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refractory

 
(rĭ-frăk'tə-rē) pronunciation
adj.
  1. Obstinately resistant to authority or control. See synonyms at unruly.
  2. Difficult to melt or work; resistant to heat: a refractory material such as silica.
  3. Resistant to treatment: a refractory case of acne.
n., pl., -ries.
  1. One that is refractory.
  2. Material that has a high melting point.

[Alteration (influenced by adjectives in -ORY) of obsolete refractary, from Latin refrāctārius, from refrāctus, past participle of refringere, to break up. See refract.]

refractorily re·frac'to·ri·ly adv.
refractoriness re·frac'to·ri·ness n.

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Material that is not deformed or damaged by high temperatures, used to make crucibles, incinerators, insulation, and furnaces, particularly metallurgical furnaces. Refractories are produced in several forms: molded bricks of various shapes, bulk granular materials, plastic mixtures consisting of moistened aggregates that are rammed into place, castables composed of dry aggregates and a binder that can be mixed with water and poured like concrete, and mortars and cements for laying brickwork.

For more information on refractory, visit Britannica.com.

One of a number of ceramic materials for use in high-temperature structures or equipment. The term high temperatures is somewhat indefinite but usually means above about 1830°F (1000°C), or temperatures at which, because of melting or oxidation, the common metals cannot be used. In some special high-temperature applications, the so-called refractory metals such as tungsten, molybdenum, and tantalum are used. See also Ceramics.

The greatest use of refractories is in the steel industry, where they are used for construction of linings of equipment such as blast furnaces, hot stoves, and open-hearth furnaces. Other important uses of refractories are for cement kilns, glass tanks, nonferrous metallurgical furnaces, ceramic kilns, steam boilers, and paper plants. Special types of refractories are used in rockets, jets, and nuclear power plants. Many refractory materials, such as aluminum oxide and silicon carbide, are also very hard and are used as abrasives; some applications, for example, aircraft brake linings, make use of both characteristics.

Refractory materials are commonly grouped into (1) those containing mainly aluminosilicates; (2) those made predominantly of silica; (3) those made of magnesite, dolomite, or chrome ore, termed basic refractories (because of their chemical behavior); and (4) a miscellaneous category usually referred to as special refractories.


Antonyms by Answers.com:

refractory

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adj

Definition: obstinate
Antonyms: manageable, obedient

A material, usually nonmetallic, used to withstand high temperatures.


Applied to a medical condition that does not respond to treatment.

Word Tutor:

refractory

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pronunciation

IN BRIEF: Resisting control or authority. Also: Capable of enduring high temperatures.

pronunciation The refractory child changed her behavior when she suffered the consequences of her actions.

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  1. (of a clinical condition) resistant to treatment.
  2. (of a cell or tissue) resistant to stimulation, as by a drug, hormone, or nerve impulse, especially during a period following previous stimulation. See also tachyphylaxis.
  3. (of a substance or material) resistant to heat, corrosion, mechanical deformation, or other aggressive agents causing alteration.
  4. a substance or material having such resistance.

Previous:refractometer, refractivity, refractive index
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Not readily yielding to treatment.

  • r. period — the period of depolarization and repolarization of the cell membrane after excitation; during the first portion (absolute refractory period), the nerve or muscle fiber cannot respond to a second stimulus, whereas during the relative refractory period, it can respond only to a strong stimulus.
  • myocardial r. state — the myocardium is refractory to stimulation during the action potential period, excitability returning in the repolarization phase; initially there is a period of supernormality.
(rē-frak′tər-ē)
adj

Pertaining to the ability to withstand the high temperatures used in certain dental laboratory procedures. See also cast, refractory.

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Wikipedia on Answers.com:

Refractory

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A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories 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)".[1]

Refractory materials are used in linings for furnaces, kilns, incinerators and reactors. They are also used to make crucibles.

Contents

Refractory materials

Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they need to 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). Fire clays are also widely used in the manufacture of refractories.

Refractories must be chosen according to the conditions they will face. Some applications require special refractory materials. Zirconia is used when the material must withstand extremely high temperatures. 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 will 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.[2][3] The ternary compound tantalum hafnium carbide has one of the highest melting points of all known compounds (4215 °C).[4][5]

Classification of refractory materials

Refractories can be classified on the basis of chemical composition, method of manufacture, physical form or according to their applications.

Based on chemical composition

Acidic refractories

These are used in areas where slag and atmosphere are acidic. They are stable to acids but attacked by alkalis. The main raw materials belongs to the RO2 group, e.g. silica (SiO2), zirconia (ZrO2), etc.

Neutral refractories

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 belongs to, but not confined to, R2O3 group. The common examples of these materials are alumina (Al2O3), chromia (Cr2O3) and carbon.

Basic refractories

These are used on areas where slags and atmosphere are basic; they are stable to alkaline materials but react with acids. The main raw materials belong to the RO group to which magnesia (MgO) is a very common example. Other examples includes dolomite and chrome-magnesia.

