Metallurgical Processes

Kinks in rails can form due to various defects: loose packing at joints allows movement, gauge/alignment defects cause stress concentrations, and cross-level issues at joints create irregularities. All three factors (options A, B, C) can contribute to kink formation, making option D the comprehensive correct answer.

Cathodic modification is the retardation of anodic reaction as the result of an increase in the ability of an alloy to be passivated by the introduction of an active cathode into the alloy e.g., the alloying of stainless steel and titanium with platinum group metals

Bethanization is a process to protect steel from corrosion by plating it with zinc.

In the context of corrosion, passivation is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few nanometers thick.

The Hall-Héroult process is the major industrial process for the production of aluminium. It involves dissolving alumina in molten cryolite, and electrolysing the molten salt bath to obtain pure aluminium metal.

The passive voice should use the past participle 'used', not the present participle 'using'. The metal is not doing the using - it is being used by others. The correct phrase is 'the metal used in this particular model' or 'the metal that was used in this particular model'.

A number of metals such as silver, gold and platinum, have been obtained in colloidal state by treating the aqueous solution of their salts, with a suitable reducing agent such as formaldehyde, phenyl hydrazine, hydrogen peroxide, stannous chloride etc.

This option is correct because the finely powdered colemanite ore is usually boiled with sodium carbonate to obtain sodium borax and sodium metaborate.

This option is correct because germanium oxide gives red heat in a current of H₂ at 540^oC, to give pure germanium.

Hydrogen corrosion is a form of metal corrosion occurring in the presence of anoxic water. Hydrogen corrosion involves a redox reaction that reduces hydrogen ions, forming molecular hydrogen.

Intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides.

Microbial corrosion, also called bacterial corrosion, bio-corrosion, microbiologically-influenced corrosion, or microbially-induced corrosion (MIC), is corrosion caused or promoted by microorganisms, usually chemoautotrophs. It can apply to both metals and non-metallic materials.

Stress corrosion cracking (SCC) is the unexpected sudden failure of normally ductile metals subjected to a tensile stress in a corrosive environment, especially at elevated temperature in the case of metals.

Micro pitting is a fatigue failure of the surface of a material commonly seen in rolling bearings and gears. It is also known as grey staining, micro spalling or frosting.

Green death is a solution used to test the resistance to corrosion of metals. It consists of 11.9% sulfuric acid, 1.3% hydrochloric acid, 1% Iron(III) chloride and 1% Copper(II) chloride boiling at 103°C.