The stability of grinding slurry is crucial for its effective function during grinding, and it is influenced by several factors:
I. Composition Factors
Abrasive Characteristics
Particle Size Distribution: Uneven abrasive particle size distribution leads to decreased slurry stability. If excessively large or small particles are present, large particles tend to settle easily in the slurry, while small particles may aggregate to form agglomerates. For example, in a grinding slurry containing alumina abrasives of various sizes, if the proportion of coarse particles is high and they have not undergone proper classification, these coarse particles will quickly settle to the bottom of the container due to gravity during settling, increasing the difference in composition between the upper and lower layers of the slurry and affecting its stability.
Abrasive Type and Surface Properties: Different abrasives have different chemical properties and surface activities. For example, silicon carbide abrasives carry a certain surface charge, which may cause them to aggregate in the slurry due to charge interactions. Additionally, some abrasives have high adsorption properties; if they adsorb components from additives into the slurry, it may alter their dispersion state and the overall stability of the slurry.
The Role of Additives
Dispersants: Dispersants are key additives affecting the stability of grinding slurries. It can adsorb onto the surface of abrasive particles, isolating them through electrostatic repulsion or steric hindrance, preventing aggregation and sedimentation. For example, some polymeric dispersants can form a thick adsorption layer on the surface of abrasive particles, generating a steric hindrance effect, keeping the abrasive particles well dispersed in the grinding fluid. If the amount of dispersant is insufficient or its compatibility with the abrasive is poor, the abrasive particles may gradually agglomerate, causing the grinding fluid to thicken or even separate.
pH adjusters and buffers: The pH value of the grinding fluid has a significant impact on its stability. Many abrasives and additives are stable only within a specific pH range. For example, some metal oxide abrasives may undergo chemical reactions under acidic conditions, while some surfactants lose their activity in excessively alkaline conditions. pH adjusters are used to adjust the initial pH value of the grinding fluid, while buffers can resist pH changes caused by chemical reactions or external factors during grinding, maintaining the chemical stability of the grinding fluid.
Preservatives and antibacterial agents: In aqueous grinding fluids, the growth and reproduction of microorganisms can seriously affect the stability of the grinding fluid. Microorganisms decompose the organic components in grinding fluids, producing acidic substances, gases, and viscous substances, leading to fluid deterioration, foul odor, and stratification. Preservatives and antibacterial agents can inhibit microbial growth and maintain the stability of the grinding fluid's chemical composition and physical properties.
Base Fluid Properties
Viscosity: The viscosity of the base fluid has a significant impact on the stability of the grinding fluid. Higher viscosity base fluids, such as some oil-based grinding fluids, can slow down the settling rate of the abrasive, allowing it to remain suspended in the fluid for a longer period. However, excessively high viscosity can affect the fluid's flowability and heat dissipation, hindering the grinding process. For water-based grinding fluids, which have lower viscosity, stability can be improved by adding thickeners or adjusting the abrasive-to-additive ratio.
Chemical Compatibility: The chemical compatibility between the base fluid and the abrasive and additives is crucial. If the base fluid reacts chemically with the abrasive or additives, it will alter the composition and properties of the grinding fluid. For example, in grinding fluids containing certain active metal abrasives, the use of an oxidizing base fluid may cause the abrasive to oxidize, affecting the fluid's stability and grinding performance.
II. External Factors
Temperature Changes
Temperature significantly affects the stability of grinding slurries. High temperatures accelerate the chemical reaction rate of components in the slurry, leading to additive decomposition and altered interactions between abrasives and additives. For example, at high temperatures, the molecular structure of some surfactants may be destroyed, causing them to lose their dispersing and emulsifying abilities. Simultaneously, increased temperature reduces the viscosity of the grinding slurry, accelerating abrasive settling. Conversely, at low temperatures, the grinding slurry may solidify and increase in viscosity, affecting its fluidity and abrasive dispersibility.
Mechanical Vibration and Agitation
Excessive mechanical vibration or inappropriate agitation can compromise the stability of the grinding slurry. Strong vibrations may cause abrasive particles to aggregate, overcoming the dispersant's effect, especially when the dispersant in the slurry is weak or the abrasive itself is prone to agglomeration. Inappropriate agitation speed and time can also cause similar problems. For example, excessively fast agitation introduces a large amount of air, generating foam. The presence of foam affects the uniformity of the grinding slurry's composition and may lead to uneven abrasive distribution after foam bursting.
Storage Conditions and Time
The storage environment of the grinding slurry is crucial to its stability. If the storage container is not properly sealed, the grinding slurry will come into contact with outside air, which may lead to moisture evaporation (for water-based grinding slurries) or oxygen ingress causing oxidation. Furthermore, prolonged storage can decrease the stability of the grinding slurry. Over time, the abrasive may gradually settle, and additives may slowly become ineffective, especially under unsuitable storage temperature and humidity conditions, where these changes will be more pronounced.