Lower Solidus Temperature Research Articles

Friction Stir Welding of Various Aluminium Alloys to Titanium

Aluminium and titanium are currently in demand as lightweight materials. However, their combination is challenging due to their significantly different thermo-mechanical properties. Here, solid-state joining processes such as Friction Stir Welding open up new opportunities. Within this study, four commercial aluminium alloys (AA2024, AA5754, AA6056 and AA7050) were welded to Ti6Al4V. The results show a direct relationship between the solidus temperature of the aluminium alloys, the process temperature, energy input and resulting lap-shear strength. Regardless of the process parameters, AA5754 and AA6056 with higher solidus temperatures (600 °C and 555 °C) show superior bonding strength compared to AA2024 and AA7050, having a lower solidus temperature of 500 °C and 490 °C, respectively. Therefore, it is assumed that the maximum process temperature, proportional to the solidus temperature, has a major influence on the bonding. This, conversely, would imply that there is a physical limitation in the achievable joint strength between aluminium and titanium alloys as the required process temperature would exceed the solidus temperature of certain alloys. This assumption is verified for AA7050 by systematic variation of the rotation speed and therefore process temperature.

Laser powder bed fusion of crack-susceptible stainless maraging steel undergoing solid-state phase transformations

For alloys that experience solid-state phase transformation upon cooling, the absence of as-solidified chemical segregation information makes the elimination of hot cracking challenging. One such material is the hot-crack-susceptible high-strength maraging steel C465. Here, we resolve its hot cracking problem under the laser powder bed fusion process through the addition of titanium nitride (TiN) particles. During solidification, TiN promotes grain refinement and reduces the formation of liquid films with low solidus temperatures. Under cooling, the partial dissolution of TiN lowers the martensite start temperature and yields more retained austenite. Upon subsequent annealing, the dissolved titanium slows down the austenite reversion kinetics, while the dissolved nitrogen improves the yield strength. Materials under tensile deformation follow a three-stage work-hardening behavior, indicative of strain-induced martensitic transformations. This work highlights that besides the nucleant's grain refinement potency, the effect of its partial dissolution during processing needs to be critically examined, when addressing the hot cracking problem for alloys prone to phase transformations.

Microstructure and Mechanical Properties of AA 6082/AISI 304 Joints Brazed Using Al-Ge-Si Filler Metal

Joining aluminum alloys with stainless steel is of great importance in many industrial sectors. Due to the low solidus temperatures of high-strength aluminum alloys, brazing with commercially available filler metals is not possible. Al-Ge-Si filler metals with a lower melting temperature of about 490 °C allow these alloys to be joined. They are manufactured in the form of foil via ultrafast solidification. AA 6082/AISI 304 joints are produced via induction brazing and vacuum furnace brazing. In this study, the tensile shear strength and the fatigue behavior of joints are investigated. Joints produced via induction brazing reached a maximum joining strength of 53 MPa, while vacuum-brazed joints achieved a maximum of 20 MPa. The fracture occurs in the reaction zone, especially inside the Al7Fe2(Si,Cr) intermetallic layer. The results of the fatigue tests show that the joints produced via induction brazing achieved 1 × 107 cycles at a stress amplitude of 7 MPa. Vacuum-brazed joints reached this at a stress amplitude of 3 MPa. All fatigue-tested samples fail in the reaction zone. The high hardness and growth of the SiGe solid solution and the Al7Fe2(Si,Cr) intermetallic layer had a major influence on the joining strength and fatigue behavior of AA 6082/AISI 304-brazed joints.

Formation of magnetite-(apatite) systems by crystallizing ultrabasic iron-rich melts and slag separation

