Volume Change Of Sample Research Articles

Preparation of exfoliated graphite by microwave irradiation

Exfoliated graphite (EG) is an important raw material for the production of flexible graphite sheets, which have been widely used as gaskets, thermal insulators, fire-resistant composites, etc. [1–3]. Recently this material was shown to have excellent capabilities for oil sorption and recovery [4,5]. The preparation of EG was usually done by rapid heating of either graphite residue or intercalation compounds, but also conducted by different heating systems, including inductively coupled plasma, laser irradiation and flame heating [1]. The exfoliation of graphite intercalation compounds by means of microwave irradiation was also reported, which gave no significant difference in resultant EG from those prepared by rapid heating [6]. The same conclusion was obtained from the analysis of pore structure inside the worm-like particles of EG prepared by microwave irradiation [7]. Exfoliation under microwave irradiation seems to be interesting process because it can be performed at room temperature. However an accumulation of the experimental data through the fundamental studies on the influences of the microwave irradiation power, the precursors of graphite and intercalate, for example, is required for the practical application of this process. In the present work, the exfoliation of two residue compounds with H2SO4 under microwave of different powers was carried out. The residue compound GIC1 was prepared through electrochemical intercalation (anodic oxidation) of H2SO4 with an electric power consumption of 7.7 A h/ kg, followed by water rinsing [8,9]. The residue compound GIC2 was prepared through washing the intercalation compound synthesized in concentrated H2SO4 with H2O2 at room temperature (chemical intercalation) [10]. SEM photos of these two residue compounds are shown in Fig. 1. The residue compound GIC2 was partially exfoliated along the c-axis of the original graphite flakes. Two precursors were exfoliated under microwave irradiation, applying different powers from 500 to 1000 W for 40 s. For each experiment, the precursor powder was placed at the bottom of the beaker in a layer of about 1 mm thickness, ensuring that all particles were in mutual contact. EG samples thus prepared were characterized by the mass loss during the exfoliation, BET surface area, bulk density, SEM observation and thermoexfoliation coefficient. Bulk density was measured from mass and volume of the samples after exfoliation. The thermoexfoliation coefficient defined as the volume ratio of exfoliated graphite to its precursor, VEG/VGIC, was calculated by measuring the change in sample volume before and after exfoliation. For comparison, two precursors were also exfoliated by a rapid heating to 1000 C. Under microwave irradiation, a marked exfoliation of the precursors was observed, accompanied by fuming and lightening. The characteristics of EGs obtained are summarized in Table 1. After microwave irradiation, a marked volume increase of the lump of both residue compounds after microwave irradiation were observed, just like in the case of rapid heating to 1000 C. EG obtained was confirmed to be composed from so-called worm-like particles as shown in Fig. 2. The pore structure in these worm-like particles was analyzed by an aid of image processing in our previous paper [7]. The apparent distance between neighbouring balloons on the worm-like particles looks different, depending on the precursor residue compound and also on exfoliation conditions. These distances in EG prepared from the precursor GIC1 under 1000 W power were not homogeneous, as shown in Fig. 2(a), but that

Microwaves phenomena during drying of apple cylinders

Dehydration of apple cylinders applying microwaves (3 and 10 W/g initial incident microwave power) combined with forced air (40 °C air temperature) was performed. Drying rate and sample temperature and volume were recorded in order to analyse the coupling of heat and mass transfer mechanisms and deformation–relaxation phenomena in line with the sample dehydration. Experimental results showed the effect of temperature raise on internal evaporation phenomena producing both plasticization of sample matrix and an increase of internal pressure. As a consequence changes in sample temperature and volume, as well as the drying rate and dissipated power showed a common pathway. A general description has been developed to explain the behaviour of apple tissue under microwave drying.

A new high pressure cell with sapphire windows for small-angle neutron scattering

The design and the construction of a cell for the study of the conformation and the structure of liquid crystal polymers under pressure is complex because of the high viscosity of these materials and the use of an external magnetic field to achieve a macroscopic alignment. We have developed a system reaching 1500 bar at 420 K, completely amagnetic, including a small leakproof inner cell sample container with a flexible wall and a larger outer cell resistant to high pressure, with sapphire windows allowing a 8 mm diameter neutron beam aperture, with scattering angles up to 14°. This cell is also equipped with a double sample volume, in order to measure sample volume changes by a differential method.

