High Ti Content Research Articles

Strengthening effect and mechanism of titanium extraction slag on the mechanical property of calcium aluminate cement

In heavy oil recovery, calcium aluminate cement (CAC) is in the working environment of “low-temperature hardening and ultrahigh temperature service.” However, the formation of C3AH6 under low temperatures results in a decrease in strength and reduce the cementing quality. In this study, titanium extraction slag (TES) was used to inhibit CAC strength deterioration. TES, characterized by a high Ti content, presents challenges in terms of utilization and poses significant ecological risks owing to its large accumulation. Cementite hydration with 0%, 20%, 30%, and 40% TES relative to CAC was examined at 30 °C for 28 d. The high C3AH6 content of the pure CAC increased the strength deterioration, pore size, and cementite carbonation. With 20% TES, a dilution effect was observed without strength improvement. Furthermore, 30% TES generated layered double hydroxides and converted C–S–H into C–A–S–H, thereby increasing compressive strength. By-products were generated with 40% TES, which inhibited the strength development while generating C–A–S–H to maintain the compressive strength. Therefore, TES can inhibit the strength decline of CAC, and the byproducts of the LDH structure can improve corrosion resistance.

Microstructure and mechanical properties of C/SiC-niobium alloy (C103) joint brazed with TiCuAg alloy for aerospace applications

In this study, niobium-based alloy C103 is joined to carbon fibre-reinforced SiC (C/SiC) composite utilising commercially available Ticusil® and Cusil® alloy braze filler material. Various characterisation techniques are employed to investigate the interfacial microstructures and evolution mechanism of C/SiC–C103 junctions. Lap shear strength (LSS) is used to evaluate the mechanical performance of the brazed joints. The results show that adding Ti promotes the growth of “nails”, a phenomenon favourable for robust joint quality. However, high Ti content deteriorates the bond strength due to the formation of significant brittle intermetallic phases, causing premature delamination of the joints. The response surface methodology (RSM) is employed to examine the interactions among various operating parameters. To attain the high LSS value, the high temperature, intermediate reaction time, and low cooling rate are necessary for a Ticusil-based joint, whereas high temperature, low reaction time, and increased cooling rate are preferred for a Cusil-based joint.

Trace element geochemistry of magnetite from Mabianshan skarn iron deposit in the Lu-Zong volcanic basin, Eastern China

The composition of host rocks is essential in determining the composition of hydrothermal magnetite formed via fluid-rock interactions in skarn deposits. The HuangLong ore field in the Luzong volcanic basin, Eastern China, hosts several stratabound iron (Fe) skarn deposits, including Mabianshan and Longqiao. In this paper, we analyse the composition of different lithologies of carbonate strata and trace element concentrations in magnetite from Mabianshan, which has complex lithology carbonate strata, and compare it with magnetite from Longqiao, which has uniform lithology carbonate strata. The objective is to investigate the influence of lithology variation on magnetite trace elements and enhance the indicative significance of magnetite trace elements in prospecting and exploration. Our results demonstrate that the lithology of ore-bearing carbonate strata varies greatly due to inversion and different degrees of denudation in the ore field, resulting in variations of Al, Si, Mg, Mn, and Ca in the protolith across different areas. The alteration mineral assemblage of the Mabianshan deposit primarily included epidote, chlorite, and magnetite, while only a few diopside-magnetite relatively high-temperature assemblages developed in the southeastern part of the deposit. Moreover, higher concentrations of Ti and V in magnetite samples from the southeastern area of the deposit suggest that the heat sources related to Fe mineralization may be located there. Compared with the regular spatial variations of Mg, Mn, Al, and Si in the magnetite from Longqiao, the magnetite from Mabianshan does not show evident spatial variations due to the complex lithology of the magnetite protolith in different regions. The protolith lithology of magnetite from Longqiao is relatively stable, mainly dolomitic limestone. However, the protolith lithology of magnetite from Mabianshan is complex and includes dolomitic marlstone, dolomitic limestone, dolomite, and Fe-Mn bearing dolomite, resulting in a significant increase of Si, Al, Mg, and Mn in magnetite. Therefore, it is difficult to effectively trace the temporal-spatial evolution of the hydrothermal fluids using these elements in magnetite. Special attention should be paid to the uniformity of the protolith lithology of the ore when using these elements in magnetite to trace the fluid source.

