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silver iodide

 
Dictionary: silver iodide

n.
A pale yellow, odorless powder, AgI, that darkens on exposure to light and is used in photographic emulsions, rainmaking, and medicine, especially as an antiseptic.


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Medical Dictionary: silver iodide
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n.

A pale yellow, odorless, tasteless powder that darkens when exposed to light and that is used as an antiseptic.

WordNet: silver iodide
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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: an iodide that is used in photography, in seeding clouds to make rain, and in medicine


Wikipedia: Silver iodide
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Silver iodide
Silver iodide
Silver-iodide-3D-balls.png
Other names Silver(I) iodide
Identifiers
CAS number 7783-96-2 Yes check.svgY
Properties
Molecular formula AgI
Molar mass 234.77 g/mol
Appearance yellow, crystalline solid
Density 5.675 g/cm3, solid
Melting point

558 °C

Boiling point

1506 °C

Solubility in water 3 × 10−7g/100mL (20 °C)
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-62.4 kJ/mol
Hazards
EU classification not listed
NFPA 704
NFPA 704.svg
0
2
0
 
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Silver iodide (AgI) is an inorganic compound. This yellow photosensitive solid is used in photography, as an antiseptic in medicine, and in rainmaking or cloud seeding. Silver iodide is highly insoluble in water.

The crystalline structure adopted by silver iodide changes with temperature. The following phases are known:[1]

  • Up to 420K (147 °C), AgI exists in the β-phase, which has a wurtzite structure. It is known as the mineral iodargyrite.
  • Above 420K (147 °C), AgI undergoes a transition to the α-phase, which has a body-centered cubic structure and has the silver ions distributed randomly between 2-, 3-, and 4-coordinate sites.
  • A metastable γ-phase also exists below 420K, which has a zinc blende structure.

Contents

Rainmaking

Cessna 210 equipped with a silver iodide generator for cloud seeding

The crystalline structure of AgI is similar to that of ice, allowing it to induce freezing (heterogeneous nucleation) in cloud seeding for the purpose of rainmaking. Approximately 50,000 kg/year are used for this purpose, each seeding experiment consuming 10-50 grams.[2]

Silver iodide as a fast ion conductor

The transition between the β and α forms represents the melting of the silver (cation) sublattice. The entropy of fusion (melting) for α-AgI is approximately half that for sodium chloride (a typical ionic solid). This can be rationalised by noting that the AgI crystalline lattice has essentially already partly melted in the transition between α and β forms. Adding the entropy of transition from α-AgI to β-AgI to the entropy of fusion gives a value that is much closer to the entropy of fusion for sodium chloride.

References

  1. ^ Binner, J. G. P.; Dimitrakis, G.; Price, D. M.; Reading, M.; Vaidhyanathan, B. (2006). "Hysteresis in the β–α Phase Transition in Silver Iodide" (PDF). Journal of Thermal Analysis and Calorimetry 84: 409–412. doi:10.1007/s10973-005-7154-1. http://www.sump4.com/publications/paper047.pdf. 
  2. ^ Phyllis A. Lyday "Iodine and Iodine Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.

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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Medical Dictionary. The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company Read more
WordNet. WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Silver iodide" Read more