Minor Ce Research Articles

Effect of Minor Ce Substitution for Pr on the Glass Formability and Magnetocaloric Effect of a Fe88Zr4Pr4B4 Metallic Glass

In the present work, Fe88Zr4Pr3B4Ce1 metallic glass (MG) was successfully prepared by minor Ce substitution for Pr, and compared with Fe88Zr4Pr4B4 MG in terms of glass forming ability (GFA), magnetic and magnetocaloric properties. The GFA, Tc and the maximum magnetic entropy change (−ΔSmpeak) of the Fe88Zr4Pr3B4Ce1 MG were found to decrease slightly. At the same time, the possible interaction mechanism of minor Ce replacing Pr was also explained. The critical exponents (β, γ and n) obtained by the Kouvel–Fisher method indicate that Fe88Zr4Pr3B4Ce1 MG near Tc exhibits typical magnetocaloric behavior of fully amorphous alloys. The considerable maximum magnetic entropy change (−ΔSmpeak = 3.84 J/(kg × K) under 5 T) near its Curie temperature (Tc = 314 K) as well as RCP (~ 646.3 J/kg under 5 T) make the Fe88Zr4Pr3B4Ce1 MG a better candidate as a component of the amorphous hybrids that exhibit table-shape magnetic entropy change profiles within the operation temperature interval of a magnetic refrigerator.

Effects of minor Ce doping on the microstructure and mechanical performances of a EH47 grade HSLA steel for ship and ocean engineering

Effects of minor Ce doping on the microstructure and mechanical performances of a EH47 grade HSLA steel for ship and ocean engineering

Achieving high heat-resistant property in dilute Mg-0.2Ce wrought alloy by retarding recrystallization process

Conventional heat-resistant Mg alloys always involve a high concentration of rare-earth solutes to produce amounts of thermostable second phases. In this work, however, the high heat resistance is achieved in a dilute Mg-0.2Ce (wt%) alloy, exhibiting a high ultimate tensile strength of ∼ 181 MPa at 250 ℃, which is superior to those of benchmark Mg alloys including ZK60, AZ80 and other rare-earth element containing Mg alloys. The high-temperature strength of present Mg alloy can be attributed to the suppressed recrystallization process due to the minor Ce addition, since the softening mechanism of grain boundary sliding at high-temperature can be effectively suppressed in the elongated un-recrystallized grains and the texture hardening is always effective in the deformed regions. In addition, the present Mg alloy exhibits excellent thermal stability during the long-term heating on account of the sluggish static recrystallized process. The high temperature strength decreases gradually with the annealing time, which can yet exceed 145 MPa after annealing at 300 ℃ for 6 h. Generally, the present work would provide important insight into developing novel low-alloyed and heat-resistant Mg wrought alloys.

Mechanistic investigation on Ce addition in tuning recrystallization behavior and mechanical property of Mg alloy

Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility synergy in Mg alloy. Formation of bimodal grain is closely related to the dynamic and/or static recrystallization process, which has not been fully understood in the typical Mg-RE based alloy. In this work, it is claimed for the first time that the minor Ce addition (∼0.3 wt%) into Mg matrix significantly promotes the pyramidal <c+a> and non-basal <a> dislocations at the early stage of extrusion, which consequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type <c+a> dislocations. At this stage, fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of <c+a> dislocations. At the later stage, the sub-grains continuously transform into dynamic recrystallized (DRXed) grains that have 〈101¯0〉 Taylor axis and also strong fiber texture, indicating substantial activation of pyramidal II-type <c+a> dislocation. The low mobility of <c+a> dislocations, accompanied with the solute drag from grain boundary (GB) segregation and pinning from nano-phases, cause a sluggish DRX process and thus a bimodal microstructure with ultra-fined DRXed grains, ∼0.51 µm. The resultant texture hardening and grain refinement hardening effects, originated from bimodal microstructure, result in a yield strength of ∼352 MPa, which is exceptional in Mg-Ce dilute alloy. This work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium, and can also shed light on designing the other high-performance Mg alloys.