Influence of sucrose solution concentration on kinetics and yield during osmotic dehydration of mango

The effect of the sucrose solution concentration on the process kinetics and yield during osmotic dehydration of mango (Kent var.) cylinders has been studied. Processes were carried out at 30 °C, using 35, 45, 55 and 65 °Brix sucrose, at atmospheric pressure (osmotic dehydration) and by applying a vacuum pulse (50 mbar for 10 min) at the beginning of the process (pulsed vacuum osmotic dehydration, PVOD). Kinetics of sugar gain, and water loss, as well as changes in sample mass and volume was analysed. Effective diffusion coefficients in the fruit liquid phase were also estimated. Microstructure of the mango samples after 15 min of PVOD treatments were examined by scanning electron microscopy. Effective diffusion coefficient in the fruit liquid phase increased when sucrose concentration decreased and was always higher in pulsed vacuum osmotic processes. These give rise to tissue impregnation with sucrose solution to an exceptional extent for the treatment with 45 °Brix, which induces a very high sugar gain-water loss ratio.

In Vitro Exposure of Proteins to Ozone

An in vitro system has been developed to expose proteins to ozone. The system is designed to deliver consistent and accurate levels of ozone over a range of concentrations (between 0.1 and ≥10 ppm) with extended exposure times (24 h or longer) in a humidified environment (100%). In the experiment presented in this article, ozone concentrations between 0.1 and 2.0 ppm were used. Ozone was generated by an electrical discharge ozonizer to ensure stability; it was continually monitored by an ultraviolet ozone analyzer and was precisely controlled by mass flow controllers, which gave reproducible results between runs. Humidity was closely regulated in the system to allow small amounts of protein solutions (50 μL or less) to be exposed without significant changes (<0.2%) in sample volume. The degree of surfactant protein-A (SP-A) oxidation by ozone was measured between runs to demonstrate the reproducibility of the system. A detailed description of the system is given, and protein oxidation detection methods and their limitations are discussed. Using these methods, we were able to assess oxidation of SP-A that apparently occurred prior to its isolation from the lung by bronchoalveolar lavage. This in vitro system allowed us to expose small amounts of protein to ozone in a simple, highly controlled, and reproducible manner.

Long Term Osmotic Dehydration Processes of Orange Peel at Atmospheric Pressure and by Applying a Vacuum Pulse

Osmotic dehydration is a useful tool to obtain orange peel products with good sensory acceptance and stability. Osmodehydration of orange peel has been carried out in different osmotic solutions (65 Brix sucrose, 55 Brix glucose and concentrated rectified grape must) at 40 and 50 C for different durations (0–10 days), at atmospheric pressure and by applying a vacuum pulse at the beginning of the process. Changes in sample composition (water and soluble solid contents), weight, volume, density and porosity were analyzed. In all conditions, samples reached the same sample solute content as the osmotic solution at about 24 h of treatment, and the concentration rate was faster when vacuum pulse was applied. Mass transfer behavior showed that impregnation of the peel pores occurred to a great extent, not only when applying vacuum pulse, but also in treatments at normal pressure, due to the capillary effects and pressure gradients generated in the tissue associated with structural changes. Impregnation contributed to compositional changes and weight development of the sample. The greater the osmotic solution viscosity, the lower the impregnation level at equilibrium, which was always promoted by vacuum pulse.

Modeling of simultaneous mass transfer and structural changes in fruit tissues

Osmotic dehydration of plant tissues promotes sample volume reduction in line with cell deformation while linked through bonding zones, thus leading to a shrunk cell network. The sample volume changes of apple slices throughout osmotic processes at 30°C, 40°C and 50°C were analysed by using sucrose solution of different concentration (25–65°Brix), in treatments carried out at atmospheric pressure and by applying a vacuum pulse. These volume changes are compared with the volume variations of sample liquid (water plus soluble solids) and gas phases in order to analyse their different contribution to sample volume development and the porous structure role.