Effects of Al and Ti on microstructure, mechanical properties and wear resistance of TiXCrFe2Ni2 alloys

Individual effects of Al and Ti on microstructure, mechanical and tribological properties of CrFe2Ni2 alloy were investigated. Al addition changed the alloy from a FCC phase to a mixture of FCC, A2 and B2 phases, increasing the mechanical strength at slight expense of ductility. While Ti made the alloy composed of the FCC phase with L12-Ni3Ti nanoparticles, DO24η-Ni3Ti and C14 Fe2Ti phases. Higher Ti contents caused a brittle Chi phase. The hard phases considerably hardened the Ti-containing alloys but markedly decreased the ductility of the alloys. Al appeared to be unfavorable for the wear resistance possibly due to inadequate balance between strength and weakened ductility, while Ti enhanced the wear resistance thanks to the hard phases. The detailed characterization would help guide tuning relevant HEAs for optimal tribological applications.

TOXIC ELEMENTS IN GROUNDWATER IN THE NORTHERN REGIONS OF THE OB-ZAYSAN FOLDED REGION

Link for citation: Maksimova A.A., Chernykh A.V., Novikov D.A., Dultsev F.F., Derkachev A.S., Sukhorukova A.F., Nikitenkov A.N., Khvachshevskaya A.A. Toxic elements in groundwater in the northern regions of the Ob-Zaysan folded region. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 5, рр.17-26. In Rus. The relevance of this research lies in the need to study the distribution of elements of the first hazard class, uranium and thorium in the groundwater of the Ob-Zaisan folded area. Objective: to establish the characteristics of the hydrogeochemical background and to study the distribution of highly toxic chemical elements in the waters of the drinking water supply of the population. Methods. Rapidly changing parameters were determined using a field hydrogeochemical laboratory and field equipment Hanna HI98195 – a multi-parameter pH/ORP/conductivity meter, Hanna HI98198 – an oximeter. The measurement of radon activity in groundwater was carried out using the Alfarad plus complex. Laboratory studies of the chemical composition by means of titration, ion chromatography, mass spectrometry with inductively coupled plasma were carried out at the Research Laboratory of Hydrogeochemistry at the School of Earth Sciences and Engineering of the Tomsk Polytechnic University. The assessment of the toxicological characteristics of waters was carried out using the current regulatory documents: SanPiN 2.1.3684-21, SS R 58573-2019 and the recommendations of the World Health Organization. The hydrogeochemical background was calculated using the Statistica 8.0 software package (StatSoft. Inc.). To determine the extent of element concentrating in natural waters, the coefficients of concentration and water migration (according to A.I. Perelman) were calculated. Cumulative curves are calculated by the formula: Pc=Ri/(N+1). Results. The studied waters are HCO3 Mg-Ca and HCO3 Na-Mg-Ca composition with total mineralization varying from 203 to 1568 mg/dm3. The geochemical parameters of the environment are both reducing and oxidizing with Eh –331,6 – +438,5 mV, pH 6,6–8,3 with the content of O2disol. 0,29–10,72 mg/dm3. The authors revealed relatively high concentrations of Ti – up to 0,04 mg/dm3, V – up to 0,03 mg/dm3, Fe – up to 93,9 mg/dm3, Zn – up to 0,38 mg/dm3, As – up to 0,27 mg/dm3, Zr – up to 0,018 mg/dm3, Sb – up to 0,016 mg/dm3, Ba – up to 0,51 mg/dm3, W – up to 0,005 mg/dm3, Hg – up to 0,0002 mg/dm3, Pb – up to 0,057 mg/dm3, U – up to 0,34 mg/dm3, which is probably related to the composition of host rocks and the spread of industrial enterprises developed in the study area. The elements of the first hazard class, as well as uranium and thorium, were studied in the work. It was found that 20 % of the studied samples were higher than the background value for beryllium, as well as for thallium and arsenic, 26 % – for thorium, and 19 % – for uranium.

