Powders Surface Technology

The solid material when transformed into fine powder creates a new material (regarding its surface properties and applications). The technology related to this subject is very expansive (found in talcum powder, cement, the clay industry, etc.). The Following areas of powder science are currently being investigated  

Formation and synthesis of particles by different procedures (e.g., grinding, crushing, precipitation, etc.) 

Characterization of the size, shape, surface area, pore structure, and strength of particles 

Packing, failure, flow, and permeability of assemblies of particle 

Handling and processing operations (e.g., slurry flow, fluidization, pneumatic conveying) 

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Particle-Size Analysis Methods for particle-size analysis are shown in Fig. 17-34, and examples of size-analysis methods are given in Table 17-1. More detailed information may be found in Lapple, Chem. Eng., 75( 11), 140 (1968) Lapple, Particle-Size Analysis, in Encyclopedia of Science and Technology, 5th ed., McGraw-Hill, New York, 1982 Cadle, The Measurement of Airborne Particles, Wiley, New York, 1975 Lowell, Introduction to Powder Surface Area, 2d ed., Wiley, New York, 1993 and Allen, Particle Size Measurement, 4th ed, Chapman and Hall, London, 1990. Particle-size distribution may be presented on either a frequency or a cumulative basis the various methods are discussed in... 

Photochemical decomposition can also be carried out in the presence of a suspension of photoactive material such as Ti02 where substrate absorption onto the uv activated surface can initiate chemical reactions e. g. the oxidation of sulphides to sul-phones and sulphoxides [37]. This technology has been adapted to the destruction of polychlorobiphenyls (PCB s) in wastewater and is of considerable interest in environmental protection. Using pentachlorophenol as a model substrate in the presence of 0.2 % TiOj uv irradiation is relatively efficient in dechlorination (Tab. 4.5) [38]. When ultrasound is used in conjunction with photolysis, dechlorination is dramatically improved. This improvement is the result of three mechanical effects of sonochemistry namely surface cleaning, particle size reduction and increased mass transport to the powder surface. 

Powder surface area and porosity.—2nd ed.— (Powder technology series)... 

Nystrom, C. Karehill, P.-G. The importance of intermole-cular bonding forces and the concept of bonding surface area. In Pharmaceutical Powder Compaction Technology Alderborn, G., Nystrom, C., Eds. Marcel Dekker, Inc. New York, 1996 17-53. 

Use of a refractive near-infrared (NIR) moisture sensor for end-point determination of wet granulation was described by several authorsJ " There are technological challenges associated with this approach, as the sensor can only measure the amount of water at the powder surface. 

S. Lowell and J.E. Shields, Powder Surface Area and Porosity, 2nd edn. Powder Technology Series, Chapman Hall, London, 1984. 

The basic concept employed in gas adsorption studies of the structure of powders is to study the way in which gas molecules are adsorbed onto the surface of the powder under specified conditions so one can deduce the surface area of the powder. The technology of this method comes from the late 1930 s. A very good review of the basic concepts has been written by Orr [1]. Although the basic principles of the method are simple, the interpretation of the data when dealing with complex powder systems can be very difficult. In this chapter we will outline the basic methodology and direct the reader to more comprehensive literature which can be consulted if the detailed structure of systems from a research perspective is of interest. Excellent books have been written describing the research methodology of gas adsorption for complex powder systems see for example references 2, 3, 4, and 5. 

Volovitch P, Masse JE, Fabre A, Barrallier L, Saikaly W, (2008), Microstructure and corrosion resistance of magnesium alloy ZE41 with laser surface cladding by Al-Si powder . Surface and Coatings Technology, 202, 4901 914. 

Kim, E. H.-J., Dong Chen, X., Pearce, D. (2003). On the mechanisms of surface formation and the surface compositions of industrial milk powders. Drying Technology, 21, 265-278. 

Lowell, S., J. E. Shields, M. A. Thomas and M. Thommes (2004). Characterisation of Porous Solids and Powders Surface Area, Pore Size and Density . In Characterisation of Porous Solids and Powders Surface Area, Pore Size and Density, 1. Particle Technology Series 16. Dordrecht Springer Netherlands. 

In 1954 the surface fluorination of polyethylene sheets by using a soHd CO2 cooled heat sink was patented (44). Later patents covered the fluorination of PVC (45) and polyethylene bottles (46). Studies of surface fluorination of polymer films have been reported (47). The fluorination of polyethylene powder was described (48) as a fiery intense reaction, which was finally controlled by dilution with an inert gas at reduced pressures. Direct fluorination of polymers was achieved in 1970 (8,49). More recently, surface fluorinations of poly(vinyl fluoride), polycarbonates, polystyrene, and poly(methyl methacrylate), and the surface fluorination of containers have been described (50,51). Partially fluorinated poly(ethylene terephthalate) and polyamides such as nylon have excellent soil release properties as well as high wettabiUty (52,53). The most advanced direct fluorination technology in the area of single-compound synthesis and synthesis of high performance fluids is currently practiced by 3M Co. of St. Paul, Minnesota, and by Exfluor Research Corp. of Austin, Texas. 

Surfa.ce, Any reaction between two powder particles starts on the surface. The amount of surface area compared to the volume of the particle is, therefore, an important factor in powder technology. The particle—surface configuration, whether it is smooth or contains sharp angles, is another. The particle surface area depends strongly on the method of production, as shown in Table 1. The method of production usually determines the particle shape. 

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