The cerium isotope fingerprints of redox fluctuation in bauxites

We measured the Ce concentration, oxidation state, and isotope composition of bauxites developed on the Columbia River Basalts (CRBs) to evaluate the impacts of redox and non-redox processes on the Ce isotopic variability on Earth's surface. Bauxites recovered from drill cores show upward increasing Ce concentration (5.4–88.7 μg/g) and overall depletion of Ce (mass transfer coefficient, τCe,Nb: -0.96 to -0.52, i.e., net depletion of 52-96% relative to their parent CRBs). There is a wide range of the Ce anomaly (Ce/Ce⁎) from 0.4 to 6.3 and 0.6 to 1.4 in the Cowlitz and Columbia bauxites, respectively. The most positive Ce anomalies appear at the shallow regolith (2-5 m depth). Cerium primarily presents in its trivalent form in deposited exogenous materials (wind-blown dust from an old, weathered region of the continent) and primary CRBs. There is a downward increase in the fraction of Ce (IV) in the regolith. Bauxite δ142Ce ranges from -0.161±0.034 to -0.018±0.043‰ and -0.277±0.034 to -0.046±0.034‰ in the Cowlitz and Columbia profiles, respectively. The Ce isotope record reflects the redox cycle of Ce and Mn and is masked by dust accretion on the top. The enrichment of Ce (IV) occurs in the transition zone (the bottom of the shallow regolith) with minor Ce isotope shifts from the CRBs (δ142Ce from -0.080±0.034 to -0.04±0.034‰) likely caused by minor isotopic fractionation linked to O2-driven CeO2 precipitation. There are negative Ce isotope shifts from the basaltic parents and the enrichment of oxidized Ce and Mn in the deep regolith (5-9 m depth), where large isotopic fractionation probably induced by Ce oxidative adsorption on MnO2 plays a vital role. The vertical difference between Ce/Ce⁎ and δ142Ce may be attributed to the climatic oxidation-reduction cycle of Mn and Ce, leaving discrete CeO2 grains in the shallow regolith while transferring isotopically light Ce associated to oxidized Mn deposits down to the deep regolith. We conclude that a combination of Ce species isotopes and anomalies potentially records terrestrial redox status and fluctuation.

Effect of micro-alloyed Ce on the microstructure evolution and mechanical properties of rolled Mg–0.6Al–0.5Mn–0.2Ca alloy sheets

In this study, the effect of minor Ce addition (0, 0.1, and, 0.3 wt.%) on the microstructure evolution and mechanical properties of rolled Mg–0.6Al–0.5Mn–0.2Ca (AMX100) alloy sheets is systematically investigated under different annealing processes. With 0.1 wt.% Ce addition, partial Al8Mn5 phases turn into Al8Mn4Ce. With 0.3 wt.% Ce addition, the number of the Al8Mn4Ce further increases and the Al–Ce phases are observed. The single-stage annealed alloys exhibit similar uniform fine-grained structures (∼6 μm) regardless of the Ce content, while the grain sizes of the two-stage annealed alloys increase obviously (∼10.9–11.9 μm). Especially, the abnormal grain growth occurs in the two-stage annealed AMX100-0.3Ce alloy. After the aging treatment, the yield strength (YS) of the two-stage annealed alloys is increased by ∼25–45 MPa, which is greatly higher than that of the single-stage annealed alloys (∼1–8 MPa). Note that the two-stage annealed AMX100–0.1Ce alloy displays a significant age-hardening response with the ultimate tensile strength (UTS) of ∼272 MPa and the elongation to failure (EF) of ∼14%, which is attributed to the formation of Al and Ca enriched Guinier-Preston (G.P.) zones. This work sheds light on the design and fabrication of low-cost dilute magnesium alloys with admirable age-hardening ability.

