Gravimetric sorption

Contact angle measurements Isothermal microcalorimetry Gravimetric sorption Inverse gas chromatography Differential scanning calorimetry Thermogravimetric analysis Isothermal microcalorimetry Infra red analysis X-ray diffraction... 

DENSITY MEASUREMENTS. Helium densities of the extracts were determined so that the gravimetric sorption data could be converted to volume fractions needed to calculate x parameters. The results of these measurements are shown in Table III. The density of the extract was observed to decrease with increasing size of the added alkyl group. These results are qualitatively similar to those of Liotta t al.(14), who studied the effects of O-alkylation on the physical structure of the native Illinois No. 6 coal. 

An all-glass apparatus was used for gravimetric sorption measurement with benzene as adsorbate. Prior to the measurement, the sample was heated to 360 C at a rate of 5 C/ min with simultaneous evacuation to 1.3 10 Pa, and further degassed at that temperature for 3 h. Then the sample was cooled down to 32X3, at which the benzene adsorption isotherm was measured. 

Hageman et al. [3.13] calculated the absorption isotherms for recombinant bovine somatotropin (rbSt) and found 5-8 g of water in 100 g of protein, which was not only on the surface but also inside the protein molecule. Costantino et al. [3.72] estimated the water monolayer M0 (g/100 g dry protein) for various pharmaceutical proteins and for their combination with 50 wt% trehalose or mannitol as excipient. They compared three methods of calculating MQ (1) theoretical (th) from the strongly water binding residues, (2) from conventional adsorption isotherm measurements (ai) and (3) from gravimetric sorption analysis (gsa) performed with a microbalance in a humidity-controlled atmosphere. Table 3.5 summarizes the results for three proteins. The methods described can be helpful for evaluating RM data in protein formulations. 

Kaltenecker-Commercon JM,Ward TC, Gungor A, McGrath JE (1994) Water resistance of poly(imide siloxane) adhesives diffusion coefficients by gravimetric sorption. J Ad hes 44 1,85... 

Differential Vapor Pressure. Gravimetric Sorption, and Piezoelectric Sorption Methods... 

The experimental values reported for the differential vapor pressure, gravimetric sorption, and piezoelectric methods are the weight fraction of solvent in the polymer solution and the pressure of the solvent vapors in equilibrium with the polymer solution. Differential vapor pressure measurements are performed by adding a known amount of solvent to a weighed polymer sample and measuring the vapor pressure of the solvent over the polymer solution (Bawn et al., 1950). 

The chemical and physical structure of coal has been shown to control the sorption of vapors in a bituminous coal. Micro-gravimetric sorption studies with nitrogen, carbon dioxide, and water have shown markedly different sorption processes. 

Currently there is considerable effort being expended in several institutions to continue sorption analyses to evaluate the porosity and internal surface area of coal. These studies involve studies of vapor (2, 3, 4 and liquid (5) sorption analyses. We have employed proven micro-gravimetric sorption equipment and techniques (6) for a detailed examination of the thermodynamics and mechanisms of sorption of various vapors on well-characterized coals. Specifically, the coals used for this study are classified as C-bituminous, Illinois No. 6, from the Sahara... 

Comparison of the porosity evaluation results based on immersion calorimetry and gravimetric sorption measurements, for activated chars from a high volatile bituminous coal... 

Supplemental gravimetric sorption/desorption data for CX>2 pressures bebw atmospheric were detained by conventional procedures using a Cahn recording vacuum microbalance, for greater precision in the low solubility range. 

Inverse Gas Chromatography. A technique that promises to circumvent many of the problems attendant to gravimetric sorption experiments is Inverse Gas Chromatography (IGO. Until recently, all reported applications of IGC to the measurement of diffusion coefficients have used packed chromatographic columns in which the stationary phase is supported on a granular substrate. Equations similar to those developed by van Deemter et al. (22) are used to calculate the stationary phase diffusion coefficient from the spreading of the elution profile. The equation developed by van Deemter is commonly written as... 

Henry constants and saturation concentrations obtained from the gravimetric sorption measurements on silicalite particles and diffusion constants obtained by the membrane method of methane and n-butane. After Vroon et al. [72-74]... 

The Rubotherm system provides gravimetric sorption measurements carried out in a closed measuring cell completely thermostated up to 700 K or down to 77 K without temperature differences or corrosive parts inside the whole measuring cell with pressures up to 100 MPa and a mass sensitivity down to 1 gg using a magnetic suspension balance to measure mass transfer under controlled environments (14). 

Figure 15. Gravimetric sorption/desorption vs. time date for the system PVC/DMP/CO2. (Reproduced with permission from Ref. 15. Copyright 1989 IUPAC.)...

Figure 9. Adsorption isotherm of nitrogen at 77 K on silicalite-l obtained with conventional gravimetric sorption equipment. (Reproduced with permission from reference 46. Copyright 1990.)...

Isopiestic sorption/desorption methods, i.e., gravimetric sorption, piezoelectric sorption, or isothermal distillation... 

A resolution of nanograms could be realized by Mikkilineni et al. Measurements were also made as a function of time to obtain diffusion coefficients. Comparison with gravimetric sorption measurements demonstrated the accuracy of the experiment. Ref presents some details about the electronic circuit, the mounting arrangements for the quartz crystals and the sorption cell. Because very thin films are applied, equilibrium solvent absorption also can be obtained at polymer mass fractions approaching 1 (i.e., for small sol-... 

Standardized density determinations are based on the displacement of a liquid by the sample in a calibrated volume. A standard for the measurement of the displacement of a gas is in preparation. Other methods apply differences of the buoyancy in gas and in a liquid by means of a hydrostatic balance. When preparing a sample for a thermogravimetric or gravimetric sorption investigation... 

However, it should be mentioned that even gravimetric sorption measurements may become uncertain at very low pressures due to gas adsorption at the vessel or basket including the sorbent or other parts of the microbalance. Therefore it is recommended always to perform calibration measurements, i. e. measurements with the empty balance bearing no sorbent material but being exposed to the same sorptive gas. 

Automation of gravimetric sorption instruments is not an easy matter and for precision measurements permanent supervision of the adsorption / desorption process by an experienced co-worker is strongly recommended. 

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