Secondary Dispersal Research Articles

Study on the thermal hazards of anionic surfactant AES on lignite via experiments and calculations

Spray dust reduction is a commonly used dust reduction method in coal mines and has been widely adopted. However, the thermal stability of coal dust after being wetted by dust suppressants remains unknown. The work aimed to investigate the potential environmental hazards posed by the secondary dust dispersion resulting from the cracking of lump coal dust after being wetted by surfactants and subsequently air-dried. Lignite and AES were used as experimental samples. Use thermodynamic equations to analyze, calculate, and compare the changes in the average apparent activation energy of lignite before and after AES solution wetting. Compared with lignite before AES solution wetting, the combustion characteristic index of lignite decreased by 1.93 % after wetting, and before and after AES solution wetting, the average apparent activation energy of lignite calculated by reaction kinetics methods decreased by 7.6 %, 6.7 %, and 17.1 % respectively. FTIR analysis shows the proportion of aliphatic hydrocarbons in lignite after AES solution wetting has decreased compared with before wetting, and the proportion of oxygen-containing functional groups has shown an upward trend. The work elucidated the complex microscopic mechanisms underlying hazards caused by secondary dust dispersion, providing new scientific evidence for preventing and controlling coal dust explosion accidents.

Direct observation of the evolution behavior of micro to nanoscale precipitates in austenitic heat-resistant steel via electron channeling contrast imaging

Precipitation directly determines the high-temperature properties of the austenitic heat-resistant steels. The precipitations of MX, Z-phase, M23C6 and σ-phase, ranging from micrometers to nanometers, are commonly characterized using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). However, details of their evolution behavior are still unclear due to the limited SEM resolution using the traditional sampling method and the limited spatial resolution of TEM. In this work, field emission SEM-based electron channel contrast imaging (ECCI) techniques with flexible sampling routes were introduced to observe the precipitation evolution behavior of HR3C steel after aging at 700 °C for 8095 h. We showed that the coarse primary-MX and Z-phase in the as-received steel are relatively stable during aging. The coarse M23C6 and tiny secondary Z-phase dispersions were rapidly formed along the grain/twin boundaries and within dislocation arrays inside the grain interior, respectively. We further found that the M23C6 at grain boundaries would change from continuous to semi-continuous due to the formation of σ-phases, while in twin boundaries, it would become continuous over aging. Moreover, we showed that the σ-phases were in-situ transformed from M23C6 at the grain boundaries via its dissolution, facilitating the nucleation of tiny Z-phase inside the σ-phase grains, and this phenomenon has not been reported so far. We have demonstrated that ECCI with an electrolytic-polishing-based sampling route is effective in revealing multi-scale precipitation with high-throughput efficiency, and it allows the direct observation of the complex behavior of precipitates down to the nanoscale using a bulk sample. This method can be used as an efficient way for the quantitative microstructure study.

Seeds go up and down: The role of dung beetles in soil seed movement in the Southern Atlantic Forest of Argentina

Abstract The vertical movement of seeds performed by dung beetles from the soil bank and in animal faeces influences seed germination and the temporal dynamic of forest regeneration. While this process has been explored at the community level, the individual role of species is less understood. Here, we investigated the role of dung beetle size and seed size in this vertical movement under experimental conditions. We performed experiments using a gradient of dung beetle sizes and three sizes of artificial seeds (plastic beads) in two situations: inside faeces (secondary dispersal) and buried in the ground (soil bank). Through regression analysis, we related dung beetle size, seed size, and the initial position of seeds on the soil bank to the final position of seeds and their potential germination. For seeds in the soil bank, upward movement and exhumation were mainly of medium and large seeds, initially located at shallower depths, with larger beetles being primarily responsible for this movement. The downward movement was similar for all seed sizes. In dung seeds, the percentage of small seeds buried gradually increased with beetle size, while larger beetles made the main contribution for medium and large seeds. Besides, all seed sizes were buried at an average maximum bury depth of nearly 4 cm (the limit of the germination zone). The relative contribution of species depended on the interaction between dung beetles and seed sizes. Moreover, large dung beetles were essential for burying large seeds in the Southern Atlantic Forest.

