The dispersion method is a method of finely dispersing bulk materials into colloidal particles. It includes mechanical grinding, ultrasonic dispersion, peptization dispersion, electric dispersion and other methods.
The grinding method is a common method for crushing and dispersing large objects, such as grinding ink in an inkstone, grinding noodles in a millstone, grinding spring rice in a stone, grinding sesame paste in a Grinder, etc., all belong to the grinding method. Due to the different initial nature of the material, there are two ways of smashing it: the attacking style and the Zhantang style (wiping and grinding style). The Grinders used in practice include both impact type, such as high-speed impact Grinder; there are also grinding types, such as three-roll mill, stone mill, colloid mill, etc.; of course, the combination of the two is the most common, such as ball mill, disk Grinding equipment such as mills and sand mills. The colloid can be obtained by crushing and grinding the solid to a size of 1~500nm and dispersing it in the medium. However, directly grinding solids can only obtain micron-sized particles at most, which cannot reach the degree of colloidal dispersion. A more effective method is to aid in the wet grinding of surfactants, or co-grind the dispersed substance (such as sulfur) with another irrelevant solid substance (such as sucrose) that can be dissolved in the dispersion medium, and finally grind The sol can be obtained by water printing of the substance in time-sharing, and another substance contained in the sol can be removed by dialysis. Here is a brief introduction to the colloid mill. The colloid mill is an ultra-fine pulverizing machine. Its basic working principle is that under the action of centrifugal force, the fluid or semi-fluid material is forced to pass through the gap between the stator and the rotor. Due to the high-speed relative motion between the stator and the rotor, the material is subjected to a strong force here. The shear force, friction force, high-speed stirring and high-frequency vibration and other physical effects can effectively continue to grind the finely divided powder to achieve the purpose of ultrafine crushing and emulsification of the material (Figure 2-3). It is widely used in coatings at present. , pharmaceutical and food industries.
Ultrasonic dispersion is a common method for preparing colloids in the laboratory. When the frequency is higher than 16ooOHz, it is ultrasonic, generally up to 1MHz. The high-frequency ultrasonic waves are introduced into the medium, and produce the same frequency of alternating density and density tearing force on the dispersed phase in the medium, so that the dispersed phase is evenly dispersed. It is widely used in emulsion preparation, colloid preparation and laboratory.
The peptization method is a method of redispersing the dispersed phase that has been temporarily coagulated (precipitated). It is a method of turning insoluble precipitates into colloids by passing through a small amount of soluble substances or washing away excess electrolyte in the system. After washing the newly generated precipitate, add the electrolyte solution as a stabilizer, and redisperse after stirring and precipitation. The added soluble substances are called peptizers. Peptization is generally only effective for fresh and relatively loose precipitates. Once the precipitation is placed for a long time, the small particles have grown into large particles, and it is difficult to use peptization to achieve the purpose of redispersion. For example, adding electrolytes such as FeCl3 to fresh Fe(OH) 3 precipitates and AgN03 to fresh AgC1 precipitates can quickly transform the precipitates into colloids.
The electrodispersion method is mainly used to prepare metal hydrosol. It inserts the metal as an electrode into the solution, and then passes a high-voltage current between the two electrodes to make the discharge between the two electrodes form an arc. Prepared metal sol. This method starts with a dispersive process, followed by a cohesive process. Stable sol can be obtained by adding a small amount of alkali in water. Sometimes in order to avoid by-products (electrolysis products), high-frequency current is used instead of direct current.
