Ti Phase Research Articles

Contemporaneous alkaline and subalkaline intraplate magmatism in the Dunedin Volcanic Group, NZ, caused by mantle heterogeneity

ABSTRACT Monogenetic volcanism in the Maniototo Basin in the Dunedin Volcanic Group was unusual because the eroded lavas, plugs and dikes comprise spatially and temporally restricted silica-saturated and silica-undersaturated magmas. 40Ar/39Ar dating coupled with existing data and field relationships indicate that volcanism was focused at ∼11 Ma. Major and trace element data show the volcanic rocks to have mafic compositions and little evidence for fractionation and/or crustal contamination, but to have been variably altered. The volcanic rocks comprise an alkaline group and an alkaline to subalkaline transitional group, with one intermediate unit. With the exception of one flow, the transitional group has more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd, 206Pb/204Pb and 208Pb/204Pb than the alkaline group, as well as smaller Ti and K primitive mantle-normalised anomalies. Overall, the different magma compositions cannot be related to varying degrees of melting of equivalent mantle sources. Trace element ratios indicate that residual Ti and K-bearing mantle phases (amphibole, phlogopite) probably played a major role in the source of alkaline group but a smaller role in the transitional group. Therefore, the varying compositions of the Maniototo volcanic rocks relates to melting of a heterogeneous lithospheric mantle, or/and varying degrees of interaction with mantle hydrous metasomes as the magmas ascended.

Diffusivities and atomic mobilities in bcc Ti–V–Mo alloys

In pursuit of a comprehensive exploration into the diffusion kinetics of bcc Ti–V–Mo alloys, sixteen sets of diffusion couples were prepared within the bcc phase of Ti–V–Mo alloys. These diffusion couples were subjected to annealing at 1373 K and 1473 K. Composition profiles were obtained by means of the electron probe micro-analysis technique (EPMA). The calculation of diffusivities in bcc Ti–V–Mo alloys was performed using the Whittle-Green and Hall methods. Based on available thermodynamic descriptions, the atomic mobility parameters of the bcc Ti–V–Mo system were assessed by using the DICTRA module of the Thermo-Calc software. A comparison is made between the simulated composition-distance curve and the diffusion path with the experimental values, revealing a significant level of concordance.

Microstructural Characterization of Al0.5CrFeNiTi High Entropy Alloy Produced by Powder Metallurgy Route.

Alloys with superior properties represent the main topic of recent studies due to their effectiveness in reducing the cost of equipment maintenance and enhancing usage time, in addition to other benefits in domains such as geothermal, marine, and airspace. Al0.5CrFeNiTi was produced by solid state processing in a planetary ball mill, with the objective of obtaining a high alloying degree and a homogenous composition that could be further processed by pressing and sintering. The metallic powder was technologically characterized, indicating a particle size reduction following mechanical alloying processing when compared to the elemental raw powder materials. The microstructural analysis presented the evolution of the alloying degree during milling but also a compact structure with no major defects in the pressed and sintered bulk samples. The X-ray diffraction results confirmed the presence of face-centered cubic (FCC) and body-centered cubic (BCC) phases, predicted by the theoretical calculations, along with a hexagonal close-packed (HCP) phase, where the Al, Cr, Fe, Ni, and Ti phase was identified in both the alloyed powder material and sintered sample.

Microstructure evolution and coarsening behavior of precipitated O phase in Ti–22Al–24Nb-0.5Mo (at. %) alloy during the heat treatment

