INTRODUCTION TO ENGINEERING MATERIALS - CERAMICS - PART 5

Audio: Introduction to engineering materials – ceramics – part 5

Ceramics are widely used types of engineering materials. So far, we discussed plain carbon and low alloy steels, then we looked into the stainless and specialty steels, and cast irons. Furthermore, we discussed nonferrous metals, and in this part, we will look at what engineering ceramics are, where they are used, and how we can classify them.

Introduction to ceramics

Contrary to belief, ceramics materials are more abundant and widely used than metals. Ceramics have been used for thousands of years, and they cover a vast range of applications, from bricks to dental implants and heat shields for spacecrafts.

Ceramics, by definition, are inorganic compounds consisting of a metal (or semimetal) and one or more nonmetals. Properties that make ceramics useful in engineered products are high hardness, good strength under compression, good electrical and thermal insulating characteristics, chemical stability, corrosion resistance, and high melting temperature.

However, ceramics are brittle and possess virtually no ductility, which could cause problems both for the processing and performance of ceramic products.

The ability to tailor the properties of engineering ceramics makes this group of materials extremely interesting for engineering applications. For example, dense ceramic materials with controlled microstructure, density, and properties can be produced using the sintering process.

Furthermore, using hot pressing high-strength ceramics can be produced. Using chemical vapor deposition, a thin film of ceramics can be deposited on other materials.

Ceramics application:

Electrical: capacitor and microwave dielectrics, electronic packaging, insulators, etc.
Magnetic: recording media (e.g., in computer memory), credit cards, isolators, magnets, etc.
Optical: fiber optics, glasses, lasers, bottles, lenses, window panels, light bulbs, etc.
High temperature: furnace walls, crucibles, molds, etc.
Construction: bricks, concrete, clay pipes, tiles, etc.
Whiteware: pottery, stoneware, fine china, porcelain, and other tableware, etc.
Cutting and abrasive tools
Bioceramics: artificial teeth, bones, implants, etc.
Other applications like defense, armor, sensors, nuclear, chemical, etc.

Classification of engineering ceramics

We can divide ceramics materials into:

oxide ceramics,
carbide ceramics,
sialons,
nitride ceramics,
glass and glass-ceramics.

Oxide ceramics

Alumina (Al₂O₃) is mainly processed from the mineral bauxite. Alumina is used where material must operate at high temperatures and where high strength is required. It is used to manufacture porcelain, crucibles, wear-resistant parts (such as cutting tools and grinding wheels), medical components, electronic packaging, medical components, refractory bricks, lasers (chromium-doped alumina), spark plugs, etc.

Titanium dioxide (TiO₂) naturally occurs in minerals rutile and anatase. The most significant use areas are to make paint, varnishes, paper, and plastics. In addition, fine particles are used to make suntan lotions (protection against UV).

Zirconia (ZrO₂) is an oxide ceramic known for high strength, wear resistance, and biocompatibility. Zirconia is used to make many other ceramics like zircon. Furthermore, it is used in dentistry, as a refractory material, insulation, abrasives, oxygen gas sensors, solid-oxide fuel cells, catalysis, etc.

Silica (SiO₂) is probably the most widely used ceramic material. It is used as a compound in many glasses and glass ceramics. Silica is available naturally in various forms; the most important is quartz. Silica-based materials are used in fiber optics, windshields, thermal insulation, refractories, tires, laboratory glassware, windows, tires, paints, etc.

Carbide ceramics

Silicon carbide (SiC) is a hard chemical compound with outstanding oxidation resistance at temperatures even above the melting point of steel. It is used as an abrasive in grinding wheels, reinforcement in both metal and ceramic matrix composites, metal coatings, heating elements for furnaces, protection from extreme temperatures, etc.

Tungsten carbide (WC) is the most widely used material in this group. It is produced by the reaction of tungsten and carbon at high temperatures. It is used in applications where hardness and wear resistance are required (e.g., cutting tools, mining drills, abrasives, etc.). Furthermore, tungsten carbide is used to produce ammunition, surgical instruments, jewelry, etc.

