COMPUTED TOMOGRAPHY

 

ABSTRACT

    This presentation will enlighten us on what computed tomography scanning of the body is all about, what are some common uses of the procedure, how should a patient prepare, what does the equipment look like, how does the procedure work, how is the CAT scan performed, what will the patient experience during and after the procedure, who interprets the results and how do the patient get them, what are the benefits and risks, what are the limitation of CT scanning of the body.

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GRAPHENE A MIRACLE MATERIAL

BY ENGR . AGBADUA SEGUN

                                                     ABSTRACT

The paper tends to look at the origin , production and relevance of Graphene to the material world.

                                                                      INTRODUCTION

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities. Graphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp²-bonded carbon atoms that are densely packed in a honeycomb crystal lattice.

The carbon-carbon bond length in graphene is about 0.142 nanometers. Graphene sheets stack to form graphite with an interplanar spacing of 0.335 nm, which means that a stack of 3 million sheets would be only one millimeter thick. Graphene is the basic structural element of some carbon allotropes including graphite, charcoal, carbon nanotubes and fullerenes. It can also be considered as an indefinitely large aromatic molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons.

 METHODS OF PRODUCING OF GRAPHENE

Growth from metal-carbon melts

Pyrolysis of sodium ethoxide

Sugar

Epitaxial growth on metal substrates

Graphite oxide reduction

Epitaxial growth on silicon carbide

Graphite oxide Reduction

Graphite oxide exfoliation can be achieved by rapid heating and yields highly dispersed carbon powder with few percents of graphene flakes. Reduction of graphite oxide monolayer films

 Growth from metal-carbon melts

The general idea in this process is to dissolve carbon atoms inside a transition metal melt at a certain temperature, and then allowing the dissolved carbon to precipitate out at lower temperatures as single layer graphene.

Epitaxial growth on silicon carbide

 This process produces epitaxial graphene with dimensions dependent upon the size of the SiC substrate (wafer). The face of the SiC used for graphene formation, silicon- or carbon-terminated, highly influences the thickness, mobility and carrier density of the graphene.

From sugar

Sucrose is turned quickly and easily into graphene with the help of  copper or nickel substrate and  subjected to 800 °C under low pressure with exposure to argon and hydrogen gas.

graphene is an isolated atomic plane of graphite. Graphene has been known since the invention of X-ray crystallography. Graphene planes become even better separated in intercalated graphite compounds. Graphene films were produced by chemical vapor deposition and used as anodes for application in photovoltaic devices. Tiny fragments of graphene sheets are produced whenever graphite is abraded, such as when drawing a line with a pencil

MECHANICAL PROPERTIES

Graphene appears to be one of the strongest materials ever tested. Measurements have shown that it  has a breaking strength 200 times greater than steel, with a tensile strength of 130GPa (19,000,000 psi).^[116] However, the process of separating it from graphite, where it occurs naturally. Not only is it lighter, stronger, harder and more flexible than steel, it is also a recyclable and sustainably manufacturable product that is eco-friendly and cost effective in its use.

aerospace companies such as Boeing have already started to replace metals with carbon fibres and carbon-based materials, and graphene paper with its incomparable mechanical properties would be the next material for them to explore.

Thermal properties

The ballistic thermal conductance of graphene is isotropic.^[111] The Potential for this high conductivity can be seen by considering graphite, a 3D version of graphene that has basal plane thermal conductivity of over a 1000 Wm⁻¹K⁻¹ (comparable to diamond). In graphite, the c-axis (out of plane) thermal conductivity is over a factor of ~100 smaller due to the weak binding forces between basal planes as well as the larger lattice spacing

Integrated circuits

Graphene has the ideal properties to be an excellent component of integrated circuits. Graphene has a high carrier mobility, as well as low noise, allowing it to be used as the channel in a FET. The issue is that single sheets of graphene are hard to produce, and even harder to make on top of an appropriate substrate, graphene was epitaxially grown on SiC in a quantity and with quality suitable for mass production of integrated circuits. The circuit handled frequencies up to 10 GHz, and its performance was unaffected by temperatures up to 127C

