In-Process Characterization

S.E. Barnes, E.C. Brown, M.G. Sibley, H.G.M. Edwards, I.J. Scowen and P.D. Coates, Vibrational spectroscopic and ultrasound analysis for in-process characterization of high-density polyethylene/polypropylene blends during melt extrusion, Appl. Spectrosc., 59, 611-619 (2005). 

Process characterization defines process capability and facilitates prospective process validation at the production scale [40]. Full process characterization is valuable in maintaining smooth manufacturing operations and minimizing lost batches, and it provides supporting information for lot release justification for atypical batches [15]. Its goals are to identify key operating and performance parameters, define control limits for key process parameters, demonstrate robustness of the commercial process, and provide technical information about the process [68]. The steps involved in process characterization include risk assess-... 

An extremely important point in process characterization is validation with, e.g., classical methods, such as gas chromatography (GC) Fig. 14) or liquid chromatography. Atrazine in surface waters was measured by means of ELISA and GC, and the results compared. The results correlate well, and confirm the theory that immunological methods can give reliable values in practice. The results of both methods are equivalent with a probability of 95 %, No false negative values were obtained. The same applies to the use of immunoassays on soil extracts. In comparison with GC analyses, ELISA usually gives higher analyte concentrations, which is put down to the effects of humic acid. 

This three-volume Handbook Sol-Gel Science and Technology was planned with the purpose of providing those who are interested in processing, characterization and application of materials with comprehensive knowledge on sol-gel science and technology. 

Melt spinning is not limited to the production of conventional polymeric filaments various developments in terms of type of filaments, structure-property relationships, introduction of nano materials, and advances in process characterization have evolved in the last few years. Some of these developments are briefly discussed below. 

It now seems clear tliat, under certain conditions, massive enhancements of what is nonnally a very weak process can be achieved. The ability to obtain vibrational spectra would be a great advance in tlie characterization of single molecules if metliods could be found to reproducibly observe all molecules in a sample, not only tliose tliat happen to bind to special sites on tlie colloid. 

Characterization of zeolites is primarily carried out to assess tire quality of materials obtained from syntliesis and postsyntlietic modifications. Secondly, it facilitates tire understanding of tire relation between physical and chemical properties of zeolites and tlieir behaviour in certain applications. For tliis task, especially, in situ characterization metliods have become increasingly more important, tliat is, techniques which probe tire zeolite under actual process conditions. 

A fundamental requirement in powder processing is characterization of the as-received powders (10—12). Many powder suppHers provide information on tap and pour densities, particle size distributions, specific surface areas, and chemical analyses. Characterization data provided by suppHers should be checked and further augmented where possible with in-house characterization. Uniaxial characterization compaction behavior, in particular, is easily measured and provides data on the nature of the agglomerates in a powder (13,14). 

When a sample of ca 100 g has been obtained, a representative sample for use in size characterization equipment must then be taken. Some of the more modem methods of size characterization require as Htde as 1 mg of powder, thus obtaining a representative sample can be quite difficult. If the powder flows weU and does not contain too many fines, a device known as the spinning riffler (Fig. 4c) can be used. A spinning riffler consists of a series of cups that rotate under the powder supply. The time of one rotation divided into the time of total powder flow should be as large a number as possible. Although this device has been shown to be very efficient, problems can be encountered on very small (1 mg) samples, and the powder must be processed several times. Moreover, in order to avoid cross-contamination, cleanup after each of the sampling processes can be quite difficult. Furthermore, if the powder is cohesive and does not flow weU, the equipment is not easy to use. A siUca flow agent can be added to the powder to enable the powder to flow... 

Frequently a piece of equipment is used in different processes during its lifecycle. This could result in process conditions that exceed the safe operating limits of the equipment. Equipment inspection may provide a poor prediction of the equipment s useful life and reliability, due to the change of material handled or change in process chemistry over the life of equipment. Batch operations are also characterized by frequent start-up and shut-down of equipment. This can lead to accelerated equipment aging and may lead to equipment failure. This chapter presents issues and concerns related to the safe design, operation, and maintenance of various pieces of equipment in batch reaction systems, and provides potential solutions. 

O. Ganschow. In Analytical Techniques for Semiconductor Materials and Process Characterization. The Electrochemical Society, Pennington, 1990,... 

Shock-compression science, which has developed and matured since its inception in 1955. has never before been documented in book form. Over this period, shock-compression research has provided numerous major contributions to scientific and industrial technology. As a result, our knowledge of geophysics, planetary physics, and astrophysics has substantially improved, and shock processes have become standard industrial methods in materials synthesis and processing. Characterizations of shock-compressed matter have been broadened and enriched with involvements of the fields of physics, electrical engineering, solid mechanics, metallurgy, geophysics, and materials science... 

In-Process Product Parameter—A parameter that characterizes the product prior to the finished product stage. 

While an extremely useful analytical tool for illustrating all the steps in a process as well as critical interactions, process mapping can be a very frustrating exercise either because the process is too difficult to map or because it is very repetitious—the same flows are repeated department after department. It can be a critical part of Process Characterization, as shown in Exhibit 5-3. 

The Nenitzescu process is presumed to involve an internal oxidation-reduction sequence. Since electron transfer processes, characterized by deep burgundy colored reaction mixtures, may be an important mechanistic aspect, the outcome should be sensitive to the reaction medium. Many solvents have been employed in the Nenitzescu reaction including acetone, methanol, ethanol, benzene, methylene chloride, chloroform, and ethylene chloride however, acetic acid and nitromethane are the most effective solvents for the process. The utility of acetic acid is likely the result of its ability to isomerize the olefinic intermediate (9) to the isomeric (10) capable of providing 5-hydroxyindole derivatives. The reaction of benzoquinone 4 with ethyl 3-aminocinnamate 35 illustrates this effect. ... 

A disease process characterized by deterioration of the macula of the retina that results in a loss of shaip central vision. AMD is the leading cause of central vision loss in the developed countries today for those over the age of fifty years. 

The detailed chemistry of radiation grafting has, in most cases, not been rigorously established. Process characterization is complicated by the fact that often only surface layers are involved and, in other cases, by the substrates being cross-linked or intractable. 

The two processes are becoming closer in concept. For instance, MOCVD is using techniques developed for MBE such as in situ characterization monitoring, load lock, and lower pressure levels, and MBE is now using chemical sources such as organome-tallics, which are typical of CVD. 

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