Triaxial tests to determine a microstructure-based snow viscosity law

AbstractThis paper describes a new triaxial testing apparatus designed to determine the creep (viscoelastic) behavior of snow. The device is deformation-controlled and can apply strain rates between 10–7 s–1 and 10–2s–1 in tension and compression. The sample volume change is determined by measuring the displaced pore-air volume. During winters 1997/98 and 1998/99, &gt;100 compression and tension tests were carried out. It is shown that snow is a highly non-linear but ideal viscoelastic material with a strong strain-rate dependency. A selection of test results is provided. We show how snow viscosity varies with density and strain rate. In a final analysis we interpret our results with respect to snow microstructure in order to develop microstructure-based constitutive relations which can be implemented in finite-element programs. Our results clearly show that for snow densities and strain rates tested, straining of the grain bonds is the primary mechanism of deformation within the snow ice lattice.

Modular™ Systems At Work

Modular™ Systems At Work

Volume averaging, effective stress rules, and inversion for microstructural response of multicomponent porous media

A general volume-averaging technique is used to derive equations satisfied by the average scalar stresses and strains in multicomponent porous rock. The resulting equations are combined with general thought experiments to produce the effective-stress rules that determine the volumetric changes of the rock induced by changes in the confining and fluid pressures. The composite porous material specifically treated is an isotropic mixture of two Gassmann materials. Two distinct cases are considered depending on whether the grains at the interface between the Gassmann materials are either (1) welded together (no ‘‘cracks’’ can open between the two constituents) or (2) nonwelded (cracks can open) . The effective-stress laws determine not only the overall volumetric changes of a given sample (i.e., changes in sample volume, total pore volume, and fluid-mass content) , but determine as well the changes within each Gassmann component individually. This additional level of detail achieved in the analysis is referred to as inversion for the microstructural response. In the nonwelded case, the effective-stress law relating the variation of crack porosity with macroscopic changes in confining and fluid stress can be used to determine optimum strategies for increasing fracture\\crack porosity with applications to reservoir production analysis.

Evaluation of a predictive steady-state flow-injection method adapted to an open flow tube with a tracer

This paper describes the development and evaluation of a new approach to processing data from flow-injection systems. In this new approach, data from the leading edges of response peaks are used with appropriate mathematical models and curve-fitting methods to predict the steady-state signal that would be measured if sufficient sample were used to fill the flow tube with undiluted sample. This predictive steady-state data-processing option is adapted to and evaluated for open flow tubes. Predictive steady-state results for triiodide detected amperometrically are compared with results obtained by processing the same data sets by the more conventional peak-height, peak-width and peak-area options as well as directly measured steady-state signals of undiluted samples. All data-processing options yielded linear calibration plots, with deviations from linearity being significantly larger for the peak-width option than for the other options. Effects of changes in sample volume and flow-rate on quantitative results obtained with the different options were compared. Minimum sample volumes required by the steady-state methods are larger than those required for the other methods. However, both measured and predicted steady-state signals were much less dependent on sample volume and flow-rate than peak heights, peak areas or peak widths. Relative error coefficients for the steady-state options were 0.006%μl for changes in sample volume and 90%/ml s −1 (1.5%/ml min -1) for changes in flow-rate. Improvements in relative error coefficients for changes in sample volume of the predictive option relative to peak-height, peak-width and peak-area options are 55-, 633- and 167-fold, respectively. Improvements for changes in flow-rates for detectors that do not depend on flow-rate are 12-, 226-, and 36-fold, respectively (same order as above). The steady-state options are much more rugged than the peak-height, peak-area and peak-width methods.