Microstructure evolution and coarsening behavior of precipitated O phase were systematically investigated in this study, and the corresponding microstructures were characterized by scanning electron microscopy and transmission electron microscopy. The results showed that the original microstructure was composed of lath O phase, α2 phase and B2 matrix. The precipitated O phase presented different morphologies and sizes during heat treatment. With the increase of solution temperature and holding time, the O phase occurred coarsening, with a thickness ranging from 0.73 increased to 2.64 μm. But the volume fraction decreased from 57.65 to 18.40 %. During aging treatment, large amounts of fine secondary acicular O phase have precipitated from the matrix. As the aging temperature increases, the O phase underwent coarsening and the thickness increases from 0.70 to 1.40 μm. However, the aging temperature has little effect on the precipitation of acicular O phase, and the volume fraction decreases from 37.66 to 33.32 %. Research found that the small-sized O phase gradually dissolved in the matrix, while the large-sized O phase grew. This phenomenon can be explained by Ostwald ripening mechanism. The TEM analysis revealed that the O phase occurred separation, mainly due to the diffusion of solute atoms and the embedding of B2 matrix. Meanwhile, the O phase had been completed and segmented. The coarsening mechanism of the O phase was also explained by the boundary splitting mechanism and terminal migration mechanism.

Effect of Co content on microstructure and mechanical properties of maraging steel

Effect of Co element on the microstructure and mechanical properties of maraging steel is studied and summarized. The microstructure and mechanical properties of five different compositions of maraging steels were characterized and tested in three heat treatment states, with the heat treatment schemes of homogenization treatment at 1300 °C × 10h, solution treatment at 800 °C × 2h, and aging treatment at 480 °C × 5h. The research has discovered that increasing the Co content in three different heat treatment states can lead to a reduction in the size of the original austenite grains and the width of martensite laths. In the aged state, higher Co content causes the precipitation phase to transform from an ellipsoidal Mo-rich phase to a needle-like Ni3(Mo, Ti) phase. These changes in the size, shape, and density of the precipitated phases result in a more pronounced effect of precipitation strengthening, leading to a significant increase in the material's strength.

New biocompatible low modulus and high strength β Ti-Fe-Nb-Sn ultrafine eutectic composites

High strength β Ti–Fe–Nb–Sn ultrafine eutectic composites are promising in structural and functional applications exhibiting high fracture strength with large plasticity. The present work aims to develop new biocompatible β Ti–Fe-based ultrafine eutectic composites using biocompatible elements (Ti, Fe, Sn and Nb) and avoiding and/or controlling the formation of metastable ω phase also known as Laves phase. Five new compositions (Ti64Fe22Nb14, Ti66Nb18Fe16, Ti63Fe23Nb8Sn6, Ti60Fe23Nb8Sn9 and Ti44Fe34Nb16Sn6 (at.%) were produced using Cu-mold suction casting and the evolution of phases and microstructure with the cooling rate and their mechanical properties were investigated. In this sense, was observed a decreasing in the melting point by the addition of eutectoid β-stabilizing elements (Fe and Sn), which leads to values down to Tl = 1215 °C. The samples were characterized by X-ray diffraction, differential scanning calorimetry, scanning and transmission electron microscopy, Young's modulus measurements by the ultrasonic method, microhardness and compression tests. Thus, in this paper are shown promising results on new biocompatible metallic alloys of the TiFeNbSn system with high strength and low Young's modulus due to the adequate combination of a microstructure formed by micrometer-sized β-Ti dendrites with ultrafine eutectics between soft β-Ti phase and hard Ti–Fe and Ti3Sn intermetallics, highlighting alloys Ti64Fe22Nb14 and Ti63Fe23Nb8Sn6. Their yield and fracture strength measured by compression and Young's Modulus measured by ultrasound were 1810 MPa, 2160 MPa and 45 GPa for alloy Ti64Fe22Nb14 and 1915 MPa, 2240 MPa and 59 GPa for alloy Ti63Fe23Nb8Sn6 (at.%)

Electrical resistivity of coatings of quasicrystalline and crystalline phases of the Ti—Zr—Ni system in the temperature range 4–300 K

