Quartz crystals vapours using

The use of a quartz crystal microbalance for measuring vapour backstreaming from mechanical pumps Vacuum, Volume 16 (11), 633-637,1966... 

Zhao, C.Z., Pan, Y.Z., Ma, L.Z., Tang, Z.N., Zhao, G.L., Wang, L.D. (2002) Assay of fish freshness using trimethylamine vapour probe based on a sensitive membrane on piezoelectric quartz crystal. Sens. Actuators B 81 218-222. 

Piezoelectric hygrometers (Fig. 6.S6) These consist of a quartz crystal with a hygroscopic coating (Fig. 6.S60 and Section 6.3.3). Two crystals are usually employed and the wet gas (sample) and dry gas (reference) are passed over them alternately (normally every 30s—Fig. 6.566). The crystals absorb and desorb. The difference in angular frequency Am is proportional to the concentration of water vapour by volume. Capable of high precision. Can monitor moisture contents of the order of 1 to 3000 ppm by volume. Usually measures up to dewpoint of 310 K. Fast response but expensive. Sample must be dean to avoid contamination of the crystals. Complex sampling system. Suitable for on-line use. 

Mercury binding leads to an increase of mass of the gold layer which can be detected by electro-acoustic transducers based on quartz microbalance (QMB the abbreviation QCM = quartz crystal microbalance is also widely used), surface acoustic waves (SAW)—devices [20] or microcantilevers [21,22], Adsorption of mercury vapour increases resonance frequency of shear vibrations of piezoelectric quartz crystals (Fig. 12.2). This process can be described by Sauerbrey equation [23]. For typical AT-cut quartz, this equation is... 

Colorimetric detection of solvent vapours using MIPs deposited on quartz crystals... 

The quartz crystal microbalance device (QCM)21-24 allows one to measure the change of the mass of the films. This method is based on the ability of a piezoelectric quartz crystal to oscillate at a resonance frequency determined by the mass of the crystal. For these measurements, gold is evaporated directly onto the surface of such a quartz sensor which is then exposed to the vapour or solution of the adsorbate. What makes this method very valuable is that it can be used like SPR for monitoring molecular adsorption/desorption at the surfaces in situ. 

From eqns. (77) and (78), the vapour cloud parameters n and A can be also obtained by variation of the coefficients. Fig. 49 shows the measured vapour distribution curves of aluminium obtained by evaporations with a standard commercially available 270° bent electron beam gun. A 12kW, lOkV electron beam power supply and a quartz crystal thickness and rate monitor were used [256]. At an aluminium evaporation rate of 1.8 nm s 1, the cosine exponent equals n = 2.3 with no isotropic component A = 0. With increasing rate the exponent increases and also the isotropic component appears. With rates of 10.5 and 81.4 nm s"1 the corresponding characteristic data are n = 4, A = 0.14 and n = 5.8, A = 0. 14. 

Transpiration or gas saturation techniques have been widely used for the measurements of vapour pressures [90,91]. An inert gas is passed over the sample and the amount of material transported as a function of temperature is determined. Different analytical methods have been used to quantify the mass transferred. The main advantages of this method are the large temperature range accessible and the small amount of sample needed (-30 mg) for the experiments. Head-space analysis has also been used by various investigators. The vapour in equilibrium with a solid is either measured directly by an absorption technique [92] or indirectly [93]. Vapour pressures can be also measured indirectly by using a quartz resonator where the frequency of the quartz crystal changes as a function of the thickness of the material deposited on its surface [94,95]. 

Lai C.S.I., Moody G.J., Thomas J.D.R., Mulligan D.C., Stoddart J.F. and Zarzycki R. (1988) Piezoelectric quartz crystal detection of benzene vapour using chemically modified cyclodextrins. J. Chem. Soc. Perkin Trans., 2,319-324. 

Chemical vapour deposition (CVD), or more specifically, organo-metallic CVD can also be used to prepare ferrite thin films (Itoh, Takeda Naka, 1986). A mixture of acetylacetonate complexes of the desired metal is evaporated in a quartz boat (number 1 in Fig. 3.27) and is reacted with O2, which is introduced directly in the deposition zone. By adding a second furnace (B), an additional component evaporating at a different temperature can be transported to the substrate. Glass or MgO single crystals can be used as the substrates an annealing up to 1(X)0°C is performed on the film to improve its crystallisation. Spinel thin films (Ni, Ni-Zn) have been prepared by this method. 

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