Enhanced mechanical properties and corrosion resistance of rolled Mg-1.5Sn-0.5Ca alloy by Ce microalloying

The aim of this study is to investigate the effect of minor cerium (Ce) on the microstructure, mechanical properties, and corrosion behavior of rolled Mg-1.5Sn-0.5Ca alloy. The results show that there are mainly α-Mg and CaMgSn phases and the rod-like CaMgSn phase broken is uniformly distributed in the Mg matrix in the form of particles after rolling. The addition of minor Ce can refine the eutectic structure between CaMgSn and α-Mg phase. Meanwhile, the minor Ce improves the strength and ductility of the rolled Mg-1.5Sn-0.5Ca alloy due to the more uniform microstructure and finer grain in the alloy. The fracture morphologies of the alloys are mainly ductile fractures. It is found that the Ce-containing Mg-1.5Sn-0.5Ca alloy has finer homogeneous dimples. In addition, the Ce addition improves the corrosion resistance of the alloy. The corrosion products are mainly Mg(OH) 2 and a small amount of Ce oxide/hydroxide. These Ce oxide/hydroxide can fill the holes in the Mg(OH) 2 film, made a denser protective film formed. The dense corrosion product film inhibits the penetration of Cl − and decreases the active sites caused by the second-phase particles on the surface of the alloy, so the corrosion rate is reduced in the Mg-1.5Sn-0.5Ca-0.1Ce alloy. • The Ce can refine the eutectic structure between CaMgSn and α-Mg and the α-Mg grains • The minor Ce improves the strength and ductility of the rolled Mg-1.5Sn-0.5Ca alloy • The Ce addition improves the corrosion resistance of the rolled Mg-1.5Sn-0.5Ca alloy • SECM observes voltage change between the α-Mg and second-phase particles

Structure and Property Modulations of 13Cr Stainless Steel Through Microgravity Solidification and Minor Ce Addition

Solidification controlling and RE doping are effective ways to manipulate the microstructures and performances of 13Cr martensitic stainless steel. In this work by Ying Ruan and co-workers, article number 2100062, the influences of microgravity solidification and Ce addition on microstructure refinement, inclusion spheroidization and mechanical properties of 13Cr steels were explored comparatively.

Effect of minor Ce and Zr on the wear property of a nickel-saving austenitic heat-resistant cast steel

ABSTRACT In this work, the effect of Ce and Zr on the wear performance of a nickel-saving austenitic heat-resistant cast steel at room temperature and 900 °C are investigated. The wear mechanism and strengthening mechanism played by the addition of Ce and Zr are also discussed. The enhanced work-hardening rate after adding Ce and Zr strengthens the worn surface during wearing and improves the wear resistance of the nickel-saving austenitic steel at room temperature. The addition of Ce and Zr reduces the dynamic recovery and recrystallisation softening effect, which is the main reason for improving the high-temperature wear performance of the nickel-saving austenitic steel. Besides, the wear-protective glaze layer formed on the worn surface of Ce- and Zr-containing alloys could also reduce the high-temperature wear of the nickel-saving austenitic steel.

Structure and Property Modulations of 13Cr Stainless Steel Through Microgravity Solidification and Minor Ce Addition

Both rare‐earth doping and microgravity solidification processing bring significant influences upon the structure formation and mechanical properties of various alloys. Herein, the microstructure and performance of 13Cr martensitic stainless steel are modulated by adding minor Ce content and microgravity solidification by means of drop tube technique. The lattice structure of constituent phase α(Fe) is deformed evidently by microgravity solidification, and the lattice parameter variation is 1.8 times of that caused by Ce addition. The microstructures of this steel processed by arc melting consist of lath‐shaped martensites and a few feather‐shaped bainites whose volume fraction increases with the Ce content. The bainite is replaced by ferrite in the rapidly solidified microstructure of 13Cr steel under microgravity condition. Although both microgravity solidification and Ce addition induce the microstructure refinement and inclusion spheroidization, the former effect plays the dominant role. The compressive properties and microhardness decrease moderately with Ce addition due to the slight increase in bainite, however, the microgravity solidification brought the hardening effect and thus the microhardness of the steel droplets increases with undercooling.

