Definition
A laboratory disperser is a mechanical device used to evenly disperse solid particles in a liquid medium and achieve processes such as mixing, emulsification, or homogenization. It typically consists of core components such as drive motors, dispersion shafts, and dispersion discs, making it suitable for laboratory-scale sample preparation and process research.
Principle
Laboratory dispersers operate on the principle of high-speed shearing. The motor drives the dispersion shaft to rotate at high speed, driving the dispersion disc mounted at the shaft end to move. Dispersion discs usually have a toothed structure, and when they rotate at high speeds, they generate strong shear forces and turbulence. The solid particles are broken under the action of shear, and the liquid medium forms a circular flow, so that the particles are gradually and evenly dispersed throughout the system. This process can be described as energy input causing a velocity gradient in the fluid that exerts shear stress on the surface of the particles. For spherical particles under laminar flow shear conditions, the shear stress τ can be approximately expressed as:
τ = η · γ
where η is the fluid viscosity and γ is the shear rate.
Measurement and evaluation methods
Dispersion is usually evaluated in combination with process parameters and final sample characteristics. Parameters such as speed, torque and temperature can be monitored during operation. After the sample is dispersed, the particle size distribution can be determined by a laser particle size analyzer, the rheological characteristics of the system can be measured using a viscometer, or the particle dispersion can be observed by a microscope. Settlement experiments can also be used to evaluate dispersion stability, i.e., to measure the stratification of suspended bodies after a period of rest. These methods need to refer to relevant industry standards, such as ASTM D1210 and other method guidelines in the field of coatings.
Influencing factors
The dispersion effect is affected by multiple factors. The equipment parameters include the diameter of the dispersion disc, tooth design, rotation speed and the position of the dispersion disc in the container. The process parameters involve dispersion time, temperature control, and feeding sequence. In terms of material characteristics, the initial particle size, hardness, and concentration of particles, as well as the viscosity and surface tension of liquid media, are crucial. The operating environment, such as the shape and size of the vessel, also affects the flow field distribution. These factors are interrelated and need to be systematically adjusted in practice.
Applications
Laboratory dispersers are widely used in R&D and quality inspection links that require fine dispersion. In the coatings and inks industry, it is used for the dispersion of pigments in substrates. The field of nanomaterials is commonly used to prepare nanoparticle suspensions. The food industry uses it for the emulsification of sauces. It is used in the research and development of cosmetics to prepare cream systems. It is also commonly used in the laboratory preparation of products such as battery pastes, ceramic glazes, dyes, and adhesives.
Selection considerations
When choosing a laboratory disperser, it is necessary to comprehensively consider the experimental needs and equipment performance. The viscosity range and expected capacity of the sample being processed determine the required motor power and torque. The corrosiveness of materials requires suitable materials for contact parts, such as stainless steel or special coatings. The speed range and control accuracy should meet the needs of process exploration. Whether the equipment has extended features such as vacuum degassing or temperature control depends on the specific application. Operational noise, safety protection, and ease of maintenance are also important considerations in the laboratory environment. It is recommended to test the machine based on actual samples to verify the suitability of the equipment for specific processes.