Podcast
Questions and Answers
What characteristic defines elastic deformation in ceramics?
What characteristic defines elastic deformation in ceramics?
Which statement best describes plastic deformation?
Which statement best describes plastic deformation?
During elastic deformation, what happens to the bonds when the load is applied?
During elastic deformation, what happens to the bonds when the load is applied?
When a load is removed after plastic deformation, what remains in the material?
When a load is removed after plastic deformation, what remains in the material?
Signup and view all the answers
Which of the following best differentiates elastic from plastic deformation?
Which of the following best differentiates elastic from plastic deformation?
Signup and view all the answers
What defines the modulus of elasticity (Young's modulus)?
What defines the modulus of elasticity (Young's modulus)?
Signup and view all the answers
Which of the following factors affects the modulus of elasticity?
Which of the following factors affects the modulus of elasticity?
Signup and view all the answers
What is the behavior of most ceramics at ambient and intermediate temperatures under short term loading?
What is the behavior of most ceramics at ambient and intermediate temperatures under short term loading?
Signup and view all the answers
What causes the increase in stiffness of silica glass-fiber under tensile deformation?
What causes the increase in stiffness of silica glass-fiber under tensile deformation?
Signup and view all the answers
At what temperature does plastic deformation occur in ceramics?
At what temperature does plastic deformation occur in ceramics?
Signup and view all the answers
What type of bonding results in a high modulus of elasticity?
What type of bonding results in a high modulus of elasticity?
Signup and view all the answers
Which ceramic has a low modulus of elasticity value?
Which ceramic has a low modulus of elasticity value?
Signup and view all the answers
What effect does temperature have on the modulus of elasticity for some ceramic materials?
What effect does temperature have on the modulus of elasticity for some ceramic materials?
Signup and view all the answers
What defines glass in terms of atomic order?
What defines glass in terms of atomic order?
Signup and view all the answers
What is a primary feature of insulating refractories?
What is a primary feature of insulating refractories?
Signup and view all the answers
Which material is commonly used to make insulating refractories?
Which material is commonly used to make insulating refractories?
Signup and view all the answers
What happens to glass when it is cooled slowly enough?
What happens to glass when it is cooled slowly enough?
Signup and view all the answers
Which of the following is NOT a property of glass?
Which of the following is NOT a property of glass?
Signup and view all the answers
What is one advantage of ceramic fiber lining?
What is one advantage of ceramic fiber lining?
Signup and view all the answers
At what temperature can insulating products be designed for continuous use?
At what temperature can insulating products be designed for continuous use?
Signup and view all the answers
What is the glass transition temperature (Tg)?
What is the glass transition temperature (Tg)?
Signup and view all the answers
How does glass respond to heat compared to metals?
How does glass respond to heat compared to metals?
Signup and view all the answers
Which type of refractory brick contains 34% Al2O3 and 30% Cr2O3?
Which type of refractory brick contains 34% Al2O3 and 30% Cr2O3?
Signup and view all the answers
What is the minimum SiO2 content required for silica refractories?
What is the minimum SiO2 content required for silica refractories?
Signup and view all the answers
Which chemical is an exception that can affect glass?
Which chemical is an exception that can affect glass?
Signup and view all the answers
Why is glass considered to have great inherent strength?
Why is glass considered to have great inherent strength?
Signup and view all the answers
What impurities are commonly found in silica refractories?
What impurities are commonly found in silica refractories?
Signup and view all the answers
What does the volume of glass do as it is cooled rapidly?
What does the volume of glass do as it is cooled rapidly?
Signup and view all the answers
What happens to aluminosilicate materials under high loads?
What happens to aluminosilicate materials under high loads?
Signup and view all the answers
What is the first step in glass manufacturing?
What is the first step in glass manufacturing?
Signup and view all the answers
Which chemical reaction is involved in the melting process of glass?
Which chemical reaction is involved in the melting process of glass?
