Quartz-crystal measuring element

Determination of the pressure as a function of the combustion time is now mainly performed by means of piezoelectric pressure transducers. They operate such that the measured pressure that acts on their quartz-crystal measuring element via a diaphragm is transformed into a corresponding electric charge. After the electric charge is amplified, it is recorded by suitable measuring equipment. Quartz-crystal, barium titanate, and lithium sulphide can be used as the measuring elements in piezoelectric transducers. 

If the unknown crystal can be shaped into a wedge similar to the EFISH cell geometry, a similar sinusoidally varying signal is observed from which tensor elements can be extracted provided a reference sample of known properties is available. Quartz crystals have been characterized extensively (17) and can be obtained in the form of a wedge. They are often used as a reference material for both EFISH measurements and other crystals. 

Finally, real-time bulk measurements include an approach in which the frequency of an oscillator such as a quartz crystal is altered as mass is deposited on the oscillating element. Surrogate measurements are also employed, such as inference of mass concentration from the decreasing transmission of electrons from a beta source to a detector as mass is deposited on an intervening substrate (see Gebhart, 1993, for a review). 

While electrochemical methods provide powerful and sensitive ways of studying modified electrodes to provide information about electron-transfer kinetics and film porosity, they cannot provide information about structure or elemental composition. Thus complete characterization requires application of many of the nonelectrochemical methods described in Chapter 17. These encompass microscopy, high vacuum surface analysis, Raman and IR spectroscopy, and methods based on scanning probes, the quartz crystal microbalance, and measurements of contact angles. 

The frequency and amplitude of an oscillating quartz crystal are influenced by even a minimal mass load. A sensitive dew sensor was developed by using a Peltier-cooled quartz plate [54]. This sensor is capable of measuring relative humidity with an accuracy better than l.St o of the measured relative humidity in automatic dew-point hygrometry. Since the frequency but not the amplitude of specially cut quartz crystals depends strongly on the temperature, the dew-point temperature can be determined simultaneously with the same sensor element. Compared with optical dew-point hydrometers, this quartz sensor combines dewpoint detection and temperature measurement in a single element. 

The quartz-crystal as a measuring element can withstand pressures up to 1000 bar, i.e., 2000-3000 bar under static and dynamic conditions, respectively. Pressures even higher than that may be measured applying the compensation pressure method. The method implies decreasing the area of either the diaphragm or the piston relating to the measuring elements area. 

D. Johannsmann, I. Reviakine, E. Rojas, and M. Gallego, Effect of sample heterogeneity on the interpretation of QCM(-D) data comparison of combined quartz crystal microbalance/atomic force microscopy measurements with finite element method modeling. Anal. Chem., 80, 8891-8899 (2008). 

The quartz crystal microbalance (QCM) is an example of a piezoelectric crystal whose frequency response to mass changes can be used for atmospheric corrosion measurements. In this technique, a metallic corrosion sensor element is bonded to the quartz sample. Mass gains associated with corrosion product buildup induce a decrease in resonance frequency. A characteristic feature of the QCM is exceptional sensitivity to mass changes, with a mass resolution of aroimd 10 ng/cm. The classification of indoor corrosivity, based on the approach of the Instrument Society of America (ISA) S71.01-1985 standard and the use of a copper sensing element and QCM technology, is presented in Table 2.7. 

Density can be measured in the laboratory in a number of different ways depending on the need for accuracy and the number of measurements required. Solution density can be easily estimated with reasonable accuracy by weighing a known volume of solution. Very precise instruments for the measurement of density that work employing a vibrating quartz element in a tube are sold by the Mettler Company (Hightstown, New Jersey). The period of vibration of the element is proportional to the density of the material placed in the tube. With careful calibration and temperature control the accuracy of these instruments ranges from 1 x 10 to 1 X 10 g/cm. It is possible to use these instruments for on-line solution density measurement of fluid in a crystallizer (Rush 1991). 

In 1912 Shibata moved to Paris to study under Georges Urbain (1872-1938). He intended to study the rare earth elements, but Urbain advised him not to do so because such study required tedious fractional crystallization, which was not suitable for a foreign chemist with only limited time to spend. Instead, Urbain suggested that Shibata carry out absorption spectrographic studies of cobalt complexes. Fortunately, Shibata was able to use the newly obtained medium-sized quartz spectrograph of Adam Hilger, type E2, and he carried out absorption measurements of cobalt-ammine complexes (5). In Urbains s laboratory Shibata also learned from Jacques Bardet the technique of emission spectrographic analysis, which Shibata later used to analyze the rare earth minerals found in Japan. 

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