The electrical conductivity of metallic surfaces plays an important role in many processes. In many instances the electrical conductivity is controlled by the type of surface on a metal. For example, steel which consists mainly of iron will have various forms of iron oxide on the surface thereof due to corrosion or scaling of the metal. The various forms of oxides which are present on the surface of the steel will include ferrous oxide (FeO), ferric oxide (Fe.sub.2 O.sub.3), and magnetite (Fe.sub.3 O.sub.4), which is also known as ferriferrous oxide. The amount or percentage of the ferrous oxide layer formed on the surface of steel will be dependent upon many variables including the oxygen content of the atmosphere to which the steel is exposed as well as the catalytic effect of the various other metals present in the steel including copper, chromium, nickel, etc. The electrical resistance or conductivity of the various iron oxides will vary, ferrous oxide possessing the least conductivity. In many instances this is a detriment inasmuch as a relatively high electrical conductivity is desired. A particular instance in which a relatively high electrical conductivity is desired comprises electrostatic precipitators which are utilized to remove fly ash from the atmosphere in power plants which burn coal to provide a source of electricity. The electrostatic precipitators which are employed in these plants are fabricated from steel and will contain wires possessing an electrical charge inside the apparatus. The gas stream resulting from the pyrolysis of coal will pass through the precipitator and any fly ash particles which are present in the gas stream will be collected on the plates of the unit. It is therefore necessary that the plates of the unit possess an electrical conductivity sufficient that an electrical charge can be built up upon the oxide surface to attract the particles to the metal surface and yet be not so great so as to prevent the particles after agglomeration from being removed from the inner surface of the unit.
A problem which arises is that an iron oxide layer in the form of ferrous oxide which is highly electrically resistive will form on the surface of the unit. While this layer can be made to have an electric charge which is positive with respect to the wire passing through the unit and the fly ash particles in the gas stream even when highly electrically resistive, the rate of charge transfer is very low and correspondingly the rate of fly ash deposition is very low. It is necessary that the electrical conductivity be increased sufficiently that the charge transfer increases to effectively remove the fly ash particles from the gas stream before the gas stream is passed to the atmosphere. In order to improve the electrical conductivity of fly ash-plate system, the presently available methods concentrate on the fly ash. There are three methods currently being employed to increase the electrical conductivity of the fly ash particles. Two methods which are currently employed comprise a method known as doping the coal with sodium compounds such as sodium sulfate, sodium carbonate, etc., or by injecting ammonia gas into the flue gas in order to form ammonium salts in situ to increase the electrical conductivity of the fly ash particles. The third method which is currently employed comprises spraying sulfuric acid into the flue gas to increase electrical conductivity of the particles. However, a serious drawback which is attendant to the use of sulfuric acid lies in the fact that noxious compounds of sulfur or sulfate are formed which must be removed from the gas which is discharged into the atmosphere. This removal will of necessity entail the use of additional equipment in order to scrub the undesired compounds from the flue gas.
As will hereinafter be shown in greater detail, it has now been discovered that metal surfaces can be regenerated to permit the presence of desirable oxides on the surface thereof, said oxides possessing the required electrical conductivity for use in many processes. These methods then improve the electrical conductivity of the plates used in electrostatic precipitator making the continuous conditioning treatments of the coal described above unnecessary.