Carolina Tallon

Controlling the microstructure of ceramic particle stabilized foams: influence of contact angle and particle aggregation

Porous cellular alumina ceramic green bodies have been produced by combining the particle stabilized foam method with gelcasting. The suspension foams were stabilized by particles rendered weakly hydrophobic with short chain sulfonate surfactants. Poly vinyl alcohol (PVA) and 2,5-dimethoxy-2,5-dihydrofuran (DHF) were used as the gelcasting reagents. The microstructure (amount of porosity, average pore size, and morphology) of alumina (Al2O3) ceramic green body foams has been studied as a function of surfactant concentration and chain length. The morphology of gelled ceramic foams changes from closed cell (bubble like morphology) to open cell (granular morphology) as the surfactant concentration is increased beyond a critical level. The density (and porosity) of the gelled alumina green body foams changes as a function of the surfactant concentration in a non-linear manner. Measurement of the suspension viscosity, contact angle and aggregate size are used to explain the changes in density and morphology. The transition from the bubble like structure to the granular structure is due to an increase in the particle aggregate size rather than phase inversion induced by an increase in the contact angle. The same behavior is observed with three different chain length surfactants (ranging from 4 to 10 carbon atoms on the hydrophobic portion of the surfactant) but at a lower surfactant concentration as the chain length increases.

Glasses and ceramics

Glasses and ceramics are the most important class of armour materials. The ceramics, in particular, make very effective disruptors. However, they are very brittle in nature and different design rules need to be applied when constructing ceramic-composite armour systems. In this powerful chapter, key properties and drivers are reported, as well as the complex array of energy-absorbing mechanisms and failure modes. The constitution of both the traditional glasses and the more advanced transparent crystalline ceramics are covered, including a new review of the alternative systems (Sapphire, AlONs and Spinels), manufacturing methods and their respective ballistic performance. The higher-performing opaque ceramics are also well covered and two important families introduced: reaction sintering/bonding of silicon carbide and a newly-developed method of producing cost-effective, ballistically-efficient, boron carbide using a combination of Viscous Plastic Processing (VPP) and Pressureless Sintering (PS). The application of such materials to body armour systems is fully described and the effects of material choice and methods of construction upon ballistic performance is well covered.

Exploring inexpensive processing routes to prepare dense TiB2 components

Titanium diboride (TiB2) is considered one of the most suitable candidate materials for applications as wettable cathodes in redesigned aluminium smelting cells. In this work, titanium diboride compacts have been produced from powders using a wet colloidal processing approach combined with pressureless sintering for densification. The approach has good potential to reduce the manufacturing cost compared to hot-pressing. Owing to the elevated cost of the raw materials, the possibility of mixing powders with different particle sizes (more expensive fine and less expensive coarse powder) has been explored. The outcome of this study is very promising, since using two different particle sizes improved the particle packing of the green material resulting in sintered densities around 80% of the theoretical density at 2000°C.