Magnetite-(apatite) ore deposits are interpreted as being formed by the crystallization of iron-rich ultrabasic melts, dominantly generated by the interaction of silicate melts with oxidized P-F-SO4-bearing sedimentary rocks. This hypothesis is supported by geologic evidence, experimental studies, numerical modeling, stable and radiogenic isotope geochemistry, mineralogy, and melt- and mineral-inclusion data. Assimilation of crustal rocks during ascent promotes separation from a silicate magma of Fe-rich, Si-Al-poor melts with low solidus temperatures and viscosities, allowing coalescence, migration, and emplacement at deep to subaerial crustal environments. When the iron-rich melt attains neutral buoyancy, fractional crystallization leads to melt immiscibility similar to that observed in industrial blast furnaces, which promotes separation of massive magnetite ore overlain by different types of “slag” containing actinolite or diopside ± phosphates ± magnetite ± feldspar ± anhydrite ± scapolite, commonly enriched in high field strength elements. The mineralogy and morphology of this iron-depleted cap strongly depend on the depth of emplacement and composition of the iron-rich magma. Most of these systems exhibit high oxygen fugacity, which inhibits the precipitation of significant sulfide mineralization. The initially high fO2 of these systems also promotes the formation of low-Ti (< 1 wt%) magnetite: Ti acts as an incompatible component and is enriched in the iron-poor caps and in the hydrothermal aureole. High fluid-phase pressures produced during massive crystallization of magnetite from the melt further facilitate the exsolution of magmatic-hydrothermal fluids responsible for the formation of aureoles of alkali-calcic-iron alteration with hydrothermal replacement-style iron mineralization. On the whole, these systems are dramatically different from the magmatic-hydrothermal systems related to intermediate to felsic igneous rocks; they are more akin to carbonatite and other ultramafic rocks.

Effect of processing route on microstructure and tensile properties of hot isostatic pressed 30CrMnSiNi2A steel: Comparison of prealloy and master alloy routes

The prior particle boundaries (PPBs) are non-negligible powder metallurgy defect, which seriously weaken the mechanical properties of hot isostatic pressed (HIPed) steels. In present study, the master alloy route is proposed to improve the PPBs in HIPed 30CrMnSiNi2A steel, and the Fe-4.40Cr-4.80Mn-4.60Si-6.80Ni-1.00Mo-0.40V-1.12C master alloy system with low solidus temperature and wide solid-liquid temperature interval is designed. The microstructure, tensile properties and fracture behavior of HIPed compacts prepared by prealloy and master alloy routes are systematically compared. The results show that the structure in prealloyed sample is granular bainite (GB); and substantial Si oxides distributed along particle boundaries constitute serious PPBs. The yield strength (YS), ultimate tensile strength (UTS) and total elongation (TE) of the sample are 723 ± 10 MPa, 1238 ± 16 MPa and 12.3 ± 0.4%, respectively. In master alloy route, the formation of local liquid disrupts the distribution of Si oxides along particle boundaries and promotes the coarsening of oxides, which results in dispersed distribution of oxides and significant reduction in oxide density. In addition, since the structural uniformity depends on element diffusion, a relatively uniform structure is obtained through the optimization of powder size. The structure of optimized sample mainly consists of GB and martensite; and good tensile properties with YS of 798 ± 7 MPa, UTS of 1310 ± 8 MPa and TE of 15.3 ± 0.6% are obtained. The higher tensile properties are mainly due to the improvement of PPBs, which avoids the initiation of microcracks along PPBs and further avoids premature failure of material.

Analysis of liquid–solid interface bonding behaviour of 7075 aluminium alloy/SiCp reinforced aluminium base alloy

The introduction of heterogeneous elements and the presence of the oxide layer on the surface of aluminum alloy usually play a negative role in the interfacial bonding of Al/Al bimetallic composites. To solve these two key problems of interfacial bonding of bimetallic composites. This work proposes to composite SiCp/7075(solid)-7075 alloy(liquid). The main alloying element Zn of 7075 alloy is selected to perform hot dip treatment on SiCp/7075(solid) to reduce the influence of the oxide layer on the surface of the aluminum alloy and the introduction of heterogeneous elements. Al/Al bimetallic composites were prepared by using a hot-dip/non-hot-dip zinc + liquid–solid composite casting process. The bimetallic composite interfacial bonding of SiCp/7075–7075 matrix alloy was studied. The results revealed that an oxide layer existed at the interface of the bimetallic composite upon preheating at 400–475 °C and hot dipping at 400–425 °C. With an increase in the hot-dip temperature, the interface oxide layer disappeared because of the combined effect of thermal expansion deformation, lower solidus temperature of the zinc-rich layer, and volume expansion of the solid–liquid phase transition. Metallurgically bonded interfaces were obtained at the hot-dip temperatures of 450 and 475 °C. The fracture location was on the SiCp/7075 Al matrix composite side, showing that this composite's interfacial bond strength was higher than that of the SiCp/7075 Al matrix composites. The results of this study provide a new idea for the preparation of lightweight wear-resistant Al/Al bimetallic composites by liquid-solid composite casting.

