Gravimetric weight loss methods

The solvent removal can also be followed by gravimetric analysis of the weight loss. This method is used to determine the time necessary for complete solvent removal. Shown in Fig. 29 are such drying curves for 5 mm diameter cy-hndrical samples prepared with 16 wt % and 20 wt % cyclohexane. It is seen that most of the solvent is removed within the first day. However, the samples are held for an additional four days to achieve a porous structure with minimal amount of residual solvent. 

Subsequent work on catalyst characterization via reduction studies has involved gravimetric or volumetric techniques. The gravimetric method measures weight loss (due to O loss), while the volumetric method measures amount of H2 consumed [and amount of water formed (O loss)]. In the latter case, the amount of H retained by the catalyst can also be determined (20). The gravimetric technique has also been applied to sulfided catalysts (27). From these measurements, the stoichiometric state of the catalyst can be determined. 

Adsorbed amounts can easily be measured with high accuracy by means of the conventional volumetric (49, 50) and gravimetric (50) techniques. For static measurements the desorption temperature is increased by certain increments and the desorption carried out at constant temperature. Thermogravi-metric analysis (TGA) is a dynamic method by which the weight loss is detected by a balance while heating the catalyst continuously. The same type of information can be obtained as with the static methods, provided the heating rate is sufficiently low to attain the characteristic irreversibly adsorbed amount at any temperature. 

Many tests (e.g., titrimetric, gravimetric, colorimetric, and volumetric tests as well as loss-of-weight measurements and pressure measurements) have been proposed in order to determine carbon dioxide content. Methods based on monitoring carbon dioxide pressure generation and weight loss have been applied.t l... 

HPLC and GC analyses are two commonly used methods for determining the levels of impurities and residual solvent in the cake. Thermal gravimetric analysis is another very powerful tool. It detects not only the level of residual solvent, but also the temperature at which the solvent evaporates. If the cake weight loss due to solvent evaporation occurs at the melting point of the solid, this is a clear indication that solvent is trapped within the cake. 

Thermal Analyses. Thermal techniques such as differential thermal analysis, thermal gravimetric analysis, and derivative thermogravimetric analysis have been successfully applied to characterizing various minerals in coal (58). The methods are based on measurements of weight loss or heat transfer during phase changes at temperatures from ambient to over 1000° C. 

It is well known that polyacetylene is oxidized in air even at room temperature. Substitituted polyacetylenes are generally more stable, but their stability varies considerably, depending on the nature of the substituent ". One of the methods to evaluate polymer stability is to measure the onset temperature (To) of weight loss in the thermo-gravimetric analysis in air (Table 12). The To values of the polymers from prim- or sec-... 

Challier and Slade [175] reported the synthesis of nanocoinposite materials consisting of polyaniline molecules encapsulated between ultra-thin mixed metal hydroxide sheets which are propped apart by spacers of terephthalate or hexacyanoferrate(II) ions acting as pillars. The layered double hydroxides (LDHs) were prepared by the method of Drezdon [176] which were refluxed with aniline to synthesize aniline intercalated LDHs. In thermo-gravimetric studies, terephthalate/Cu/Cr LDHs as well as hexa-cyanoferrate(lI)/Cu/Al LDHs showed weight losses in two steps attributed to the removal of trapped water and thermal breakdown of the intercalated systems. The former material exhibited somewhat better thermal stability than the latter one. 

Silica content may be determined by either the precise, tedious gravimetric silica procedure (2 or the more rapid but less precise fluosilicate method (3), The gravimetric method involves precipitation of the silica with acid, collecting the precipitate, ashing, volatilizing the silica with hydrofluoric acid and determining the weight loss after volatilization. 

Thermo gravimetric analysis (TGA) is another method of thermal analysis that measures the weight loss of a material as a function of increasing temperature. TGA is commonly used to determine selected characteristics of materials that exhibit either weight loss or gain due to desolvation... 

For the systems in which the trihydrate or the anhydrous salt was the solid phase, the solubility was determined by evaporating the solution to dryness. Where the hexahydrate was the solid phase, a visual polythermic method was used. Analyses were carried out gravimetrically K O was determined as KCIO P2O5 was determined as Mg2P207l and water was determined by weight loss during calcination. 

The permeation rate is determined by the gravimetric method. The permeation device, after it has been assembled, is weighed and then placed in a temperature-controlled cavity with constant flow of nitrogen or clean air to sweep away the permeated chemical vapor. After a period of time, perhaps days, the tubing is weighed again and the permeation rate is determined by weight loss over elapsed time. Since... 

Of the various physical techniques that can be used for mineral identification, thermal methods such as weight-loss curves, differential thermal analysis, and differential thermo-gravimetric analysis are the most useful. However, as these methods are only appUcable to minerals that undergo some reaction involving a change in weight, or the evolution or absorption of heat, their use for heavy minerals is limited. A punched card system with differential thermal analysis data for minerals (Mackenzie [1962]) contains information on a number of heavy minerals. 

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