Crystallizers temperature recorders

The heat capacity of the crystal was measured in the 0.06-0.28 K temperature range using a relaxation method (see Section 12.2.3). A small power supplied by the heater rose the temperature Tc of the crystal above TB by a few millikelvin. When the thermal equilibrium was reached, the heating power was switched off, and the exponential decay of the crystal temperature was recorded by means of an LR700 bridge (see Section 10.8), at a rate of 5 sample/s. 

The rate of ethylidyne formation was measured by recording the partial electron yield signal as a function of time after setting the crystal temperature to a preestablished value. An example of the results is shown in Figure 2 for the conversion of at... 

A model for crystallization point of the urea melt sprayed into the granulator was developed based on acoustic spectra recorded from sensor position A during a trial period of 24 hours. A flow sheet of the liquid urea feed process can be seen in Figure 9.7. Sensor A is mounted onto an orifice plate inserted in the main supply pipeline of liquid urea (see Figures 9.6 and 9.7). The reference values used to calibrate the model are the crystallization temperature (called the jc point ), as determined by the pilot plant laboratory (heat table visual nucleation/crystallization detection). 

Fig. 9 Initial rates of growth of C246H494 crystals normal to 110 and 100 planes, Gno and G10o, versus crystallization temperature from an initially 4.75% solution in oc-tacosane. The associated interference optical micrographs show typical crystal habits recorded in situ during growth from solution at selected temperatures. The experimental G values are averages over many crystals (from [29] by permission of American Chemical Society)...

In Fig. 5 we compare HREEL spectra recorded after exposing the flat and stepped Ag surfaces at T = 105 K to small amounts of 02 dosed with E[ = 0.39 eY and at a crystal temperature T = 105 K. The angle of incidence was chosen normal to the crystal for Ag(l 0 0) and nearly normal to the (1 1 0) nanofacets for Ag(4 1 0) and Ag(2 1 0). HREEL spectra indicate that at this temperature only ad-molecules are observed on Ag(l 00), at least for small exposures. This is witnessed in the HREEL spectra by the loss at 81 meV [55], corresponding to the internal stretch motion of adsorbed 02, and by the absence of intensity in the frequency region of the O/Ag stretch, between 30 meV and 40 meV [62]. On Ag(4 1 0) partial dissociation occurs since two Ag/O stretch losses are present, at 32 meV and at 40meV, while the internal 02 vibration is visible at 84meV [96]. On Ag(2 1 0), on the contrary, only the low frequency losses are present, indicating that the admolecules are unstable [97]. Our first conclusion is therefore that open steps cause 02 dissociation and that this mechanism is very effective on Ag(2 1 0) and less efficient on Ag(4 1 0) where the terraces have a finite width. Also in this latter case,... 

When the deposition rate and the system pressure shown on the recorder are confirmed to be steady, the deposition rate reading and the crystal temperature were recorded. Then changing the thermostat control of the circulating bath, while the plasma polymerization is kept at the steady state, lowered the temperature of the crystal. The deposition rate at the next temperature is read and recorded after steady-state readings are obtained at the new temperature. In this way, the relationship between deposition rate and substrate temperature can be obtained at a set of flow rates and power. A similar procedure is repeated for another set of flow rates and power. 

Figure 6. ISRS data from a-perylene crystal at two temperatures, recorded with transient grating experimental arrangement. Oscillations in each sweep due to 80- and 104-cm optic phonons. Data contain sum and difference frequencies that produce beating pattern.

The crystallization behaviour ofthe material is probed by DSC. A sample of the polymer (0.01 g) is accurately weighed and encapsulated in an aluminium container for DSC. The sample is placed in the DSC chamber (see Chapter 1) and then heated to 250°C and the temperature held for 5 min. The sample is then cooled at 20°C/min to room temperature. The same sample is then scanned at 20°C min from room temperature to 250°C in order to record the melting transition curve. To observe non-periodic phenomena, the sample is first heated up to 250°C at 20°C min and held at this temperature for 5 min. The sample is then rapidly cooled to 160°C and held at this temperature for 12 h it is then rapidly cooled to 120°C and held for 12 h, then cooled and held at 90°C. The sample is then cooled at 20°C min to room temperature. Recording a heating scan will reveal multiple transition peaks. 

Adjust the pressure to the selected value (for example, a pressure which gives a desired melting temperature). Melt the sample, then lower the temperature rapidly to the value chosen for crystallization, and record how the crystals grow with time. 

If an experiment is performed in which the temperature is recorded to detect the point where crystallization begins, one is more likely to find a zone instead of a point. This is due to the different nucleation conditions in each measurement, which is dependent strongly on the statistical distribution of nucleation incidents (metastabile zone). Thus, a different supercooling will occur in each measurement before nucleation starts, which will then control the crystal growth. This leads, of course, to differently detected crystallization temperatures (hence a zone and not a point). 

Differential scanning calorimeter (DSC, Netzsch 409PC) was employed to record the crystallization temperature of the samples. Measurements were carried out in the temperature range of 50 — 1000 "C at a heating ratio of 10 °C /min. 

A TG-DTA system was employed for recording crystallization temperature. Measurements were done in the temperature from 30 800°C employing a heating rate of 10°C /min. Based on the result of DTA, conversion of glass into glass-ceramics was carried out in a resistance furnace. By the DTA results, the sample was raised to 700°C at a rate of 5°C /min for 2 hours, then the temperature was decreased to room temperature at a rate of lO C /min. 

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