Focused beam reflectance method

Laser scattering—focused beam reflectance method, FBRM with high P cell (Clarke and Bishnoi, 2004) Yes P, T, particle formation (min) 1500 psi size range 1-1000 pm stirred Hydrate particle size distribution during growth/decomposition... 

Since the inherent growth rate of many organic compounds is relatively slow, addition times may be long in order to achieve supersaturation control within the metastable zone. Higher addition rates can result in nucleation and the creation of a bimodal distribution. Experimentation to determine acceptable addition rates can be evaluated by focused beam reflectance measurement (FBRM) and other in-sim, online methods (Chapter 2) or microscopic observation of the crystal slurry which could reveal the presence of fines. These issues are highhghted in the examples below. 

Su et al. [24] studied the polymorphic transformation of n-mannitol by in situ Raman spectroscopy coupled with FBRM (focused beam reflectance measurement) and PVM (particle vision measurement). In this way, relationships between fine particles and metastable-form dissolution, and also between coarse particles and stable-form crystallization, could be defined. The different polymorphs were identified by Raman spectroscopy. FBRM provided a method for independently verifying these observations. PVM, in turn, verified the data interpretation strategy employed for FBRM. 

In addition to the characterization of the product, the characterization of the system during the crystallization process may be very important as it may help to ensure a stable and controlled crystallization process leading to material of the desired quality. A number of methods have been adapted for online use. These include XRPD, IR, ultrasound absorption, and Fraunhofer diffraction. The most commonly and conveniently used ones are turbidity, NIR, Raman, FBRM (focused beam reflectance measurement), and PVM (particle vision measurement). 

Along with the ever increasing demand for on-line or in-line particle characterization in process control, requests for direct measurements of particles in pipelines or reactors are on the rise. In process control, any bias of the characterization method or precise physical meaning of the parameters determined are not of the utmost importance. Robusmess, reliability, and precision of measurement are often the primary concerns. Besides focused beam reflectance and fiber optical PCS probe, back scattering intensity measurement is among the optical techniques preferred for in-process measurement due to the obvious reasons that when the concentration of a suspension is high, the... 

Femtosecond laser excitation makes it possible to produce in a synchronous manner accurate to within a few femtoseconds an ensemble of molecules in an excited state and observe thereafter the evolution of this ensemble in the subsequent processes of decay, relaxation, and so on, by means of other femtosecond pulses. Another femtosecond pulse is usually used as a probe pulse [1]. However, one can directly observe changes in the geometry of molecules, specifically in molecular vibrations, by the method of electron diffraction using ultrashort electron pulses. This was successfully demonstrated in Ref. 2. Whereas the production of synchronous probe laser pulses is a standard technique, the situation with femtosecond electron pulses is more complicated. I would like to call attention to the possibility of using intense femtosecond laser pulses to control electron beams, specifically to obtain femtosecond electron pulses and to focus and reflect them, and so on [3, 4]. 

Fig. 5. a Schematic representation of the SFM set-up using the optical beam deflection method, b When the tip interacts with the sample surface, the cantilever exhibits deflection perpendicular to the surface as well as torsion parallel to the surface plane. The normal force Fn and the lateral force FL corresponds to the force components which cause the deflection and torsion, respectively. Both responses are monitored simultaneously by the laser beam which is focused on the back side of the cantilever and reflected into a four-quadrant position sensitive detector (PSD)... 

Another method of measurement of diffuse reflectance does not require an integrating sphere. In this method, the sample beam is focused onto the sample by means of ellipsoidal or spherical mirrors and collected by another ellipsoidal mirror, at either 180 or 90° from the incident beam. This method has been used for many years in the infrared, since proposed by Fuller and Griffiths (1978, 1980). The advantage is very high collection efficiency and the ability to measure very small samples. Such geometry is known by a number of names, including biconical, Praying Mantis (a trade-... 

Doppler Flow Meters. Doppler flow meters sense the shift in apparent frequency of an ultrasonic beam as it is reflected from air bubbles or other acoustically reflective particles that ate moving in a Hquid flow. It is essential for operation that at least some particles ate present, but the concentration can be low and the particles as small as ca 40 p.m. CaUbration tends to be influenced by particle concentration because higher concentrations result in mote reflections taking place neat the wall, in the low velocity portion of the flow profile. One method used to minimize this effect is to have separate transmitting and receiving transducers focused to receive reflections from an intercept zone neat the center of the pipe. 

The coil (wound on a light metal former) can be suspended by a fine strip of phosphor bronze between the pole pieces. Attached to this suspension is a small mirror which reflects on to a scale a beam of light which is focused upon it. An instrument of this kind is known as a D Arsonval galvanometer and is used in potentiometer circuits and various methods of measurement of resistance. 

Fig. 6. Experimental arrangement for lifetime measurements by the phase-shift method, using laser excitation. The laser beam is amplitude-modulated by a Pockel cell with analysing Nicol prism and a small part of the beam is reflected by a beam splitter B into a water cell, causing Rayleigh scattering. This Rayleigh-scattered light and the fluorescence light from the absorption cell are both focused onto the multiplier cathode PMl, where the difference in their modulation phases is detected. (From Baumgartner, G., Demtroder, W., Stock, M., ref. 122)).

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