Titanium carbide (TiC) has a high melting point and efficiently absorbs heat, and it is used as an abrasion-resistant surface coating on metal parts (pump shafts, feed screws, packing sleeves), heat shield coatings, welding wire, etc.

Tantalum carbide (TaC) has a high melting point and is heat resistant. Furthermore, it has excellent hardness and wear resistance. Therefore, Tantalum carbide is used for cutting tools, armor plating, precision ceramics, coatings, etc.

Chromium carbide (Cr₃C₂) has high strength and hardness and excellent chemical stability and corrosion resistance. In combination with good wear resistance, it is suitable for gage blocks, vale liners, spray nozzles, coating, etc.

Sialons

Oxynitride ceramic alloys formed from elements Si – Al – O – N (Silicon – Aluminum – Oxygen – Nitrogen) are called Sialon ceramics. The chemical composition of Sialons is variable, and its properties are similar to silicon nitride but with better oxidation resistance at high temperatures. One example of Sialon ceramics is Si₄Al₂O₂N₆. The primary application is for cutting tools, thermocouple protection tubes, injectors, seals, bearings, etc.

Nitride ceramics

Silicon nitride (Si₃N₄) has high strength, wear resistance, hardness, and good chemical and thermal stability. In addition, it has a low thermal expansion, good resistance to thermal shock and creep, and resist corrosion. It is used in the automotive industry (engine parts), for gas turbine engines, bearing rollers, ball bearings, nozzles, seal rings, sealings, etc.

Boron nitride (BN) is a refractory compound that has high thermal and chemical resistance. It has multiple forms like amorphous, hexagonal, cubic, and wurtzite forms. Based on the form, it can be used for nozzles, crystallization tubes, molten metal handling, surface coating, lubrication, cosmetics, ceramic screws, insulation gaskets, etc.

Titanium nitride (TiN) has high hardness, good wear resistance, and a low coefficient of friction with ferrous metals, and it conducts electricity. It is used for surface coating on cutting tools, coating on sliding surfaces, coating for decorative purposes, etc.

Glass and glass-ceramics

Glass and glass – ceramics at first sound like the same thing. However, glass describes the state of matter (amorphous or non-crystalline structure of a solid matter). Both ceramics and polymers can assume the glassy state, and rarely metals can too. Glass ceramics are crystalline inorganic nonmetallic compounds or a mixture of compounds. They are produced by converting glass into a polycrystalline structure through heat treatment.

The most used type of glass is based on silica, called soda-lime glass. It is used primarily due to its optical transparency and the relative ease with which it can be fabricated. Soda-lime glass is mostly used for windows, lenses, fiberglass, tableware, packaging, laboratory glassware, art (painted glass), etc.

Glass-ceramics have a low coefficient of thermal expansion, high mechanical strength, excellent resistance to thermal shock, high chemical resistance, machinability, etc. Some well-known types are Pyroceram, Cercor, Pyrosil, Zerodur, etc. Glass-ceramics are used for cookware, bakeware, cooktops, sealing, abrasives, bearings, etc.

Closing words

Engineering ceramics are widely used materials due to their versatile range of properties and applications. Most of us are not aware of how often we use these types of materials. For mechanical design engineers, it is crucial to understand different types of materials so that they could choose the correct one for the intended application.

Next time you encounter a challenging environment where high strength under high temperature is required, look into engineering ceramics. Maybe you could combine base metal material with ceramics coating. Keep your mind open; you never know where you can find the right solution.

Now you have an excellent overview of engineering ceramics you could encounter as a mechanical design engineer. However, I suggest you go through the text once more and identify areas you think need more understanding and clarity. Then, once you have identified those areas, start building up your knowledge in those areas.

To make it easier for you to find related posts, check the “Further reading” chapter below. Do you have any questions or need something to be clarified better? Leave a comment below, and I will give my best to adjust the post accordingly.

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