Quartz microbalance measurements

Mechanical investigations, for example, gravimetric measurements with the electrochemical quartz microbalance. Measurements of elasticity and deformation, for example, by indentation or by the film deflection method. 

Lead Pronounced effects of Pb (Fig. 3) were interpreted in terms of a third-body effect by Adzic and coworkers [35]. Pb adatoms suppress adsorption of hydrogen and strongly bound intermediates, in particular, those interacting with two or three surface sites. The same model was assumed for Bi and Tl. Adsorbed H was considered to take part in the formation of strongly bound intermediates [18,19]. Current responses to potential sweeps into the H adsorption region [18,19, 65] and crystal quartz microbalance measurements [66]... 

The hydrogen gas was later" shown to originate from the formaldehyde, not the water. Instead of cumbersome and slow ex situ weighing, Wiese and Weil measured the plating rate in situ with a quartz microbalance. They connected the electrode to a potentiostat to keep it at the plating... 

Figure 2. Examples of data characterized by strong concentration effects. Data are related to a quartz microbalance array exposed to six volatile compounds each measured three times at different concentrations. Only triethylamine (TEA in the plot) data emerge (experimental details in [10]).

Fig. 5 Quartz crystal microbalance measurements during potentiodynamic polymerization of 4,4 -dimethoxy-bithiophene in CH2CI2, 0.1 M TBAPFe,...

Deposition was performed using a vacuum system [1]. Before deposition of the alkoxlde, the sample was evacuated at 673 K for 2 hr, and the temperature was then lowered to 593 - 293 K for the deposition of silicon methoxlde. S1(0CH3)4 vapor was then admitted to the dried zeolite at a vapor pressure of 2.5 Torr. The resultant Increase of weight was measured by the quartz microbalance. After the deposition, the decatlonlzed zeolite was calcined Iji situ by oxygen at 673 K to remove the coke residue, while the Na-type mordenlte was treated with water vapor at 593 K. The amount of SI deposited was... 

Direct measurement of oxygen uptake can be performed with O2 sensors in the headspace of a closed system and organic deposition by measuring the weight changes with a quartz microbalance. This method was applied to investigate the dependence of jet fuel autoxidation on temperature and the presence of antioxidants . 

Daujotis et al. [32] have described the use of electrochemical quartz microbalance for the quantitative studies on monolayer adsorption on working mercury electrodes. Mercury was deposited on Pt at negative potentials (—0.4 to —0.5 V versus AgjAgCljKClgat)- In order to avoid undesirable transformation of mercury into, for example, larger droplets, the thickness of mercury film could not exceed 20 nm. Then, the linear dependence of the frequency change on the added mass was achieved. Applicability of such an electrode for EQCM measurements has been demonstrated by performing electroreduction of Pb(II) and T1(I), as an example. 

Figure 15 Modified Pourbaix diagram for Ti02 illustrating the origins of pH-dependent band energetics and the pH-independent back-ET kinetics for covalently anchored dye species. The open circles are experimentally determined values of Ecb (combined electrochemical quartz microbalance and reflectance measurements). The driving force for the overall back reaction [coupled electron and proton transfer cf. Eqs. (10) and (11) for analogous reactions at Sn02] is pH dependent, but the driving force for the back ET in isolation [cf. Eq. (10)] is pH independent. (Data from Ref. 78.)...

Film electrodes have been essential components of quartz microbalance studies of stoichiometry of many electrodeposition and dissolution experiments as well as polymer electrode characterization [25]. In the quartz microbalance, changes in mass are detected by measurement of changes in the resonant frequency of a quartz crystal oscillator as the mass adhering to the surface changes. The oscillation is feasible because thin-film metal electrodes (typically gold) applied to opposing faces of a piezoelectric quartz crystal serve both to induce the oscillation and to provide a site for electrochemical reaction. 

Experimentally, adsorption isotherms are determined by gravimetric or volumetric measurements for powders or porous adsorbents. For isolated flat surface a quartz microbalance or an ellipsometer can be applied to measure adsorption isotherms. 

As with all supramolecular structures, one of the most important issues is whether a direct relationship between the structure of a material and its function or properties can be established. In the following, some examples of polymer systems which show such a correlation will be discussed. The materials addressed will include block copolymers, polyalkylthiophenes and a multilayer system based on the self-assembly of polyelectrolytes. Detailed studies on the electrochemical properties of redox-active polymers, based on poly(vinyl pyridine) modified with pendent osmium polypyridyl moieties, have shown that electrochemical, neutron reflectivity and electrochemical quartz crystal microbalance measurements can yield detailed information about the structural aspects of thin layers of these materials. 

