Compression cell

For tensile tests the Instron 1125 tester is fitted with pneumatic-hydraulic grips which can be opened and closed by remote control. We have installed microswitches to indicate when a specimen is in place, and pneumatic actuators to eject the specimens from the grips after each test. For flexure tests either a three or a four-point compression-cell flexure fixture is substituted for the grips. We have attached air jets to the lower supports to eject the specimens. 

The compressive behavior of a DL is a very important mechanical property. Therefore, to study the mechanical properties of various diffusion materials (carbon cloths, carbon fiber papers, and carbon felts), Escribano et al. [251] used a compression cell. The sample diffusion materials were placed between the two plates of the cell, and the thickness and deflection of each sample were measured as a function of the compression pressure. These researchers... 

PP bead foams of a range of densities were compressed using impact and creep loading in an Instron test machine. The stress-strain curves were analysed to determine the effective cell gas pressure as a function of time under load. Creep was controlled by the polymer linear viscoelastic response if the applied stress was low but, at stresses above the foam yield stress, the creep was more rapid until compressed cell gas took the majority of the load. Air was lost from the cells by diffusion through the cell faces, this creep mechanism being more rapid than in extruded foams, because of the small bead size and the open channels at the bead bonndaries. The foam permeability to air conld be related to the PP permeability and the foam density. 15 refs. 

FTIR Microspectroscopy.3 A microscope accessory coupled to a liquid-nitrogen-cooled mercury-cadmium-telluride (MCT) detector can be used to obtain an IR spectrum. This is possible in both the transmission and reflectance modes. Several beads are spread on an IR-transparent window (NaCl, KBr, diamond) and possibly flattened via a hand-press or a compression cell. The IR beam is focused on a single bead using the view mode of the microscope. The blank area surrounding the bead is isolated using an adjustable aperture, and a spectrum is recorded using 32 scans (<1 min). A nearby blank area of the same size on the IR transparent window is recorded as the background. 

Beam Condensers.4c Beam condensers are used to focus the IR radiation from a beam that is typically 8 mm in diameter to one that is around 2 mm at the sample plane. This allows the analysis of 50-100 resin beads without KBr dilution. A diamond compression cell is used to flatten beads and to support the sample throughout the measurement. The same diamond cell without beads is then used to record a background spectrum. 

Kramer shear/compression cell (single-blade or multiblade cells)... 

Voisey, P.W. 1977. Interpretation of force-deformation curves from the shear-compression cell. J. Texture Studies 8 19-37. 

The forces between sterically stabilised particles have been measured with a compression cell (see page 223)213, and have been shown (as expected in the light of the foregoing discussion) to be short-range, with a range comparable with twice the contour length of the lyophilic chains. For sterically stabilised systems the total interaction energy can be written as... 

Szczesniak, A.S., et al. 1970. Behavior of different foods in the standard shear compression cell of the shear press and the effect of sample weight on peak area and maximum force. J. Texture Studies 1 356-378. 

Breakdown by confined compression can be tested in a compression cell similar to that in compaction tests, except that the normal forces used are greater here. A British Standard method59 packs a sample of specified quantity and size grade into a steel cylinder, 150 mm nominal diameter a plunger is inserted into the open end of the cylinder and the whole compressed in a compression testing machine. The load is slowly increased up to 400 kN and the product is then sized. A similar test has been used in assessing friability of pellets and coal. 

Schubert (1987) proved that friction between the piston and compression cell wall was the main cause of inaccurate results in previous works on compressibility. The use of strain gauges on the inner part of the piston to measure the pressure directly at the powder surface facilitated separating the effects of wall friction from those of true pressure on the surface of the consolidated powder (Figure 7). 

FIG. 7 Device for measuring piston pressure used with compression cell in place of the standard piston. 1, Pressure knob 2, miniature receptacle 3, cover 4, PTFE rings 5, guideway 6, threaded ring 7, beam 8, resistance strain gauges 9, piston 10, thin foil (drawn to enlarged scale in figure) (from Ehlermann and Schubert, 1987). 

If different researchers used cells of various dimensions for compressibility evaluation, results might not be comparable. To prove this, Yan and Barbosa-Canovas (2000) investigated how compressibility (C2) values statistically responded at compression cells of different geometry. Cylindrical confined uniaxial compression cells of diameters 10, 21, and 30 mm and depths 20, 40, and 60 mm, respectively, were used for the experiments. Results showed that the cell diameter and compression bed height had significantly different effects on the compressibility of ground coffee and cornmeal powders. 

FIG. 21 Three positions for padding foam in the powder bed, as confined in compression cells (from Yan and Barbosa-Canovas, 2000). 

Yan, H. and Barbosa-Canovas, G.V. 2000. Compression characteristics of selected food powders The effect of particle size, mixture composition, and compression cell geometry. In Selected physical properties of food powders , Doctoral Thesis, pp. 82-113. Biological Systems Engineering Department, Washington State University. 

Figure 4.25 Micrograph of a polymer laminate, showing two broad layers and a narrow middle layer. The sample was mounted in an NaCl compression cell and spectra were collected automatically in 2 p,m steps along the white line indicated. A Centaurp,s Analytical FTIR Microscope System from ThermoNicolet was used for the automatic data collection and results presented in this figure and in Figs. 4.26-4.28. [Courtesy of ThermoNicolet, Madison, WI (www.thermonicolet.com).]...

In addition to the engineering skills and the access to the full range of supporting laboratory capabilities (bench development, in-process, analytical, physical chemistry, microbiology), scaling-up requires a variety of measurement apparatus (e.g., compressibility cell to measure flows through beds of solids at different compression), as well as the frequent assembly of dedicated apparatus or pilot units (e.g., units to measure fouling rates of surfaces over short-term test, small-scale... 

The thickness of the steric layers attached to colloidal particles can be measured by a variety of techniques viscometry (Doroszkowski and Lambourne, 1968 Fleer e/a/., 1972), sedimentation coefficient measurements (Garvey et ai, 1974), photon correlation spectroscopy (Garvey et al., 1976), surface balance measurements (Doroszkowski and Lambourne, 1971 1973), compression cell measurements (Cairns et al., 1976) and even electrophoretic measurements (Homola and Robertson, 1975). 

Kim YC, Kanga JH, Park SJ, Yoon ES, Park JK (2007) Microfluidic biomechanical device for compressive cell stimulation and lysis. Sensor Actuator B 128 108-116... 

Values of (l-8o) and r a limited number of materials are given in Table 11.7. These values were measured in a compression cell (Section 2.9.2, Chq>ter 2). Egure 11.34 relates to a typical filtration-compression cyde, conpared with a conventional separation. 

This article covers the preparation and presentation methods, both traditional and the more recently developed, used in sample analyses by mid-infrared spectroscopy. It focuses more on the so-called macrosampling techniques, and does not cover in detail some of the sample presentation methods, for example diamond-window compression cells (see example in Figure 7), more particularly used nowadays in studies made using an infrared microscope many of the microsampling techniques are, however, merely adaptations of the macrosampling techniques. 

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