Silicone greases
Composition, characteristics and industrial applications

Silicone greases (also known as dielectric greases) are synthetically-derived pseudoplastic lubricants. Formulated from silicone oils of the same name, they are characterised by superior adhesiveness and permanence at friction points due to the use of thickening agents that are:

• Organic – lithium soaps; or,
• Inorganic – pyrogenic silica or polytetrafluoroethylene (PTFE).

The family of silicone lubricating greases contains numerous variations both in terms of the composition of the base oil and the nature of the thickener. The thickener is responsible for the thixotropic conduct and thus the adhesive and cohesive properties for the lubrication zones, along with the lubricating power.

The strengths of silicone greases are closely linked to the type of base oil used in their formulation and can be distinguished as:

• Dimethylsilicone oils – the most widely-used silicone-base oils due to their price-performance ratio, consisting of a polymer chain built on a silicon-oxygen framework with organic methyl terminations;
  
  
• Phenylsilicone oils – widely employed for their superior thermo-oxidative stability;
  
  
• Fluorosilicone oils – more chemically stable and unsurpassed in terms of chemical inertness;
  
  
• Ogranosilicone hybrid oils – characterised by the combined presence of organic and siloxane chains, where organo-silicones combine both the lubricating properties of organic oils and those of silicones.

Silicone greases are part of the family of synthetic lubricants and thus enjoy many strengths that make them the preferred choice where mixed friction combinations between polymeric materials and metals under prolonged and extended thermal stresses are envisaged.

Amongst the main characteristics we can distinguish:

• High viscothermal stability – minimal viscosity variation upon changes to the operating temperature;
  
  
• Inertia with plastics – do not attack polymeric materials, even amorphous ones, ensuring material integrity also under mechanical stress;
  
  
• High slipping power – offer a low coefficient of friction, especially for mixed rubber-metal and metal-plastic couplings;
  
  
• Good mechanical noise-inhibiting effect – the use of high-viscosity base oils, due to their high thermal viscosity index, facilitating a good damping effect to be achieved;
  
  
• Extensive operating temperature range – depending on the viscosity of the base oil from -60° to 250° C for phenyl silicones;
  
  
• Rubber compatible – do not produce significant changes in the mechanical properties of elastomer compounds including EPDM material.