Handling And Care Of Hygroscopic Materials; Introduction; Hygroscopic Materials - ABB MR Series Startup Procedure

6. HANDLING AND CARE OF HYGROSCOPIC MATERIALS

a. INTRODUCTION
The window and beamsplitter materials that are frequently used in the field of FT-IR (Fourier Transform
InfraRed) spectrometry can be damaged by exposure to moisture in the surrounding environment of the
instrument or storage location. It is the purpose of this documentation to introduce (or remind) the user of this
fact and to encourage practices by which such materials may be handled and used routinely while attempting to
prevent optical material deterioration. Adhering to these practices will serve to prolong the life of integral
components used in the FT-IR instrumentation as well as uphold the experimental integrity associated with
measurement concerns.
b. HYGROSCOPIC MATERIALS
The word hygroscopic means the absorption of moisture from the air and is a property of many of the optical
materials used in infrared spectroscopy. By far the most hygroscopic materials are the alkali halide components
(commonly referred to as salt substrates.) Such halide materials include: cesium iodide (CsI), potassium bromide
(KBr), potassium chloride (KCl), sodium chloride (NaCl), and many others. While these materials provide
relatively high transmittance of infrared radiation, they are also susceptible to damage by interaction with
atmospheric moisture. The damage to these materials, caused by moisture, will be to introduce absorption
features (water bands) and/or to degrade the surface quality of polished surfaces that may cause scattering of
radiation. In both cases, the resulting effect is to reduce the amount of infrared energy that may pass through the
optical material.
The level to which any halide material will be affected by atmospheric moisture can be approximately related to
known water solubility data for the specific material. That is, the optical materials with high solubility in water
will be more susceptible to water damage, which is commonly called "fogging." The solubility of different
materials is presented in figures I-1 and I-2, which shows many of the typical materials utilized with FT-IR's.
Many of the highly hygroscopic materials are shown in the bottom plot. These materials tend to be less
expensive than other materials and provide excellent transmittance of infrared energy, however, they also are
very sensitive to water interaction and should be handled and used with care.
Start-Up Procedure 19