Collapse behavior of sand: Discussion

The test data that are presented in paper are of most interest. The two constant deviator stress path tests may be compared with tests done by Lade et al. (1988) and Lade and Pradel (1990) for very loose sand under undrained conditions and by Chu (1991) and Chu et al. (1993) for medium loose to dense sand under non-undrained (or strain path controlled) conditions. It should be noted that testing procedures used in and test results obtained from these tests are verv similar. All above-mentioned tests were conducted uhder a constant deviator load and decreasing effective confining stress conditions. The prefailure instability observed in these tests appears to be same type. Although authors called instability observed in constant deviator stress path tests collapse behaviour, word drained does not carry same meaning as in a drained conventional compression test. This is because pore-water pressure of sample was controlled during tests, and thus volume change of sample is not totally free. As the volume of sample for constant deviator stress (q = 125 kPa) test was essentially unchanged and remained at 0.804 before sample collapse, this test was actually conducted under an undrained condition. Therefore, 'paper by S. Sasitharan, P.K. Robertson, D.C. Sego, and N.R. Morgenstern. 1993. Canadian Geotechnical Journal, 30: 569-577.

Kinetics of MoSi2 pest during low-temperature oxidation

The kinetics of MoSi2 pest, caused by oxidation in air, has been studied. Experimental results indicated that pest disintegration occurred at temperatures between 375 and 500 °C. The volumes of test samples increased with oxidation duration. Analysis of change in sample volume versus oxidation duration revealed that the pest disintegration consisted of two stages, namely nucleation (or incubation) and growth. The onset of the growth stage depended on the test temperature. More importantly, changes in sample volume were found to obey a linear relationship with time during the growth stage. Equations were formulated to demonstrate that the growth kinetics of pest disintegration was proportional to the rates of change in sample volume. The rates of volume change during MoSi2 pest were calculated to be 4.9 × 10−6, 2.8 × 10−5, 3.7 × 10−5, and 5.4 × 10−5 cm3/s at 375, 400, 425, and 450 °C, respectively; the growth kinetics increased with oxidation temperature. The activation energy for the growth stage of pest disintegration was determined to be 27.6 kcal/mole, which agrees well with the activation energy for the low-temperature oxidation of MoSi2.

Use of the 1294 keV photopeak of41Ar to correct for variations in liquid sample volume

A measurement of the41Ar content in the vial containing a liquid sample can be used to correct for variations in sample geometry due to changes in liquid sample volume. This technique makes use of the residual argon in the atmosphere when performing INAA of relatively short-lived radionuclides. The correction factor requires somea priori knowledge of the argon content of the solvent. Application of this correction technique requires the use of sample vials with consistent internal volumes. The need for correction is most evident with samples contained in vials of small cross section when using a vertically facing detector.

Elimination of signal strength dependency upon coil loading–an aid to metabolite quantitation when the sample volume changes

The phase, height, and width of NMR spectral lines from a constant number of nuclei are frequently dependent upon changes in probe Q factor and tuning, caused by motion of the sample and/or changes in its electrical conductivity and size. Thus quantitation of metabolites in biological samples can be difficult. When probe tuning and matching are rendered independent by the use of a tuned coupling coil for matching, use of a very low input impedance preamplifier can virtually eliminate such dependencies in the received signal. Likewise, by reciprocity, the use of a low output impedance transmitter greatly reduces the dependence of pulse flip angle upon sample characteristics. Experimental results verifying these statements are presented, and the time course of signals from a swelling, perfused pig heart and an external reference are plotted.

Deformation behavior of HDPE/(PEC/PS)/SEBS blends

AbstractImmiscible blends of high density polyethylene (HDPE) and an amorphous glassy phase consisting of either pure polystyrene (PS) or a miscible blend of PS and a polyether copolymer (PEC) were compatibilized with various amounts of a styrene‐hydrogenated butadiene block copolymer (SEBS). PEC is structurally similar to poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO). Using a liquid displacement stress dilatometer, the volume change of samples during uniaxial mechanical straining was determined and related to the various modes of deformation. Blends were fabricated by both injection and compression molding. Miscible PEC and PS blends were found to undergo a craze to shear yielding transition between 40 and 60% PS, which occurred at higher PS concentrations as SEBS was added. Blends with a HDPE matrix and a dispersed glassy phase showed reduced volume dilatation on adding SEBS, indicating better interfacial adhesion between the incompatible blend components. Increases in the sample volume were substantially less in blends with a PEC/PS glassy phase instead of pure PS, suggesting more effective compatibilization by the SEBS copolymer in blends with PEC. This trend is presumed to stem from an exothermic heat of mixing between the PS endblocks of SEBS and the PEC‐rich phases in the blend. Microscopic evidence of the improved adhesion and modes of deformation agrees with the results obtained by dilatometry. The volume dilatation of compression‐molded materials do not seem to be similarly affected by the composition of the glassy phase which may reflect morphological differences between injection‐and compression‐molded blends.

