Environmental Chemistry, Chemical Safety, and Semiconductor Materials

Comprehensive practice flashcards covering atmospheric pollution control, water chemistry and wastewater treatment, soil chemistry and remediation technologies, industrial chemical safety and SDS standards, and semiconductor physics and fabrication chemistry.

Primary Pollutants

Substances directly released into the atmosphere from an identifiable source, such as carbon monoxide ($\text{CO}$) and sulfur dioxide ($\text{SO}_2$).

Secondary Pollutants

Pollutants that are not emitted directly but form within the atmosphere through chemical or physical reactions involving primary pollutants, such as ground-level ozone ($\text{O}_3$) and photochemical smog particles.

Photochemical Smog

A form of atmospheric pollution generated when sunlight catalyzes photochemical reactions between nitrogen oxides ($\text{NO}_x$) and volatile organic compounds ($\text{VOCs}$), producing ozone and secondary oxidants.

Cyclone Separator

A particulate control device that uses centrifugal force to throw heavier suspended dust particles to the outer chamber walls, causing them to settle downward by gravity into a collection hopper.

Fabric Filter (Baghouse System)

An industrial particulate removal device that passes dust-laden gas through woven or felted fabric filter bags, achieving removal efficiencies up to $99.9\%$ even for fine particulate matter.

Electrostatic Precipitator (ESP)

An air pollution control device that imparts an electrostatic charge to suspended particles in a gas stream and collects them onto oppositely charged collection plates.

Flue-Gas Desulfurization (FGD)

A chemical scrubbing process used in power and smelting plants that absorbs sulfur dioxide ($\text{SO}_2$) using alkaline limestone ($\text{CaCO}_3$) slurry to yield calcium sulfate ($\text{CaSO}_4$, or gypsum) byproduct.

Selective Catalytic Reduction (SCR)

An exhaust treatment system that injects ammonia ($\text{NH}_3$) over a catalyst to convert nitrogen oxides ($\text{NO}_x$) into nitrogen gas ($\text{N}_2$) and water ($\text{H}_2\text{O}$) with up to $90\%$ reduction efficiency.

Diesel Particulate Filter (DPF)

An automotive exhaust aftertreatment unit comprising a porous ceramic honeycomb filter that traps soot and fine particles ($\text{PM}_{2.5}$) and oxidizes them into gaseous products.

Exhaust Gas Recirculation (EGR)

An internal combustion engine technology that routes a metered portion of inert exhaust gas back into the engine intake to lower peak combustion temperatures and reduce the rate of $\text{NO}_x$ formation.

Biochemical Oxygen Demand (BOD)

A standard water quality indicator representing the quantity of dissolved oxygen consumed by aerobic microorganisms while decomposing organic contaminants present in a water sample.

Coagulation and Flocculation

Water purification stages where chemical coagulants neutralize surface electrostatic charges on suspended colloids, followed by gentle mixing that aggregates destabilized particles into larger flocs for sedimentation.

Ion Exchange Softening

A water softening method that percolates hard water through a synthetic resin bed to replace dissolved calcium ($\text{Ca}^{2+}$) and magnesium ($\text{Mg}^{2+}$) ions with sodium ($\text{Na}^+$) or potassium ($\text{K}^+$) ions.

Reverse Osmosis (RO)

A pressure-driven membrane desalination technology that forces saline water across semi-permeable membranes under hydrostatic pressures exceeding osmotic pressure, rejecting dissolved ions and polar solutes.

Multi-Stage Flash Distillation

A thermal desalination process in which heated feed brine enters a sequence of lower-pressure vacuum chambers, causing rapid spontaneous vaporization and subsequent condensation into pure distillate.

Advanced Oxidation Processes (AOPs)

Water treatment technologies that generate highly reactive oxidizing radicals (such as hydroxyl radicals) using combinations of ultraviolet light, ozone ($\text{O}_3$), hydrogen peroxide ($\text{H}_2\text{O}_2$), or catalysts to destroy recalcitrant organic contaminants.

Constructed Wetland Filtration

An engineered, passive wastewater biofiltration system that utilizes aquatic substrates and native vegetation to absorb nutrients ($\text{nitrates}$, $\text{phosphates}$), degrade trace organics, and reduce biochemical pollution loads.

Cation Exchange Capacity (CEC)

The total capacity of a soil to hold and reversibly exchange positively charged mineral cations (such as $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, and $\text{K}^+$) through electrostatic binding on clay and organic colloid surfaces.

