Summary

Eng (ISSN 2673-4117) is an international, peer-reviewed open access journal which publishes original papers, critical reviews, rapid communications, technical notes, and discussions on all areas of engineering. Eng's aim is to encourage scientists to publish their experimental and theoretical research relating to engineering science and technology in as much detail as possible. There is no restriction on the maximum length of the papers. Launched in 2020, Eng was indexed in Scopus in 2023. The journal was subsequently included in the Emerging Sources Citation Index (ESCI, Web of Science) in March 2024 and Ei Compendex in April 2025. It holds a 2025 Impact Factor of 3.5 and is ranked JCR Q1 in the “ENGINEERING, MULTIDISCIPLINARY” category. Its 2025 CiteScore is 4.1, and it currently ranks Q2 in Scopus’ “Engineering (miscellaneous)” category.

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Topic Review
Red Mud Valorization
Red mud valorization denotes the set of processes by which red mud—the highly alkaline, iron-rich solid residue generated when bauxite is digested with hot sodium hydroxide in the Bayer process for alumina production—is converted from a waste stockpile into a resource of recoverable or useful materials rather than being simply disposed of [1]. The residue is dominated by iron oxides, titanium-bearing minerals, undigested alumina phases, sodium aluminosilicates, and residual caustic soda, together with minor valuable metals such as scandium and other rare earth elements. Valorization therefore comprises hydrometallurgical routes such as acid leaching, alkali treatment, and solvent extraction for metal recovery, pyrometallurgical reduction for iron recovery, and the use of the neutralized residue as a raw material in construction, cement, ceramics, adsorbents, or catalysts [2]. Because the composition is dominated by stable iron and titanium oxides that resist dissolution in caustic liquor, the valorization pathway is governed by the mineralogy of these phases, the removal of residual sodium alkalinity, and the selective separation of valuable constituents from the bulk oxide matrix [3]. The concept is defined as the resource-oriented recovery and reuse of a Bayer-process by-product.
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  • 26 Sep 2026
Topic Review
Liquid Metal Corrosion
Liquid metal corrosion is the degradation of a solid structural material caused by its contact with a molten metallic phase—such as liquid gallium, sodium, lead-bismuth eutectic, mercury, or lithium—wherein the liquid metal dissolves the solid at its surface, penetrates grain boundaries, and attacks the alloy environment rather than acting through an aqueous electrochemical electrolyte [1]. The phenomenon encompasses several coupled mechanisms: dissolution of the more reactive or more soluble constituent of the solid alloy into the liquid, intergranular penetration of the liquid metal along grain boundaries, and liquid metal embrittlement, in which a small amount of liquid metal wets a crack tip and lowers the energy required for crack propagation, producing brittle intergranular or cleavage fracture in an otherwise ductile solid [2]. Because the liquid metal attacks the interface atomically, the process is controlled by the solubility of the solid in the liquid, the diffusion rate of the liquid-metal atoms along boundaries, temperature gradients that drive mass transport, and the protective properties of any adherent oxide layer on the solid. The mechanism is therefore one of interfacial dissolution and grain-boundary penetration rather than electrochemical oxidation in a conducting solution [3].
  • 15
  • 26 Sep 2026
Topic Review
Ceramic Sintering
Ceramic sintering is a thermal consolidation process in which a compacted, porous green body of ceramic powder is heated to a temperature below the melting point of its principal constituent, causing the particles to bond together and the body to densify through the motion of atoms rather than by bulk fusion [1]. At the sintering temperature, solid-state diffusion, viscous flow of a transient liquid phase, evaporation–condensation, and grain-boundary transport operate to reduce the total solid–vapor interfacial area: material is transported from particle contacts to fill the interparticle pores, necks grow between adjacent grains, and the porosity shrinks and eventually becomes isolated. Because densification and grain growth proceed simultaneously, the final microstructure—grain size, pore size, and residual porosity—is determined by the balance between the driving force for shrinkage, which scales with surface energy, and grain-boundary mobility [2]. The process is governed by powder particle size, packing homogeneity, temperature, time, atmosphere, and the presence of sintering additives that form a transient liquid phase. Sintering is therefore defined as the heat-induced, diffusional bonding and densification of a particulate ceramic compact in the solid state or with a minor liquid phase, distinct from melting and casting [3].
