Chemist

Alloy From Wikipedia, the free encyclopedia

Jump to: navigation, search This article is about the material. For the specification language, see Alloy (specification language).

Steel is a metal alloy whose major component is iron, with carbon content between 0.02% and 2.14% by mass. An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal (heat treatment) history. Alloys usually have different properties from those of the component elements. Alloying one metal with other metal(s) or non metal(s) often enhances its properties. For instance, steel is stronger than iron, its primary element. The physical properties, such as density, reactivity, Young's modulus, and electrical and thermal conductivity, of an alloy may not differ greatly from those of its elements, but engineering properties, such as tensile strength[1] and shear strength may be substantially different from those of the constituent materials. This is sometimes due to the sizes of the atoms in the alloy, since larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation. Alloys may exhibit marked differences in behavior even when small amounts of one element occur. For example, impurities in semiconducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura.[2][3] Some alloys are made by melting and mixing two or more metals. Brass is an alloy made from copper and zinc. Bronze, used for bearings, statues, ornaments and church bells, is an alloy of copper and tin. Unlike pure metals, most alloys do not have a single melting point. Instead, they have a melting range in which the material is a mixture of solid and liquid phases. The temperature at which melting begins is called the solidus and the temperature when melting is complete is called the liquidus. However, for most alloys there is a particular proportion of constituents which give them a single melting point or (rarely) two. This is called the alloy's eutectic mixture.

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1 Terminology

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2 See also

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3 References

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4 External links

[edit] Terminology In practice, some alloys are used so predominantly with respect to their base metals that the name of the primary constituent is also used as the name of the alloy. For example, 14 karat gold is an alloy of gold with other elements. Similarly, the silver used in jewelry and the aluminium used as a structural building material are also alloys. The term "alloy" is sometimes used in everyday speech as a synonym for a particular alloy. For example, automobile wheels made of aluminium alloy are commonly referred to as simply "alloy wheels". The usage is obviously indefinite, since steels and most other metals in practical use are also alloys.

Glass-ceramic From Wikipedia, the free encyclopedia

Jump to: navigation, search Glass-ceramic materials share many properties with both glass and more traditional crystalline ceramics. It is formed as a glass, and then made to crystallize partly by heat treatment. Unlike sintered ceramics, glass-ceramics have no pores between crystals. While materials such as "vaseline" glass are also glass-ceramics, the term mainly refers to a mix of lithium-, silicon-, and aluminium-oxides which yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. Originally developed for use in the mirrors and mirror mounts of astronomical telescopes, these materials have become known and entered the domestic market through its use in glass-ceramic cooktops, as well as cookware and bakeware.

A glass-ceramic cooktop

The crystalline component of thermal glass-ceramics, beta spodumene, has a negative coefficient of thermal expansion, which contrasts with the positive coefficient of the glass. Adjusting the proportion of these two materials offers a wide range of possible coefficients in the finished composite. When an interface between materials will be subject to thermal fatigue, glass-ceramics can be adjusted to match the coefficient of the material they will be bonded to. At a certain point, generally between 70% and 78% crystallinity, the two coefficients balance such that the glass-ceramic as a whole has a thermal expansion coefficient that is very close to zero. Glass-ceramic is a mechanically strong material and can sustain repeated and quick temperature changes up to 800–1000 °C. At the same time, it has a very low heat conduction coefficient and can be made nearly transparent (15–20% loss in a typical cooktop) for radiation in the infrared wavelengths. It is not, however, totally unbreakable. There have been instances where users reported damage to their cooktops when the surface was struck with a hard or blunt object (such as a can falling from above or other heavy items). Today, there are two major types of electrical stoves with cooktops made of glass-ceramic: •

A glass-ceramic stove uses radiant heating coils or infrared halogen lamps as the heating elements. The surface of the glass-ceramic cooktop above the burner heats up, but the adjacent surface remains cool because of the low heat conduction coefficient of the material.

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An induction stove heats a metal pot's bottom directly through electromagnetic induction.

Some well-known brands of glass-ceramics are Ceran (cooktops), Eurokera (cooktop, stoves and fireplaces), Zerodur (telescope mirrors), or Macor. German manufacturer Schott introduced Zerodur in 1968, Ceran followed in 1971. Nippon Electric Glass of Japan is another worldwide manufacturer of glass ceramics, whose related products in this area include Firelite and Neoceram fire-rated glass. The same class of material is also used in Corningware dishes, which can be taken from the freezer directly to the oven with no risk of thermal shock. It is interesting to note that this technology is not entirely new, as glass-ceramic ranges were first introduced in the 1970s using Corningware tops instead of the more durable material used today. These first generation smoothtops were problematic and required the use of certain cookware.[1]

[edit] Care and cleaning Compared to conventional kitchen stoves, glass-ceramic cooktops are relatively simple to clean, due to their flat surface. However, glass-ceramic cooktops can be scratched very easily, so care must be taken not to slide the cooking pans over the surface. Food with a high sugar content (such as jam) should never be allowed to dry on the surface if it spills, otherwise damage will occur. Cleaning is best carried out by using a soft cloth along with a special glass-ceramic cleaner that applies a thin protective film on the glass. [2] For best results, all cookware should be flat-bottomed with no warps or dents. [hide] v•d•e

Glass science topics Basics Glass definition · Is glass a liquid or a solid? · Glass-liquid transition · Glass transition temperature · Physics of glass ·

Kauzmann paradox · Supercooling

Glass formulation

Glass-ceramics

AgInSbTe · Bioglass · Borophosphosilicate glass · Borosilicate glass · Ceramic glaze · Chalcogenide glass · Cobalt glass · Cranberry glass · Crown glass · Flint glass · Fluorosilicate glass · Fused quartz · GeSbTe · Gold ruby glass · Lead glass · Milk glass · Phosphosilicate glass · Photochromic lens glass · Silicate glass · Soda-lime glass · Sodium hexametaphosphate · Soluble glass · Ultra low expansion glass · Uranium glass · Vitreous enamel · ZBLAN Bioactive glass · CorningWare · Glass-ceramic-to-metal seals · Macor · Zerodur

Annealing · Chemical vapor deposition · Glass batch calculation · Glass forming · Glass melting · Glass modeling · Ion Glass preparation implantation · Liquidus temperature · Sol-gel technique · Viscosity Dispersion · Gradient index optics · Hydrogen darkening · Optical Optics amplifier · Optical fiber · Optical lens design · Photochromic lens · Photosensitive glass · Refraction · Transparent materials Anti-reflective coating · Chemically strengthened glass · Surface Corrosion · Dealkalization · DNA microarray · Hydrogen modification darkening · Insulated glazing · Porous glass · Self-cleaning glass · Sol-gel technique · Toughened glass Diffusion · Glass-coated wire · Glass databases · Glass electrode · Glass fiber reinforced concrete · Glass history · Glass ionomer Diverse topics cement · Glass microspheres · Glass-reinforced plastic · Glass science institutes · Glass-to-metal seal · Porous glass · Prince Rupert's Drops · Radioactive waste vitrification · Windshield