ムライト 化学特性,用途語,生産方法
解説
ムライト，ケイ酸アルミニウムの化合物。天然にはまれに産する。名称は、英国スコットランド西岸のマル島で発見されたことに由来する。磁器やスラグの中に一般的に存在。無色透明。斜方晶系。耐熱性に優れる。化学式3Al2O3・2SiO2～2Al2O3・SiO2 マル石。ムル石。
性質
ムライト，斜方晶系，長柱状ないし針状の結晶形を示す。ケイ線石とよく似た結晶構造をもち｛010｝に完全なへき開がある。無色透明，ガラス光沢をもち，比重約3.16，モース硬度7.5。SiO2‐Al2O3系では，広い組成範囲で固溶体を形成し，常圧下では，常温から1850℃で溶融するまでの広い温度領域で安定に存在する。高温領域で安定な，唯一のアルミノケイ酸塩であり，紅柱石，ラン晶石，ケイ線石を常圧で加熱すると容易に生成される。
用途
耐火度が高く機械的強度が大きく，荷重軟化性もすぐれており，理化学用あるいは点火栓がいしなどムライト磁器，シリカ-アルミナ系耐火物として用いられる．
説明
Mullite [Al
6Si
2O
13 = 3Al
2O
3·2SiO
2], with 71.8 wt.% Al
2O
3 , is an important silicate mineral that
occurs in high-silica alumina refractories. Mullite exhibits a high melting point of 1810°C
combined with low thermal expansion coefficients (i.e., 4.5 × 10
–6 K
–1 parallel to the a-axis
and 5.7 × 10
–6 K
–1 parallel to the c-axis), a good mechanical strength with a tensile strength of
62 MPa, and resilience at elevated temperatures that make mullite a highly suitable mineral
for highly refractory materials. In nature, mullite is an extremely scarce mineral that occurs
only in melted argillaceous inclusions entrapped in lavas from the Cenozoic Era on the Island of Mull, Scotland, but no deposit was found to be economically minable.
化学的特性
colorless; rhomb, a=0.7557nm, b=0.76876 nm, c=0.28842 nm; hardness: hot pressed 13.6GPa, sintered 12.7GPa; indentation microfracture 2.02MPa ·m1/2; submicrometer powder(s) can be prepared by hydrolysis of mixed alkoxides, followed by drying and calcining up to 1600°C; sinter, microstructure [SOM91]; phases equilibria in mullite [PAS88]; other data in [HIR89] [ROB67] [MIZ89]
使用
Mullite is present in the form of needles in porcelain, it is used in high-mullite based products is in hot blast stove checker bricks, melting and firing processes, and is used as a refractory material, manufacture of a type of crucible, steel industry, electronic substrates and protective coatings.
工業用途
Artificial mullite, or synthetic mullite, a ceramic material made by a prolonged fusing in the electric furnace of a mixture of silica sand or diasphoric clay and bauxite, has the composition 3Al
2O
3·2SiO
2, has a melting point of 1810 C, and softens at 1650 C.
Mullite occurs in nearly all ceramic products containing alumina and silica but, with the exception of refractories, is seldom introduced as such except as calcined kyanite.
The bricks are resistant to flame and to molten ash, and have a low, uniform coefficient of thermal expansion and a heat conductivity only slightly above that of fireclays. Normally, mullite has very fine crystals that change form and become enlarged after prolonged heating, making the product porous and permeable. For stable high-temperature refractories the mullite is prefused to produce larger crystals. At very high temperatures mullite tends to decompose to form corundum and alkali-silicate minerals of lower heat resistance. Mullite is also used for making spark plugs, chemical crucibles, and extruding dies, and a foamed mullite is used as a uniformly latticed honeycomb structure for lightweight, heat-resistant structural parts.
ムライト 上流と下流の製品情報
原材料
準備製品