Fabrication Of Ceramic Structures Research Articles

Application of gel-casting to the fabrication of 1–3 piezoelectric ceramic–polymer composites for high-frequency ultrasound devices

A modified gel-casting technique was used to fabricate a 1–3 piezoelectric ceramic/polymer composite substrate formed by irregular-shaped pillar arrays of small dimensions and kerfs. This technique involves the polymerization of aqueous piezoelectric (PZT) suspensions with added water-soluble epoxy resin and polyamine-based hardener that lead to high strength, high density and resilient ceramic bodies. Soft micromoulding was used to shape the ceramic segments, and micropillars with lateral features down to 4 µm and height-to-width aspect ratios of ∼10 were achieved. The composite exhibited a clear thickness resonance mode at approximately 70 MHz and a keff ∼ 0.51, demonstrating that the ceramic micropillars possess good electrical properties. Furthermore, gel-casting allows the fabrication of ceramic structures with non-conventional shapes; hence, device design is not limited by the standard fabrication methods. This is of particular benefit for high-frequency transducers where the critical design dimensions are reduced.

Processing and characterization of Ti–B-based functionally graded materials produced by microwave-activated combustion synthesis

Single as well as graded compositions were fabricated in the Ti–B system using a microwave-activated combustion synthesis (MACS) process. When synergistically combined with microwave processing, combustion synthesis offers great potential for the fabrication of ceramic structures and composites. Combustion waves were triggered using a SiC susceptor to initially absorb microwaves. The effects of processing variables, such as thermal insulation, and atmosphere on the process were investigated. Examination of reacted samples by means of x-ray diffraction indicated the presence of titanium monoboride and diboride along with unreacted titanium. Compared with conventional combustion synthesized products, MACS resulted in smaller pores. However, the total amount of porosity remained almost the same. The microstructure of the graded layers and interfaces were examined using optical and scanning electron microscopy. Over the entire cross section, the interfaces were continuous and crack free.

Capillary-infiltrated conductors in ceramics

The infiltration of high conductivity metals into capillaries in ceramic structures have been reported by Schwartz and Wilcox. Others have used the infiltration concept for the fabrication of composite structures for a variety of reasons, thermal expansions, machinability of hard metals, and so forth. In electronic applications, that is the fabrication of ceramic structures for support and interconnection of devices, the reasons for infiltration are evident. They provide highly conductive paths in a controlled manner for dimensions and configurations which approach those of device structures. Experiments were conducted to investigate the wetting and spreading of copper on molybdenum metallized alumina slips. Various surface-active and viscosity-active metals were added to the copper, and ambient conditions were varied. The results indicate that the primary controlling parameters for wetting are the ambient conditions. The infiltrations of copper into porous molybdenum lines were observed by X-radiographs of experimental substrates after increments of time at 1120°C. The substrates were moved from an average temperature of 1040°C into a hot zone at 1120°C, then after an incremental soak time were returned to 1040°C, and subsequently cooled for observation. The penetrations of copper are clearly seen on the X-radiographs so that the process of infiltration may be closely monitored. The results indicate that reliable infiltrations at predictable rates may be obtained. Thus, the technique is a reliable means of achieving high conductivity metals within a ceramic substrate. There is no indication of a limitation on penetration distance on well formed lines as small as 5 mil wide. Electrical conductivity of infiltrated lines was observed to follow the volume relationship: Σ=vCuΣCu + vMoΣMo where Σ = conductivity andv = volume proportion.