Primary properties characteristic particle size

The respirable powders of a DPI cannot be characterized adequately by single-particle studies alone bulk properties must also be assessed since they contribute to ease of manufacture and affect system performance. Primary bulk properties include particle size, particle size distribution, bulk density, and surface area. These properties, along with particle electrostatics, shape, surface morphology, etc., affect secondary bulk-powder characteristics such as powder fiow, handling, consolidation, and dispersibility. 

Dozens of reactions of free radicals (SiCla, SiClsO, Cl, OCl, H, OH, HO, =Si, =SiO, etc.), charged particles, ion-radicals, O atoms, molecules and proto-particles in the flame with SiCU, O2, H2 and related compounds on synthesis of fumed silica are worthy of special attention, since variations in synthesis conditions allow one to prepare materials strongly different in their morphological (primary and secondary particle size distributions, type of contacts between adjacent particles) and surface (concentrations of silanols and intact water) properties. These problems as well as structural and adsorptive characteristics of different silicas were analyzed in details by Mironyuk and coworkers in a series of publications [36]. 

Many physicochemical properties of fumed silica depend significantly not only on the primary and secondary particle size distributions but also on the concentration of adsorbed water (C ) in the form of intact molecules and =SiOH groups (Cqh) [1-3,6,7]. For instance, marked amounts of adsorbed water can negatively affect the characteristics of fumed silica as a filler of liophilic media or polymers. There are several methods to change C and Cqh such as chemical modification... 

Specific gravity is the most critical of the characteristics in Table 3. It is governed by ash content of the material, is the primary deterrninant of bulk density, along with particle size and shape, and is related to specific heat and other thermal properties. Specific gravity governs the porosity or fractional void volume of the waste material, ie. 

The specific surface area, i.e. primary particle size, and the corresponding order of aggregation of primary particles, as well as the content of silanols, are key-parameters affecting many physicochemical properties of powders and aqueous suspensions of nanosilica. These key characteristics are responsible for the properties of Silics as a medicinal preparation acting as a sorbent. 

Estimation of Average Primary Particle Size Method of Characteristic Times 346 Primary Particle Size Effects of Aerosol Material Properties 350 Particle Neck Formation 353 Particle Crystal Structure 355 Basic Concepts 355 Experimental Obsetyafions 355 Problems 356 References 357... 

Cyclones are seldom used as the primary means of particulate collection, but often serve as first-stage air cleaning devices that are followed by other methods of particulate collection. Cyclone collection efficiency is probably more susceptible to changes in particulate characteristics than are other types of devices, therefore, care should be taken if used. Cyclone operation is dependant, generally, on physical parameters such as particle size, density, and velocity, as opposed to the chemical nature or properties of the material being collected. 

The above listed characteristics depend on many primary particle properties and operation conditions, such as the nature of the material (brittle or soft), particle size, kind of loading in the mill, intensity and velocity of loading, the shape and hardness of the loading surfaces and the environmental conditions, namely temperature. 

Fillers. Fillers for elastomers are not generally used just to fill space and cheapen the compositions. They are very important to modify the properties of rubber compositions in very positive ways. This is especially true for the so-called reinforcing fillers. Their presence in the compound can improve the strength- and durabihty-related properties of vulcanizates and can strongly enhance processing characteristics. The choice and amount of filler can have a profound effect on vulcanizate properties. These effects depend on several factors level of use (concentration), primary particle size, surface area (inverse function of primary particle size), and structure (shape factor, e.g., spherical, chain or rod-like, plate-like, and so forth). 

Particle size analysis and measurement is an important operation in many industries. The stability, chemical reactivity, opacity, flowability, material strength, and some other properties of many materials are affected by the size distribution and characteristics of the particles within them. There are numerous techniques and instrumentation for all types of particle size analysis and characterization available. Some primary properties of particulate materials, mainly shape, will determine the way the particles are detected or... 

At constant position and spraying parameters (suspension and nozzle gas mass flow) also the sprayed feed has an influence on the resulting droplet sizes. Compared to pure water, the characteristic droplet sizes increase if a suspension consisting of water and ceramic primary particles is spray dried. A further size increase was detected at additional binder addition (Fig. 11.35), what might be an effect of changed suspension properties (surface tension, viscosity, etc.). 

Fillers have been used in the formulation of rubber compounds since the early days of the rubber industry. Whilst their primary function is to reduce cost, it has been found that fillers have a reinforcing effect in the rubber mechanical properties sueh as tensile strength, modulus, tear resistance and abrasion resistanee and thus very few mbber compounds are prepared without substantial quantities of filler. The performance of filler in the rubber matrix is governed by its characteristics, such as the particle size and concentration, particle shape, surface activity, degree of interactions with rubber matrix and structure of the particle agglomerates. 

---