EPMA Results Research Articles

Insight into the effect of Ce content on the magnetic properties of Ce-magnets with grain boundary diffusion Pr-Al alloys

The development of cost-effective Ce-magnets with high Ce content is urgent to realize the vision of cost reduction and performance enhancement. Dual-main-phase Ce-magnets with different Ce content (Ce accounted for the total amount of rare earths is 40%, 50% and 60%) are prepared. The Pr80Al20 (at%) alloy is selected as diffusion source for the three magnets using the grain boundary diffusion technique under the same conditions. The correlation of magnetic properties and microstructures before and after diffusion with different Ce contents are systematically analyzed. According to the EPMA results, the presence of Ce in the magnets facilitates the diffusion of Pr elements along the grain boundaries, which significantly increases the diffusion depth of Pr inside the magnets. As a consequence, the percentage increment of coercivity increase with the Ce content due to the increased diffusion depth. This study provides new insight into the preparation of dual-main-phase Ce-magnets with high Ce content of 40–60%.

Comprehensively improved magnetic performance of Nd-Fe-B magnets with high-efficiency grain boundary diffusion of heavy rare earth

Comprehensively improved magnetic performance Nd-Fe-B magnets with extremely limited amount of Heavy Rare Earth (HRE) elements are obtained to meet the increasingly demanding applications. In this work, Tb–Co thin film with uniform distribution, flat surface and strong adhesion is successfully prepared by magnetron sputtering, and the effects of Tb–Co film thickness on the magnetic properties are investigated. The magnets with optimal magnetic properties are achieved when the film thickness is about 3.5 μm, the coercivity of 1284.81 kA/m, the remanence of 1.48 T, and the maximum magnetic energy product of 437.32 kJ/m3, compared with the original magnets, enhancing by 47.9 %, 0.4 % and 5.7 %, respectively, so the magnetic properties have been comprehensively improved using little amount of HRE and Co elements. HRTEM and EPMA results revealed that Tb-rich shell distributed around the Nd2Fe14B grain. The mechanisms of the remanence and coercivity simultaneous enhancement of Nd-Fe-B magnets is elaborated in detail. Besides, the diffusion of Tb–Co thin film can enhance thermal stability of the magnets.

A Novel Preparation Method of (Ti,Zr,Nb,Mo,W)B2-SiC Composite Ceramic Based on Reactive Sintering of Pre-Alloyed Metals

High-entropy diboride-based (MeB2-based) ceramics are promising high-temperature structural materials because of their excellent mechanical properties, high-temperature stability, and oxidation resistance. In order to achieve low-temperature sintering of the high-entropy ceramics, a novel preparation method of high-entropy (Ti,Zr,Nb,Mo,W)B2-SiC ceramics based on reactive sintering of pre-alloyed solid-solution metals and nonmetals of Si, C, B4C was conducted in the current work. Mechanical alloying behavior of the mixed metal powders, as well as the phase composition, microstructure, mechanical properties, and oxidation behavior of the as-sintered MeB2-SiC ceramic were investigated. The XRD, SEM, and EPMA results indicated that the primary MeB2 solid-solution and SiC phases could be successfully formed during reactive sintering at a relatively low temperature of 1650 °C. The as-sintered MeB2-SiC ceramics had a high relative density of 97.8% and high mechanical properties (hardness of 19.74 ± 0.8 GPa, flexure strength of 533 ± 38 MPa, and fracture toughness of 6.01 ± 0.77 MPa·m1/2). Combining the oxidation behavior and microstructure evolution of the oxidation layer, a continuous and relatively dense MeOx-SiO2 oxidation layer was gradually formed and covered on the external surface, leading to decelerating oxidation behavior after an oxidation exposure time of 10 min.

Cobalt mineralization in the Northeastern Hunan Province of South China: New evidence from the Jintang hydrothermal Co polymetallic ore district

