Kulim ASTM D971

ASTM D971 standard test method for interfacial tension of oil againstwater by the ring method

This application note describes how the Attension Sigma 702ET

can be used to measure interfacial tension of oil against water

according to the ASTM D971 standard.

Description of the standard

This application note describes the measurement of interfacial

tension between oil and water under non- equilibrium conditions

by using the ring method according to the ASTM standard. The

Attension Sigma 702ET allows a precise characterization of wateroil

interfacial tension with this standard. The method is especially

important in petroleum industry as it can be used to determine oil

purity.

In this interfacial tension measurement the platinum ring is lifted

through the water-oil interface. The oil is lying on the water surface

due to the density difference of these two liquids. Water has a

higher surface tension than the oil and therefore force is needed

to detach the ring from the water surface. The force measured is

used to calculate the interfacial tension (mN/m) between oil and

water. The measurement is made within 60 seconds after formation

of the interface with a tensiometer determining tension

between 0-100mN/m. The Sigma 702ET fulfills the requirements

of the ASTM D971 standard. The instrument allows the measurement

do be done fully automatically. A high interfacial tension

value (40mN/m) [1] indicates the absence of undesirable polar

contaminants in the hydrocarbon fluid which means that the fluid

is immiscible with water. A decrease in interfacial tension occurs

for example due to accumulation of contaminants or due to formation

of oxidation by-products. The impurities in the hydrocarbon

fluid encourage the oil to mix with water.

ATTENSION SIGMA 702ET

General applications

The ASTM D971 standard is used to determine the possible

contaminants of hydrocarbon fluids. The purity of hydrocarbon

fluids is important in many industrial areas, such as in aviation,

diesel fuels and transformer oils. For example in aviation, jet fuel

needs to be highly purified as water or dirt contaminations can

cause serious danger in flight safety. Surfactants in jet fuel can

cause the lifting of rust in storage tanks as well as absorption of

water on coalescing surfaces [2]. The ASTM D971 standard is also

a useful indicator of the cetane number of diesel fuels [3]. The

cetane number of diesel fuels is used to define the quality of

combustion during ignition.