Dynamic Directional Ultrasonically In Situ-Generated N,S-Codoped Carbon Dots in Poly(ethylene glycol) for Improved Tribological Performance.

The dispersion stability of nanomaterials in lubricants significantly influences tribological performance, yet their addition as lubricant additives often presents challenges in secondary dispersion. Here, we present a straightforward method for in situ preparation of N,S-codoped CDs (N,S-CDs)-based lubricants using heterocyclic aromatic hydrocarbons containing N/S elements in poly(ethylene glycol) (PEG) base oil by a directional ultrasound strategy. Two types of N,S-CDs were successfully prepared via the directional ultrasound treatment of PEG with benzothiazole (BTA) and benzothiadiazole (BTH) separately. The resultant N,S-CDs have a uniform distribution of N and S elements and maintain good colloidal dispersion stability in PEG even after 9 months of storage. The N,S-CDs can enter the surface gap of the friction pairs and then induce a tribochemical reaction. Benefiting from the synergistic effect of N and S activating elements, a robust and stable protective film consisting of iron sulfides, iron oxides, carbon nitrides, and amorphous carbonaceous compounds is formed, thus endowing N,S-CDs-based lubricants with improved antiwear and friction-reducing performance. Compared with pure PEG, the coefficient of friction (COF) of the N,S-CDs(BTH)-based lubricant decreased to 0.108 from 0.292, accompanied by a 91.2% reduction in wear volume, and the maximum load carrying capacity increased to 450 from 150 N.

Biotic and abiotic dispersal of a large-seeded keystone genus in Madagascar

In tropical forests, most plant species rely on frugivorous animals for seed dispersal services. Such mutualisms are imperiled by defaunation, which disproportionately affects large-bodied vertebrates and may impact the interactions of the large-seeded plants they disperse. However, frugivore-mediated seed dispersal (zoochory) may not be the only mechanism ensuring the dispersal of a given plant species. With a focus on large-seeded canopy trees in the genus Canarium in the rainforests of Madagascar, thought to be dispersed by large-bodied lemur species, we investigated the contribution of multiple dispersal mechanisms to the movement of large seeds. Specifically, we (1) examined the potential for dispersal by abiotic factors, such as winds and runoff associated with frequent cyclones, (2) documented the animal species that could effectively contribute to their primary and secondary seed dispersal, and (3) determined how non-lemur and abiotic dispersal compare to the imperiled function of extant, though threatened, lemur primary dispersers. Using field observations and experiments, we found that wind, water, and secondary dispersal can move seeds considerable distances away from the parent plants, though they were less effective at long-distance dispersal than primary dispersers (i.e., large-bodied lemurs). For secondary dispersal, we found that dispersal distance is positively correlated with predation, potentially reducing dispersal effectiveness. Future comparisons with predation of primary or abiotically dispersed seeds will be necessary. Our research highlights the role of understudied mechanisms in the dispersal of large-seeded plants in Madagascar. Understanding the existence and impact of non-lemur dispersers in these imperiled forests can help complete our understanding of the mechanisms that shaped their astounding biodiversity and may mediate their response to ongoing environmental change.

Improving energy storage properties of polyarylene ether nitrile with coral-like CaCu3Ti4O12 nanorods

