Materials

Overview of Materials in Chemistry

In chemistry, “materials” are substances that have been deliberately designed, selected, or processed for specific technical, everyday, or biological uses. In this part of the course, “materials” mainly refers to solids whose properties can be tailored: metals, ceramics, glasses, and especially polymers and plastics.

This chapter provides the framework for the more specialized subsections that follow. It connects basic chemical principles (structure, bonding, thermodynamics, kinetics) with the observable properties and technical use of materials.

Classes of Materials

For a first orientation, it is useful to distinguish several broad classes of materials. Each later subsection will focus on one or more of these in more detail.

Metals and Metallic Materials

Metallic materials consist of metal atoms held together primarily by metallic bonding. Typical characteristics:

• Good electrical and thermal conductivity
• Metallic luster
• Usually high mechanical strength and good deformability (malleability, ductility)
• Often crystalline with a regular arrangement of atoms (lattice)

In this course, “metallic materials” include pure metals and alloys (mixtures of metals, sometimes with small amounts of non‑metals) tailored for specific purposes like construction, electronics, or corrosion resistance.

Ceramics and Glasses

Ceramic materials are mostly inorganic, non‑metallic solids made from metal oxides, carbides, nitrides, or similar compounds. They are typically:

• Hard and wear‑resistant
• Chemically and thermally stable
• Brittle (they break rather than deform plastically)

Glasses (e.g. silicate glasses) are amorphous (non‑crystalline) inorganic solids. Despite their typical transparency, they share many ceramic‑like features: hardness, chemical resistance, brittleness, and thermal stability.

Silicates and glasses will be covered later with a focus on composition, structure, and resulting properties.

Polymers and Plastics

Polymers are large molecules built from many repeating units (monomers). Plastics are materials whose main component is one or more polymers, often with added substances (additives) to adjust processing and properties.

Typical polymer/plastic properties:

• Low density (lightweight)
• Usually poor conductors of heat and electricity (insulators)
• Properties that strongly depend on molecular structure and processing (flexible vs. rigid, transparent vs. opaque, etc.)

Subsequent sections on synthetic organic polymers, plastics, and tailor‑made polymers will show how chemical structure and processing routes allow very precise “design” of material properties.

Composite Materials

Many modern materials are composites: combinations of two or more distinct materials (e.g. fibers embedded in a polymer matrix) designed so that the overall material inherits the best properties of each component.

Examples:

• Fiber‑reinforced plastics (glass fibers or carbon fibers in a polymer)
• Metal matrix composites (ceramic particles in a metal)
• Concrete (stone aggregate in a cement matrix)

Although this course does not have a dedicated composite chapter, the ideas behind composites often appear in discussions of plastics, metallic materials, and silicates.

From Chemical Structure to Material Properties

What makes “materials chemistry” distinct is its focus on how microscopic chemical structure and bonding lead to macroscopic properties relevant for applications.

Some key structural levels:

• Atomic and molecular level
  Element type, bonding type (ionic, covalent, metallic), and functional groups determine basic strength, thermal behavior, and chemical stability.
• Supramolecular and microstructural level
  Crystal structures, grain boundaries, amorphous vs. crystalline regions, polymer chain orientation and entanglement, pores, and defects strongly influence mechanical, optical, electrical, and diffusion properties.
• Macroscopic level
  Overall shape, layering, and processing history (e.g. extrusion, rolling, annealing) influence toughness, strength, formability, and surface properties.

Later subsections on structure and formation of synthetic polymers, metallic materials, and silicates/glasses will illustrate typical structure–property relationships for those material classes.

Materials Lifecycle: From Raw Material to Recycling

Materials do not only differ in their properties but also in how they are made, used, and disposed of. For a complete picture, it is useful to consider the entire lifecycle.

Raw Materials and Synthesis

• Origin:
• Metals from ores
• Polymers from petrochemical or bio‑based monomers
• Silicates and glasses from minerals like quartz, limestone, and feldspar
• Processing and synthesis:
  Chemical reactions and physical steps (melting, casting, polymerization, forming) transform raw substances into usable materials.

Later sections like “Structure and Formation of Synthetic Organic Polymers” and “Metallic Materials” will detail typical synthesis and processing pathways.

Processing and Shaping

Technically useful materials are rarely used in their crude form. They must be shaped and processed:

• Casting, rolling, forging (metals)
• Extrusion, injection molding, thermoforming (plastics)
• Sintering (ceramics), melting and molding (glass)

How a material is processed can drastically alter its internal structure and thus its properties. The specific chapter “Processing of Plastics” will highlight this interplay for polymeric materials.

Use Phase and Service Conditions

In use, materials are exposed to mechanical loads, temperature changes, chemicals, light, and sometimes radiation. These conditions can lead to:

• Deformation (elastic or plastic)
• Fatigue and fracture
• Corrosion (metals), degradation (polymers), or weathering (glasses, ceramics)

Careful materials selection matches the material to the expected service conditions.

End of Life and Recycling

Because materials and energy resources are limited, what happens at the end of a product’s life is essential:

• Re‑use (same product, possibly after refurbishment)
• Recycling (material recovery, sometimes with down‑cycling)
• Energy recovery (e.g. combustion of certain plastics)
• Disposal (landfill, incineration without energy use)

The section “Plastic Recycling” will treat these issues comprehensively for polymers; many of the same principles (separation, purity, thermodynamic limits) also apply to metals and glass.

Criteria for Selecting Materials

When choosing a material for a specific application, multiple criteria must be balanced. From a chemist’s perspective, important groups of criteria include:

• Mechanical properties:
  Strength, stiffness, hardness, toughness, fatigue resistance.
• Thermal properties:
  Melting or softening temperature, thermal expansion, thermal conductivity, fire behavior.
• Chemical properties:
  Corrosion resistance, solvent resistance, stability against oxidation, hydrolysis, or UV light.
• Electrical and optical properties:
  Conductivity or insulation, transparency or opacity, refractive index, color.
• Processing behavior:
  Process temperatures, viscosity (for polymers), weldability or bondability, compatibility with additives.
• Economic and ecological aspects:
  Cost, availability of raw materials, energy demand in production, recyclability, environmental and health impact.

Many of these criteria are ultimately rooted in the material’s chemical structure and bonding, concepts that you will see applied repeatedly in the specialized subsections of this chapter.

The Role of Materials Chemistry

Materials chemistry brings together several themes from earlier parts of the course:

• Atomic structure and bonding:
  Explain why metals conduct electricity, why glass is brittle but transparent, and why polymers can be flexible or rigid.
• Thermodynamics and kinetics:
  Control which phases form in alloys, how polymers crystallize or remain amorphous, and how corrosion or degradation proceeds.
• Chemical reactivity and equilibrium:
  Determine stability and durability under environmental conditions.
• Organic and inorganic chemistry:
  Provide building blocks for organic polymers, inorganic glasses, ceramics, and hybrid materials.

This chapter’s subsections will apply these principles to particular material families—polymers and plastics, metals, silicates and glasses—showing how chemists can design, produce, modify, and recycle materials for a wide range of applications.