関: sand、silica、silicon dioxide

WordNet

a white mineral consisting of silica; found in volcanic rocks
a loose material consisting of grains of rock or coral
a white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earths crust as quartz or cristobalite or tridymite or lechatelierite (同)silicon oxide, silicon_dioxide

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/05/18 21:29:26」(JST)

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The mineral cristobalite is a high-temperature polymorph of silica, meaning that it has the same chemical formula, SiO₂, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group, which also include coesite, tridymite and stishovite. Cristobalite occurs as white octahedra or spherulites in acidic volcanic rocks and in converted diatomaceous deposits in the Monterey Formation of the US state of California and similar areas. Cristobalite is stable only above 1470 °C, but can crystallize and persist metastably at lower temperatures.

The persistence of cristobalite outside of its thermodynamic stability range occurs because the transition from cristobalite to quartz or tridymite is "reconstructive", requiring the breaking up and reforming of the silica framework. These frameworks are composed of SiO₄ tetrahedra in which every oxygen atom is shared with a neighbouring tetrahedron, so that the chemical formula of silica is SiO₂. The breaking of these bonds required to convert cristobalite to tridymite and quartz requires considerable activation energy and may not happen on a human time frame. Framework silicates are also known as tectosilicates.

There is more than one form of the cristobalite framework. At high temperatures, the structure is cubic, Fd3m, No.227, Pearson symbol cF104.^[5] A tetragonal form of cristobalite (P4₁2₁2, No. 92, Pearson symbol tP12^[6]) occurs on cooling below ca. 250 °C at ambient pressure, and is related to the cubic form by a static tilting of the silica tetrahedra in the framework. This transition is variously called the low-high or transition. It may be termed "displacive"; i.e., it is not generally possible to prevent the cubic β-form from becoming tetragonal by rapid cooling. Under rare circumstances the cubic form may be preserved if the crystal grain is pinned in a matrix that does not allow for the considerable spontaneous strain that is involved in the transition, which causes a change in shape of the crystal. This transition is highly discontinuous. The exact transition temperature depends on the crystallinity of the cristobalite sample, which itself depends on factors such as how long it has been annealed at a particular temperature.

The cubic β-phase consists of dynamically disordered silica tetrahedra. The tetrahedra remain fairly regular and are displaced from their ideal static orientations due to the action of a class of low-frequency phonons called rigid unit modes. It is the "freezing" of one of these rigid unit modes that is the soft mode for the α–β transition.

In the α–β phase transition only one of the three degenerate cubic crystallographic axes retains a fourfold rotational axis in the tetragonal form. The choice of axis is arbitrary, so that various twins can form within the same grain. These different twin orientations coupled with the discontinuous nature of the transition can cause considerable mechanical damage to materials in which cristobalite is present and that pass repeatedly through the transition temperature, such as refractory bricks.

When devitrifying silica, cristobalite is usually the first phase to form, even when well outside of its thermodynamic stability range. The dynamically disordered nature of the β-phase is partly responsible for the low enthalpy of fusion of silica.

The micrometre-scale spheres that make up precious opal are made of cristobalite, crystallized metastably at low temperature.

An idealized model of β-cristobalite, showing corner-bonded SiO₄ tetrahedra. In reality the tetrahedra are constantly tumbling.
β-cristobalite viewed along another direction.
The crumpled framework of α-cristobalite, related to the β-form by static tilting of the tetrahedra.
Unit cell of α-cristobalite; red spheres are oxygen atoms.

References

^ Deer, W. A., R. A. Howie and J. Zussman, An Introduction to the Rock Forming Minerals, Logman, 1966, pp. 340–355 ISBN 0-582-44210-9
^ Cristobalite. Handbook of Mineralogy.
^ Cristobalite. Mindat.
^ Cristobalite Mineral Data. Webmineral.
^ Wright A. F., Leadbetter A. J. (1975). "The structures of the b-cristobalite phases of SiO₂ and AlPO₄". Philosophical Magazine 31: 1391–1401. doi:10.1080/00318087508228690.
^ Downs R. T., Palmer D. C. (1994). "The pressure behavior of a cristobalite" (PDF). American Mineralogist 79: 9–14.

External links

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UpToDate Contents

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1. 珪肺症 silicosis

English Journal

Adhesion of mussel foot proteins to different substrate surfaces.