The temperature dependence of the electrical resistivity in the temperature range from 4.4 to 300 K for Ti41Zr41Ni18 (at. %) thin coatings of different crystal perfection and phase composition was studied. The coatings were deposited by magnetron sputtering with subsequent vacuum annealing in various modes ensuring the formation of several heterophase combinations, which included 1/1 and 2/1 approximation phases, a quasicrystalline icosahedral phase, a Laves phase (Ti, Zr)2Ni, and an α-Ti (Zr) solid solution. The structure before and after annealing was studied by X-ray diffractometry. It was established that coatings with a predominant content of amorphous, quasicrystalline, or approximant 2/1 phases have a temperature coefficient of resistance less than zero, while samples with a predominance of crystalline phases demonstrate characteristic metallic conductivity. The temperature dependence of the electrical resistivity of the Ti41Zr41Ni18 quasicrystalline coating turned out to be similar to the dependence in bulk samples of the Ti40Zr40Ni20 composition. The electrical resistivity of the approximant 2/1 phase with a low content of the additional Laves phase in the film has an almost constant value in the entire investigated temperature range.

Interfacial microstructure and mechanical properties of diffusion bonded joints of additive manufactured 17-4 PH stainless steel and TC4 titanium alloy

A novel atomic diffusion additive manufactured 17-4 PH stainless steel and TC4 titanium alloy was successfully joined by vacuum diffusion bonding with Cu foil + Ni foil interlayers at the temperature range of 880°C–960 °C for 60 min with 2 MPa pressure. The interfacial microstructural evolution, interfacial diffusion of elements, and mechanical properties of joints were analyzed. The results indicated that the interfacial transition zone was composed of diffusion affect zone (DAZ) and interface reaction zone (IRZ). With Cu foil + Ni foil composite interlayers, reaction layers such as DAZ 1/IRZ 1/IRZ 2/DAZ 2 were formed in the transition zone, and the interface consisted of CuTi + CuTi2 eutectic phase, CuTi2, Ti (Cu, Ni) and α-Ti. Striped Ti (Cu, Ni) phases were surrounded by serrated CuTi2 phases, which contained Cu-poor, Ni poor areas, and the segregation of Ti atoms. The maximum microhardness of 693 HV0.1 and the maximum shear strength of 163 MPa were obtained at the bonding temperature of 920 °C and 960 °C, respectively.

Mechanisms leading to exceptional niobium concentration during lateritic weathering: The key role of secondary oxides

Niobium (Nb) is considered as one of the most immobile elements during supergene weathering due to its low solubility and the expected resistance of the pyrochlore mineral group (A2B2X6Y) in which Nb occupies the B site. Although the resistance of pyrochlore is challenged by direct evidence of alteration in lateritic profiles, the geochemical and mineralogical processes controlling its behavior in the critical zone remains elusive. This study uses a multiscale geochemical, mineralogical and spectroscopic approach to monitor Nb solid speciation in a thick weathering profile. The weathering of the pyrochlore-bearing core carbonatite facies from Morro dos Seis Lagos has resulted in a Fe-enriched laterite with exceptional Nb concentrations (2.91 wt% Nb2O5 on average). The preservation of the successive secondary phases (Ti-, Fe-, Ce-oxides) resulting from weathering processes along the horizons offers the opportunity to track Nb during pyrochlore alteration from the fresh parent rock to the final stages of weathering. Intense lateritization processes have led to an enrichment in Fe and Ti in the pyrochlore B-sites, resulting in the weakening of the structure and its ultimate destabilization due to weaker B-O bonds. After the release of Nb from pyrochlore, the fate of Nb is dependent on the secondary phases formed during weathering. In the lower horizons dominated by Fe oxides, goethite is the main host for Nb (1 wt% Nb2O5) due to its capacity to substitute Fe3+ for Nb5+, in contrast to hematite. In the upper horizons, where Ti oxides have formed during the reworking of the laterite, Nb5+ is preferentially incorporated into brookite and rutile (20 wt% Nb2O5), which may have formed owing to slightly acidic pH and high Nb activity during their growth. The presence of Nb in hollandite and cerianite in a vein from the manganiferous horizon involves the transport of Nb with mobile elements at the scale of the laterite. With this study, we describe a new model accounting for the formation of Nb-enriched laterites. The latter is based on the ability of Nb5+ to substitute for Fe3+, Ti4+, Ce4+ in minerals formed by lateritization processes after its release from pyrochlore. The nature of the secondary Nb-bearing oxides is dependent on the chemistry of the parent rock and the conditions of formation of the laterite. This work, evidencing the mobilization of Nb both at the scale of the mineralogical assemblage and of the entire profile questions the pervasive use of Nb as a geochemical invariant in the critical zone.