The hydrothermal vein-hosted Co deposits as one of the significant deposit types, have economic importance in the world. The Jiangnan Orogen of South China hosts abundant hydrothermal Co deposits, of which several Co (-polymetallic) deposits cluster together along the Changsha-Pingjiang fault zone in the northeastern Hunan Province. However, the variations of cobaltiferous mineral assemblages exhibit along the Changsha-Pingjiang fault zone. The Jintang ore district as the new prospecting target could provide an insight into the understanding of Co mineralization in the northeastern Hunan Province. The TIMA and EPMA results identify pyrite, arsenopyrite and minor cobaltite and glaucodot as the main cobaltiferous sulfide phases in the Jintang district, of which Co and Ni occur via substituting Fe in pyrite and arsenopyrite. In contrast with the barren pyrite (PyI) associated with marcasite in the early stage, the PyII of the middle stage is featured by the successive precipitation of Co-rich PyII-a (Avg. 2.93 wt%, up to 5.05 wt% Co), Ni-rich PyII-b (Avg. 1.56 wt%, up to 3.84 wt% Ni) and As-rich PyII-c (Avg. 1.36 wt%, up to 4.10 wt% As). The sharp chemical gradients across the different pyrite species as well as irregular reaction fronts indicate fluid-mediated dissolution and reprecipitation are principal mechanism for the incorporation of Co, Ni and As into sulfides. The fractionation of Co and Ni in pyrite was possibly caused by the decreasing salinity which favors high Ni/Co ratios in pyrite, rather than different fluid origins. Successively, the As-rich PyII-c together with arsenopyrite and glaucodot were precipitated, indicating a progressive increase of As concentrations in fluids and decreasing fO2 condition. The sulfur isotopic analyses yield the δ34SV-CDT values of −8.0 to −4.9 ‰ for the Jintang sulfides, suggesting both magma and wall rock as potential sulfur reservoirs. In combination with S and Pb isotopic results in this area, the Co mineralization in the northeastern Hunan Province was most likely formed via fluid-rock interactions along cataclastic fault zones with metal leached from the crystalline basement. The migration of ore-forming fluids along the Changsha-Pingjiang fault zone potentially contributed to the development of contrasting cobaltiferous mineral assemblages in the region, but the changes in local physicochemical conditions generated the partitioning of elements within a single deposit.

Color Origin of Greyish-Purple Tremolite Jade from Sanchahe in Qinghai Province, NW China

Greyish-purple tremolite jade has become well known in the past few years, and the origin of its color has attracted the attention of gemologists. In this study, FT-IR spectra, EPMA, EPR spectra, micro-XRF, UV–Vis–NIR spectra, and LA-ICP-MS in situ mapping were analyzed to investigate the chromophore elements. The study sample was chosen from the Sanchahe mine, Qinghai Province, NW China, which has the typical characteristics of a gradual color change. The FT-IR and EPMA results revealed that the mineral composition of the dark and light greyish-purple regions of the sample are primarily composed of tremolite. UV–Vis–NIR spectra demonstrated that the greyish-purple color is mainly due to strong absorptions at 560 nm and 700 nm and weak absorption at 745 nm in the visible range. The EPR spectra presented ~3400 G six hyperfine lines resulting from the hyperfine interactions of the unpaired electron with the Mn2+ nucleus in the octahedral site. The UV–Vis–NIR and EPR spectra analyses demonstrated that Mn2+ is the origin of the purple color. A comparison of the major elements in the light and dark regions indicated that the chromogenic elements have strong positive correlations with Mn, Cu, and Fe. LA-ICP-MS mapping used to analyze the first transition metals indicated possible positive correlations between the greyish-purple color and the trace chromogenic elements. This suggested that the Mn, Cu, and Fe contents are significantly high in the dark band region. Combining in situ LA-ICP-MS mapping of trace elements, UV–Vis spectra, and EPR analysis results, it was suggested that Mn, Cu, and Fe are the major contributors to the greyish-purple color. This study provides a reference for the specific experimental methods to determine chromophores and the origin of color in tremolite jades.

Microstructure evolution and vacuum tribological properties of surface nitriding layer on a TiZrAlV alloy fabricated by laser nitriding

The evolution mechanisms of phase, microstructure and vacuum tribological properties for Ti–20Zr-6.5Al–4V under different laser beam diameters have been investigated by using laser surface nitriding (LSN). Results indicate that all the LSN samples are mainly composed of α phase and Ti(Zr)N phase, besides, Ti(Zr)N0.3 phase can also be obtained, which is based on a change in the ratio of liquefied nTi(Zr)/nN. With the laser beam diameter decreasing from 3 to 1 mm, the thickness and density of nitride layer increase significantly, which contribute to the increased energy input density. EPMA results indicate that the nitrides mainly exist in the form of Ti(Zr)xNy, and the distribution transformation of Al and V elements has also been analyzed. As the laser beam diameter decreases, the coefficient of friction decreases, and the sample with 1 mm laser beam diameter display the lowest coefficient of friction (∼0.333). Also, the wear volume and wear rate of the LSN sample with 1 mm laser beam diameter are the smallest, which are both reduced by about 40% compared with the original sample. After analysis, the wear pattern of the LSN samples can be confirmed as the composite of adhesive wear and abrasive wear. Nitride dendrites can form a support skeleton between the wear surface and friction pair, which can significantly reduce the wear of LSN sample surface. The results of this work prove the feasibility of improving the surface wear resistance of Ti–20Zr-6.5Al–4V by LSN.

