The influence of moisture on potassium bromide disks used in infrared spectrometry

Abstract

Abstract-When using the alkali-halide disk technique in infrared spectrometry we noticed that moisture from the atmosphere can penetrate into a KBr disk, causing recrystallization of the KBr. A critical relative humidity was observed above which moisture is taken up. This value depends on the fineness and structure of the KBr; for optical grade, handground KBr (Merck) it is about 70 per cent. "Wet" disks lose water if stored in an atmosphere of a lower humidity; replaced in the original atmosphere, they take up water again but to a lower extent.In order t,o study the water sensitivity of KBr disks containing a sample, KSCN was used. KSCS has two C-N stretching bands dependent on the form in which it occurs: as a solution at 4.84 ,u and in the solid phase at 4.87 ,u. The latter can be converted into the former by water uptake of the disk; on drying of the disk the band is shifted back to its original wavelength.In the disk are small cracks through which condensed moisture and dissolved sample can be transported. This is demonstrated by the behaviour of KSCN. If a KBr disk, containing a single KSCN crystal completely surrounded by carrier material, is exposed to a moist atmosphere the KSCN is transported through the whole disk.The same t,ransport. due to the presence of water in a disk, was observed with a number of similar inorganic salts. Sometimes the accompanying bandshifts could be eliminated by drying, sometimes t,hey persisted, probably indicating that a solid solution has been formed. In the absence of water none of these phenomena were observed.1.nteraction between sample and water can be demonstrated also with D,O. In a moist D,O atmosphere active H atoms of sample molecules in a disk are substituted by D atoms. This phenomenon can be applied successfully in structure determination.

Infrared Optical Constants from Pressed Pellets of Powders: I. Improved n and k Values of (NH4)2SO4 from Single-Angle Reflectance

“…Another parameter known to affect the optical quality of the pellet is the duration and magnitude of the press, i.e., at what pressures for what time intervals? Many of these procedures have, e.g., been optimized for KBr pellets 39,40 as used in IR transmission spectroscopy, but KBr is softer than salts such as ammonium sulfate. It is known that incrementally increasing the weight (pressure) generally leads to better pellets.…”

Sur les carbonates basiques de fer (III): I. Carbonate basique de fer (III) amorphe

“…Le rapport des surfaces des deux sonimets des courbes de 1'Climination de l'anhydride carbonique ddpend de la composition initiale du produit. [7]. Le spectre du carbonate basique de fer(II1) dans une pastille de KBr et le spectre de la m&me pastille aprks 6 jours dans une atmosphgre d'une humiditk relative de 75% de vapeur d'eau lourde sont repr6sentks dans la Fig.…”

Sur les carbonates basiques de fer (III): II. Préparation, radiocristallographie et spectres IR. du (NH4)2Fe2(OH)4(CO3)2 · H2O

“…Comme la prkparation du composC deutCri6 B partir de produits de dCpart deutCriCs aurait 6tC coQteuse, nous avons effect& 1'Cchange des atomes H par les atomes D directement dans la pastille de KBr [2] (sCjour dans une humidit6 relative de 75% env. en vapeur d'eau lourde), ce qui nous a permis non seulernent d'obtenir un produit partiellement deutCriC, mais aussi de distinguer les bandes des vibrations de celles de vNH (Fig.…”