Chee Final
Assertion: Glaas fibers have a lower elongation but higher tensile strength than carbon fibers and aramid fibers Reason: glass fibers offers good electrical insulation and are corrosion resistant
(V) Assertion is wrong statement and reason is correct statement
Assertion: Glass is considered as a ceramic material but are distinguished from other conventional ceramics. Reason: Constituents in glass are heated to fusion and then cooled to a rigid state without crystallization.
(ii) Assertion and reason are both correct
Assertion: Aramid fibers are used in composites because of high tensile strength. Reason: Strong intermolecular forces (like Hydrogen bonding in Aramid fibers) lead to close packing of chains and increase the crystalline character, hence provide high tensile strength
(ii) Assertion and reason both are correct
Assertion: Wood is anisotropic in nature. Reason: cellulose fibers are oriented longitudinally
(ii) Assertion and reason both are correct
Wood moisture content =
(wt. of water in sample/at of dry wood sample)X100
True statements about corrosion
-corrosion is an oxidation reaction -corrosion is a combination of chemical and physical process -corrosion involves the loss of a material
Describe the ways to improve the strength of thermoplastics.
-effect of bulky side groups on the main chains -strength is directly related to molecular mass -the degree of crystallization. Crystallization leads to high density, high density leads to high strength -the effect of high polar atoms on the main chains -the effect of oxygen, nitrogen and sulfur atoms in main carbon chains -the effect of phenyl rings in the main chains -the addition of glass-fiber reinforcement
What is the difference between a random copolymer and gaft copolymer
-random copolymers are different monomers randomly arranged in chains -gaft copolymers are one type of monomer grafted to long chain of another
After ionization, the size of the sodium ion is____________than sodium atom, while chloride ion is_____________than the CL atom
1) smaller 2) larger
Write and explain three differences between Scottky and Frenkel defects under the heads 1) effect on density 2) effect on electrical conductivity 3) effect on stability of the crystal
1. Schottky decreases density because both a cation and an anion are missing while Frenkel defects don't change density because the cation only moves into the interstitial state 2. Scottky is missing electrons which çarry electricity, therefore it would increase electrical conductivity Frenkel also increases electrical conductivity 3. Frenkel defects cause greater repulsion between cations due to closer proximity, making it less stable. Schottky defects also causes crystal to be less stable
Process of corrosion is accelerated by
Air and moisture Electrolytes in water Metallic impurities
Kevlar is a commercial name for
Aramid fibers
Assertion: during galvanic corrosion, large cathode area to small anode area should be avoided. Reason: smaller anode is responsible for higher current density
Assertion is correct statement Reason is correct statement and explains assertion
Assertion: bone is anisotropic in nature Reason: bone is stronger in the transverse direction
Assertion is correct statement Reason is incorrect statement
Assertion: stress shielding can be avoided by using bio materials with high elastic modulus Reason: corrosion in biometals leads to osteolysis
Assertion is wrong statement Reason is correct statement
Solid A is a very hard, electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it
Covalent (diamond)
What is crevice corrosion?
Crevice corrosion is when a crack is small enough to allow water into the crack but won't allow water to get out. The water becomes stagnant and causes corrosion
Which point defect in ionic crystal does not alter the density of the relevant solid
Frenkel Imperfection
Cooling a non crystallizible polymer liquid below Tg results in the formation of a:
Glass
Cooling a non-crystallizable (amorphous) polymer liquid below TG results in the formation of a
Glass
__________ are added to obtain smaller grains during solidifications of metals.
Grain refiners
Which statement BEST describes why graphite is soft:
Graphite is layered
Lower the pH, corrosion is:
Greater
What are the advantages of Czochralaski method
Growth of larger oriented single crystals
(Image from test)
Identify types of defect from images 1-5
(Image)
Transition X is a TG while transition Y is a crystalline melting point.
Bone is anisotropic in nature
True
TRUE OR FALSE: Point defects can affect the density of any solid crystal
True
Following is NOT a zero-dimensional defect:
Twin boundary
___________are the class of materials with the highest thermal and electrical conductivity
Metals
MEMS is
Micro Electrical Mechanical Systems
The word polymer meant for a material made from:
Multiple monomers
Which of the following compound does IONIC BONDING PREDOMINATE:
NaCl
___________have a characteristic size smaller than 100 mm.
Nanomarterial
A neutral atom with atomic number greater than one consist of
Neutrons, protons, and electrons
Almost the entire mass of the atom is located in
Nucleus
Correct sequence of for nucleation during solidification of metal:
Nucleus-->crystal-->grain
Coordination number:
Number of equidistant nearest neighbors to an atom or ion in a unit cell of a crystal structure
Polyethylene and poly-propylene (in the melt) will:
Only interact weakly through secondary inter-molecular forces
The metal is solidified and cooled to room temperature. A metallographic analysis shows that large columnar grains extend from the wall of the vessel into the center of the sample. Do you conclude that these grains were nucleated homogeneously or heterogeneously, and why?
