Gravimetric blending

Standard Mixture—Use a gravimetrically blended gas standard containing levels of 2 to 204 mg/kg (4 to 340 ppmV) of each of the trace components listed in Table 1 to calibrate the detector s response. The standard gas mixture shall be prepared gravimetrically from known raw materials, and cross... 

Determination of the thermal decomposition temperature by thermal gravimetric analysis (tga) defines the upper limits of processing. The tga for cellulose triacetate is shown in Figure 11. Comparing the melt temperature (289°C) from the dsc in Figure 10 to the onset of decomposition in Figure 11 defines the processing temperature window at which the material can successfully be melt extmded or blended. 

The secondary gas standards are blended using the same apparatus as that employed to prepare the primary gravimetric standards. Precise measurements of the gas pressure and gas mass are carried out at each stage in the process and these enable the concentrations of the mixtures to be produced to within 1% of the concentration of the appropriate NPL primary standards. Up to three mixtures with the same nominal concentrations can be produced together. The mixtures are subjected to stability checks before their concentrations are certified with respect to NPL primary standards. 

To a continuing process the pigment dispersions are added directly to the plasticising equipment by volumetric or gravimetric measuring units. Further blending can then be done on a single- or twin-screw extruder. 

These synergy effects can be explained in two ways by investigating the process kinetics and by investigating the chemistry of the process. In our investigation of the co-processing of blends of crude oil vacuum residue and plastics we have used both methods. Data from thermo-gravimetric analysis were used for study of the process kinetics. The dynamic method for reaction (9.15) was used for the evaluation of the data. 

The blend morphology was characterized by dissolving the PEBA matrix, followed by gravimetric and microscopic analysis of the LCP phase. As expected, the average fiber diameter decreased as a function of DR °. It was noted that only relatively large drops were deformed into fibers, leaving nearly 50% of LCP in the form of small dispersed nodules. The fiber content as a function of DR followed a trend parallel to that of the mechanical properties. Longitudinal and trans-... 

The sample is then gravimetrically spiked with an isotopic analogue of the analyte (this analogue is termed the spike) such that the spike concentration matches the prior estimate of the natural analyte concentration in the sample. To prepare a sample solution blend, extraction (organic analysis) or acid mineralisation (inorganic analysis), followed by any clean-up stages necessary is carried out. 

This step is required if the spike solution of the isotopically enriched analogue only has an indicative concentration value. The spike solution is blended with a gravimetrically prepared solution of the pure reference isotope of known concentration. The concentration of the enriched isotope in the spike solution can then be calculated from a first reverse IDMS run of this blended solution. The revised value of the concentration can then be used to prepare a second blended solution. The first blend can be used as a mass bias standard, with the revised value for the concentration, and run alternately with the second blended spike solution. This second iteration should give an acceptable value for the spike concentration but if necessary a third iteration can be carried out. The run sequence for characterising the second blend is shown in Figure 6. 

All dilutions and blended solutions should be prepared gravimetrically. 

Calibration. The laboratoiy GC was cahbrated with a calibration gas which was blended gravimetrically. The amount of each component in the calibration gas was weighed with weights traceable to the National Bureau of Standards (NBS). The gas composition was verified on a GC, and composition values stated in the manufacturer s certification were used in the calibration. 

Gravimetric Method. This method determines the average linear density of the sample, irrespective of the variability of the density of fibers within the sample. It is therefore unsuitable for fiber blends in which the linear densities of the fibers are markedly different. This does sometimes happen, and blends of fibers having different crimp rigidities are sometimes processed to permit changes in yarn properties or fabric properties to be developed later, but generally speaking the staple yarn spinner will try to blend fibers of the same linear density, as this creates fewer problems in production. 

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