High corrosion resistant materials for fluorine based applications

Fluorine is the strongest oxidizing agent among all chemical elements. It is used in large magnitudes on an industrial and lab scale in atomic energy sector. Fluorine also develops the most stable metal fluoride layers. In alloy selection, the diffusing element in the alloy must develop only single and nonvolatile fluoride. Different metals provide different levels of corrosion resistance. Nickel offers the best corrosion resistance while the steel provides nominal performance.

Suitable choice of materials of construction is important for the safe operation of any system or piece of equipment. The common metallic materials of construction for use with fluorine near room temperature or below about 250oF are steel, Monel, nickel and aluminum. These materials develop thin, protective corrosive layers and are more corrosion resistant as compare to others. Iron and steel are the common commercial storage container materials: Monel and Nickel provide the best performance as systems, tubing and are preferred for high temperature operations. Copper tubes are useful in various applications, particularly near room temperature, although with increase, its reactivity more increases as compare to Monel and Inconel.

In alloy selection, the diffusing elements in an alloy should develop only single stable and nonvolatile fluoride. Using nickel based alloys, the fluoride layer developed is NiF2. The chosen alloy should be single phase because in multiple phase alloys, one phase is attacked at a higher rate and it rapidly attains intergraular corrosion and stress corrosion cracking. One phase should be leached out fully. Alloys may become incompatible at lower temperatures as compare to resistant basic metal. Intermetallic compounds are attacked faster as compare to pure component.

While using less resistant materials, it is recommended to plate the metal with a resistant metal. Use of electroplated nickel is best. On the other hand, while using Monel400 for fluorine based processes, the layer formed is a mixed fluoride of the major alloy compositions of approximately the composition of the alloy. For nickel 200, the fluoride layer is fluoride of the main element.

Metals for Fluorine based rocket fuels

In aerospace applications where propellants considered for storage in space at temperatures below -200oF include fuels like oxygen difluoride, fluorine-oxygen mixtures and chlorine trifluoride. The recommended metals and alloys for use for this application are aluminum, nickel, copper, titanium and stainless steels. These materials are found suitable for construction of equipments for storage and handling the semicryogenic propellants for duration of two to ten years. These high functional materials are found to provide suitable physical properties at extremely low temperatures, resist corrosion and corrosion as well as not to induce propellant decay.

Corrosion rates of Nickel based alloys are very low in fluorine based solutions and environments. Therefore these alloys are recommended for use in these applications. These materials are sturdy, durable and corrosion resistant that they can withstand fluorine based conditions at various temperatures for long period. So contact Heanjia Super-Metals for finding more information about these materials and choosing a suitable one.