Geochemistry and mineralogy of rare earth elements in high-phosphorus ooidal ironstones: A case study of the Kamysh-Burun deposit (Azov–Black Sea iron Province)

This study is aimed at characterizing the distribution and speciation of the rare earth elements and yttrium (REE + Y) in ooidal ironstones from the Kamysh-Burun deposit (Kerch Peninsula), with implications for the depositional environments and contributions of different REE + Y carriers to the ore budget. The Lower Pliocene ooidal ironstone sequence of the so-called Kerch ores, up to 15 m thick, occupies an area of 28 km2. The ore sequence lies between Miocene – Lower Pliocene shell limestones and Upper Pliocene – Pleistocene sandy and clayey sediments and consists of horizontal ooidal ironstone beds composed mainly of goethite and X-ray amorphous Fe3+-(oxy)hydroxides intercalated with siderite and/or rhodochrosite beds. Iron is a main component in ooidal ironstones (50.03–66.19 wt% Fe2O3 and ≤1.61 wt% FeO), as well as in fresh carbonate ores (~34 wt% FeO and ≤14.70 wt% Fe2O3). The Kerch ores contain up to 4.59 wt% P2O5 and show significant positive correlation between P and Fe (r = 0.75). The bulk ore samples and their coarse (1–10 mm) fractions are goethite-dominated and have similar phase, major- and trace-element, and REE compositions. The fine (<1 mm) fractions are poorer in goethite and P2O5 but enriched in SiO2, Al2O3, Ti, Zr, Y, and Th due to greater percentages of Fe-saponite and fine detrital matter (including very scarce rutile, zircon, monazite, and xenotime). The average ΣREE values of 400 ppm in bulk ooidal ironstones and 405 ppm in the coarse fractions markedly exceed those in the Post Archean Australian Shale (PAAS). They have similar PAAS-normalized REE + Y patterns, with moderate enrichment in middle REE (MREE), minor Ce* (0.67–1.09), and moderate negative Y* anomalies (0.57–0.70). The fine ore fractions are markedly enriched in ΣREE (Xav = 858 ppm) mainly due to the presence of authigenic light REE phosphates of rhabdophane-tristramite series with Ce > La ≈ Nd ≈ Ca > Pr > Sm. The ΣREE content in fresh carbonate ores is below that in PAAS (Xav = 103 ppm), but approaches the latter in oxidized crusts (Xav = 178 ppm). The Kerch ironstones also contain REE-poor early-diagenetic Fe2+ phosphate vivianite (ΣREE Xav = 0.93 ppm) and Ca-Fe2+ phosphate anapaite (ΣREE Xav = 6.95 ppm) with typical seawater REE + Y distributions. The ooidal ironstones show MREE-enriched patterns with distinct negative Y* anomalies, which reveals Fe3+-(oxy)hydroxides as chief carriers of adsorbed REE (mainly MREE). The Kerch ironstones accumulated REE progressively due to hysteretic dissolution and precipitation of Fe3+-(oxy)hydroxides in oscillating redox conditions. The diagenetic source of REE stored in ooidal goethite ironstones was inferred from the PAAS-normalized values: CeN/CeN* vs Nd and CeN/CeN* vs YN/HoN discrimination diagrams. In general, the REE + Y budget of the Kerch ooidal ironstones mainly formed during early diagenesis and scavenging from pore water, with a minor contribution of siliciclastic inputs, in the absence of hydrothermalism.