Optimization of Zinc and Germanium Recovery Process from Zinc Oxide Dust by Response Surface Methodology

AbstractBased on the problems existing in the existing process, the ultrasonic field enhanced potassium dichromate atmospheric leaching of zinc and germanium in zinc oxide dust was studied, and three main factors (liquid‐solid ratio, leaching temperature and potassium dichromate concentration) were optimized by the Box‐Behnken design (BBD) model. XRD, ICP‐OES, EPMA and SEM results show that the occurrence state of Ge is highly correlated with ZnS. Promoting the dissolution of ZnS is the basis for improving the leaching rates of Zn and Ge. Finally, under the conditions of liquid‐solid ratio of 7 mL/g, leaching temperature of 90 °C and potassium dichromate concentration of 19.16 g/L, the leaching rates of zinc and germanium were 99.968 % and 90.395 %, respectively. The error between the prediction results of the quadratic model and the experimental results is small, and the correlation coefficients are greater than 0.99, indicating that the model is credible.

Mineralogical and Geochemical Characteristics of the H-Pit of the Chatree Gold Deposit, Central Thailand: A Case Study for Assessment of Acid Rock Drainage and Heavy Metal Sources

H-pit is one of the significant ore lenses of the Chatree mine in Thailand. Au-Ag mineralization mainly occurs as veins, stockworks, and minor breccias hosted by volcanic and volcaniclastic rocks. Disseminated pyrites are commonly present near mineralized veins in the hanging wall zone. This study aims to assess the acid rock drainage (ARD) potential and heavy metal content from the H-pit area. The results indicate that hanging wall rock is a potential acid-forming (PAF) material related to disseminated pyrite formed by hydrothermal alteration. In contrast, the footwall and ore zone materials are classified as non-acid forming (NAF). Because the ore zone has calcite in the veins, it may help buffer the material’s acidity. The results of heavy metal analysis reveal that the ore zone has significantly higher contents of As, Cd, Cu, Pb, and Zn than those in the hanging wall and footwall zones. Moreover, the hanging wall and footwall materials have exceeding values for As, Cd, and Zn compared to those in typical igneous rocks. These heavy metals are interpreted to be sourced from (1) the primary composition in base metal sulfides (e.g., Cu, Pb, and Zn), (2) the substitution of trace elements in sulfides (e.g., As and Cd), and (3) the substitution of trace elements in calcite (e.g., Mn), as evidenced in the EPMA results. In conclusion, the hanging wall rocks in this study containing high sulfur in proximity to the ore zone are a PAF material with heavy metal contaminant sources, whereas the footwall and ore zone materials have a lower potential to be such sources at the Chatree mine.

High temperature oxidation resistance of TNM alloy coated with/without 8YSZ/NiCoCrAlY thermal barrier coatings

The oxidation resistance of the TNM alloy (Ti-44Al-4Nb-1.5Mo (B, Y) (at. %)) coated with/without 8YSZ/NiCoCrAlY thermal barrier coating (TBC) was conducted through cyclic oxidation at 950 ℃. The formation mechanism of oxide scale, interface interdiffusion mechanism, and evolution law of thermal growth oxide (TGO) were systematically investigated. Results show that the weight gains of the TNM alloy coated with/without TBC are 2.45 mg/cm2 and 6.98 mg/cm2, respectively. The Ti-Al-N layer and the (Nb, Mo)-rich layer near the surface play a role in blocking the internal diffusion of air and the external diffusion of metal ions. After a comprehensive analysis of EPMA and SEM results, it is concluded that the diffusion rate of elements in NiCoCrAlY is Ni > Co > Cr. At the same time, the relationship between the interface diffusion layer thickness and oxidation time is built based on Fick’s first law. In addition, as the oxidation time increases, TGO evolves from a dense Al2O3 layer to CS (chromia, spinel oxide) layer, and CSN (chromia, spinel, and nickel oxide) cluster oxides. The mixed oxides induce crack nucleation and growth, thereby reducing TBC lifetime.

Sulfide micro-textures and in-situ compositions from the Wulong gold deposit, northeastern North China Craton: Implication for ore-forming processes

Lode gold deposits in the North China Craton (NCC) form the only known giant late Mesozoic gold province in the world’s Precambrian cratons. Understanding the ore genesis for these deposits is of great scientific and economic importance. In order to provide constraints on the ore-forming processes, this study presents a combination of micro-textures and in-situ compositions of sulfide from the Wulong gold deposit (80 t @ 5.35 g/t Au; 127–122 Ma), northeastern NCC. Five sub-generations of pyrite (Py1–Py5) are identified based on micro-textural observations and EPMA results. In-situ trace elemental concentrations show that pyrite from the stage 1 (Py1) has high Co and Ni contents but no Au (<0.02 ppm). In contrast, euhedral Py2 and porous Py3 from stage 2 exhibit much higher Au (average 3.08 ppm and 1.66 ppm), As (average 1400 ppm and 946 ppm), and Ag (average 2.81 ppm and 3.21 ppm). Anhedral Py4 from stage 3 shows lower Au (average 0.31 ppm) and As (average 337 ppm) concentrations when compared to Py3. However, Py5 from stage 3 exhibits significant increases of As (average 7102 ppm) and Au (average 5.46 ppm) again and is featured by the alternation of Co-Ni- and Au-As-rich zones. Other sulfides, including pyrrhotite, chalcopyrite, and sphalerite, are poor in Au and As. Apart from visible gold grains related to Bi-rich melts, LA-ICP-MS spot and mapping analyses reveal that invisible gold hosted in Py2 to Py5 occurs dominantly as lattice-bound solid solutions (Au+). Direct gold precipitation from anomalously As-rich auriferous fluids induced by fluid immiscibility is proposed as the dominant mechanism of invisible gold enrichment. In-situ δ34S values of Py1 to Py4 exhibit narrow ranges of 1.0 to 3.8 ‰, indicating a deep-seated magmatic sulfur source. The elevated δ34S values (2.3–6.3 ‰) of Py5 are ascribed to some wall-rock contributions during fluid-rock interaction. These findings shed new light on the link between multistage fluid immiscibility and the chemical and micro-textural fingerprints of pyrites and the role of fluid immiscibility in the deposition of invisible gold.

