Void detectors

Non-destructive testing. NDT represents a large and diverse field in which a number of review papers have been published in recent years(6,10-13). Brief mention only of the most important techniques is given below because few are currently readily applicable to adhesive joints in civil engineering. The techniques in general are void detectors. 

Void Detector for Boiling Water Systems - W. K. Anderson... 

By far the majority of non-destructive testing (NDT) techniques associated with adhesive bonds take place after the joint has been made, and can usually be carried out at the manufacturing point or during service. Most techniques are void detectors and, although it is claimed that the cohesive strength of the adhesive is being assessed, this is unlikely to be the case. 

Figure 9.14 Calibration curve for GPC as log M versus the retention volume Vj, showing how the location of the detector signal can be used to evaluate M. Also shown are the void volume Vy and the internal volume Vj in relation to Vj, and KVj as a fraction of Vj.

The retention time of the non-adsorbing methane (ti) is the measure of the column void volume or holdup. Ethylene is adsorbed by the catalyst, hence it does not reach the detector until the available surface is saturated, at which point ethylene breaks through and is detected by the sensor (t2). The adsorbed volume of ethylene is given simply by ... 

Reaction products were analyzed by on-line gas chromatography with a Shimadzu GC-14A gas chromatograph equipped with a 50 m CP Sil-5 fused silica capfllary column and a flame ionization detector. Reaction intermediates were identified by GC-MS. Samples were taken after 50 h on stream when the activity of the catalyst was stable, with n-nonane and n-dodecane as internal standards. Space time was defined as t = e Voat/vgas, where e is the void fraction of the... 

Virial coefficients (GC) 5 Viscosity detector (SEC) 452 Viscous fingering (SEC) 447 Visualization techniques (TLC) (see derivatization (TLC)] Void volume, column (LC) 371 measurement 372 Volman trap (GC) 211 Volume of a theoretical plate 49... 

Figure 1.3 A schematic chromatogram-. VR, retention volume VK-, adjusted retention volume V, elution volume of peak V0, void volume W, peak width VM, holdup volume OX, volume of injector XY, volume of detector, including volume of tubing.

Several compounds have been proposed for the measurement of the void volume, including sodium nitrate solution, water, deuterium oxide, fructose, acetonitrile, tetrahydrofuran (THF), meso-erythritol, gluconolactone, and 2,4-dinitronaphthol. The elution volume of a number of these compounds has been measured in 10-90% aqueous acetonitrile and acidic-aqueous acetonitrile. The results are given in Figure 3.9 where the volumes in A and B were measured in aqueous acetonitrile and in C and D were measured in aqueous acetonitrile containing 50 mM phosphoric acid. Methanol (a) and deuterium oxide (g) showed two peaks when monitored by a refractive index detector (Figure 3.9C). 

Figure 1 shows a typical chromatogram, which includes a time axis, an injection point, and an analyte peak. The time between the sample injection point and the analyte reaching a detector is called the retention time (t ). The retention time of an unretained component (often marked by the first baseline disturbance cansed by the elution of the sample solvent) is termed void time (tg)- Void time is related to the column void volume (Vq), which is an important parameter that will be elaborated later. 

The void created by raised panel floors should be provided with smoke detectors and considered as a separate detection zone. The actual design and detection method used depends on several variables including ventilation and routing of electrical/data cables. Passive or active protection may be considered based on the results of a fire hazard analysis. 

The second stage is data acquisition. This stage is entered when the operator starts the instrument. The instrument makes the first injection and signals the microcomputer via Intelink. After a delay proportional to the void volume of the column set, data are collected on a time basis (constant flow rate assumed) at the predetermined rate from each of the detectors selected, up to a maximum of three simultaneous detectors. VHien the sample run is complete, the instrument again signals the microcomputer which places the instrument in a hold state while it reads the operational parameters from the instrument for that sample and... 

Figure 8. Gel filtration of ethylated (/ -0-4)-(/ -/ )-DHP 16. Solid line Ethylated (/ -0-4)-(/ -/ )-DHP 16 after removal of low molecular weight fractions. The column was calibrated with (/ -0-4)-(/ -/ ) lignin substructure model trimer 6 (molecular weight 642) /3-0-4 lignin model dimer 1 (molecular weight 348) and polystyrenes of molecular weight 9000, 4000 (void), 2200 (indicated by A). Column Sephadex LH-20, 1.1 x 48 cm. Eluent DMF, 13.5-14.4 ml/hr. Detector Refractive index detector RI-2 (Japan Analytical Industry Co., Ltd.).

The onset of thermal diffusion depends on the gas concentrations, the sample surface area, the rate at which the sample cools to bath temperature, and the packing efficiency of the powder. In many instances, using a conventional sample cell, surface areas less than 0.1 m can be accurately measured on well-packed samples that exhibit small interparticle void volume. The use of the micro cell (Fig. 15.10b) is predicated on the latter of these observations. Presumably, by decreasing the available volume into which the lighter gas can settle, the effects of thermal diffusion can be minimized. Although small sample quantities are used with a micro cell, thermal conductivity detectors are sufficiently sensitive to give ample signal. 

One of the rare drawbacks of the detector is its total lack of response for any volatile material. Accordingly, the classical method of the determination of the void volume by elution of an isotopic analog of one of the eluent components cannot be used. 

Improved separation of natural oil TGs using short columns packed with 3-//m alkyl bonded-phase particles was reported by Dong and DiCesare (88). The HPLC columns used were HS-3 high-speed columns packed with 3-/um C18 bonded-phase particle (100 X 4.6-mm ID) with a column void volume of ca. 0.8 ml and efficiencies in the range of 13,000-15,000 theoretical plates (measured under optimized conditions) and HS5 C,8 columns (125 X 4.6-mm ID packed with 5-yttm particles). Two detectors were used a modified refractive index detector having an 8-/rl flow cell and 0.007-in. ID inlet tubing and a variable-wavelength UV/visible detector. 

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