Materials Inspection and Characterization-I PDF

Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Biomaterials Characterization These levels of testing will be needed before a biomaterial can be considered for clinical trials or in actual device manufac...

Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Biomaterials Characterization These levels of testing will be needed before a biomaterial can be considered for clinical trials or in actual device manufacturing. The final part of this book deals with device-level characterization with special emphasis on orthopedic and cardiovascular devices. Researchers with industrial product development background contributed toward these chapters. Figure 1.1 outlines how different chapters are linked to understand properties of biomaterials and biomedical devices. Figure 1.1 Schematic outline shows different properties related to biomaterials. 1 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Physical and Chemical Characterization of Biomaterials 1-Microstructural Characterization The microstructure of the material involves specifying the crystallography, morphology and chemical composition of the material. Crystallographic analysis includes identifying the different phases which are present in the structure of the material and the nature of the atomic packing within the phases. The morphological analysis corresponds to the characterization of the size, shape and spatial distribution of the phases or particles. 1. Optical Microscopy An optical microscope creates a magnified image of an object specimen with an objective lens and magnifies the image further more with an eyepiece to allow the user to observe it by the naked eye. Optical microscopy is commonly used in many research areas including microbiology, microelectronics, nanophysics, biotechnology and pharmaceutical research. It can also be useful to view biological samples for medical diagnoses, known as histopathology. Preparing the microscope slide with the sample to be examined, including a coverslip over the sample. 2 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Adjusting the objective lens to the lowest power of resolution. Placing the microscope slide with the sample to be examined onto the stage and fasten in place. Components involved in formation of images by the microscope optical train are the collector lens (positioned within or near the illuminator), condenser, objective, eyepiece (or ocular), and the refractive elements of the human eye or the camera lens. The optical microscopy is the oldest and simplest of the microscopes. But its resolution, defined as the ability of an objective to separate clearly two points or details lying close together in the specimen, is poor. As the resolution is about half the wavelength of illumination used in the measurement, the resolving powder of an optical microscope is limited by the wavelength of the visible light (around 400–700 nm) and by aberrations to be around 200 nm. 3 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim 2. Scanning Electron Microscopy(SEM) The SEM is one of the multipurpose methods for characterization of biomaterials. In SEM, an electron beam of relatively low energy from few hundred eV to 50 keV but with a very fine spot size of ~5 nm is scanned across the sample surface instead of transmitted through the sample as show in figure 1. A variety of interactions occur during the penetration and passage through the sample which results in the emission of electrons and photons from the sample as shown in Figure 2. The reflected type electrons and photons from the sample are used for imaging and characterization. Some of the SEM modes widely used to characterize biomaterials include secondary and backscattered electrons, X-ray mapping, electron-beam- induced current, electron channelling, electron backscattered diffraction and Auger electron microscopy. 4 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Figure 1 SEM spectroscopy. Figure 2. Schematic diagram of electron-material interactions. 5 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim How Scanning Electron Microscope (SEM) works 1-The electron gun produces an electron beam when tungsten wire is heated by current and accelerated by the anode. 2-The beam travels in the vacuum column through electromagnetic fields and lenses, which focus the beam down toward the sample. 3- A mechanism of deflection coils enables to guide the beam so that it scans the surface of the sample in a raster pattern. 4- When the incident beam touches the surface of the sample and produces signals, -Secondary electrons (SE) - Auger electrons -Back scattered electrons (BSE) - Characteristic X – Rays - Cathodoluminescence -The emitted signals are trapped by electrical detectors, convert into digital images and displayed on a screen as digital image. 6 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim -Provides information sample’s elemental composition, structural variation and morphology. -In the SEM, use much lower accelerating voltages to prevent beam penetration into the sample since the requirement is generation of the secondary electrons from the true surface structure of a sample. Therefore, it is common to use low KV, in the range 1-5kV for biological samples, even though the SEMs are capable of up to 30 kV. The image is formed the beam is scanned across the sample. Typical SEM micrograph of compacted magnesium metal powder is shown in Fig.3. SEM micrographs (a) grain composition and (b) grain boundary composition. 