Metals, Alloys & Corrosion High-Yield Review

Vocabulary flashcards covering crystal structures, alloy types, titanium properties, and electrochemical corrosion principles for dental materials.

FCC (Face-Centered Cubic)

A crystal structure with a coordination number (CN) of $12$ and an atomic packing factor (APF) of $0.74$; examples include $Ag$, $Al$, $Au$, $Cu$, and $Pt$.

BCC (Body-Centered Cubic)

A crystal structure with a coordination number (CN) of $8$ and an atomic packing factor (APF) of $0.68$; examples include $Cr$, $Fe$, and $Mo$.

HCP (Hexagonal Close-Packed)

A crystal structure with a coordination number (CN) of $12$ and an atomic packing factor (APF) of $0.74$; examples include $Zn$ and $\alpha\text{-Ti}$.

Substitutional Alloy

An alloy where minor atoms replace bulk atoms because they possess similar atom size and bonding characteristics, such as brass ($Cu$/$Zn$).

Interstitial Alloy

An alloy where small atoms fit into the gaps of the bulk lattice, such as steel ($C$ in $Fe$).

Heterogeneous Alloy

An alloy that is not uniformly dispersed and consists of multiple phases, such as pearlite (ferrite + cementite).

Intermetallic Alloy

An alloy with a fixed or discrete composition, such as $Fe_3C$ or $Ag_3Sn$ in amalgam.

High Noble (HN) Alloy Threshold

An alloy where the composition is $\ge 40\%$ $Au$ and $\ge 60\%$ total noble metal.

Noble (N) Alloy Threshold

An alloy containing $> 25\%$ noble metal (typically $Pd$).

Predominantly Base (PB) Alloy Threshold

An alloy with $< 25\%$ noble metal and $> 75\%$ base metal (e.g., $Ni\text{-}Cr$ crowns).

Stainless Steel Composition

A corrosion-resistant alloy containing $0.1\%$ $C$, $18\%$ $Cr$, and $8\%$ $Ni$.

Titanium Density

Approximately $4.51\,\text{g/cm}^3$, providing the strength of steel ($\sim 7.60\,\text{g/cm}^3$) at a fraction of the weight.

Allotropic change of Titanium

The structural transition from $\alpha\text{-Ti}$ (HCP at room temp) to $\beta\text{-Ti}$ (BCC) occurring above $882^\circ\text{C}$.

Ti-6Al-4V

A titanium alloy where $Al$ increases strength, decreases density, and promotes the $\alpha$ phase, while $V$ promotes the $\beta$ phase; tensile strength is $\sim 950\,\text{MPa}$.

$TiO_2$ surface layer

A surface layer providing corrosion resistance and biocompatibility, which enables osseointegration.

Spontaneous Electrochemical Reaction

A reaction where $E_{cell}$ is positive and $\Delta G$ is negative, based on the equation $\Delta G = -nFE_{cell}$.

LOSSOX

A mnemonic indicating that Oxidation is the LOSS of $e^-$, which occurs at the anode.

Anode (Iron Rusting)

The oxidation site where metal is lost (pitting): $Fe(s) \rightarrow Fe^{2+}(aq) + 2e^-$.

Cathode (Iron Rusting)

The reduction site where no metal loss occurs: $O_2(g) + 4H^+ + 4e^- \rightarrow 2H_2O(l)$.

Galvanic Corrosion

Corrosion occurring between dissimilar metals where the more active or less noble metal acts as the anode.

Concentration Cell Corrosion

Corrosion where the LOW-oxygen region (e.g., under plaque) acts as the anode.

Crevice Corrosion

Corrosion where the anode is located inside the low-$O_2$ crevice (e.g., at the implant/bone interface).

Stress Corrosion

Corrosion where the anode is the deformed or stressed region where the oxide layer has been disrupted.