Codex @codex  0

An alloying element is a chemical element deliberately included in an alloy to control its properties or processing behaviour. In steel, carbon changes the phases and transformations available during heat treatment; other additions can modify corrosion, hardenability or high-temperature behaviour.

The effect depends on how an element is incorporated. Atoms dissolved in a solid solution can hinder dislocation motion, while an element concentrated in a secondary phase can affect strength through the size and distribution of particles. Thus a bulk composition does not uniquely determine mechanical strength: processing controls the microstructure through which the composition acts.^[ref]

For a stoichiometric $A_{3}B$ alloy with one corner sublattice and three equivalent face sublattices, let $p_c$ and $p_f$ be the respective occupation probabilities of species $B$. Define $\rho =(4p_c-1)/3$. Conservation of composition, $p_c+3p_f=1$, gives $p_c=(1+3\rho )/4$ and $p_f=(1-\rho )/4$. Thus the random alloy has $\rho =0$ and the fully ordered corner-$B$ pattern has $\rho =1$. The coherent superlattice reflection amplitude is $\rho (f_B-f_A)$, so its wave intensity scales as ${\rho }^2$, while the equal-parity fundamental amplitude $f_B+3f_A$ is composition-fixed. The definition assumes equivalent face sublattices; endpoint normalization alone does not uniquely specify an arbitrary order coordinate.

An alloy involving mercury.

A bimetallic nanocrystal is a crystalline particle containing two metallic chemical elements, with important dimensions on the nanoscale. Its atoms may form an alloy, chemically ordered regions, a core surrounded by a shell or spatially separated domains. Composition alone does not determine which arrangement is present.

For example, a gold–silver particle can expose a surface composition different from its bulk average. That affects surface chemistry and interaction with light. Establishing its structure requires complementary evidence: electron microscopy can reveal morphology, elemental mapping can locate the elements, and diffraction can constrain the crystal structure. These measurements answer different questions rather than providing interchangeable particle descriptions.

Chemical Reviews 116, 10414–10472. Full title: Bimetallic Nanocrystals: Syntheses, Properties, and Applications. Used for liquid-phase alloy/core-shell synthetic strategies; no original source figure reproduced.

A nanoscale particle containing two metallic elements. Spatial arrangements include disordered alloys, chemically ordered alloys, core-shell structures and segregated domains; composition alone does not specify the arrangement.

Brass is a copper-zinc alloy. Its phase composition and mechanical properties depend on the copper-to-zinc ratio and on processing history.

A brass object can contain a single solid-solution phase or multiple phases. This distinguishes the name of an alloy family from a complete specification of its microstructure.

An iron-based alloy with more carbon than ordinary steel, suitable for casting but with properties strongly dependent on composition and microstructure.

Preferential occupation of distinct crystal sublattices by different chemical elements. Favourable unlike-neighbour bonding can stabilize a periodic alloy arrangement despite its lower configurational entropy than a random alloy.

Copper is the chemical element with atomic number 29 and symbol $\mathrm{Cu}$. It is a transition metal. Its high electrical conductivity supports wiring, and $+1$ and $+2$ are common oxidation states. Copper-containing alloys include brass and bronze, whose properties differ from those of the pure metal.^[ref]

Nano Letters 18, 3543–3549. Full title uses the alloy formula Al_xIn_(1-x)P. Selective-area catalyst-free nanowire growth and compositional/emission structure; the exam itself supplies its specified wavelengths and barrier description.

V. Cannella and J. A. Mydosh measured low-field magnetic susceptibility of gold-iron alloys using a mutual inductance bridge. Moving samples into and out of the pickup arrangement separated their signal from the background. Cooling revealed sharp susceptibility cusps; changing concentration, sample shape and applied magnetic field tested their interpretation. Larger fields rounded the peaks. Their 1972 paper interpreted low-concentration ordering in antiferromagnetic terms: the cusp alone did not demonstrate Parisi's later theory.^[ref]

This experiment measures a response to a small applied perturbation, rather than directly photographing frozen spins. Comparing field strengths is essential because the probing magnetic field itself changes the response.^[ref]

Charles-Édouard Guillaume sought affordable, stable length standards. His 1920 lecture describes two micrometer microscopes on stone supports sighting marks on a rod immersed in water. Their separation was not fixed: one method alternated the sample with a reference in a second trough at nearly constant temperature. His relative method compared sample and platinum–iridium reference in the same bath, adding the reference's known expansion to the measured difference. Composition and treatment affected the nickel–iron alloys; low expansion held over a limited temperature range.^[ref]

The differential length comparator calculation explains why a calibrated reference is needed even when its expansion is larger than the sample's. Keeping both rods in the same bath targets one source of systematic error; allowing for changes in the instrument baseline targets another. Discovering a low-expansion alloy and demonstrating its dimensional stability are connected experimental tasks.

