A ZDDP tribofilm experiment consists of the following:

A ZDDP tribofilm experiment consists of the following:

1. The test chamber containing lubricant is heated while rotating the ball and disk in pure rolling with no applied load until the test temperature is reached.

2. Motion is then halted and the glass window is loaded against the stationary steel ball. An interference image of the window/ball contact is captured for subsequent analysis to determine the spacer layer thickness.

3. The glass window is withdrawn from the steel surface and a rubbing test carried out for a set duration at the set temperature. In this, the steel ball is loaded against the steel disk and the two are rubbed together in mixed rolling/sliding at low rolling speed to produce mixed or boundary lubrication. This generates a ZDDP tribofilm on the rubbed track of both the steel ball and steel disk.

4. Motion is then halted, the glass window loaded against the rubbed track on the stationary steel ball, and an interference image of the window/ball contact is captured. By comparison with the initial image, interference colors present can be used to determine the thickness of any solid-like tribofilm formed on the track.

5. Procedures 3 and 4 are then repeated over a total test time of several hours to obtain a series of interference images and thus maps of the variation of ZDDP tribofilm thickness on the ball over time.

It is important to note that the tribopair that forms the ZDDP film is the steel ball/steel disk sliding contact. The glass window is only loaded against the stationary ball to displace any supernatant oil and measure the thickness of the residual solid-like film present and this is done without rinsing or cooling the ball in any way and without removing it from the test apparatus.