Signup and view all the answers
What does the annealing process in glass manufacturing achieve?
What does the annealing process in glass manufacturing achieve?
Signup and view all the answers
What is the purpose of nucleating agents in glass-ceramic processing?
What is the purpose of nucleating agents in glass-ceramic processing?
Signup and view all the answers
What is typically not included in the finishing step of glass manufacturing?
What is typically not included in the finishing step of glass manufacturing?
Signup and view all the answers
At what temperature does the melting process typically occur in glass manufacturing?
At what temperature does the melting process typically occur in glass manufacturing?
Signup and view all the answers
What characterizes glass-ceramic materials?
What characterizes glass-ceramic materials?
Signup and view all the answers
What is the role of the viscous mass obtained from melting?
What is the role of the viscous mass obtained from melting?
Signup and view all the answers
What is a positive property of advanced ceramic materials?
What is a positive property of advanced ceramic materials?
Signup and view all the answers
Which of the following is a component of technical porcelain?
Which of the following is a component of technical porcelain?
Signup and view all the answers
What type of ceramics does aluminium titanate belong to?
What type of ceramics does aluminium titanate belong to?
Signup and view all the answers
Which ceramic material is predominantly composed of soapstone?
Which ceramic material is predominantly composed of soapstone?
Signup and view all the answers
Silicon nitride is an example of which type of ceramic?
Silicon nitride is an example of which type of ceramic?
Signup and view all the answers
Which of the following properties is associated with advanced ceramic materials?
Which of the following properties is associated with advanced ceramic materials?
Signup and view all the answers
What is the formula for magnesium oxide?
What is the formula for magnesium oxide?
Signup and view all the answers
Which carbide is an advanced ceramic material?
Which carbide is an advanced ceramic material?
Signup and view all the answers
Study Notes
Fundamentals of Ceramic Materials
- This course covers the fundamentals of ceramic materials, including their mechanical properties, elastic constants, strength, and fracture mechanics.
- The course also addresses measurement techniques for different properties, such as modulus of elasticity, and discusses glass and glass-ceramics, refractories, and the processing and properties of different ceramic materials such as alumina, silicon carbide, and silicon nitride.
- Course was taught by Prof. Dr. Filiz Şahin in the Fall of 2024-2025.
Mechanical Properties of Ceramic Materials
- Elastic deformation is reversible; bonds stretch under a small load and return to their initial state when the load is removed.
- Linear-elastic means the stress-strain relationship is linear.
- Non-linear-elastic means the stress-strain relationship is non-linear.
- Plastic deformation is permanent; bonding planes shear and still remain sheared even after the load is removed.
Introduction - Stress-Strain Curve
- Material I shows high strength, high Young's modulus (E), but low ductility.
- This is typically seen in ceramics.
- Material II shows moderate strength and ductility and deforms plastically before failure, which is common for many metals.
- Material III shows low Young's modulus(E) and high ductility, common for many elastomers.
Introduction - Stress-Strain Curve (continued)
- Ceramics generally have a critical elasticity of approximately 0.01%, and a plasticity of approximately 0%.
- Metals have a critical elasticity of approximately 1-2%, and a high plasticity range, from 50-100%.
- PMMA (Plexiglas) demonstrates critical elasticity of several% and 100% plasticity.
- Examples for SiC whisker, Al2O3, Si3N4, MgO, silica fiber and NaCl single crystal have been provided in diagram in the form of stress-strain relationships.
Introduction - Elastic Constants
- Modulus of elasticity (Young's modulus, E) is the ratio of stress to strain in the elastic region.
- Poisson's ratio (v or μ) relates longitudinal and lateral deformations.
- Bulk modulus (stress to strain) relates to hydrostatic compression (-P(ΔV/V)).
- Elastic constants are related to bonding forces between atoms.
Introduction - Modulus of Elasticity (Young's Modulus)
- Modulus of Elasticity (E) is the slope of the stress-strain curve in the elastic region.