Electrochromic devices

Graphene Oxide can be reversibly reduced and oxidized using electrical stimulus. Controlled reduction and oxidation in two-terminal devices containing multilayer graphene oxide films are shown to result in switching between partially reduced graphene oxide and graphene, a process which modifies the electronic and optical properties

Transparent conducting electrodes

Graphene's high electrical conductivity and high optical transparency make it a candidate for transparent conducting electrodes, required for such applications as touchscreens, liquid crystal displays

Organic light-emitting diodes (OLEDs) with graphene anodes have also been demonstrated. The electronic and optical performance of devices based on graphene are shown to be similar to devices made with indium-tin-oxide.

Graphene biodevices

Graphene's modifiable chemistry, large surface area, atomic thickness and molecularly-gatable structure make antibody-functionalized graphene sheets excellent candidates for mammalian and microbial detection and diagnosis devices.

The most ambitious biological application of graphene is for rapid, inexpensive electronic DNA sequencing. Integration of graphene (thickness of 0.34 nm) layers as nanoelectrodes into a nanopore can solve one of the bottleneck issues of nanopore-based single-molecule DNA sequencing

Anti-bacterial

The Chinese Academy of Sciences has found that sheets of graphene oxide are highly effective at killing bacteria such as Escherichia coli. This means graphene could be useful in applications such as hygiene products or packaging that will help keep food fresh for longer

CONCLUSION

Graphene has taken over from the silicon and germanium etc , that are doping materials.

It has shown how invaluable carbon is to the Engineering world.

 

 

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Capacitor and their usage

What do we mean by the word capacitor?

Capacitors are electric device used for storage electrical charges. This device is like a condenser. It is an important device in any electrical or electronic and in telecommunication industries. E.g. in radio, television receiver and in transmitter circuit.

Types of capacitor

There are different types of Capacitors available in the market place and each one has its own set of characteristics and applications from small delicate trimming capacitors up to large power metal can type capacitors used in high voltage power correction and smoothing circuits. Like resistors, there are also variable types of capacitors which allow us to vary their capacitance value for use in radio or "frequency tuning" type circuits. Either way, capacitors play an important part in electronic circuits so here are a few of the more "Common" types of capacitors available.

1.Dielectric
 Dielectric Capacitors are usually of the variable type such as used for tuning transmitters, receivers and transistor radios. They have a set of fixed plates and a set of moving plates that mesh with the fixed plates and the position of the moving plates with respect to the fixed plates determines the overall capacitance.

The capacitance is generally at maximum when the plates are fully meshed. High voltage type tuning capacitors have relatively large spacing's or air-gaps between the plates with breakdown voltages reaching many thousands of volts.

Variable Capacitor Symbols

2. Film Capacitors
Film Capacitors are the most commonly available of all types of capacitors, consisting of a relatively large family of capacitors with the difference being in their dielectric properties. These include polyester polystyrene,polypropylene,polycarbon-ate, metalized paper etc.

 Film type capacitors are available in capacitance ranges from 5pF to 100uF depending upon the actual type of capacitor and its voltage rating. Film capacitors also come in an assortment of shapes and case styles which include:

Rectangular & Round film capacitors are the rectangular metalized film and cylindrical film & foil types are shown below

Cylindrical  Type

3. Ceramic Capacitors
Ceramic Capacitors or Disc Capacitors as they are generally called, are made by coating two sides of a small ceramic disc with silver and are then stacked together to make a capacitor.

For very low capacitance values, a single ceramic disc of about 3-6mm is used. Ceramic capacitors have a high dielectric constant (High-K) and are available so that relatively high capacitance can be obtained in a small physical size.

They are large non-linear changes in capacitance against temperature and as a result are used as de-coupling or by-pass capacitors as they are also non-polarized devices. Ceramic capacitors have values ranging from a few picofarads to one or two microfarads but their voltage ratings are generally quite low.