Based on method of manufacture

  1. Dry press process
  2. Fused cast
  3. Hand molded
  4. Formed (normal, fired or chemically bonded)
  5. Un-formed (monolithic-plastic, ramming and gunning mass, castables)

Shaped

These have fixed size and shapes. These may be further divided into standard shapes and special shapes. Standard shapes have dimension that are conformed by most refractory manufacturers and are generally applicable to kilns or furnaces of the same types. Special shapes are specifically made for particular kilns or furnaces.

Unshaped

These are without definite form and are only given shape upon application. These types are better known as monolithic refractories. The common examples are plastic masses, Ramming masses, castables, gunning masses, fettling mix, mortars etc.

Refractory anchorage

All refractory require anchorage systems such as wire formed anchors, formed metal (for example, hexmetal) or ceramic tiles to support the refractory linings. The anchorage used for refractory on roofs and vertical walls are more critical as they must remain able to support the weight of refractory even at the elevated temperatures and operating conditions.

The commonly used anchorages have circular or rectangular cross-section. Circular cross-section are used for low thickness refractory and they support less weight per unit area; whereas the rectangular cross-section is used for high thickness refractory and can support higher weight of refractory per unit area. The number of anchors to be used depend on the operating conditions and the refractory materials. The choice of anchors material, shape, numbers and size has significant impact on the useful life of the refractory.

Refractory heat-up

Usually, refractories require special heat-up techniques to ensure that their performance will be attained as designed, and to avoid thermal shock and drying stresses until the operational status is achieved.

See also

References

  1. ^ ASTM Volume 15.01 Refractories; Activated Carbon, Advanced Ceramics
  2. ^ Hugh O. Pierson (1992). Handbook of chemical vapor deposition (CVD): principles, technology, and applications. William Andrew. pp. 206–. ISBN 9780815513001. http://books.google.com/books?id=NF3W6zlN9WsC&pg=PA206. Retrieved 22 April 2011. 
  3. ^ Hafnium, Los Alamos National Laboratory
  4. ^ McGraw-Hill encyclopedia of science and technology: an international reference work in fifteen volumes including an index. McGraw-Hill. 1977. p. 360. ISBN 9780070795907. http://books.google.com/books?id=TjYLAQAAIAAJ. Retrieved 22 April 2011. 
  5. ^ "Hafnium". Encyclopædia Britannica. Encyclopædia Britannica, Inc.. http://www.britannica.com/EBchecked/topic/251419/hafnium. Retrieved 17 December 2010. 

External links


Translations:

Refractory

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Dansk (Danish)
adj. - stædig, uregerlig, upåvirkelig, uimodtagelig
n. - modstandsdygtigt materiale, ildfast materiale

Nederlands (Dutch)
weerspannig, immuun, niet makkelijk te genezen, bestand tegen hoge temperaturen, (mv) materiaal bestand tegen hitte/corrosie

Français (French)
adj. - réfractaire (tous contextes)
n. - réfractaire

Deutsch (German)
adj. - störrisch, hartnäckig, hitzebeständig
n. - hitzebeständiges Metall

Ελληνική (Greek)
adj. - ανυπότακτος, ατίθασος, ανυπάκουος, δύσκολος, επίμονος
n. - αλεξίπυρη ύλη

Italiano (Italian)
ricalcitrante, refrattario

Português (Portuguese)
adj. - refratário
n. - refratário (m)

Русский (Russian)
огнеупорный, тугоплавкий, упрямый

Español (Spanish)
adj. - refractario, obstinado
n. - persona obstinada, objeto refractario

Svenska (Swedish)
adj. - motspänstig, svårarbetad
n. - kem o fys stabilt material

中文(简体)(Chinese (Simplified))
执拗的, 难治的, 有抵抗力的, 耐火的, 耐火物质, 倔强的人, 耐火砖

中文(繁體)(Chinese (Traditional))
adj. - 執拗的, 難治的, 有抵抗力的, 耐火的
n. - 耐火物質, 倔強的人, 耐火磚

한국어 (Korean)
adj. - 난치의, 용해하기 어려운, 감당할 수 없는
n. - 내화 물질

日本語 (Japanese)
adj. - 手に負えない, 難治の, 不応の, 溶解しにくい, 耐火性の, 強情な
n. - 頑固な人, 耐火材

العربيه (Arabic)
‏(صفه) عنيد, مقاوم للعلاج, ذو مناعه (الاسم) مادة مقاومه للحرارة‏

עברית (Hebrew)
adj. - ‮עקשן, מרדני, שקשה להתיכה (מתכת), קשה-ריפוי, מחוסן‬
n. - ‮עקשן, מרדני, שקשה להתיכה (מתכת), קשה-ריפוי, מחוסן, חומר בעל כושר התנגדות חזק לחום ולאיכול‬


 
 
Related topics:
crucible
hot patching (engineering)
refractory coating (materials)

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