Material characteristics selection

The properties of fillers which induence a given end use are many. The overall value of a filler is a complex function of intrinsic material characteristics, eg, tme density, melting point, crystal habit, and chemical composition and of process-dependent factors, eg, particle-si2e distribution, surface chemistry, purity, and bulk density. Fillers impart performance or economic value to the compositions of which they are part. These values, often called functional properties, vary according to the nature of the appHcation. A quantification of the functional properties per unit cost in many cases provides a vaUd criterion for filler comparison and selection. The following are summaries of key filler properties and values. 

The CRC-Elsevier materials selector , 2nd edition, N.A. Waterman, and M.E Ashby CRC Press (1996) ISBN 0412615509. (Now, also available on CD-ROM). Basic reference work. Three-volume compilation of data for all materials includes selection and design guide. The Materials Selector is the most comprehensive and up-to-date comparative information system on engineering materials and related methods of component manufacture. It contains information on the properties, performance and processability of metals, plastics, ceramics, composites, surface treatments and the characteristics and comparative economics of the manufacturing routes which convert these materials into engineering components and products. 

Most polymers are applied either as elastomers or as solids. Here, their mechanical properties are the predominant characteristics quantities like the elasticity modulus (Young modulus) E, the shear modulus G, and the temperature-and frequency dependences thereof are of special interest when a material is selected for an application. The mechanical properties of polymers sometimes follow rules which are quite different from those of non-polymeric materials. For example, most polymers do not follow a sudden mechanical load immediately but rather yield slowly, i.e., the deformation increases with time ( retardation ). If the shape of a polymeric item is changed suddenly, the initially high internal stress decreases slowly ( relaxation ). Finally, when an external force (an enforced deformation) is applied to a polymeric material which changes over time with constant (sinus-like) frequency, a phase shift is observed between the force (deformation) and the deformation (internal stress). Therefore, mechanic modules of polymers have to be expressed as complex quantities (see Sect. 2.3.5). 

Covalent linkage of amino acid, peptide or protein moieties onto the hydrolyzed and/or oxidized polymers (Control and Oxidized starches) was examined for its ability to improve the potential for microregion lipophilicity within the carbohydrate polymer. Proteinaceous materials are often strongly surface active (39) and may, if carefully selected, contribute positively to wall material characteristics. This selection process was carried-out using maltodextrins (DE 10 and/or 25) as the carbohydrate framework and various amino acid-derived materials as the function-altering accessory, ranging from gelatin and casein proteins to simple amino acids. 

The resistivity of certain semiconductors such as tin oxide (SnOx) and zinc oxide (ZnO) can be strongly modulated by the presence of certain gaseous species in the ambient. Several gas sensors have been developed based on such material characteristics (1-5). The principal advantages of semiconductor gas sensors are (a) relative simplicity of fabrication (b) relative simplicity of operation (c) low cost (fabrication and maintenance). However, the major drawback of these sensors is their low sensing selectivity among various gases. 

The selectivity of the sensor is determined by the efficiency of the coating material. Developing selective coatings is an ongoing research area. Figure 3 shows a useful metric for sensor performance called the receiver operating characteristic (ROC) curve [16]. 

Luminous vapor treatment without depositing film (LGT) could be used to modify the surface characteristics of membranes. Type B plasma polymer also could be used for this purpose. General schemes of membrane application of LGT and LCVD are schematically depicted in Figures 34.2 and 34.3, respectively [2]. Since the luminous gas interacts with the substrate material, the selection of the membrane material and the gas to be used in these possible schemes is important, and it should not be considered that any combinations of gas and material could be used in any mode of application. 

As previously discussed, differences in the particle sizes of materials being blended can lead to segregation. Therefore, proper formulation development entails the selection of materials that have comparable particle size distributions whenever possible. Many excipients, such as lactose and microcrystalline cellulose, are available in a variety of grades, which are reflective of the particle size, density, or flow characteristics of the respective material. Careful selection of the grade to be used in the formulation enhances the ability of the blending process to prepare uniform blends. 

Selection of a specific method for a particular application is primarily governed by the measuring range of the analyzer and the approximate particle size distribution of the powder. Efforts should be made to measure the entire particle size range with only one method. Also, that dispersion characteristic should be determined which can be used directly in later applications of the data and/or calculations. Furthermore, considerations of cost, time requirement, and special material characteristics may contribute to the selection criteria. There is no known method that could be the best choice for all applications. 

In some cases, for example, toxic characteristics of the material may prohibit shipment of test quantities to vendors laboratories and/or contamination of laboratory buildings and equipment may be irreversible. In other cases, particularly in hot agglomeration, the material must be tested in statu nascendi because cooling and reheating a sample after shipment does not recreate the original material characteristics and the actual binding mechanisms. In those cases, construction of a pilot plant on the project site or other suitable location must be considered which may be equipped with purchased or rented machinery. If this solution is selected, the above remarks on scale-up must still be kept in mind. 

Prom the point of the shape of the gradation, multi-stewed and continuously graded type are proposed. The optimal FGM approach should be selected or integrated in consideration of operating condition and material characteristics. 

Priority tasks have been the selection of high temperature, high strength alloys and testing of candidate commercial alloys. The material characteristics investigated included creep behavior, fatigue properties, structural stability, and corrosion resistance [32]. 

Selecting the correct tool material requires knowing which material characteristics are important for each friction stir application. Many different material characteristics could be considered important to friction stir, but ranking the material characteristics (from most to least important) will depend on the workpiece material, expected life of the tool, and the user s own experiences and preferences. In addition to the physical properties of a material, some practical considerations are included that may dictate the tool material selection. 

---