A damage-tolerant Ti-rich multiphase metallic-glass composite with hierarchically heterogeneous architecture

Lightweight materials with good combinations of properties, such as high strength, ductility and damage tolerance, are highly desirable in engineering applications; nevertheless, it remains a challenge to “defeat” the generally exclusive relationships between different properties for structural materials. One viable means is to construct complicated architectures in materials. Here, we employ a lightweight Ti-based metallic glass (MG) and pure Ti as constituents and assemble them into a hierarchically-structured multiphase composite with tailored heterogeneity. The Ti-rich multiphase composite exhibits a relatively low density of 4.95 g∙cm−3 owing to its high Ti content and a high strength of ∼1408 MPa derived primarily from the MG phase. The hierarchical architecture with tailored heterogeneity promotes the formation of abundant shear bands and microcracks in MG, yet inhibits their extension to avoid catastrophic fracture, thereby endowing the Ti-rich multiphase composite with a remarkable tensile ductility of ∼7.1% which is nearly two times that of the MG composite having similar phase constitution but a uniform structure. Moreover, this architecture causes crack-tip blunting by promoting plastic deformation, together with crack bifurcation and microcracking ahead of the crack tip, which bestows a high (notched) fracture toughness of ∼109 MPa∙m1/2 which is around three times that of its counterpart. This study is intended to give insight for the architectural design of new materials by offering a viable means for their architectural construction to achieve good combinations of properties.

Effective recovery of Ti as anatase nanoparticles from waste red mud via a coupled leaching and boiling route.

Red mud (RM) a solid waste generated by the bauxite smelting industry, is a rich source of metal resources, especially Ti, and its recycling can bring significant environmental and economic benefits. In this study, precious metal Ti was efficiently recovered from red mud using a coupled acid leaching and boiling route for the effective separation of low-value metals. The red mud which contained mainly 10.69% Si, 12.1% Al, 15.2% Ca, 10.99% Fe, and 4.37% Ti, was recovered in five steps. First, a nitric acid solution was used to leach the metals in multiple stages, resulting in an acidic leach solution with high concentrations of Fe, Al, Ti, and Ca ions 2.7g/L, 4.7g/L, 5.43g/L, and 1.8g/L, respectively. Then, a small amount of sucrose was added as a catalyst to recover Ti from the leach solution under hydrothermal conditions, resulting in the targeted recovery of 98.6% of Ti in the form of high-purity anatase while Fe, Al, and Ca remained in the solution. Next, the Fe in solution was separated as hematite products at a temperature of 110°C and a reaction time of 4h. Similarly, the Al in the solution was separated and precipitated as boehmite by heating it at 260°C for a reaction time of 20h. Finally, the remaining Ca in solution was recovered by simple pH regulation. Economic accounting assessment showed that the method yields $101.06 for 1t of red mud treated, excluding labor costs. This study provides a novel approach to recover precious metals from metal wastes through the whole process resource recovery of solid waste red mud.

BCC/B2 structure and dislocation strengthening behavior in high Ti content TiAlVCrNb high-entropy alloys

In this work, we designed and successfully prepared new lightweight refractory high entropy alloys (HEAs) Ti75Al10V5Cr5Nb5, Ti67Al12V7Cr7Nb7 and Ti55Al15V10Cr10Nb10 with BCC/B2 structure. It was found that TiAlVCrNb high-entropy alloy plasticity is mainly generated by dislocation aggregation at grain boundaries and intracrystalline, and strength is provided by solid solution strengthening and BCC/B2 structure. The results show that the Ti75Al10V5Cr5Nb5 high-entropy alloy have a great room temperature compressive plasticity of> 50% and a tensile elongation after break of 6% with the preferential orientation (200) and more dislocations, resulting in good plasticity. The Ti55Al15V10Cr10Nb10 high-entropy alloy has a room temperature compressive a yield strength of 1465 MPa and a compressive strength of 1835 MPa, as the Ti content decreases, the effect of solid solution strengthening will decrease, but the B2 structure content increases so that the mixed structure formed by BCC/B2 structure provides more strengthening. The light refractory high entropy alloy can control the Ti content to change the BCC/B2 structure content to obtain higher strength and plasticity.