7 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Applications of Scanning Electron Microscopy Topography: The surface features of an object or “how it looks”, its texture; direct relation between these features and materials properties (hardness, reflectivity...etc.) Morphology: The shape and size of the particles making up the object; direct relation between these structures and materials properties (ductility, strength, reactivity...etc.) Composition: The elements and compounds that the object is composed of and the relative amounts of them; direct relationship between composition and materials properties (melting point, reactivity, hardness...etc.) Crystallographic Information: How the atoms are arranged in the object; direct relation between these arrangements and materials properties (conductivity, electrical properties, strength. etc.) Advantages of SEM -It gives detailed 3D and topographical imaging and the versatile information garnered from different detectors. - This instrument works very fast. - Modern SEMs allow for the generation of data in digital form. -Most SEM samples require minimal preparation actions. 8 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Disadvantages of SEM - SEMs are expensive and large. - Special training is required to operate an SEM. -The preparation of samples can result in artifacts. - SEMs are limited to solid samples. - SEMs carry a small risk of radiation exposure associated with the electrons that scatter from beneath the sample surface. X-RAY Diffraction and Scattering Method Knowledge of the structure and composition over small distances is a key requirement for understanding the properties of biomaterials. The wavelength of X-rays is on the atomic scale and, hence, provides a variety of primary tools such as X-ray diffraction (XRD) to reveal structural information of nanomaterials over a macroscopic sample volume. The XRD method provides a wealth of information from phase identification to crystallite size, from lattice strain to crystallographic orientation of nanostructured materials. In this method, a monochromatic X-ray beam is incident on the crystalline material and the intensity of the elastically scattered (diffracted) beam due to the periodic arrangement of atoms in the sample is measured as a function of the diffracted angle ‘2Ɵ’. 9 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Then using the Bragg’s law, the interplanar spacing d between atomic planes in the material is calculated: where λ is the wavelength of the X-rays used and the structural parameters like unit cell dimensions, cell volume, etc. are subsequently obtained from d. 10 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Why XRD? Measure the average spacing’s between layers or rows of atoms Determine the orientation of a single crystal or grain Find the crystal structure of an unknown material Measure the size, shape and internal stress of small crystalline regions 11 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Each diffraction peak is attributed to the scattering from a specific set of parallel planes of atoms. Miller indices (hkl) are used to identify the different planes of atoms Observed diffraction peaks can be related to planes of atoms to assist in analyzing the atomic structure and microstructure of a sample. 12 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim 2.4. FT-IR Spectroscopy IR spectroscopy is a fast, relatively inexpensive and widely used analytical technique for the characterization of biomaterials. It is a form of vibrational spectroscopy based on the interaction of IR radiation and natural vibrations of the chemical bonds among atoms that compose the material. In IR spectroscopy, the sample is irradiated with IR radiation and the changes in the absorption of this radiation by the sample are measured. The sample absorbs radiation in the IR region only whenever there is a coincidence (resonance) among the frequencies of the IR radiation with the molecular vibration and the natural vibration causes a change in the dipole moment during vibration. 13 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim Molecular vibrations are two types: stretching (that changes the bond length) and bending (that changes the bond angle). These changes in vibrational motion give rise to absorption bands in the vibrational spectrum. For the FTIR region, the position of absorption bands in the spectra are presented not as wavelength (l) but as wave number (v), using the reciprocal centimetre as its unit (cm-1), because it is directly proportional to energy (E) and frequency (n) of radiation. The IR region is subdivided into three spectral regions, i.e. the near IR (NIR – from 4000 to approximately 14,000 cm-1), mid IR (MIR –from 400 to 4000 cm-1) and far IR (FIR -from approximately 25–400 cm-1 ). The MIR is the most common and widely employed region for the characterization of materials as it depicts the primary molecular vibrations. The NIR and FIR are not frequently employed because only skeletal and secondary vibrations (overtones) occur in these regions producing spectra that are difficult to analysis. 14 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim The advantage of FTIR 1-FT-IR spectrometers offer many advantages over other analysis techniques. 2-The most important include a drastic reduction of the time needed for data acquisition, component specificity, and sensitivity. 15 Lec 3,4 Materials Inspection and Characterization-I Dr.Ishraq A.Kadhim 3-Other benefits include the internal wavelength calibration, which ensures the precision of the analysis. Disadvantages of FTIR spectroscopy? 1-The sampling chamber of an FTIR can present some limitations due to its relatively small size. 2-Mounted pieces can obstruct the IR beam. Usually, only small items as rings can be tested. Several materials completely absorb Infrared radiation; consequently, it may be impossible to get a reliable result. The application of FTIR FTIR spectroscopy is used to quickly and definitively identify compounds such as compounded plastics, blends, fillers, paints, rubbers, coatings, resins, and adhesives. It can be applied across all phases of the product lifecycle including design, manufacture, and failure analysis. 16