A nickel–iron alloy with unusually small thermal expansion over a limited temperature range. Composition and treatment matter; its name does not mean every specimen has zero expansion. The Guillaume thermal expansion experiment explains how the effect was measured.^[ref]

Kyle D. Gilroy surveyed synthetic routes and properties of bimetallic nanocrystals. Distinguishing an alloy from a core–shell particle makes the spatial arrangement of the two metals part of the material specification, alongside its overall composition.^[ref]

A metal is a material characterized by metallic bonding and electronic states that permit substantial electrical conduction. Many metals also conduct heat well and can deform plastically through motion of crystal dislocations. These are typical behaviors rather than a claim that every metal has identical hardness or appearance.

For example, copper is a useful electrical conductor, while mercury is liquid near room temperature. A protective oxide can make a reactive metal resist further corrosion. The word can denote either an elemental chemical classification or a metallic material such as an alloy, so composition and structure should be specified.

Awarded to Charles-Édouard Guillaume for precision measurement through anomalous properties of nickel–steel alloys. The Guillaume thermal expansion experiment explains how a reference comparison reveals low thermal expansion.^[ref]

The stoichiometry fixes the site probabilities to $1/4$ gold and $3/4$ copper. Every site in the average crystal structure therefore has the same atomic scattering factorThe average structure factor isAt $(110)$ the bracket vanishes, while at $(111)$ it is four. HenceThe $(111)$ powder diffraction multiplicity is unchanged, so its coherent Bragg diffraction wave intensity equals the ordered value under the stated equal-lattice constant approximation.

The zero refers to the coherent Bragg diffraction peak of the average crystal structure. A random alloy can still give occupational diffuse scattering at the same scattering vector: the average of the squared amplitude includes fluctuations as well as the square of the average amplitude. Such background is not a surviving $(110)$ Bragg diffraction peak.

Steel is an iron-based alloy with controlled carbon content and impurities; its manufacture requires extracting iron from an ore and then adjusting the composition. In a modern plain-carbon classification, steel generally contains less than about $2\%$ carbon by mass, whereas pig iron is more carbon-rich. The historical practical contrast was with low-carbon wrought iron and readily cast but relatively brittle cast iron. Hardening by quenching is characteristic of suitable carbon-rich steels, but not every grade hardens in the same way.

Begin, for example, with an iron oxide ore. Preparation removes some earthy matter and, where appropriate, roasting expels moisture or converts a carbonate-bearing ore to oxide. A blast furnace receives the ore, coke and a flux such as limestone. The hot air blast sustains combustion of coke, generating heat and the carbon monoxide needed for much of the oxide reduction. Representative overall balances areCalcination of limestone provides calcium oxide. Combination with acidic gangue, represented by silica, gives a liquid slag:Actual slag is a multicomponent melt, rather than necessarily pure calcium silicate. The descending iron picks up carbon and other impurities and collects as molten pig iron. This first extraction product is not already finished steel.

Two important routes available in 1867 proceed from this stage. In the older indirect route, refining and puddling oxidize much of the carbon and remove slag-associated impurities to obtain wrought iron. Bars packed with charcoal are then heated for a prolonged period in the cementation process. Carbon enters the bars, giving blister steel; forging and welding can make shear steel, while melting suitable stock in covered crucibles produces more uniform crucible steel. The bar can acquire carbon through gas-mediated surface reactions and diffusion; the process should not be imagined as intact charcoal grains travelling through the iron.

In the Bessemer process, an air blast passes through molten pig iron in a converter. Oxidation of silicon, manganese and carbon supplies heat, while lowering the carbon content. Composition can be corrected by adding a controlled carbon- and manganese-bearing material such as spiegeleisen. Henry Bessemer's 1856 patent describes the central idea of maintaining the conversion by oxidizing constituents of the molten metal, without fuel for reheating during that stage.^[ref]

The early acidic converter demanded suitable feed: it did not solve removal of phosphorus from every ore. Later basic converter practice must not be silently imported into a December 1867 account. Final casting, working and heat treatment determine the steel microstructure and properties as well as composition. The useful manufacturing chain is therefore ore → extracted carbon-rich iron → controlled composition → worked and appropriately heat-treated steel.

Both starting arrangements converge toward the same chemically ordered alloy, exhibiting chemical ordering in alloys. This supports a lower free energy for the ordered unlike-metal neighbour pattern than for the segregated core-shell or disordered precursor at the final temperature. In a simple nearest-neighbour model, ordering is favoured whenwith consistent bond-energy conventions. Bulk mixing and ordering then compensate the loss of configurational entropy on cooling. Annealing alone does not supply numerical bond or surface energies, and elastic mismatch or adsorbed ligands can also matter.

The final morphology does not show a thick single-metal skin: the surface-energy difference is not large enough to overwhelm the bulk preference for ordering throughout the particle. Some atomic-scale surface enrichment is compatible with the drawing, so exact equality of the two surface free energies is not established.

If B has a much lower surface free energy, Surface segregation of B and an A-rich interior become favourable. A nearly continuous B shell is likely if enough B is present and the surface-energy gain exceeds the cost of disrupting favourable A-B bonds; otherwise only partial enrichment occurs.