Specialized Techniques

1. Specialized Techniques

2. AUGER ELECTRON SPECROSCOPY http://www.google.de/imgres?imgurl=http%3A%2F%2Fwiki.utep.edu%2Fdownload%2Fattachments%2F39194437%2Fauger%252520process.jpg%253Fversion%253D1%2526modificationDate%253D1286942426453%2526api%253Dv2&imgrefurl=http%3A%2F%2Fwiki.utep.edu%2Fpages%2Fviewpage.action%3FpageId%3D39194437&h=411&w=976&tbnid=T_SlyWcJNp-6qM%3A&zoom=1&docid=Oo-TMJteWf9qHM&ei=qc07U-mBEIToywPvtYLABg&tbm=isch&iact=rc&dur=2552&page=2&start=31&ndsp=35&ved=0CMIBEK0DMCA

3. Auger Electron Spectroscopy (AES) was developed in the late 1960's • deriving its name from the effect first observed by Pierre Auger, a French Physicist, in the mid-1920's. • It is a surface specific technique • Auger electrons have low energies – vacuum needed • mainly used for conductive samples

4. KE = ( EK - EL1 ) - EL23 KE = EK - ( EL1 + EL23 ) The Auger process is initiated by creation of a core hole - this is typically carried out by exposing the sample to a beam of high energy electrons (typically having a primary energy in the range 2 - 10 keV). Such electrons have sufficient energy to ionise all levels of the lighter elements, and higher core levels of the heavier elements. In the diagram above, ionisation is shown to occur by removal of a K-shell electron, but in practice such a crude method of ionisation will lead to ions with holes in a variety of inner shell levels. The ionized atom that remains after the removal of the core hole electron is in a highly excited state and will rapidly relax back to a lower energy state e.g. by Auger emission. An electron falls from a higher level to fill an initial core hole in the K-shell and the energy liberated in this process is simultaneously transferred to a second electron ; a fraction of this energy is required to overcome the binding energy of this second electron, the remainder is retained by this emitted Auger electron as kinetic energy. In the Auger process illustrated, the final state is a doubly-ionized atom with core holes in the L1 and L2,3 shells.

5. AUGER SPECTROSCOPY is based upon the measurement of the kinetic energies of the emitted electrons. Each element in a sample being studied will give rise to a characteristic spectrum of peaks at various kinetic energies. This is an Auger spectrum of Pd metal - generated using a 2.5 keV electron beam to produce the initial core vacancies and hence to stimulate the Auger emission process. The main peaks for palladium occur between 220 - 340 eV. The peaks are situated on a high background which arises from the vast number of so-called secondary electrons generated by a multitude of inelastic scattering processes. Often the spectra are differentiated for better sensitivity /better peak visibility.

6. Auger Depth Profiling To obtain information about the variation of composition with depth below the surface of a sample, it is necessary to gradually remove material from the surface region being analysed, whilst continuing to monitor and record the Auger spectra. This controlled surface etching of the analysed region can be accomplished by simultaneously exposing the surface to an ion flux which leads to sputtering (i.e. removal) of the surface atoms.

8. This example is the result of studies on the adsorptive behavior of organic admixtures on each cement mineral at the initial stage of cement hydration. Carbon and sulfur, main components of organic admixture, and calcium, one of the main components of clinker minerals, were analyzed by AES in the direction of the depth from the surface of the adsorbed layer. The sample was prepared in such a way that the polished surface of clinker was dipped in a practical concentration of aqueous solution of admixture for thirty seconds. From these results it is concluded that the organic admixtures are adsorbed preferably more on interstitial phase Relativeconcentration (arbitraryunits) Depth from the surface of the adsorbedlayer

9. SCANNING TUNNELING MICROSCOPY http://www.nanoscience.de/nanojoom/index.php/en/methods/stm.html?layout=blog

10. The name of the technique arises from the quantum mechanical tunnelling-type mechanism by which the electrons can move between the tip and substrate. Quantum mechanical tunnelling permits particles to tunnel through a potential barrier which they could not surmount according to the classical laws of physics - in this case electrons are able to traverse the classically-forbidden region between the two solids as illustrated schematically on the energy diagram below. The probability of tunnelling is exponentially-dependent upon the distance of separation between the tip and surface : the tunnelling current is therefore a very sensitive probe of this separation.

