Evolution monitoring

The productivity and quaiity objectives of today s industry require tighter controi and the development of new process technologies. These new demands have led to the development of more sophisticated sensors for all process stages. 

The evolution of US-induced crystallization around the glass transition temperature for metallic glass was monitored by electromagnetic acoustic resonance, which allowed resonance frequencies and internal frictions to be measured. In an as-cast glassy sample, such frequencies jumped up just above the glass temperature transition at the beginning of the process under ultrasonic vibration this was ascribed to nano-crystallization as confirmed by an X-ray diffraction profile, which was absent in the absence of US. Irregular A-shaped internal-friction peaks were also observed prior to abrupt crystallization [48]. 

Resonant US spectroscopy is also the technique of choice for studying the vibration behaviour of the metastable p phase near the martensic transformation of a single crystal Cu-27.96 at.% AI-3.62 at.% Ni shape memory alloy. The elastic constants C, of the anysotropic material and the internal friction Q (Cj) were determined, and the elastic constants C and C44 found to be the quantitities controlling the vibrational response of the p phase near the martensic transformation on the other hand, the evolution of the internal friction was found to be correlated with the elastic behaviour of the alloy [49], 

Ultrasound-based sensors for metal-coated fiber optic measurements based on interferometric determination of the displacement using a Michelson interferometer have also been designed. The input acoustic field can be detected by using two reference methods, namely (a) time-delay spectroscopy with a calibrated hydrophone (a hydrophone with known frequency response determining the sound pressure, the input displacement being obtained by simple algebra) and (b) the interferometric foil technique (the displacement of a metallized foil situated at the surface of the fluid measured by the interferometer used for fibre tip measurements). The frequency dependence of the transfer function compared well with the theoretical models [51]. 

---

Aberg, U., Akesson, E., Alvarez, J.-L., Fedchenia, I. and Sundstrom, V. Femtosecond spectral evolution monitoring the bond- twisting event in barrierless isomerization in solution, Chem.Phys., 183 (1994), 269-288... 

Conductivity and Hj evolution monitoring of Na in liq NHj treated with stannane (SnH4.) give NaSnHj and Na2SnH2- The former decomposes at — 63.5°C in the absence of NH3, whereas the latter is more stable, decomposing at > 0°C. Nuclear magnetic resonance studies confirm Na[SnH3] in solution ... 

Styrene SLS/CA Micro- fluidizer K2S2O8 70 20 PSD evolution monitored nucleation period past rate maximum [14] Miller et al. 1994... 

Purpose Purification monitor of ventilating exhaust and gas evolution monitor of industrial zone... 

Fortunately, the shape of the fluid/crystal phase boundary is quite sensitive to the local heat and mass transfer and this information, being available in the majority of growth experiments (either via visualization of the growth striations or using intentional pulsed doping for interface evolution monitoring), is certainly one of... 

Finally, preliminary diagnostic evaluation criteria, based on preventive identification of critical areas of interest on the monitored item, spatial concentration of localized AE events as compared with average AE event density and evolution of local event concentration vs time and/or plant parameters, have been worked out and submitted to extensive testing under real operation conditions. Work on this very critical issue is still to be consohdated. 

Figure Al.6.20. (Left) Level scheme and nomenclature used in (a) single time-delay CARS, (b) Two-time delay CARS ((TD) CARS). The wavepacket is excited by cOp, then transferred back to the ground state by with Raman shift oij. Its evolution is then monitored by tOp (after [44])- (Right) Relevant potential energy surfaces for the iodine molecule. The creation of the wavepacket in the excited state is done by oip. The transfer to the final state is shown by the dashed arrows according to the state one wants to populate (after [44]).

Assuming that an equilibrium is now well established, the simulation may be restarted (not newly started) to begin with the sampling of structural and thermodynamic data. In our model case, data acquisition was performed for 3 ns (trajectory data plot not shown). For the production phase, also, the time evolution of the variables mentioned above should be monitored to detect stability problems or con-... 

The cinnamate ester prepared as above (23.2 g. 79 mmol) was added as a solid slowly to refluxing xylene (500 ml) over a period of 3 h at a rate that prevented accumulation of unreacted azidocinnamate in the solution (monitored by gas evolution through a gas bubbler). The solution was refluxed for an additional 2 h after gas evolution ceased. The reaction mixture was cooled and the solvent removed in vacuo. The residue was recrystallized from methanol to give pure product (20.7 g, 99% yield). 

When low boiling ingredients such as ethylene glycol are used, a special provision in the form of a partial condenser is needed to return them to the reactor. Otherwise, not only is the balance of the reactants upset and the raw material cost of the resin increased, but also they become part of the pollutant in the waste water and incur additional water treatment costs. Usually, a vertical reflux condenser or a packed column is used as the partial condenser, which is installed between the reactor and the overhead total condenser, as shown in Figure 3. The temperature in the partial condenser is monitored and maintained to effect a fractionation between water, which is to pass through, and the glycol or other materials, which are to be condensed and returned to the reactor. If the fractionation is poor, and water vapor is also condensed and returned, the reaction is retarded and there is a loss of productivity. As the reaction proceeds toward completion, water evolution slows down, and most of the glycol has combined into the resin stmcture. The temperature in the partial condenser may then be raised to faciUtate the removal of water vapor. 

The changes in the optical absorption spectra of conducting polymers can be monitored using optoelectrochemical techniques. The optical spectmm of a thin polymer film, mounted on a transparent electrode, such as indium tin oxide (ITO) coated glass, is recorded. The cell is fitted with a counter and reference electrode so that the potential at the polymer-coated electrode can be controlled electrochemically. The absorption spectmm is recorded as a function of electrode potential, and the evolution of the polymer s band stmcture can be observed as it changes from insulating to conducting (11). 

B. Cyclohexylidenecyclohexane. In a Hanovia 450-watt immersion photochemical reactor (Note 2), equipped with a side arm attachment to monitor gas evolution, is placed 15 g. (0.068 mole) of dispiro[5.1.5.1]tetradecane-7,14-dione dissolved in 150 ml. of methylene chloride. The sample is irradiated, and carbon monoxide starts to evolve rapidly after a few minutes. Irradiation is continued until gas evolution has ceased, usually... 

The system should be relatively free of oxygen during irradiation. Oxygen apparently combines with a photochemical intermediate to form cyclohexanone.3 Under the conditions recommended in the procedure, oxygen is prevented from entering the system by the water trap which also serves as a monitor for gas evolution. 

During the development of this procedure, evolution of carbon dioxide was monitored with a wet-test meter. At the bath temperature given (160°), sodium chlorodifluoroacetate... 

There are three phases in the evolution of most QC systems (1) defect detection where an army of inspectors tries to identify defects (2) defect prevention where the process is monitored, and statistical methods are used to control process variation, enabling adjust-... 

Essential prerequisites for the evolution of combinatorial methods were the progress in reaction monitoring and analytics. Of specific importance was the analytics... 

---