Application of principal component analysis to µ-PIXE data in lapis lazuli provenance studies

The application of multivariate analysis is extremely useful when dealing with large datasets and can be applied also in provenance studies. In this work, Principal Component Analysis (PCA) was applied for the first time to the study of the provenance of lapis lazuli rocks used for glyptic art in ancient times, on a database including four different sources in Afghanistan, Tajikistan, Siberia and Myanmar. Results of the application of PCA on µ-PIXE data collected in mineralogical phases contained in lapis lazuli rocks, in particular diopside and pyrite, confirmed the role of some trace element contents as characteristics for different provenances, i.e. as provenance markers. As an additional important result, PCA seems to strengthen the role of previously found weaker markers (i.e. trace elements not sufficient alone to distinguish univocally among provenances) such as, for example, the coexistence of high Ti, V, Cr and Mn concentrations in diopside in Afghan lapis lazuli. This can be relevant when other discriminant phases like pyrite cannot be found in the sample or are not suitable for analysis.Moreover, for geological purposes and to try to distinguish among different quarries inside an extraction area, a study on intra-provenance variability was carried out on diopside data for Myanmar and Siberian samples. The separation into three groups for Myanmar samples, previously identified by means of minero-petrographic and elemental analysis, is confirmed and a partial differentiation was identified also for samples coming from the two Siberian areas of Sludyanka River and Malaya Bistraya River.

Effect of the Ti/Ta ratio on the feasibility of porous Ti25+x-Nb25-Zr25-Ta25-x (X= 0, 5, and 10) alloys for biomedical applications

Non-toxic biomedical HEAs by powder metallurgy methods have been scarcely studied despite their promising mechanical and biological behaviors. This work studied the microstructural, mechanical, electrochemical, and ion release effects of the Ti/Ta ratio on three porous Ti–Nb–Zr–Ta (TNZT) alloys. The microstructure of the TNZT alloys consisted of semi-equiaxed and micrometric BCC-phases (matrix) with lower contents of HCP phase. Elastic moduli (82–91 GPa), hardness (373–430 HVN), ultimate bending (225–475 MPa), and tensile (119–256 MPa) strength, electrochemical corrosion (4.5–9.6 μm year−1), and ion release (toxicity, 0.9–1.1 μm year−1) were within acceptable limits for implant biomaterials. Increasing the Ti content (and decreasing Ta) was advantageous for improving mechanical strengthening and reducing the elastic modulus. The medium value of elastic modulus may be beneficial to reduce the mechanical mismatch between the implant and the organic tissue. However, the corrosion rate and metallic ion release increased as a function of the Ti content. Besides, the alloy with the lowest Ti content (highest Ta content) showed local corrosion. Based on the above, the porous TNZT alloys with medium and highest Ti contents (30 and 35 wt%) were demonstrated as promising candidates for biomedical implant applications.

Origin of ironstones of the Udokan Cu deposit (Siberia, Russia): A key study using SEM and LA-ICP-MS