Film capacitors have attracted widespread attention in the field of power electronics due to their advantages of long service life, high-power density, rapid charging and discharging rates, operational safety, among others. Nonetheless, the persisting challenge regarding the dielectric capacitors’ insufficient energy storage density remains the primary obstacle impeding their advancement. Herein, one-dimensional (1D) coral-like calcium copper titanate (CaCu3Ti4O12) nanorod (CCTONR) is fabricated and interface modified to enhance energy storage properties of polyarylene ether nitrile (PEN). The CCTONR is fabricated through a two-step hydrothermal reaction followed by calcination, and then modified by KH550 and sulphonated PEN sequentially offering SPEN@CCTONR. Due to the 1D nature and the functionalization of SPEN on the surface of CCTONR, the compatibility and the distribution state of SPEN@CCTONR in the PEN matrix are conspicuously improved. Furthermore, a secondary dispersion of SPEN@CCTONR is achieved in the SPEN@CCTONR/PEN composite via uniaxial hot-stretching. As a result, the dielectric permittivity is increased to 17.96, while the breakdown strength remains 199.4 kV/mm for the stretched SPEN@CCTONR/PEN film with filler content of 15 wt%. Correspondingly, an energy storage density of 3.16 J/cm3, with an boosting of 320 % in comparing with that of PEN, is achieved. This stretched SPEN@CCTONR/PEN film with leaped energy storage density would be a promising candidate for future flexible dielectric materials.

Seed traits and burial state affect plant seed secondary dispersal mediated by rodents

Seed dispersal is an important ecological process and has important implications for plant population expansion and regeneration. Seed dispersal not only reduces the probability of death due to seed density but also facilitates seedling establishment. Many studies have focused on the effect of one or two factors on seed dispersal. However, little is known about studies on the effect of multiple factors and their interactions on seed dispersal. Here, we conducted a field experiment to explore how seed size, soil burial, and seed peeling affect the dispersal and hoarding of seeds of Quercus liaotungensis in dispersal animals. We found that large seeds were preferentially selected by animals, and the predation after dispersal, hoarding after dispersal, predation distance after dispersal, and hoarding distance after dispersal of large seeds were significantly greater than small seeds, which is more beneficial to the plant expansion and regeneration. Soil burial increased the time of seed intact in situ, significantly increased predation in situ, and reduced predation after dispersal, predation distance after dispersal, and hoarding distance after dispersal, which is not beneficial to the plant population expansion and regeneration. Seed peeling reduced the time of seed intact in situ, and the predation after dispersal was significantly greater than that of unpeeled seeds, which is not beneficial to the plant population. We did not find the interactions between seed size, soil burial, and seed peeling on dispersal. The effects of a single factor may be more than their interactions between seed size, soil burial and seed peeling on dispersal. These results implied that seed size, soil burial and seed peeling may affect plant population expansion and regeneration by affecting the dispersal and hoarding of animals.

Effect of Vegetation Structure on Lift-Off and Dispersal Velocities of Diaspores with Different Morphological Characteristics in Secondary Wind Dispersal

Diaspore dispersal is crucial in shaping plant population dynamics, biodiversity, and ecosystem functions. The effect of the vegetation structure on the secondary wind dispersal of diaspores with different appendage types is not well understood. Using a wind tunnel and a high-definition video camera, we accurately measured the lift-off and dispersal velocities of diaspores from sixteen plant species across six wind velocities (2, 4, 6, 8, 10, and 12 m s−1) under six simulated vegetation structures. Vegetation structure and appendage type were pivotal factors, explaining 41.1% and 42.3% of the variance in lift-off velocity and accounting for 12.0% and 25.3% of the variability in diaspore dispersal velocity, respectively. Vegetation coverage was the main factor influencing near-surface wind velocity, and the lift-off and dispersal velocities of diaspores changed significantly when vegetation coverage exceeded 40%. Diaspores with one wing, having high lift-off velocities and low dispersal velocities, adopt the anti-long-distance wind dispersal strategy, whereas diaspores with pappus, having low lift-off velocities and high dispersal velocities, adopt the long-distance wind dispersal strategy. In contrast, diaspores with thorn, discoid, balloon, and four wings adopt the non-long-distance wind dispersal strategy, suitable for environments such as low-coverage deserts and desert steppes but not high-coverage typical steppes. This study could help comprehend the effect of the vegetation structure on the dispersal process of diaspores, which facilitate habitat restoration and biodiversity conservation of grassland and forest ecosystems.

