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Asked: 2020-05-07T20:55:55+05:30 In:

GATE MT 2020 Q15. Which one of the following statements regarding selective leaching of a binary alloy is TRUE?

Poll Results

68.97%The more electronegative element is leached. ( 40 voters )
6.9%The lower atomic weight element is leached. ( 4 voters )
6.9%The element with lower density is leached. ( 4 voters )
17.24%The element having higher diffusivity is leached. ( 10 voters )
Based On 58 Votes

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GATE MT 2020 Q15. Which one of the following statements regarding selective leaching of a binary alloy is TRUE?
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    4 Answers

    1. official account of Askmemetallurgy
      This answer was edited.

      Correct answer is option A. @Rohit.km described it best. Thank you. Some peripheral lines related to this topic: Selective leaching, also called dealloying, demetalification, parting and selective corrosion, is a corrosion type in some solid solution alloys, when in suitable conditions a component oRead more

      Correct answer is option A. Rohit jha.km described it best. Thank you.

      Some peripheral lines related to this topic:

      • Selective leaching, also called dealloying, demetalification, parting and selective corrosion, is a corrosion type in some solid solution alloys, when in suitable conditions a component of the alloys is preferentially leached from the material.
      • The less noble metal is removed from the alloy by a microscopic-scale galvanic corrosion mechanism.
      • The most susceptible alloys are the ones containing metals with high distance between each other in the galvanic series, e.g. copper and zinc in brass.
      • The elements most typically undergoing selective removal are zinc, Aluminium, iron, cobalt, chromium, and others.
      • There are three steps of mechanism in dezinfication:
      1. First entire brass alloy is dissolved.
      2. The noble metal is re-plated (i.e. Cu in brass)
      3. Active metal is leached away (i.e. Zn in brass)
      • Zinc is quite reactive metal while copper is more noble metal.
      • Zinc can corrode slowly in corrosive environment and leaching occurs in brass which makes porous structure of copper.
      • The higher electronegative element is leached.

       

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      • Respected sir/madam, I had this doubt regarding electronegativity. Generally its seen more electropositive metals corrode while more electronegative act as cathode. I checked for electronegativity values for Cu and Zn, they were 1.9 and 1.65 respectively. Then why does the option say more electronegRead more

        Respected sir/madam,

        I had this doubt regarding electronegativity. Generally its seen more electropositive metals corrode while more electronegative act as cathode. I checked for electronegativity values for Cu and Zn, they were 1.9 and 1.65 respectively. Then why does the option say more electronegative is leached?

        Thank you

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    2. Gold B.TECH, NIT DURGAPUR

      The higher electronegative elements is more active and acts as anode

      The higher electronegative elements is more active and acts as anode

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    3. Gold B.TECH, NIT DURGAPUR

      More electronegative elements leached

      More electronegative elements leached

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    4. Best Answer
      Platinum Gate aspirant.

      Selective leaching ( or dealloying ) of an alloy is the preferentially attacking of one of its components in presence of some electrolyt occurring as a result of oxidation-reduction reactions. In Binary alloys( or other multiphase alloys) it is  usually common when elements have high electode potentRead more

      Selective leaching ( or dealloying ) of an alloy is the preferentially attacking of one of its components in presence of some electrolyt occurring as a result of oxidation-reduction reactions.

      In Binary alloys( or other multiphase alloys) it is  usually common when elements have high electode potential difference. In that case the lower electrode potential element act as anode or called ACTIVE element and the higher act as cathode or called NOBLE element.

      Example Dezincification of Brass(Cu-Zn) alloy

      Here the Zn has lower electrode potential act as Active metal and Cu having higher act as Noble metal. In one method in suitable condition only Zn leaves as Zn2+ and thus corrodes.

      Another method it says that Cu and Zn leaves together but Cu being noble metal returns back to alloy thus selective corrosion occurs.

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