Introduktion til røntgenfluorescens (XRF) og skanning elektron mikroskopi (SEM) Michelle Taube Nationalmuseet Bevaringsafdelingen

Transcription

1 Introduktion til røntgenfluorescens (XRF) og skanning elektron mikroskopi (SEM) Michelle Taube Nationalmuseet Bevaringsafdelingen

2 Introduktion til røntgenfluorescens (XRF) og skanning elektron mikroskopi (SEM)

3 Since we received our XRF in July 2008, we ve used it in:

4 our conservation department

5

6 our museum

7 other conservation departments

8 churches

9 even outside

10 Short background

11 schematic of nose standard XRF system with separate x-ray tube and detector Bruker Tracer III-V handheld XRF

12 Niels Bohr Danish physicist

13 Bohr Model of the Atom Lshell nucleus (contains protons and neutrons) Mshell Nshell Kelectron shell electrons circle the nucleus in orbits with specific energies

14 incoming x-rays inner shell electron absorbs x-ray energy and is removed from the atom (or to an empty electron shell)... M-shell L-shell K-shell

15 atom in the excited state witha core electron missing to reduce energy, an electron from an outer shell takes the place of the missing electron the extra energy is given off as a characteristic x-ray... M-shell L-shell K-shell

16 ... M-shell L-shell K-shell this characteristic x-raywas created by an electron transition from the L shell into the K shell

17 other transitions also occur, for example:... M-shell L-shell from M shell into K shell K-shell... M-shell L-shell from M shell into L shell K-shell

18 resulting spectrum shows a peak for each transition heavy elements (like lead) have many electrons and many peaks Pb M-lines Pb L-lines

19 Which elements can we detect? a few more light elements can be detected by adjusting the settings and using the vacuum attachment

20 Selected case studies

21 Turkish saddle

22 dark flower center bright thread

23 x 1E3 Pulses Cu Hg Ag Hg Au Rh Cu Au Rh Ag kev -

24 Gottorfer Codex sheet 2947 Statens Museum for Kunst Pb Pb Hg Hg Pb Pb Pb Pb Rh Pb Ca Hg Hg Rh Energy (kev)

25 Fredensborg Castle silk wallpaper

26 table green fabric

27 wooden ship rudder Fe Fe 0 Ca Rh Ca Energy (kev)

28 Tracer III-V is portable XRF conclusions Many different types of material can be analyzed Some knowledge/insight into the material being tested is necessary

29 Introduktion til røntgenfluorescens (XRF)og skanning elektron mikroskopi (SEM)

30 scanning electron microscope (SEM) simple light microscope eyepiece electron source electron beam lenses lenses sample light beam detector sample light source images 2011 FEI Company

31 electron beam sample commonly detected signals electrons secondary (weak) electrons backscattered (energetic) electrons characteristic x-rays

32 JEOL 5310 LV-SEM at the School of Conservation large sample chamber can be used in low vacuum (LV) mode a small amount of air is present in the sample chamber means that samples do not need to be coated with a conductive material (such as carbon or gold) only backscattered electrons are detected

33 Hammerumpigens grav Herning Museum SEM3: red warp, degraded SEM4: red warp, ok

34 Hammerumpigen SEM4: red warp, ok

35 Hammerumpigen SEM3: red warp, degraded

36 kalot slag Metro cityring project FO204166B

37 iron kalot slag cross-section backscattered electron micrograph brighter areas have higher molecular weight

38 can use x-ray detectorto do elemental analysis in SEM -very similar to XRF

39 microscope is called scanning electron microscope because the electron beam scans across the sample we can use scanning function to make element maps that show where specific elements occur in the sample

40 element of interest marked on the spectrum

41 bright areas in each element map show where that element is in the sample

42 It is also possible to stop the beam and analyze a spot. The rectangle is a hercynite(feal 2 O 4 ) crystal. cps 40 Al O Fe 10 0 Fe Mg Si K Ca K Ca Energy (kev) Fe

43 Ribe Domkirke wall paintings optical micrograph backscattered electron micrograph cross-section and optical micrograph: Vibeke Rask

44 SEM conclusions Highly detailed pictures with good depth of focus Can perform elemental analysis of the sample in combination with imaging General conclusion Sometimes the analysis leads to more questions cannot expect a single technique to answer all questions

45 Other analytical tools optical microscopy: reflected and transmitted light ion chromatography: salt analysis FT-IR (Fourier Transform Infrared Spectroscopy):identification of organic and some inorganic compounds GC-MS (Gas Chromatography -Mass Spectroscopy):analysis of organic compounds, incl. binding media