For example, 10³ would indicate 10 x 10³pF which is equivalent to 10,000 pF or 0.01μF.
4. Electrolytic Capacitors
Electrolytic Capacitors are generally used when very large capacitance values are required. Here instead of using a very thin metallic film layer for one of the electrodes, a semi-liquid electrolyte

solution in the form of a jelly or paste is used which serves as the second electrode (usually the cathode). The majority of electrolytic types of capacitors are polarized, that is the voltage applied to the capacitor terminals must be of the correct polarity as an incorrect polarization will break down the insulating oxide layer and permanent damage may result.

    Electrolytic Capacitors are generally used in DC power supply circuits to help reduce the ripple voltage or for coupling and decoupling applications. Electrolyte's generally come in two basic forms; Aluminium Electrolytic and Tantalum Electrolytic capacitors.

Electrolytic Capacitor

Also tantalum capacitors although polarized, can tolerate being connected to a reverse voltage much more easily than the Aluminium types but are rated at much lower working voltages. Typical values of capacitance range from 47nF to 470uF

Aluminium & Tantalum Electrolytic Capacitor

Capacitor Characteristics
The characteristics associated with the humble capacitor so here are just a few of the more important ones.
1. Working Voltage, (Vn)
The Working Voltage (Wvdc, Wvac) is the maximum continuous voltage that can be applied to the capacitor without failure during its working life.

DC and AC values are usually not the same as the AC value refers to the r.m.s. value. Common working DC voltages are 10V, 16V, 25V, 35V, 63V, 100V, 160V, 250V, 400V and 1000V and are printed onto the body of the capacitor. 2. Tolerance, (±%)
As with resistors, Capacitors also have a tolerance rating expressed as a plus-or-minus value either in Picofarads (±pF) for low value capacitors generally less than 10pF or as a percentage (±%) for higher value capacitors generally higher than 10pF. Capacitors are rated according to how near their actual values are to the rated capacitance with coloured bands or letters used to indicated the actual tolerance. The most common tolerance for capacitors is 5% or 10% but some electrolytic capacitors are rated as high as 20%.

3. Leakage Current
The dielectric used inside the capacitor is not a perfect insulator resulting in a very small current flowing or "leaking" through the dielectric when applied to a constant supply voltage. This small current flow in the region of micro amps (μA) is called the Leakage Current. This leakage current is a result of electrons physically making their way through the dielectric medium, around its edges or across the leads. The "leakage current" of a capacitor is sometimes called the "insulation resistance" and can be found using Ohm's law.

4. Working Temperature, (T)
Changes in temperature around the capacitor affect the value of the capacitance because of changes in the dielectric. If the air or surrounding temperature becomes to hot or to cold the capacitance value of the capacitor may change so much as to affect the correct operation of the circuit. The normal working range for most capacitors is -30°C to +125°C with nominal voltage ratings given for a working temperature of no more than +70°C. Generally electrolyte's can not be used below about -10°C, as

the electrolyte jelly freezes.
6. Polarization
Polarization generally refers to the Electrolytic type capacitors but mainly the Aluminium Electrolyte's, with regards to their connection. The majority are polarized types, that is the voltage connected to the capacitor terminals must have the correct polarity, i.e. +ve to +ve and -ve to -ve. Incorrect polarization can cause the oxide layer inside the capacitor to break down resulting in very large currents flowing through the device.

The majority of electrolytic capacitors have their -ve terminal clearly marked with a black stripe or black arrows down the side to prevent any incorrect connection. Some electrolyte's have their metal can connected to the negative terminal but high voltage types.

Types of connection in  capacitors.
1. parallel and series connection.

Capacitance and Charge
We saw in the previous tutorials that a Capacitor consists of two parallel conductive plates (usually a metal) which are prevented from touching each other (separated) by an insulating material called the "dielectric". We also saw that when a voltage is applied to these plates an electrical current flows charging up one plate with a positive charge with respect to the supply voltage and the other plate with an equal and opposite negative charge. Then, a capacitor has the ability of being able to store an electrical charge Q (units in Coulombs) of electrons.

