An Introduction To Ceramics And Refractories Pdf

[Do Kieu]

Ceramicsand refractories cover a wide range of fields and applications, and their relevance can be traced as far back as 24,000 BC to the first man-made piece of earthenware, and as recently as the late 1900s when ceramics and ceramic matrix composites were developed to withstand ultra-high temperatures. Beginning with a detailed history of ceramics, An Introduction to Ceramics and Refractories examines every aspect of ceramics and refractories, and explores the connection between them. The book establishes refractories as a class of ceramics with high fusion points, introduces the fundamentals of refractories and ceramics, and also addresses several applications for each.

The book details applications for natural and synthetic ceramics, as well as traditional and engineering applications. It focuses on the various thermal and thermo-mechanical properties of ceramics, classifies refractories, describes the principles of thermodynamics as applied to refractories, and highlights new developments and applications in the ceramic and refractory fields. It also presents end-of-chapter problems and a relevant case study.

Addressing topics that include corrosion, applications, thermal properties, and types of refractories, An Introduction to Ceramics and Refractories provides you with a basic knowledge of the fundamentals of refractories and ceramics, and presents a clear connection between refractory behavior and ceramic properties to the practicing engineer.

Section I Ceramics and Refractories. General Aspects. Selection of Materials. New Developments in Ceramic and Refractory Fields. Phase Equilibria in Ceramic and Refractory Systems. Corrosion of Ceramics and Refractories. Failure in Ceramics and Refractories. Design Aspects. Section II Ceramics. Bonding in Ceramics. Structures of Ceramics. Defects in Ceramics. Ceramic Microstructures. Production of Ceramic Powders. Forming Processes. Thermal Treatment. Mechanical Properties. Thermal and Thermo-Mechanical Properties. Section III Refractories. Classification. Refractory Thermodynamic Principles. Properties and Testing. Production. Silica. Alumina. Alumino-Silicate. Chrome-Magnesite. Carbon. Insulating Refractories. Appendices. Index.

In materials science, a refractory (or refractory material) is a material that is resistant to decomposition by heat or chemical attack that retains its strength and rigidity at high temperatures.[1] They are inorganic, non-metallic compounds that may be porous or non-porous, and their crystallinity varies widely: they may be crystalline, polycrystalline, amorphous, or composite. They are typically composed of oxides, carbides or nitrides of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium.[2] Many refractories are ceramics, but some such as graphite are not, and some ceramics such as clay pottery are not considered refractory. Refractories are distinguished from the refractory metals, which are elemental metals and their alloys that have high melting temperatures.

Refractories are defined by ASTM C71 as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 F (811 K; 538 C)".[3] Refractory materials are used in furnaces, kilns, incinerators, and reactors. Refractories are also used to make crucibles and molds for casting glass and metals. The iron and steel industry and metal casting sectors use approximately 70% of all refractories produced.[4]

Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they must be resistant to thermal shock, be chemically inert, and/or have specific ranges of thermal conductivity and of the coefficient of thermal expansion.

The oxides of aluminium (alumina), silicon (silica) and magnesium (magnesia) are the most important materials used in the manufacturing of refractories. Another oxide usually found in refractories is the oxide of calcium (lime).[5] Fire clays are also widely used in the manufacture of refractories.

Refractories must be chosen according to the conditions they face. Some applications require special refractory materials.[6] Zirconia is used when the material must withstand extremely high temperatures.[7] Silicon carbide and carbon (graphite) are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, as they would oxidize and burn.