Lu Q, Danner E, Waite JH, Israelachvili JN, Zeng H, Hwang DS.SourceChemical and Materials Engineering, University of Alberta, , Edmonton, Alberta, Canada , T6G 2V4.
Journal of the Royal Society, Interface / the Royal Society.J R Soc Interface.2013 Feb 6;10(79):20120759. doi: 10.1098/rsif.2012.0759.
Mussel foot proteins (mfps) have been investigated as a source of inspiration for the design of underwater coatings and adhesives. Recent analysis of various mfps by a surface forces apparatus (SFA) revealed that mfp-1 functions as a coating, whereas mfp-3 and mfp-5 resemble adhesive primers on mica
PMID 23173195

Physicochemical characterization of fish protein adlayers with bacteria repelling properties.

Meyer RL, Arpanaei A, Pillai S, Bernbom N, Enghild JJ, Ng YY, Gram L, Besenbacher F, Kingshott P.SourceInterdisciplinary Nanoscience Center (iNANO), Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; Department of Biological Sciences, Aarhus University, Ny Munkegade 116, DK-8000 Aarhus C, Denmark. Electronic address: rikke.meyer@biology.au.dk.
Colloids and surfaces. B, Biointerfaces.Colloids Surf B Biointerfaces.2013 Feb 1;102:504-10. doi: 10.1016/j.colsurfb.2012.08.044. Epub 2012 Sep 2.
Materials coated with aqueous fish protein extracts can reduce bacterial adhesion, but the mechanism behind the observed effect is not fully understood. In this study we explore the physicochemical properties of fish muscle protein adlayers on four substrates: gold, stainless steel, polystyrene and
PMID 23104021

Japanese Journal

砥石結合剤組成と砥石性能の相関解析:第1報：結合剤中の酸化ホウ素の影響

角田勝俊,吉川孝之,尾倉秀一 [他],古南博
砥粒加工学会誌 59(3), 140-144, 2015
自動車部品やベアリングといった高精度・高能率が求められる機械部品の研削加工に対して，要求された表面粗さと設定した寸法にいち早く到達させるためのCBN（立方晶窒化ホウ素）ビトリファイド研削砥石の開発効率化を研究目的とする．調製したNa2O-B2O3-SiO2の三成分ガラスを砥石結合剤に用いてB2O3の配合比率を変化させた際の結合剤の熱特性とその結合剤を用いて作製した砥石の抗折力と内面研削試験結果を対 …
NAID 130005097943

Effect of soda-lime-silica glass addition on the physical properties of ceramic obtained from white rice husk ash

BATENI Nasim Heidari,HAMIDON Mohd Nizar,MATORI Khamirul Amin
Journal of the Ceramic Society of Japan 122(1422), 161-165, 2014
… The XRD analysis results show the formation of cristobalite to be a major phase and some tridymite phase was detected in the specimens. …
NAID 130004950929

熱水条件におけるクリストバライト準安定相間相転移と結晶化過程

磯部博志,西林佑真
日本鉱物科学会年会講演要旨集 2013, 90, 2013-09-05
NAID 10031191123

Related Pictures

Cristobalite Cristobalite Description Cristobalite-Obsidian-280504 Description Cristobalite-Fayalite-39952 Cristobalite - Wikipedia, the free CRISTOBALITE (Silicon Dioxide)

★リンクテーブル★

リンク元	「sand」「silica」「クリストバル石」「silicon dioxide」

「sand」

Cristobalite
	Cristobalite spheres formed via devitrification (loss of silica) from the obsidian matrix (California, USA) 5.9×3.8×3.8 cm.
General
Category	Silicate mineral
Formula; (repeating unit)	SiO2
Strunz classification	04.DA.15
Dana classification	75.1.1.1
Crystal symmetry	Tetragonal (α) space group P41212, cubic (β) Fd3m
Unit cell	a = 4.9709(1) A, c = 6.9278(2) A, Z = 4 (α);; a = 7.166 A, Z = 8 (β)
Identification
Color	Colorless, white
Crystal habit	Octahedra or spherulites up to several cm large
Twinning	on {111}
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	6–7
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	2.32–2.36
Optical properties	Uniaxial (-)
Refractive index	nω = 1.487; nε = 1.484
Birefringence	0.003
Pleochroism	None
Melting point	1713 °C (β)
References