Isothermal hold

Figure 2.7 Activity test of an uncoated fused silica capillary after deactivation with poly(phenyliaethylhydrosiloxane), (A), and before deactivation, (B). Precolunn 15 x 0.20 m I.D. coated with SE-54. Test columns 10 a x 0.20 I.D. The column tandem was programmed from 40 to I80 c at a C/min after a 1 min isothermal hold with a hydrogen carrier gas velocity of 50 cm/s. The test mixture contained 10 n-decane, Cg-NH = l-aminooctane, PY 3,5-dimethylpyrimidine, C 2 n-dodecane, - 1-amlnodecane, DMA ...

The spray paint can was inverted and a small amount of product was dispensed into a 20 mL glass headspace vial. The vial was immediately sealed and was incubated at 80°C for approximately 30 min. After this isothermal hold, a 0.5-mL portion of the headspace was injected into the GC/MS system. The GC-MS total ion chromatogram of the paint solvent mixture headspace is shown in Figure 15. Numerous solvent peaks were detected and identified via mass spectral library searching. The retention times, approximate percentages, and tentative identifications are shown in Table 8 for the solvent peaks. These peak identifications are considered tentative, as they are based solely on the library search. The mass spectral library search is often unable to differentiate with a high degree of confidence between positional isomers of branched aliphatic hydrocarbons or cycloaliphatic hydrocarbons. Therefore, the peak identifications in Table 8 may not be correct in all cases as to the exact isomer present (e.g., 1,2,3-cyclohexane versus 1,2,4-cyclohexane). However, the class of compound (cyclic versus branched versus linear aliphatic) and the total number of carbon atoms in the molecule should be correct for the majority of peaks. 

In the rate equations, Eqn. 9-14 through Eqn. 9-18, we have assumed that Langmiiir s adsorption isotherm holds this assumption applies to the range of low adsorption coverages. 

This identity of formulation means that in normal cases correct results for the velocity equation will be obtained by assuming that adsorption equilibrium is established and the adsorbed molecules react at a rate proportional to their surface concentration when they possess the critical energy. Then, for the surface concentration 07 of every reactant the Langmuir adsorption isotherm holds ... 

A typical cure cycle used to process many thermoset epoxy composite parts is shown in Figure 10.3. It contains two ramps and two isothermal hold periods. The first ramp and... 

The more useful and common type of program used is the linear with isothermal holds of selectable durations before and after the temperature program ramp (Figure 6.17B). The duration of one or both of the isothermal holds may be zero. 

Figure 30 shows the CTL glow curves for the catalyst pre-adsorbed ethanol or acetone vapor. The catalyst is heated at a rate of 0.5 °C/s in synthetic air. The CTL intensity increases at high temperatures, and the total amount of CTL intensity L depends on the adsorption time At and the gas concentration C during adsorption. We can measure the gas at a very low concentration by measuring the value of L because L is proportional to the product of At and C in a region of low AtC where a Henry-type adsorption isotherm holds. 

Figure 34 shows the results for alcohol (methanol, ethanol, 1-propanol and 1-butanol), ketone (acetone and diacetyl), terpene (pinene and linalool), aldehyde (n-nonyl aldehyde) and ester (acetic acid n-amyl ester and n-butyric acid ethyl ester) of various concentrations. Because of the linear characteristics of the CTL-based sensor, the plots are located in a similar region for a certain type of gas of various concentrations where the Henry-type adsorption isotherm holds. Thus, we can identify these gases with various concentrations by simple data-processing. 

During further isothermal holding, the ApBq and AtBn layers will grow until one of initial substances A or B is consumed completely. The ArBs layer can then form and grow either in the ApBq-ArBs-AiBn-B system or in the A-ApBq-ArBs-AiBn system. 

Assuming the Butler-Volmer equation and Langmuir adsorption isotherm hold for this reaction, the charge-transfer rate in the presence of CO adsorption is... 

DOS neat resin. The value above the curve indicates the isothermal hold temperature (95° profile—refer to the lower time scale). 

Figure 17. Dynamic viscosity profiles for the TGDDM/DDS neat resin including isothermal holds at 115, 135, 155, and 170 °C.

Figure 7. Effects of pressure and coal particle size on yields of total volatiles, tar plus hydrocarbon liquids, all hydrocarbon gases, and methane, from bituminous coal pyrolysis. Heating rate = 1000°C/sec. Temperature = 1000°C. Isothermal holding time = 2-10 sec. Particle diameters, ixm C) 74 (X) 297-833 (O) 833-991 (14).

After reaching the upper temperature set limit, the temperature was held constant (isothermal hold) for several hours. The weight-loss curves (TG) are shown in Fig. 1. The weight losses recorded on lithium and sodium fluxes alone (Spec-troflux 100 and 200) caused by thermal decomposition above i000°C were negligible. Similar results were obtained with mixtures of anhydrite and sodium tetraborate. The latter showed a weight loss of less than 0.1% when heated at lOOO C for 1 h. 

FIGURE 255 Thermogravimetric analysis of silica samples, each heated at 40 °C per hour to 900 °C but interrupted by a 24 h isothermal hold period at various temperatures. 

The fact that water loss occurred at each isothermal hold period indicates that the dehydration was not instantaneous [74,75]. Had it been instantaneous, there would have been no discontinuous drop in mass indicated in Figure 255. Instead, the dehydration involves surface mobility and annealing that does require time. The time dependence of this annealing process is presented in Figure 256, which is a plot of the mass loss over time during each isothermal hold period. The shape of the curves looks much like what one would expect, with an initially fast loss in mass that gradually slows down. 

FIGURE 256 Amount of water lost by the silica samples in Figure 255 as a function of time during the 24 h isothermal hold periods. 

Figure 257 is a plot of the mass (H2O) loss observed at each isothermal hold temperature. It clearly shows the trend described above. At low temperatures, there is not much structural movement to release water vapor through silanol group condensation. At 600 °C there is considerable rearrangement of the surface, allowing significant loss of water over a period of 24 h. At 800 °C the process is so fast that condensation has almost reached its equilibrium limit before the temperature has been reached. Furthermore, because most of the water has already been lost by 800 °C, the change in mass is relatively smaller. 

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