The TSA Degradation Process Within Cement-Based Materials in the Electrical Field Environment

The thaumasite form of sulfate attack (TSA) of cement-based materials is a complex degradation process. The degradation process needs abundant water, carbonate, sulfate and silicate. However, there is no detailed study on the TSA degradation process. X-Ray Diffraction (XRD) and chemical analyses were used to study the TSA degradation process based on the present studies. The results indicated that the degradation process of the electrical field was similar to the full immersion, with the main difference being the degradation rate. The electrical field can obviously accelerate the TSA degradation process. The degradation had progressed to the core of the sample, and the amount of pulp was found at 120 days. The degree of degradation of the MgSO4 full immersion affected only the surface of the sample at 360 days. The degree of degradation of the MgSO4 full immersion was the lowest at 360 days. Meanwhile, combining the XRD, chemical analysis data, the degradation rule was summarized as there being a fixed range to generate the pulp (the representative thaumasite form of sulfate attack), and the pH and the Ca/S need to meet the following conditions: 10.6

Plasma reforming of naphthalene as a tar model compound of biomass gasification

The contamination of producer gas with tars from biomass gasification remains a significant challenge in the bioenergy industry and a critical barrier, limiting the commercial applications of biomass gasification. Non-thermal and non-equilibrium plasma offers an unconventional and emerging technology for the effective reduction of problematic tars from gasification. In this study, we investigated plasma reforming of naphthalene as a two-ring tar model compound using a gliding arc discharge (GAD) reactor with/without steam. The influence on the plasma conversion of naphthalene based on the inlet naphthalene concentration, discharge power and steam-to-carbon ratio was examined to understand the effects of these operating parameters on the destruction of tar, gas selectivity/yield and energy efficiency. Adding H2O in the plasma process generates oxidative OH radicals, creating additional reaction routes for the step-wised oxidation of naphthalene and its fragments towards the CO, CO2 and water. The optimum ratio (2.0) of steam-to-carbon was identified to achieve the highest naphthalene conversion (84.8%), C2H2 yield (33.0%), total gas yield (72.2%) and energy efficiency (5.7 g/kWh). The effect of the amount of steam on the plasma reduction of tars was dependent on the balance between two opposite effects due to the presence of steam: positive effect of OH radicals and the negative effect of electron attachment on water molecules. Introducing an appropriate amount of steam to the plasma reduction of naphthalene also substantially minimized the formation of by-products and enhanced the carbon balance. Plausible reaction mechanisms for the plasma decomposition of naphthalene were proposed through a comprehensive analysis of gaseous and condensable products combined with plasma spectroscopic diagnostics

Participant involvement in the development of an online learning community for future faculty

Although research has suggested that creating online learning community can be an effective strategy to improve student learning, there is a need for examining the process of online learning community development. The purpose of this study was to explore a user-centered approach to developing an online learning community for a university program called preparing future faculty. Under the umbrella of Design-Based Research, this study was guided by Reflective Recursive Design and Development (R2D2) instructional design model and conducted through three phases. In Phase 1, after analyzing the student manual and existing course web site, a prototype online learning community was developed. In Phase 2, participants were actively involved in the design process. Six semi-structured interviews were conducted to understand students\u27 social leaning context and their needs from PFF. By reflecting on their suggestions and opinions, solutions were discovered and applied in the online learning community development. In Phase 3, participants were invited to use the online learning community developed in Phase 2, and to provide suggestions for further development. The input from the students to the developer resulted in several specific features in the online learning community. To a great extent, the online learning community was about organizing content for students. Many participants suggested that this online learning community should be a central place for retrieving program related materials. According to these needs, archives were created for weekly announcements, speakers\u27 information, handouts, and forms. All the PFF assignments were listed chronologically with specified due dates and instructions. Another key component in this online learning community was online discussion structured to respond to learners\u27 needs for social conversation, information sharing, and providing course feedback. Results suggest the value of including the end users of an online learning community in the development process both in terms of specific suggestions for development and in terms of their ultimate ownership of the site

Identifying crystal accumulation in granitoids through amphibole composition and in situ zircon O isotopes in North Qilian Orogen

Granitoids are the main constituents of the continental crust, and an understanding of their petrogenesis is key to the origin and evolution of continents. Whether crystal fractionation is the dominant way to generate evolved magmas has long been debated, mostly because such processes would produce large volumes of complementary cumulates, which remains elusive. Mafic magmatic enclaves (MMEs) are ubiquitous in granitoids and their presence was initially recognized as cumulates. However, because many MMEs lack obvious evidence of accumulation, such as the classic cumulate textures and modal layering, the cumulate origin of MMEs has been abandoned and the model of magma mixing between mafic and felsic magmas has become popular. In this study, we conduct a combined study of amphibole composition and in situ O isotopes in zircons on three suites of orogenic granitoids with MMEs from the North Qilian Orogenic Belt (NQOB). We find that the MMEs and their host granodiorites show overlapping zircon δ18O values, affirming that they share the same parental magmas. The amphibole compositions indicate that amphiboles from the MMEs are not in equilibrium with a melt whose composition was that of the bulk-rock. These new data, together with the published bulk-rock data, suggest that the MMEs in our study have clear cumulate signatures and are thus of cumulate origin. Our study provides evidence for crystal accumulation in granitoids in the NQOB. This new understanding calls for re-examination on the petrogenesis of some intermediate magmatic rocks (granitoid/andesite) in discussing models of continental crustal growth

