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Question: metal microscphy sample preparetion of metallurgy?
By: sourav dash     Date: 2012-10-02

Answer: For examination under microscope metal surface should be free from scratches. It should have mirror finish. This is achieved by polishing the surface in stages. This consists of polishing by belt grinder followed by manual polishing using different grades (0, 00, 000)of emery papers from coarse to fine. For hard metals like steel dry polishing is good enough. For soft metals like aluminum you need wet emery paper. Take care to wash the sample after each stage. If the sample is too small to grip by hand it may be mounted (fixed) in Bakelite or sample holder. After emery paper finish move over to wet polishing on cloth mounted on rotating disc. The cloth is kept soaked in water having fine suspension of polishing powder. After this if you look under microscope you would see a shining flat surface. Inclusions (or graphite in cast iron) if present may be visible. You need to etch the sample to see other fine details like grain structure. Use nital (2% HNO3 in alcohol)to etch steel.

By: Prof. R.N. Ghosh     Email: click8sourav@gmail.com     Date: 2012-10-05


Question: Sir, Why Cant A Face Centered Cubic Be Called A Body Centered Tetragonal?And Why There Are Only 14 Bravias Lattices Instead Of 28?
By: Ravi Verma     Date: 2013-10-08

Answer: 1)Yes FCC lattice can be considered as a BCT lattice whose c/a ratio = 1.414. This makes BCT lattice as symetric as a cubic lattice. 2)Lattice is an array of points in 3D where every point has identical surrounding. There are only 7 primitive lattice having points only at the corner of the unit cell. This denotes 7 crystal system. By placing additional points within unit cells only 7 more lattices can be obtained(eg face centre, body centre & base centre). If you put additonal points at any other locations it could be easily shown that either it is not a new lattice or it violates the the main definition of lattice (means all points may not have identical surrounding). This is why you cannot have more than 14 Bravais Lattice.

By: Prof. R.N. Ghosh     Email: Verma.Metallurgist@gmail.com     Date: 2013-10-21


Question: Respected sir, The lecture no 10 and 11 are same. There is introduction lecture on Crystal Defects in Metals. Kindly check this matter.
By: srinu     Date: 2013-09-22

Answer: The two are not the same. Please go beyond the first slide. Lectures 10-14 cover the points given in the first slide. Five lectures have been devoted to crystal defects and interaction.

By: Prof. R.N. Ghosh     Email: srinumichel@gmail.com     Date: 2013-09-30


Question: Respected Sir, I am sorry to disturb you again. I have gone through all the videos on Crystal Defects from lecture no 10-14 posted in this site.The lecture no 10 is replaced by lecture 11 itself. There is no original Introduction lecture on Crystal Defects in Metals. Thanking you
By: srinu     Date: 2013-10-02

Answer: I again looked at the lectures 10-14 on my computer as well as through youtube. They are all different. I donot know which website you are looking at. It may be a problem with the website. How could lecture 10 get replaced by lecture 11 is not clear to me. Are you looking at downloaded files? If so there may have been a mixup while down loading.

By: Prof. R.N. Ghosh     Email: srinumichel@gmail.com     Date: 2013-10-04


Question: Sir, In case of an Isomorphous system, if the two components have the same melting point, then how the phase diagram will be constructed?
By: Irshad     Date: 2014-04-11

Answer: It is possible only if there is an intermediate composition of an alloy that melts at a fixed temperature. These are known as isomorphous system exhibiting a maximum or a minimum. The solidification behavior of the intermediate alloy is exactly same as that of a pure metal.

By: Prof. R.N. Ghosh     Email: irshad7861980@rediffmail.com     Date: 2014-04-21


Question: Respected Sir, I Have a Question About Iron-Carbon Equlibrium Diagram.Why, After 4.3% C In Iron The Melting Point Of Iron Decreass???
By: BikramLenka     Date: 2015-07-17
The co-ordinator will post his answer


Question: respected sir closed structures are stable at low temperatures and open structures are stable at high temperatures. but in case of pure iron it is totally opposite why
By: md imtyazuddin     Date: 2015-10-21
The co-ordinator will post his answer

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