Material Properties Comparison

Cheatsheet Content

Mica vs. Porcelain: Material Properties Property Mica Porcelain Composition Complex aluminosilicate mineral. Layered structure with weak interlayer bonds. Ceramic material, typically Kaolin mixed with feldspar and quartz. Fired at high temperatures. Structure Sheet silicate mineral, monoclinic crystal system. Layers held by strong bonds within planes, weak forces between layers. Allows for easy cleavage into thin sheets. Microcrystalline structure with a glassy (vitreous) matrix. Densely packed, non-porous after firing. Fine-grained. Form Naturally occurring in thin, flexible, transparent sheets (lamellae). Can be ground into powder or reconstituted into mica paper/boards. Molded into various shapes (insulators, tiles, dinnerware). Glazed or unglazed. Typically rigid, brittle, and opaque. Electrical Use Excellent electrical insulator. High dielectric strength ($>200 \, \text{kV/mm}$). Low dielectric loss. Stable across wide temperature range. Used in capacitors, high-voltage insulation, heating elements. Excellent electrical insulator. High dielectric strength ($15-30 \, \text{kV/mm}$). Good arc resistance. Used for high-voltage insulators (e.g., power lines), spark plugs, fuse bodies. Lower dielectric loss than many plastics. Thermal Stability Very high thermal resistance, up to $500-900^\circ C$ depending on type. Excellent dimensional stability at high temperatures. Low thermal conductivity parallel to layers, higher perpendicular. Good thermal shock resistance. High thermal resistance, typically up to $1000-1200^\circ C$. Good dimensional stability at high temperatures. Relatively low thermal conductivity. Can be susceptible to thermal shock if rapidly heated/cooled. Glass: Material Properties Property Description Composition Amorphous solid, primarily silica, often with additives like soda, lime, magnesia, alumina to modify properties (e.g., soda-lime glass). Structure Amorphous (non-crystalline) atomic structure. Atoms are randomly arranged, lacking long-range order. This leads to its transparent nature and isotropic properties. Form Can be cast, blown, drawn, or molded into various shapes (sheets, fibers, containers, lenses). Typically rigid and brittle. Electrical Use Excellent electrical insulator. High dielectric strength (e.g., $9-18 \, \text{kV/mm}$ for soda-lime). Low electrical conductivity. Used for electrical insulation, bulb envelopes, capacitor dielectrics (specialized glass). Thermal Stability Generally good thermal resistance, but varies greatly with type. Softens over a range, not a sharp melting point. Thermal shock resistance is typically poor (e.g., soda-lime glass cracks easily). Specialized glasses (e.g., borosilicate) have much better thermal shock resistance and higher operating temperatures ($>500^\circ C$). Asbestos: Material Properties Note: Asbestos is a hazardous material due to health risks (carcinogenic fibers) and its use is highly regulated or banned in many countries. Property Description Composition Naturally occurring fibrous silicate minerals. Main types: Chrysotile (serpentine group, magnesium silicate) and Amphibole (complex iron/magnesium silicates). Structure Crystalline structure forming long, thin, separable fibers. Chrysotile fibers are curly; amphibole fibers are straight and needle-like. This fibrous nature gives it unique properties. Form Occurs as fibrous bundles. Can be woven into fabrics, mixed with binders (e.g., cement) to form sheets, pipes, tiles, or used as loose insulation. Electrical Use Excellent electrical insulator. High dielectric strength. Used historically in electrical insulation products, arc chutes, wire coatings, and electrical panel components due to its combined electrical and thermal properties. Thermal Stability Outstanding thermal resistance – non-combustible and withstands very high temperatures (up to $900-1500^\circ C$ depending on type). Excellent thermal insulation properties. Good dimensional stability at high temperatures. Dielectric Loss and Dipolar Relaxation in Common Insulators Dielectric loss refers to the energy dissipated in an insulating material when subjected to an alternating electric field. It's often quantified by the loss tangent ($\tan \delta$). Dipolar relaxation is a key mechanism contributing to dielectric loss, especially in polar materials, where molecular dipoles reorient themselves in response to the changing electric field. Key Concepts Dielectric Loss ($\tan \delta$): Ratio of dissipative to reactive power in a dielectric. Lower values indicate better insulation. $$ \tan \delta = \frac{\text{Lossy Current}}{\text{Charging Current}} = \frac{I_R}{I_C} = \frac{G}{\omega C} = \frac{\epsilon''}{\epsilon'} $$ Where $G$ is the equivalent parallel conductance, $\omega$ is the angular frequency, $C$ is the capacitance, $\epsilon''$ is the imaginary part of the complex