Gravimetric Monitoring Research Articles

Enzymatic assay of hydroxybutyric acid monomer formation in poly(β-hydroxybutyrate) degradation studies

A novel method for monitoring the degradation of poly(β-hydroxybutyrate) based on the enzymatic assay of β-hydroxybutyrate (HBA) monomers has been developed. The method is particularly applicable to forms of the polymer, such as fibre and microcapsules, for which conventional surface and gravimetric monitoring techniques are not readily applicable. The method involves the use of enzyme HBA dehydrogenase in a reaction that converts nicotinamide adenine dinucleotide (NAD) to its reduced form (NADH). The conversion is associated with an increase in light absorbtion at 340 nm which thus serves to indicate the concentration of HBA monomer in the sample. The application of the methodology to the degradation of poly(β-hydroxybutyrate) gel spun fibres has been used to demonstrate its potential use as a quantitative monitoring technique in the study of the hydrolysis of this polymer.

In situ gravimetric monitoring of arsenic desorption in GaAs atomic layer epitaxy

The As desorption from an (001) GaAs surface in atomic layer epitaxy (ALE) is investigated by a real-time in situ gravimetric monitoring system. The direct gravimetric information from the growing surface is monitored during an ALE cycle. It is shown that the growth rate decreases to 0.75 ML/cycle with increasing H2 purge time according to the As desorption from the surface, and two kinds of stable reconstructions exist in the ALE process. Based on the results, a growth model is proposed for the growth of the smooth ALE surface on a (2 × 4) reconstructed surface.

Formation of air-cast cellulose acetate membranes Part II. Kinetics of demixing and microvoid growth

In Part I of this work, we described results concerning formation of macrovoids in air-cast cellulose acetate (CA) membranes. In Part II, we report on the kinetics of membrane formation in one of the systems studied in Part I. The system consisted of 2-methyl-2,4-pentanediol (MPD), acetone and CA 394-60S (with a weight-average molar mass, M w=2.39·10 5 g/mol). The evaporation rate of MPD was found to be negligible at room temperature and gravimetric monitoring of acetone evaporation allowed determination of the average mixture composition during membrane formation. Acetone evaporation rates were measured gravimetrically for MPD/acetone mixtures and for two ternary membrane-forming solutions. Composition change of the ternary mixture at the plate (belt) side during 20 min of membrane formation was monitored by infrared spectroscopy. Microvoid (pore) growth kinetics was studied by quenching partially formed air-cast membranes (precursors) in water after predetermined intervals of air exposure. The microvoids on precursor surfaces were then visualized by scanning electron microscopy (SEM). The image analysis of electron micrographs yielded modal (most frequent) values of microvoid diameters, D, for the two surfaces of each precursor. Plots of D 2 versus time were found to be linear with slope values around 1·10 −10 cm 2/s. We suggest that the microvoid growth rates may be related to the “slow” reptational diffusion of entangled polymer chains. Polymer reptation is about five orders of magnitude slower than diffusion of solvent or nonsolvent and may be, therefore, rate-controlling.

Factors affecting the gravimetric determination of the oxidative stability of oils

The variables affecting the gravimetric determination of the oxidative stability of oils were evaluated, including the storage temperature, amount of sample and surface area of the sample in contact with atmospheric oxygen, which was varied by using containers of different diameters. Based on this study, we propose the optimal working conditions for development of the oxidation step prior to gravimetric monitoring.

Gravimetric corrosion monitoring and mathematical fitting of atmospheric corrosion data for carbon steel

AbstractThe corrosion of carbon steel was studied in different atmospheres at sites in the Basque Country. A bilogarithmic law relating weight losses and exposure time is proposed. Coefficienss a and b in the basic equation were formulated as functions of the measured atmospheric parameters. The system of equations was solved by a multiple linear least squares regression. The final equation In p = 2·689 + 2·784[SO2]0.4 + 3·102[NaCl]0.6 + 0·846 In tw − 3·853[SO2]0.5[NaCl]0.6 − 0·212 In t + 0·024[SO2] In t−0·32[NaCl] In t + 0·381[SO2][NaCl] In t − 0·178tw In t, where p is penetraiion (μm) and t and tw are total exposure and time of wetness (years), fits the experimental results with a correlation coefficient of 0·985. Its predictive power, using results from the literature, was good when the environmental parameters were in the studied range.

Exceptional susceptibility of ceria-supported rhodium catalyst to inhibitory SMSI effects including acetone hydrogenation

Complementary lines of evidence, as follows, are presented to show that hydrogen pretreatments of a ceria-supported rhodium catalyst (Rh-CeO 2) at rather moderate temperatures (653–573 K) cause this system to progress deeply into a strongly inhibitory SMSI state: (i) by comparative measurements, with a continuous-flow microcatalytic reactor system at a fixed reaction temperature of only 343 K, of the activities of samples of the Rh–CeO 2 material for hydrogenation of acetone vapour to isopropanol, after prereduction at temperatures in the range 413 - 653 K. Complete loss of hydrogenation activity is thus demonstrated after reduction at 653 K, but full restoration of activity is shown to be achieved upon reoxidation in O 2 at 673 K followed by re-reduction at 413 K; (ii) by selective identifications, using proton NMR, of hydrogen chemisorbed on the rhodium of Rh-CeO 2 and its differentiation from hydrogen absorbed by, or adsorbed onto, the ceria support. These results of selective characterizations of H-Rh upon Rh-CeO 2 samples prereduced in H 2 at temperatures in the range 473–573 K confirm a severe inhibition of the ability to produce H-Rh species after prereduction at 573 K, and thus provide complementary evidence for creation of an SMSI-state in Rh/CeO 2 after prereduction at this relatively low temperature. Additional information on rhodium-induced modifications of surface and bulk properties of Rh/CeO 2 samples exposed to vacuum, H 2 or O 2 at various temperatures emerges from comparative measurements of Rh/CeO 2 and CeO 2 using the techniques of electron spin resonance, volumetric evaluation of carbon monoxide chemisorption, and gravimetric monitoring of hydrogen absorption/adsorption.

Gravimetric crustal motion and movement monitoring: Problems and interpretation

Gravimetric crustal motion and movement monitoring: Problems and interpretation

An Extended Range Liquid Extrusion Method for Determining Pore Size Distributions

A liquid extrusion method for determining pore volume distributions has been developed that is especially useful for, but not restricted to, characterizing fibrous materials. It involves gravimetric monitoring of liquid that drains from an initially saturated sample as incremental increases in pressure gradient are applied across it. Any liquid that wets the material can be used. Using techniques devised for applying an extended range of pressure gradients, it is possible to detect pore radii from 0.5 to 1,000 μm. Results for a variety of substrates show the sensitivity of the method. For example, bimodal distributions obtained for woven fabrics reflect the larger interyarn and smaller intrayarn pores. Advantages and limitations of the method and the meaning and usefulness of the data are discussed.