| 翻訳と辞書 |
| Clay mineral X-ray diffraction ： ウィキペディア英語版 |
Clay mineral X-ray diffraction
Clay minerals are one of the most diverse minerals but all have a commonalty of crystal or grain sizes below 2 µm. Chemically clays are defined by crystal structure and chemical composition. Sometimes fine grain sediments are mistakenly describes as clays, this is actually a description of the “clay-size fraction” rather than the mineralogy of the sediment. There are three crystallographic clay groups: platy clays (phyllosilicates), fibrous clay minerals, and amorphous clay. Phyllosilicates are the most abundant clays and are categorized based on the layering of a tetrahedral and an octahedral layer. For most clays, the octahedral layer is centered with Al3+, Fe3+, or Mg(OH)2, but sometimes Zn2+, Li+, and Cr3+ can substitute as well. Si4+ is normally the center of the tetrahedral layer but Al3+ will often partially substitute and create a charge imbalance. Two-layer clays are composed of a tetrahedral layer and an octahedral layer (T-O) while three-layer clays contain an octahedral layer sandwiched by two tetrahedral layers (T-O-T). When substitution of Al3+ for Si4+ creates a charge imbalance, an interlayer cation will fill in between tetrahedral layers to balance the charge of the clay.
==X-Ray Diffraction and Clays==
Typically, powder X-ray diffraction (XRD) is an average of randomly oriented microcrystals that should equally represent all crystal orientation if a large enough sample is present. X-rays are directed at the sample while slowly rotated which produce a diffraction pattern which show intensity of x-rays collected at different angles.
Randomly oriented XRD samples are not as useful for clay minerals because clays typically have similar X and Y dimensions. The Z dimension differs from clay to clay and is most diagnostic because the Z dimension represents the height of the tetrahedral-octahedral (T-O) or tetrahedral-octahedral-tetrahedral (T-O-T) layer. The Z dimension can increase or decrease because of substitution of the central cation in both the tetrahedral and octahedral layers. The presence and size of a charge balancing cation in the interlayer of T-O-T clays will also affect the Z dimension. Because of this, clay minerals are typically identified by preparing samples so that they are oriented to increase basal (00''l'') reflection . D positions are calculated using Bragg’s law but because clay mineral analysis is one dimensional, ''l'' can substitute n, making the equation ''l'' λ = 2d sinΘ. When measuring the x-ray diffraction of clays, d is constant and λ is the known wavelength from the x-ray source, so the distance from one 00''l'' peak to another is equal.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
■ウィキペディアで「Clay mineral X-ray diffraction」の詳細全文を読む
スポンサード リンク
| 翻訳と辞書 : 翻訳のためのインターネットリソース |
Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.
|
|