permittivity (loss factor), and $\epsilon'$ is the real part of the complex permittivity (dielectric constant). Dipolar Relaxation: The time-dependent reorientation of permanent or induced molecular dipoles in an electric field. This process absorbs energy, contributing to dielectric loss, particularly at certain frequencies and temperatures. Polar vs. Non-polar Materials: Polar materials have permanent molecular dipoles and thus exhibit more significant dipolar relaxation. Non-polar materials have induced dipoles, leading to lower loss. Properties of Common Insulators Material Dielectric Loss ($\tan \delta$) Dipolar Relaxation Characteristics Notes/Applications Mica Very Low ($0.0001 - 0.0006$ at $1 \, \text{kHz}$) Minimal dipolar relaxation. Its highly ordered, inorganic, and non-polar structure means very few permanent dipoles. Loss is mainly due to ionic conductivity at high temperatures. Excellent high-frequency and high-temperature insulator. Used in capacitors, high-voltage equipment, and RF applications. Glass (Soda-lime) Moderate to High ($0.008 - 0.02$ at $1 \, \text{kHz}$) Contains mobile ions ($Na^+$) and some non-bridging oxygen, leading to ionic conduction and some induced polarization. Dipolar relaxation from network defects or impurities. Specialized glasses (e.g., fused silica) have much lower loss. General purpose insulation, bulb envelopes. High loss limits high-frequency application for common types. Porcelain Low ($0.004 - 0.008$ at $1 \, \text{kHz}$) Primarily inorganic and non-polar. Loss primarily due to ionic impurities and conduction. Dipolar relaxation is minor, mostly from structural defects or bound water. High-voltage insulators (power lines), spark plugs. Good mechanical strength and weather resistance. Asbestos Low ($0.005 - 0.01$ at $1 \, \text{kHz}$) Primarily inorganic silicate fibers. Low inherent dipolar relaxation. Loss mainly due to ionic conductivity from impurities. Historically used in high-temperature electrical insulation. (Hazardous material, use is restricted/banned). Paper (Cellulose) Moderate ($0.002 - 0.005$ for dry; higher with moisture) Cellulose contains hydroxyl groups (OH), making it polar. Significant dipolar relaxation occurs, heavily influenced by moisture content. Water molecules are strongly polar and increase loss. Cable insulation, transformer insulation (oil-impregnated). Drying and impregnation are crucial to reduce loss. Rubber (Natural) Moderate ($0.005 - 0.02$ at $1 \, \text{kHz}$) Some polarity due to residual polar groups or additives. Dipolar relaxation present, contributing to loss. Synthetic rubbers vary widely. Flexible insulation, seals, protective coverings. Dielectric properties can degrade with aging and environmental exposure. Cotton Moderate to High ($0.005 - 0.04$ for dry; very high with moisture) Similar to paper, cotton is cellulose-based and highly polar due to hydroxyl groups. Very susceptible to moisture absorption, leading to high dielectric loss via dipolar relaxation of water. Textile insulation, historic wire insulation. Must be kept dry. Silk Moderate ($0.004 - 0.02$ for dry; higher with moisture) Protein-based, containing polar peptide bonds and side chains. Exhibits dipolar relaxation, and like other natural fibers, its dielectric loss is sensitive to moisture. Historic fine wire insulation, specialized textiles. Fibre (e.g., fiberglass) Low to Moderate ($0.001 - 0.005$ for dry glass fiber) Inorganic glass fibers (like E-glass) are relatively non-polar. Loss mostly from ionic conduction and surface contamination. When embedded in resins, the resin's properties dominate. Reinforcement in composites (e.g., PCBs), insulation for high-temperature wiring. Wood Moderate to High ($0.01 - 0.05$ for dry; extremely high with moisture) Complex organic material (cellulose, hemicellulose, lignin) with many polar groups. Highly hygroscopic. Dielectric loss is dominated by moisture content and associated dipolar relaxation of water. Historic electrical poles, some structural insulation. Not suitable for high-performance electrical insulation unless heavily treated and dried. Plastics Varies widely: Non-polar: Very Low ($0.0001 - 0.0005$) Polar: Moderate to High ($0.01 - 0.05$) Non-polar: Very little dipolar relaxation, low loss across wide frequencies. Polar: Significant dipolar relaxation due to permanent dipoles (e.g., C-Cl bond). Loss is frequency and temperature dependent. Wide range of applications: wire insulation, cable sheathing, electronic components. Choice depends on required electrical performance. Bakelite (Phenolic Resin) Moderate ($0.01 - 0.05$ at $1 \, \text{kHz}$) Highly cross-linked polymer with polar hydroxyl groups. Exhibits significant dipolar relaxation, especially at higher temperatures due to molecular segment mobility. Early plastic for electrical components, circuit boards, switches. Good heat resistance for a plastic.