Infrared hydraulic press

A major difference between infrared and ultraviolet spectroscopy is in the concentrations required for assay In infrared spectroscopy as much as a 10% w/v solution of sample must be prepared. This means that the path length of the cells used in infrared must be very short, usually 0.025-0.1 mm (otherwise absorbance values would be too high). Another problem with infrared spectra is that the solvent used in the assay (usually chloroform or dichloromethane) also possesses chemical bonds that will absorb infrared radiation in some part of the spectrum, obscuring the absorption by the sample at these wavelengths. Samples are prepared in solution, in a mull or paste made with liquid paraffin (Nujol), or in a solid disc prepared by trituration with dry potassium bromide followed by compression in a hydraulic press. 

A typical hydraulic press of lOOkN ( 10 ton ) capacity is shown in Fig. 17.4. This model has a ram advance speed of 475mm/s, a pressing speed of 34mm/s and a return speed of 280mm/s. The model shown is fitted with a light-screen guard operated by a continuous curtain of infrared light. 

Surfaces, because of their unsaturated surface fields, normally require to be cleaned from contamination derived from the atmospheric environment before systematic research can be carried out on them. For finely divided samples of high area it is adequate to mount them in a high-vacuum enclosure ( 10 mbar) provided with infrared-transparent windows and the means for treating the sample in oxygen or hydrogen at elevated temperatures. The samples themselves are most often studied in transmission, usually in the form of pressed discs derived from powders. These are prepared using a hydraulic press... 

Ti02 powder (Degussa P-25) was used in all experiments. It consists of anastase particles with a mean diameter of 0.03 microns and a surface area of approximately 50 m2/g. The powder was heated in air to 500°C for several hours and then stored in moist air. Approximately 50 mg of powder was pressed into a translucent pellet using a 13 mm diameter die and a hydraulic laboratory press. The pellet was mounted in a vacuum IR cell (CaF2 windows) which could be sealed, detached from the vacuum line, and inserted in the spectrometer. All spectra were recorded on a Perkin-Elmer 283B Infrared Spectrophotometer with a P-E computer data station. 

Figure 7 Extreme examples of presses for preparing from solids films suifable for mid-infrared examinafion (A) hand-operafed, hydraulic, heafed, molding press for preparing fhin films from polymer samples for macro mid-infrared examinafions (B) diamond anvil minicell for solid sample compression and confainmenf, particularly for FT-IR microscopy sfudies and (C) schemafic of diamond anvil minicell. (A) Reproduced by kind permission of George E. Moore Son Lfd., Birmingham, Wesf Midlands, UK. (B and C) Reproduced by kind permission of High Pressure Diamond Optics, Inc., Tucson, AZ, USA.)...

To press a disc, the following is required infrared-quality KBr, a press (hand-held or hydraulic) capable of delivering from 15 000 to 25 000 psi pressure, a die, and a mortar and pestle (usually made of agate). The KBr should be kept in a clean, dry environment— preferably a desiccator or a drying oven maintained at 105 C. The storage unit should not be used for anything which might contaminate the KBr by sublimation or evaporation. The die is a simple infrared accessory which holds the powder between two platens while pressure is applied. 

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