INVESTIGADORES
LAGORIO MarÍa Gabriela
artículos
Título:
Why do marbles become paler on grinding? Reflectance, Spectroscopy, Color, and Particle size.
Autor/es:
M. GABRIELA LAGORIO
Revista:
JOURNAL OF CHEMICAL EDUCATION
Editorial:
American Chemical Society
Referencias:
Lugar: Wisconsin; Año: 2004 vol. 81 p. 1607 - 1611
ISSN:
0021-9584
Resumen:
The observed color of a material is due to interaction
between light and matter. This interaction is usually more
easily understood for transparent media than for solid opaque
media. When dealing with solids some surprising phenomena
occur in the observed colors upon grinding, which results
for many materials at constant chromophore concentration.
If a colored glass marble is ground, it will look paler. The
same phenomenon takes place with copper sulfate,
CuSO4.5H2O, which appears blue in large crystals and almost
white as a powder. Oppositely, some compounds like
potassium permanganate, KMnO4, increase their color at very
small particle sizes. In this article, the theoretical aspects of
the spectroscopy of solids will be presented to explain the
physical principles involved in these observations. The concepts
presented here may be useful for an advanced course
in UV?vis spectroscopy involving solids.
In the first part of this article, a qualitative description
of the color-change problem is presented to rationalize what
happens from a simple physical picture. In the second part
of the article the topic is more rigorously presented and the
discussion is directed to those who are interested in the quantitative
dependence of diffuse reflectance on particle size. Finally
color changes in nanoparticles are discussed.
4.5H2O, which appears blue in large crystals and almost
white as a powder. Oppositely, some compounds like
potassium permanganate, KMnO4, increase their color at very
small particle sizes. In this article, the theoretical aspects of
the spectroscopy of solids will be presented to explain the
physical principles involved in these observations. The concepts
presented here may be useful for an advanced course
in UV?vis spectroscopy involving solids.
In the first part of this article, a qualitative description
of the color-change problem is presented to rationalize what
happens from a simple physical picture. In the second part
of the article the topic is more rigorously presented and the
discussion is directed to those who are interested in the quantitative
dependence of diffuse reflectance on particle size. Finally
color changes in nanoparticles are discussed.
4, increase their color at very
small particle sizes. In this article, the theoretical aspects of
the spectroscopy of solids will be presented to explain the
physical principles involved in these observations. The concepts
presented here may be useful for an advanced course
in UV?vis spectroscopy involving solids.
In the first part of this article, a qualitative description
of the color-change problem is presented to rationalize what
happens from a simple physical picture. In the second part
of the article the topic is more rigorously presented and the
discussion is directed to those who are interested in the quantitative
dependence of diffuse reflectance on particle size. Finally
color changes in nanoparticles are discussed.