mineral processing 1&2

smelting

melting down of solid charge/preheated product followed by separation of valuable from non-valuable material

reductive smelting

reduction of oxides to metal and formation of slag

sulphide smelting

melting of sulphides to obtain two liquid phases

copper smelting complications

iron sulphide soluble in matte; copper oxide soluble in slag; richer copper matte means more copper oxide dissolved in slag

magnetite problem

solid magnetite makes slag viscous; solid magnetite denser than matte; combines with other oxides to produce solids of densities between matte and slag

Cu-sulphide converting

slag forming stage, where FeS oxidised to FeO and SO2, followed by copper making stage where remaining S removed as SO2

coke

solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal

benefits of ferroalloys over pure metal additions

alloying element may be thermodynamically difficult to obtain in pure form; prevents premature oxidation of alloying elements; cost of alloying elements lower in ferroalloy form

solid solution

solute component becomes part of crystalline structure without altering basic structure

substitutional solid solution

solute element occupies position of one of the solvent elements in solvent crystal

interstitial solid solutions

solute element occupies vacant spaces between solvent elements in solvent crystal lattice without displacing solvent element

isomorphous

solid has same structure for all compositions

eutectic point

temperature and composition where liquid transforms into two solid phases

peritectic reaction

reaction of one solid with a liquid to form a second solid

incongruent phase transformations

phase transformations for which at least one phase will experience change in composition

congruent phase transformations

phase transformations with no composition changes

solidus temperature

temperature where first liquid formed

liquidus temperature

temperature where all material is liquid

physical factors affecting matte-slag separation

entrainment of matte in slag; higher SiO2 concentration of melt gives higher viscosity

structural levels

subatomic; atomic; nanostructure; microstructure; macrostructure

subatomic structure

electrons, neutrons, protons

atomic structure

arrangement of atoms; chemical bonding

nanostructure

< 100 nm; nanoparticles; crystallites

microstructure

100 nm - several mm; grains in metals; fibres in composities; pores in ceramics

macrostructure

visible features; overall shape; large defects

property

response of material to external stimulus

property categories

mechanical; thermal; electriccal; magneti; optical; deteriorative

mechanical properties

strength; toughness; hardness; ductility

thermal properties

thermal conductivity; thermal expansion

electrical properties

electrical conductivity; resistivity; dielectric behaviour

magnetic properties

magnetisation; permeability

optical properties

refractive index; reflectivity

deteriorative properties

corrosion resistance; chemical stability

load

force applied to material during testing

stress

applied load divided by original cross-sectional area of material

strain

relative deformation of material during tensile test

yield strength

point of stress at which material starts to deform plastically

upper yield point

stress at which dislocations first break free

lower yield point

stress at which plastic deformation continues steadily

plastic deformation

permanent change in shape or size of material when applied stress exceeds yield strength

defects

natural imperfections in material’s atomic structure

point defects

small atomic-scale irregularities that help atoms move more easily through lattice

edge dislocations

extra half-plane of atoms which moves when stress applied allowing atomic planes to slip gradually

types of defects

point defects; edge dislocations

ultimate tensile strength

max stress material can withstand under tension before necking begins

fracture

separation of material in two or more peices under action of stress

ductility

measure of degree of plastic deformation that has been sustained at fracture

brittle material

material that experiences very little or no plastic deformation upon fracture

hardness

measure of material’s resistance to plastic deformation or cracking

hardness indicates

strength and wear resistance; hard materials resist identation or surface damage

failure

loss of load-carrying capabilities

creep

time-dependent permanent deformation under constant stress at high temperatures

primary creep

creep rate decreases with time

secondary creep

steady state

tertiary creep

creep rate increases with time

creep induced fracture

during tertiary creep, voids form at grain boundaries, grow and coalesce

brittle fracture

sudden separation of material via rapid crack propagation, with little or no plastic deformation

ductile fracture

local plastic deformation leading to separation

impact toughness

energy absorbed by material during fracture under impact loading

fracture toughness

resistance of material to fracture in presence of crack or flaw

impact test

test used to measure material’s ability to absorb energy under sudden loading

impact energy

energy required to fracture standard speciment during impact test

brittle transangular fracture

crack propagates through grains along crystallographic planes

brittle interangular fracture

crack propagates along grain boundaries

ductile to brittle transition temperature

temperature below which normally ductile material begins to fracture in brittle manner

fatigue

progressive failure of material under repeated or cyclic loading

improving fatigue life

impose compressive surface stress; remove stress concentration

shot peening

shots strike surface causing plastic deformation resulting in compression in surface layer

carburizing

introduces carbon-rich hardened layer which creates residual compressive stresses at surface

methods for imposing compressive surface stress

shot peening; carburizing

methods for removing stress concentrations

smooth transitions; surface finishing

eutectoid point

temperature and composition where one solid transforms into two solid phases

carbon content of hypereutectoid steel

0.76 - 2.14 wt%

carbon content of hypoeutectoid steel

0.022 - 0.76 wt%

composition of hypoeutectoid steel

proeutectoid ferrite; eutectoid pearlite (eutectoid ferrite + cementite)

composition of hypereutectoid steel

proeutectoid cementite; eutectoid pearlite (eutectoid cementite + ferrite)

bainite transformation

forms via diffusion-controlled transformation with restricted atomic diffusion

martensite transformation

transformation of austenite to martsenite without diffusion

formation of pearlite

transformation controlled by carbon diffusion in solid steel

tempering

heat treatment process in which martensite reheated to just below eutectoid temperature then cooled to improve toughness and reduce brittleness while retaining some hardness

annealing

steel heated and held at suitable temperautre to allow uniform temperature and structure to form before being cooled slowly at controlled rate

stress relief annealing

reduce stress caused by plastic deformation, nonuniform cooling, phase transformation

purpose of annealing

heat treatment used to soften steel and improve workability

spheroidize annealing

make very soft steels for good machining; heat just below Te and hold for 15-25 hours

process anneal

negate effect of cold working by recovery or recrystallisation

full anneal

make soft steels for good forming by heating to get austenite, then cool in furnace to get coarse particles

normalize annealing

deform steels with large grains, then normalize to make grains small

advantage of aluminium alloys

light weight; high electrical conductivity; high thermal conductivity; good ductility; easy to melt and cast; versatile mechanical properties

disadvantages of aluminium alloys

low melting points

applications of non-heat-treatable wrough aluminium alloys

electrical components; foil; food processing; beverage cans; filler metal for welding; marine components

application of heat-treatable wrought aluminium alloys

truck wheels; aircraft skins; pistons; canoes; railroad cars; aircraft frames

applications of casting aluminium alloys

transmission housings; general purpose castings; aircraft fittins; motor housings; automotive engines; food-handling equipment; marine fitting

applications of magnesium alloys

aerospace; high-speed machinery; transportation and materials handling equipment

properties of copper alloys

heavier than steel; low specific strength; good ductility; corrosion resistant; relatively good fatigue, creep, wear resistance compared to Al alloys; high electrical conductivity; high thermal conductivity; easiliy joined and fabricated

strengthening of copper alloys

cold-working; solid solution; age-hardenable; phase transformations

applications of copper alloys

electrical components; pumps; valves; plumbing parts

brass

copper alloys containing zinc

bronze

copper alloys containing tin

advatages of titanium alloys

corrosion resistant

application of titanium alloys

chemical processing equipment; marine components; biomedical implants; aerospace material