Introduction of the South American slipper limpet Crepipatella dilatata in Europe: Secondary spread in the Northeast Atlantic and first records for the Mediterranean Sea

The slipper limpet Crepipatella dilatata, native to Chile and Argentina, was introduced in north-western Spain in 2005 and since then has spread to the Galician and Cantabrian coasts. In this work, we provide the first molecularly validated record of an established population of C. dilatata in central Portugal (Aveiro), and of reproductive individuals (i.e. brooding females) of C. dilatata in the Mediterranean Sea, from three Italian mussel farms (in eastern Sardinia and northern Adriatic). DNA barcoding and phylogenetic analyses based on mitochondrial markers indicate that limpets from Italian farms belong to the C. dilatata ‘clade1’, whereas limpets collected in Aveiro cluster within the C. dilatata ‘clade2’. All these limpets share the same COI haplotypes with introduced populations from Galicia. The arrival of C. dilatata to Europe is undoubtedly due to transoceanic live mussel trade from southern Chile to Galicia. Mussel trade and farming are also the most likely drivers for the post-border dispersal of C. dilatata from Spain to Portugal and to Italy. Several countries have a potential role as a hub for the primary and secondary dispersal of slipper limpets towards and within Europe. This calls the attention for future research focused on assessing the current occurrence and ecological impact of established populations of slipper limpets within and nearby mussel farms along the eastern Atlantic and Mediterranean coasts.

Complex European invasion history of Anoplophora glabripennis (Motschulsky): new insights in its population genomic differentiation using genotype-by-sequencing.

Anthropogenic activities like trade facilitate increasing rates of biological invasions. Asian long-horned beetle (ALB), which is naturally distributed in eastern Asia (China, Korean peninsula), was introduced via wood packing materials (WPM) used in trade to North America (1996) and Europe (2001). We used 7810 single nucleotide polymorphisms (SNPs) derived by a genotype-by-sequencing (GBS) approach to decipher the introduction patterns into Europe. This is applied for the first time on European ALB outbreaks from Germany, Switzerland, and Italy, both from still active and already eradicated infestations. The genome-wide SNPs detected signs of small and highly structured populations within Europe, showing clear founder effects. The very high population differentiation is presumably derived from multiple independent introductions to Europe, which are spatially restricted in mating. By admixture and phylogenetic analyses, some cases of secondary dispersal were observed. Furthermore, some populations suggest admixture, which might have been originated by either multiple introductions from different sources into the new sites or recurrent introductions from an admixed source population. Our results confirmed a complex invasion history of the ALB into Europe and the usability of GBS obtained SNPs in invasion science even without source populations.

Integrative species delimitation and biogeography of the Rhinella margaritifera species group (Amphibia, Anura, Bufonidae) suggest an intense diversification throughout Amazonia during the last 10 million years

The accumulation of studies delimiting species in Amazonia has not only shed light on the patterns of its outstanding species richness but also allowed a better understanding of the processes of diversification within this immense region. Nevertheless, vast knowledge gaps remain even for prominent anuran species complexes, such as the Rhinella margaritifera species group. This clade of toads comprises 23 valid species-level taxa, mainly distributed in Amazonia but also in South America’s Dry Diagonal and Atlantic and trans-Andean rainforests. Species boundaries and taxonomy in this group are notoriously complex, with studies suggesting the existence of several unnamed species. Available phylogenetic information suggests an Andean-western Amazonian origin of the group with subsequent diversification within Amazonian lowlands during the last 10 Myr and secondary dispersals into other Neotropical regions. To further test this biogeographic scenario and improve knowledge on species diversity, we used an unprecedentedly large mtDNA sampling (>800 16S sequences) across the clade’s distribution and comprising all but one described species. We delimited 54 Molecular Operational Taxonomic Units, which we tested further based on patterns of variation of a nuclear locus and acoustic and morphological data. This approach confirmed the existence of at least 25 candidate species, 19 of which correspond to currently recognized taxa whereas 30 remained ‘unconfirmed’. Our results clarify the taxonomic status of some species but also suggest multiple introgression events that blur some mtDNA-based species boundaries. Lastly, to provide a temporal framework for the clade’s diversification, we generated a time-calibrated phylogenetic tree based on a mitogenomic matrix, which confirmed a Miocene (∼9 Ma) western Amazonian origin and six major clades in the group, each having initially diversified in different regions within Amazonia. Most of these clades have later dispersed throughout Amazonia during the establishment of the modern Amazonian hydrographic system, i.e., in the last 6 Myr.

