Efficacy of an external chromia layer in reducing nitridation of high temperature alloys

Six high temperature alloys have been exposed in N2/H2 environments at 900 \ub0C. In order to study the efficacy of a chromia barrier layer against nitrogen ingress, experiments were performed in two environments having the same N2/H2 ratio but slightly different water content, chromia formation being spontaneous in one case only. The samples were evaluated by SEM/STEM/EDX, XRD, gravimetry and GD-OES. The presence of an external chromia scale reduced nitridation of the alloy by 50–95%. Furthermore, in the presence of a continuous alumina layer no nitridation of the alloy was detected

Manual mapping of drumlins in synthetic landscapes to assess operator effectiveness

Mapped topographic features are important for understanding processes that sculpt the Earth's surface. This paper presents maps that are the primary product of an exercise that brought together 27 researchers with an interest in landform mapping wherein the efficacy and causes of variation in mapping were tested using novel synthetic DEMs containing drumlins. The variation between interpreters (e.g. mapping philosophy, experience) and across the study region (e.g. woodland prevalence) opens these factors up to assessment. A priori known answers in the synthetics increase the number and strength of conclusions that may be drawn with respect to a traditional comparative study. Initial results suggest that overall detection rates are relatively low (34–40%), but reliability of mapping is higher (72–86%). The maps form a reference dataset

Patterns in recent and Holocene pollen accumulation rates across Europe - the Pollen Monitoring Programme Database as a tool for vegetation reconstruction

The collection of modern, spatially extensive pollen data is important for the interpretation of fossil pollen assemblages and the reconstruction of past vegetation communities in space and time. Modern datasets are readily available for percentage data but lacking for pollen accumulation rates (PARs). Filling this gap has been the motivation of the pollen monitoring network, whose contributors monitored pollen deposition in modified Tauber traps for several years or decades across Europe. Here we present this monitoring dataset consisting of 351 trap locations with a total of 2742 annual samples covering the period from 1981 to 2017. This dataset shows that total PAR is influenced by forest cover and climate parameters, which determine pollen productivity and correlate with latitude. Treeless vegetation produced PAR values of at least 140 grains cm(-2) yr(-1). Tree PAR increased by at least 400 grains cm(-2) yr(-1) with each 10% increase in forest cover. Pollen traps situated beyond 200 km of the distribution of a given tree species still collect occasional pollen grains of that species. The threshold of this long-distance transport differs for individual species and is generally below 60 grains cm(-2) yr(-1). Comparisons between modern and fossil PAR from the same regions show similar values. For temperate taxa, modern analogues for fossil PARs are generally found downslope or southward of the fossil sites. While we do not find modern situations comparable to fossil PAR values of some taxa (e.g. Corylus), CO2 fertilization and land use may cause high modern PARs that are not documented in the fossil record. The modern data are now publicly available in the Neotoma Paleoecology Database and aid interpretations of fossil PAR data

Comparison of early stages of precipitation in Mo-rich and Mo-poor maraging stainless steels

The precipitation process during ageing in the Mo-poor alloy Carpenter 455 has been investigated by three-dimensional atom probe (3DAP) and energy-filtered transmission electron microscopy. The ageing treatment was performed at 475 degrees C for 5 min, 25 min, 1 h and 2 h. The precipitation of a mixed Ni-, Ti- and Cu-rich phase was observed after 25 min of ageing. A complete separation between Ni/Ti-rich and Cu-rich regions occurred within 1-2 h of ageing. After 2 h of ageing at 475 degrees C, coarsening of the eta-Ni3Ti precipitates was observed. Moreover, large Ni/Ti-rich and Cu-rich particles were observed in the lath boundaries after 2 h of ageing. The results were compared with the precipitation process in the Mo-rich alloy 1RK91. Copyright (C) 2007 John Wiley & Sons, Ltd

Age, formation and significance of loess deposits in central Sweden

Loess deposits are common in the mid-latitudes and are excellent records of past climate, landscape change and dust. However, loess deposits are seldom reported from Fennoscandia. Here we investigate two former glaciofluvial areas in central Sweden, Brattforsheden and Bonasheden, where post-glacial loess and sand dune activity have been documented previously. Based on detailed mapping, grain size, scanning electron microscopy and optically stimulated luminescence dating analyses, we confirm the presence of loess deposits at the sites and extend the known area of loess coverage. Our results suggest that loess deposits are more common than previously thought in Sweden. The results also demonstrate that basal parts of the loess are often mixed with underlying sediment, which may be a common feature of thin loess deposits close to former ice margins. Quartz luminescence is well suited for dating these deposits, but ages from the mixed basal loess layers are older than expected, while ages from undisturbed loess extend to c. 5 ka. The loess ages contrast with the timing of main dune activity in these areas, which is dominantly in the 1-3 kyr post-deglaciation (c. 10.9-10.5 cal kyr BP). We suggest that either sediment mixing during soil formation is responsible for the mid-Holocene loess ages, or that the loess deposits record periodic landscape destabilization into the mid-Holocene. Furthermore, there is a clear topographic control on aeolian sedimentary facies, with loess mantling high ground and dunes restricted to valleys. Loess deposits are also primarily found to the south and southwest of source areas, implying transport from the north and east. This pattern contrasts with evidence for NW winds inferred from associated sand dunes. At present, the reasons for this mismatch are unclear, although one possible explanation is that silts deposited at higher elevations were affected by Ekman flow deflection of NW surface winds

