Bulk surface measurement setups

Teissie and coworkers detected rapid lateral movement of protons on a phospholipid monolayer-water interface by a number of measurements fluorescence from a pH indicator dye near the membrane surface, electrical surface conductance, and surface potentiaL These investigators found that the conduction of protons along the surface is considerably faster than proton conduction in the bulk phase (2 to 3 min versus 40 min for a comparable distance in their measurement setup). This novel conduction mechanism is proton-specific, as confirmed by a radioactive electrode measurement as well as by replacement with deuterated water. It is a consequence of cooperativity between neighboring phospholipid molecules the conduction mechanism disappears when phospholipid molecules are not in contact with each other. 

Figure 14.12 CO bulk electro-oxidation at PtRu alloys, (a, b) PcRui j /Ru(0001) (x = 0.07, 0.25, 0.47) surface alloys measured in a flow cell with a CO-saturated electrolyte, (c) Freshly sputtered Pto.sRuo.s bulk alloy in a rotating disk electrode setup (data from Gasteiger et al. [1995]), compared with a Pto.53Ruo,47/Ru((X)01) surface alloy.

The setup used to obtain CPAP data was different from that of the last section. Pre-deactivated samples of catalyst are available, and the HT reactions themselves do not (further) deactivate the catalyst. Hence we worked with the pre-deactivated samples, measuring observed rates of an HT reaction as a fiinctimi of temperature, with each sample generating an Arrhenius-type plot at a constant level of deactivation. The samples were from Run 242, using Illinois number 6 coal as the feed solid and Shell 324M as the catalyst. The catalyst pdlet is O.S mm in diameter and 4 mm in length and has a bulk density of 0.78 g/ml, an average pore diameter of llsA. and a specific surface area of 180 m /g. It contains 3.4 percent NiO, 19 percent MoO, and 63 percent AlnO. The HT reaction used... 

It is important to determine the conductivity and flat-band potential ( ft) of a photoelectrode before carrying out any photoelectrochemical experiments. These properties help to elucidate the band structure of a semiconductor which ultimately determines its ability to drive efficient water splitting. Photoanodes (n-type conductivity) drive the oxygen evolution reaction (OER) at the electrode-electrolyte interface, while photocathodes (p-type conductivity) drive the hydrogen evolution reaction (HER). The conductivity type is determined from the direction of the shift in the open circuit potential upon illumination. Illuminating the electrode surface will shift the Fermi level of the bulk (measured potential) towards more anodic potentials for a p-type material and towards more cathodic potentials for a n-type material. The conductivity type is also used to determine the potential ranges for three-electrode j-V measurements (see section Three-Electrode J-V and Photocurrent Onset ) and type of suitable electrolyte solutions (see section Cell Setup and Connections for Three- and Two-Electrode Configurations ) used for the electrochemical analyses. 

IR surface analysis is not restricted to solid/gas or solid/liquid interfaces, but can also be used to investigate liquid substrate surfaces (liquid/gas interfaces) and even solid/solid interfaces buried in the bulk of a solid sample. Even though the experimental setup and the measurements of such samples are fairly complex and far from a routine analytical technique, two examples shall be described here in order to show the potential and the diversity of IR spectroscopy in the field of surface analysis. In both cases, an experimental setup equal or similar to RAIRS is used with the light incidence angle being the only variable that must be adapted to the specific requirements of the sample system. In the first... 

Figure 18.8 Setups for measuring surface and bulk resistivity. (After Ref [74].) Table 18.7 Resistivity classification of conductive thermoplastics.

There are three ways of measuring ultrasonic birefringence. To measure stress in an entire specimen, one may measure the time of flight of ultrasonic waves as a function of propagation direction. For smaller sections of sample, shear wave velocities are measured as a function of the orientation of the plane of oscillation of the shear wave. Surface stress can be ultrasonically measured using the velocity of Rayleigh waves as a function of direction. Any of these methods will yield the direction of principle stress and relative stress intensities between samples of identical materials. To find actual values of stress, one must know the value of the acoustoelastic coefficient of the material. An experimental setup for measuring bulk acoustoelastic coefficients has been reported by Koshti. ... 

The negligence of the bulk resistance of metallic samples due to the ratio of high contact resistance to low bulk resistance is comprehensible. But for composite material development, for example, it is reasonable to take bulk properties into account. Therefore, the test setup maybe modified according to Figure 6.15. Two needles have only punctiform contact and measure the potential difference across the sample regardless of the surface properties (Kreuz, 2008). Hence, in addition to information about contact properties, information about bulk properties are provided within the same measurement due to slight intrusion of the needles into the surface and a straight-line current path assumed. 

The X-ray attenuation is a measure to describe the X-ray interaction with a respective element or compound. Overall it decreases with rising energy of the photons and increases with increasing atomic number. This results in rather large penetration depth and thus enables studies of volumes representative for the regarded material. In comparison to other spatially resolved characterization techniques such as electron microscopy. X-ray microscopy is therefore generally considered a bulk technique, unless special experimental setups or low energy X-rays are employed to e.g. remain surface sensitive. 

A febrication procedure of bulk electrodes was first proposed by Lev s group [19] and was subsequently widely employed for the development of carbon ceramic electrodes. The common feature of these electrodes is the high content of carbonaceous materials. Generally, a sol is first mixed thoroughly with the desired amount of the carbon-based material. Then, the mixture is packed into one end of a plastic body that includes a stainless steel wire as an electrical contact (Figure 46.5). After sol condensation, polymerization, and gel drying, the resulting electrodes are polished to yield a smooth surface required for electrochemical measurements. In this setup, the sol-gel material, with or without nanomaterials, serves as a binder for the carbon-based conductive material. 

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