Effects of minor additions of cerium, silicon and calcium on microstructure and mechanical properties of AZ91 magnesium alloy

Abstract The effects of minor Ce, Si and Ca additions on the microstructure and mechanical properties of the as-cast and T6 state AZ91 alloy were analyzed and compared in this paper by means of optical microscopy, scanning electronic microscopy, X-ray diffraction and tensile testing. Results showed that the addition of Ce and Ca could effectively modify the β-phase and the average grain size was refined from 239.7 ± 16.9 μm in AZ91 alloy to 57.8 ± 1.4 μm in AZ91-1.0Ce-0.5Ca alloy. Accordingly, the as-cast AZ91-1.0Ce-0.5Ca alloy showed optimum yield strength of 119 MPa and elongation of 10.7 %. Furthermore, AZ91-1.0Ce-0.5Ca alloy possesses a higher effect in the reduction of the discontinuous precipitates after aging and the yield strength increased to 164 MPa with elongation of 11.8 %.

Influence of minor Ce additions on the microstructure and mechanical properties of Mg-1.0Sn-0.6Ca alloy

The microstructure and mechanical properties of Mg-Sn-Ca-Ce alloys with different Ce contents (0.0, 0.2, 0.5, 1.0 wt%) were studied at room temperature. Ce additions to ternary Mg-Sn-Ca alloy resulted in grain refinement as well as a change in the category of second phase from CaMgSn to (Ca, Ce)MgSn and Mg12Ce. The volume fraction of second phase increased with rising Ce content, which aggravated the restriction of DRXed grain growth during the extrusion process and eventually led to texture weakening of as-extruded Mg-Sn-Ca based alloys. In terms of plasticity, owing to vigorously activated basal slip and homogeneous distributed tensile strain in tension, the tensile ductility of as-extruded alloys reached the maximum value of 27.6% after adding 0.2 wt% Ce, which enhanced by about 26% than that of ternary Mg-Sn-Ca alloy. However, further Ce additions (0.5 and 1.0 wt%) would coarsen the second phase particles and then impair ductility. The tension-compression yield asymmetry of as-extruded Mg-Sn-Ca ternary alloy was alleviated greatly via Ce additions, due to the joint effects of grain refinement, increased amount of strip distributed second phase particles and texture weakening.

The microstructure, mechanical properties and corrosion behaviour of Ce-containing Mg-3Sn-1Ca alloy

The effects of minor Ce on the microstructure, mechanical properties and corrosion behaviour of Mg-3Sn-1Ca alloy are investigated systematically. The minor Ce can refine the eutectic structure between α-Mg and CaMgSn and make the microstructure more uniform. The maximum ultimate tensile strength and elongation of the alloy with the Ce content of 0.3 wt-% were 152.5 MPa and 4.1%, respectively. Meanwhile, the corrosion resistance of the Ce-containing alloys is improved by Tafel curves and electrochemical impedance spectra, especially when the Ce is up to 0.3 wt-%. The minor Ce can promote the formation of the surface film and makes the corrosion product film to become more compact, which effectively prevents further the occurrence of corrosion of the Mg matrix.

Ultramafic–mafic and granitoids supra‐subduction magmatism in the southern Ashanti volcanic belt, Ghana: Evidence from geochemistry and Nd isotopes

