Aquadag
Aquadag is a trade name for a water-based
Properties
Aquadag consists of a dispersion of colloidal graphite in distilled water.[2][3] It is provided in concentrated paste form and is usually diluted with distilled water to a desired consistency before application. It can be applied by brushing, swabbing, spraying, or dipping, after which the surface is dried, leaving a layer of pure graphite.
After drying the coating is electrically conductive. Its resistance and other electrical properties vary with degree of dilution and application method. When diluted 1:1 and applied by brush its resistance is:
- Air-dried ~800 ohms per square
- Heated to 200 °C ~500 ohms per square
- Heated to 300 °C ~20–30 ohms per square
Use in cathode ray tubes
A conductive aquadag coating applied to the inside of the glass envelope of
The aquadag coating has two functions: it maintains a uniform electric field inside the tube near the screen, so the electron beam remains collimated and is not distorted by external fields, and it collects the electrons after they have hit the screen, serving as the return path for the cathode current.
In some CRTs the aquadag coating performs a third function, as a
In the television tube manufacturing industry, the manufacturing step that applies the aquadag is called "dagging".
Other uses
Aside from its use in the production of CRTs, Aquadag is used in many types of high-voltage lab apparatus where a conductive coating is needed on an insulating surface. The surfaces of some metals (most notably aluminum) can develop nonconductive oxide layers, which tend to disrupt the electrostatic field produced around the surface of the metal when used as an electrode. Aquadag is not subject to such effects and provides a completely uniform equipotential surface for electrostatics.
Producers of continuous filament fiberglass will coat their product with Aquadag when a conductive property is required.
Aquadag was also used in the production of some copper oxide rectifiers, to help make the ohmic connections to their counterelectrodes.[7]
Other dags
There are also deflocculated graphite products dispersed in liquids other than water. Acheson has extended the use of the dag
References
- ^ Acheson, Edward Goodrich. "Original AquaDAG Patent US844989A". Google. US Patent Office.
- ^ "Data Sheet AGG303: Colloidal Graphite - "Aquadag"" (PDF). Products. com Agar Scientific. 2015. Retrieved August 25, 2015.
- ^ "AQUADAG E - Water Based Colloidal Graphite Resistance Coating" (PDF). Technical data sheet E25/08/00-GL. Emerson & Cuming, a division of National Starch & Chemical. 2000. Retrieved August 25, 2015.
- ^ ISBN 978-8129704962.
- ^ ISBN 978-8122416077.
- ISBN 978-0174387336.
- .