**4.6 Sintering processes for ceramic production**

The production of ballistic ceramic production requires far higher temperatures than for crosslinking polymeric materials used in the manufacture of ballistic composites. At high sintering temperatures of ceramic materials, none of the polymeric materials such as Kevlar®, Twaron®, and others can resist. Therefore, ceramic materials must be specially made of a backing made of plastic. According to new research, ceramic and/or glass fibers that can withstand high sintering temperatures can be added to ceramic materials before sintering.

## *Ballistic Composites, the Present and the Future DOI: http://dx.doi.org/10.5772/intechopen.102524*

In accordance with the pressure amount applied, sintering can be divided into pressureless and pressurized sintering. Further, pressureless sintering can be divided into reaction sintering, thermal plasma sintering, microwave sintering, and atmospheric sintering. The second group is pressurized sintering which can be divided into solid (hot pressing, spark plasma sintering, and ultra-high-pressure sintering) and gas compaction (hot isostatic pressing and high-pressure gas reaction sintering).

The methods that represent pressureless sintering are usually economically acceptable methods for fabrication of ballistic ceramics than pressurized sintering, but these methods require the use of a high sintering temperature (≥1200°C) and the process least longer than 120 min for densification and solute homogenization. Nowadays, ballistic ceramics are mostly produced by spark plasma sintering [20, 43, 49] and hot-pressing sintering [37, 45].

Spark plasma sintering is a pressurized sintering method assisted by the pulseddirect current process. The powder of raw material is loaded in an electrically conducting matrix and sintered under uniaxial pressure. Bypassing direct current through a matrix and sintered powder, if they are conductive, they act as a heating source, so in addition to external heating, internal heating is provided, which leads to improved heat transfer and rapid consolidation during sintering, which speeds up the production of ceramic materials for ballistic composites. This method can be used to produce large plates that can be machined later. Hot pressing is the most commonly used technique for fabricating dense, non-oxide monolithic ceramics and their composites. The ceramic materials can be produced in a mixture matrix (coil and graphite) and metal or metal-oxide powder under a uniaxial pressure hot-pressing but in the absence of direct current. At maximum pressure, the contact points between raw materials develop very high stress, increasing the local diffusion rates.

The time of processing, heating, densification, particle size, temperature, pressure, heating rate, and holding time all influence the physical and mechanical properties of the hot-pressed ceramics whilst a controlled atmosphere is required for the non-oxides. Carbides and borides are often hot-pressed under a vacuum or an inert gas such as argon whilst the nitrides are generally densified under a nitrogen atmosphere. Often, the pressure is applied when the maximum sintering temperature is reached, though it can be increased at intervals as the temperature increases.