When a capacitor is charged there is a potential difference between its plates, and the larger the area of the plates and/or the smaller the distance between them (known as separation) the greater will be the charge that the capacitor can hold. The Capacitors ability to store this electrical charge (Q) between its plates is proportional to the applied voltage, V for a capacitor of known capacitance in Farads, capacitance C is always positive. The greater the applied voltage the greater will be the charge on the plates. Likewise, the smaller the applied voltage the smaller the charge. Therefore, the actual charge Q on the plates of the capacitor can be calculated as:

Capacitor Charge

where A is the area of the plates in square metres, d is the distance between them and ε (epsilon) is the value of the dielectric constant.

Parallel Plate Capacitor

The capacitance of a parallel plate capacitor is proportional to the area A and inversely proportional to the distance, d between the plates. The capacitance can be increased by inserting a dielectric which has a relative permittivity or dielectric constant greater than that of air with typical values of epsilon ε being: Air = 1, Paper = 2.5, Glass = 5, Mica = 7 etc.

Charging & Discharging a Capacitor
Consider the following circuit.

Assume that the capacitor is fully discharged and the switch connected to the capacitor has just been moved to position A. The voltage across the 100uf capacitor is zero at this point and a charging current i begins to flow charging up the capacitor until the voltage across the plates is equal to the 12v supply voltage. The charging current stops flowing and the capacitor is said to be "fully-charged".
Then, Vc = Vs = 12v. Once the capacitor is "fully-charged" in theory it will maintain its state of voltage charge even when the supply voltage has been disconnected as they act as a sort of temporary storage device.

However, while this may be true of an "ideal" capacitor, a real capacitor will slowly discharge itself over a long period of time due to the internal leakage currents flowing through the dielectric. This is an important point to remember as large value capacitors connected across high voltage supplies can still maintain a significant amount of charge even when the supply voltage is switched OFF.
If the switch was disconnected at this point, the capacitor would maintain its charge indefinitely, but due to internal leakage currents flowing across its dielectric the capacitor would very slowly begin to discharge itself as the electrons passed through the dielectric.

The time taken for the capacitor to discharge down to 37% of its supply voltage is known as its Time Constant.  If the switch is now moved from position A to position B, the fully charged capacitor would start to discharge through the lamp now connected across it, illuminating the lamp until the capacitor was fully discharged as the element of the lamp has a resistive value. The brightness of the lamp and the duration of illumination would ultimately depend upon the capacitance value of the capacitor and the resistance of the lamp (t = CxR). The larger the value of the capacitor the brighter and longer will be the illumination of the lamp as it could store more charge.

Example No1.
Calculate the then the charge on the capacitor is 1.2 millicoulombs.


The Farad
We now know that the ability of a capacitor to store a charge gives it its capacitance value C, which has the unit of the Farad, F. But the farad is a extremely large unit on its own making it impractical to use so submultiples or fractions of the standard Farad unit are used instead. The prefixes used in charge in the above capacitor circuit.

electronic formulas and component values are the micro (μ), nano (n) and the pico (p). For example;
Sub-units of the Farad
Convert the following capacitances a) 22nF to uF, b) 0.2uF to nF, c) 550pF to uF a)  22nF = 0.022uF
b)  0.2uF = 200nF
c)  550pF = 0.00055uF
Energy When a capacitor charges up from the power supply connected to it, energy in Joules is stored in the capacitor and is given by the formula;

REFERENCES

contact us for full project

Terrell Croft "Library of Practical Electricity"(1917)

 J. Ho, T. R. Jow, S. Boggs, Historical Introduction to Capacitor Technology

 Adam Marcus Namisnyk (23 June 2003). "A Survey of Electrochemical Supercapacitor Technology" (PDF). Retrieved 2011-06-24.