- Substances like Al2O3, Dy2O3, Er2O3, MgO, etc. have been provided with their Young's Moduli (E).
- Two factors affecting E are bond strength and temperature. Higher bond strength and lower temperature result in higher E values.
Introduction - Modulus of Elasticity (Young's Modulus) (continued)
- At ambient and intermediate temperatures for short-term loading, most ceramics behave elastically with no plastic deformation to fracture.
- Common ceramics, like LiF, NaCl, and MgO, exhibit plastic deformation at room temperature under sustained loading.
- The strength of atomic bonds determines the magnitude of the elastic modulus. Stronger bonds require more stress to increase interatomic spacing and lead to higher elastic moduli.
Introduction - Modulus of Elasticity (Young's Modulus) (continued)
- Ceramics with weak ionic bonding have low E values (e.g., E for NaCl: 44.2 GPa).
- Ceramics with strong covalent bonding have high E values (e.g., E for diamond: 1035 GPa).
Strength Measurements
- Tensile strength is typically only measured in metals.
- Bending strength, commonly measured using 3-point or 4-point bending methods.
- Compressive strength, used mostly for concrete.
- Surface preparation is important to minimize the effects of cracks, pores, large grains, or scratches on strength testing. These imperfections can cause stress concentrations and lead to an inaccurate strength value.
Strength Measurements (continued)
- The severity of strength reduction is affected by the shape of a pore, cracks or grain boundaries adjacent to a pore, the distance between pores, the size and shape of inclusions, and the difference in the elastic modulus and coefficient of thermal expansion between the inclusion and matrix.
Introduction - Elastic Constants
- Modulus of elasticity (Young's modulus, E)
- Poisson's ratio (v or μ)
- Bulk modulus (stress to strain for hydrostatic compression)
- Shear modulus (ratio of shear stress to shear strain)
Bending Strength Measurement
-
The loading rate is between 0.5–1.0 mm/min
-
The formula for 3-point bending strength is σ = 3LF/(2bd²) where: L = specimen length, F = load force, b = width, d = thickness
-
ASTM C1161 is a standard test method for 3-point bending test.
Bending Strength Measurement (continued)
- The formula for 4-point bending strength is σ = 3Fa/(bd²) where: a = distance between supporting and loading pins, F = load force, b = width, d = thickness
3- and 4- Point Bending Strength Measurement
- The 4-point bending method is preferred over the 3-point bend test because a constant bending moment exists between the inner supports in the former
Bending Strength
- Data on the bending strength at 25°C for various ceramic materials like GG-20, ST-37, Aluminum, Si3C, RSIC, SSIC, SIALON, RBSN, SSN, PSZ, Aluminum Oxide, Steatite, and Porcelain have been provided in graph form.
Compressive Strength
- The compressive strength (σc) is calculated by dividing the load (P) by the cross-sectional area (A): σc = P/A
Hardness
- Hardness is a material's resistance to permanent deformation.
- Hardness is a function of the crystal structure, crystal defects, bond type, fractional density, and grain size.
- External variables affecting hardness include temperature, the presence of reactive species (e.g., acids, alkalis, and water).
Hardness (continued)
- Hardness is determined by indentation tests such as the Brinell, Vickers, Knoop, and Rockwell methods.
- Each test uses a specific indenter and equation to calculate a hardness number.
Hardness (continued)
- Vickers hardness is a common method for ceramics.
Fracture Mechanics
- Measured fracture strength is significantly lower than theoretical values, primarily due to microscopic flaws and cracks.
- These flaws act as stress concentrators. The crack tip is a stress concentrator. Stress concentration at the crack tip influences the magnitude of the crack's amplification, which depend on the crack orientation and geometry.
- Macroscopic internal discontinuities (e.g. voids) and sharp corners or notches act as stress concentrators or stress raisers in the large structural components.