Climate warming increases insect-driven seed removal of two elaiosome-bearing invasive thistle species.

Ants and other insects are often a source of localized secondary dispersal for wind-dispersed plants and thus play an important ecological role in their spatial dynamics, but there is limited information on how climate change will affect such dispersal processes. Here, we use field experiments to investigate how climate warming affects seed removal, as this initiation of movement represents the first step in insect-driven secondary dispersal. Our results indicate that for the invasive thistles Carduus nutans and Carduus acanthoides, increased growing temperature influences seed attractiveness to insect dispersers, with seeds from maternal plants grown at temperatures 0.6°C above ambient removed by insect dispersers at higher rates than their unwarmed counterparts. We also observe that seed elaiosomes in these two species play an important role in dispersal, as seeds without elaiosomes were significantly less likely to be removed over the same period. Significant interactions between elaiosome presence/absence and warming treatment were also observed, though only for C. acanthoides, with the boost in seed removal from warming dampened when the elaiosome was present compared to when it was absent. These findings provide evidence that climate warming may alter aspects of dispersal such as seed removal by secondary dispersers, with potential ramifications for dispersal in future climates since seed-bearing plants around the world may be subject to increased growing temperatures, and many of these plant species bear elaiosomes and experience seed dispersal by insects.

Ore deposit prospecting using the chlorine and bromine secondary dispersion halos

The Cland Brions, that form complex compounds with metals, produce secondary dispersion halos in the hypergenesis zone at Au, Ag, Cu, Pb, and Zn ore deposits which ore bodies are controlled by fracturing and fault structures. The appearance of anomalies of the highly mobile water-soluble ions, manifested on the surface and in the wall rocks, is explained by their transfer from the deep sources to the surface by a gas flow. The migration of the ions to the earth's surface and further into the atmosphere is influenced by many factors (atmospheric pressure, temperature, humidity, rock porosity, etc.) that complicate the observation results.

Using the Gini coefficient for assessing heterogeneity within classes and schools

This study demonstrates that the Gini coefficient works as a dispersion measure for gauging educational heterogeneity in and between classrooms and schools. The method for this is to compare Gini coefficients for empirical data from various areas such as gender proportions in upper secondary school programmes and dispersion in achievement within classroom and between schools. The main results are that the Gini coefficient works for gauging heterogeneity on different statistical measurement scales and different sample sizes. An example of small sample is the nominal categories of upper secondary school study programmes, for which the Gini coefficient gauges differences in gender proportions while this sample size should be too small for several other measures of inequality and dispersion. An example of large sample of quotient scale data is two neighbour schools that mainly enrol different achievement strata from the same student cohort. Here the Gini coefficient displays the two schools’ student heterogeneity to be different. An example of moderate size sample is to explore how the teaching group heterogeneity, gauged as Gini coefficient on achievements, re-distributes from within to between classes as the same students proceed from cohesive compulsory school to the students’ individual choice of upper secondary school programmes. Since the Gini coefficient can gauge heterogeneity on small samples, a suggestion for further research is to use it for exploring the relation between strategies for classroom orchestration and levels of classroom heterogeneity, for example between teaching groups at different achievement strata.

Molecular insights on the historical dispersion of Piezodorus guildinii (Hemiptera: Pentatomidae) in Brazil.