Iron is an important element involved in the formation of sedimentary-hosted copper deposits. Its accumulation in sedimentary basins and subsequent redistribution ultimately affect the position of copper mineralization. The Udokan copperstone deposit contains considerable Fe reserves as magnetite and hematite. The Fe oxides form disseminated and layered aggregates in both Cu-bearing horizons and host metasandstones. The layered aggregates of Fe oxides contain detrital (zircon, chromite and apatite) and authigenic (a Th silicate) components. The ironstones bear chemical features both of clastic and chemical sediments. The enrichment of ironstones in Cr, Zr and Hf is due to the presence of relics of detrital chromite and zircon. The presence of rare earth elements (REEs), U, and Th in composition of ironstones is a result of chemical precipitation/sorption.According to the LA-ICP-MS data, Al, Mg, and V are the most significant trace elements of magnetite, whereas Ti and V are hosted in hematite. The extremely high Ti, Cr and Cu contents of magnetite are associated with inclusions of minerals of these elements. In hematite, the high Ti contents are due to inclusions of rutile or titanite. The correlations between the trace elements in Fe oxides reflect the mineral assemblages characteristic of two stages of sediment transformation: (i) earlier diagenetic with the formation of a hematite-rutile assemblage and early Cu sulphides and Th and REE mineralization and (ii) later metamorphic, which is related to the formation of magnetite metacrysts and recrystallization of Cu sulphides.The Fe-rich sediments formed at a river–sea geochemical barrier as a result both of sedimentation of clastic Fe oxides and flocculation of dissolved iron. The maturation of gel and lithification of sediments were accompanied by desorption of metals that accumulated in the ferruginous sediments. Some of them formed the authigenic phases (like Th), while others were isomorphically incorporated in other authigenic minerals (e.g., Nb, Ta and Sn in rutile).

Influence of Ti elements on the evolution of microstructure, mechanical properties and thermal stability of Al-Cu alloy

This paper compares the evolution patterns of microstructure, mechanical properties and heat exposure response behavior of alloys with low (0.15 wt%) and high Ti (0.75 wt%) content prepared by conventional casting processes. The results show that the alloy with high Ti content has slightly finer grains and no improvement in the thermal stability of the θ' precipitates compared to the low Ti content alloy. Moreover, after exposing the as-aged alloy to 300 ℃ for 100 h, the high Ti content alloy exhibits higher tensile strength at room temperature, attributing to the reinforcement effect of Al3Ti nanoparticles. The results of geometric phase analysis and transmission electron microscope images reveal that the compressive strain field occurring on the Al3Ti/matrix interface can validly block the movement of dislocations, thus hardening the alloy. Finally, the classical nucleation theory was referred to explain the difference on the thermal exposure response behavior of two alloys with various Ti contents at 300 ℃. With increasing thermal exposure time, the stiffening role of the Al3Ti nanoparticles gradually overcomes the softening behavior caused by the destabilization of coarsened θ' and becomes the dominant factor governing the mechanical properties of the alloy. The theoretical analysis is consistent with the microstructure and the thermal exposure hardness response behavior.

Ultrahigh-Temperature Mafic Granulites in the Rauer Group, East Antarctica: Evidence from Conventional Thermobarometry, Phase Equilibria Modeling, and Rare Earth Element Thermometry