Measurements of the first normal-stress difference in a new Rheo-dilatometer for molten polymers: Triple-step-shear-strain tests for all K-BKZ constitutive equations

Following the 3rd of a triple-step-shear-strain sequence, the relaxation of the first normal-stress difference,N1 (t), has been measured for a sample (IUPAC “A”) of low-density polyethylene at 150 °C over a range of shear-strain magnitudes up to 28 shear units. A new cone-plate “Rheodilatometer” was used, giving sample volume change data as well as thrust and torque data during cone rotation. At 130 °C, prior measurements (described elsewhere) gave an upper limit of 0.001% for the volume change with IUPAC A; this gave an estimated error of only 1.7% in determiningN1(t) from time-dependent thrust data. Wagner's network-rupture model (based on a postulated strain-induced irreversible network disentanglement process) gave quantitative agreement withN1(t) data for IUPAC A at 150 °C over some of the ranges of time and shear-strain investigated. Wagner's earlier constitutive equation (of K-BKZ type) gave no quantitative agreement. Using a special choice of strain magnitudes in which the 3rd is half that of the 1st and 2nd, it is shown that a critical test of all K-BKZ equations can be made on the basis ofN1 (t) data only. This test excludes all K-BKZ equations for IUPAC A under the conditions here used. In all the present investigations, the 1st and 3rd shears had the same sign while the 2nd had the opposite sign.

EFFECTIVE STRESS AND SOIL CONSTANTS OF UNSATURATED KAOLINE

New concept of effective stress for unsaturated soil is proposed. It is assumed that the effective stress consists of two components. One is (σ-ua), which acts as if (σ-uw) of saturated soil and when soil is saturated, ua=uw is assumed. Another one is suction. It controls not only water content but also soil constants such as c' and mv. To prove above concept and to look into the relationship between suction and soil constants, drained (suction controlled) triaxial compression tests, including anisotropic consolidation and repeated loading, were performed on compacted Kaoline. When suction is kept constant, it seems that volume change and water content of sample are given only by the present stress state. Unified stress-strain equations were obtained using a factor α, which is defined by the new effective stress.

A Rheodilatometer for Molten Polymers

A new cone‐plate rheometer has been constructed in order to measure torque‐induced sample volume change ΔVs as well as the usually measured total thrust F and torque M. One aim is to use ΔVs data to assess the accuracy of time‐dependent values N1(t) of the first normal stress difference calculated from F data obtained in step shear and step shear rate experiments. The cone‐plate gap has an 8° angle and 25.4 mm radius. The total axial stiffness is 31.4 MN/m (when F is 100 N); F resolution is about 1 N. ΔVs resolution is about 0.001% at 130 °C; a silicone liquid is used as a dilatometer indicator. First applications made with a low‐density polyethylene sample (“IUPAC A”) at 130 °C subjected to a step shear rate of 1 s−1 for a duration of 14 s gave no detectable change in sample volume; it follows that, under these conditions, the maximum possible error (caused by sample volume changes) in N1 values is only 1.3% in our Rheodilatometer and 4.2% in the BASF Weissenberg Rheogoniometer which was modified by Meissner. It also follows that the effects of any temperature rise (e.g., due to work done in shearing the sample) are negligible in the present measurements. This gives reason to question the reliability of certain torque data recently obtained by Y.‐H. Lin with a Rheometrics System Four rheometer.

A method for dynamic dielectric measurements at microwave frequencies: Applications to polymerization process studies

A method for measuring dynamic variations of dielectric permittivity at microwave frequencies is given. The technique implies an extension of the cavity perturbation method. Possible volume or density changes of samples are taken into account. Measurements of polymerization processes show that the capabiities of the technique that proved to be very useful for fast, precise, and on-line measurements.