Powders properties

Probably the most important powder property governing the formation of atomic bonds is the surface condition of the particles, especially with respect to the presence of oxide films. If heavy oxide layers are present, they must be penetrated by projections on the particles. This results in only local rather than widespread bonding. A ductile metal such as iron which has a heavy oxide layer may not form as strong or as many bonds as a less ductile metal. 

Surface Area Determination The surface-to-volume ratio is an important powder property since it governs the rate at which a powder interacts with its surroundings. Surface area may be determined from size-distribution data or measured directly by flow through a powder bed or the adsorption of gas molecules on the powder surface. Other methods such as gas diffusion, dye adsorption from solution, and heats of adsorption have also been used. It is emphasized that a powder does not have a unique surface, unless the surface is considered to be absolutely smooth, and the magnitude of the measured surface depends upon the level of scrutiny (e.g., the smaller the gas molecules used for gas adsorption measurement the larger the measured surface). 

Significant improvement of tantalum powder properties was achieved by the application of molten alkali halides as solvents for potassium heptafluorotantalate, K2TaF7. Variation of the initial concentration of K2TaF7 in the melt, stirring and rate of sodium loading enable a well-controllable production of tantalum powder with a wide variety of specific charges. Heller and Martin [590] proposed the use of a reactor equipped with a stirrer in 1960. Fig. 142 shows a typical scheme of the reactor [24, 576]. All metal parts of the reactor are made of nickel or nickel alloy. 

SB Tan, JM Newton. Influence of capsule dosator wall texture and powder properties on the angle of wall friction and powder-wall adhesion. Int J Pharm 64 227-234, 1990. 

NM Concessio, MM Van Oort, M Knowles, AJ Hickey. Pharmaceutical dry powder aerosols correlation of powder properties with dose delivery and implications for pharmacodynamic effect. Pharm Res 16 833-839, 1999. 

The stress terms F at the front of the plug and B at the back of the plug, dependent on the pressure drop and powder properties, can be developed from a momentum balance but often times they are set equal to each other. Using the momentum balance... 

Evaluation of the morphology of a pharmaceutical solid is of extreme importance, since this property exerts a significant influence over the bulk powder properties of the material. In addition to providing insights into the micromeritic properties of the solid, microscopy can also be used to develop preliminary estimations of the particle-size distribution. A determination can be easily made regarding the relative crystallinity of the material, and it is often possible to deduce crystallographic information as well. Unknown particulates can often be identified solely on the basis of their microscopic characteristics, although it is useful to obtain confirmatory support for these conclusions with the aid of microscopically assisted techniques. 

Production of tablets at medium-to-large scale requires more stringent control of powder properties due to the high-speed compression step. Processing of tablets and the physics of tablet compaction have been the subject of extensive investigation and voluminous literature exists on the topic. 

Bulk powder properties are important in understanding the handling properties of an excipient or a granulated product. Common parameters measured are bulk and tap density. From these values the compressibility can be calculated using the following ... 

Compacts were milled and final blends were compressed into tablets (Table 8 gives resultant powder properties). Tablets were tested for friability, thickness, hardness, and drug release. 

Table 8 Powder Properties from Non-Roller Compacted Formulation and Powder Properties from Vector Freund Lab and Pilot Roller Compaction Processes...

PTFE powder properties L100Xa MP1100b MP1200b... 

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