Piezodorus guildinii (Westwood, 1837) (Hemiptera: Pentatomidae) is an important arthropod pest of soybean (Glycine max (L.) Merr.) throughout American continents. However, the historical events associated with its dispersion are poorly understood. In this study, we employed a phylogeographic approach to investigate the origin and demographic history of P. guildinii in Brazil. We analyzed the cytochrome c oxidase subunit I and Cytb gene sequences of P. guildinii individuals collected in Brazil's 5 soybean production macro-regions and cross-referenced this information with sequences available in public databases. Our findings support an older Caribbean basin establishment for the current genealogical strains of P. guildinii, with subsequent dispersion to Brazil around 0.97 Mya. No secondary dispersion of this species from the Caribbean region to soybean areas in Brazil was identified. The Brazilian populations of P. guildinii are genetically structured across the country's soybean macro-regions and show strong signals of continuous demographic and spatial expansion in Brazil, which may be accelerated by the soybean cropping landscape in the country. The populations from the northern region (MR5) are older than the Central and South populations. The signs of demographic expansion indicate that P. guildinii populations are increasing their effective size in soybean regions, which could reflect its importance as a soybean pest in the coming years.

Seed settling and trapping during submerged secondary dispersal: Implications for saltmarsh recruitment and restoration

Given the decline of global salt marshes, there is a pressing need to pinpoint the key processes that limit and facilitate seed-based pioneer recruitment. Secondary seed dispersal, in the form of short-distance submerged movement, is a prerequisite for initiating pioneer establishment in adjacent tidal flats but has not been fully appreciated and understood. In this study, using a settling tube and race-track flume, seeds of four global occurring saltmarsh species were studied in terms of their settlement speed and trapping opportunity to understand how seed traits and physical settings affect submerged dispersal behavior and thus seed-based saltmarsh recruitment. Present study led to the following novel insights: 1) Seeds have density-dependent settling speeds, which are comparable to that of fine sand, but much faster than that of very fine sand and silt. Since the latter is the type of sediment commonly found in many estuaries worldwide (such as the Scheldt), seeds will typically settle faster than local sediments. A sufficiently long hydrodynamic-calm period allows slowly settling sediment to bury settled seeds, otherwise, seeds will remain uncovered if the period is short. 2) Seed trapping ratio increased linearly with surface roughness (a proxy for local topographic complexity), but this effect becomes smaller with increasing hydrodynamic intensity. Seed drag coefficient was identified as the key biotic factor contributing to interspecies variability in trapping ratio. Overall, present results suggest that submerged seed dispersal may form a primary bottleneck for salt marsh recruitment by limiting seed availability via two mechanisms: i) reduced chance of seed burial through asynchronous settling of seeds and sediment particles; ii) reduced probability of seed trapping due to encountering smooth tidal flat surfaces. This study provide mechanistic and data basis for the targeted application of biophysical models in predicting outcomes of saltmarsh recruitment and long-term maintenance, thereby informing seed-based conservation and restoration.

The influence of vegetation structure on lift-off velocity of diaspores during secondary wind dispersal

Lift-off velocity, the wind speed at which a diaspore starts moving during secondary wind dispersal, representing diaspore mobile capacity, may greatly depend on vegetation where dispersal takes place. However, how vegetation structure influences lift-off velocity and which is the most important vegetation attribute remain unknown. The vegetation with various attributes (four coverages-0, 10 %, 20 % and 30 %, three life-form compositions-herb, shrub and herb + shrub, two vertical patterns-one and two layers, and two horizontal patterns-uniform and aggregated) were set up for the wind tunnel experiment. Diaspores of 30 species varied in wing loading, terminal velocity, mass, projected area, length, width, height, and shape index were selected to measure their lift-off velocity within various vegetation structures. Lift-off velocity significantly increased with the increasing vegetation coverage, in the case of any life-form composition, vertical pattern and horizontal pattern of vegetation. For the vertical pattern of vegetation, the lift-off velocity in one-layer vegetation was significantly higher than that in two-layer vegetation, but only for 10 % vegetation coverage. Both the life-form composition and the horizontal pattern of vegetation had no influences on lift-off velocity. The correlation between lift-off velocity and diaspore attributes (length, width, height, projected area, mass and wing loading) increased with vegetation coverage and the correlation in two-layer vegetation was larger than that in one-layer vegetation. Our results indicate that vegetation coverage is the key vegetation attribute determining lift-off velocity during secondary wind dispersal. Lift-off velocity is also influenced by diaspore traits, but their relationships tend to be regulated by vegetation attributes, especially the coverage and vertical pattern of vegetation. Our study demonstrates the important role of vegetation coverage in determining the second dispersal capacity, which is helpful to understand the dispersal strategies of plants in response to vegetation structure and succession.