 WIMA, Characteristics of Metallized Film Capacitors in Comparison with Other Dielectrics [1]

Film Capacitors, TDK Epcos, General technical information

 AVX, Dielectric Comparison Chart

 Holystone, Capacitor Dielectric Comparison, Technical Note 3

  P. Bettacchi, D. Montanari, D. Zanarini, D. Orioli, G. Rondelli, A. Sanua, KEMET Electronics Power Film Capacitors for Industrial Applications

 S. P. Murarka, Moshe Eizenberg, A. K. Sinha (2003) (in German), Interlayer dielectrics for semiconductor technologies, Academic Press, pp. 338–339, ISBN 9780125112215

  General technical information of (RFI/EMI)Noise suppression capacitors on AC mains

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INTRODUCTION TO THE DESIGN OF MACHINE COMPONENTS

WHAT IS A MACHINE ?

1. Mechanical device: a device with moving parts, often powered by electricity, used to perform a task, especially one that would otherwise be done by hand a washing machine

2. Simple unpowered device: a simple device used to overcome resistance at one point by applying force at another point, e.g. a lever, pulley, or an inclined plane

3. Powered form of transportation: an engine-driven means of transportation, e.g. an aircraft, car, or motorcycle

4. Group of people in control: an organized group of people that controls or directs something, especially a political group. the party machine

5. Complex system: a complex system structured so as to accomplish a particular goal. the war machine.

6. Somebody who behaves mechanically: somebody who is regarded as behaving like a mechanical device, e.g. somebody who is efficient but uncreative. men trained as deadly machines.

 

A machine is composed of three elements

Main parts of machine

•       Power Block: Supplies the required energy plus power for mechanical motion.

•       Transmission/Drive: Connects the power the executive organ.

•       Executive organ: Performs both primary and secondary motions required for the transformation process, determines the diversity of technological functions performed by the machine.

Machine Classification

Machine can be simple or complex;

   

Examples of simple machines are; the wedge, Lever, Inclined plane, the screw jack, pulley.

   

Examples of complex machines are; Industrial Robots, Manipulators, Space rockets, aero plane, Computer Numerical Control (CNC), Machine centers, combined Harvesters etc.

 

Machine Classification

   

    Machine can be as small as a coin and as big as a 10 storey building e.g. hydraulic press or as large as 500 metres sailing ship.

    Machine can also be manual (mechanical), semi automatic (electronic) or fully automatic, and by functions, electrical, hydraulic, pneumatic vacuum, magneto hydrodynamic, nuclear powered.

 

Basic Definition

 

    Machines, mechanisms, equipment, apparatus, fixtures, instruments and similar products of primary and secondary industries are made from smaller components (details) and sub-assemblies.

 

    A detail is a machine component made of uniform material of one make without the need for any assembly operation (e.g. bolt, nuts shaft, gear etc.)

 

Basic Definition cont’d.

   

    Two or more details, assembled together in the factory to form part of a machine, equipment or instrument is referred to as an assembly unit (e.g. bearing, reductor, speed box, clutch).

   

    A machine may contain hundreds, thousands and even millions of components depending on its complexity.

Basic components of machines

•       Examples of these are: shafts and axle, springs, bolts, Nuts, studs, screws, rivets, gears, bearings, clutches and shaft couplings, keys, and splines, brakes, gaskets, washers, body or carcass, pulleys, sprockets, ratchet, cam, tappet push rods, bushings racks, worms, instrument dials etc.

•       Machine components are as diverse as the types of machine.

•       Some components, however, are found more frequently in machine than others. These are referred to as the basic components.

 

Machine components can be grouped into

1. A Fasteners: they are divided into

(i) Temporary such as Bolt, Nut, Screw, Studs, etc. and

(ii) Permanent Joint: Welding, Riveting, Glue, Brazing, Soldering, etc.

2. Joints such as Fits: Press fit, Forced fit, Interference fit, Pin & Cotter, Loose fit etc.

3. Transmission elements: Belt, Gear, Chain.                                                                            Gear drive is very important and versatile in transmission. Examples are Hypoid (for heavy load), Spur, Bevel, Worm & Wheel, Rack & Pinion.