  • 18
  • 26 Sep 2026
Topic Review
Hydroxyapatite Composite
A hydroxyapatite composite is a multiphase biomaterial in which hydroxyapatite, the calcium phosphate mineral Ca10(PO4)6(OH)2 that is chemically and crystallographically analogous to the inorganic phase of natural bone and teeth, is combined with a second constituent to overcome the intrinsic brittleness and low fracture toughness of the monolithic ceramic [1]. The reinforcing or second phase may be a bioresorbable polymer such as collagen or polylactide, a second ceramic such as beta-tricalcium phosphate, a bioactive glass, or an inert phase such as zirconia, carbon fibers, or bioglass particles. Because hydroxyapatite itself is osteoconductive and forms a direct bond with living bone while remaining stiff and stable, the composite is designed to retain this bioactive mineral interface while the second phase provides toughness, compliance, or controlled biodegradation. The composite is therefore characterized by a hydroxyapatite matrix or dispersed apatite phase embedded within a continuous secondary phase, with the interface between the two controlling load transfer and dissolution behavior [2]. The material is defined structurally as an apatite-containing multiphase solid and functionally as a synthetic analogue of the natural composite architecture in which stiff mineral platelets are bound within a compliant organic matrix [3].
  • 9
  • 28 Sep 2026
Topic Review
Electrodeposition
Electrodeposition is an electrochemical manufacturing process in which dissolved metal ions are reduced onto a conductive cathode surface under the drive of an externally imposed electric current, producing a coherent, adherent metallic film or coating on the substrate [1]. The process is carried out in an electrolyte bath that contains the ions to be deposited together with supporting salts, pH buffers, and organic additives; at the cathode, the cation accepts electrons and is converted into neutral metal atoms that adsorb, diffuse over the surface, and nucleate crystallites that grow into a film. Because deposition proceeds atom by atom from the liquid phase, the morphology, grain size, internal stress, alloy composition, and texture of the deposit are governed by bath chemistry, current density, temperature, mass transport, and the kinetics of electrochemical nucleation rather than by the melting and solidification of bulk metal [2]. The same fundamental mechanism underlies electroplating of protective or decorative coatings, electrodeposition of multilayer and alloy films, electrowinning of metals from solution, and electroforming of free-standing parts. The process is thus defined as the electrochemical reduction and consolidation of metal ions from an ionic medium onto an electrically conductive interface [3].
  • 9
  • 26 Sep 2026
Topic Review
Ceramic-Metal Joining
Ceramic-metal joining denotes the set of processes by which a monolithic ceramic or ceramic component is bonded to a metal or alloy component to produce a single, load-bearing assembly that combines the high-temperature strength, hardness, and chemical stability of the ceramic with the ductility and toughness of the metal [1]. The central scientific difficulty is that the two materials are chemically and thermally mismatched: the ceramic is generally non-wetting to conventional molten braze alloys, and its lower coefficient of thermal expansion generates residual stress on cooling from the joining temperature. This is overcome by active metal brazing, in which a reactive element—most commonly titanium, zirconium, or hafnium—is alloyed into an Ag–Cu or Au–Ni filler so that it segregates to the ceramic interface and chemically reduces or reacts with the ceramic surface, forming a thin reaction layer of oxides, nitrides, or carbides that permits wetting and metallurgical adhesion [2]. Diffusion bonding, brazing through a prior metallized layer, and interlayer insertion are alternative routes that control the interfacial reaction and redistribute thermal stress. The resulting joint is therefore defined by an engineered interfacial reaction zone between the ceramic and the filler rather than by simple fusion welding [3].