Genesis of Chaxi Gold Deposit in Southwestern Hunan Province, Jiangnan Orogen (South China): Constraints from Fluid Inclusions, H-O-S-Pb Isotopes, and Pyrite Trace Element Concentrations

The Chaxi gold deposit is located in the southwestern Hunan Province (South China). Extremely high-grade (up to 3 × 105 g/t, avg. 5.3 g/t) Au mineralization is developed in quartz-sulfide veins controlled by WNW- and NNE-trending faults. The sulfide/sulfosalt assemblage is dominated by pyrite, chalcopyrite, and galena, with minor tetrahedrite and chalcocite. The alteration includes beresitization and carbonation. Based on the vein crosscutting relationship and mineral assemblages, the hydrothermal period comprises three stages: (1) pre-ore quartz-pyrite, (2) syn-ore quartz-ankerite-native gold-sulfide-sulfosalts, and (3) post-ore quartz-calcite-pyrite alteration. The Au occurrence is dominated by native gold, with minor native Au nanoparticles (inside sulfides) as indicated by EPMA. Fluid inclusions (FIs) in the ore-related quartz yielded homogenization temperatures and salinities of 139.6–267.1 °C and 2.7–17.6 wt.% NaClequiv (Stage I), 137.5–387.2 °C and 2.7–19.9 wt.% NaClequiv (Stage II), and 139.7–330.5 °C and 3.1–21.4 wt.% NaClequiv (Stage III). Such varying and high FI salinities can be attributed to fluid boiling. The calculated δ18OH2O values are of 2.40–5.63‰, and the fluid inclusion δD values for quartz are of −71.73 to −49.8‰. The auriferous sulfide δ34S values (6.26–19.33‰) overlap with those of the Chang’an formation (16.31–21.66‰) and Banxi Group metamorphic rocks. The auriferous sulfides have 206Pb/204Pb = 16.7215–17.2281, 207Pb/204Pb = 15.4413–15.6177, and 208Pb/204Pb = 36.9731–38.7232, distinct from those of the wallrocks. The analyzed pyrites yield Co/Ni ratio &gt; 1 (0.539–77.000, avg. 10.559). The isotope (H, O, S, Pb) signatures coupled with EPMA results indicate that the ore-forming fluids were derived from the magmatic fluid and mixed with meteoric water, and the Pb was originated from the mantle. The ore sulfur was likely leached from the Neoproterozoic meta-clastic rocks. The Chaxi gold mineralization shares many geological and geochemical similarities with (albeit also with minor differences) typical orogenic gold deposits, and is best classified as broad sense orogenic deposit, as proposed for many other gold deposits in the Jiangnan Orogen.

Dielectric and Piezoelectric Properties of Mn-Doped Bi(Mg1/2Ti1/2)O3-PbTiO3 Piezoelectric Single Crystals with MPB Composition

Mn-doped BMT-PT single crystals were grown using a flux method. The crystals were irregular and 4–10 mm in size. The EPMA and XRD results showed that the composition of the crystals was in the range of MPB. The room temperature dielectric permittivity εr and dielectric loss tanδ were 806 and 3.4% at 1 KHz. As the temperature increased, the rhombohedral phase did not first transform into the tetragonal phase, but transformed into the cubic phase directly. Owing to the Mn-doping, the ferroelectric hysteresis loops of the sample were quite narrow. The Curie temperature Tc, piezoelectric coefficient d33 and thickness electromechanical coupling factor kt of the single crystals along the &lt;001&gt; direction were 464 °C, 392 pC/N and 0.51, respectively. The piezoelectric properties are much better than the values of the ceramics and the undoped BMT-PT single crystals with a MPB composition.

