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Basic concept of pharmaceutical powder
1. Overview of “powder†and “granule†of powder
Powder is a general term for a myriad of aggregates of solid particles. The particles are the small unit of powder movement. Powder science is the study of the basic properties of powders and the science of their application. The so-called "powder" and "granules" are commonly used. It belongs to the category of powder. Generally, particles smaller than 100 μm are called “powderâ€, and particles larger than 100 μm are called “granules†[1] . When the particle diameter is less than 100 μm, the interaction between the particles is likely to occur, and the fluidity is poor. When the particle diameter is larger than 100 μm, the particles are more likely to have fluidity than the interaction between the particles, and the "granules" can be visually observed.
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2, super-fine concept
Ultra-fine powders are confusing in the domestic concept, and the names are used differently. Most of them are called “super-micro†in the country, and some are called “super-fine†or “super-fineâ€, which are not strictly defined. Some powders having a particle diameter of less than 3 μm are referred to as ultrafine, and powders having a particle diameter of less than 30 μm or 10 μm are referred to as ultrafine, and powders having a particle diameter of less than 100 μm or 300 μm are also referred to as ultrafine. According to China's ultra-fine powder technology status and national conditions, the domestic authoritative book [2] refers to the powder with a particle size of 100% less than 30μm as ultra-fine powder.
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3. Particle diameter and particle size distribution
The size of the particles is the basic property of Zui which determines the other properties of the powder. Generally, the shape of each particle of the treated powder is different and irregular, and the lengths of the respective directions are different and the sizes are different. It is difficult to express the size of the regular particles such as spheres and cubes by the characteristic length. For an irregular particle, the particle diameter (lower particle size) is measured differently, and its physical meaning is different, and the measured values ​​are also different [1] . According to the actual application, select an appropriate measurement method, and find the equivalent diameter or effective diameter.
3.1, particle size
There are four types of particle size representation methods: geometric particle diameter, sieve diameter, effective diameter and specific surface area equivalent diameter.
3.1.1. Geometric particle size is the particle size defined by geometric dimensions. Generally there is [1] :
(1) The triaxial diameter is measured on the plane projection of the particle, and the thickness of the particle is measured in the vertical direction of the projection plane, thereby indicating the major axis diameter, the minor axis diameter, and the thickness, and the three-axis diameter reflects The actual size of the particles;
(2) The directional diameter (projection diameter) often has a Feret diameter (the distance between parallel lines when the parallel plane of a certain direction circumscribes the projection surface of the particle), and the Krummbein diameter (the length of the Zui of the particle projection surface in a certain direction) ), Martin diameter (the length of the line in a certain direction when the projected area of ​​the particle is divided into equal parts);
(3) Heywood diameter, the projected area is a circle with a diameter that is the same as the projected area of ​​the particle;
(4) The equivalent diameter of the sphere, the sphere diameter of the same volume as the particle.
3.1.2. Screening diameter (also known as pore passing through a considerable diameter). When particles pass through a coarse screen and are trapped in a fine screen, the arithmetic or geometric mean of the diameter of the thickness of the sieve is called the sieve diameter.
3.1.3. Effective Diameter The particle size corresponds to the diameter of spherical particles having the same settling velocity in the liquid phase.
3.1.4. The equivalent surface area is equivalent to the diameter of the sphere having an equal specific surface area with respect to the particle to be measured, and is calculated by measuring the specific surface area by a permeation method or an adsorption method. The particle diameter obtained by this method is an average diameter, and a particle size distribution cannot be obtained.
3.2, particle size distribution
The particle size distribution indicates the distribution of particle groups of different particle sizes in the powder, reflecting the uniformity of the particle size. The particle size distribution of a particle swarm can be expressed in the form of simple tables, plots, and functions. The way of particle size distribution is [1] :
(1) a frequency distribution indicating the percentage of particles corresponding to respective particle sizes in the whole particle group;
(2) Cumulative distribution, which means the percentage of particles smaller or larger than a certain particle size in the whole particle group. Among them, the percentage reference can be based on a number reference, an area reference, a volume reference, a length reference, and the like.
Frequency distribution and cumulative distribution are representations of commonly used particle size distributions. The measurement basis is different, and the particle size distribution curve is very different. Therefore, the measurement standard must be indicated when indicating the particle size distribution. The particle size distributions of different benchmarks can theoretically be converted to each other. In the powder processing of the pharmaceutical industry, the practical application of mass and number basis distribution is more [1] .
3.3, average particle size
In order to obtain the average particle diameter of the particle group composed of different particle diameters, the representative particle diameter described above is first determined, and then the average value [1] is obtained . Zui median diameter is the average diameter of commonly used, the value accumulated in the accumulation distribution is exactly 50% of the particle diameter corresponding to, commonly represented by D 50