Peukert’s Law

Hydrogen embrittlement (HE) is a process where metals, most notably high-strength steels, become brittle and fracture following exposure to hydrogen. Atomic hydrogen diffuses into the metal lattice and reduces its ductility and load-bearing capacity. Key proposed mechanisms include Hydrogen-Enhanced Decohesion (HEDE), which weakens atomic bonds, and Hydrogen-Enhanced Localized Plasticity (HELP), which facilitates dislocation motion and localized failure.

The chloralkali process is an industrial method for the electrolysis of sodium chloride (NaCl) solution, known as brine. It is the primary source for producing chlorine (Cl₂), sodium hydroxide (NaOH), and hydrogen (H₂), which are essential commodity chemicals. Modern methods use a membrane cell to separate the anode and cathode products, ensuring high purity and efficiency.

The fire triangle is a simple model illustrating the three essential elements required for most fires: heat, fuel, and an oxidizing agent, typically atmospheric oxygen. Removing any one of these elements prevents a fire from starting or causes an existing fire to be extinguished. It is a fundamental concept in fire safety and prevention.

The properties of an oxy-acetylene flame are controlled by the volumetric ratio of oxygen to acetylene. A neutral flame (ratio ≈ 1.1:1) is standard for steel welding. A carburizing or reducing flame (ratio 1.1:1) has excess oxygen, is hotter, and is used for braze-welding.

Concentrated solar power systems use mirrors or lenses to concentrate a large area of sunlight onto a receiver. The concentrated light heats a fluid, which then drives a heat engine (usually a steam turbine) connected to an electrical power generator. This method contrasts with photovoltaics, which convert light directly into electricity. CSP allows for thermal energy storage.

The principal stresses, \(\sigma_1\) and \(\sigma_2\), are the maximum and minimum normal stresses at a point, occurring on planes with zero shear stress. On Mohr's circle, these correspond to the two points where the circle intersects the horizontal (\(\sigma_n\)) axis. The maximum in-plane shear stress, \(\tau_{max}\), is equal to the radius of the circle, \(R\).

The Hall-Héroult process is the major industrial method for smelting aluminum. It involves dissolving alumina (aluminum oxide, Al₂O₃) in molten cryolite (Na₃AlF₆) and electrolyzing the molten salt bath. Aluminum metal is deposited at the cathode, while oxygen from the alumina reacts with the carbon anode, producing carbon dioxide. This process made aluminum widely available and affordable.

Exothermic welding, also known as thermite welding, is a technique that uses the superheated molten metal from an aluminothermic reaction to create a strong, permanent molecular bond between metal components. The process is self-contained, requiring no external power source. It is most famously used to join sections of railway track into continuous welded rail, creating a smoother and more durable track.

Oxy-acetylene welding uses a flame produced by the combustion of acetylene (\(C_2H_2\)) with pure oxygen. The reaction occurs in two stages. The primary reaction in the inner, white-hot cone is incomplete, producing carbon monoxide and hydrogen: \(2C_2H_2 + 2O_2 \rightarrow 4CO + 2H_2\). These hot gases then react with atmospheric oxygen in the outer envelope, completing the combustion.

Oxy-fuel cutting, or flame cutting, severs ferrous metals by a rapid, exothermic oxidation process. First, a preheating flame raises the steel's surface to its kindling temperature (approx. 870 °C or 1600 °F). A high-pressure jet of pure oxygen is then directed at the spot, initiating a chemical reaction, \(3Fe + 2O_2 \rightarrow Fe_3O_4\), which forms molten iron oxide (slag) and releases heat.