Mineralogy and Geochemistry of “Laoshan Jade” from Shandong Province, China: Implications for Petrogenesis

“Laoshan Jade” is located in the Yangkou area of the Sulu UHP metamorphic belt. This is the first time a systematic research study is performed on its conventional gemological characteristics, mineral compositions, geochemical characteristics, and petrogenesis using a polarized light microscope, an electron probe microanalyzer (EMPA), an X-ray fluorescence spectrometer (XRF), and a Raman spectrometer. The gemological characteristics of “Laoshan Jade” are consistent with serpentine jade. It can be named serpentinite, mainly composed of serpentine (antigorite), chlorite (clinochlore), and magnetite. Some samples contain magnesite and chromite. Only small amounts of unaltered forsterite, chrysolite, and diopside can be found in poor-quality serpentine jade. The protolith of “Laoshan Jade” is metamorphic peridotite. Antigorite is altered from olivine. Clinochlorite is altered from the diopside. Disseminated magnetite is the metamorphic product. Unaltered olivine and diopside belong to protolith. Chromite with zonal texture also belongs to protolith. The average temperature and pressure of its core are calculated to be 1348 °C and 3.1 GPa, which indicates that the protolith comes from the mantle asthenosphere. The formation temperature of its edge is lower than 500 °C, with metamorphic origin. XRF experiments show that “Laoshan Jade” samples are relatively rich in Mg and more depleted in fusible elements (Al, Ca) than the original mantle peridotite, indicating that serpentinite protolith has undergone a certain degree of partial melting. Combined with EPMA results, the findings of this study reveal that protolith belongs to the depleted mantle peridotite in the subduction zone, partially melted in the mantle wedge, and reacted with subduction zone fluid. Pyroxene is altered into chlorite, olivine is altered into serpentine, and magnet is generated. The edge of chromite in the protolith is altered by the iron-rich fluid into magnetite. Finally, serpentinite is formed.

Analysis and application of yttrium element in garnet by electron micro-probe analyzer: A case study of garnet-mica schist from Foziling Group

石榴石是最重要的造岩矿物之一，通常能够保留早期的矿物结构和物质并记录较为晚期的变形和变质反应。石榴石钇（Y）元素环带特征丰富、复杂，不同的环带特征通常暗示不同的形成环境或经历了不同的变质事件，是变质演化历史研究的重要媒介之一。以往的研究中，多以LA-ICP-MS作为石榴石Y元素的主要分析手段，EPMA主要用于主量元素的分析。但是，LA-ICP-MS的束斑尺寸（44μm）和基底效应较EPMA （0~5μm）大，当石榴石颗粒小、包体和裂隙发育或成分环带以微区尺寸内存在较大变化时，大束斑更容易覆盖某些特殊信息。通过对石榴石Y元素测试参数的调试和标样验证，最终确定峰位测试时长和背景测试时长分别为140s和70s，并进行了PHA谱峰干扰剥离，降低检测限至54×10^-6。本文将通过对比佛子岭石榴云母片岩（LD025）4颗石榴石的EPMA主、微量原位分析（Ca、Mg、Mn、Fe、Y、Al、Si、Cr、Ti、Na）和LA-ICP-MS石榴石Y元素分析结果，论证EPMA分析Y元素的可行性。石榴石X-ray Mapping和主量成分剖面揭示该4颗石榴石均为生长环带，Mn呈钟形分带，Y与XSps呈强烈正相关性，与XGrs、XAlm、XPrp相关性不清晰。EPMA和LA-ICP-MS分析结果显示Y含量曲线在核部和幔部具有良好的一致性，Grt1~Grt3中Y均表现出自核部（500×10^-6~1200×10^-6）向幔部（200×10^-6~500×10^-6）逐渐降低，极边部Y含量低（20×10^-6~200×10^-6）且变化复杂；Grt4中Y含量差异相对较小（180×10^-6~450×10^-6），仅在边部出现不同程度的升降。因EPMA对于Y元素含量较低（<200×10^-6）时灵敏度不够或者LA-ICP-MS束斑尺寸大容易掩盖边部窄带成分真实变化等原因，二者在边部Y元素差异较大。分别对EPMA和LA-ICP-MS的分析结果应用Grt-Xtm温度计和Grt单矿物压力计获得的变质PT结果显示Grt1~Grt3（核-幔-边）和Grt4（核-边）均记录较为完整、统一的温压演化过程。M1→M2→M3的变质温压变化分别为T=530~544℃、P=0.78~0.82GPa→T=577~616℃、P=0.89~0.98GPa→T=631~661℃、P=1.01~1.07GPa，表现为顺时针演化型式，M1至M3反映的是一个暖俯冲过程。根据温度评价结果，Grt1~Grt3（1.2~1.4mm，自形程度高）形成时间应早于Grt4（0.8mm，自形程度低）。由此可知，大颗粒的石榴石Y元素含量及变化特征通常更容易揭示相对完整的变质演化历史。本次研究为变泥质岩演化历史、变质温压评价等研究提供了不同视角和思路，结合EPMA主量（矿物成分、X-ray mapping、BSE分析）和微量元素（Y等）分析能够更加精准、全面地解读地质信息。;Garnet is one of the most rock-forming mineral in the earth, it can record not only the former mineral's composition and structure, but also later deformation history and metamorphic reactions of rocks. In previous studies, LA-ICP-MS was mostly used as the main analysis method of yttrium (Y) in garnet, and EPMA was mainly used for analysis of major elements. However, the beam spot size (44μm) and basement effect of LA-ICP-MS are larger than those of EPMA (0~5μm). When garnet particles are small, inclusions and fractures are developed, or there are large changes in the micro area size of the composition ring, the large beam spot is easier to cover some special information. Through the debugging of garnet Y analysis parameters and standard sample verification, it is finally determined that the peak position and background counting time are 140s and 70s respectively, and the PHA spectrum peak interference stripping is carried out to reduce the detection limit to 54×10^-6. The paper will demonstrate the feasibility of EPMA analysis of Y by comparing the results of EPMA main and micro in-situ analysis (Ca, Mg, Mn, Fe, Y, Al, Si, Cr, Ti, Na) and LA-ICP-MS garnet Y content analysis. Garnet X-ray mapping and component profile reveal that the four garnets are characterize by growth ring, and the bell shaped zoning of Mn is typical. Among them, Y has a strong positive correlation with XSps, and the correlation with XGrs, XAlm and XPrp is not clear. The results of EPMA and LA-ICP-MS analysis show that the Y content curves are in good agreement both core and rim. Yttrium in Grt1~Grt3 is characterized by a gradual decrease from the core (500×10^-6~1200×10^-6) to the mantle (200×10^-6~500×10^-6), the extreme rim with low Y (20×10^-6~200×10^-6) and the change is complex. The difference of Y content in Grt4 is relatively small (180×10^-6~450×10^-6), and there are only different degrees of rise and fall at the outer edge. Due to the insufficient sensitively of EPMA to low Y content (<200×10^-6) or the large beam spot size of LA-ICP-MS, which is easy to cover up the real change of narrow rim Y composition, the two have great differences Y contents in the rim section. Based on the analysis results of EPMA and LA-ICP-MS, the metamorphic PT conditions obtained by Grt-Xtm thermometer and Grt single mineral geobarometer show that Grt1~Grt3 (core-mantle-rim) and Grt4 (core-rim) record a relatively complete and unified metamorphic PT evolution process. The metamorphic PT changes of M1→M2→M3 are T=530~544℃and P=0.78~0.82GPa→T=577~616℃ and P=0.89~0.98GPa→T=631~661℃ and P=1.01~1.07GPa respectively, showing a clockwise evolution pattern. M1 to M3 reflect a warm subduction process. According to the PT results, the formation time of Grt1~Grt3 (1.2~1.4mm, high automorphism) should be earlier than Grt4 (0.8mm, lower automorphism). Therefore, the content and variations characteristics of Y in large grain garnet are usually easier to reveal the relatively complete metamorphic evolution process. This study provides different perspectives and ideas for the study of metamorphic argillaceous rock evolution history and metamorphic temperature. Combined with EPMA major element (composition, X-ray mapping and BSE analysis) and trace element (Y, etc.) analysis, the geological information can be interpreted more accurately and comprehensively.