Interface analyses and mechanical properties of stainless steel/nickel alloy induced by multi-metal laser additive manufacturing

Multi-metal laser additive manufacturing is an emerging technology to fabricate complex components with excellent comprehensive performances. In this study, stainless steel/nickel alloy multi-metal has been induced by laser direct energy deposition. The microstructural evolution, compositional segregation, and crack formation at the interface of the two metals have been investigated by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, electron backscattering diffraction, and microhardness test. The results show that the microstructure morphologies are predominated by equiaxed dendrite and columnar dendrite for stainless steel and nickel alloy, respectively. The Marangoni convection effect promotes the serious compositional segregation of stainless steel on the nickel alloy side and serious segregation of 316L SS occurs locally in near the IN 718 side of the interdiffusion region. During the cooling process, the segregated stainless steel has a lower solidification temperature than the surrounding nickel alloy. The compositional segregation and different physical properties of the two metals are the main causes for the ductility dip cracking near the interface. During tensile deformation, the multi-metal fractures on the stainless steel side, and the ultimate tensile strength and elongation of the multi-metal have achieve 524 MPa and 24.8 %, respectively.

Electron Beam Brazing of Titanium and Stainless Steel Dissimilar Joints with Ag-Based Filler

In this work, electron beam was used for butt brazing of austenitic stainless steel with grade 2 titanium. Due to its low solidus temperature and high silver content, AWS BAg-21 filler containing Ag, Cu, Sn and Ni was selected. The joints were brazed with a defocused oscillating beam using offset. The resulting brazed joints were subjected to static tensile testing, light microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) analysis and hardness tests. By using appropriate parameters it was possible to reduce the phenomenon of diffusion of titanium atoms into the joint, which improved the properties of the obtained joints. The maximum tensile strength obtained was 244.2 MPa.

Microstructure and mechanical properties of Cu/Al joints brazed using (Cu, Ni, Zr, Er)-modified Al—Si filler alloys

To design a promising Al—Si filler alloy with a relatively low melting-point, good strength and plasticity for the Cu/Al joint, the Cu, Ni, Zr and Er elements were innovatively added to modify the traditional Al—Si eutectic filler. The microstructure and mechanical properties of filler alloys and Cu/Al joints were investigated. The result indicated that the Al—Si—Ni—Cu filler alloys mainly consisted of Al(s,s), Al2(Cu,Ni) and Si(s,s). The Al—10Si—2Ni—6Cu filler alloy exhibited relatively low solidus (521 °C) and liquidus (577 °C) temperature, good tensile strength (305.8 MPa) and fracture elongation (8.5%). The corresponding Cu/Al joint brazed using Al—10Si—2Ni—6Cu filler was mainly composed of Al8(Mn,Fe)2Si, Al2(Cu,Ni)3, Al(Cu,Ni), Al2(Cu,Ni) and Al(s,s), yielding a shear strength of (90.3±10.7) MPa. The joint strength was further improved to (94.6±2.5) MPa when the joint was brazed using the Al—10Si—2Ni—6Cu—0.2Er—0.2Zr filler alloy. Consequently, the (Cu, Ni, Zr, Er)-modified Al—Si filler alloy was suitable for obtaining high-quality Cu/Al brazed joints.

Newly detected shock-induced high-pressure phases formed in amphibolite clasts of the suevite breccia (Ries impact crater, Germany): Liebermannite, kokchetavite, and other ultrahigh-pressure phases

Amphibolite clasts in the suevite of the Ries impact crater contain shock-induced melt veins (SMVs) with high-pressure phases such as majoritic garnet, jadeitic clinopyroxene and others. In addition, heat conduction from hot SMVs into adjacent rock portions locally produced further high P–T melt pools. These melts were preferentially generated in rock domains, where the SMVs cross older (‘pre-Ries’) veinlets with analcime or prehnite and larger grains of sericitized plagioclase. Melting of such chemically different local bulk systems (Na-, Ca-, Ca-Na- and K-Na-rich) was facilitated by low solidus temperatures of the original secondary OH-bearing phases. From the resulting shock-induced melts, liebermannite, kokchetavite, jadeite, nonstoichiometric and albitic jadeite, grossular, vuagnatite, lawsonite + coesite, and clinozoisite crystallized during pressure release. Vuagnatite is now proven to be a genuine high-pressure phase. Its ubiquitous distance of 20–35 μm from the hot shock veins suggests a temperature sensitivity typical for an OH-bearing phase. In local Na-rich melts albitic jadeite appears instead of the assemblage jadeite + SiO2. Liebermannite, a dense polymorph of K-feldspar was identified by Raman spectroscopy. After stishovite, liebermannite constitutes the second known high-pressure phase in the Ries that contains silicon exclusively in six-fold coordination. The KAlSi3O8-polymorph kokchetavite was formed in alkali-rich melt glasses. Pressure and temperature values in the range of about 8–11 GPa and ~ 800–1100 °C were estimated from the chemical compositions of locally occurring majoritic garnets (Si = 3.21–3.32 and 3.06–3.10 apfu), respectively, and the presence of fine-grained aggregates of lawsonite and coesite. Generally, the neighboring areas of the veins are characterized by a sequence of variable high-pressure phases documenting strongly falling P–T conditions with increasing distance from the vein. These novel features enlighten the dynamic event during passage of a shock wave.

