Composites production processes

Environmental Impact Considerations 319 Table 15.5 A Composite production process for a typical medium-sized protein. 

AH of these factors contribute to the manufacturing cost of the composite product and thereby determine not only the most cost-effective composite process to use but also the competitive position of composites with the other materials of constmction. 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

To determine if a process unit is at steady state, a program monitors key plant measurements (e.g., compositions, product rates, feed rates, and so on) and determines if the plant is steady enough to start the sequence. Only when all of the key measurements are within the allowable tolerances is the plant considered steady and the optimization sequence started. Tolerances for each measurement can be tuned separately. Measured data are then collec ted by the optimization computer. The optimization system runs a program to screen the measurements for unreasonable data (gross error detection). This validity checkiug automatically modifies tne model updating calculation to reflec t any bad data or when equipment is taken out of service. Data vahdation and reconciliation (on-line or off-line) is an extremely critical part of any optimization system. 

This process of conversion from a metals production environment to a composite materials production environment is much more involved than just laminate layup and curing. Issues of inspection arise to make certain that the composite product is put together properly. Some of those inspection techniques are much more complicated than they were for a metallic structure. Truly, the picture is not totally rosy for composite materials. It would be quite unrealistic to say (1) there are no problems and (2) composite materials are absolutely the best way to go. 

All processes may be classified as batch, continuous, or semibatch depending on how materials are transferred into and out of the system. Also, the process operation may be characterized as unsteady state (i.e., transient) or steady state, depending on whether the process variables (e.g., pressure, temperature, compositions, flowrate, etc.) are changing with time or not, respectively. In a batch process, the entire feed material (i.e., charge) is added instantaneously to the system marking the beginning of the process, and all the contents of the system including the products are removed at a later time, at the end of the process. In a continuous process, the materials enter and leave the system as continuous streams, but not necessarily at the same rate. In a semibalch process, the feed may be added at once but the products removed continuously, or vice versa. It is evident that batch and semibatch processes are inherently unsteady state, whereas continuous processes may be operated in a steady or unsteady-state mode. Start-up and shut-down procedures of a steady continuous production process are examples of transient operation. 

The physicochemical properties of carbon are highly dependent on its surface structure and chemical composition [66—68], The type and content of surface species, particle shape and size, pore-size distribution, BET surface area and pore-opening are of critical importance in the use of carbons as anode material. These properties have a major influence on (9IR, reversible capacity <2R, and the rate capability and safety of the battery. The surface chemical composition depends on the raw materials (carbon precursors), the production process, and the history of the carbon. Surface groups containing H, O, S, N, P, halogens, and other elements have been identified on carbon blacks [66, 67]. There is also ash on the surface of carbon and this typically contains Ca, Si, Fe, Al, and V. Ash and acidic oxides enhance the adsorption of the more polar compounds and electrolytes [66]. 

The difficulty of obtaining pure / "-material for the electrolyte has been tackled in many production processes worked out in the past. Unless precautions are taken, sintering of a -alumina-derived / "-alumina compositions invariably results in the duplex microstructure and a low-strength ceramic. Therefore a balance has to be struck between conductivity and strength. The problem arises because the conversion from —alumina to / " -alumina is slow... 

Measurements of overall reaction rates (of product formation or of reactant consumption) do not necessarily provide sufficient information to describe completely and unambiguously the kinetics of the constituent steps of a composite rate process. A nucleation and growth reaction, for example, is composed of the interlinked but distinct and different changes which lead to the initial generation and to the subsequent advance of the reaction interface. Quantitative kinetic analysis of yield—time data does not always lead to a unique reaction model but, in favourable systems, the rate parameters, considered with reference to quantitative microscopic measurements, can be identified with specific nucleation and growth steps. Microscopic examinations provide positive evidence for interpretation of shapes of fractional decomposition (a)—time curves. In reactions of solids, it is often convenient to consider separately the geometry of interface development and the chemical changes which occur within that zone of locally enhanced reactivity. 

These materials are useful semiconductors and have a wide range of industrial applications, particularly in opto-electronics. One of their attractive features is the possibility of tailoring the band gap and the lattice constant in the ternary alloys by varying the composition. CVD is now a major production process of these materials. 

Every separation process divides one or more feeds into at least two products of different composition. Separation processes that operate on heterogeneous feeds usually involve screening or settling. Those that involve physically homogeneous mixtures must use more subtle means to create products of different composition. These latter processes are pervasive in industry they consume large amounts of energy and require sophisticated research and design. 

Note on GMPs The assays are conducted on individual dosage units (here tablets) and not on composite samples. The CU test serves to limit the variability from one dosage unit to the next (the Dissolution Rate test is the other test that is commonly used). Under this premise, outlier tests would be scientific nonsense, because precisely these outliers contain information on the width of the distribution that one is looking for. The U.S. vs. Barr Laboratories Decision makes it illegal to apply outlier tests in connection with CU and DR tests. This does not mean that the distribution and seemingly or truly atypical results should not be carefully investigated in order to improve the production process. 

Myriad FRP products are available for either the repair or the outright replacement of existing structures. In addition to chemical-process pipes and tanks, FRP composite products include structural shapes, bridge systems, grating, handrail ladders, etc. 

V. R. Negomedzyanov, V. P. Bortsov, V. S. Denisov, V. V. Slepov, and S. S. Volkova. Plugging composition for use in oil and gas extraction industry—contains Portland cement and aluminium-containing additive in form of slag dust waste from aluminium production process. Patent RU 2029067-C, 1995. 

The experimental designs discussed in Chapters 24-26 for optimization can be used also for finding the product composition or processing condition that is optimal in terms of sensory properties. In particular, central composite designs and mixture designs are much used. The analysis of the sensory response is usually in the form of a fully quadratic function of the experimental factors. The sensory response itself may be the mean score of a panel of trained panellists. One may consider such a trained panel as a sensitive instrument to measure the perceived intensity useful in describing the sensory characteristics of a food product. 

The composition of steels or other metals is commonly analyzed by emission or X-ray spectrometry during and after the production process. Both methods have to be calibrated by solid samples. These are either exactly analyzed samples taken from the same process or synthetic melted mixtures of the matrix with added accompanying elements (RMs). Available CRMs are then used to control the slope of the calibration function. Today, available RMs and CRMs are increasingly and exclusively used in spectral laboratories as the chemical analysis became much restricted and typical control laboratories were totally closed (Slickers 1993). 

Table 8.2 Product compositions and processing times for the second illustrative example...

First, the pharmaceutical market failures mentioned above may be empirically inconsequential, which may either render their regulation unnecessary or make it advisable to use more flexible price control policies. For example, justifications for regulation that are based on the virtual absence of competition seem weak when one observes markets with products whose patent has expired. When a patent expires barriers to entry should disappear, since the composition of the active ingredient becomes public, and other companies should not have too many problems to reproduce the production process. The reasons brandished for price regulation when any company can manufacture a generic to compete with the brand product find no justification in theory. 

Pork is the product of a very complex process. All the various characteristics of pork quality cannot be assessed directly in each carcass because these measurements and assessments would be too expensive. Therefore, previous scientific quality assessment of meat is primarily an indirect approach based on a few easily detectable quantitative traits and on the prescription of minimal standards in relation to the product in terms of size or composition and in relation to the production process. The prescriptions and the exclusion criteria vary between countries or between labelling programmes. The most encompassing prescriptions are enshrined in the EC regulation on organic livestock production (EEC No. 2092/91). Owing to this approach, extreme deviations in quality traits and deleterious effects are prevented. However, there is still space left within these framework conditions for huge variability in pork quality. 

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