Search

North Pacific Ocean sediments are important archives of geomagnetic field and paleoenvironmental evolutions, yet late Quaternary sedimentary sequences in the North Pacific Ocean are less explored because of generally low sedimentation rates and the challenge of dating sediments deposited below the calcite compensation depth. Core NP02 sediments from the North Pacific Ocean contain three visible tephra layers, which are identified as the To‐Of, Spfa‐1, and Kt‐3 tephra, respectively. An age model for core NP02 is established based on tephra correlation and one radiocarbon date, which gives a mean sedimentation rate of ∼11.6 cm/kyr. Magnetic analyses suggest the dominance of two remanence carriers; detrital vortex state and biogenic single domain magnetite. Variable depth offsets between the relative paleointensity (RPI) signals carried by the two remanence carriers adds a negligible age error (<0.5 kyr) to the core NP02 RPI record. Pronounced RPI amplitude variations are observed, and the Rockall and Laschamp excursions are identified in the core NP02 RPI record based on the age model. The fidelity of the core NP02 RPI record is further verified by comparison with other RPI stacks and records, and we demonstrate that the RPI variations can assist in chronology refinement. Plain Language Summary: The North Pacific Ocean is too deep to preserve materials effectively for the oxygen isotope chronology, and sediments deposit slowly in this region. Therefore, dating is a big problem for late Quaternary sedimentary cores. In this study, core NP02 sediments from the North Pacific Ocean are studied. The To‐Of, Spfa‐1, and Kt‐3 tephra layers are identified in core NP02 sediments based on the geochemical features. An age model for this core is reconstructed with the aid of tephra ages and one radiocarbon date. Magnetic analyses suggest that both small biogenic and relatively large detrital magnetite record geomagnetic information, and the two groups of magnetite deposit at about the same time. Based on the age model, core NP02 RPI record preserves the Rockall and Laschamp excursions, and the RPI pattern is consistent with other RPI stacks and records, which verifies core NP02 RPI fidelity. Therefore, we demonstrate that RPI variations is a promising dating tool for North Pacific Ocean sediments. Key Points: We use an age model based on tephra correlation and one radiocarbon date to assess the fidelity of relative paleointensity variationsDetrital vortex state and biogenic single domain magnetite are the dominant remanence carriers, and they introduced <0.5 kyr age errorAssessment of component‐specific magnetic properties should be considered to ensure the reliability of relative paleointensity variations [ABSTRACT FROM AUTHOR]

Continental shelves serve as a bridge between the continent and ocean and sediments in this region are sensitive to land-sea interaction, sea-level variation and local subsidence. In this study, we present a comprehensive magnetic study of the longest sediment core (CSDP-1, 300.1 m) recovered from the South Yellow Sea. The major magnetic minerals in the studied sediments are magnetite, hematite and greigite. Greigite records a chemical remanent magnetization, which can be removed effectively by thermal demagnetization. The magnetostratigraphy defined in this study contains the Matuyama-Brunhes boundary (M/B, 781 ka) at ∼73.68 m, which is consistent with results from adjacent cores. The base of the Quaternary (∼2.6 Ma) in the Yellow Sea is recovered for the first time at a depth of 227.16 m. The basal age of the core is estimated to be ∼3.50 Ma. It indicates that the first transgression of the Yellow Sea occurred no later than ∼1.7 Ma. Succeeding large amplitude regressions occurred in some cold periods such as during MIS 20, MIS 18, and MIS 10. Our results provide the first chronology that brackets the entire Quaternary and we reconstruct the sedimentary evolution of the Yellow Sea with robust age constraints, which provides an important framework for further paleoenvironmental and tectonic studies. [ABSTRACT FROM AUTHOR]

The present work studied the softening and melting properties of different burden structures including pellet, sinter and mixed burden (pellet mixed with sinter) with a pellet ratio of 33.65%. The content of high chromic vanadium titano-magnetite in sinter and pellet was different. The experimental results indicated that the compositions of the burden have an important effect on the softening and melting properties. The softening and melting properties of pellet burden structure were improved when the high basicity sinter was added into the acid pellet forming mixed burden. The softening and melting properties of mixed burden with a pellet ratio of 33.65% were better than other burden structures. The initial softening temperature, the temperature interval of softening, the starting melting temperature, the temperature interval of melting, and maximum differential pressure were 1100 °C, 130 °C, 1250 °C, 130 °C and 15.7 kPa, respectively. By comparing the contents of Ti, V and Cr of iron that had dripped through the different burden structures, the content of valuable components (Ti 0.349%, V 0.244% and Cr 0.094%) was highest of the pig iron collected from the mixed burden. [ABSTRACT FROM AUTHOR]

In the present study, the reduction process of pellet containing high chromic vanadium-titanium magnetite in cohesive zone has been investigated. To elucidate the reduction process including the softening and melting properties, structure changes and migration processes of valuable components (Fe, V, Ti, and Cr) in pellet containing high chromic vanadium-titanium magnetite in cohesive zone, the experiment was carried out at different temperatures and the pellet samples were analyzed by the methods of XRD, SEM, and chemical analysis. The results of reduction process show that the temperature range of cohesive zone of pellet is from 1087.9 to 1338.3 °C and the maximum differential pressure of the burden is 15 859 Pa at the temperature of 1291 °C. The reduction process of pellet was gradually conducted from outside to inside, which could form a layer of iron shell on the outer surface of the pellet. A lot of wustite could be generated in the core of pellet when the reduction temperature exceeded 1100 °C. The migration process of iron is Fe2O3→Fe3O4→FeO→Fe, while the generated FeO could react with SO2 forming 2FeO·SO2. The reduction process of titanium is Fe2O3·3TiO2→Fe5TiO8→Fe2TiO4→FeTiO3→Ti(O0.19C0.53N0.32)→Ti(C,N)→[Ti] and MgO·TiO2→Ti(C,N)→[Ti]. The migration process of vanadium is V2O3→VN, VC→[V] and the chromium oxide was reduced as follows: (Fe0.6Cr0.4)2O3→FeCr2O4→[Cr]. [ABSTRACT FROM AUTHOR]

The loss of permeability affects the reduction of the ferrous burden in the cohesive zone of a blast furnace (BF). Vanadia–titania magnetite (VTM) burden of various chemical compositions have different metallurgical properties. The reduction and softening-melting-dripping properties of different kinds of VTM were investigated. The results showed that the core of sinter or pellet is indirectly reduced to wustite and (Fe,Ti)Ox, and the periphery contains interlinked metallic iron and CaSiO3 in the cohesive zone. Wustite and (Fe,Ti)Ox are directly reduced in the melting-dripping zone. The aggregate (Fe, V, Cr) present in the non-dripping causes a loss of valuable components. With the increase in TiO2 content, the substrate phase of molten slag changes from melilite to titanaugite, and the mass of dripping decreases gradually. In addition, the permeability index S increased and the melting zone widened, which indicates that the increase in TiO2 content negatively affected the melting-dripping performance. The mass of the dripping is directly proportional to the pellet ratio. Considering the adverse effect of TiO2 on softening-melting-dripping properties, it is recommended that high TiO2 VTM is smelted while mixed with ordinary ores or with an increased pellet ratio in the burden structure. [ABSTRACT FROM AUTHOR]