Fracture Mechanics - Critical stress for crack propagation
- Brittle materials contain cracks and flaws, and a stress level exceeding the critical stress causes cracking. The critical stress is calculated for brittle materials as follows: σc = (2EYs)/(πa)
Fracture Mechanics - Fracture Toughness
- Fracture toughness (Kc) measures a material's resistance to brittle fracture when a crack is present.
- This is also referred to as the stress intensity factor at which crack propagation leads to fracture. The higher the fracture toughness, the more difficult it is to initiate and/or propagate a crack.
- The higher the fracture toughness, the more difficult to initiate or propagate a crack.
Fracture Mechanics - Fracture Toughness (continued)
- Factors affecting Kc include specimen thickness, specimen size and geometry, as well as the manner of load application.
- Kc value for a relatively thick sample is known as Plane Strain Fracture Toughness or Fracture Toughness (Kic or K1c).
Fracture Mechanics - 3 modes of crack surface displacement
- Mode I (opening or tensile) mode is the most commonly encountered mode and when the stress is applied perpendicular to the crack.
- Mode II (sliding) mode happens when the stress is applied tangentially to the fracture and Mode III (tearing) when load is applied perpendicular to the fracture.
Fracture Mechanics - Fracture Toughness (continued)
- Temperature and strain rate are parameters that affect Kc. Higher temperatures and higher strain rates usually lead to lowered Kc values.
- Some example materials with their critical stress and fracture toughness data have been provided.
Glass and Glass-Ceramics
- Glass is an amorphous solid material. That is, it has no long-range crystalline order.
- It does not have a sharp melting point.
- Traditional glasses are made of inorganic materials like silica, sand, sodium and calcium carbonates, feldspars, borates, and phosphates. These inorganic materials form metallic oxides as they are melted together.
Glass and Glass-Ceramics (continued)
- Glass composition is not limited to inorganic material only. It also includes organic compounds.
Glass and Glass-Ceramics (continued)
- Glass is a metastable solid -with no long-range atomic order. Its atoms are arranged in a short-range order.
- Glasses are metastable in comparison to their stable, crystalline phases.
- Rapid cooling is a necessary process for producing glass that prevents reorientation into crystalline regions.
Glass - Properties
- Amorphous
- Brittle
- Transparent or translucent
- Good electrical insulator
- Unaffected by air, water, acid or most chemicals( but hydrofluoric acid, HF is an exception)
- High compressive strength
Glass Transition Temperature (Tg)
- Glass transition temperature is the temperature at which a material's properties change from the viscous-liquid to a rigid-solid.
- At Tg, the volume- temperature curve is almost parallel to the crystalline material curve and exhibits a change in gradient; below Tg, the material behaves as a glass.
- Viscosity is very high around 10^12 Pa.s in glass and transition range, Viscosity increases from about 10^8 to 10^12 Pa.s.
Volume vs Temperature
- The volume of a material decreases as the melt is cooled at a constant rate.
- If the cooling rate is slow enough, nucleation occurs, and the material crystallizes at the freezing point (Tg).
- If the cooling rate is high, crystallization doesn't occur at Tg, and the volume follows a different path for the supercooled liquid.
- The material reaches a more stable state when it crystallizes.
Structural Theories of Glass Formation
- Tammann (1925) proposed that glasses are undercooled liquids.
- Goldschmidt (theory-radius ratio criterion) assumed that glass formation occurs only if the coordination number of cations and anions is 4.
- Zachariasen's random network theory was developed, in which network structures are formed by corner-sharing oxygen polyhedra.
Structural Theories of Glass Formation (continued)
- Zachariasen's rules for glass formation state that:
- An oxygen atom is linked to not more than two glass-forming atoms.
- The coordination number of glass-forming atoms (cations) is small (3 or 4).
- The oxygen polyhedra share corners with each other, not edges or faces.
- The polyhedra are linked in a three-dimensional network (with at least three corners shared).
- The theory explains that glasses are typically disordered structures.
