Sample Mounting

Radioactivity in environmental waters can originate from both natural and artificial sources. The natural or background radioactivity usuaUy amounts to <100 mBq/L. The development of the nuclear power industry as weU as other industrial and medical uses of radioisotopes (qv) necessitates the deterrnination of gross alpha and beta activity of some water samples. These measurements are relatively inexpensive and are useful for screening samples. The gross alpha or beta activity of an acidified sample is deterrnined after an appropriate volume is evaporated to near dryness, transferred to a flat sample-mounting dish, and evaporated to dryness in an oven at 103—105°C. The amount of original sample taken depends on the amount of residue needed to provide measurable alpha or beta activity. 

An alternative method of studying the molecular motions of a polymeric chain is to measure the complex permitivity of the sample, mounted as dielectric of a capacitor and subjected to a sinusoidal voltage, which produces polarization of the sample macromolecules. The storage and loss factor of the complex permitivity are related to the dipolar orientations and the corresponding motional processes. The application of the dielectric thermal analysis (DETA) is obviously limited to macromolecules possessing heteroatomic dipoles but, on the other hand, it allows a range of frequency measurement much wider than DMTA and its theoretical foundations are better established. 

The development of modern surface characterization techniques has provided means to study the relationship between the chemical activity and the physical or structural properties of a catalyst surface. Experimental work to understand this reactivity/structure relationship has been of two types fundamental studies on model catalyst systems (1,2) and postmortem analyses of catalysts which have been removed from reactors (3,4). Experimental apparatus for these studies have Involved small volume reactors mounted within (1) or appended to (5) vacuum chambers containing analysis Instrumentation. Alternately, catalyst samples have been removed from remote reactors via transferable sample mounts (6) or an Inert gas glove box (3,4). 

For the copper/aluminum catalyst analyses later described, the sample mount was transfered from the XPS system following treatment and analysis to an inert atmosphere dry box without air exposure. From there individual pellets were transferred to the SAM for subsequent analysis without air exposure. The reverse process was employed for the next reaction cycle. 

Figure 1. Schematic Diagram of the off-axis radiant heated reactor. A. cell body B. linear/rotary motion feedthrough C. transport rod D. projector bulb E. reflector F. insulated stainless steel enclosure G. air cooling port H. gas inlet I. gas outlet/pumping port J. chromel/alumel thermocouple K. high vacuum gate valve L, sample mount.

Figure 1 shows two reactor configurations we have used to measure reaction rates on clean surfaces. In Figure 1(a) is shown a high pressure cell inside the UHV system ( ) with the sample mounted on a bellows so it can be moved between the reaction cell and the position used for AES analysis. In Figure 1(h) is shown a reaction cell outside the analysis system with the sample translated between heating leads in the reactor and in the UHV analysis system ( ). 

The XPS spectra of the freshly sulfided Co-Mo/NaY catalysts were measured on an XPS-7000 photoelectron spectrometer (Rigaku, A1 anode 1486.6 eV). The sample mounted on a holder was transferred from a glove bag into a pretreatment chamber attached to the spectrometer as possible as carefully not to be contacted with air. The binding energies (BE) were referenced to the Si2p band at 103.0 eV for the NaY zeolite, which had teen determined by the Cls reference level at 285.0 eV due to adventitious carbon. 

The single crystal catalysts, -1 cm in diameter and 1 mm thick, are typically aligned within 0.5 of the desired orientation. Thermocouples are generally spot-welded to the edge of the crystal for temperature measurement. Details of sample mounting, cleaning procedures, reactant purification, and product detection techniques are given in the related references. The catalytic rate normalized to the number of exposed metal sites is the specific activity, which can be expressed as a turnover frequency (TOF), or number of molecules of product produced per metal atom site per second. 

Fig. 7.18. Instrumental arrangement for the measurement of total reflection x-ray fluorescence. The x-rays from the source (A) are allowed to impinge on the sample mounted on a reflector plate (B). Most of the incident radiation bounces off the sample (C), but some results in the production of XRF (D), which is measured by the detector (E).

Microreactor, in UHV analysis compact design, 36 8 GC analysis, 36 9-13 sample mounting, 36 4-8 small-volume design, 36 9 Middle-distillate oils... 

In electrochemical measurements it is necessary to establish good insulated electrical contact with the sample and furthermore to have a well-defined exposed surface area. It is difficult to comply with these demands without creating, at the sample/mount interface, a crevice between the sample and the sample holder. If the bulk solution is not prevented from entering the crevice, crevice corrosion attack is often initiated. ... 

Here distilled water instead of argon is pumped into the test cell at the crevice between the sample and the sample mounting. With a few exceptions, the Avesta cell is like the usual electrochemical cell for corrosion measurements (Figs. 14 and 15). The Avesta cell is made up of two concentric cylindrical glass pieces with a top and bottom made of polyvinylidene fluoride pieces. 

SneU, G., et al. (2004). Automated sample mounting and ahgnment system for biological crystallography at a synchrotron source. Structure 12, 537-545. 

Outdoor exposure of polymer samples, mounted at a 45° angle and facing south, has been used to measure the resistance of polymers to outdoor weathering (ASTM-D1345). Since these tests are expensive and time-consuming, tests such as ASTM-G23 have been developed in an attempt to gain accelerated test results. 

The rather variable results of half-life determinations made by direct alpha-counting of samples mounted on metallic supports may be due to... 

The TiC>2 samples, mounted in a helium cryostat (10-300 K), are lmm-thick (001) and (110)-cut single crystals to study the electronic response with the (THz) electric field perpendicular ( L) and parallel (//) to the c axis, respectively. Rutile is the most common and stable TiC>2 polymorph and has a tetragonal structure with a=4.6A and c=2.9A. The band gap of rutile is 2.9 eV at room temperature, increasing slightly at lower temperatures. 

Oven-aging was carried out on 0.075-inch samples mounted on a rotating turntable in an air-circulating oven (port velocity 1000 ft./minute) for seven days at 100°C. 

The X-ray photoelectron spectroscopy (XPS) experiments were performed in an ultra-high vacuum (UHV) chamber coupled to an atmospheric pressure reaction cell. All XPS results were obtained from samples treated in situ in the reaction cell and transferred into UHV without exposure to air. Detailed sample mounting procedures and instrument details are described elsewhere.16 Ar+ bombardment was done with 3 KeV Ar+ ions at a current density of 0.8 pA/cm2 for 1 h in an attempt to remove the carbon overlayer and expose the underlying carbide phase. 

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