Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound with the formula FeS. In the oil/gas industry, iron sulfides are often present in a sour system due to reaction between corrosion products and hydrogen sulfide.
A material that conducts (see conduction) electricity poorly or not at all. If a voltage is applied to a dielectric, the atoms in the material arrange themselves in such a way as to oppose the flow of electric current. Glass, wood, and plastic are common dielectrics. (See insulator.)
The dielectric constant k is the relative permittivity of a dielectric material. It is an important parameter in characterizing capacitors. It is unfortunate that the same symbol k is often used for Coulomb's constant, so one must be careful of this possible confusion.