Past and future impact of glacial erosion in Forsmark and Uppland. Final report

The following report constitutes a final report of a comprehensive study on denudation and glacial erosion conducted at Forsmark and in the surrounding Uppland province, Sweden, between 2015 and 2019. The aim was to quantify the amount of past denudation at the Forsmark site and the broader Uppland region, with special focus on glacial erosion, by employing a range of methodologies. The methods included geomorphological mapping and analysis of the bedrock surface and Quaternary deposits, cosmogenic exposure dating, bedrock fracture mapping, and shallow bedrock stress modelling. The results were also used together with results from a long-term climate modelling study to quantify the potential amount of glacial erosion at Forsmark over the coming one million years. The study was initiated by Jens-Ove Näslund (SKB) and it was jointly designed by Jens-Ove Näslund, Adrian Hall (Stockholm University), Karin Ebert (Södertörn University), Bradley Goodfellow (Stockholm University, SGU), Clas Hättestrand (Stockholm University), Jakob Heyman (University of Gothenburg) and Arjen Stroeven (Stockholm University). Adrian Hall coordinated the scientific work within the study, and also conducted the studies on long-term burial and erosion history (Chapter 2) and glacial erosion (Chapter 4). Karin Ebert developed the digital elevation models of the unconformity and derived the glacial erosion estimates derived from summit erosion surfaces. Bradley Goodfellow contributed across the project and conducted the study of topographic stress perturbation, with mathematical modelling by Seulgi Moon (University of California, Los Angeles) (Chapter 3). Clas Hättestrand developed geomorphological maps of the unconformity and of glacial bedforms. Maarten Krabbendam (British Geological Survey) contributed to Chapter 2 on the longterm burial and erosion history and to Chapter 4 on glacial erosion and mapped landforms associated with glacial ripping in Uppland. Sample site selection and cosmogenic nuclide sample collection was carried out by Jakob Heyman, Bradley Goodfellow, Arjen Stroeven, Marc Caffee and Adrian Hall. Jakob Heyman conducted the modelling of cosmogenic nuclide erosion and burial histories. Bradley Goodfellow was involved in cosmogenic nuclide sample preparation at Purdue University. Reporting and interpretation of cosmogenic nuclide results in Chapter 5 was done by Jakob Heyman, Arjen Stroeven and Bradley Goodfellow. All authors contributed to the final revision of the report. The study includes several additional important contributions. Marc Caffee (Purdue University) was responsible for all cosmogenic isotope laboratory analyses and guided and participated in the discussions of interpretation of results (Chapter 5). Stephen Martel (University of Hawaii) and Taylor Perron (Massachusetts Institute of Technology) were involved in the fracture mapping and modelling (Chapter 3). Mikis van Boeckel (Stockholm University) produced many of the figures in the report from digital elevation model data from the Swedish mapping, cadastral and land registration authority (Lantmäteriet) and SGU. In connection to the present study, two additional studies have been performed employing similar methods (e.g. geomorphological analysis and cosmogenic exposure dating) for studying the sub- Cambrian unconformity in the Trollhättan area in south-western Sweden. The two associated studies will be published in separate reports (Goodfellow et al. 2019, Hall et al. 2019a). The results will be used, together with other published scientific information, for constructing future scenarios of climate and climate-related processes in SKB’s work on assessing long-term safety of nuclear waste repositories in Sweden. The safety assessments performed for the planned repository for spent nuclear fuel in Forsmark, Sweden, cover a total time span of one million years. Since this time span covers the timescales relevant for glacial cycles, the effect of future glacial erosion needs to be analysed in the safety assessments. In this context, the present study provides important results on the potential amount of glacial erosion that may be expected in the topographical, geological, and glaciological setting of the Forsmark site. A separate study models changes in climate over the next 1 million years and has been published ahead of this report (Lord et al. 2019)

Palaeoglaciology of Bayan Har Shan, NE Tibetan Plateau: exposure ages reveal a missing LGM expansion

The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined Be-10 exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in exposure ages for individual sites and within the recognised four morphostratigraphical groups. The exposure age disparity cannot be explained by differences in inheritance without using unrealistic assumptions but it can be explained by differences in post-depositional shielding which produces exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40-65 ka. More extensive glaciations occurred before 60-100 ka and 95-165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Hat Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is further supported by high-resolution glacier modelling experiments. (C) 2011 Elsevier Ltd. All rights reserved