notes/mechanical/mmme1029_materials.md

author	date	title	tags
Alvie Rahman	\today	MMME1029 // Materials	uni nottingham mmme1029 materials

Lecture 1 (2021-10-04)

1A Reading Notes

Classification of Energy-Related Materials

• Passive materials---do not take part in energy conversion e.g. structures in pipelines, turbine blades, oil drills

• Active materials---directly take part in energy conversion e.g. solar cells, batteries, catalysts, superconducting magnests

• The material and chemical problems for conventional energy systems are mostly well understood and usually associated wit structural and mechanical properties or long standing chemical effects like corrosion:

  • fossil fuels
  • hydroelectric
  • oil from shale and tar
  • sands
  • coal gasification
  • liquefaction
  • geothermal energy
  • wind power
  • bomass conversion
  • solar cells
  • nuclear reactors

Applications of Energy-Related Materials

High Temperature Materials (and Theoretical Thermodynamic Efficiency)

• Thermodynamics indicated that the higher the temperature, the greater the efficiency of heat to work:

   \frac{ T_{high} - T_{low} }{ T_{high} } 

• The first steam engines were only 1% efficient, while modern steam engines are 35% efficient primarily due to improved high-temperature materials.

• Early engines made from cast iron while modern engines made from alloys containing nickel, molybdenum, chromium, and silicon, which don't fail at temperature above 540 \textdegree{}C

• Modern combustion engines are nearing the limits of metals so new materials that can function at even higher temperatures must be found--- particularly intermetallic compounds and ceramics are being developed

Types of Stainless Steel

• Type 304---common; iron, carbon, nickel, and chromium
• Type 316---expensive; iron, carbon, chromium, nickel, molybdenum

Self Quiz 1

1. What is made of billion year old carbon + water + sprinkling of stardust?

   Me

2. What are the main classifications of materials?

   Metals, glass and ceramics, plastics, elastomers, polymers, composites, and semiconductors

3. [There are] Few Iron Age artefacts left. Why?

   They rusted away

4. What is maens by 'the micro-structure of a material'?

   The very small scale structure of a material which can have strong influence on its physical properties like toughness and ductility and corrosion resistance

5. What is a 'micrograph' of a material?

   A picture taken through a microscope

6. What microscope is used to investage the microstructure of a material down to a 1 micron scale resolution?

   Optical Microscope

7. What microscope is used [to investigate] the microstructure of a material down to a 100 nm scale resolution?

   Scanning Electron Microscope

8. What length scales did you see in the first slide set?

   1 mm, 0.5 mm, 1.5 \textmu{}m

9. What material properties were mentioned in the first slide set?

   Hardness, brittleness, melting point, corrosion, density, thermal insulation

Self Quiz 2

1. What is the effect of lowering the temperature of rubber?

   Makes it more brittle, much less elastic and flexible

2. What material properties were mentioned in the second slide set?

   Young's modulus, specific heat, coefficient of thermal expansion

Lecture 2

Properties of the Classes

Metals

• Ductile (yields before fracture)
• High UFS (Ultimate Fracture Stress) in tension and compression
• Hard
• Tough
• High melting point
• High electric and thermal conductivity

Ceramics and Glasses

• Brittle --- elastic to failure, no yield
• Hard (harder than metals)
• Low UFS under tension
• High UFS under compression
• Not tough
• High melting points
• Do not burn as oxide ceramics are already oxides
• Chemically resistant
• Poor thermal and electric conductivity
• Wide range of magnetic and dielectric behaviours

Polymers

• Organic---as in organic chemistry (i.e. carbon based)

• Ductile

• Low UFS in tension and compression

• Not hard

• Reasonably tough

• Low threshold temperature to charring and combustion in air or pure oxygen

• Low electrical and thermal conductivity

  • There are some electrically conductive polymers

Composites

• Composed of 2 or more materials on any scale from atomic to mm scale to produce properties that cannot be obtained in a single material

  • Larger scale mixes of materials may be called 'multimaterial'

• Material propertes depends on what its made of

Terms

Organic vs Inorganic Materials

• Organic materials are carbon based
• From chemistry, organic compounds are ones with a C-H bond
• Inorganic compounds do not contain the C-H bond

Crystalline vs Non-Crystalline Materials

• Most things are crystalline

  • Ice
  • Sugar
  • Salt
  • Metals
  • Ceramics

• Glasses are non-crystalline

Material Properties

Density

\rho = \frac m v

• Density if quoted at STP (standard temperature and pressure---298 K and 1.013\times 10^5 Pa)