AbstractThe Rauer Group in East Antarctica is a typical high- to ultrahigh-temperature (HT–UHT) granulite-facies terrane. As UHT metamorphism has been recognized only in Mg–Al-rich pelitic granulites from the Mather Paragneiss, the regional extent of UHT metamorphism remains uncertain, which has hindered our understanding of the genesis and tectonic setting of UHT metamorphism in the Rauer Group. In this study, representative samples of mafic granulite were selected from Archean crustal domains to constrain the peak metamorphic conditions and P–T path and to assess the regional extent of UHT metamorphism in the Rauer Group. Integrated results from mineral reaction histories, thermobarometry, and phase equilibria modeling indicate a multi-stage clockwise P–T evolution for mafic granulites involving pre-peak compression, heating to UHT peak conditions, post-peak near-isothermal decompression under UHT conditions, and subsequent decompressional cooling. The pre-peak prograde history is based mainly on the inclusion assemblage of clinopyroxene + plagioclase + amphibole + quartz + ilmenite ± orthopyroxene ± k-feldspar within porphyroblastic garnet and clinopyroxene and records the transformation from a quartz-present to quartz-absent system. The UHT peak conditions are well constrained at 930°C–1030°C and 10.6–12.8 kbar on the basis of the stability field of the observed peak assemblage of (orthopyroxene–quartz)-free garnet + clinopyroxene + plagioclase + amphibole + ilmenite + melt, as well as measured mineral compositions, including the high Ti content in amphibole (Ti = 0.38–0.42 p.f.u.), the anorthite content of coarse-grained plagioclase cores (XAn = 0.35–0.42), and the grossular content in garnet (XGrs = ~0.21) in P–T pseudosections. The peak T conditions are consistent with thermometric estimates in the range of 930°C–1030°C obtained from garnet–clinopyroxene, garnet–orthopyroxene, and Ti-in-amphibole thermometers, and are slightly lower than estimates (1020°C–1120°C) obtained from thermometers based on rare earth elements. The near-isothermal decompression under UHT conditions can be divided into two stages. The early stage is recorded by coronae of orthopyroxene + plagioclase around clinopyroxene and core–mantle/rim anorthite-increasing zoning in plagioclase. The late stage is identified from symplectites of orthopyroxene + plagioclase ± amphibole around porphyroblastic garnet, which were formed at the expense of garnet at 915°C–950°C and 7.6–8.2 kbar as inferred from the amphibole–plagioclase thermometer. The subsequent decompressional cooling to fluid-absent solidus conditions (~875°C and ~6.5 kbar) is indicated by the growth of biotite, which formed at the expense of symplectic minerals, reflecting back-reaction of melt with symplectite minerals. The peak UHT metamorphic conditions and clockwise P–T path of the studied mafic granulites from the Archean crustal domains are similar to those of Mg–Al-rich pelitic UHT granulites from the Mather Paragneiss. The UHT conditions recorded by the mafic granulites, combined with previously identified isolated UHT localities in the Rauer Group, imply that UHT metamorphism in the Rauer Group occurred over a much wider region than previously thought and probably extends over the whole Archean crustal domain. Our findings have general significance in understanding the regional extent of other UHT granulite-facies terranes worldwide.

A peridotite source for strongly alkalic ultrabasic HIMU lavas of the Oslo Rift, Norway

High alkali (Na2O + K2O) low SiO2 lavas generally have highly fractionated trace element compositions and their petrogenesis is debated. Both pyroxene-rich (pyroxenite) and olivine-rich (peridotite) mantle sources have been proposed for such lavas. HIMU (high 238U/204Pb) lavas usually have such compositions and are often interpreted as being derived from garnet-pyroxenite (eclogite) residue of subducted recycled oceanic crust, possibly including a carbonate component. In some cases, an origin from a garnet peridotite source has also been considered.We present new Mg, Pb, Nd, and Sr isotopic data and elemental data for alkalic ultrabasic lavas (melilitites, nephelinites) from the Oslo Rift, Norway. The magmatic province of the Permo-Carboniferous Oslo Rift is interpreted as part of the much larger Skagerrak-Centered Large Igneous Province (SCLIP) which may be related to a mantle plume source originating from the African Large Low Shear Velocity Province (LLSVP) at the core-mantle boundary. The range of δ26Mg is narrow (−0.32 to −0.28) and is similar to typical mantle values, and therefore is inconsistent with a carbonated source as has been suggested for other similar lavas. The 206Pb/204Pb values of all the lavas are high, which identifies them as HIMU lavas. The εNd of +1 to +2 are substantially lower than for typical HIMU lavas, and in the εNd-εSr diagram they plot on the LoNd array between HIMU and EMI. The lavas are more like archetypal kimberlites (formerly, Group I kimberlites), as these also have εNd slightly higher than the chondritic value and Pb isotopes consistent with a HIMU source. The REE patterns of the lavas are also almost as fractionated as in Group I kimberlites.We used major and trace elements to infer the primary magma composition of these lavas. This primary magma composition is compared with experimental melts of both carbonated peridotite and carbonated eclogite source compositions and shows that their major element compositions are only consistent with either a very high degree of melting of eclogite or a very low degree melting of garnet peridotite. The strongly fractionated REE patterns of the lavas can only be made by low-degree melting of either eclogite or garnet peridotite, which therefore effectively rules out eclogite as a major component of the mantle source of these lavas. Further trace element modeling points to a mantle source composition with >97% garnet peridotite that was lightly carbonated (<0.5 wt% CO2) and melted to a very low degree (∼0.4%) to produce these lavas. The modeled source trace element pattern was constrained by the Nd, Sr, and Pb isotopic compositions of the lavas. The measured high Ti contents of these lavas (3.8–6 wt%) are quantitatively shown to be the result of enrichment by both partial melting and fractional crystallization, using experimentally determined DTi for melting of this type of source. We also show that a low degree of melting of a slightly carbonated source is sufficient to result in the likely very high CO2 content (10–15 wt%) of the primary magma.The rather uniform Pb isotope composition of HIMU magmas suggests that the HIMU source is rather uniform in composition, but the Pb isotope composition requires this source to form late in Earth's history. The similarity of these lavas and kimberlites suggests a very deep source, possibly in the LLSVP that gave origin to the SCLIP. This means that LLSVPs do not represent some primordial layer around the core that escaped homogenization of the mantle by the Moon-forming giant impact. Instead, this layer must have formed late in Earth's history. The constraint that this source contains <3% of garnet-pyroxenite (eclogite) residue of recycled basaltic oceanic crust shows that this layer is primarily not a subducted slab graveyard. The process by which the LLSVPs formed, however, remains obscure.

