Distinguishing Between Different Crystal Modifications of Titanium Dioxide by Raman Spectroscopy
Raman spectroscopy provides a unique chemical fingerprint of a substance. Not only the chemical composition, but also the structure within a crystal can be distinguished using the Raman technique. Anton Paar’s Cora Raman systems are able to discriminate between the different forms of titanium dioxide (E171), a non-toxic white pigment widely used in the pharmaceutical, food, and paint industries.
Crystalline materials such as minerals come in different crystal forms – a phenomenon also known as polymorphism. It means their molecular compositions are identical but the structural make-up of the crystal, i.e. how the molecules are arranged within the crystal, is different.
Raman spectroscopy is ideally suited to distinguish between these different crystal forms as it is sensitive to molecular vibrations present in the sample which strongly depend on the specific crystal structure. In addition, the Cora 5001 enables quantification of these modifications within a mixture of polymorphs.
Titanium dioxide (E171) is widely used as a white pigment, for example, in healthcare products such as toothpaste, in the pharmaceutical industry as a coating material for tablets, or in the paint industry in wall paints. As a pigment it provides an extremely high brightness and opacity. Because it also shows UV resistance, it is further used to enhance UV stability in plastics and other materials or in the cosmetics industry in sunscreen cream.
The overall production of titanium dioxide makes up 70 % of the pigment production worldwide- Titanium dioxide has several crystal modifications which differ in their physical properties e.g. in hardness, refractive index, or density.
The two most common forms are rutile and anatase. Rutile is a hard mineral and exhibits a high brightness whereas anatase is softer but exhibits catalytic activity. Therefore, both forms are produced for different applications and it is crucial for the manufacturer to know which crystal modification has been produced. Similarly, a customer in the downstream processing industry might be interested to confirm that the correct form has been delivered.
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