12. The direction of current flow is determined by the polarity of the bias If the sample is biased -ve with respect to the tip, then electrons will flow from the surface to the tip as shown above, whilst if the sample is biased +ve with respect to the tip, then electrons will flow from the tip to the surface as shown below. Electrically conductive sample surface is needed

13. Imaging of the surface topology may then be carried out in one of two ways: in constant height mode (in which the tunnelling current is monitored as the tip is scanned parallel to the surface) If the tip is scanned at what is nominally a “constant height” above the surface, then there is actually a periodic variation in the separation distance between the tip and surface atoms. At one point the tip will be directly above a surface atom and the tunnelling current will be large whilst at other points the tip will be above hollow sites on the surface and the tunnelling current will be much smaller. A plot of the tunnelling current v's tip position therefore shows a periodic variation which matches that of the surface structure - hence it provides a direct "image" of the surface

14. Constant current mode (in which the tunnelling current is maintained constant as the tip is scanned across the surface) This is achieved by adjusting the tip's height above the surface so that the tunnelling current does not vary with the lateral tip position. In this mode the tip will move slightly upwards as it passes over a surface atom and slightly in towards the surface as it passes over a hollow. The image is then formed by plotting the tip height versus the lateral tip position. As for STM a conductivesamplesurface is needed, it is notverycommonlyusedin concrete science. Instead, e.g the AtomicForceMicroscope is used.

15. ATOMIC FORCE MICROSCOPE http://www.nanoscience.de/nanojoom/index.php/en/methods/afm.html?layout=blog

16. The Atomic Force Microscope was developed to overcome a basic drawback with STM - that it can only image conducting or semiconducting surfaces. The AFM, however, has the advantage of imaging almost any type of surface, including polymers, ceramics, composites, glass, concrete and biological samples.

17. The AFM images of the surfaces of alite before and after dipping in water for thirty seconds. The surface is smooth before dipping. The roughness of surface, after etching, is enlarged by the dissolution of elements. The surface after etching is rough. The distance between the peaks is 100- 200nm.

18. Using AFM technique, it is observed (Fig. 4) that the fly ash consists primarily of large spheroid particles with a smooth surface, and of smaller irregular shaped particles High-calcium fly ash (Fig. 5) consists of smooth, irregularly shaped particles, some too large to be seen by AFM, others much smaller.

19. CHROMATOGRAPHY

20. Chromatography is a method for separating the components contained in the sample from each other by mixing the sample with the mobile phase comprising liquid or gas, passing the mixture through the stationary phase comprising solid or liquid The components in the samplehave to havedifferentaffinities (”attraction”) to the stationaryphase. • mobile phase: solvent + sample • sample-solventflowthrough the columntogether • the stationaryphase is consisting of a material for which the samplecomponentshavedifferentaffinities→ and thereforearegettingseperated The smaller the affinity the shorter the time in the column. Depending on the solventyoucandestinguishbetween: • Gas Chromatography (GC), • Liquid Chromatography (LC) and • Supercritical Fluid Chromatography (SFC), according to whether the mobile phase is gas, liquid or a super critical fluid.

21. Gas Chromatography (GC)uses gas as the moving phase and is classified into gas-solid chromatography, using a solid inert porous adsorbent as the stationary phase, and gas-liquid chromatography, using a nonvolatile liquid. The former is appropriate for separating inorganic gas and hydrocarbons with low boiling points, while the latter is appropriate for separating general organic compounds. The components to be separated by GC are limited to gas or liquids vaporizable at a temperature of approximately 450°C. The applications in the field of cement and concrete research include an example of the measurement of the polymerization degree of silicate anions in the C-S-H by GC after trimethylsilylation of a hydrate of silica-fume-blended portland cement and examples of the identification and determination of organic compounds contained in hydrated cement by analyzing gas produced by decomposing hydrated cement in a pyrolysis unit.

22. Liquid Chromatography (LC) uses the liquid moving phase. The classical liquid chromatography (LG), including thin-layer chromatography, paper chromatography, and column chromatography, has a low transport speed of the moving phase because it transports through the stationary phase by gravity and diffusion so that a long time is required for the analysis. HPLC (high performance LC) uses a high-pressure-resistant filler as the stationary phase to force the moving phase to move with a pump. The transport speed of the moving phase is as high as milliliters per minute, therefore, analysis is carried out more rapidly than conventional LC. Various HPLCs have recently been applied to the characterization of organic admixtures for concrete. The figure reveals that even the same series of admixtures mainly composed of the same type of compounds have different molecular weight distributions and mean molecular weights in accordance with the brand .

