Particle size, control using chemical principles

ETEM is thus used as a nanolaboratory with multi-probe measurements. Design of novel reactions and nanosynthesis are possible. The structure and chemistry of dynamic catalysts are revealed by atomic imaging, ED, and chemical analysis (via PEELS/GIF), while the sample is immersed in controlled gas atmospheres at the operating temperature. The analysis of oxidation state in intermediate phases of the reaction and, in principle, EXELFS studies are possible. In many applications, the size and subsurface location of particles require the use of the dynamic STEM system (integrated with ETEM), with complementary methods for chemical and crystallographic analyses. 

Quality measurement is a totally difterent issue than flow, level, temperature or pressure measurement. The primary reason is that there are so maity different quality characteristics that can be measured and they are vastly different with respect to the type of measurement and measuring principles. Just to name a few examples of quality measurements viscosity, odor, color, taste, pH, octane number, particle size distribution, etc. In traditional chemical engineering one type of measurement that is often encountered is composition analysis by means of a gas chromatograph. Because these devices are expensive they are usually used to analyze multiple streams. To give an example, it may be required to analyze the feed flow composition, top and bottom composition of a distillation tower. If one analysis takes a few minutes (residence retention time), and three streams are analyzed it is obvious that composition measurement caimot be realized without a delay or dead time. This is characteristic for numerous quality measurements they often have a measurement delay associated with them, which can vary from a few minutes to tens of minutes. In control this will pose a problem and a dead time compensation technique may be required to achieve adequate control loop performance. 

There are six integrated steps that may be employed in the development of a particle system with tailored size and morphology. These are (i) know the material (ii) determine synthesis conditions to prepare the desired phase (iii) develop methods to control particle size within the context of the material system (iv) develop techniques to control particle morphology within the context of the material system (v) control the state of agglomeration using colloid chemical principles and (vi) control yield of the material by selection of the starting materials and their concentrations. 

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