Off-rift Axis Channelized Melt and Lithospheric Metasomatism along Mid-ocean Ridges—A Case Study from Iceland on the Limits of Melt Channelling

AbstractMagmatism in Iceland is classically explained by the interaction of the mid-Atlantic ridge with the Iceland plume. The growth of Iceland through time is the result of volcanic activity at the rift axis. However, Holocene volcanism (0–11.5 ka) is not restricted to the rift zone (RZ) but also occurs off-axis, specifically in the western Snæfellsnes Volcanic Belt (SVB) and in the Southern Flank Zone (SFZ). The rift and off-axis postglacial volcanic zones are separated by a gap of ~60–80 km. While the volcanic activity of the SFZ seems correlated with the actual location of the Iceland plume, the plume relation to the SVB is uncertain. To address the origin and relationships between rift and off-rift magmas, we present new data from two transects perpendicular to the Reykjanes rift. The lavas in the SVB are characterized by transitional to alkaline compositions, with elevated incompatible trace element content. In contrast, the RZ volcanic rocks have tholeiitic compositions with trace element signatures slightly more enriched than Mid-Ocean Ridge Basalt (MORB). Rift and off-rift Iceland lavas are all characterized by positive Ba and Nb anomalies, particularly in alkaline rocks. Tholeiitic and alkaline lavas show distinct differentiation sequences, with the main difference being the delayed crystallization of plagioclase in the fractionating assemblage of alkaline magmas. We apply these sequences to calculate primary magma compositions, which are then used to constrain melting conditions. Geochemical modelling indicates that Iceland rift and off-rift magmas can be produced from a peridotitic mantle source if lithospheric processes are involved. We demonstrate that recycled crust in the form of pyroxenite is not required to generate Snæfellsnes alkaline lavas. The low solidus temperature and high productivity of pyroxenite favour early and more extensive melting producing primary magmas that are not sufficiently enriched in incompatible trace elements to explain the compositional variation of Snæfellsnes magmas. An alternative mechanism to involve pyroxenite in the source of Snæfellsnes lavas relates to the hybridization of recycled oceanic crust with peridotite, but such reacted pyroxenite requires specific compositions to reproduce the Ba and Nb anomalies. As an alternative, we suggest that Snæfellsnes alkaline lavas are the result of channelized low-degree melts produced on the periphery of the melting column at distances exceeding 65 km from the ridge axis. These melts accumulate and percolate into the lithosphere producing amphibole ± phlogopite-bearing hydrous cumulates. Incongruent melting of these cumulates via renewed magmatic activity and melt-peridotite reaction can reproduce the alkaline compositions observed in the SVB, including the Ba and Nb anomalies. Numerical simulations of melt extraction below mid-ocean ridges suggest that low-degree melts produced as far as ~65 km from the central ridge axis rise vertically to the base of the lithosphere and are then focussed towards the ridge axis in decompaction channels. We propose that these melts interact with hydrous cumulates previously formed during the development of decompaction channels at the lithosphere–asthenosphere boundary and acquire specific Ba and Nb anomalies. The mixing of these distal enriched melts with more depleted melts extracted from the central part of the melting regime explains the composition of RZ lavas. Alkaline lavas observed in the SFZ show numerous analogies with the Snæfellsnes magmas, suggesting that similar lithospheric processes control their chemistry. The high thermal regime in Iceland and thick lithosphere explains the difference between Icelandic tholeiite and typical MORB. Our results highlight the importance of mantle dynamics below mid-ocean ridges and lithospheric interaction to produce off-axis magmatism with enriched alkaline signatures.