4. Transmission Support: Shaft, Pulley, Bearings, Clutches and Couplings. Seals, springs and lubricators, Keys & Spline.

5. Motor Power Block (which are normally based on the power need)

 

Machine functionality

Ability to perform its function effectively within the machine is one of the most important demands of a component.

•       Criteria for functionality are:

•       Strength: Ability to resist destroying force, a most important criterion

•       Rigidity : Ability to retain its form

•       Wear Resistance

•       Vibration resistance

 

Approach to Machine Design

Machine design is a creative multi-phased process with its own peculiarity. It is characterized by

•       Multi-variant decision making.

•       Conformity with existing standard and industry norms.

•       Conformity with both general and specific demands to the construction.

•       Orientation towards innovativeness and to accommodate as many new ideas as possible.

 

Stages in Machine Design.

The following are the 5 stages of a new machine design project:

Stage 1: Prepare a Technical Brief

Stage 2: Preparation of Technical & techno-economic feasibility based on the clients brief.

Stage 3: Preparation of initial design sketches

Stage 4: Preparation of Final Design which includes design drawings

Stage 5: Preparation of final working document

•       Stage 1: Prepare a Technical Brief: – This document contains the name, main function, specifications, quality indices, economic indices and any special demand of the client. (In preparing this document, use is made of the client or customer brief (need), latest information on the latest and most modern and similar products, patent search, scientific research and prognosis pertaining to such machine).

•       Stage2: Preparation of Technical & techno-economic feasibility based on the clients brief. Preliminary sketches of possible design variants are brought forward for selection and confirmation of the best choice by the client and his consultants.

Stage 3: Preparation of initial design sketches showing more details as to the general view, working principle, dimension and basic parameters of the selected variant.

Stage 4: Preparation of Final Design which includes design drawings and working documents showing full view (2D&3D), assembly drawings of sub-assemblies which must reflect best practices and bench marked against the best of its type anywhere in the world. At this stage also consideration is given to reliability, safety, storage and transportation issues.

Stage 5: Preparation of final working document. Full detail drawings of components to be produced. Full design, reliability and economic analysis to justify production.

     Please note that use of computer is highly recommended at every stage considering the very difficult calculations and drafts involved. Computer aided Design project Management Software should be used.

 

Mechanisms and their functions

    Mechanisms form parts of machines when the working process is purely mechanical motion.

    They have chain structure and may have two or more connected members called links.

Main types of mechanisms used in machines:

•       Lever mechanisms (which may have one or more translator or rotary kinematics pair included in the chain).

•       Cam mechanisms which consist of the forced contact of a cam and a tappet follower. Can give any displacement, velocity or acceleration. It is a very versatile mechanism. Examples are Drum cam, Disc cam, etc.

•       Friction mechanisms e.g. braking system.

•       Gear mechanisms (spur, gear drive, bevel gear)

•       Maltese-cross (Geneva stop)

•       Hydraulic/ Pneumatic mechanisms

 

Functional Characteristics of Machine

•       Quality of performance

•       Reliability

•       Ergonomics (Aesthetics quality) composition of the machine.

•       Technological – ease of maintenance & repair; works easily.

•       Economical – cheap, justifies cost.

 

Three basic models for machine component analysis.

According to strength of materials / solid mechanics, there are 3 models in application.

(a) Material model i.e. assumption of uniformity (isotropy not anisotropy) of material.

(b) Computational model for the material i.e.

•       Elasticity

•       Plasticity

•       Yield strength

(c) Model of Geometric form i.e.

•       Cylindrical, Plate, disc, Ring, Spherical, Massive, Bar, Round.

 

Theoretical principles

•       Hook’s law

•       Principle of Superposition & Independence of forces

•       The elements of a machine in the process of operation experience different externally applied forces which can damages or deform them.

•       Hence, methods used are;

•       Stress – computation of the stressed and strained condition.

