Oriented mount

Clay minerals are frequently platy and a high degree of preferred orientation is required when preparing sample mounts for XRD analysis. This is related to their layer lattice characteristics and atomic sequence normal to the surface of the clay plate. There are numerous ways of preparing orientated mounts, and these include precipitation onto glass slides (Brown, 1953), suction onto unglazed ceramic tiles (Gibbs, 1965 Rich, 1975 Rhoton et al., 1993) and suction onto membrane filters (McAlister and... 

True random orientation mounts are difficult to prepare, and numerous techniques for filling powder sample holders have been described (Brindley and Brown, 1980). For example, powder samples have been embedded in plastic (Brindley and Kurtossy, 1961), polyester foam (Thompson et al., 1972), mixed with powdered cork (Wilson, 1987), pasted in acetone prior to smearing onto glass slides (Paterson et al., 1986) and spray dried (Hillier, 2002). 

Figure J. Flowchart showing the usual routes used at University of Manitoba for handling lake sediiiicnl samples for mineralogical analyses and other analyses. See Figure 4 for details on the clay mineral (oriented mount) analysts stream.

Table II, Summary of oriented mount (clay mineral) XRD sample preparation methods (continued). 

Mineral group d spacing from an oriented mount with °29 (copper Ka radiation) in hrackcls Effect of glycolation 500-550 >C Effect of heating higher temp... 

Multiple slides Normally it is sufficient to make only one oriented mount. However, depending on the number of personnel in the laboratory and the timing of access to XRD equipment, it may be efficient to make several slides of the same sample, with the different slides being processed and irradiated with different treatments (i.e., one slide heated, another slide glycolated, a third slide untreated). Let the slide(s) dry at room temperatnre. Many of the expandable lattice clays react rapidly to ambient humidity conditions, so if the laboratory normally experiences fluctuations in relative humidity, place the slide in a desiccator until irradiated. 

X-ray diffraction analyses were performed either on non-oriented or oriented mounts. The XRD patterns were obtained on a Philips powder diffractometer using Ni-filtered, fine-focus CuK -radiation. 

If the detection system is an electronic, area detector, the crystal may be mounted with a convenient crystal direction parallel to an axis about which it may be rotated under tlie control of a computer that also records the diffracted intensities. Because tlie orientation of the crystal is known at the time an x-ray photon or neutron is detected at a particular point on the detector, the indices of the crystal planes causing the diffraction are uniquely detemiined. If... 

Use of the peUetted converter, developed and used by General Motors starting in 1975, has declined since 1980. The advantage of the peUetted converter, which consists of a packed bed of small spherical beads about 3 mm in diameter, is that the pellets were less cosdy to manufacture than the monolithic honeycomb. Disadvantages were the peUetted converter had 2 to 3 times more weight and volume, took longer to heat up, and was more susceptible to attrition and loss of catalyst in use. The monolithic honeycomb can be mounted in any orientation, whereas the peUetted converter had to be downflow. AdditionaUy, the pressure drop of the monolithic honeycomb is one-half to one-quarter that of a similar function peUetted converter. 

Frequently, so-called crevice washers are used in coupon studies to test the environment for its ability to produce crevice corrosion (Fig. 2.22). There are several designs most consist of a small Teflon washer with radially oriented, wedge-shaped teeth. The washer is held to the coupon by a mounting bolt that passes through a central hole. The spaces between teeth form small crevice-shaped areas in which attack may occur (Fig. 2.23). The test is somewhat subjective and is not easily quantified. Using this test, attack in crevices either occurs or does not. 

Orientation. Certain fittings are designed specifically for either horizontal or vertical mounting others may be installed either horizontally or vertically, or even at oblique angles. 

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. 

It is important for predictive maintenance programs using vibration analysis to have accurate, repeatable data. In addition to the type and quality of the transducer, three key parameters affect data quality the point of measurement, orientation, and transducer-mounting techniques. 

The best method of ensuring that the point of measurement, its orientation, and the compressive load are exactly the same each time is to permanently or hard mount the transducers, which is illustrated in Figure 43.26. This guarantees accuracy and repeatability of acquired data. However, it also increases the initial cost of the program. The average cost of installing a general-purpose accelerometer is about 300 per measurement point or 3000 for a typical machine-train. 

For general-purpose use below 1000 Hz, a transducer can be attached to a machine by a magnetic base. Even though the resonant frequency of the transducer/magnet assembly may distort the data, this technique can be used with some success. However, since the magnet can be placed anywhere on the machine, it is difficult to guarantee that the exact location and orientation is maintained with each measurement. Shows common magnetic mounts for transducers. 

Each measurement point, typically located on the bearing housing or machine casing, should provide the shortest direct mechanical link to the shaft. Figure 44.16 illustrates such a location oriented in both the axial and radial planes. If a transducer is not mounted in an appropriate location, the data will be distorted by noise such as fluid flow in the bearing reservoir or through the machine. 

Measurement locations should be permanently marked to ensure repeatability of data. If transducers are permanently mounted, the location can be marked with a center punch, paint, or any other method that identifies the point. The following sections give the recommended locations and orientations of measurement points for the following common machines or machine components compressors, electric motors, fans and blowers, gearboxes, process rolls, and pumps. 

Dial-indicator methods (i.e., reverse-dial indicator and the two variations of the rim-and-face method) use the same type of dial indicators and mounting equipment. However, the number of indicators and their orientations on the shaft are different. The optical technique does not use this device to make measurements, but uses laser transmitters and sensors. 

An oven in the form of a tunnel mounted over or containing a continuous conveyor belt is used to shrink oriented films in the shrink packaging process. Also use a hot air blower on the film to provide the heat required in specific areas. 

The SIMS system is mounted on a UHV spectrometer which also has XPS, UPS, LEED and thermal desorption capabilities ( ). Heating is achieved by electron bombardment from a filament mounted on the manipulator behind the sample. Cooling is achieved by circulating liquid N2 or He. Temperatures of 25K can be reached. The samples used, Ni(lOO), Cu(17%) Ni(83%) (100) and (111) and Ag(lll) were oriented within 1 and cleaned in situ by standard heating and Ar ion sputtering procedures. 

All MC-ICPMS instruments are equipped with a multiple Faraday collector array oriented perpendicular to the optic axis, enabling the simultaneous static or multi-static measurement of up to twelve ion beams. Most instruments use Faraday cups mounted on motorized detector carriers that can be adjusted independently to alter the mass dispersion and obtain coincident ion beams, as is the approach adopted for MC-TIMS measurement. However, some instruments instead employ a fixed collector array and zoom optics to achieve the required mass dispersion and peak coincidences (e.g., Belshaw et al. 1998). 

Fig. 2.3.1 A schematic diagram of GARField magnet pole pieces and the field pattern they produce together with a magnified sketch of the sample and sensor mounting showing the relative field, gradient and profile [/(r)] orientations.

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