Mechanisms and conditions of Ti and Cr incorporation in mantle phlogopite: the results of atomistic simulation

Modeling of eight mechanisms for the incorporation of Ti4+ and Cr3+ impurity components into phlogopite was carried out by a semi-empirical method using the GULP (General Utility Lattice Program) software. The calculation of thermodynamic mixing properties in the range of 1–7 GPa and 373–1573 K and the analysis of the structure geometry for the simulated solid solutions provided the following energy-preferred schemes of isomorphic substitution: VI(Mg2+) + 2IV(Si4+) = VI(Ti4+) + 2IV(Al3+) and VI(Mg2+) + 2IV(Al3+) = VI(□) + 2IV(Ti4+), VI(Mg2+) + IV(Si4+) = VI(Cr3+) + IV(Al3+), and 3VI(Mg2+) = VI(Al3+) + VI(Cr3+) + VI(□). It is shown the scheme 2VI(Mg2+) = VI(Ti4+) + VI(□) illustrating entrance of Ti with the formation of a vacancy is realized in the case of microconcentrations of Ti only. Accumulation of high-Ti contents associates with the formation of a vacancy in the octahedral site. This provides incorporation of Ti via the schemes VI(Mg2+) + 2IV(Al3+) = VI(□) + 2IV(Ti4+) and (Mg, Fe2+) + 2OH− = Ti4+ + 2O2− only. It is shown that incorporation of high-Cr concentrations (> 5.5 wt % Cr2O3) is accompanied by an increase in the number of vacancies in the octahedral site with an increase in the proportion of the dioctahedral component K(Al, Cr, □)2AlSi3O10(OH)2.

Effect of the Synthesis Route on the Microstructure of HfxTi(1−x)NbVZr Refractory High-Entropy Alloys

In the present work, the effects of (i) Ti replacement by Hf and (ii) the synthesis method on microstructure and crystal structure evolution in the high-entropy alloy HfxTi(1−x)NbVZr are reported. The results of scanning electron microscopy and X-ray diffraction analysis of alloys prepared by both arc-melting and induction-melting are compared with theoretical thermodynamic calculations using the CALPHAD approach. The non-equilibrium thermodynamic calculations agree well with the experimental observations for the arc-melted alloys: a mixture of body-centered cubic (BCC) and cubic C15 Laves phases occurs for low-Ti-concentration alloys and a single BCC phase is obtained for high-Ti alloys. The agreement is not as good when using the induction-melting method: equilibrium solidification calculations predict that the most stable state is a phase mixture of BCC, hexagonal close-packed, and a cubic C15 Laves phase, while experimentally only one BCC and one hexagonal C14 Laves phase were found. The estimation of the exact cooling rate and the lack of a thermodynamic database can explain the difference. In addition, for both methods, the thermodynamic calculation confirms that for a high Ti concentration, the BCC phase is stable, whereas phase separation is enhanced with a higher Hf concentration.