The influence of the metallic phase on the microstructure and properties of Al2O3/Ti/Ni composites, taking into account environmental influences related to their production

The performed tests showed that obtaining a finished product from the Al2O3/Ti/Ni system in the shape of a sleeve is possible using the Centrifugal Slip Casting method. A gradient arrangement of the metallic phase characterized the produced samples. The content of the metallic phase did not influence the rheological properties. Research has shown that the density of composites decreases with the increase in the content of the metallic phase. Using an air atmosphere made producing a spinel phase (NiAl2O4) in molded composites possible. The increase in the content of the metallic phase in the slip used to form composites limits the growth of Al2O3 grains. The cross-sectional hardness test confirmed the gradient microstructure of the composites for both series. The life cycle analysis results indicate that the increase in the share of the Ti and Ni phases leads to an increase in the environmental footprint of the materials produced concerning acquiring and processing raw materials.

The Effect of Al and Ti Additions on Solid Solution Strengthening and Precipitation Hardening in CoNiFe Medium-Entropy Alloys.

The effect of Al and Ti additions on the microstructure and properties of CoNiFe alloys was studied in this paper. The investigations were conducted on four specially designed and produced arc furnace alloys (from 3 to 5 components, with medium to high entropy). Samples in various states were analyzed, i.e., as-cast, after homogenization, after solution heat treatment, and after solution heat treatment and aging. The obtained samples were characterized by: SEM observations, EDS, XRD, TEM analyses, and finally, hardness measurements. The solid solution strengthening coming from the addition of 5 at. pct. Al was negligible, while the effect from the 5 at. pct. of Ti addition was significant. The precipitation hardening effect related to the presence of the (CoNi)3Ti phase caused by the Ti addition is comparable with the total effect of the Al and Ti addition, which caused the precipitation of (NiCo)3AlTi.

Improving strength and toughness of Ti–6Al–4V alloy/pure copper diffusion bonded joint with VCrAl1.86Ni1.86 eutectic medium-entropy alloy interlayer

To solve the metallurgical incompatibility of titanium alloy/copper dissimilar metal joining, a suitable interlayer was used to adjust the interface structure, achieving the strength and toughness of joint. The vacuum diffusion bonding between Ti–6Al–4V alloy (TC4) and pure copper (T2) with VCrAl1.86Ni1.86 eutectic medium entropy alloy (EMEA) foil was investigated. Ti3Al, Al(V, Cr)Ti2, Al(V, Cr, Ni)Ti, and AlNi2Ti phases formed in the TC4/EMEA interface. FCC and BCC double-phase solid solution appeared in the EMEA/T2 diffusion zone, resulting in the high-entropy seam between VCrAl1.86Ni1.86 interlayer and T2. The maximum shear strength of joint made at 880 °C for 90 min reached 215 MPa. The growth activation energy of reaction layers (I-III) in the TC4/EMEA interface were 283 kJ/mol, 379 kJ/mol and 431 kJ/mol, respectively. The Ti3Al/Al(V, Cr)Ti2/Al(V, Cr, Ni)Ti/AlNi2Ti interface was coherent. Nevertheless, the AlNi(V, Cr)2/Al(Cu, Ni)2 and AlNi(V, Cr)2/FCC-Cu interface was non-coherent with high strain energy. All joints broke through the EMEA/T2 interface during test. The fracture surface presented some cleavage ravines and auspicious cloud features. This study provided an effective strategy for the joining of titanium alloy and copper in high precision components of aerospace engines.

