Ramp cooling

Equilibrium cooling or ramp cooling is a linear growth cooling from the equilibrium temperature. The temperature of the solution is lowered at a rate a, (K min-1) from the liquidus temperature (7 ) to the end temperature (Tg), while in contact with substrate. In this case, the kinetics of growth is limited by diffusion. 

Solution controlled temperature gradient could be step-wise or ramped cooling, or combination. 

Figure 2 Shelf and vial temperature for shelf-ramp cooling 2mL of 10% hydroxyethyl starch (HES) in a 5 mL vial instrumented with a 36 gauge externally attached thermocouple. Nucleation occurs at —14°C, after which the supercooling is consumed by the latent heat of ice crystallization. The subsequent solidification of the nucleated volume occurs with a gradual temperature decrease (From Ref 3).

The next stage in the zone-refining process is to move the furnace slowly and steadily to the right. The left-hand end of the bar will then cool and refreeze but with the equilibrium composition /cCq (Fig. 4.4c). As the furnace continues to move to the right the freezing solid, because it contains much less impurity than the liquid, rejects the surplus impurity into the liquid zone. This has the effect of inereasing the impurity concentration in the zone, which in turn then increases the impurity concentration in the next layer of freshly frozen solid, and so on (Fig. 4.4d). Eventually the concentrations ramp themselves up to the situation shown in Fig. 4.4(e). Flere, the solid ahead of the zone has exactly the same composition as the newly frozen solid behind the zone. This means that we have a steady state where as much impurity is removed from the... 

Adipic acid, 219.2 g (1.5 mol), and 77.6 g (1.25 mol) of 1,2-ethanediol are weighed into a 500-mL glass reactor equipped with a mechanical stirrer, a nitrogen inlet, and a distillation head connected to a condenser and a receiver fiask. The reactor is placed in a salt bath preheated at 180°C and the temperature is dien raised gradually to 220°C (see note at end of procedure) until the greater part of water has been removed (3 h). The reactor is cooled down to 160°C and vacuum is applied slowly to ca. 0.07 mbar (30 min). Temperature is ramped to 220°C (see note below) at a rate of l°C/min and reaction is continued for an additional 90 min. At the end of reaction, the carboxylic acid endgroup content is close to 1.90 mol/kg. No purification of final polyester is carried out. 

The steam valve is initially opened slowly by increasing Xg from 0 to 1 and then kept open until the reactor temperature, T), reaches Tmax- Then it is closed and the temperature is controlled at Tmax for time tjhoid- Then the cooling ramp is started. 

When the reactor temperature (Tl) becomes greater than Tmax (=240 F), PERIOD = 2, and the program turns the cooling water on with flow rate Fw. This flow is controlled with a proportional controller using control constant Kc, whose set point (Pset) is varied according to the time ramp function with setting kR and whose output to the valve is Pc. This ramp is horizontal until time period Tihold has passed. Then the setpoint is decreased linearly. The temperature is sensed using a pressure transmitter with output Ptt. 

Study the effects of the parameters of the cooling water ramp function (Tihoid and kg) on the selectivity, SEL. 

In situ XRD stndies of thermally and chemically induced transformations were monitored with a totally automated diffractometer-micrometer system (9). Samples were thermally ramped in 5°C increments from 30 to 160°C, maintained at 160°C for 0.5 hr, and then cooled in 5°C increments to 30°C under 500 torr hydrogen. 20 scans were obtained after each temperatnre increment. The individnal scans conld be stacked to show the temperature evolution of the stracture. 

Shown in Figure 15.5 are the temperature dependent XRD data for the 5% Pd-1% Sn catalyst. As noted above, the scans were offset in the order that they were obtained (the Time axis, as shown, is the scan sequence number and not the actual temperature). The inset of Figure 15.5 illustrates the temperature profile for the scan sequence. The first scan was obtained at room temperature, at which time hydrogen was introduced into the chamber at 500 Torr. The temperature was then ramped in 10°C increments to 160°C and XRD scans were taken after each increment. The sample was held at 160°C for I/2 hour, and then cooled to room temperature. After I/2 hour at room temperature, the sample was purged with dry nitrogen. 

