Light Alloys- Titanium Background and Extraction Flashcards
Demand for Ti compared to Ni, stainless steel and quality steel
Ti: 68 thousand tonnes
Ni: 234 thousand tonnes
Stainless steel: 13,307 thousand tonnes
Quality steel: 1,130,000 thousand tonnes
How has the amount of Ti in aircraft changed over time?
Almost exponential increase
Biggest consumers of Ti and biggest sponge producers
US biggest consumer by far then Europe.
Biggest sponge producers Japan and Russia
Corrosion resistance and abundance
Is very reactive but forms a stable adherent oxide film giving it good corrosion resistance in oxidising conditions. Is 4th most abundant metal in the earth’s crust after Al, Mg and Fe
Which industries use the most Ti?
Commercial aerospace (40%).
Military aerospace (13%)
Power generation (15%)
CPI and desalination (27%)
Other (5%)
The cyclical aerospace market
1991 end of Cold War led to 42% drop in US sponge consumption.
1997 resurgence in civil aircraft orders resulted in US sponge Ti consumption reaching record 32,000 tonnes.
911 downturn in demand for Ti from commercial aircraft industry. SARS outbreak and war against terrorism.
2008 credit crunch affected financing of new aircraft, airlines lost $5.2bn, high fuel prices stalled market growth.
It costs $1bn for a new sponge plant
Where is Ti used on commercial aircraft?
Main landing gear
Nos gear
Wing food hinge
Doors
Nos landing gear
Anti-icing ducts
Fan and compressor blades
Why is Ti good for joining with carbon fibre?
Ti and carbon have similar linear expansion coefficients (reducing residual stresses in components with changes in temperature).
Both near catholic end of galvanic series in flowing seawater.
Similar Young’s modulus
Why is the galvanic series important for Ti joining with carbon fibre?
Al alloys and steel are ear the anodic (active) end (more negative voltage range) of the galvanic series. Graphite is at the catholic (noble) end (more positive voltage range). When joined in a saline electrolyte (sea water) an electrolytic cell is formed and galvanic corrosion occurs. Ti is also near the catholic end so an electrolytic cell is unlikely to form, reducing galvanic corrosion
Why is YM important for Ti joining with carbon fibre?
They have a similar YM so when loaded will have similar strains (compared to Al which extends more). This lowers residual stresses formed in the component and reduces degradation of fasteners.
What else uses Ti?
Consumer and sports good like watches, phones, golf clubs, glasses.
Paints (TiO2).
Bone replacements as good biocompatibility
Advantages of Ti
Low density about 4.5g/cm3
Excellent corrosion resistance
High specific strength
Good comparability with CFRP (carbon fibre) structures
Excellent properties at elevated temperatures
Disadvantages of Ti
Expensive to machine
Low wear resistance
Difficult to form
Pick up of oxygen and nitrogen above 500C
Expensive (elemental Ti £5000/tonne, aero-engine Ti alloy £25,000/tonne, Al alloy £1500-2000/tonne)
Titanium’s affinity for oxygen compared to Al and Fe and energy for extraction
Enthalpy of reaction to extract Ti from TiO2 is greater than that for Al from Al2O3 and much greater than for Fe from Fe2O3.
Total energy cost for metal extraction:
Ti- 125,000kWh/tonne
Al- 75,000kWh/tonne
Steel- 15,000kWh/tonne
How does Kroll process work?
Mix rutile (TiO2), chlorine (Cl2) and coke (C) to make TiCl4 (tickle). This is corrosive and volatile. Add excess (so no tickle remains) of Mg to form MgCl2 (removed) and Ti sponge. Add alloy additions to sponge and maybe scrap (from previous process in same plant). Form electrodes and then melt process
