Solid samples, flat

Some care must be exercised with this technique, as errors are introduced at very low frequencies and at very high frequencies, as well as for low values of dielectric constant and loss factor. The technique is valid for the frequencies of 915 and 2,450 MHz, for materials with loss factors greater than 1. The temperature range of the probe is limited to approximately 60°C. However, new probe development is nearing completion. Interpretation for lower loss materials such as fats and oils must be treated with caution. Typical open-ended probes utilize 3.5 mm (0.138 in) diameter coaxial line. For the measurement of solid samples, probes with flat flanges may be utilized (Hewlett Packard 1991). 

There are numerous ways to prepare a solid sample for XPS-analysis 17K Because of the 360° angle of acceptance, the optimum sample geometry is a cylinder of 11 mm diameter and 2 mm width. However, with a certain loss in sensitivity, flat samples as well as odd shaped samples can be analyzed as well, if they do not exceed the maximum size defined by the vacuum interlock. Sample powders are normally mounted on sticky tape or pressed into a metal grid 17). Excellent results were also obtained by pressing pellets 31) or by subliming the sample directly unto the sample holder. 

The technique of filling the sample holder is to fill it 1/3 to 1/2 full of liquid. Place the lower end into the dry ice-acetone or isopropanol container, and tilt the holder to about a 60 angle or as flat as possible without spilling the liquid. Slowly turn the holder so a film of solid sample freezes around the inside of the sample holder. Freeze the sample for a few minutes longer, connect the top section and then connect it to the condenser before it begins to melt. This rotation technique increases the surface area, and the water in this thin film, about 1 cm thick at most, can be sublimed rapidly. 

The spark discharge is often applied to solid samples in the form of rods approximately a quarter-inch in diameter or cast disks or flats a half-inch thick by 1 to 3 inches in diameter. Powders are most often pressed into pellets and treated as solid samples for spark analysis. Liquid samples are also analyzed by spark discharges in many cases. Several different ways of analyzing liquid samples have been developed ... 

XRF is used for the analysis of solid and liquid samples. For quantitative analysis the surface of the sample must be as flat as possible, as will be discussed in the applications section. There are two classes of sample holders, cassettes for bulk solid samples and cells for loose powders, small drillings, and liquids. A typical cassette for a flat bulk solid such as a polished metal disk, a pressed powder disk, a glass or polymer flat is shown in Fig. 8.26(a). The cassette is a metal cylinder, with a screw top and a circular opening or aperture, where the sample will be exposed to the X-ray beam. The maximum size for a bulk sample is shown. The sample is placed in the cassette. For a system where the sample is analyzed face down, the cassette is placed with the opening down and the... 

Sodium silicate is somev at more difficult to analyze than many other materials because of the formation of the relatively long lived radionuclide Na whose emissions interfere with the detection of other elements. Nevertheless we were able to determine, in a sample of sodium silicate, that many heavy elements of toxicological concern were undetectable down to the ppm to ppb level in the undiluted silicate (13), An XRF spectrometer can be configured to perform sequential multi-elemental analyses. It is less sensitive to the elements of lower atomic number. Also, since the X-rays penetrate only to a depth of about 10 urn, the sample must be homogeneous. Solid samples must be presented to the X-ray beam with a flat surface. However, the relative ease of sample preparation and the ability to run glasses and solutions with only minor dilution make X-ray fluorescence a useful technique where analysis for a wide range of impurities is required,... 

Flat-ended electrodes have been used to make off-line measurements directly on the surfaces of soHd substrates [174,175]. However, off-line measurements are usually made by measuring the pH of aqueous suspensions or extracts of the solid sample. 

A flat solid sample is needed, the size should be of the order of centimeters. 

UHV compatible, solid samples. Samples must be reasonably flat to avoid excessive topographic distortions. 

Thermal diffusivity has usually been measured using a quenching method, i.e.. the. solid sample at a uniform temperature is immersed in a temperature-controlled bath at a different temperature. The rate of change of temperature at the center is then monitored with an embedded thermocouple. The sample dimensions are usually chosen so that lateral heat flow can be ignored and regular sample geometries, i.e., "infinite flat slabs, "infinite" cylinders, or spheres, are used. 

Internal reflection spectroscopy of solids Mid-infrared internal reflection accessories were developed initially largely for studying the surface layer characteristics of a continuous flat solid sample, e.g., a polymer film although they may also be used as convenient methods of sample identification, when a surface layer spectrum may be taken as indicative of a sample s bulk characteristics. The sample surface is brought and held under low pressure into optical contact with the clean surface of an internal reflection element. Other common traditional uses have included the direct examination of fibers, foams, and malleable (soft) powders. It has, however, become common practice nowadays, with the sensitivity now available with FT-IR spectroscopy, to use single (or low-number) internal reflection accessories to conveniently and easily record a mid-infrared fingerprint... 

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