Binary compounds such as tungsten carbide or boron nitride can be very refractory. Hafnium carbide is the most refractory binary compound known, with a melting point of 3890 C.[8][9] The ternary compound tantalum hafnium carbide has one of the highest melting points of all known compounds (4215 C).[10][11]

Refractories have multiple useful applications. In the metallurgy industry, refractories are used for lining furnaces, kilns, reactors, and other vessels which hold and transport hot media such as metal and slag. Refractories have other high temperature applications such as fired heaters, hydrogen reformers, ammonia primary and secondary reformers, cracking furnaces, utility boilers, catalytic cracking units, air heaters, and sulfur furnaces.[12] They are used for surfacing flame deflectors in rocket launch structures.[13]

Acidic refractories are generally impervious to acidic materials but easily attacked by basic materials, and are thus used with acidic slag in acidic environments. They include substances such as silica, alumina, and fire clay brick refractories. Notable reagents that can attack both alumina and silica are hydrofluoric acid, phosphoric acid, and fluorinated gases (e.g. HF, F2).[14] At high temperatures, acidic refractories may also react with limes and basic oxides.

These are used in areas where slags and atmosphere are either acidic or basic and are chemically stable to both acids and bases. The main raw materials belong to, but are not confined to, the R2O3 group. Common examples of these materials are alumina (Al2O3), chromia (Cr2O3) and carbon.[2]

Refractory objects are manufactured in standard shapes and special shapes. Standard shapes have dimensions that conform to conventions used by refractory manufacturers and are generally applicable to kilns or furnaces of the same types. Standard shapes are usually bricks that have a standard dimension of 9 in 4.5 in 2.5 in (229 mm 114 mm 64 mm) and this dimension is called a "one brick equivalent". "Brick equivalents" are used in estimating how many refractory bricks it takes to make an installation into an industrial furnace. There are ranges of standard shapes of different sizes manufactured to produce walls, roofs, arches, tubes and circular apertures etc. Special shapes are specifically made for specific locations within furnaces and for particular kilns or furnaces. Special shapes are usually less dense and therefore less hard wearing than standard shapes.

These are without prescribed form and are only given shape upon application. These types are known as monolithic refractories. Common examples include plastic masses, ramming masses, castables, gunning masses, fettling mix, and mortars.

Dry vibration linings often used in induction furnace linings are also monolithic, and sold and transported as a dry powder, usually with a magnesia/alumina composition with additions of other chemicals for altering specific properties. They are also finding more applications in blast furnace linings, although this use is still rare.

Refractoriness is the property of a refractory's multiphase to reach a specific softening degree at high temperature without load, and is measured with a pyrometric cone equivalent (PCE) test. Refractories are classified as:[2]

Refractories may be classified by thermal conductivity as either conducting, nonconducting, or insulating. Examples of conducting refractories are silicon carbide (SiC) and zirconium carbide (ZrC), whereas examples of nonconducting refractories are silica and alumina. Insulating refractories include calcium silicate materials, kaolin, and zirconia.

Insulating refractories are used to reduce the rate of heat loss through furnace walls. These refractories have low thermal conductivity due to a high degree of porosity, with a desired porous structure of small, uniform pores evenly distributed throughout the refractory brick in order to minimize thermal conductivity. Insulating refractories can be further classified into four types:[2]

The term ceramics originally referred almost exclusively to china. Today, we often refer to non-metallic, inorganic substances such as refractories, glass, and cements as ceramics. For this reason, ceramics are now regarded as "non-metallic, inorganic substances that are manufactured through a process of molding or shaping and exposure to high temperatures."

Among ceramics, porcelains are used in electronics and other high-tech industries, so they must meet highly precise specifications and demanding performance requirements. Today, they are called Fine Ceramics (also known as "advanced ceramics")* to distinguish them from conventional ceramics made from natural materials, such as clay and silica rock. Fine Ceramics are carefully engineered materials in which the chemical composition has been precisely adjusted using refined or synthesized raw powder, with a well-controlled method of forming and sintering.

The term "Fine Ceramics" came into common use in the 1970s. Kyocera Corporation, founded as Kyoto Ceramic Co., Ltd., has primarily manufactured ceramics for the electronics industry since its inception in 1959. Founder Dr. Kazuo Inamori has maintained that "unlike conventional ceramics, Fine Ceramics possess high added-value in industrial applications. Their value should not be measured based on volume and they must be 'fine' both physically and structurally." He was therefore the first person to use the term "Fine Ceramics" in the contemporary sense.

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