Unique strength-ductility balance of AlCoCrFeNi2.1 eutectic high entropy alloy with ultra-fine duplex microstructure prepared by selective laser melting

• A highly densed AlCoCrFeNi 2.1 eutectic high entropy alloy with ultra-fine structure and remarkable strength-ductility balance is fabricated by selective laser melting (SLM). • The ultra-fine grains and heterogeneous eutectic structures are introduced into the AlCoCrFeNi 2.1 due to the rapid solidification. • The SLM-ed AlCoCrFeNi 2.1 presents an excellent match of high tensile strength (1271 MPa), yield strength (966 MPa), and good ductility (22.5%) at room temperature. • A fan blade with smooth and bright surface is successfully produced with gas-atomized powders. As a typical dual-phase eutectic high entropy alloy (EHEA), AlCoCrFeNi 2.1 can achieve the fair matching of strength and ductility, which has attracted wide attention. However, the engineering applications of as-cast AlCoCrFeNi 2.1 EHEAs still face challenges, such as coarse grain and low yield strength resulting from low solidification rate and temperature gradient. In this study, selective laser melting (SLM) was introduced into the preparation of AlCoCrFeNi 2.1 EHEA to realize unique strength-ductility balance, with emphasis on investigating the effects of processing parameters on its eutectic microstructure and properties. The results show that the SLM-ed samples exhibit a completely eutectic structure consisting of ultra-fine face-centered cubic (FCC) and ordered body-centered cubic (B2) phases, and the duplex microstructure undergoes a morphological evolution from lamellar structure to cellular structure as laser energy input reducing. The SLM-ed AlCoCrFeNi 2.1 EHEA presents an excellent match of high tensile strength (1271 MPa), yield strength (966 MPa), and good ductility (22.5%) at room temperature, which are significantly enhanced by the ultra-fine grains and heterogeneous structure due to rapid solidification rate and high temperature gradient during SLM. Especially, the yield strength increment of ∼50% is realized with no loss in ductility as compared with the as-cast samples with the same composition. On this basis, the precise complex component with excellent mechanical properties is well achieved. This work paves the way for the performance improvement and complex parts preparation of EHEA by microstructural design using laser additive manufacturing.

Genesis of the Xiarihamu Magmatic Ni-Co Sulfide Deposit in the East Kunlun Orogen, Northern Tibetan Plateau: In Situ Oxygen Isotope and Geochemical Perspectives

Abstract Convergent margins are commonly deemed to have poor potential to form giant magmatic Ni-Cu-(platinum group element) sulfide deposits, due to the possibly low lithospheric geothermal gradient and the small basaltic magma fluxes. This view, however, is challenged by the recent discovery of the Xiarihamu Ni-Co deposit in the East Kunlun orogen (northern Tibetan Plateau), which contains ~157 million metric tons (Mt) of sulfide ores at 0.65% Ni, 0.013% Co, and 0.14% Cu, making it the world’s 20th largest magmatic sulfide deposit. To investigate the mantle source nature, magmatic processes, and their genetic linkage to Ni-Co mineralization in orogenic belts, we presented new in situ orthopyroxene oxygen isotope and pyroxene trace element data from the mafic-ultramafic cumulate rocks at Xiarihamu. Our results show that orthopyroxene crystals have much higher δ18O (6.40–8.58‰) than those in unmodified mantle peridotite (5.72 ± 0.14‰). Orthopyroxene grains in the primitive harzburgite cumulates have the lowest δ18O values (6.40–7.71‰) and the highest Mg# contents (88.7–83.9). From the harzburgite to the evolved lithologies (e.g., websterite and gabbronorite), the δ18O values of orthopyroxene increase, whereas the Mg# values, Ni contents, and heavy/light rare earth element (HREE/LREE) ratios of orthopyroxene decrease, implying crustal contamination during magma fractionation. The δ18O variations and sharp increases in V/Sc and LREE/HREE ratios from the primitive orthopyroxene crystals (with the highest Ni and Mg#) to the evolved ones (with low Ni and Mg#) indicate that crustal contamination played a critical role in sulfide saturation. The absences of any trend in orthopyroxene δ18O values versus Mg# contents, Ni concentrations, and La/Yb ratios toward unmodified mantle values suggest an enriched mantle source. On the mid-ocean ridge basalt (pyroxene)-normalized multielement plots, both orthopyroxene, clinopyroxene, and calculated parental magma show LREE and large ion lithophile element (LILE) enrichments and depletions in Nb-(Ta), Sr, and Zr-(Hf). The predicted primitive magma trace element compositions and the high-δ18O characteristics of the high-Mg# orthopyroxene grains suggest that the Xiarihamu primitive magma was partly originated from the pyroxenite mantle metasomatized by subducted slab-derived melts and fluids. Given the lower solidus temperature of clinopyroxene relative to olivine, pyroxenites in the mantle wedge may generate voluminous high-Ni magmas during partial melting. The high-Ni magmas are likely conducive to magmatic Ni-Cu sulfide mineralization in orogenic belts.

