Ceramic

Ceramics are hard, brittle materials that resist heat and corrosion, produced by shaping and firing inorganic, nonmetallic substances like clay at high temperatures. Common examples include earthenware, porcelain, and brick. The category now covers domestic, industrial, and building products, along with advanced engineering materials such as semiconductors.

The word "ceramic" traces back to the Ancient Greek *keramikós*, meaning "of or for pottery," itself from *kéramos* ("potter's clay, tile, pottery"). The earliest known reference to the root is the Mycenaean Greek *ke-ra-me-we*, meaning workers of ceramic, recorded in Linear B script. The term can serve as an adjective for a material, product, or process, or as a noun—often in the plural form "ceramics."

Ceramic materials are inorganic and include metallic oxides, nitrides, or carbides. Some elements, like carbon or silicon, may also be considered ceramics. They are brittle, hard, strong under compression, but weak in shear and tension. They resist chemical erosion from acidic or caustic environments and can withstand very high temperatures, typically between 1,000 °C and 1,600 °C (1,800 °F to 3,000 °F). Their crystallinity varies widely; most fired ceramics are vitrified or semi-vitrified, as seen in earthenware, stoneware, and porcelain. The mix of ionic and covalent bonds, combined with varying crystallinity, makes most ceramics good thermal and electrical insulators—a focus of ceramic engineering. Because nearly all elements, bonding types, and levels of crystallinity are possible, the group’s overall properties are hard to generalize. Common traits include high melting temperature, high hardness, poor conductivity, high elastic moduli, chemical resistance, and low ductility, though exceptions exist (e.g., piezoelectric, low-glass-transition-temperature, and superconductive ceramics). Composites like fiberglass and carbon fiber, despite containing ceramic materials, are not classified as ceramics.

Highly oriented crystalline ceramics require specific processing methods: either forming the desired shape through reaction in situ, or shaping powders and then sintering them into a solid. Techniques include hand shaping (sometimes using a rotating "throwing" process), slip casting, tape casting (for thin ceramic capacitors), injection molding, dry pressing, and others. Many experts exclude amorphous materials like glass from the ceramic family, even though glassmaking shares several ceramic process steps and similar mechanical properties; however, heat treatment can convert glass into a semi-crystalline glass-ceramic.

Traditional ceramic raw materials include clay minerals like kaolinite, while more recent ones include aluminium oxide (alumina). Advanced ceramics, such as silicon carbide and tungsten carbide, are valued for abrasion resistance and used in applications like wear plates in mining crushers. They also appear in medical, electrical, electronics, and armor industries.

Humans have made ceramics for at least 26,000 years, subjecting clay and silica to intense heat to fuse them. The earliest known examples, found in southern central Europe, were sculpted figures rather than dishes. The oldest pottery was made by mixing animal products with clay and firing it at up to 800 °C (1,500 °F). Pottery fragments exist from 19,000 years ago, but regular pottery only became common about 10,000 years later. The Corded Ware culture, named for its pottery, spread across much of Europe; its people decorated wet clay with rope, which burned off during firing, leaving grooved patterns. The invention of the wheel enabled smoother, more even pottery through wheel-forming (throwing). Early ceramics were porous and absorbed water, but glazing techniques—coating pottery with silicon, bone ash, or other materials that melt into a glassy surface—made vessels less permeable.

Ceramic artifacts are crucial in archaeology for understanding past cultures, technologies, and behaviors, as they are among the most common finds.