CER133 - Lecture 2 PDF

MICROSTRUCTURE OF CERAMICS Shem Q. Saldia Dept. of Materials and Resources Engineering and Technology MSU-Iligan Institute of Technology A. Bonifacio Ave., Tibanga Iligan City, Philippines What is microstructure? crystal structure vs microstructure The term ‘crystal structure’...

MICROSTRUCTURE OF CERAMICS Shem Q. Saldia Dept. of Materials and Resources Engineering and Technology MSU-Iligan Institute of Technology A. Bonifacio Ave., Tibanga Iligan City, Philippines What is microstructure? crystal structure vs microstructure The term ‘crystal structure’ is used to The term ‘microstructure’ is describe the average positions of atoms used to describe the within the unit cell, and is completely appearance of the material on specified by the lattice type and the the nm-cm length scale. fractional coordinates of the atoms (as determined, for example, by X-ray A reasonable working definition diffraction). In other words, the crystal of microstructure is: structure describes the appearance of the material on an atomic (or Å) length scale. “The arrangement of phases and defects within a material.” https://inference.org.uk/prlw1/minp/CourseC/CP1.pdf One of the key material factors behind such property improvements is the quality of the materials microstructure. What do we mean by microstructure? The structure of the material at a magnification that allows us to see features at the scale of 1 μm. In addition to the machining, it may also be a prerequisite that before the structure can be viewed microscopically it is necessary to “etch” the surface to reveal the underling features. This may be achieved by a heat treatment to reveal the key surface structures or chemical etching with acids to reveal grain boundary features by preferentially Nano Structure – 10-9 Length scale that pertains a.) to clusters of atoms b.) c.) that make up small particles or material features Show interesting properties because increase surface area to volume ratio –More atoms on surface compared to bulk atoms –Optical, magnetic, mechanical and electrical properties change 12  -6 MICROSTRUCTURE – 10 Microscopic structure of a material. Features are visible with high magnification in light microscope. - Grains, inclusions other micro-features that make up material a.) b.) c.) “Fracture evaluation of thermally sprayed coatings in dependence on cohesive strength” by J. Schubert and Z. Cesanek 12 Macrostructure – 10-3 m Macrostructure pertainsa.)to b.) c.) collective features on microstructure level Grain flow, cracks, porosity are all examples of macrostructure features Light-optical images of the macrostructure of sintered Si 3 N 4 -ZrO 2 /MLG ceramics. a) single layer with 5% MLG, b) single layer with 30% MLG, c) sandvich structure with 5-30-5 wt% MLG, and d) sandvich structure with 30-5-30 wt% MLG. 12 https://www.researchgate.net/figure/Light-optical-images-of-the-macrostructure-of-sintered-Si-3-N-4-ZrO-2-MLG-ceramics-a_fig2_340450296  Studying ceramic microstructure is crucial for: 1. Understanding Properties 5. Predicting Performance and Reliability microstructure directly influences mechanical, thermal, behavior prediction of ceramics under and electrical properties of ceramics. Ex, grain size and stress, temperature changes, or in shape can affect strength and toughness, while porosity corrosive environments, to anticipate and influences density and thermal conductivity. mitigate potential failures. 2. Designing Materials for Specific Applications 6. Research and Development like electronics, aerospace, and biomedical devices. Example: bioactive ceramics for medical 3. Optimizing Processing Techniques implants or high-performance ceramics for extreme environments. The methods used to fabricate ceramics (e.g., sintering, casting, or additive manufacturing) can lead to different 7. Cross-disciplinary Applications microstructures. collaboration with other engineering fields, 4. Quality Control such as materials science, mechanical engineering, and nanotechnology to identify and control defects such as porosity, cracks, or undesirable grain growth, which can adversely affect performance.  Characteristics of Microstructure a.) b.) c.) (1) number and identification of phases present (2) relative amounts of the phases (3) size, shape, and orientation Fig. 1. Microstructure of ceramics a.) SN10 sintered for 30 mins; b.) SN12 sintered for 5 mins; c.) SN12 sintered for 30 min. “Effect of microstructure and mechanical properties on wear resistance of silicon nitride ceramics” by Svex, Brusilova, and Kozankova(2009) 12 Porosity Can be characterized by the volume fraction of pores present and their size, shape, and distribution compared with other phases. “Introduction to Ceramics” by W. D. Kingery, H. K. Bowen D. R. Uhlmann ISBN 0 471 47860 1 12 Porosity Can be characterized by the volume fraction of pores present and their size, shape, and distribution compared with other phases. o Apparent Porosity o Total Porosity -- Open Pores -- Open and closed pores 12 Quantitative Analysis of Ceramic Microstructure Quantities measured Two types of methods -- Volume Concentration -- Comparison method of phases -- Measurement method -- Grain size -- Particle size and surface area -- Volume ratio of constituents Optical/SEM/TEM images 12 Comparison Method The microstructure image or micrograph is compared with series of standard charts. The standard charts and templates have been issued by ASTM, and ISO. Measurement Method Microscopic measurements can be made either, -- On the virtual image in the microscope -- On the micrograph -- On the ground glass screen 12  Microstructural Analysis Techniques Examples 1. Optical Microscopy Uses visible light and lenses to magnify samples. It allows for the observation of microstructural features like grain boundaries and phases. Commonly used for metals and ceramics; often enhanced with etching to reveal structures. 