In the Bayer's process, bauxite is digested under pressure using
H2SO4
NaOH
NH3
HCl
Correct Answer :
B. NaOH
Related Questions
A cylindrical rod subjected to a tensile strain within the elastic limit undergoes a volume change. If the volume strain is equal to half the tensile strain, then the Poisson's ratio of the rod is
0
0.33
0.44
0.25
The lightest non-inflammable gas is
H2
He
Ar
O2
In electrical resistance welding, distortion results from the use of improper
Clamping methods
Electrodes
Current
Filler material
Addition of __________ to steel does not impart hardness.
Nickel
Copper
Chromium
Silicon
Temper brittleness of a material can be fairly detected by the __________ test.
Fatigue
Notched bar impact
Tensile
Hardness
Maximum permissible sulphur content in steel is __________ percent.
0.015
0.055
0.505
0.805
The product (s) of roasting of a sulphide ore is (are)
Oxide only
Sulphate only
Oxide and sulphate
Dependent on temperature and partial pressure of oxygen & sulphur dioxide
__________ test is the appropriate test to determine whether a material is ductile or brittle.
Impact
Cupping
Hardness
Tensile
Which of the following contributes maximum as main source of sulphur in the blast furnace charge?
Sinter
Coke
Iron ore
Limestone
Upto the critical radius of insulation, added insulation, will
Increase the heat loss
Decrease heat loss and will have no effect beyond that
Decrease heat flux
Reduce convection heat loss compared to conduction heat less
Annealing of cast iron
Softens it to facilitate machining
Decreases the free carbon
Increases the strength
None of these
The behaviour of a metal specimen, which when plastically strained in tension reduces its yield stress in compression and vice versa; is termed as the
Work hardening
Bauschinger effect
Creeping effect
Stress recovery effect
High endurance limit of carburised machine parts is because of the fact that carburisation
Suppresses any stress concentration produced in the parts
Enhances the yield point of the material
Introduces a compressive layer on the surface
Produces a better surface finish
Maximum hardenability of steel depends upon its
Chemical composition
Carbon content
Grain size
Alloying elements content
All of the following alloying elements of steel increases hardness but sacrifice ductility, except
Nickel
Vanadium
Molybdenum
Chromium
Metallic surveying tapes are made of __________ which has a low co-efficient of expansion & enough strength.
Invar
Hastelloy
Duralumin
Monel metal
Two solutions A1 & A2 have pH value of 2 & 6 respectively. It implies that the solution
A1 is more alkaline than solution A2
A1 is highly acidic
A2 is very slightly acidic
Both (B) & (C)
Babbitt lining is used on brass/bronze bearings to increase the
Antifriction properties
Compressive strength
Bearing resistance
Wear resistance
Rankine cycle comprises of two isothermal and two __________ processes.
Isobaric
Polytropic
Isentropic
None of these
A common disinfectant used in village wells for disinfection of water is
Free chlorine
Bromine
Iodine
Potassium permanganate
__________ of grey cast iron produces white cast iron.
Tempering
Rapid heating
Rapid cooling
Slow cooling
The activity co-efficient of the solute in a dilute solution
Decreases with the increase of concentration of the solute
Increases with the increase of concentration of the solute
Remains constant
Is unity at infinite dilution
__________ is the trade name assigned to a nonferrous cast alloy composed of cobalt, chromium & tungsten.
Stellite
High speed steel
Cermet
Alnico
Identify the correct statement with reference to the extractive metallurgy of aluminium.
The electrolyte consists of molten Na3AlF6 with approximately 1 to 8% Al2O3
Approximately 80% of the aluminium deposited on the cathode comes from cryolite
Sodium is deposited along with aluminium, but is immediately vaporised
Anode effect sets in when the cryolite concentration goes below 40%.
Which of the following is an example of stress corrosion?
Season cracking of brass
Caustic embrittlement of steel
Both (A) & (B)
Neither (A) nor (B)
A furnace is made of a refractory brick wall of thickness 0.5 metre and thermal conductivity 0.7 W/m.°K For the same temperature drop and heat loss, this refractory wall can be replaced by a layer of diatomaceous earth of thermal conductivity 0.14 W/m.K and thickness __________ metre.
0.01
0.1
0.25
0.5
Pick out the wrong statement.
Ductile fracture of a stressed material, which exhibits a large plastic deformation is commonly caused by the formation and coalescence of voids in the necked region
Brittle fracture is caused by the propagation of pre-existing cracks in the material and involves minimum plastic deformation
Fatigue fracture of a material is always brittle in nature and takes place due to the existence of line imperfections
Brittle materials are generally tested in tension
A metal having a Poisson's ratio = 0.3 is elastically deformed under uniaxial tension. If the longitudinal strain = 0.8, then the magnitude of thickness strain is
-0.8
0.8
+0.08
-0.24
Secondary hardening in steels arises out of the
Precipitation of fine alloy carbides at high temperatures
Refinement of ferrite grain size by working
Decomposition of retained austenite upon heat treatment
Precipitation of complex inter-metallic upon heat treatment
Alloys having more than 80% copper are generally more
Abrasion resistant
Corrosion resistant
Prone to season cracking
Machinable