Catalyst characterization - Characterization of mixed metal oxides was performed by atomic emission spectroscopy with inductively coupled plasma atomisation (ICP-AES) on a CE Instraments Sorptomatic 1990. NH3-TPD was nsed for the characterization of acid site distribntion. SZ (0.3 g) was heated up to 600°C using He (30 ml min ) to remove adsorbed components. Then, the sample was cooled at room temperatnre and satnrated for 2 h with 100 ml min of 8200 ppm NH3 in He as carrier gas. Snbseqnently, the system was flashed with He at a flowrate of 30 ml min for 2 h. The temperatnre was ramped np to 600°C at a rate of 10°C min. A TCD was used to measure the NH3 desorption profile. Textural properties were established from the N2 adsorption isotherm. Snrface area was calcnlated nsing the BET equation and the pore size was calcnlated nsing the BJH method. The resnlts given in Table 33.4 are in good agreement with varions literature data. 

Before performing TPO, the wet catalyst was dried under N2 flowing 10 Fh at 120°C for a period of 17 h before being slowly cooled to 20°C. Once the catalyst was stabilized at 20°C the pure N2 was switched to a 4 vol.% O2 in N2 mixture flowing at 10 1/h while the catalyst s temperature was ramped to 800°C at the rate of 8°/min. The O2 content of the gas mixture leaving the catalyst bed was measured by an Oxynos 100 paramagnetic detector and plotted with respect to either time or temperature. The plot of the vol.% O2 with respect to time was used to determine the O2 consumption of the catalyst. 

Cool on-column Capillary Ramped temperature Track oven Low concentration or thermally labile Minimal sample discrimination and decomposition... 

Heating and cooling ramps should be very small to ensure thermal equilibrium within the sample a maximum of 0.5 °C/min is recommended. 

Fig. 4.4 Temperature and power profiles for a Biginelli condensation (Scheme 4.24.a) under sealed quartz vessel/microwave irradiation conditions (see Fig. 3.17). Linear heating ramp to 120 °C (3 min), temperature control using the feedback from the reference vessel temperature measurement (constant 120 °C, 20 min), and forced air cooling (20 min). The reaction was performed in eight quartz vessels...

The immobilized carbamates (40 pmol) were transferred to a sealable 96-well Weflon plate, and admixed with 10 pmol each of various primary or secondary amines dissolved in 400 iL of anhydrous toluene. After sealing, the plate was irradiated in a multimode microwave instrument, first generating a ramp to reach 130 °C within 45 min and then holding this temperature for an additional 15 min. After cooling, the resins were filtered with the aid of a liquid handler and the filtrates were concentrated to obtain the desired substituted ureas in good purity and reasonable yields. Anilines reacted rather sluggishly and 2-substituted benzyl carbamates afforded somewhat inferior results. 

For catalyst treatments, the sample is transferred into the quartz reactor in vacuo, the reactor isolated, the gas flow commenced, and temperature linearly ramped to the desired value. After the sample has been at temperature for the desired time period, the sample is cooled to room temperature in the gas flow, the gas flow is stopped, and the reactor is evacuated. 

Figure 4.18 shows the results of a cyclic DSC evaluation of a sample of the aqueous IV formulation. The sample was analyzed in an open aluminum pan, being cooled and then heated (under nitrogen purge) through a series of three and a half freeze/thaw cycles at a temperature ramp of 10°C per min over the range of -50 to +25°C. This range was... 

Indium also has many of the characteristics that make Al and Ga very useful for such applications. Particularly important is its capacity to dissolve Si, Ge and several lanthanide and transition metals, producing highly reactive forms of the elements. Moreover In does not form binaries with Si and Ge and has a low-melting point. RNiGe2 compounds, for instance, were prepared from stoichiometric quantities of the components in fine powder mixed with a 10 fold quantity of In in alumina tubes. These, flame sealed in fused silica tubes, were slowly heated to 1000°C, held at this temperature for a few hours, ramped down to 850°C, held for an additional 4 days and finally cooled down to room temperature over the course of another 4 days. Compound isolation from the In excess was performed by centrifugation at 300°C through a coarse frit. Further purification was carried out by a 15-minute submersion and sonication in 6 M aqueous HC1 (Salvador et al. 2004). 

The experiments were carried out in a 2-L Parr reactor fitted with an internal cooling coil to cool the reaction mixture if necessary and to prevent runaway reactions. The temperature was controlled by a proportional-integral-differential (PID) controller. All experiments started at ambient temperature, which was raised to the desired reaction temperature, 93°C, in a nearly linear ramp over about 15 minutes for the propellants or 25 and 35 minutes for Composition B-4 and tetrytol, respectively. 

---