What is the primary characteristic of ceramics that differentiates them from metals?

The primary characteristic that differentiates ceramics from metals is their excellent hardness and brittleness. Ceramics typically exhibit a high level of hardness, which allows them to withstand scratching and wear better than most metals. However, this hardness comes with a trade-off; ceramics are generally brittle, meaning they can fracture or break under tension or impact rather than deforming. This behavior is in stark contrast to metals, which tend to have more ductility, allowing them to be deformed into different shapes without breaking.

In comparison to the other options, high thermal conductivity is commonly associated with metals, as they are typically good conductors of heat, while ceramics are generally poor conductors. High ductility is a characteristic of metals, which can undergo significant plastic deformation before failure. Lastly, while ceramics do exhibit great resistance to deformation, the combination of excellent hardness and brittleness is a defining feature that distinctly sets them apart from metals. This hardness and fragility affect how they are used in applications, making them suitable for specific purposes like cutting tools and wear-resistant surfaces, while metals are often used where flexibility and toughness are required.