Structural Theories of Glass Formation (continued)
- Dietzel and field strength classification of elements categorize them according to their field strength.
- In the classification, the forces between cations and anions in the glass are considered.
Glass Raw Materials
- The main materials used in glassmaking are oxides, such as quartz (SiO2), soda (Na2CO3), limestone (CaCO3), potash (K2CO3), and dolomite (MgCa(CO3)2).
- Auxiliary materials are used for discoloring, clarification, coloring, and giving opacity to glass.
Glass Raw Materials (continued)
- Quartz, soda, limestone, potash, and dolomite are the base materials for glass production.
- Crushed glass forms 25-30% of the glass mix.
- Auxiliary materials are added to adjust color, clarity, opacity.
Glass Manufacturing
- The steps of glass manufacturing include melting, forming and shaping, annealing and finishing.
Glass Manufacturing (continued)
- Melting: Raw materials are mixed and melted in a furnace. This step involves removal of CO2 and additives.
- Forming and shaping: The viscous molten glass is formed into desired shapes using molds or rollers.
- Annealing: The formed glass is slowly cooled in annealing lehrs to relieve stress and prevent cracking.
- Finishing: Glass products are cleaned, ground, polished etc
Characterization of Materials
- Methods used for characterizing materials include X-ray/electron/neutron diffraction, X-ray absorption spectroscopy (XAS), Raman spectroscopy, Nuclear magnetic resonance (NMR), Atomic emission spectroscopy (AES), Energy-dispersive X-ray spectroscopy (EDX), Infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), Differential thermal analysis (DTA), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), Thermomechanical analysis (TMA), Temperature-dependent electrical conductivity measurement, Impedance spectroscopy(AC conductivity), and Electron paramagnetic resonance(EPR).
Mechanical and Rheological Behavior of Materials
- Techniques for measuring mechanical properties of materials include indentation, ultrasonic wave propagation, fracture toughness test and 3/4 point bending test.
- Viscometry is also used to measure the viscosity of materials. A wide range of techniques and instruments for spectroscopy is used to characterize optical properties.
Fracture Mechanics (continued)
- Kc and Kic (plane strain fracture toughness) values are given for different materials such as concrete, soda-lime glass, aluminum oxide, and various polymers.
Fracture toughness
- Factors affecting fracture toughness (Kc): Temperature and strain rate.
- Measurement techniques: Indentation and bending tests.
Fractography, Intergranular and Transgranular Fracture
- Fractography is used to determine the failure mechanism and origin of fracture.
- Intergranular fracture propagates along grain boundaries.
- Transgranular fracture propagates across grains, often along cleavage planes.
Conchoidal Fracture
- Conchoidal fracture exhibits no distinct cleavage planes and occurs in materials like flint, cubic zirconia, diamond, and glass.
Toughening Mechanisms
- Approaches to increase ceramic toughness include fiber reinforcement, whisker reinforcement, ductile network strengthening, transformation toughening, and microcracking.
Toughening Mechanisms (continued)
- Key parameters for toughening include crack deflection, crack bowing, crack branching, crack tip shielding by process zone activity and crack bridging
Properties of Refractory Materials
- Refractories withstand high temperatures and high loads (high creep resistance), maintain high volume stability, withstand sudden temperature changes (high thermal shock resistance).
- They also have resistance to corrosion by molten metals, slag, and gases, are resistant to wear and abrasion, can conserve heat (conservation of heat), and possess low thermal conductivity (for insulation).
Properties of Refractory Materials (continued)
- There are dense and less dense refractories and they have different thermal conductivity values (in W/m.K) at different temperatures (C).
Classification of Refractories
- Refractories can be classified according to their basicity (acidic, basic, and amphoteric), form (shaped, monolithic or castable), manufacturing process, method of application, special chemical properties, and insulating properties
Classification of Refractories (continued)
- Acidic refractories react readily with bases at high temperatures (e.g., silica).