Effects of Cu on the Morphology and Growth Mode of Graphite in Compacted Graphite Iron

In this article, Cu is found to have a great influence on the graphite morphology and growth mode in compacted graphite iron (CGI). Metallographic pictures show that the number of vermicular graphite of the surface of CGI casting is significantly higher than that of the core, and there is more spheroidal graphite in the core of casting. In addition, a special form of graphite, which is defined as distorted graphite appears in the matrix. From the EPMA results, it can be concluded that the segregation of Cu promotes the distortion of graphite, and part of distorted graphite is transformed into vermicular graphite under the action of vermicular elements (Mg, La, and Ce). The increase in the number of spheroidal graphite improves the strength of casting, but it reduces the thermal conductivity.

Fission gas release from irradiated mixed-oxide fuel pellet during simulated reactivity-initiated accident conditions: Results of BZ-3 and BZ-4 tests

Fission gas release from high-burnup mixed-oxide (MOX) fuel pellet with Pu fissile contents of 4.1% during reactivity-initiated accident (RIA) was estimated based on radial Xe concentration profiles in fuel pellet using scanning electron microscopy/electron probe microanalysis (SEM/EPMA) before and after pulse irradiation tests called BZ-3 and BZ-4. The tests were conducted at the Nuclear Safety Research Reactor (NSRR) in Japan Atomic Energy Agency (JAEA). The depression of Xe concentration in the Pu-spot and the crack formation in the peripheral region of fuel pellet were observed after BZ-3 and BZ-4. This kind of cracks was considered to promote the release of the fission gas retained in the Pu-spot. Based on the EPMA results and the effect of the crack formation, the amounts of the release of the gas retained in Pu-spot was estimated to be 0.13 and 0.04 in BZ-3 and BZ-4 tests, respectively. Moreover, taking account of the release of the gas accumulated in the grain boundary in Pu-spot-excluded region and the release of the gas dissolved in the matrix, the total amount of fission gas release was evaluated as 0.33–0.43 and 0.15–0.27 in BZ-3 and BZ-4 tests, respectively. Comparing the results of the fission gas release with the results of rod-puncture test, it was suggested that fission gas release from not only the Pu-spot but also the Pu-spot-excluded region.