  • 7
  • 28 Sep 2026
Topic Review
Molten Salt Electrochemistry
Molten salt electrochemistry is the branch of electrochemistry concerned with electrode and interfacial processes that occur in ionic media consisting of molten inorganic salts—alkali halides, cryolite, chlorides, fluorides, or oxide-containing melts—at elevated temperatures typically ranging from several hundred to above one thousand degrees Celsius [1]. Because the solvent is itself an ionic liquid, the electrolyte possesses exceptionally high electrical conductivity, a wide electrochemical window, and the ability to dissolve stable oxides, sulfides, and refractory compounds that are inaccessible to aqueous electrochemistry. At the working electrode, dissolved metal cations or oxygen anions undergo reduction or oxidation under an applied potential, so that the field embraces electrowinning, electrorefining, electroplating, and the direct electrolytic reduction of solid oxide feedstocks to metal [2]. The reactions are governed by the thermodynamics of the melt, the speciation and activity of dissolved ions, mass transport through the viscous salt, and the nature of the electrode–melt interface. The field therefore forms the electrochemical foundation of the Hall–Héroult aluminum process and of high-temperature metal extraction, recycling, and materials synthesis in which the molten salt serves simultaneously as electrolyte, reactant, and reaction medium [3].
  • 9
  • 26 Sep 2026
Topic Review
Nitride Coatings
Nitride coatings are thin, adherent layers of transition-metal nitrides—most commonly titanium nitride (TiN), chromium nitride (CrN), titanium aluminum nitride (TiAlN), and related ternary or quaternary compounds—deposited onto a substrate to modify its surface properties without altering the bulk material [1]. These compounds crystallize in the rock-salt or related cubic lattice in which nitrogen atoms occupy interstitial sites of the metal sublattice, producing a strongly covalent, chemically bonded structure that combines high hardness, a high melting point, and low chemical reactivity. The deposition is conventionally carried out by physical vapor deposition routes such as cathodic arc evaporation and magnetron sputtering, in which energetic metal or metal-ion fluxes react with a controlled nitrogen partial pressure to build a dense, fine-grained film atom by atom [2]. Because the coating and substrate possess different coefficients of thermal expansion, the as-deposited layer typically retains residual compressive stress, which must be managed together with grain morphology, composition gradients, and multilayer architecture to suppress crack initiation and delamination [3]. Functionally, nitride coatings constitute a surface system in which the nitride phase acts as a hard, wear-resistant and oxidation-resistant barrier while the underlying metal or cemented-carbide substrate supplies toughness.
  • 7
  • 26 Sep 2026
Topic Review
Magnetic Coercivity
Magnetic coercivity, or coercive field, is the magnitude of the reverse magnetic field that must be applied to a magnetized material to reduce its magnetic induction—or magnetization—to zero after the material has been driven to saturation [1]. On the hysteresis loop, coercivity is measured as the field at which the B–H or M–H curve crosses the axis opposite to the original magnetization direction, and it quantifies the resistance of the material to demagnetization: a large coercivity means a strong reverse field is required to erase the magnetization, while a small coercivity means the material is readily demagnetized [2]. Coercivity is a microstructurally sensitive property that originates from the pinning of magnetic domain walls and from the energy barriers to reversal of magnetization, so its value reflects defects, inclusions, grain boundaries, and the shape and anisotropy of the material that impede domain-wall motion [1]. It is distinguished from remanence, which measures the magnetization retained at zero field, by measuring the field needed to remove that magnetization, and it is the parameter that separates magnetically hard materials, with high coercivity suitable for permanent magnets, from magnetically soft materials, with low coercivity suitable for cores [2]. Its defining meaning is the reverse field needed to annul magnetization [3].
  • 10
  • 26 Sep 2026
Topic Review
Impact-Resistant Structure
An impact-resistant structure is a structural system designed to withstand, absorb, and dissipate large, rapidly applied dynamic loads—such as those arising from collision, projectile impact, blast, or crash—without suffering catastrophic failure [1]. Such structures rely on material and geometric arrangements that undergo controlled, energy-dissipating deformation, employing members and materials whose plastic collapse, progressive folding, or crushing spread the kinetic energy of impact over a deforming volume and decelerate the impacting mass rather than transmitting the load elastically to the rest of the structure [2]. Impact-resistant structures are distinguished from ordinary static-load structures by their design for impulsive loading rates, under which material strength and energy absorption depend on strain rate, inertia effects become significant, and the distinction between elastic and inelastic response determines survivability [1]. The defining principle is the controlled dissipation of impact energy through designed inelastic deformation, so that the structure manages the rapid delivery of kinetic energy by deforming in a predictable manner that protects the load-bearing function, rather than by rigidly resisting the load [2]. Its defining characteristic is energy absorption under high-rate loading [3].
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  • 28 Sep 2026
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