Cristobalite Clinker and Paralavas of Ferroan and Melilite–Nepheline Types in the Khamaryn-Khural–Khiid Combustion Methamorphic Complex, East Mongolia: Formation Conditions and Processes

Abstract —Rock samples from the Khamaryn-Khural–Khiid combustion metamorphic (CM) complex, including cristobalite clinker, ferroan tridymite–sekaninaite and cristobalite–fayalite paralavas, which are rock types new to the complex, as well as clinker xenoliths in melilite–nepheline paralava, have been studied in terms of chemistry and mineralogy. The obtained data on rock-forming, minor, accessory, and rare phases (silica polymorphs, cordierite-group minerals, fayalite, Fe and Ti oxides, ferrosilite, etc.) have implications for the formation conditions and processes of the CM rocks. The Raman spectra of sekaninaite, indialite, ferroindialite, mullite, and anhydrous Fe–Ca–Mn phosphate, presumably from the graftonite group, have several specific features. The diversity of mineral assemblages in the CM rocks is due to heterogeneous lithology of the sedimentary protolith and to local effects in the multistage history of the Khamaryn-Khural–Khiid complex. According to geochemical data, all CM rocks of the complex are derived from the Early Cretaceous Dzunbain Formation, their protolith molten to different degrees. The cristobalite clinker and tridymite–sekaninaite and cristobalite–fayalite paralavas were produced by partial melting of pelitic rocks containing different amounts of iron in a wide temperature range. The formation of mullite developed from dehydration–dehydroxylation and incongruent partial melting of amorphous pelitic matter. Large-scale crystallization of mullite in clinker, occurred from the high-silica potassic aluminosilicate melt at >850 °C. Combustion of subsurface coal seams heated the overburden to >1050 °C or locally to >1300–1400 °C (melting point of detrital quartz) or even, possibly, to >1470 °C corresponding to the stability field of β-cristobalite. Melilite–nepheline paralava was formed by incongruent melting of silicate (pelitic) and carbonate (calcite) components of marly limestone under elevated CO2 partial pressure. Oxygen fugacity (fO2) during combustion metamorphism changed from strongly reducing conditions favorable for crystallization of Fe phosphides (barringerite, schreibersite) and metallic iron from silica-undersaturated melts parental to melilite–nepheline paralava to high fO2 values that can maintain the formation of hematite in Fe-rich CM rocks.

Phase Equilibria, Solidified Microstructure, and Hydrogen Transport Behaviour in the V-Ti-Co System.

At present, the V-Ti-Co phase diagram is not established, which seriously hinders the subsequent development of this potential hydrogen permeation alloy system. To this end, this article constructed the first phase diagram of the V-Ti-Co system by using the CALculation of PHAse Diagrams (CALPHAD) approach as well as relevant validation experiments. On this basis, hydrogen-permeable VxTi50Co50-x (x = 17.5, 20.5, …, 32.5) alloys were designed, and their microstructure characteristics and hydrogen transport behaviour were further studied by XRD, SEM, EDS, and so on. It was found that six ternary invariant reactions are located in the liquidus projection, and the phase diagram is divided into eight phase regions by their connecting lines. Among them, some alloys in the TiCo phase region were proven to be promising candidate materials for hydrogen permeation. Typically, VxTi50Co50-x (x = 17.5-23.5) alloys, which consist of the primary TiCo and the eutectic {bcc-(V, Ti) and TiCo} structure, show a high hydrogen permeability without hydrogen embrittlement. In particular, V23.5Ti50Co26.5 exhibit the highest permeability of 4.05 × 10-8 mol H2 m-1s-1Pa-0.5, which is the highest value known heretofore in the V-Ti-Co system. The high permeability of these alloys is due in large part to the simultaneous increment of hydrogen solubility and diffusivity, and is closely related to the composition of hydrogen permeable alloys, especially the Ti content in the (V, Ti) phase. The permeability of this alloy system is much higher than those of Nb-TiCo and/or Nb-TiNi alloys.

The Influence of Ultrasonic Activation on Microstructure, Phase Transformation and Mechanical Properties of Porous Ni-Ti Shape Memory Alloys via Self-Propagating High-Temperature Synthesis.