This was nucleated homogeneously. The reason being is that the grain is the same throughout the sample. To be heterogeneously there would be exquiated grains near the wall of the cell and then columnar grains near the nucleus
explain what glass transition temperature is and what role of a plasticizer in affecting a polymer property
-Glass transition temperature is the temperature at which a polymer transitions from being rubbery if over the temperature -the role of a plasticizer is to impart the flexibility to polymeric
Bone is a composite material of:
Calcium phosphate and collagen
Solution of 2 or more metals is known as an ____________
Alloy
The following is a ceramic material
Alumina Glass Porcelain
A surgeon want to use hip implants with ceramic bearing surfaces as the corrosion properties of ceramic is excellent and the life expectancy of the athlete is long. What advice would you give to surgeon on his choice of the bearing metal
Ceramic is typically a good biomaterial because it has similar properties as bone. However, ceramic has a higher elasticity modulus than bone and therefore causes stress shielding. The stress shielding will cause the bone around the hip to weaken because of wolf's law. With an athlete with a long life expectancy, having bone loss is not the best solution
A crucible needs to have extremely high temperature strength to melt metals. What material class would likely contain a suitable material for a metal?
Ceramics
A ________________ is seen in a perfect crystal
Closed burger circuit
Equiaxed grains are smaller than_________ grains
Columnar
What is/are the type of attraction between water molecule in ice:
Dipole-Dipole interaction Electrostatic interaction between charged atoms Hydrogen bonds
Which one(s) of the following descriptions would NOT be applicable to ceramics
Ductile
Explain how fluctuations dipoles attract each other? Is this a strong or weak force?
Due to asymmetrical distribution of electron charges in the electron cloud, nearby atoms create interatomic non directional bonds. This is a weak secondary bond
Zinc (Zn) is more..........than iron
Electronegative (more corrosive)
Schottky defect is observed in crystals when
Equal number of cation and anion is missing from the lattice
Biomaterials and biological materials are same.
False
Galvinization is the coating of stainless steel on copper
False
Homogeneous nucleation method of solidification of metals is an industrially favorable method
False
TRUE OR FALSE: Atomic number changes during the conversion of an atom to cation or anion
False
TRUE OR FALSE: Grain refiners increase the grain size
False
TRUE OR FALSE: Silicone is a load bearing engineering metal
False
Which one(s) of the following is/are characteristics of thermomsetting polymers:
Heavily branched cross-linked polymer Become infusible on molding so cannot be reused
Waters high boiling point can be explained by ___________ bonding.
Hydrogen
FALSE STATEMENT:
In edge dislocation, burger vector is parallel to the dislocation line
Describe how compressive stresses are introduced in pre-tensioned pre-stressed concrete
In pre-tensioned pre-stressed concrete, a steel rod is stretched and concrete is poured on top. The concrete is allowed to cure over the stretched rod and then the force of the rod is released. The rod attempts to return to its original shape and introduces compression on the concrete that is cured
Molecular weight of a polymer usually:
Increases Tg value
A pure silicon ship consist of single crystal of silicon. Which one of the following types of corrosion is less likely to occur
Intergranular
The radius of silicone and lithium are quite different. Being smaller in size, what type of impurity will lithium be:
Interstitial impurity
Electron sea model best explains the following
Ionic
Which of the following is NOT true of a single silica tetrahedron (silicate) unit:
It has 4 silicon atoms
Defect where some atoms are are misaligned
Linear
This defect is responsible for large mechanical deformations in crystalline solids
Linear
Low-density poly ethylene is weaker than high density poly ethylene
Low density poly ethylene is weaker than high density poly ethylene because less dense poly ethylene has more branches and looks like this while high density poly ethylene
Stereoisomers:
Same chemical composition but different structural arrangements
Sintering:
Small particles are bonded together by solid state diffusion producing dense coherent product
__________ materials have the ability to sense and respond to external stimuli
Smart
In selecting a material for the windshield of automobiles, what types of glass would you use? Propose a process that would keep glass shards from dispersing if the glass fractures.
Tempered glass is the best option for automotive windshields. To make tempered glass melted glass is cooled rapidly. The surface cools first & contracts, then the interior cools. The tension of the interior is directed outward as compression is applied to the surface, the only way for the glass to break is if the tension applied is bigger than the applied compression force. The tensile strength directs forces away from the centers of the glass
Describe how the addition of sodium oxide to a regular glass will affect the silica- glass network structure, and why are they added to silica glass?
The addition of sodium oxide to the regular glass is to lower the viscosity, so that it can be worked and form easier. The oxygen atoms at these oxides enter the silica network at pants of joining the silica tetrahedral and break up the network, producing oxygen atoms with unshared election. The sodium and potassium ions ionically bonded in the interstices of the network. By filling the same of the interstices, these ions promote crystallization of the glass
PVC tubing is being used for transporting water. If organic solvents are run through this tubing it becomes stiff and somewhat brittle. This is because:
The solvent removes plasticizer, raising the Tg.
Explain why prolonged weightless environment leads to bone loss
Wolf's law states that bone reacts to stress. Without weight on the bone, it is not being stressed and therefore stops remodeling & strenghthening in order to accommodate the weight being placed on it. When it stops remodeling, it weakens & is more easily corroded, leading to bone loss
Why does wood shrunk much more in the transverse direction than in the longitudinal direction?
Wood shrinks as moisture is eliminated when water is eliminated from exterior parts, the cellulose microfibuls become closer together and the wood becomes more dense. The wood shrinks transversely because the microfibuls are mainly oriented in the longitudinal direction