- Basic refractories react readily with acids at high temperatures (e.g., magnesite, dolomite).
- Neutral refractories (e.g., mullite) are tolerant to both acidic and basic atmospheres.
Manufacturing and Properties of Refractories
- Manufacturing steps include crushing, grinding, screening, batch weighting, mixing, shaping, drying, and firing (at high temperatures)
- Properties include refractoriness, strength, dimensional stability, and porosity.
Physical Properties of Refractories
- Refractoriness is a material's ability to withstand heat without significant deformation or softening. Usually measured by the softening or melting temperature of the material.
- Pyrometric Cone Test(Seger cone test), is used to determine the softening temperature of refractory materials using the standard cones with specific compositions.
- PCE is a numerical scale used for the determined softening temperature.
Physical Properties of Refractories (continued)
- Dimensional stability is the material’s resistance to volume changes at high temperatures and prolonged exposure to heat.
- Porosity is calculated as P= (W-D)/(W-A)x100 where W= weight of saturated specimen, D= weight of dry specimen and A = weight of submerged in water specimen. Porosity occurs either due to the nature/composition and methods during manufacture.
- Thermal Spalling refers to cracking, breaking, peeling-off behaviors of refractory materials under high temperatures, which mainly occurs due to uneven physical stresses in the material.
- Thermal expansion is the change in dimension of a refractory material caused by temperature change. Lower thermal expansion coefficient is a desirable property for refractory materials in furnace use to minimize cracking.
- Thermal conductivity refers to the ability of the refractory to conduct heat transfer. Higher thermal conductivity is desirable in certain furnace applications as it results in faster heat dissipation.
Powder Processing
- Purity, particle size distribution, reactivity, polymorphic form, availability, and cost of raw materials affect the properties of a ceramic component.
- Traditional raw materials include clay minerals and quartz sand, used in making ceramics like tiles, sanitary ware, whitewares, bricks, and refractories.
- Advanced raw materials are synthesized, mostly from high purity powders using special methods, for high demanding applications such as space shuttle tiles, engine parts, artificial implants and cutting tools.
Powder Processing (continued)
- Powder morphology (shape and size of the particles) is very important for making dense and uniform ceramic bodies.
- Important powder types include primary, agglomerates, and granules; each having significant influence on powder properties . (i.e. density, flow characteristics and processing.)
Powder Preparation and Sizing
- Control of the particle size and distribution is required to develop optimum properties of the ceramic components.
- Different methods for controlling particle sizing include mechanical methods (screening, air classification, ball milling, attrition milling, and vibratory milling, fluid energy milling and roll crushing) as well as chemical methods (precipitation, freeze drying, sol-gel, spray roasting, decomposition, and hydrothermal process, and Plasma).
Shape Forming Processes
- Methods to give final shape to ceramic component include dry methods (die pressing, isostatic pressing) and wet methods (slip casting, tape casting, freeze casting, and gel casting).
- Plastic forming includes extrusion and injection molding.
Additives for preconsolidation
- Various additives including binders, lubricants, compaction aids, deflocculants, and others are used in the preconsolidation of ceramic components.
Wet Forming
- Wet forming is a method for producing ceramic green articles with uniform microstructure, low flaws, and complex shapes. It involves using slurry or similar compounds to achieve these characteristics.
Wet Forming (continued)
- Techniques in wet forming include slip casting, tape casting, freeze casting, and gel casting.
Introduction of specific ceramic materials
- Various ceramic materials are introduced, such as alumina (Al2O3), silica (SiO2), silicon carbide (SiC), and silicon nitride (Si3N4).
Specific Ceramic Materials (continued)- Properties, processing techniques, and applications.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge on the mechanical properties of ceramics, focusing on elastic and plastic deformation. This quiz covers key concepts such as Young's modulus, temperature effects, and bonding types in ceramics. Ideal for students studying material science or ceramics engineering.