Porous Ni-Ti shape memory alloys (SMAs) have been widely studied in biomedical and engineering applications. Porous Ni-Ti SMAs were obtained via self-propagating high-temperature synthesis (SHS), and their microstructure, phase transformation, and mechanical properties were investigated. This article presents the results of a study of changes in the microstructure, phase transformation, and mechanical properties of porous Ni-Ti SMAs when Ni and Ti metal powders were preliminarily subjected to ultrasonic activation at various periods. It was determined that the porosity of the obtained alloy samples was 62-68 vol%. The microstructure was composed of the main matrix Ni-Ti phase and the accompanying Ti and Ti2-Ni phases. The results show that the hardness 34.1-86.8 HB and elastic modulus 4.2-10.8 GPa increased with an increase in the ultrasonic activation time of the samples. The phase transformation temperature of the Ni-Ti shape memory alloy remained almost unchanged under the influence of ultrasonic treatment.

Effect of prior processing on the decomposition of the β phase in Ti–Nb alloys during intermediate heat treatments

Metastable β-Ti alloys exhibit multiple decomposition pathways during isothermal ageing. Ages at intermediate temperatures below the α/β transus result in the formation of α or isothermal ω. The effect of prior processing on these pathways remains largely unexplored within the literature. Therefore, the role of processing on a Ti–Nb alloy was investigated in cold rolled and solutioned conditions. The solutioned sample showed evidence of recrystallisation, with shear bands remnant from the prior cold rolling that exhibited a greater degree of texture than the surrounding material. During isothermal ageing ωiso was observed outside of these bands whilst α phase precipitated within the bands and throughout the cold rolled sample. This shows that the remnant strain from the rolling process facilitated α nucleation over ωiso due to accommodation of the α/β interface. Additionally, it was seen that the magnitude of internal strains had a marked effect on the α morphology observed.

Grain refinement of aluminium welds by Ti, TiB_2, and TiC filler wire inoculation

A fine-grained fusion zone characterises a tough aluminium weld. To improve the solidification characteristics and refine the grains in aluminium welding, different inoculation particle combinations were introduced to the filler wire by solid state metal screw extrusion. Filler wires were I-joint welded with two different welding methods to reveal the potency for grain refinement. Grain size, microstructure, porosity content, and hardness across the weld was revealed. Gas metal arc welding with a Ti-TiC inoculated filler wire exhibited a remarkable grain refinement of 91% compared to a base reference of commercial pure aluminium. The Al_3Ti intermetallic phase was found as nucleation point. Gas tungsten arc welding showed lower grain refinement potency, and no Al_3Ti phase was found in any weld. Thus, the effect of welding method must be taken into consideration upon development of inoculant containing filler wires.

Effect of different hydrogen Fugacities on the microstructure of additively manufactured Ti-6Al-4V

In this study we compared the microstructural changes in the presence of hydrogen of Ti-6Al-4V alloy prepared by two different additive manufacturing (AM) methods: electron beam melting (EBM) and selective laser melting (SLM). Cathodic hydrogenation of AM Ti-6Al-4V resulted in significant expansion of β Ti phases due to the solute hydrogen, increasing of micro-strains, and α → titanium hydride/βH transformation. It was shown that SLM Ti-6Al-4V with acicular martensitic structure is more prone to hydrogen-induced phase transformation and hydrogen-assisted damage, compared to EBM. Moreover, it was revealed that different hydrogen charging environments cause different microstructural changes in EBM Ti-6Al-4V. Unlike cathodic hydrogen charging, gaseous hydrogen charging at elevated temperature reduced the process-induced micro-strains and promoted Al redistribution within the EBM Ti-6Al-4V. This resulted in massive precipitation of brittle α2-Ti3Al intermetallic compound, which act as a strong hydrogen trapping site aside from the Ti hydride phase.