• Metals, ceramics, and glasses are high density materials

• Polymers are low density

• Composites span a wide range of density as it depends on the materials it is composed of

  e.g. composites with a metal matrix will have a much higher density than those with a polymer matrix

Melting Points

• Measured at standard pressure and in an intert atmosphere (e.g. with Nitrogen, Argon, etc)

  • Diamond and graphite will survive up to 4000 \textdegree{}C in an inert atmosphere but would burn at around 1000 \textdegree{}C in oxygen

• High melting points -> high chemical bond strength

Corrosion

• It's not just metals that corrode

• Polymers

  • UV degradation
  • Water absorption can occur in degraded polymers

• Glass

  • Leaching
  • Sodium ions can leave the glass when covered in water. If the water stays, the high pH water can damage the class

Self Quiz

Consolidation Questions 1

i. Metal ii. Titanium

2. i. Polymer ii. Polyester

i. Ceramic ii. Alumino-silicate

i. Composite ii. GFRP or CFRP

i. Metal ii. Aluiminium alloy

i. Metal ii. Aluiminium alloy

i. Polymer ii. Acrylic

i. Ceramimc ii. Glass

i. Composite ii. Concrete

Consolidation Questions 2

C B

Polymers

Introduction to Polymers

There are 3 types of polymers:

• thermoplastics

  

  No cross links between chains. The lack of cross links allows recycling of polymers by heating it above the glass transition material, T_g, lowering the viscosity.

  An example of thermoplastics is PET, used in water bottles

• thermosets

  

  has lots of cross-links between chains, making it more rigid. Heating does not lower its viscosity making them much harder/impossible to recycle.

  and example of thermosets is melamine formaldehyde, used on kitchen tabletops

• elastomers

  

  has some cross links and a lot of folding of chains

  Latex is an example of an elastomer

Polymers are relatively new materials, lightweight, durable, flammable, and degraded by UV light. They are made of long carbon-carbon chains.

Stress-Strain Curve of Polymers

Thermoplastics

The simplest polymer is poly(ethene):

When 2 polymer chains get close together, Van der Waals (vdw) forces keep them together. vdw forces are very weak, much weaker than the covalent bonds inside the polymer.

Stress Strain Curve

• During linear deformation, the carbon chains are strethed.
• At yield stress, the carbon chains get untangled and slide past eache other.
• Necking initially allows the chains to slide at lower stress.
• As the chains pull, align, and get closer, the vdw forces get stronger and more stress is required to fracture.

Crystalline and Amorphous/Glassy Solids (Heating and Cooling)

Amorphous Thermoplastics

• As you heat above T_g, the chains get easier to move past each other.
• It is known as an amorphous supercooled liquid.
• There is not really a melting point are there are no crystals, but T_m is the point where the chains are easy to move

Crystalline Polymers

• The glass transition point does not exist for crystalline polymers
• The solid is difficult to deform below T_m and is not ductile
• Above T_m the chains are very easy to move past each other

Semi-Crystalline

• Below T_g, only local movements in chains are possible, so the material is less ductile. The solid crystalline regions makes it difficult to move the chains.
• Between T_g and T_m, the glassy chains are easier to move but the crystalline regions remain difficult
• Above T_m the chains easily move past each other

Specific Volume vs Temperature

Path ABCD

• a-b --- Start cooling the true liquid
• b-c --- At the freezing point, T_m, the true liquid freezes diretly to a crystalline solid
• c-d --- The crystalline solid cools t room temperature as the temperature is lowered

Path ABEF

• a-b --- start cooling the true liquid

• b --- at the freezing point nothing freezes

• b-e --- the liquid becomes supercooled and contracts and becomes more viscous as the temperature decreases.

  The supercooled liquid region is between T_g and T_m

  Supercooling requires you to cool the sample quicker than you would for path ABCD

• e --- T_g is reached and the supercooled liquid sets to a amorphous solid

• e-f --- the amorphous solid cools from room temperature and contract as the temperature is lowered

Relative Molar Mass and Degree of Polymerisation

• Number Average RMM --- \bar M_n = \sum x_iM_i
• Weight Average RMM --- \bar M_w = \sum w_iM_i
• Degree of polymerisation --- n_n = \frac {\bar M_n} m and n_w = \frac {\bar M_w} m

where

• M_i is the RMM of the chain
• x_i is the fraction of the polymer that is composed of that chain by number/quantity
• w_i is the fraction of the polymer that is composed of that chain by mass/weight
• m is the RMM of the monomer from which the polymer was made

Making Polymers

There are two ways to make polymers:

• Addition Poymerisation
• Condensation Polymerisation