Constraints on the formation of basaltic magmas. Comment on “Lithosphere thickness controls the extent of mantle melting, depth of melt extraction and basalt compositions in all tectonic settings on Earth – a review and new perspectives” – by Niu Y. (2001)

Niu (2021) reviews fundamental topics of basaltic magma generation in the oceans and continents, including passive and active margins as well as intraplate regions. In his approach, Niu (2021) focuses on the role exerted by lithospheric (“LID”) thickness in controlling basalt compositions and volumes, proposing only a minor role, if any, for the thermal state of the mantle. A consequence of this is rejection of mantle plumes in controlling the compositions of MORB and OIB, albeit not excluding completely their existence to explain basalt petrogenesis.Although the fundamental role of the lithospheric mantle on continental breakup, deformation and volcanism was recognized over 50 years ago, this region has only rarely been considered a candidate source for basaltic rocks, being thought to be too cold, stiff and sterile to produce significant amounts of partial melt. However, the stability of C-H-bearing mineral phases such as carbonates, phlogopite and pargasitic amphibole at lithospheric mantle depths indicates relatively low solidus temperature, and the possibility to produce partial melts even under relatively cold thermal regimes.We contribute to this debate by proposing that a wide range of variables explain igneous activity on Earth and, likely, the other rocky planets. The “lid effect” is certainly important but there is evidence that other factors and variables also influence the compositions and volumes of melts produced in the upper mantle. Among these, bulk- and trace-element chemical heterogeneities, the distribution and speciation of volatiles, and large-wavelength variations in temperature caused by radiogenic decay, are the most relevant.

Experimental Investigation on Enhanced Energy Storage Characteristics of Spherically Encapsulated 1-Decanol/Expanded Graphite Composite for Cold Storage System

The low solidification temperature (0°C), sporadic nucleation behaviour and supercooling phenomenon of ice are the major factors affecting the energy storage efficiency of an ice-based cold thermal energy storage system (CTESS). Due to the non-supercooling nature and high solidification temperature (~4.1°C), 1-Decanol-Expanded graphite composite (CPCM) is proposed as a prospective replacement for ice in CTESS. The CPCM was macro encapsulated inside the various diameter (42, 51 and 64 mm) spherical enclosures (S.Es), and its energy storage performance was studied at different wall temperatures (Tw) for charging (0,-3 and -6°C) and discharging (10, 13 and 16°C). It is found that the latent heat can be stored in CPCM even at a higher wall temperature (-3°C), which is not possible in the case of ice. To freeze the same mass of 1-Decanol at Tw = -6°C, the CPCM filled 51 mm S.E requires 85.37% lower time than that of PCM filled S.E. Based on experimental results, -3 and 13°C is found as an optimum wall temperature for charging and discharging, respectively. The charging and discharging rates increase with diameter. Besides, in a 51 mm S.E, the time required to store (Tw = -3°C) and recover (Tw = 16°C) a stated amount of energy in CPCM is 81.27%, and 76.45% lower than that of PCM, respectively. CPCM has superior phase change and energy storage characteristics. Therefore, the use of CPCM in CTESS ensures effective storage and recovery of cold energy.

Oil characteristics and influence of heat processing on fatty acid profile of wild harvested termite (Macrotermes subhylanus) and long-horned grasshopper (Ruspolia differens)

The aim of this study was to assess the physico-chemical characteristics and fatty acid profile of oil from termite (Macrotermes subhylanus), green and brown long-horned grasshopper (Ruspolia differens). The insects were harvested in Siaya county of Western Kenya from the wild during swarming seasons. Physico-chemical characteristics of insects oil and the effect of two traditional heat processing methods (frying and solar drying) on the fatty acid profile were determined using standard methods. The insects oil was a clear, golden or light yellow colored liquid at room temperature, with a low solidification temperature (8–12 °C) for M. subhylanus and10–15 °C for R. differens. M. subhylanus showed an iodine value of 83.51 g iodine/100 g oil, peroxide value 0.19 mEq/Kg, saponification value 160.61 mg KOH/Kg and 38.77 mg/100 ml of total cholesterol. R. differens showed an iodine value of 86.97 g iodine/100 g oil, peroxide value 0.13–0.14 mEq/Kg, saponification value 229.67–234.40 mg KOH/Kg and 27.51–31.40 mg/100 ml of total cholesterol. Oleic acid was the major fatty acid in all the fresh insect samples (M. subylanus 52.1%, green R. differens 43.2%, brown R. differens 37.1%) while palmitic acid was the second most abundant fatty acid. Total unsaturated fatty acids were proportionately more than the total saturated fatty acids. The level of saturated fatty acids increased from fresh insect samples to heat processed samples (fried, fresh-dried and fried-dried), while the level of unsaturated fatty acids decreased with processing though insignificantly. The insects have high quality oil that maybe exploited in processing of nutritional food products and they may therefore be heat processed domestically without adversely affecting the quality of the oils.

