What is it?
Differential Scanning Calorimetry, or DSC, is a thermal analysis technique that looks at how a material’s heat capacity (Cp) changes with temperature in the presence of oxygen, air or an inert gas. High Pressure (HP) DSC is a technique used to accelerate oxidative stability testing, a method that is required when testing high performance lubricants.
Why do we use it?
In the presence of air or oxygen, lubricants will degrade through oxidation. At ambient temperature and atmospheric pressure oxidation is almost immeasurably slow but the rate of oxidation doubles for every 10OC increase in temperature. Lubricating oils can be subjected to high temperature operating conditions, for example automotive engine oils or turbine oils and by using HPDSC we can determine the relative stability of different base fluids, effectiveness of different anti-oxidants and additive packages and potential in-use performance of fully formulated oils.
How does it work?
For lubricants, the “Oxidation Induction Time” (OIT) is typically investigated using ASTM D6186. This is a standardised test which measures the level of thermal stabilisation of a material by determining the time of oxidative decomposition.
In a typical OIT test, the test sample (usually 15 mg) is heated in an inert atmosphere (nitrogen) to a temperature above the melting point of the sample. At a constant temperature (isothermal) the sample atmosphere is switched from inert gas to an oxidative gas. The time elapsing until the exothermal oxidation of the sample begins is the oxidation induction time and represents the point at which unconstrained oxidation of the lubricant takes place after the anti-oxidants have been effectively consumed.
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