Gestão e Produção Sustentável. Durability Electromagnetic radiation. ENG K49 Materiais de origem vegetal aplicados na construção

Transcription

1 Gestão e Produção Sustentável Durability Electromagnetic radiation ENG K49 Materiais de origem vegetal aplicados na construção Ricardo Fernandes Carvalho

2 Electromagnetic radiation spectral band Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays Thermal radiation Where v is the speed of the wave f is the frequency λ is the wavelength h is Planck's constant c is the speed of light E is a photon energy m, n constants λ=r H (1/n 2-1/m 2 ) Ε = h.λ

3 Electromagnetic radiation

4 Ε = h.λ Electromagnetic radiation

5 Absorption wavelength UV absorption For example Aliphatic polyurethanes are known to degrade rather rapidly with a simultaneous decrease in carbonyl absorption when exposed to UV radiation,

6 Photodegradationmechanisms Photoreduction Photodissociation Photosensitization Photoelimination Photoaddition Secundary photoreactions

7 ABSORPTION OF SOLAR RADIATION

8 Natural Weathering Climatic indicators Radiation energy [MJ/m 2 ] UV, Temperature, RH Exposure Site Racks: Under Glass Exposure, Black Box Exposure, Exposure: with Spray, Dry Exposure Sun-Tracking Devices, Light Concentrating Devices ASTM D4364 plastics in concentrated natural sunlight

9 Artificial weathering Artificial weathering equipment wavelength of radiation radiation intensity irradiance uniformity energy dosage and exposure time temperature Rain, humidity Objectives Product evaluation Study of degradation principles.

10 Sample preparation In order to study degradation principles: well-defined prepared under conditions which can always be repeated uniform in structure and composition representative of the particular group of materials, processes, etc. not contaminated permits the drawing of adequate conclusions.

11 Methods of exposure Continuous exposure to light and intermittent exposure to water spray Alternative exposure to light and darkness and intermittent exposure to water spray Continuous exposure to light without water spray Alternative exposure to light and darkness without water spray

12 Parameters of exposure Black panel temperature Water temperature, ph, solids Light duration in cycle Spray duration in cycle Relative humidity (light or dark cycles) Temperature during dark cycle Duration of light and darkness cycles

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15 EFFECTONWOOD

16 Methods of weathered specimen evaluation Visual evaluation Surface roughness and morphology Imaging color changes Spectroscopic methods (UV, FTIR) X-ray analysis Physical properties of materials Mass change, density, contact angle, diffusion of gases and water transport in polymers Rheological properties of materials Mechanical properties Tensile strength, elongation, flexural strength, other mechanical properties

17 Effect on Wood Extractives change color when exposed to UV radiation or visible light, and this color change indicates degradation of extractives near the surface. Carbohydrates (cellulose and hemicelluloses) Carbohydrates do not absorb UV radiation and are therefore resistant to UV degradation. Lignin If exposed to UV radiation, lignin in the middle lamella, at the surface of wood, begins to degrade within a few hours. Lignin photodegrades, leaving cellulose fibers loosely attached to the surface.

18 Applied_spectroscopy X-ray crystallography IR FTIR, ATR Ultraviolet visible spectroscopy

19 X-RAYS

20 20 Principle of EDS

21 21 Energy-dispersiveX-rayspectroscopy Technological variants Auger electron spectroscopy (AES) X-ray photoelectron spectroscopy (XPS) - kinetic energy wavelength dispersive X-ray spectroscopy (WDS) X-ray fluorescence (XRF) Planck's Law: Bragg Equation synchrotron

22 22 Energy-dispersiveX-rayspectroscopy The fluorescence process is inefficient, then the path from tube to sample to detector is maintained under vacuum (around 10 Pa residual pressure). Four primary components of the EDS setup are the excitation source (electron beam or x-ray beam) the X-ray detector the pulse processor the analyzer.