Two different adsorbents, activated carbon Norit R 0.8 Extra (Norit N.V., The Netherlands) and molecular sieve (type 4A, Merck), were used to study tert-butylbenzene, cyclohexane, and water vapour breakthrough dynamics. Structural parameters of the carbon adsorbent were calculated from benzene vapour adsorption-desorption isotherms measured gravimetrically at 293 K using a McBain-Bakr quartz microbalance, and nitrogen adsorption-desorption isotherms recorded at 77.4 K using a Micromeritics ASAP 2405N analyzer described in detail elsewhere.22,24 Activated carbon Norit has a cylindrical... 

Plasma polymer layers were deposited in the same reactor as described before. However, in this case, the pulsed plasma mode was applied. The duty cycle of pulsing was adjusted generally to 0.1 and the pulse frequency to 103Hz. The power input was varied between P 100 ()() V. Mass flow controllers for gases and vapours, a heated gas/vapour distribution in the chamber, and control of pressure and monomer flow by vaiying the speed of the turbomolecular pump were used. The gas flow was adjusted to 75-125 seem and the pressure was varied between 10 to 26 Pa depending on the respective polymerization or copolymerization process. The deposition rate was measured by a quartz microbalance. 

For measuring the Al-polymer (PP) peel strengths the plasma polymerization was performed using the previously described reactor. Then, the plasma polymer coated polymer samples were transferred into a separate electron beam metallizer (Auto 306, Edwards, UK). The thickness of deposited aluminium layers was adjusted to 150-200 nm using a quartz microbalance. The metal peel-... 

During the past few years four methods have been developed for the study of the kinetics of oxide film formation, all being semicontinuous in nature. The polarimetric method has been adapted by Lustman and Mehl (14) for the measurement of the oxidation of copper. A spectro-photometric method has been applied by Waber, Sturdy, Wise, and Tipton (15) to the study of the oxidation of tantalum while a differential pressure method has been developed by Campbell and Thomas (16) for a study of the oxidation of a series of metals and alloys at elevated temperatures. We have chosen to use a sensitive weight gain method (17,18) in which a quartz microbalance is placed directly in the vacuum system. 

Y. Ebara, H. Ebato, K. Ariga, Y. Okahata, Interactions of Calciinn Ions with Phospholipid Membranes. Studies on jr-A Isotherms and Electrochemical and Quartz-Crystal Microbalance Measurements , Langmuir, 10, 2267 (1994)... 

Recently, Feldmann and Melroy [131] utilized a quartz microbalance technique to simultaneously determine the net current and the partial anodic and cathodic currents in a single complete electroless copper bath. The cathodic current is calculated by converting the deposition rate measured with the microbalance into the unit of current, while the anodic current is computed by subtracting the cathodic current from the net current measured directly on the microbalance electrode. Using this technique, Feldmann and Melroy showed that the potential at which the reduction of the Cu-EDTA complex begins at 70 °C shifts by as much as 0.3 V in positive direction upon addition of formaldehyde. It was also shown that at a given potential, the rate of copper deposition increases with increasing formaldehyde concentration (Fig. 23). The observed catalytic effect of formaldehyde is attributed to an interaction between formaldehyde and the Cu-EDTA complex, possibly to the formation of Cu(EDTA)/formaldehyde complex. However, the detailed mechanism of this catalytic effect has not been clarified. 

As already mentioned, the principle of electroneutrality must be fulfilled in charged polymers. Consequently, in freshly prepared p-doped polymers, anions must compensate the positive charges within the polymeric chains. However, spectroelectrochemical studies [114], electrochemical quartz microbalance (EQMC) measurements [115], and SIMS and XPS measurements [116] on the mechanism of ion transport during charging and discharging of conducting polymers prove that discharging involves not only the expulsion of... 

Apparently, epitaxial thin-film model catalysts provide a well-defined initial state for a systematic study of microstructural changes and structure-activity correlations. Model catalysts were prepared for various noble metal-oxide combinations, including Pt, Rh, Ir, Pd, Re supported by Al Oj, SiO, TiO, CeO, VO, Ga Oj, etc. The number density of the metal particles (island density particles per cm ) and their size can be controlled via the NaCl(OOl) substrate temperature during evaporation and the amount of metal deposited (as measured by a quartz microbalance), respectively (Pig. 15.4). 

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