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Super Black

Super Black. “Scientists at the National Physical Laboratory in Teddington, West London, have developed a black pigment reckoned to be 25 times darker than any existing shade.” The Guardian 10.02.03. The blackest black ever made. What use is Super Black?. Road Signs.

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Super Black

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  1. Super Black “Scientists at the National Physical Laboratory in Teddington, West London, have developed a black pigment reckoned to be 25 times darker than any existing shade.” The Guardian 10.02.03 The blackest black ever made

  2. What use is Super Black? Road Signs less reflective symbols are more easily seen at night

  3. What use is Super Black? eg the Hubble Space Telescope which needs to absorb as much light as possible Light detectors The Cone Nebula 2,500 light-years away in the constellation Monoceros

  4. What is Super Black? First NiSO4(aq) is reduced by NaH2PO2 (aq) to coat a surface with an alloy of Ni and P A redox reaction equation: Does it lose or gain electrons? H2PO2- is the reducing agent. It loses electrons. Ni2+ (aq) + H2PO2- (aq) + H2O (l) + H+ (aq)  Ni (s) + H2PO3- (aq) 2 Check that elements and total charge balance Balance the reaction equation. What is the change in oxidation state for Ni here? So what is the Ni2+ : H2PO2- reaction ratio? Where will the extra O come from? What is the change in oxidation state for P here? reactants: 1Ni 1P 4H 3O total charge 1+ = products reaction ratio is 1Ni2+ : 1H2PO2- ie as equation P (+1  +3) ie 2e-lost Ni (+2  0) ie 2e- gained

  5. What is Super Black? First NiSO4(aq) is reduced by NaH2PO2 (aq) to coat a surface with an alloy of Ni and P Where does the P come from? H2PO2- is absorbed into the new surface and has a catalytic reaction there: 3H2PO2- (ads)  2P + H2PO3- (aq) + H2O + 2OH- What type of redox reaction is this? What are the changes in oxidation state? disproportionation 3P(+1)  2P(0) + 1P(+3)

  6. What is Super Black? nickel and phosphorus alloy aluminium surface 0.00001 m First NiSO4(aq) is reduced by NaH2PO2 (aq) to coat a surface with an alloy of Ni and P This process is called electroless (not electrolysis)

  7. What is Super Black? light absorbing surface First NiSO4(aq) is reduced by NaH2PO2 (aq) to coat a surface with an alloy of Ni and P Then the Ni-P surface is etched using nitric acid

  8. What is Super Black? etching in progress First NiSO4(aq) is reduced by NaH2PO2 (aq) to coat a surface with an alloy of Ni and P Then the Ni-P surface is etched using nitric acid A possible etching reaction equation? Ni + 2HNO3  Ni(NO3)2 (aq) + H2 (g) ?? In fact brown gas and NiO form

  9. What is Super Black? etching in progress First NiSO4(aq) is reduced by NaH2PO2 (aq) to coat a surface with an alloy of Ni and P Then the Ni-P surface is etched using nitric acid A possible etching reaction equation? Ni + 2HNO3  NiO (s) + 2NO2 (g) + H2O (l) What does HNO3 behave as here? An oxidant (oxidising agent)

  10. What is Super Black? light absorbing surface The sequence of metal plating followed by surface etching forms surface craters

  11. Why is Super Black so black? The craters’ curved faces reflect less light than flat surfaces do ie light is absorbed very efficiently Crater formation depends upon % P. 8% P gives etched surfaces with least reflection. light absorbing surface

  12. Why is Super Black so black? SEVEN times less reflected back than with black paint light 90o to surface eg with road signs light 45oto surface eg with space telescopes TWENTY FIVE times less reflected back than with black paint Reflection is reduced still further if light reaches the Super Black surface at an angle of 45o when it reflects 25 times less than black paint. light absorbing surface

  13. References • Steve Lewis for the Royal Society of Chemistry • Many thanks to Dr Richard Brown of the National Physical Laboratory (www.npl.co.uk/) for contributing helpful comments and photographs • NPL Super Black images, used with permission of NPLwww.npl.co.uk/optical_radiation/superblack.htmlwww.rsc.org/CFmuscat/intermediate_abstract.cfm?FURL=/ej/JM/2002/b204483h.PDF • Road signs, used with permission of HMSO http://www.highwaycode.gov.uk/signs05.shtml • Space images courtesy of NASA / STScI • Hubble Space Telescope photo, http://hubblesite.org/gallery/showcase/telescope/t5.shtml • Cone Nebula,http://imgsrc.hubblesite.org/hu/db/2002/11/images/b/formats/640_wallpaper.jpg

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