Structure and Solidification Process Observation of Fe-C-Cr Alloy Using Confocal Laser Scanning Microscope

In this study, we investigated the growth process of M7C3 carbide by a Confocal Laser Scanning Microscope. Fe-C-Cr alloy was prepared using an arc furnace. The composition was determined to be Fe:C:Cr=55:5:40(wt%). From the results of XRD and EPMA, the Fe-C-Cr alloy contained M7C3 carbide in the internal structure. In condition of two cooling rates 60°C/min and 30°C/min observed with a Confocal Laser Scanning Microscope. Corners of the Hexagonal structure grew in the preferred orientation direction of M7C3 carbide at 60°C/min. After the growth of preferred orientation direction, the M7C3 carbide formed to connect between the corners. At a cooling rate of 30°C/min, M7C3 carbides grew in oblique direction to the observation area. At the beginning, the structures were hidden in the fluid. But the structures started to grow, the shape of the hexagon became eventually. After the melting experiment, the samples were observed by Optical Microscope and Scanning Electron Microscope. As a result, since hexagonal structure arose a difference in height between the outside and the inside. M7C3 carbides grew from the outside in the solidification process.

Zircon U-Pb dating and Hf isotopic compositions of intrusions in the Erdaohe silver-lead-zinc deposit, Inner Mongolia and the metallogenic process of the deposit

二道河银铅锌矿为大兴安岭中段最新发现的一处大型矽卡岩型矿床。银铅锌矿的形成与矿区多期岩体密切相关，矿体主要赋存于矽卡岩、大理岩及细粒花岗闪长岩内。本文对矿区主要岩体及石榴子石矽卡岩开展了锆石LA-ICP-MS U-Pb年代学、Hf同位素研究和石榴子石电子探针分析，获得了绿帘石化细粒花岗闪长岩、绿帘石化细粒闪长岩、花岗斑岩的²⁰⁶Pb/²³⁸U加权平均年龄分别为506±4.3Ma、213±2.8Ma和128±1.1Ma。二道河矿区石榴石矽卡岩与绿帘石矽卡岩常呈相互穿插关系，闪锌矿、方铅矿等矿石矿物具有重结晶特征，矽卡岩矿物石榴子石电子探针分析结果显示在矿区至少存在两期不同性质的流体活动，表明二道河银铅锌矿至少经历了两期以上的矿化事件。获得的三类岩体的锆石ε_Hf（t）值分别为0.9~6.9、8.3~15.1和7.9~14.1，对应的二阶段模式年龄（t_DM2）分别为1.6~1.1Ga、0.8~0.3Ga和0.8~0.3Ga，表明这些花岗岩类均来源于新生地壳部分熔融，它们的成因可能分别与额尔古纳地块和兴安地块的拼合、蒙古-鄂霍茨克洋闭合及古太平洋板块俯冲有关。这些构造体系的叠加与演化对二道河银铅锌矿床的形成和富集具有非常重要的作用。;The Erdaohe silver-lead-zinc deposit is a newly discovered large skarn deposit in central Great Xing’an Range, and its formation is closely related to multi-stage intrusions. The ore bodies in the deposit mainly occur in skarns, marble, and fine-grained granodiorites. In this study, we conducted LA-ICP-MS zircon U-Pb dating, Hf isotopic analysis, and the electron microprobe analysis (EPMA) of garnets for the major intrusions and garnet granites in the deposit. Zircon grains from the epidotized fine-grained granodiorites, epidotized fine-grained diorites, and granite porphyry yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 506±4.3Ma, 213±2.8Ma, and 128±1.1Ma, respectively. The garnet skarns and epidote skarns in the Erdaohe deposit are frequently interspersed with each other, and the ore minerals such as sphalerite and galena in the deposit are characterized by recrystallization. Moreover, the EPMA results of garnets in the skarns show there were at least two stages of fluid activities with different natures. All these indicate that the Erdaohe deposit has undergone at least two stages of mineralization events. Zircons from three types of intrusions obtained yielded ε_Hf(t) values of 0.9~6.9, 8.3~15.1, and 7.9~14.1, respectively, with t_DM2 values of 1.6~1.1Ga, 0.8~0.3Ga, and 0.8~0.3Ga, respectively. This indicates that all these granitoids are originated from the partial melting of the juvenile crust, and their formation may be related to the combination of the Erguna and Xing’an blocks, the closure of the Mongol-Okhotsk Ocean, and the subduction of the Paleo-Pacific Plate, respectively. The superimposition and evolution of tectonic systems play a crucial role in the formation and enrichment of the Erdaohe silver-lead-zinc deposit.