Geochemical and Nd isotope data are presented for Palaeoproterozoic ultramafic to mafic rocks and granitoids which are associated with volcanic rocks in the southern part of the Ashanti greenstone belts of Ghana. The Prince's Town granitoids display subduction‐zone geochemical features, with some showing signatures similar to high‐SiO2 adakites (HSA). Their initial εNd (2.1 Ga) values range from −1.01 to +2.92, and they have TDM2 of 2.17–2.51 Ga. The gabbros show slightly LREE‐depleted and ‐enriched patterns, Th–U troughs, negative Nb, Zr–Hf and Ti anomalies, spikes in Sr and Pb, have εNd (2.1 Ga) values ranging from −1.23 to +5.23, and TDM2 values from 2.08 to 2.57 Ga. The Ahama ultramafic body is characterized by two groups of pyroxenites. Both groups show LREE enrichment patterns, display Th–U and Nb–Ta troughs, minor or pronounced negative Zr–Hf and Ti anomalies. However, the Group I pyroxenites exhibit minor Ce anomalies and lower total REE contents (28.1–32.8 ppm) whereas Group II pyroxenites show significant negative Ce anomalies and relatively higher total REE contents of 57.1–124 ppm. The pyroxenites show negative initial εNd (2.1 Ga) values (−0.58 to −5.68) and have TDM2 values of 2.52 to 2.75 Ga. The pyroxenitic and gabbroic rocks were most likely originated from a subduction‐related lithospheric mantle. The Aketakyi ultramafic–mafic complex is made up of mainly cumulate dunite, harzburgite, pyroxenites, and gabbro. The rocks display LREE‐depleted to flat patterns with low total REE contents (1.71 to 22.3 ppm) and demonstrate a supra‐subduction affinity. They show high positive initial εNd (2.1 Ga) values (+3.69 to +4.93), and TDM2 values of 1.99 to 2.04 Ga, which suggest that they were derived from depleted mantle magmas and were juvenile at their time of formation. The Nd isotopic data provides evidence for a possible contamination of the juvenile Birimian crust of the southern Ashanti belt by some amount of a pre‐Birimian (or Archaean?) crustal material. The trace element and isotopic signatures as well as the field relations of the studied granitoids and mafic–ultramafic rocks show they were derived through supra‐subduction‐related magmatism during the Palaeoproterozoic.

Effect of rare earth cerium and impurity tin on the hot ductility of a Cr-Mo low alloy steel

The specimens of 1Cr-0.5Mo low alloy steel, undoped, Sn-doped and Ce+Sn-doped, were austenitized at 1300 °C and then cooled down to different temperatures in the range of 700–1050 °C, followed by tensile tests with the aid of a Gleeble machine. The reduction of area (RA) obtained from the test was employed to evaluate the hot ductility of the steel. The tested specimens were characterized using different techniques. Minor Sn could considerably reduce the RA values of the steel in the whole temperature range, and the hot ductility curve could be widened and deepened. Nevertheless, minor Ce could improve the hot ductility of the Ce+Sn-doped steel by fully suppressing the Sn-induced hot ductility deterioration. FEGSTEM microanalysis showed that the Sn or Ce and Sn atoms segregated to austenite grain boundaries in the Sn-doped or Ce+Sn doped specimens. The detrimental effect of Sn on the hot ductility could be attributed mainly to the segregation of Sn as it could decrease the grain boundary cohesion and in turn enhanced the grain boundary sliding and cracking. However, this detrimental effect of Sn could be counteracted by the segregation of Ce which could increase the grain boundary cohesion and in turn restrained the grain boundary sliding and cracking. Accordingly, a minor addition of rare earth Ce could be an effective method of suppressing the detrimental effect of impurity elements on the hot ductility of a Cr-Mo low alloy steel.

Effects of minor additions of Ce and Y on as cast microstructure of Mg–3Sn–2Ca magnesium alloy

The effects of minor additions of Ce and Y on the as cast microstructure of Mg–3Sn–2Ca (wt-%) magnesium alloy are investigated and compared. Results indicate that adding minor Ce or Y to Mg–3Sn–2Ca alloy does not cause formation of any new phases in the alloy. The as cast Mg–3Sn–2Ca alloy with addition of 0·5 wt-%Ce or Y is still composed of α-Mg, CaMgSn and Mg2Ca phases. However, after adding 0·5 wt-%Ce or Y to Mg–3Sn–2Ca alloy, not only the formation of CaMgSn phase in the alloy is suppressed but also the CaMgSn phases in the alloy are effectively refined. In addition, adding 0·5 wt-%Ce to Mg–3Sn–2Ca alloy exhibits higher refinement efficiency to the CaMgSn phase in the alloy than adding 0·5 wt-%Y. Further investigations need to be considered in order to understand the difference of minor Ce and Y with regard to the refinement of CaMgSn phase in the Mg–3Sn–2Ca alloy.

