An electrochemical test cell apparatus is disclosed for enabling in-situ X-ray transmission of a flowing fluid using a small angle X-ray scattering technique. A base has a recessed portion that partially defines a volume for containing a test sample. The base may have a fluid supply passage for providing a flowing fluid into the volume, a fluid return passage for allowing the flowing fluid to exit the volume and flow out of the test cell, and a first hole for allowing an X-ray beam to pass through the volume. A clamp member is coupled to the base to help define the volume and may have a second hole aligned with the first hole that allows the X-ray beam to pass through the clamp member. A pair of material portions may be clamped between the base and the clamp member to retain the fluid within the volume while allowing passage of the X-ray beam through first and second holes. A pair of electrodes may be used to supply a potential difference to the flowing fluid.
STATEMENT OF GOVERNMENT RIGHTS
 The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the U.S. Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Laboratory.