Ophiolites in the Xing’an-Inner Mongolia accretionary belt of the CAOB: Implications for two cycles of seafloor spreading and accretionary orogenic events

The Xing'an-Inner Mongolia accretionary belt in the southeastern segment of the Central Asian Orogenic Belt (CAOB) was produced by the long-lived subduction and eventual closure of the Paleo-Asian Ocean and by the convergence between the North China Craton and the Mongolian microcontinent. Two ophiolite belts have been recognized: the northern Erenhot-Hegenshan-Xi-Ujimqin ophiolite belt and the southern Solonker-Linxi ophiolite belt. Most basalts in the northern ophiolite belt exhibit characteristics of normal-type to enriched-type mid-ocean ridge basalt affinities with depleted Nd isotopic composition (εNd(t) > +5), comparable to modern Eastern Pacific mid-ocean ridge basalts. Most basaltic rocks in the southern belt show clear geochemical features of suprasubduction zone-type oceanic crust, probably formed in an arc/back-arc environment. The inferred back-arc extension along the Solonker-Linxi belt started at circa 280 Ma. Statistics of all the available age data for the ophiolites indicates two cycles of seafloor spreading/subduction, which gave rise to two main epochs of magmatic activity at 500–410 Ma and 360–220 Ma, respectively, with a gap of ~50 million years (Myr). The spatial and temporal distribution of the ophiolites and concurrent igneous rocks favor bilateral subduction toward the two continental margins in the convergence history, with final collision at ~230–220 Ma. In the whole belt, signals of continental collision and Himalayan-style mountain building are lacking. We thus conclude that the Xing'an-Inner Mongolia segment of the CAOB experienced two cycles of seafloor subduction, back-arc extension, and final “Appalachian-type” soft collision

Sublithosphere mantle crystallization and immiscible sulphide melt segregation in continental basal magmatism: evidence from clinopyroxene megacrysts in the Cenozoic basalts of eastern China

This study explores the effects of high-pressure crystallization and immiscible sulphide melt segregation under mantle conditions on the compositional variation of basaltic magmas, using clinopyroxene megacrysts in the Cenozoic basalts of eastern China. These clinopyroxene megacrysts are large (up to > 10 cm in size) and homogeneous at the grain scale. They were crystallized from variably evolved parental magmas and then captured by their host basalts. The large and systematic variations of [Sm/Yb]N, Lu/Hf, Fe/Mn, Sc/La, Ni and Cu with Mg# in the clinopyroxene megacrysts suggest their co-precipitation with garnet and with immiscibility between sulphide and silicate melts. This is consistent with the appearance of garnet megacrysts in the host basalts and abundant sulphide globules in the clinopyroxene megacrysts. The covariation between Ni contents of sulphide globules and Mg# of the clinopyroxene megacrysts suggests a genetic relationship between sulphide globules and clinopyroxene megacrysts. High-pressure crystallization of clinopyroxene and garnet results in decrease of Mg# and concentrations of CaO, MnO and heavy rare earth elements (e.g., Yb) and increase of Fe/Mn and [Sm/Yb]N in the residual melts. Therefore, geochemical characteristics of low Mg#, low CaO and MnO contents and high Fe/Mn and [Sm/Yb]N in basalts do not necessarily indicate a pyroxenite mantle source. In addition, caution is needed when applying the olivine addition method to infer the primary compositions of alkali basalts without considering the effects of highpressure crystallization of clinopyroxene and garnet. The calculated P-T conditions of the clinopyroxene megacrysts are close to those of the lithosphere-asthenosphere boundary (LAB) beneath eastern China, and the low primitive [Sm/Yb]N (~ 4.0) of melts parental to the clinopyroxene megacrysts suggests final equilibration at relatively low pressures most likely beneath the LAB. Hence, a melt-rich layer is expected close beneath the LAB. Melt pools in this melt-rich layer provide a stable and closed environment for the growth of compositionally homogeneous clinopyroxene megacrysts. As a result, melts in these melt pools are compositionally evolved with low and variable Mg#. Subsequent pulses of melt aggregation/supply from depths with primitive compositions and high Mg# will disturb these melt pools, cause magma mixing and trigger the eruption of magmas carrying clinopyroxene and garnet megacrysts

Magmatic record of India-Asia collision

This work was financially co-supported by Chinese Academy of Sciences (XDB03010301) and other Chinese funding agencies (Project 973: 2011CB403102 and 2015CB452604; NSFC projects: 41225006, 41273044, and 41472061).New geochronological and geochemical data on magmatic activity from the India-Asia collision zone enables recognition of a distinct magmatic flare-up event that we ascribe to slab breakoff. This tie-point in the collisional record can be used to back-date to the time of initial impingement of the Indian continent with the Asian margin. Continental arc magmatism in southern Tibet during 80-40 Ma migrated from south to north and then back to south with significant mantle input at 70-43 Ma. A pronounced flare up in magmatic intensity (including ignimbrite and mafic rock) at ca. 52-51 Ma corresponds to a sudden decrease in the India-Asia convergence rate. Geological and geochemical data are consistent with mantle input controlled by slab rollback from ca. 70 Ma and slab breakoff at ca. 53 Ma. We propose that the slowdown of the Indian plate at ca. 51 Ma is largely the consequence of slab breakoff of the subducting Neo-Tethyan oceanic lithosphere, rather than the onset of the India-Asia collision as traditionally interpreted, implying that the initial India-Asia collision commenced earlier, likely at ca. 55 Ma.Publisher PDFPeer reviewe