The micro-arc oxidation (MAO) technique was employed to produce calcium phosphate coatings on titanium surfaces using an electrolyte composed of hydroxyapatite and calcium carbonate in an aqueous solution of orthophosphoric acid. The coatings’ morphology and composition were regulated by adjusting electrical parameters, specifically the duty cycle and voltage. This study examined the effects of the duty cycle and voltage during the MAO process on the microstructure and composition of calcium phosphate coatings on VT1–0 titanium substrates. Scanning electron microscopy (SEM) was utilized to analyze the microstructure and thickness of the coatings, while X-ray diffraction (XRD) was employed to determine their phase composition. The findings reveal that the surface morphology of the calcium phosphate coatings transitions from a porous, sponge-like structure to flower-like formations as the duty cycle and voltage increase. A linear increase in the voltage within the applied duty cycles led to a rise in the size of the forming particles of amorphous/crystalline structures containing phases of monetite (CaPO₃(OH)), monocalcium phosphate monohydrate (Ca(H₂PO₄)₂·H₂O), and calcium pyrophosphate (γ–Ca₂P₂O₇).

This study focuses on optimizing the alkali roasting conditions for chromite beneficiation tailings with the goal of enhancing chromium oxide (Cr₂O₃) extraction. Within the experimental framework, the variables included roasting temperature, the amount of added Na₂CO₃, and reaction time. The results revealed that temperature is the most critical factor directly affecting the extraction efficiency. Increasing the amount of Na₂CO₃ contributed to an increase in Cr₂O₃ recovery, although excessive addition may not be economically justified. The optimal conditions—1000 °C, 120%–130% Na₂CO₃ (relative to tailings mass), and 120 min—enabled a Cr₂O₃ extraction rate of up to 98.6% through aqueous leaching. The phase transformation analysis confirmed the breakdown of the spinel structure and formation of water-soluble sodium chromate. Microanalysis observations and measurements validated the progressive destruction of chromite grains and sodium enrichment in the reaction zones. The remaining leaching residue consisted of inert Na₂Mg₂Si₂O₇ and MgO, suitable for further metal recovery. The proposed approach enables efficient detoxification of hazardous tailings and serves as a basis for integrated utilization of Cr-bearing industrial waste.

Niobium commonly occurs as a minor component in Fe–Ti–O oxide systems associated with ilmenite ores and titanium-bearing metallurgical materials, yet its speciation and incorporation mechanisms remain insufficiently resolved. This study investigates the distribution, structural incorporation, and microphase localization of niobium in the Fe–Ti–O system, with emphasis on TiO₂-rich domains. Electron probe microanalysis with EDS/WDS, X-ray diffraction, thermal analysis, and thermodynamic modeling in HSC Chemistry were combined to characterize niobium-bearing phases in natural and model oxide systems. Niobium was found to occur in two principal modes: as a low-level isomorphic impurity in Fe–Ti oxide matrices and as localized enrichments in TiO₂-rich domains, particularly rutile lamellae. A first-order area-based estimate for representative analyzed grains suggests that approximately 60–80% of the detected niobium is associated with the lamellar TiO₂ channel. The combined observations are consistent with a sequential mechanism involving isomorphic substitution of Nb in Ti sites, followed by microphase enrichment and segregation into more compositionally distinct niobium-bearing oxide or titanate microphases. In the studied material, integrated mapped-field Nb is about 0.04 wt.%, whereas matrix Nb commonly lies at trace levels of about 0.02–0.05 wt.% under the applied analytical conditions, consistent with low-level background incorporation, whereas locally Nb-enriched rutile-like domains reach about 0.70–1.00 wt.%. TiO₂-rich domains are therefore identified as the principal concentrators of niobium in Fe–Ti oxide systems. Taken together, the natural observations, model experiments, and thermodynamic calculations support an integrated mechanistic sequence of Nb evolution in the Fe–Ti–O system: isomorphic substitution → microphase enrichment in TiO₂-related domains → segregation into distinct Nb-bearing oxides/niobates. These findings provide a practical framework for interpreting Nb behavior in natural and technological Fe–Ti–O materials.

Commercially pure titanium is widely used for load-bearing implants but its low surface hardness and high friction coefficient limit durability. In this work, calcium- and silicon-bearing coatings were deposited on CP-Ti (VT1-0/ASTM Grade 2) by micro-arc oxidation (MAO) in an aqueous electrolyte of 30 wt.% H₃PO₄, 60 g/L hydroxyapatite and 75 g/L wollastonite, at a fixed filling-parameter setting of 8% and two voltages, 200 and 300 V. The coatings were characterised by SEM, EDS, FIB cross-sectioning, progressive-load scratch testing, instrumented indentation (ISO 14577-1) and single-pass ball-on-flat sliding with 3D profilometry. Raising the voltage from 200 to 300 V thickened the layer from about 28 to 37 µm but rendered the cross-section coarsely porous and the coating–substrate interface markedly rougher. The first cohesive critical load fell from 6.15 N at 200 V to 3.73 N at 300 V, and the kinetic friction coefficient rose from 0.41 to 0.75. Instrumented indentation gave comparable properties for both coatings (Martens hardness 2254 versus 2169 N/mm²; modulus 103 versus 102 GPa), indicating that the higher-voltage penalty lies in coating architecture and interface quality rather than in intrinsic hardness. The lower voltage is therefore preferable for tribologically loaded coatings of this type.