TeCHNICAL CERAMICS

The material field of technical ceramics opens new possibilities of productivity for the progressively growing industry. These possibilities arise from the extension of the operating conditions and lifetime of tools, plant components and products.

As technical ceramics, non-metallic, inorganic and (partly) crystalline materials are referred to, which are applied in industry due to their specific properties[RIE08]. In contrast to classical ceramics, no naturally occurring minerals but chemically prepared or synthetically produced starting materials are used, whose composition can be precisely adjusted, especially for high-performance ceramics[GAU01]. Thus, the properties can be specifically and reproducibly adapted to the desired industrial application.

Ceramics are generally characterized by high hardness and wear resistance, good corrosion resistance and outstanding thermal properties, in particular a high melting point and low thermal expansion[HEI10]and can therefore be used in fields in which conventional materials would fail.

For example, in high-temperature engineering refractory linings and burner nozzles made of ceramic. The high wear resistance of technical ceramics allows their use as sliding and sealing elements with long service life [KOL18].

Thanks to their wide range of electrical properties, technical ceramics are just as essential for the electrical and electronics industry. Among others, they are used as isolators, (semi) conductors, piezo elements and varistors[HEI10]. Due to their biocompatibility and chemical resistance, ceramics are also indispensable in medical technology, especially implantology [KOL18].

Based on their composition, ceramics can be subdivided into three main groups:
– Silicate ceramics
– Oxide ceramics
– Non-oxide ceramics

Silicate ceramics were the first ceramics used for technical applications. They are still mostly produced with naturally occurring minerals and are usually composed of a high proportion of silicate glass phase [KOL18]. Due to the high availability of the raw materials and their relatively low sintering temperatures, silicate ceramics are among the cheapest representatives of technical ceramics. They are mainly used as insulators in high and low voltage engineering.

The oxide ceramics include essentially single-phase metal oxides such as aluminum(Al₂O₃),magnesia(MgO) and zirconia (ZrO₂). They are characterized by significantly higher melting points than silicate ceramics, high hardness and a fine microstructure with very small particle size[KOL18].

The most important representatives of non-oxide ceramics are carbides and nitrides, but also borides, silicides and fluorides, as well as modifications of carbon (diamond, graphite, etc.). The extremely wide range of elements and chemical bonding conditions causes the heterogeneity of this group. Common features are very high hardness (HV ≥ 2000N/mm-2) and a high melting point (Tm ≥ 2400°C, apart from Tm (Si3N4) = 1900 ° C)[HEI10]. The processing of these high-performance ceramics requires extremely fine powders and very high sintering temperatures, usually in an oxygen-free atmosphere[KOL18]. This leads to higher costs for the processing and consequently for the material itself.

SHOW LESS

Alumina (Al₂O₃)

Due to its excellent price-performance ratio, alumina (Al₂O₃) ceramics are predestined for many technical applications and the most widely used oxide ceramic material [KOL18]. Its low costs are due to the high availability of aluminum (3rd most common element in the earth’s crust) and the costeffective preparation and sintering processes.

Zirconia (ZrO₂)

Ceramics made from zirconia (ZrO₂), occupy a special position among engineering ceramics due to their exceptional mechanical properties. For example, some zirconium oxide ceramics exhibit extremely high flexural strength and fracture toughness previously considered as unattainable for ceramics.

Silicon Nitride (Si₃N₄)

Silicon nitride is a light gray to black ceramic, which is used in high-temperature technology in particular because of its good mechanical properties up to 1800°C. Silicon nitride ceramics are characterized by a low density, high fracture toughness, low coefficient of friction and very good thermal shock resistance.

Silicon Carbide (SiC)

The annual production of silicon carbide (SiC) exceeds 800,000 t, making it by far the most used non-oxide ceramic. In the past it has been used almost exclusively as an abrasive material, which still accounts for a major part of its usage. The development of new processes for the production of dense components with favourable mechanical properties enabled new fields of application.

Boron Carbide (B₄C)

Boron carbide is one of the hardest known materials being only second to diamond. Its composition ranges from B_4.3C to B_10.4C. Technical boron carbide usually has a high carbon content and is labelled B₄C, for convenience. Due to its high hardness and Young’s modulus it is very resistant against abrasion and thus used in blast or spray nozzles and as an abrasive.