituted. The trimmings and other scrap tape that has the binder in it can be added back into the starting mix and re-used.
Density control – The green density of the tape can be controlled. The upstream processes can be adjusted to yield a constant green tape density regardless of the thickness. Even if the raw materials vary slightly from batch to batch the green tapes can be made to have identical green densities.
Density adjustments – The green density of the tape can be adjusted. The total binder solids content can be adjusted over a wide range and still yield a tape that can be handled. This allows different tape types to be matched for fired shrinkage. The resulting tapes can then be laminated and co-fired and still remain flat.
Dense tape – Higher green densities can be achieved. Due to the high shear forces that are imparted on the particles, they tend to pack together more tightly. In addition to this lower binder concentrations can also be used as compared to tape casting. These factors combine to increase the green density of the tape. Tapes with densities as high as 85% of the theoretical fired density have been produced with HSC™.
Reduced shrinkage – Thick ceramic tapes with higher green density will have reduced shrinkage rates. The tapes also tend to fire at slightly lower temperatures.
Improved dispersion – With the HSC™ process materials that have high specific gravity are easily formed into tapes. Materials such as tungsten carbide tend to settle rapidly while cast tapes are drying. This is not the case with HSC™. The cast tape is formed form a very high viscosity mix. The materials remain dispersed and never settle.
Ceramic porous tape – Pore formers, therefore, are easily dispersed. Many fuel cell companies must mix fugitive pore formers into the mix of ceramic powders. The low mass powders are very well dispersed and cannot settle or agglomerate during ceramic porous tape forming.
Ceramic tape development – Very small test batches can be produced. With the RTI lab scale HSC™ module, samples have been produced from as little as one or two grams of powder. Small batches of 1 or 2 kilograms can easily be made into tape on even a production module. This allows rapid raw material testing and development without the need to formulate custom slurries for each iteration.
High volume manufacturing – The HSC™ system is extremely efficient. Production modules are capable of producing thousands of square feet of thick ceramic tape in a single shift.
Reduced contamination – The tapes made with HSC™ have very little contamination. All surfaces that come into contact with the tape are either tungsten carbide or Teflon. Where iron contamination is not an issue, lower cost steel rolls can be substituted.
Surface finish – Tapes made with HSC™ have controlled surface finish. The tapes can be mirror finished or have a texture embossed. Both sides of the tape can be controlled.