Sample preparation metal coating

The clean laboratory for trace metals was divided into three areas entrance laboratory (with clothes changing annex), instrument laboratory, and ultraclean sample preparation laboratory, all under positive pressure with active charcoal filtered air. Personnel using the clean rooms were required to wear hair caps, polyethylene gloves, laboratory coats, and designated shoes. These items are worn only in the clean rooms. 

Broadband Dielectric Spectroscopy provides a direct experimental access to the molecular relaxations of polymers over a broad frequency and temperature range. It is also especially suitable for the investigation of thin polymer films, because it does not suffer sensitivity loses with decreasing sample amount. This technique does require a special sample preparation for thin films, because of the need to have metal electrodes and good electrical contacts at both interfaces. Spin-coating, one of the most commonly employed methods for the preparation of... 

Materials. Biaxially oriented polypropylene (PP) films of 50 um thickness were obtained from 3M and have been described (2). PMDA-ODA (PI) was Kapton H polyimide from Dupont. Copper-plated PTFE films were obtained from Spire Corporation (Bedford, MA). They were prepared using the Ion Beam Enhanced Deposition (IBED) process in which a 100 nm thick Cu film was vapor-deposited onto a PTFE substrate in the presence of a beam of 400 eV Ar+ ions of 25 uA/cm2 (IQ). Shortly before SIMS analysis, the Cu film was removed slowly by peeling at 90° in ambient conditions. Metal-coated PI films were prepared by sputtering 50 nm Cr and 1 um Cu onto a 50 um thick Kapton film on both sides. Thermal annealing was performed in a vacuum chamber at 2xl0 6 torr using a quartz lamp as the heating source. The samples were held for 15 min at the desired temperature and then cooled down to ambient temperature inside the chamber for about 2 hours. Just prior to SIMS analysis, the metal films were peeled slowly at 90° and then immediately introduced into the vacuum chamber of the instrument. 

The two main techniques commonly discussed in the literature are known as direct observation (or frozen hydrated observation) and the observation of replicas. Both techniques involve the fast freezing of the sample in a cryogen such as liquid nitrogen, propane, or freon. The frozen sample is then fractured to reveal the interior features. This fractured surface can be coated with a metal film or observed directly. Often, the metal film is removed from the sample and observed as a replica. This type of procedure allows the creation of a permanent archive of the samples prepared, and the observation is the same as with any other electron microscope sample with no concern about contamination of the microscope or beam damage to the sample. 

Figure 24. Electron micrograph showing the relatively featureless surface and the fractured interior of a water-in-oil emulsion. This image was prepared with a metal-coated frozen sample, a modification of direct observation in which the sample is coated sufficiently to prevent sample charging but not enough to produce a replica. This technique still requires an electron microscope with...

For the preparation of the three-way catalysts several procedures were used, which are summarized in Table 1. The reference catalyst samples were prepared by coating monolithic ceramic substrates with a cell density of 400 cpsi and a wall thickness of 6.5 mil. After drying and calcination of the coated monoliths, they were impregnated Avith the precious metals, precious metal loadings and precious metal ratios of choice. This method will be referred to as preparation method A. The novel catalyst technologies were prepared by placing the precious metals directly onto the washcoat. To do so, several methods were used. Preparation method C was used to apply the precious metals on all the washcoat components. The methods B and D were used to apply the precious metals selectively on one or more of the washcoat components. Details of the catalysts are given in Table 2. 

Research on the dielectric characteristics of coating films was performed using a teraohmmeter. Five samples of different coating compositions were examined on a metal substrate. Samples were prepared on the basis of two types of water dispersion rubbers, CSM-200 and CSM-400. The test samples were placed in a drying oven. The electrical resistance of the samples was measured via thermocouple wires that were connected to the teraohmmeter. The results of tests are shown on Figures 5.3 and 5.4. 

Atomic force microscopy is a powerful method for surface characterization. It is based on an interaction between a tip mounted to a cantilever and the substrate. The latter is systematically scanned to obtain a three-dimensional picture of its surface (Figure 3.105). Contrary to other methods in high-resolution microscopy, the samples can be examined at ambient conditions, and even nonconducting materials do not require coating with a metallic conductor, so the effort for sample preparation is markedly reduced. 

Freeze-Fracture Method A sample preparation technique used in electron microscopy in which specimens are quickly frozen in a cryogen and then cleaved to expose interior surfaces. In some techniques, the sample is then observed directly in an electron microscope equipped with a cryogenic stage in other cases, the cleaved sample is coated with a metal coating to produce a replica, which is observed in the electron microscope. See also Electron Microscopy. 

SPME is a solventless sample preparation technique that can be applied to the analysis of BTEX in water, air, and soils. In SPME, analytes from aqueous or gas phases are concentrated by absorption into a solid phase. The sampling device consists of a short, thin rod of fused silica (typically 1 cm length and 0.11 mm diameter), coated with an absorbent polymer (SPME fiber), attached to a metal rod (fiber holder), and surrounded (in the standby position) by a protective sheath. This fiber holder is mounted in a modified gas chromatography (GC) syringe (see Figure 2.12 Chapter 2 of this book). 

In order to obtain more fundamental catalytic activity data of the catalytic materials of interest a number of model catalysts consisting of alkali metal and precious metal were prepared and tested for their ability to promote the reactions of water and carbon dioxide with solid carbon. These tests provide basic information about the ability of the catalysts to catalyse soot combustion with CO2, H2O and O2. Results are summarized in Table 2. Both alkali metal and precious metal (PM) doped supports were used. Two supports were used which can be categorised as an inert and a reducible oxide support. Clearly the presence of the alkali metal has a significant effect on catalysing the soot combustion as anticipated. The effect of the reducible oxide support is not significant. In addition to the experiments summarised in Table 2 two further samples of alkali metal supported on an alumina foam and cordierite wall flow filter were prepared and coated with soot in a similar manner to that described above. Measurement of the soot combustion characteristics of these samples in O2, CO2 and H2O were very similar to the powder samples. 

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