Petrogenesis of early syn-tectonic monzonite-granodiorite complexes – Crustal reprocessing versus crustal growth

The 563.7 ± 6.1 Ma old, early-syntectonic Mon Repos complex is a predominantly metaluminous, magnesian, calc-alkalic granodioritic to granitic intrusion. Major and trace element variations imply that the rocks evolved through fractional crystallization processes involving amphibole, biotite, Fe-Ti oxides, zircon, and apatite. Rocks less evolved than granodiorite show evidence of hornblende accumulation. Initial Sr (87Sr/86Sr: 0.7090–0.7111) and Nd (εNd: −5.3 to −12.3) isotopic compositions of the granodiorites and granites are highly heterogeneous and vary with SiO2 contents indicating that assimilation of older crustal components occurred. Initial 206Pb/204Pb (16.65–17.65) and 207Pb/204Pb ratios (15.52–15.60) are similar to other mafic-intermediate complexes from the Damara belt. One monzodiorite and two quartz monzonites are K2O-, LILE-, and HFSE enriched and have similar SiO2 contents as the granodiorites. These samples are similar to post-collisional mafic magmas from elsewhere in the world. Their ε Nd values (−3.8 to −4.3), 87Sr/86Sr ratios (0.7051–0.7073) and trace-element characteristics imply that their unexposed parental melts are derived from a lithospheric mantle source that was contaminated and metasomatized by crustal material during ancient subduction processes. The data are explained by assuming a “flat” subduction model where melting predominantly involves ancient continental mantle lithosphere and crust with limited, if any, melting of the underlying asthenospheric mantle. During flat subduction, a sliver consisting of buoyant oceanic lithosphere was amalgamated with the base of the ancient continental lithosphere of the overriding plate. The oceanic mantle lithosphere and the oceanic crust dehydrated (but did not melt) and these fluids lowered the solidus of the overlying continental mantle lithosphere and crust. This scenario can explain the occurrence of rare K2O- and LILE-enriched monzodiorites and quartz monzonites with crustal-like isotopic compositions observed in this study as well as some more alkaline rocks in the belt. Because the metasomatized continental lithospheric mantle has lower solidus temperatures than peridotitic mantle, it is very likely that such metasomatized rocks may melt early during flat subduction. Thus, K2O-enriched monzodiorites to monzogranites are not restricted to late stages of the evolution of an orogen but may already form at the onset of an orogeny.

The role of sub-continental mantle as both “sink” and “source” in deep Earth volatile cycles

