Microballs

A second general type of procedure, due to McBain [29], is to determine n by a direct weighing of the amount of adsorption. McBain used a delicte quartz spiral spring, but modem equipment generally makes use of a microbalance or a transducer. An illustrative schematic is shown in Fig. XVII-6. 

This method is smiple but experimentally more cumbersome than the volumetric method and involves the use of a vacuum microbalance or beam balance [22], The solid is suspended from one ann of a balance and its increase in weight when adsorption occurs is measured directly. The dead space calculation is thereby avoided entirely but a buoyancy correction is required to obtain accurate data. Nowadays this method is rarely used. 

Alongside tliese teclmiques, microbalance measurements of adsorjDtion capacities and kinetics, microcalorimetric measurements of adsorjDtion processes and temperature-programmed desorjDtion of base molecules have provided useful infonnation about tire tliennochemistry of adsorjDtion processes and tire acidity characteristics of zeolites [46]. 

P. A. Cutting, in Vacuum Microbalance Techniques 7,51, Plenum Press, New York (1970). 

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

Microbalances typically have capacities from 2 g to 5 g, with 20 to 50 million displayed divisions. 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as Hquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many Hquids in real time (14). 

Bulk and surface imprinting strategies are straightforward tools to generate artificial antibodies. Combined with transducers such as QCM (quartz crystal microbalance), SAW (surface acoustic wave resonator), IDC (interdigital capacitor) or SPR (surface plasmon resonator) they yield powerful chemical sensors for a very broad range of analytes. 

Isotherm measurements of methane at 298 K can be made either by a gravimetric method using a high pressure microbalance [31], or by using a volumetric method [32]. Both of these methods require correction for the nonideality of methane, but both methods result in the same isotherm for any specific adsorbent [20]. The volumetric method can also be used for measurement of total storage. Here it is not necessary to differentiate between the adsorbed phase and that remaining in the gas phase in void space and macropore volume, but simply to evaluate the total amount of methane in the adsorbent filled vessel. To obtain the maximum storage capacity for the adsorbent, it would be necessary to optimally pack the vessel. 

The tapered-element oscillating microbalance (TEOM) sensor, as described by Patashnick and Rupprecht, consists of an oscillating tapered tube with a filter at its free end (Fig. 13.40). The mass of the filter increases due to the collected aerosol and produces a shift in the oscillation frequency of the tapered tube that is directly related to mass. 

Patashnick, H. and F..G. Rupprecht. Conrinuoiis PMm Measurements Using Tapered Element Oscillating Microbalance. /. Air Waste Manage. Assoc. 41 (1991), pp. 1079-1083. 

Balken,m. beam girder band (Anat.) corpus callosum, mikrowage,/. beam microbalance, -wage, /. beam balance. 

Mikro-spatel, m. micro spatula, -stativ, n, micro stand, -tomschnitt, m. microtome section. -trichter, m. micro funnel, -verbren-nung,/. microcombustion, mikrovolumetrisch, a. microvolumetric. Mikro-wa(a)ge, /. microbalance, -welle, /. 

When using a modern thermobalance which incorporates an electronic microbalance requiring small sample weights, the following operating precautions should be noted. 

An electrochemical quartz crystal microbalance (EQCM or QCM) can be used to estimate the surface roughness of deposited lithium [43],... 

Film-forming chemical reactions and the chemical composition of the film formed on lithium in nonaqueous aprotic liquid electrolytes are reviewed by Dominey [7], SEI formation on carbon and graphite anodes in liquid electrolytes has been reviewed by Dahn et al. [8], In addition to the evolution of new systems, new techniques have recently been adapted to the study of the electrode surface and the chemical and physical properties of the SEI. The most important of these are X-ray photoelectron spectroscopy (XPS), SEM, X-ray diffraction (XRD), Raman spectroscopy, scanning tunneling microscopy (STM), energy-dispersive X-ray spectroscopy (EDS), FTIR, NMR, EPR, calorimetry, DSC, TGA, use of quartz-crystal microbalance (QCMB) and atomic force microscopy (AFM). 

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