Mineralogy, temporal and spatial distribution of Mo mineralization in Guilinzheng Mo-W deposit, Jiangnan W mineralization belt and its significance

安徽桂林郑钼钨矿床位于江南钨矿带北部，是目前区内唯一钼储量达到大型的钼钨矿床。本文在对该矿床地质特征和已有成果总结基础上，详细观察了各代表性矿化蚀变样品的岩相学特征，提出该矿床具镁质矽卡岩矿床特征，是桂林郑花岗斑岩熔体与奥陶系白云质灰岩地层交代的产物。矿石类型可分为靠近岩体（<100m）浸染状矿石和远离岩体（>100m）的条带状矿石，分别赋存在接触交代矽卡岩和层控矽卡岩中。桂林郑矿床的矿石矿物为富钼白钨矿（钼钙矿-白钨矿系列），可分为三个世代，分别形成于无水矽卡岩阶段（Sch-I）和含水矽卡岩-氧化物阶段（Sch-II和Sch-III），辉钼矿仅在浸染状矿石富钼白钨矿（Sch-III）边部少量发育。不同矿石类型、不同世代富钼白钨矿的电子探针成分分析显示，富钼白钨矿的钼含量（MoO₃%）在5.75%~71.02%之间，均值为46.00%（n=224），总体具有超常富钼的特点；从无水矽卡岩阶段到含水矽卡岩-氧化物阶段（早→晚）、从浅部的条带状矿石到深部的浸染状矿石（浅→深），富钼白钨矿MoO₃含量有降低趋势。桂林郑钼钨矿床是首个以富钼白钨矿为主要矿石矿物的钼-多金属矿床，这一特殊钼钨矿床的发现深化了矽卡岩钼钨矿床的成因认识，同时对江南钨矿带内区域成矿规律与找矿勘探工作的推进提供了依据。;The Guilinzheng Mo-W deposit is located in the northern sector of the Jiangnan W mineralization belt (JWB), which is the largest molybdenum-poly-metallic deposit in JWB at present. Based on the understanding of the geological background and previous studies of the Guilinzheng Mo-W deposit, the authors systematically observed the petrographic characteristics of various mineralization and alteration samples, which showed that it is a Mg-rich skarn deposit. This deposit was formed by metasomatism between the Guilingzheng granite porphyry melt and Ordovician dolomitic limestones. It can be classified as disseminated and banded ore types, which occur in the contact metasomatic skarn (<100m to the granite porphyry) and strata bound skarn (>100m to the granite porphyry), respectively. The main ore mineral is Mo-rich scheelite (powellite-scheelite series), which can be subdivided into 3 stages in order:the first-stage Mo-rich scheelite (Sch-I) was formed during anhydrous skarnization; the two later ones (Sch-II and Sch-III) were both formed during hydrous skarnization. There are some molybdenite occurring in the edges and gaps of the Sch-III grains. The EPMA results of those different types Mo-rich scheelite showed that the MoO₃ contents varied from 5.75% to 71.02%, with an average value of 46.00% (n=224), indicating an extremely high-Mo ore mineral. Decreasing MoO₃ contents of Mo rich scheelite in Guilinzheng deposit is observed from shallow banded ore to deep disseminated ore spatially, and from early anhydrous skarn stage to late hydrous skarn stage temporally. Guilinzheng Mo-W deposit is the firstly reported Mo deposit with Mo-rich scheelite, instead of molybdenite as the main ore mineral. Systematic studies of this ore deposit can deepen the genetic understanding of the powellite-scheelite mineralization and promote researches on the regional metallogeny and prospecting indicators in JWB.

Floating Grain Characterization and Its Effects on Centerline Segregation of Direct-Chill Cast Al–Mg–Si Alloy Billets

Microstructure and microsegregation analysis were performed on a direct-chill (DC) cast Al–Mg–Si alloy billet, aiming to quantitatively investigate the microscopic features of floating grain and its contribution to the negative centerline segregation. Microstructure results show some irregular grains, whose grain size and secondary dendrite arm spacing (DAS) are two times larger than that of the regular fine grains, appear only in the billet central region. The duplex grain structure, a mixture of internal coarse and peripheral finer dendrites within one grain, was clearly shown by the EPMA results, exhibiting special microsegregation features. The coarse dendrites are more solute-depleted than the nearby finer-DAS structure, in which the average concentration of solute Mg nearly equals to the nominal content. Based on the microscale features and solidification information of the alloy, the irregular grains exhibiting duplex dendrite feature are confirmed to be floating grain, which internal coarse dendrites are believed to mainly contribute to the negative centerline segregation. And the resulting segregation degree is quantitatively evaluated to be ∼0.041 for solute Mg considering the floating grains in the billet center as against with the assumed 100% fine-DAS microstructure.