ENGINEERING CHEMISTRY (2019 PATTERN)
Maximum Marks : 70
Answer key
Q.1 a. Classify the composites on the basis of reinforcement. Give
any three properties and application of polymer composites. (7)
Answer-
1. Polymer Composite - is the material which is made up of
polymer matrix & reinforcing materials being put together with
a definite interface.
Composites on the basis of reinforcement classified as
Fibre, Particulate and Sheets.
They are structural constituents like fibres, sheets, particles
which are embedded in matrix phase and provide high strength,
rigidity & enhance matrix properties.
Fibres: Long thin filaments of glass, carbon, aramides are added
to matrix to give high tensile strength, high stiffness & low
density & higher elastic modulus.
Particulates: Small metallic or non-metallic particles can be
added to the polymer matrix to increase surface hardness,
abrasion, resistance & strength. They reduce shrinkage, friction
& cost. Particles carry major portion of the load applied. E.g.
Metal oxides, carbon black.
Fibre reinforced can be further divided into three categories
continuous aligned
(a), discontinuous aligned (b) & discontinuous randomly
oriented fibre.
, The characteristic properties of FRP depends upon:
Nature, orientation & distribution of fibres.
Nature of polymer matrix.
Strength of interfacial bonds between fibre phase & polymer
matrix phase.
, Q.1 (b) (i) Define quantum dots. Give any two properties of
quantum dots. (3M)
Answer-
Definition-
Quantum dots are semiconductor nanoparticles that glow a particular
colour after being illuminated by light.
The tiny nanoparticles have diameters which range from 2 nanometers
to 10 nanometres.
Properties of quantum dots:
1.Optoelectronic properties:
Quantum dots have properties intermediate between bulk
semiconductors and discrete atoms or molecules.
The properties of quantum dots are determined by shape,
size, composition and structure. Larger QDs of 5-6 nm
diameter emit longer wavelengths, with colours such as
orange or red. Smaller QDs 2-3 nm emit shorter
wavelengths, yielding colours like blue and green,
, 2.Fluorescence:
Nanoparticles of any semiconductor substance have the
property of a quantum dot.
The gap between the valance band and conduction band,
which is present for all semiconductor material, causes
quantum dots to fluoresce.
Excitons (electron – hole pairs) for a given semiconductor
material have a particular size called the “Exciton Bohr
radius “. In a quantum dot, relatively few atoms are
present (which cut down on splitting) and the excitons are
confined to a much smaller space on the order of the
material’s exciton Bohr radius.
This leads to discrete, quantized energy level more like
those of an atom than the continuous bands of a bulk
semiconductor. For this reasons quantum dots have
sometimes been referred as “artificial atoms”.
The main property of quantum dots is they show colour
glow when illuminated by UV light. The colour of that
light depends on the energy difference between the
conductance band and valance band.
Q.1 (b) ii. What are nanomaterials? Give any two important
applications of nanomaterials with example.
Answer –
Definition-
“Nanomaterials are defined as a set of substance where at least one
dimension is less than approximately 100 nanometre
Applications:
Being transparent and flexible conductor, it can be used
for solar panels, LEDs, touch panels, smart phones.
Its powder can be used in making polymer composites.
Capacitors, batteries, 3D printer materials.
As transistors for integrated circuits.
As sensor for gas detection.
Energy storage material.
As filtration material.
Maximum Marks : 70
Answer key
Q.1 a. Classify the composites on the basis of reinforcement. Give
any three properties and application of polymer composites. (7)
Answer-
1. Polymer Composite - is the material which is made up of
polymer matrix & reinforcing materials being put together with
a definite interface.
Composites on the basis of reinforcement classified as
Fibre, Particulate and Sheets.
They are structural constituents like fibres, sheets, particles
which are embedded in matrix phase and provide high strength,
rigidity & enhance matrix properties.
Fibres: Long thin filaments of glass, carbon, aramides are added
to matrix to give high tensile strength, high stiffness & low
density & higher elastic modulus.
Particulates: Small metallic or non-metallic particles can be
added to the polymer matrix to increase surface hardness,
abrasion, resistance & strength. They reduce shrinkage, friction
& cost. Particles carry major portion of the load applied. E.g.
Metal oxides, carbon black.
Fibre reinforced can be further divided into three categories
continuous aligned
(a), discontinuous aligned (b) & discontinuous randomly
oriented fibre.
, The characteristic properties of FRP depends upon:
Nature, orientation & distribution of fibres.
Nature of polymer matrix.
Strength of interfacial bonds between fibre phase & polymer
matrix phase.
, Q.1 (b) (i) Define quantum dots. Give any two properties of
quantum dots. (3M)
Answer-
Definition-
Quantum dots are semiconductor nanoparticles that glow a particular
colour after being illuminated by light.
The tiny nanoparticles have diameters which range from 2 nanometers
to 10 nanometres.
Properties of quantum dots:
1.Optoelectronic properties:
Quantum dots have properties intermediate between bulk
semiconductors and discrete atoms or molecules.
The properties of quantum dots are determined by shape,
size, composition and structure. Larger QDs of 5-6 nm
diameter emit longer wavelengths, with colours such as
orange or red. Smaller QDs 2-3 nm emit shorter
wavelengths, yielding colours like blue and green,
, 2.Fluorescence:
Nanoparticles of any semiconductor substance have the
property of a quantum dot.
The gap between the valance band and conduction band,
which is present for all semiconductor material, causes
quantum dots to fluoresce.
Excitons (electron – hole pairs) for a given semiconductor
material have a particular size called the “Exciton Bohr
radius “. In a quantum dot, relatively few atoms are
present (which cut down on splitting) and the excitons are
confined to a much smaller space on the order of the
material’s exciton Bohr radius.
This leads to discrete, quantized energy level more like
those of an atom than the continuous bands of a bulk
semiconductor. For this reasons quantum dots have
sometimes been referred as “artificial atoms”.
The main property of quantum dots is they show colour
glow when illuminated by UV light. The colour of that
light depends on the energy difference between the
conductance band and valance band.
Q.1 (b) ii. What are nanomaterials? Give any two important
applications of nanomaterials with example.
Answer –
Definition-
“Nanomaterials are defined as a set of substance where at least one
dimension is less than approximately 100 nanometre
Applications:
Being transparent and flexible conductor, it can be used
for solar panels, LEDs, touch panels, smart phones.
Its powder can be used in making polymer composites.
Capacitors, batteries, 3D printer materials.
As transistors for integrated circuits.
As sensor for gas detection.
Energy storage material.
As filtration material.