Effect of Al content on the microstructure, properties, and oxidation behaviors at 900 ℃ of (MoNbCoCrAlxSi0.2)70Ti30 refractory high-entropy alloys coatings fabricated by electron beam cladding

Electron beam cladding (MoNbCoCrAlxSi0.2)70Ti30 RHEAs coatings with different Al contents on the surface of Ti600 alloy, and their microstructure and properties were investigated. Two solid solution phases, A2/B2-BCC1 and A2-BCC2, and precipitated phases (Ti,Mo,Nb,Al)5Si3-IMC were found. The mechanical properties and wear resistance of RHEAs coatings increase and then decrease with increasing Al. The mechanism of the change in mechanical properties and wear resistance is based on the strong and weak relation between solid solution strengthening and precipitation strengthening. The improvement of high-temperature oxidation resistance is due to the promotion of Al2O3 formation at the early oxidation stage.

Electrocatalytic Nitrate Reduction to Ammonia at Atomically Dispersed Titanium Sites on Carbon Nanoflowers

Active nitrogen species are widely acknowledged as pollutants that are both harmful to the environment as well as human health. Emissions from wastewater and agricultural applications contain nitrogen in many forms, but in soils and waterways nitrate (NO3 -) predominates due to the presence of nitrifying bacteria. In comparison to more reduced forms of nitrogen such as total ammonia (NH3/NH4 +), nitrate is not only a less versatile species from a chemical manufacturing and energy standpoint; it is also more difficult to selectively separate from wastewater streams. For instance, we have conducted considerable work on electrochemical ammonia stripping, achieving high selectivities and even enabling concentration of ammonia in the form of strong ammonium salt solutions.1 Moreover, it is estimated that recovery of active nitrogen species from municipal and agricultural wastewaters could offset the need for ~30% of Haber-Bosch ammonia synthesis. From this perspective, it is desirable to develop catalysts that are active and selective for the conversion of nitrate to ammonia. Titanium metal has been demonstrated as a relatively active and selective catalyst for nitrate reduction to ammonia in acid;2 however, similarly active and selective catalysts under neutral-to-alkaline conditions are a subject of active research.3–6 Here we report on the performance of atomically dispersed titanium sites on carbon nanoflowers7 for the reduction of nitrate to ammonia under alkaline conditions. The dispersity of these catalysts was supported by XAS (little/negligible Ti-Ti scattering, putative Ti-N and Ti-N-C scattering), STEM (visual confirmation of atoms), and XRD (no crystalline Ti phases observed). We contrast the performance of these atomically dispersed catalysts with that of bulk titanium foil, which shows comparably low activity and selectivity for nitrate reduction at similar pHs and potentials. In addition, we compare the atomically dispersed titanium catalysts with titanium nanoparticles, as a first-order check for catalyst aggregation under reductive reaction conditions. Moreover, the performances of all of these catalysts are compared with the baseline/controls of bare carbon paper, as well as carbon nanoflowers supported on carbon paper without titanium dopant. Additional control experiments include tests conducted in the absence of nitrate. These lines of evidence, together with the relatively high rate of ammonia production (>0.01 mmol / cmgeo 2 / h, >10 mmol / mg Ti / h), support the notion that atomically dispersed titanium is uniquely active and selective for NO3RR under alkaline conditions.Further, for the above catalysts at pH ~13, we show the impacts of potential on the product distribution, including nitrogen mass balance and Faradaic efficiency. As a best practice, we demonstrate consistent closure of both metrics. Potential was varied between -0.4 V and -0.85 V vs. RHE. Partial current toward NO3RR increases with increasing overpotential, as another sanity check supporting the findings. Notably, in addition to observing ammonia and nitrite as products of NO3RR, we also checked for other stable intermediates (in addition to N2) along the 8-electron reaction pathway – and as a result, we are able to report small amounts (FE ~5-10%) of hydroxylamine (NH2OH) product.In the specific case of atomically dispersed titanium on carbon nanoflowers, we also report on certain observed electrolyte effects, such as the incorporation of perchlorate vs. sulfate as a supporting electrolyte. We demonstrate the role of supporting salt both in modifying selectivity – e.g. sulfate suppressing HER, possibly via site-blocking – as well as in altering the carbon support itself. These observations contribute to a growing body of work that will enable the engineering of these catalysts for high-rate reduction of nitrate to ammonia, aiding both wastewater remediation and the decarbonization of ammonia synthesis.