Effect of Ce addition on the oxidation behaviour of Mo–Si–B–Al ultrafine composites at 1100 °C

Mo 73.4 Si 11.2 B 8.1 Al 7.3 ultrafine eutectic–dendrite composites undergo severe oxidation at 1100 °C in dry air, being transformed completely into mullite and cristobalite. However, the net mass loss is reduced by at least ∼ 40 % during 24 h exposure upon minor Ce addition to the alloy, indicating an unusual improvement in oxidation resistance. The presence of Ce hinders mullatization, and leads to the formation of a protective Si–O-rich layer in the scale. The relationship between oxide scale composition and the oxidation kinetics has been examined.

The mafic rocks of Shao La (Kharta, S. Tibet): Ordovician basaltic magmatism in the greater himalayan crystallines of central-eastern Himalaya

In the Kharta area, east of Mount Everest, the Greater Himalayan Crystallines are significantly richer in mafic rocks than the surrounding areas, Sikkim–West Bhutan and Makalu–Cho Oyu. These rocks are lenses with a complex metamorphic history. The mafic lenses of Shao La, in the Greater Himalayan Sequence south of Kharta, are here considerated as dismembered dykes apparently escaped the Himalayan high-temperature metamorphism and only record a low-grade metamorphic event. They are calc-alkaline medium-K basalts to basaltic andesites, consisting of plagioclase (core 62% An and rim 55% An), augite (Wo 43–47En36 36–37Fs 16–20), hypersthene (Wo 1.6–3.3En 50–52Fs 46–48), and minor brown hornblende, biotite and ilmenite. They show strong enrichment in low ionic potential elements relative to high-field-strength elements, and only minor Ce and P enrichment with respect to MORB. Combined Sr–Nd systematics suggest contamination of a basic magma from a subcontinental mantle source with a small amount of crust (about 4 vol.%). This in turn indicates that the Shao La basalts and basaltic andesites have the geochemical fingerprint of a supra-subduction zone magma. U–Pb dating of zircon from one sample yielded an age of 457 ± 6 Ma for the crystallisation of the Shao La basic rocks, assigning them to the Cambro-Ordovician Bhimphedian orogenic event. The age and geochemical characteristics of the Shao La rocks are similar to those of the basic rocks of the Cambro-Ordovician Mandi pluton further west. This suggests the existence of an extensive supra-subduction zone magmatism along the Indian margin of Gondwana. Like the bimodal granite-gabbro magmatism in the Mandi-Kaplas area, the Shao La basic rocks are contemporaneous with the emplacement of granitic plutons in the Everest-Kharta area. This acid plutonism is interpreted as crustal melt triggered by the upwelling of metasomatised mantle in a back-arc setting. The age of basic and acidic plutonism in the Everest-Kharta area is evidence that the Bhimphedian Orogeny was still active as late as the Late Ordovician

Further attempts to constrain the nature of the impact residues in the HST solar array panels

An analytical study has been carried out on an impact feature within a solar cell from the Hubble Space Telescope Solar array. Optical investigation of the feature in question showed that it was the result of a partially penetrating impact, and as such might expect to record evidence of the particle responsible for the damage. Chemical analyses obtained by X-ray emission elemental mapping identified a residue in part of the inner impact crater. The residue was found to contain Fe, Ti, K, Ca, Si, Mg, Na and minor Ce. The presence of Mg, Fe and Ti (elements foreign to the solar cell), suggested an impact residue of natural or man-made origin. Subsequent detailed analysis showed Fe and Mg in concentrations of about 10% with Ti in only limited amounts, implying that the residue might be from a particle of natural origin. Quantitative X-ray micro-analysis of the residue indicated it was chemically similar to a pyroxene, which suggests that the impact residue was a natural micrometeoroid. Partially-penetrated impacts are common features in solar cell materials (3 out of 6 randomly selected samples). Although conditions present in the selected cell are rare, the essential feature was the limited deposition of material from upper layers of the cell. This created an almost homogenous substrate which made the identification of extraneous material easier.