Particle size surface average

Nanostructured LaNiOs was prepared by co-precipitation under ultrasonic radiation [120], Using various characterization methods and evaluation of catalytic activity, the effects of ultrasound on the structural properties and catalytic activity of LaNiOs were studied. The TEM showed that the ultrasound could cause a decrease in the particle size. The average particle size of LaNiOs prepared by sonochemistry is 20 nm. The specific surface area of LaNiOs is 11.27 m g h Ultrasound could lead to increased surface oxide content and surface crystal oxygen vacancies. The TPR result showed that the LaNi03 prepared by sonochemistry has a lower reduction temperature and a higher ratio of surface oxygen to crystal oxygen. The evaluation of catalytic activity showed that ultrasound could increase the catalytic activity of LaNiOs for NO decomposition. 

AVERAGE PARTICLE SIZE. The average particle size for a mixture of particles is defined in several different ways. Probably the most used is the volume-surface mean diameter which is related to the specific surface area At,. [See Eqs. 

Table 1. Specific surface area (Sbet), average particle size (dBEi), average crystallite size (Dxrd), microstrain and crystalline degree of LSM powders.

Group number Typical average primary particle size (nm) Average surface area (m jg)... 

Porosity Mass density Average pore size Pore size distribution Particle size Surface area Surface roughness Surface groups ... 

Table 1 lists such properties of catalysts as average particle size, surface, silver content. On the whole, we observe a satisfactory coincidence of the average sizes determined by TEM and oxygen chemisorption techniques. Note that the silver lattice parameters found with the X-ray analysis correspond with a good accuracy to the reference values for the bulk silver. Thus, the silver atoms in the bulk of the particles (himdreds of Angstroms in size) are identical to those in the structure of the bulk metal. Moreover, according to HREM, there are no data proving metal-support interactions. 

Chemisorption Particle sizes (metals), adsorption sites (ionic surfaces) Particle size determination averaging adsorption stoichiometry not always clear no... 

Physical properties of TLC alumina are somewhat similar to TLC silica in terms of particle size, surface area, and average pore diameter. Aluminas for chromatography have surface areas between 50 and 350 m /g, average pore diam-eters..between 20 and 150 A, and specific pore volumes between 0.1 and 0.4 ml/ g (Rossler, 1969 Hahn-Deinstrop, 1992 Robards et al., 1994). 

Jorand et al. (1995) developed a modified sol-gel process for synthesis ofzirconia in which the precursor was a mixed monomeric solution in association with organic polymers. This precursor was sprayed in an ammonium hydroxide solution to obtain gel particles. These particles, heat-treated at 700°C for 4 h, yielded doped zirconia particles of composition Zr02-3.6 mol% Y2O3. X-ray diffraction showed them to be 100% tetragonal zirconia. The particle size dso—average particle size at 50% cumulative mass) was 34 /rm, mean crystallite size 9 nm, and the specific surface area had a relatively high value of 100 m /g. 

Particle Size. The soHds in a fluidized bed are never identical in size and foUow a particle size distribution. An average particle diameter, is generally used for design. It is necessary to give relatively more emphasis to the low end of the particle size distribution (fines), which is done by using the surface mean diameter, to calculate an average particle size ... 

Specific Surface. The total surface area of 1 g of powder measured ia cm /g is called its specific surface. The specific surface area is an excellent iadicator for the conditions under which a reaction is initiated and also for the rate of the reaction. It correlates in general with the average particle size. The great difference in surface area between 6-p.m reduced iron powder and 7-p.m carbonyl iron powder (Table 3) cannot be explained in terms of particle size, but mainly by the difference between the very inregular-shaped reduced and the spherical carbonyl iron powders. 

Deterrnination of the specific surface area can be made by a variety of adsorption measurements or by air-permeability deterrninations. It is customary to calculate average particle size from the values of specific surface by making assumptions regarding particle size distribution and particle shape, ie, assume it is spherical. 

Atomization of one liter of condensed product to an average particle size of 50 )J.m dia equals 341,000 cm surface. 

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