Sample holders measurements

Basic components of a spectrophotometer include a radiation source, a monochromator, a sample cell, and a detector. To minimize errors in spectrophotometty, samples should be free of particles, cuvets must be clean, and they must be positioned reproducibly in the sample holder. Measurements should be made at a wavelength of maximum absorbance. Instrument errors tend to be minimized if the absorbance falls in the range A — 0.4—0.9. 

Use a tungsten or copper X-ray source and a powder diffractometer. Load cmshed NaCl powder into the sample holder. Measure the diffraction pattern of the NaCl. Repeat with powdered KCl. Note the difference in spectra. Make mixtures by varying the amounts of NaCl and KCl. Can you distinguish the mixtures and the relative amounts of each component from the powder patterns ... 

As described above, the main purpose of the chemisorption methods is to evaluate the number of active sites that can be reached or that can interact with a fluid phase. These techniques are based on a chemical reaction between a suitable reactive gas and the surface reactive site. There are different methods to perform the above operation, the static volumetric, the static gravimetric or the flow methods. In the volumetric method, the sample is kept under high vacuum before the analysis. The analytical instrument then introduces known doses of reactive gas into the sample holder, measuring afterwards the equilibrium... 

VPD-TXRF is also a facile technique for interface analysis [4.78, 4.79]. Automated VPD equipment (Fig. 4.16) improves both the detection limit (upper range 10 atoms cm ) and the reliability (by > 50%) of the VPD-TXRF measurement [4.14]. Current research focuses on sample holders [4.80, 4.81] and light-element detection capability [4.82-4.84]. 

F Cu-30Ni-2Fe 2Mn 0-014 <1 Very slight pitting attack beneath brown tubercles of corrosion products. Also pitting in areas next to sample holder. No measurable attack opposite jet... 

Infrared (IR) investigations can be made on a sample of reactant previously heated to a known extent of reaction (a) and studied in the form of a mull or in an alkali halide disc. An alternative approach is to incorporate the reactant substance in a compact alkali halide disc [287] which is intermittently withdrawn from the reaction vessel for infrared measurements at appropriate intervals. Heated sample holders [288,289] permit repetitive scanning of the spectrum or continuous monitoring of a peak of interest during decomposition. 

The ESR measurements were made at RT or 77 K on a Varian E-9 spectrometer (X-band), equipped with an on-line computer for data analysis. Spin-Hamiltonian parameters (g and A values) were obtained from calculated spectra using the program SIM14 A [26]. The absolute concentration of the paramagnetic species was determined from the integrated area of the spectra. Values of g were determined using as reference the sharp peak at g = 2.0008 of the E i center (marked with an asterisk in Fig. 3) the center was formed by UV irradiation of the silica dewar used as sample holder. 

FTIR spectra were collected with a Nicolet 740 spectrometer and a custom built in situ gas flow cell. The spectrometer was equipped with a MCT-B detector cooled by liquid nitrogen. Approximately 15 mg of the MgO catalyst sample was pressed into a self-supported disc and placed in a sample holder located at the center of the cell. The temperature in the cell was measured with a thermocouple placed close to the catalyst sample. Transmission spectra were collected in a single beam mode with a resolution of 2 cm 1. Prior to introduction... 

Background is measured without the sample - but including the sample holder and all kind of wrapping that does not belong to the material of interest (e.g., aluminum foil, empty cuvette, or cuvette with solvent, respectively). 

The absorption factor of the studied sample is measured by means of the moving slit device, as well. For this purpose the sample is mounted in the sample holder and the moving slit measurement is performed. We measure Ns = 50031 in 16 scans. Because the heights of the moving and the fixed vertical slits are 2 cm, the moving slit registers the SAXS as well - as is required from the definition of absorption. Then... 

The way the sample is filled in a holder affects the orientation of the crystallites. Numerous methods of sample preparation have been described in the literature [1], Morris et al. [61] avoided preferred orientation by using a sample holder in which the top face had a rectangular cavity that extended to one end of the holder. Building on that concept, an x-ray holder has been fabricated wherein the powder is filled from the side [49]. By using this holder, reproducible and reliable intensity measurements have been obtained [49,56]. 

Mercury porosimetry is based on the fact that mercury behaves as a nonwetting liquid toward most substances and will not penetrate the solid unless pressure is applied. To measure the porosity, the sample is sealed in a sample holder that is tapered to a calibrated stem. The sample holder and stem are then filled with mercury and subjected to increasing pressures to force the mercury into the pores of the material. The amount of mercury in the calibrated stem decreases during this step, and the change in volume is recorded. A curve of volume versus pressure represents the volume penetrated into the sample at a given pressure. The intrusion pressure is then related to the pore size using the Washburn equation... 

The dilatometer is generally made of glass and is the vessel where the mercury is intruded into the sample pores. The design is dependent on the pressure source and monitoring system of the instrument. The dilatometer consists of a sample holder and a calibrated stem, which is used to measure the amount of mercury intruded into the sample. The sample in the dilatometer must be cleaned from adsorbed species by degassing the material in a vacuum [42], Most commercial instruments degas the sample in the instrument before mercury intrusion. Once the sample is degassed, the dilatometer (sample holder and stem) are filled with mercury. 

Fig. 2 Schematic diagram of a hydrogen depth profiling setup using a high efficiency BGO detector. A cooled sample holder is placed close to the front surface of the BGO scintillator in ultra-high vacuum. The sample holder can be moved perpendicular to the plane of the figure to bring different samples into the 15N beam and is surrounded by a Faraday cup arrangement to ensure accurate measurement of the analyzing beam dose.

Figure 14.3. Sample holders for various spectrophotometric measurements. (A) UV-Vis cells (B) infrared ATR plate and stand-plate behind which B is attached when in use (C) simple KBr pellet maker using the two bolts and the center dye (D) a sample tube for NMR spectroscopy. 

Melting point instruments consist of a resistance heater to increase temperature, a sample holder and a temperature-measuring device. In its simplest form, an oil bath can be heated with a Bunsen burner, while a capillary tube with a few milligrams of sample is attached to a thermometer with the sample next to the mercury bulb. 

As with any normal analytical balance, it is necessary to arrest the balance for all operations between the measurements. Also in case of unexpected, explosionlike reactions which can displace the sample holder from its normal position it is better to arrest the balance for a moment and then continue the measurement. 

For very high temperatures up to 2400 °C a different Micro TG/DTA sample holder (Fig. 13 f) must be used which usually is equipped with tungsten crucibles. The thermocouple in this case is a combination of W — W 26% Re. This type can be applied for thermoanalytical measurements in high vacuum and in inert atmosphere (noble gases). 

Very easy to change samples and sample holders and to carry out other operations simple compatibility with other apparatus for simultaneous measurements convection goes the natural way, no additional shielding is required for protection of the balance against radiation from the furnace. The other two arrangements 15 B and 15 C which are used besides the first variant are equal in the distribution of use. The advantages of variant C are similar to that of A ... 

The sample is used in finely powdered form and spread on a fine platinum wire mesh which is mounted in the sample holder frame (Pt). The thermocouple (PtRh 10%) for temperature measurement is directly in contact with the sample holder. 

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