Intraregional variability of exotic and native zooplankton in Basque coast estuaries (inner Bay of Biscay): effect of secondary dispersion, estuary features and regional environmental gradients

The zooplankton of five estuaries of the Basque coast (southeast Bay of Biscay) was surveyed in summer 2019 to check the intraregional spread of exotic species and analyse the cross-estuary differences in brackish and neritic communities related to the arrival of exotic species and the summertime geographic gradient of water temperature. Results revealed that all the studied estuaries have been colonized by Oithona davisae but not by Acartia tonsa and Pseudodiaptomus marinus. Environmental constraints due to estuarine hydrological features partly explained such differences, and the role of secondary spread opportunities remained less clear. Cross-estuary differences in the brackish community mainly reflected changes in the dominance of the native species Acartia bifilosa relative to different exotic copepod species. The neritic holoplankton differed in the contribution of thermophilic species in agreement with the thermal west–east increase of surface water temperature in the inner Bay of Biscay in summer. The detection of large numbers of larvae of the exotic crab Rhithropanopeus harrisii only in one of the estuaries highlighted the role of exotic benthic species in enhancing intraregional differences in estuarine meroplankton. Differences in the dominance of neritic or brackish species as a function of salinity and distance from coastline were also explored.

The complexity of vegetation structure decreases the seed-hanging ability of the vegetation layer during secondary wind dispersal

The complexity of vegetation structure decreases the seed-hanging ability of the vegetation layer during secondary wind dispersal

Oxygen content effect on mechanical properties and microstructure of TZM alloy

A series of molybdenum‑titanium‑zirconium (TZM) alloys with continuous oxygen content gradients were fabricated by powder metallurgy and the correlation between microstructure and properties was investigated. By controlling the carbon source, TZM-like alloys with an oxygen content of 2000 ppm, 1000 ppm, and TZM alloy with an oxygen content of 300 ppm (±100) were obtained, followed by rolling and heat treatment, and the effect of oxygen on the development of the microstructure and the mechanical properties of the alloy was studied. The results show that the changing of the oxygen content has a significant impact on the mechanical properties and microstructure of the alloy. With the increase in oxygen content, titanium and zirconium are more inclined to combine with oxygen to form oxide particles of titanium and zirconium (TiO2, ZrO2), the secondary phase particles increase significantly, and the alloy strengthening mode changes from solid solution strengthening to secondary phase dispersion strengthening. Owing to the inhibition of grain boundary migration by the secondary phase, the grain size of the alloy decreases as its oxygen content rises, which causes an increase in hardness of around 10 HV0.1 for every 1000 ppm increase in oxygen content. According to the Hall-Petch relationship, the yield strength of the annealed alloy increased from 336 MPa (300 ppm) to 556 MPa (2000 ppm) with smaller grain size. Kernal Average Misorientation (KAM) is used to characterize the dislocation density of the alloy, and the results show that the value of KAM is negatively correlated with the toughness of the alloy. The KAM value of the alloy is the lowest at 1000 ppm and its greatest elongation reaching 16.8%. Dislocation cells formed in the long-striped grains with an oxygen content of 300 ppm, greatly enhancing the strength of the material and maintain good plasticity. TZM alloy with 300 ppm oxygen has the highest tensile strength of 866 MPa and has an elongation of 15%, which is the leading performance compared with ASTM-specification B386/B386M.