•       Strain – computation of the extent of deformation

•       Structural stability test (Slenderness ratio)

•       Rigidity.

 

Types of Deformation of machine component

•       Tensile & Compressive

•       Shear & Twist

•       Bending & Compound Resistance

•       Lateral / Structure Stress under dynamic/impact load

•       Fatigue wear & Failure of shafts & rotors

•       Buckling of Columns

 

Design Criteria

    The most important criterion for selection of machine component is that of allowable or limiting stress.                                                                                                                                             

   Where  stress at some point in the biggest load
 is limiting stress due to the material and type of details.

   E.g. To determine the diameter of bolt in a bolted joint

   If the bolt experiences a force F, then

s    dp= F/A = 4F/ ²

   Let [s] the limiting stress due to the material which is given,

   Then d² sp= 4F/

  

Design Criteria cont’d.

Another criterion is that of safety factor.                                      In this case n = s_min/s_max . Where n = safety factor 

s     = limiting stress or

s    _max = maximum stress at the most dangerous point in the detail or structure.

 

FINALLY.

   The design process is clearly a systematic process that calls for creativity.

   However, creativity also involves risk.

Basic Characteristics of Steel

•       Pure iron is a relatively soft, ductile, low strength metal with few practical engineering applications.

•       The addition of Carbon to pure iron increases strength and hardenability to useful levels. However it decreases ductility.

•       Since mechanical behaviour is directly related to the phases present it is important to study these phases and how they are influenced by temperature. A study of the Iron- Carbon phase diagram is used for this purpose.

Iron-carbon phase equilibrium

•       notes on iron and what happens when iron /carbon mixtures are cooled from liquid to solid.   The notes are based on the Iron Phase Diagram (equilibrium diagram ).  

•       A "Phase" is a form of material having characteristic structure and properties. It is a form of the material which has identifiable composition, structure and boundaries separating it from other phases in the material volume.

•       This phase diagram tells us the various phases a particular alloy of Iron and Carbon will go through when allowed to cool down to room temp.

•       In general iron carbon alloys up to 2% are known as steels while from 2% upwards the alloys are identified as cast iron.

•       The diagram below shows the phases present when when Fe-C alloys (C up to 7%) are cooled from liquid to solid.
The left side of the diagram represents pure iron and the right hand of the diagram represents an alloy with 6,67% C. which result on cooling in the formation of Cementite.  This is a intermetallic compound (iron carbide-Fe₃ C) which although not 100% stable, but is to all practical purposes a stable phase.  The phase diagram shown is therefore a meta-stable phase.

 

Different reference sources indicate the Eutectoid point at 0,8% C and 0,77% C.

Steels

•       If the carbon content of the cooled solid is less than Eutectoid (about 0,8% C) the solid is identified as a hypoeutectoid steel: most steels are this form.   If the carbon content is more then 0,8% then the solid is a hypereutectoid steel.   Hypereutectoid steels with carbon content over 1,2% C are very brittle.  Few steels are made with carbon contents over 1,2%.

    Generally in order to increase the strength of steel other alloying elements are added which increase the strength while retaining toughness and ductility.

CONCLUSION

 

*    There are basically two approaches to engineering design

– Forward and

– Reverse engineering

(developing & developed countries)

 

*    The general knowledge of engineering materials helps in material selection for professional engineering design.

 REFERENCES

       Thomson, Ross (2009), Structures of Change in the Mechanical Age: Technological Invention in the United States 1790-1865, Baltimore, MD: The Johns Hopkins University Press, ISBN 978-0-8018-9141-0

      Zelinski, Peter (2013-11-08), "Hybrid machine combines milling and additive manufacturing", Modern Machine Shop.

      Robert L. Norton, Machine Design, (4th Edition), Prentice-Hall, 2010

      Matthews, Clifford; American Society of Mechanical Engineers (2005), ASME engineer's data book (2nd ed.), ASME Press, p. 249, ISBN 978-0-7918-0229-8.

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