The extent to which Earth’s sub-continental lithospheric mantle modulates the flux of volatile elements from our planet’s deep interior to its atmosphere (via volcanism) is poorly constrained. Here, we focus on “off-craton” sub-continental lithospheric mantle because this long-lived reservoir potentially acts as both a volatile “sink” and “source” during major heating and rifting events. The sub-continental lithospheric mantle is primarily formed of peridotites with subordinate amounts of pyroxenites. While both lithologies are dominated by nominally-volatile-free mantle minerals, some of these phases have been shown to contain non-negligible amounts of H2O (e.g. 100’s of ppmw in clinopyroxene). Data for volatile elements other than Li are, however, limited. We present new, high-precision, in-situ Secondary Ion Mass Spectrometry analyses of H, F, Cl, Li and B in olivine and pyroxenes from well-characterised garnet- and spinel-bearing peridotites and pyroxenites (from southern Patagonia and the Antarctic Peninsula). Our study confirms that clinopyroxene is the main host of H2O and F. The maximum F contents we report (up to 154 ppmw) are higher than those in previous studies and occur in Ti-Cr diopsides in highly-metasomatised peridotites and Ti-Al augites from clinopyroxenite veins. Water contents of clinopyroxenes (up to 615 ppmw) are within the range previously published for continental mantle. Lithium concentrations are low (<5 ppmw) in all analysed phases and both Cl and B are below detection levels (14 ppmw and 0.03 ppmw, respectively).Unique to our study is the large variation in major- and trace-element concentrations of the clinopyroxenes, which allows us to place quantitative constraints on how volatiles are stored in the mantle. We demonstrate that: (i) F contents of clinopyroxenes closely correlate with Ti and (ii) DHCpx-Opx and DFCpx-Opx is systematic and inversely correlated with temperature. Despite the redistribution of volatiles during sub-solidus re-equilibration, we show that the first order control on the concentration of volatiles in clinopyroxene is the style of metasomatism, i.e. channellised flow versus reactive percolation. The mean bulk volatile contents of peridotites from Pali Aike and the Antarctic Peninsula (H2O = 89 ± 31 ppmw, F = 16 ± 11.2 ppmw and Li = 2 ± 0.7 ppmw) are within the range previously published for continental “off-craton” mantle. The pyroxenites have significantly higher mean bulk concentrations of H2O (260 ± 59 ppmw), F (86 ± 43 ppmw) and Li (1.0 ± 0.35 ppmw). While the greater capacity of mantle pyroxenites to host H2O relative to the associated peridotites has previously been observed in global “off-craton” mantle xenolith suites (e.g. Oahu, Hawaii; eastern China and the Rio Grande Rift, SW USA), here we show for the first time that pyroxenites are also major hosts of F (but not Cl, Li or B). Because of their relatively low solidus temperatures, pyroxenites in “off-craton” settings will be readily re-mobilised during lithospheric extension (and heating). We suggest these pyroxene-rich mantle lithologies may be responsible for the elevated concentrations of H2O and F observed in basalts and volcanic gasses from major continental rift zones and flood basalt provinces, and hence an important consideration in models of global volatile cycles.

Characterization of eutectic borides formed during solidification of borated stainless steel 304B4

AISI 304B4 stainless steel (SS) containing 1.3 wt.% boron was cracking extensively during fabrication of neutron shields for Prototype Fast Breeder Reactor (PFBR). However, earlier study on 304B4 steel showed good resistance to weld solidification cracking due to eutectic backfilling in the cracks during welding. In order to understand the backfilling mechanism in this steel, microstructural characterization was performed on 304B4 SS in solution-annealed and re-melted and solidified conditions. In solution-annealed condition, microstructure of 304B4 SS consists of austenite matrix with random distribution of blocky Cr2B-type borides. On contrary, as-solidified microstructure reveals the primary austenite dendrites and interdendritic eutectic of (Fe,Cr)2B-type borides of varying morphologies. In addition to (Fe,Cr)2B, spheroidal non-equilibrium Fe23(CB)6-type borides were also found inside the austenite dendrites. The eutectic liquid rich in boron and Fe, which has low solidus temperature, contributes significantly to backfilling of hot cracks formed during welding. This was confirmed through characterization of eutectic borides in the as-solidified structure which shows Fe-rich (Fe,Cr)2B and Fe23(CB)6 types of borides. Finally, reasons behind severe liquation cracking of 304B4 SS observed during fabrication of neutron shield has been explained based on Scheil’s solidification simulations.

Controle estrutural dos pegmatitos ricos em ETR associados ao depósito Madeira (Sn-Nb-Ta), mina Pitinga, Amazonas, Brasil

We have studied the structural control of pegmatites (F-REE-Li vein-type granite pegmatite) associated with the albite-enriched granite facies (AEG) of the Madeira A-type granite (~1.83 Ga). This facies corresponds to the Madeira world-class Sn-Nb-Ta-F (cryolite) deposit at the Pitinga mine. These REE-rich pegmatites [xenotime-(Y) and gagarinite-(Y)], presently exploited together with the disseminated ore, have potential to exploitation by selective mining. They have a common geometric arrangement and share the same mineralogy, therefore they all originated from the same source. They have the same mineralogical composition of the host rock and their emplacement occurred in the parental rock itself. The geometric arrangement of the pegmatites is settled by contractional brittle structures (reverse faults, imbrication fans and horses). The reverse fault planes (~N320/60SW) were essentially the conduits for the fluid. The preferential sites for the pegmatites bodies were horizontal tensile fractures. The well-marked geometric arrangement of the tectonic structures and the fact that there are also reverse faults planes without pegmatites show that the fractures that host the pegmatites were not formed by the fluid pressure. The orientation of the contractional structures in the AEG indicates a transport from SW to NE. With reduced dimensions, the AEG cooled fast, however its location in the cold upper crust and the low solidus temperature allowed pegmatites formation. The pegmatites were formed with the AEG emplaced in a structural level above the critical crustal depth, where minimum normal stress is vertical.