Nanocrystalline material

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A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definitions vary, but nanocrystalline material is commonly defined as a crystallite (grain) size below 100 nm. Grain sizes from 100–500 nm are typically considered "ultrafine" grains.

The grain size of a NC sample can be estimated using x-ray diffraction. In materials with very small grain sizes, the diffraction peaks will be broadened. This broadening can be related to a crystallite size using the Scherrer equation (applicable up to ~50 nm), a Williamson-Hall plot, or more sophisticated methods such as the Warren-Averbach method or computer modeling of the diffraction pattern. The crystallite size can be measured directly using transmission electron microscopy.

Synthesis[edit]

Nanocrystalline materials can be prepared in several ways. Methods are typically categorized based on the phase of matter the material transitions through before forming the nanocrystalline final product.

Solid-state processing[edit]

Solid-state processes do not involve melting or evaporating the material and are typically done at relatively low temperatures. Examples of solid state processes include mechanical alloying using a high-energy ball mill and certain types of severe plastic deformation processes.

Liquid processing[edit]

Nanocrystalline metals can be produced by rapid solidification from the liquid using a process such as melt spinning. This often produces an amorphous metal, which can be transformed into an nc metal by annealing above the crystallization temperature.

Vapor-phase processing[edit]

Thin films of nanocrystalline materials can be produced using vapor deposition processes such as MOCVD.[1]

Solution processing[edit]

Some metals, particularly nickel and nickel alloys, can be made into nanocrystalline foils using electrodeposition.[2]

References[edit]

  1. ^ Jiang, Jie; Zhu, Liping; Wu, Yazhen; Zeng, Yujia; He, Haiping; Lin, Junming; Ye, Zhizhen (February 2012). "Effects of phosphorus doping in ZnO nanocrystals by metal organic chemical vapor deposition". Materials Letters. 68: 258–260. doi:10.1016/j.matlet.2011.10.072. 
  2. ^ Giallonardo, J.D.; Erb, U.; Aust, K.T.; Palumbo, G. (21 December 2011). "The influence of grain size and texture on the Young's modulus of nanocrystalline nickel and nickel–iron alloys". Philosophical Magazine. 91 (36): 4594–4605. doi:10.1080/14786435.2011.615350. 

See also[edit]