Letter: P
Painting A chemical treatment that prevents the adhesion of the non-vulcanized tyre (the so-called 'green' tyre) to the moulds and/or the vulcanizing chamber.
Pascal An international unit of pressure equal to 1 Newton per square metre (Pa = N/m2).
Patenting The thermal treatment necessary to restore the structure of steel wire so as to make it suitable for further deformation via cold drawing.
PCB/PCT Acronyms for polychlorinated biphenyls and polychlorinated terphenyls, substances that are potentially dangerous, bioaccumulable, with insulating and fire-resistant characteristics, principally used in electrical equipment transformers and/or capacitors (see entry).
Photochemical Atmospheric pollution principally caused by the exhaust emissions of urban vehicular smog traffic; it is the result of a complex chain of photochemical oxidation reactions triggered by sunlight and favoured by particular meteorological conditions (inversion...). One of the consequences of photochemical smog is an increase in ozone in the troposphere (see entry), which thus becomes a secondary pollutant. Furthermore, the relatively non-volatile organic compounds that form may condense, creating a characteristic mist of tiny droplets.
Photonics Science and technology relating to a class of devices using photons. The term photonics was introduced as an analogy with the term electronics in reference to the replacement of the electron with the photon in operations typical of electronics such as the processing, transmission and memorization of data.
Pickling The elimination of the oxidization of metal surfaces (for example, copper and steel). The operation is generally conducted in baths containing solutions of phosphoric or sulphuric acid.
Primary energy sources Energy sources consumed while supplying final energy services (e.g. heating and transport) or generating intermediate forms of energy, like for instance electricity and steam. Examples of primary energy are: coal, natural gas, liquid propane gas, fuel oil, biomasses.
Pressure A physical measurement expressing the ratio between the intensity of a force (expressed in Newtons) exerted on a surface in the normal direction and the area of that surface (expressed in square metres).