23 Energy-dispersive X-ray spectroscopy Intensidade (cps) ,879-3,425-2,971-2,789-1,838 Gesso α Intensidade (cps) ,445-4,234-3,763-3,041-2,851 Gesso β 2θ θ Intensidade (cps) ,445-5,926-4,234-3,440-3,041-2,983 Gesso α Gesso β θ

24 LAPOL -UFRGS

25 Covalent Bond INFRA-RED

26 26 Theory of infra red absorption IR radiation does not have enough energy to induce electronic transitions. Absorption of IR is restricted to compounds with small energy differences in the possible vibrational and rotational states. For a molecule to absorb IR, the vibrations or rotations within a molecule must cause a net change in the dipole moment of the molecule. The alternating electrical field of the radiationinteracts with fluctuations in the dipole moment of the molecule. If the frequency of the radiation matches the vibrational frequency of the molecule then radiation will be absorbed, causing a change in the amplitude of molecular vibration.

27 27 Theory of infra red absorption Stretching vibrational modes for H 2 O Molecular rotations Rotational transitions are of little use to the spectroscopist. Rotational levels are quantized, and absorption of IR by gases yields line spectra. Molecular vibrations The positions of atoms in a molecules are not fixed; they are subject to a number of different vibrations. Vibrations fall into the two main catagories of stretching and bending. Stretching: Change in inter-atomic distance along bond axis Symmetric x Asymmetric Stretching vibrational modes for CO 2

28 28 Theory of infra red absorption Bending vibrational modes for H 2 O Bending Change in angle between two bonds. Rocking (balanço) Scissoring (tesoura) Bending vibrational modes for CO 2 Wagging (abano) Twisting (torcer) scissoring (in and out of the plane) scissoring (in the plane of the paper)

29 29 Absorbance or Transmission x wavenumber (cm -1 )

30 30 SignalIntensity The Signal intensity depend on Molecular polarity: more polar, more Energy Mass of atoms: lighter, more energy Bond Strength: More strength, more energy

31 31 Equipament

32 32 Samplepreparation Solid samples can be prepared in a variety of ways. One common method is the "cast film" technique, which is used mainly for polymeric materials. The sample is first dissolved in a suitable, non hygroscopic solvent. A drop of this solution is deposited on surface of KBr or NaCl cell.

33 33 Fourier Transform A data-processing technique called Fourier transform turns this raw data into the desired result (the sample's spectrum): Light output as a function of infrared wavelength (or equivalently, wavenumber). As described above, the sample's spectrum is always compared to a reference.

34 34 Attenuated Total Reflectance spectroscopy A useful way of analysing solid samples without the need for cutting samples uses ATR or attenuated total reflectance spectroscopy. Using this approach, samples are pressed against the face of a single crystal. The infrared radiation passes through the crystal and only interacts with the sample at the interface between the two materials. With increasing technology in computer filtering and manipulation of the results, samples in solution can now be measured accurately.

35 Comparing to a reference

36 36 Lectureonline Infra-red Spectroscopy: Lecture. IR Spectroscopy Lecture Introduction to infrared spectroscopy A Simple explanation of Infrared Spectroscopy.

37 37 SCANNINGELECTRONMICROSCOPE (SEM)

38 38 Produces images of a sample by scanning it with a focused beam of electrons Information about the sample's surface topography and composition The most common SEM mode is detection of secondary electrons emitted by atoms excited by the electron beam The number of secondary electrons depends on the angle at which beam meets surface of specimen, on specimen topography

39 39 Back-scattered electrons (BSE) Reflected electrons from the sample by elastic scattering. The intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen.

40 40 Sample preparation specimen stub specimens must be electrically conductive, and electrically grounded to prevent the accumulation of electrostatic charge at the surface. conducting material, deposited on the sample either by low-vacuum sputter coating or by high-vacuum Conductive materials in current use for specimen coating include gold or graphite. Nonconducting specimens may be imaged uncoated using environmental SEM (E-SEM) or low-voltage mode Biological specimen is normally required to be completely dry, since the specimen chamber is at high vacuum. Hard, dry materials such as wood, bone, feathers, dried insects, or shells can be examined with little further treatment,

41 41 Scanning process and image formation Magnification Colour Detection of secondary electrons (topograpfic) Detection of backscattered electrons (Z) Cathodoluminescence, X-ray microanalysis, Resolution of the SEM, Environmental SEM Transmission SEM