Explosion properties of nanopowders P Holbrow Explosion Safety Unit An Agency of the Health and Safety Executive

Transcription

1 Explosion properties of nanopowders P Holbrow Explosion Safety Unit

2 Nanopowders Explosible dust Particle size Oxidant Dust concentration Ignition source Turbulence

3 Nanopowders Engineered nanomaterials Unique shapes Unique properties Size < 100 nm in one dimension Medicine Clean water Energy Solar plastics Materials

4 Nanopowders HSE project Potential fire and explosions hazards Nanopowder increased surface area to volume ratio Spherical 1 micron particle reduced to 100 nm particles increases the surface area x 10 Increased reactivity

5 Explosions violence, dp/dt and Pmax Test equipment, micron-scale 20 litre sphere BS EN series Typical values: Micron-scale aluminium Kst bar m/s Pmax up to 12 bar Micron-scale carbon Kst up to 151 bar m/s Pmax up to 8 bar Test material kg

6 Nanopowder explosion test apparatus 2 Litre enclosed spherical chamber 20 bar maximum working pressure External dust injection Central ignition source Piezo-electric pressure transducers Dispersion nozzle External dust injection

7 Nanopowders explosion test apparatus Control, software, data analysis system Dedicated fume cupboard and glovebox

8 Minimum Ignition Energy MIE BS EN 13821:2002 MIKE3 Kuhner Modified Hartmann tube 1mJ 1 J Variables: capacitive discharge, dust concentration, ignition delay Typical values for micron powders variable: Aluminium <1-10 mj

9 Minimum Ignition Energy Existing equipment modifications included: Isolation valve and dispersion chamber enables nanopowder to be handled in a sealed system. HEPA filtration on the extraction system

10 Nanopowders Nanopowder Sample Information from supplier Number Aluminium EC/104/08 Nominally 100 nm Aluminium EC/011/09 Nominally 210 nm Multi-walled carbon EC/153/07 Outside diameter: nm; Inside diameter: 5-10 nm; Length: um; nanotubes Carbon nanofibre EC/042/08 Diameter nm Length micron Carbon nanofibre EC/158/07 Outside diameter: nm; Core diameter: 1-10 nm; Length um; Carbon Nanofibre EC/116/08 Diameter nm Length 2-5 micron Carbon Nanofibre EC/117/08 Diameter nm Length 2-10 micron Iron EC/147/07 APS: 25 nm Zinc EC/152/07 APS : 130nm; Copper EC/148/07 APS: 25 nm

11 Commissioning tests 20 litre sphere Ignition source P max (barg) dp/dt (bar/s) K St m/s) (bar Lycopodium <63 micron (sample EC/026/08) Electric fuse head kj Sobbe kj Sobbe kj Sobbe Aluminium nm (sample EC/060/07) 10 kj Sobbe

12 Commissioning tests 2 litre vessel Ignition source P max (barg) dp/dt (bar/s) Lycopodium (sample EC/026/08) Electric fuse head kj Sobbe kj Sobbe Aluminium (sample EC/060/07) 1 kj Sobbe kj Sobbe kj Sobbe

13 Commissioning tests Ignition strength in the 2 litre vessel (without dust) Ignition source P max (barg) dp/dt (bar/s) Electric fuse head kj Sobbe x 1 kj Sobbe kj Sobbe

14 Commissioning tests comparison of 20 litre and the 2 litre vessel Material 20 litre sphere results 2 litre sphere results Rate of pressure rise (bar/s) K St m/s) (bar P max (bar) R ate of pressure rise (bar/s) P max (bar) Lycopodium E C /026/08 A lum inium E C /060/07 Zinc stearate E C /118/08 Coal E C /120/08 Toner E C /122/08 Carbon black E C /076/ A lum inium E C /104/

15 Commissioning tests comparison of 20 litre and the 2 litre vessel 700 Kmax 20 litre sphere vessel (bar m/s) Rate of pressure rise in 2 litre vessel (bar/s)

16 Nanopowder explosion tests Material Pmax (bar g) dp/dt (bar/s) Equivalent Kst (bar m/s) MIE (mj) Aluminium nanopowder <1 (210 nm) Aluminium <1 nanopowder (100 nm) Iron <1 Zinc Copper > 1000

17 Nanopowder explosion tests Material Pmax (bar g) dp/dt (bar/s) Equivalent Kst (bar m/s) MIE (mj) Carbon nanofibre Carbon nanofibre Carbon nanofibre Carbon nanofibre Multiwalled carbon nanotubes Not measured Not measured > Not measured >1000

18 Nanopowder v micron-scale powder

19 Nanopowder v micron-scale powder

20 Aluminum sample EC/11/08 2 litre sphere test results Sample number EC/011/09 Aluminium nanopowder Average particle size 210 nm Supplier: Intrinsiq Sample number EC/011/09 Aluminium nanopowder Average particle size 210 nm Supplier: Intrinsiq Explosion pressure (bar g) Rate of pressure rise (bar/s) Dust concentration (g/m3) Dust concentration (g/m3)

21 Aluminum sample EC/11/08 2 litre sphere test results Sample number EC/104/08 Aluminium nanopowder Average particle size 100 nm Supplier: Intrinsiq Batch: QNA 2607 Sample number EC/104/08 Aluminium nanopowder Average particle size 100 nm Supplier: Intrinsiq Batch: QNA Explosion pressure (bar g) Rate of pressure rise (bar/s) Dust concentration (g/m3) Dust concentration (g/m3)

22 Carbon nanofibre sample EC/042/08 2 litre sphere test results Sample number EC/042/08 Carbon Nanofibre Supplier: Pyrograph Products Inc. PR-19-LD-PS Sample Number EC/042/08 Carbon nanofibre Pupplier: Pyrograph Products Inc PR-19-LD-PS Explosion pressure (barg) Rate of pressure rise (bar/s) Dust concentration (g/m3) Dust concentration (g/m3)

23 Aluminium sample EC/104/08 2 litre sphere test results aluminium nanopowder EC/104/08 Dust concentration 3000 g/m 3 aluminium nanopowder EC/104/08 Dust concentration 2500 g/m 3

24 Nanopowder explosion test apparatus

25 Aluminium nanopowder explosion

26 Electrostatic Charging Resistivity test cell ρ= Rs [H W/L] Charge test apparatus I = C x dv/dt

27 Resistivity Resistivity v Relative Humidity for Aluminium Powders Aluminium nanopow der EC/104/08 Aluminium standard pow der EC/085/ E E E E E+08 Ω 1.00E E E E E E E E Relative Humidity (%)

28 Resistivity Resistivity v Relative Humidity for Carbon Powders Multi-w alled carbon nanotubes EC/153/07C Pyrograf III nanofibres EC/042/08 Carbon nanofibres EC/158/07A Carbon micron pow der EC/113/ E E+0 3 Ω E E E E Relative Humidity (%)

29 Charge Carbon Nanofibres All the powders produced charge, Some materials developed negative and some developed positive charge. Generally, the charge developed by nanopowders was comparable with the micron-scale powders. Rate of change of voltage (V/s) Capacitance (F) Current (A) -1.16E E E-08 Ambient environmental conditions: Humidity: 65.3%RH Temperature: 17.8ºC

30 Conclusions Special equipment has been developed to measure the explosion characteristics and electrostatic properties of nanopowders Explosion characteristics measured to-date are broadly comparable with micron-scale powders MIE zinc and iron more ignitable than micron-scale powders Electrostatics resistivity and charging tests increasing relative humidity resulted in decrease in resistivity. Resistivity generally greater than micron-scale powders