23. THERMOLUMINESCENCE ANALYSIS

24. Thermoluminescence (TL) dating is a technique that is based on the analysis of light release when heating crystalline material. TL-dating is used in mineralogy and geology, but is also increasingly being applied for dating of anthropological and archaeological samples.

25. Typical phenomenon of thermoluminescence, when sample is heated above 200 oC, light emission in blue range is observed up to 400 oC. At higher temperatures, the material emits a red glow. For a second heating no blue light emission is observed, only the red glow curve remains at the higher temperature range.

26. Origin of thermoluminescence (TL) Long-term internal and external exposure to nuclear radiation from natural sources (40K, 238U, 232Th) frees electrons from atoms in the sample. These electrons are trapped in the lattice at imperfections and can be only released by heat. As more time goes by, as more electrons are trapped. The electronsaretrapped as theylack the sufficientenergy to escape the lattice. Electronsareprovided the means to escape and return to the normalstatebyemittinglightbyheatstimulation. The amount of TL from the sample is used to determine the number of electrons and therewith the age. The temperature of the measurementrangesfrom 0-500°C. The minimum amount of sample is tens of milligrams. Clay example: The dating clock starts with the initial firing of the material, when originally accumulated TL is being driven out.

27. If a sample has been exposed to light for considerable time “bleaching” may occur meaning a de-excitation of TL traps by photon interaction. TL drops, suggesting a lower paleodose & age.

28. In the field of cement and concrete research the thermoluminescence method is used for analyzing the impurities contained in cement and estimating the heat history and the remaining strength of concrete exposed to, e.g.a fire or other treatments. Glow curves drawn by irradiating white portland cement with γ-rays emitted from the radiation source of 60Co are illustrated in Fig. 73. Figure 73 reveals that red, blue, and green lights are from monochrome thermoluminescence, especially the red, being bright. Although the red light is emitted by the radiation from Mg and Mn it is mainly caused by the radiation from Mn. The impurity of Mn causing the coloring of white portland cement can be determined using those results. This is, therefore, able to be employed as the indicator for sorting the raw materials.

29. Changes of the thermoluminescence of hardened concrete according to the changes of the heating time and heating temperature can be determined, and the exposure temperature and exposure time of concrete exposed to heat such as a fire can be estimated.

30. RADIO TRACER TECHNIQUE

31. The radio tracer technique is an analytical method using a radioactive isotope as the tracer and used in wide fields, including science, medicine, and industry. Radioactive tracing was developed by George de Hevesy who won the 1943 Nobel Prize for Chemistry for his pioneering work using radioactive tracers to study metabolic processes in plants and animals. The radio tracer technique is conducted by measuring the radioactive energy emitted from a radioactive isotope added to the sample. Radioactive tracers are compounds that contain one or more radioactive atoms that allows for easy detection and measurement. Tracers are frequently used to track the localization of a specific compound or to trace the path of a compound through a series of chemical reactions. A radioactive tracer is identical in chemical composition to the compound of interest and is administered in tiny amounts that do not perturb the experimental system. The tracer behaves in exactly the same way as an unlabeled molecule, but the tracer molecule continually gives off radiation that can be detected with a “Geiger counter¨, scintillation counter or other type of radiation detection instrument.

32. Radioactivation analysis as a microanalysis technique is nondestructive and is made by proceeding with a nuclear reaction by irradiating nonradioactive elements with protons and neutrons and determining the spectra of radioactive rays emitted from the newly produced radioactive elements. Since operators handle the radioactive elements it is indispensable to protect the operator from exposure to radioactive rays. Radioactivation analysis is widely used as an elemental analysis. This technique is superior in the detection sensitivity and analytical accuracy to other microanalytic methods and has the advantage that the concentrations of various elements can be determined by only a simple procedure. The detecting sensitivity of the technique is high and it is relatively simple to determine the sample because the number of radioactivenuclidesare large. Table 9 and Table 10 list the main β and γ radioactive substances.

34. The radio tracer technique is mainly applied to check the uniformity of the mixed raw material in the field of cement and concrete. Applications including the tracing of the state of blending using the 197Au radioactive isotope aiming at judging the homogenizing effect in a silo when the raw material, particle diameter, blending time, volume of air blown, and amount of raw material in a silo are changed. Publications can be found, e.g. on the mixing effect of raw materials and required mixing time in a concrete mixer using experimentally manufactured 24Na containing cement.