2. Scanning Electron Microscopy (SEM) Uses a focused beam of electrons to scan the surface of a sample, producing high-resolution images. SEM can provide detailed information on surface morphology and topography. Widely used in materials science to analyze surface features, fracture surfaces, and to obtain elemental composition via Energy Dispersive X-ray Spectroscopy (EDS). 3. Transmission Electron Microscopy (TEM) Involves passing electrons through a thin sample, allowing for extremely high-resolution images at the atomic level. It provides information on both morphology and crystallography. Ideal for studying nanostructures and defects within materials. 4. X-ray Diffraction (XRD) Analyzes the diffraction patterns of X-rays scattered by crystalline materials. This technique provides information on phase identification, crystal structure, and texture. Useful for determining the phases present in a material and their relative amounts. 5. Thermal Analysis Techniques Description: Techniques like Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) can provide insights into phase changes and stability. Application: Useful for understanding thermal properties and transitions in materials. Optical Microscopy Light optical microscopy images of Cu and Cu/Al 2 O 3 coatings with different alumina content. All the depositions are obtained at 450°C. https://www.researchgate.net/figure/Light-optical-microscopy-images-of-Cu -and-Cu-Al-2-O-3-coatings-with-different-alumina_fig3_289522833 Scanning Electron Microscopy (SEM) SEM image of alumina powder. https://www.researchgate.net/figure/SEM-image-of-alumina-powder_fig4_3 18793663 Advantages and Disadvantages Between Optical Microscopy vs SEM Optical Microscopy SEMs Pros: Pros: Low magnification (typically 200 nm) Slower inspection times Smaller depth of field, compared to SEM Greyscale only Light reflections can mask certain features https://www.thermofisher.com/ph/en/home/materials-science/le arning-center/applications/sem-optical-microscopes-difference. html Transmission Electron Microscopy (TEM) TEM images of the alumina support in K2CO3/Al2O3 composite: (a) aggregate of needle-shaped Al2O3 particles, (b) sheet-shaped particle. https://www.researchgate.net/figure/TEM-images-of-the-alumina-support-i n-K2CO3-Al2O3-composite-a-aggregate-of_fig6_257691895 XRD shows the XRD pattern of raw alumina which confirms the presence of α-alumina (corundum) by ICDD 089-7717. α-Alumina is the most stable https://www.researchgate.net/figure/shows-the-XRD-pattern-of-raw-alumin a-which-confirms-the-presence-of-a-alumia-corundum_fig7_319089968 TGA Thermogravimetric analysis (TGA) curves of four types of alumina after adsorbent treatment. https://www.researchgate.net/figure/Thermogravimetric-analysis-TGA-curv es-of-four-types-of-alumina-after-adsorbent_fig3_264128816 TGA-DTA TGA and DTA curves of perovskite powder. https://www.researchgate.net/figure/TGA-and-DTA-curves-of-perovskite-p owder_fig1_332826705 Determination of Grain Size o Comparison method compared with standard charts and templates 12 Determination of Grain Size o Measurement method ≥ 50 grains 12 Determination of Grain Size o Measurement method Intercept Method -- The number of grains which are cut by a straight lines are measured. Measurement is carried out in three directions at right angles & one is parallel to elongated direction. ≥ 50 grains 12 Microstructure of glass ceramics Glass ceramics are polycrystalline ceramics made by controlled crystallization of glasses. They have properties that place them between ceramics and glasses, with at least one glassy and one crystalline phase in their composition. Their most attractive property is their surface bioactivity, which makes them of interest for use as coatings on prostheses. https://www.sciencedirect.com/topics/materials-science/glass-ceramics ASSIGNMENT NO. 3 – Give at least 1 micrograph image of the microstructure of the following: 1. Triaxial Whiteware Compositions 2. Refractories and Structural Clay Products 3. Glazes and Enamels 4. Glasses and Glass-Ceramics 5. Abrasives, Cement, and Concrete 6. Some Special Compositions -Due: October 14, 2024 at 11 PM - Submission: In PDF format, upload in GDrive https://drive.google.com/drive/folders/14GDO12hJmACCnSaErAH aa0rpveq5yuR0?hl=en PRELIMINARY EXAMINATION on October ____ 2022 at 10 AM COET room 318 -The End- Lecture 2 Some images used in this lecture are Google images.