Quartz linear thermometer: L Hammond and A Benjaminson, Measures Regulat Autom, 31, 1966, 73–79 (in French)

Abstract

Etched insulated carbon fiber electrodes can be prepared from a suitable source of graphitized carbon fibers, copper wire, colloidal graphite, and a cathodic electrophoretic paint. The processes involved in the production of these electrodes involve mounting the carbon fibers, etching them to produce a sharp tip, and subsequent insulation of the tip so that only the very end of the tip is exposed. Etching of the electrodes requires a variable voltage AC source (50 Hz, 1–10 Vac), an AC current meter capable of measuring in the μA range and a suitable linear translation stage. Insulation of the electrode requires a DC power supply (0–20 V), linear translation stage, microscope, and oven. The insulation process involves two separate stages: electrophoretic deposition of paint onto the tip surface followed by a curing step at high temperatures during which the paint particles fuse together. Cathodic electrophoretic paint is the preferred polymeric material used to insulate the carbon fibers as the negative potentials required for deposition avoid any possibility of oxidative dissolution of the carbon fiber. Testing of electrodes requires a high-gain low-noise potentiostat. Testing is performed to determine the presence of any pinholes in the insulation. The quality of the coating of the electrode may be assessed in a nondestructive manner by measuring the diffusion limited current response as a function of the extent of immersion of the electrode into a suitable electrolyte solution. A more destructive approach to assessing the quality of the coating may be performed by polarizing the electrode in an electrolyte containing a suitable metal salt.