Soil Colloids

Extremely small, high-surface-area charged mineral (clay) and organic (humus) particles in the soil matrix that govern ion exchange, nutrient availability, and contaminant adsorption.

Mollisols

A fertile grassland soil order characterized by a deep, dark, organic-matter-rich surface horizon (mollic epipedon), representing some of the most agriculturally productive soils on Earth.

Laterite Soil

An intensely weathered, iron- and aluminum-oxide-rich tropical soil formed under heavy rainfall that exhibits low natural fertility due to severe leaching and hardens upon exposure to air.

Soil Washing

An ex-situ soil remediation technique in which excavated contaminated soil is scrubbed with water or chemical wash solvents to physically separate and concentrate heavy metals and hydrocarbons.

Stabilization and Solidification

A soil treatment technique that introduces inorganic binding reagents (such as cement, lime, or pozzolans) to immobilize hazardous heavy metals and chemically fix contaminants, preventing leaching.

Phytoremediation

An eco-engineering bioremediation approach that employs living plant root networks and biomass (such as vetiver grass and sunflowers) to extract, sequester, or immobilize heavy metals and chemical toxins from soil.

Mycoremediation

A biological remediation process utilizing fungal mycelium and extracellular fungal enzymes to degrade persistent organic pollutants, petroleum hydrocarbons, and pesticides in contaminated soils.

Hierarchy of Hazard Control

A structured safety framework prioritizing industrial risk mitigation in five sequential stages: Elimination, Substitution, Engineering Controls, Administrative Controls, and Personal Protective Equipment (PPE).

Safety Data Sheet (SDS)

A standardized 16-section technical document established under the Globally Harmonized System (GHS) that details chemical identity, potential hazards, handling instructions, exposure limits, and emergency response protocols.

Local Exhaust Ventilation (LEV)

An engineering control system designed to capture toxic gases, airborne dusts, and hazardous chemical vapors directly at their point of generation before they enter the workplace breathing environment.

Inert Gas Blanketing

An explosion prevention practice that purges the vapor headspace of flammable liquid storage vessels with an unreactive gas (such as nitrogen) to displace oxygen below combustible thresholds.

GHS Section 2 (Hazard Identification)

The mandatory section of an SDS that specifies chemical hazard classifications, required GHS warning pictograms, signal words ("Danger" or "Warning"), and physical or health risk statements.

Band Gap ($E_g$)

The energetic separation between the top of the electron-filled valence band and the bottom of the empty conduction band in an insulator or semiconductor.

Direct Band Gap Semiconductor

A semiconductor material (such as $\text{GaAs}$ or $\text{CdTe}$) wherein the valence band maximum and conduction band minimum coincide at the same crystal momentum value ($\mathbf{k}$), enabling efficient radiative recombination without phonon participation.

N-Type Doping

The intentional substitution of Group 15 donor atoms (such as $\text{P}$, $\text{As}$, or $\text{Sb}$) into a Group 14 semiconductor crystal, providing loosely bound fifth valence electrons as majority charge carriers.

P-Type Doping

The intentional incorporation of Group 13 acceptor atoms (such as $\text{B}$, $\text{Ga}$, or $\text{In}$) with three valence electrons into a semiconductor lattice, generating positive electron vacancies (holes) as majority carriers.

Czochralski (CZ) Process

A metallurgical crystal growth method in which an oriented seed crystal is dipped into molten semiconductor-grade silicon and slowly drawn upward while rotating to produce large single-crystal cylindrical ingots.

Atomic Layer Deposition (ALD)

A specialized vapor-phase thin film deposition technique utilizing sequential, self-limiting gas-surface chemical reactions to grow dielectric or metallic layers with sub-angstrom thickness control.

Chemical-Mechanical Planarization (CMP)

A wafer polishing process combining chemical surface dissolution using oxidizing slurries and mechanical abrasion using silica or alumina nanoparticles to achieve global planarization of wafer topography.

Electromigration

The mass transport of metallic atoms within an interconnect conductor driven by the momentum transfer from high-density electric currents, creating voids and hillocks that lead to circuit failure.

High-k Dielectrics

Metal oxide materials possessing a high dielectric constant (such as $\text{HfO}_2$ or $\text{ZrO}_2$) deployed in sub-micron transistor gate stacks to suppress direct quantum tunneling leakage currents.