GEOCHEMICAL AND MAGNETIC CHARACTERISTICS OF PLACER GOLD DEPOSITS FROM CENTRAL KALIMANTAN, INDONESIA

Massive tailings have resulted from the extensive use of placer deposits in Central Kalimantan, Indonesia, by artisanal and small-scale gold mining (ASGM) activities. Recently, the placer deposits and their tailings have been exploited for heavy minerals. In this study, geochemical and magnetic analyses were carried out on these deposits to identify the prospect of REE (rare earth element) exploration in the materials already collected by ASGM activities. Samples were collected from ten different locations. For each location, two different fractions were prepared for analyses, i.e. the heavy mineral (HM) fraction and the panned (M60) fraction. All HM and M60 samples were subjected to magnetic susceptibility measurements, but only representative samples were subjected to x-ray fluorescence (XRF) measurements (for Si, Ti, Fe, Zr, and Al) and to inductively coupled plasma-emission spectroscopy (ICP-OES) measurements (for Eu, Tb, Dy, and Sc). The results showed that the concentrations of major elements (Ti, Fe, Zr, and Al) vary significantly from deposits along one river to another, while the concentration of Si is rather similar. Compared to M60 samples, the HM samples have higher concentrations of Ti, Fe, Zr, Al, and Sc, implying that the sluice-box separation enhances the concentration of valuable minerals. Magnetic susceptibility is found to be correlated with Fe and Sc concentrations, confirming the potential use of magnetic measurements as a complementary tool for Fe and Sc exploitation in placer deposits. It is believed that both the source rocks and the sedimentary settings of these deposits determine whether certain elements (Sc, Fe, and Zr) are present or absent in Central Kalimantan placer deposits. The prospect of exploring and exploiting Sc in these placer deposits might augment the ASGM activities in Central Kalimantan.

Synthesis of titanosilicate nanoparticles with high titanium content from a silsesquioxane-based precursor for a model epoxidation reaction.

In conventional hydrothermal synthesis of porous titanosilicate materials, undesired aggregation of TiO2 species during the synthesis limits the content of active four-coordinated Ti to an Si/Ti ratio of about 40. Aiming to increase the content of active four-coordinated Ti species, we report a bottom-up synthesis of titanosilicate nanoparticles using a Ti-incorporated cubic silsesquioxane cage as a precursor, which allowed incorporating a larger number of four-coordinated Ti species in the silica matrix to reach an Si/Ti ratio of 19. Even at this relatively high Ti concentration, the catalytic activity in the epoxidation of cyclohexene over the titanosilicate nanoparticles was comparable to that of a conventional reference Ti catalyst, Ti-MCM-41, with an Si/Ti ratio of 60. The activity per Ti site was not affected by the Ti content in the nanoparticles, suggesting that well dispersed and stabilized Ti species were the active sites.

Multifunctional amorphous FeCoNiTixSi high-entropy alloys with excellent electromagnetic-wave absorption performances.

Amorphous high-entropy alloys (HEAs) as electromagnetic-wave absorbing materials have been rarely reported. In this work, amorphous FeCoNiTixSi HEAs were synthesized by introducing a high content of large-atom Ti using the high-energy ball-milling technique. This amorphous structure could improve the saturated magnetization and coercivity of HEAs, but slightly degraded the mechanical and oxidation resistance properties. In terms of electromagnetic properties, FeCoNiTi0.01Si and FeCoNiTiSi exhibit excellent electromagnetic-wave absorption performances, with significant absorptions of -68.4 dB at 6.14 GHz and -63.4 dB at 9.12 GHz, corresponding to bandwidths of 5.15 GHz (1.69 mm) and 3.64 GHz (1.43 mm), respectively. Overall, the prepared FeCoNiTixSi HEAs exhibited superior comprehensive performances compared to other HEA absorption materials. This work provided a novel strategy for the development of new electromagnetic-wave absorption materials with low weight, high absorption efficiency, and resistance to harsh environments.

Electronic transport properties of Ti-supersaturated Si processed by rapid thermal annealing or pulsed-laser melting

In the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work.