Precipitation Of Different Phases Research Articles

Changes in precipitation phases based on the multi-discrimination method in the Tibetan Plateau

Global warming is rapidly changing the precipitation structure, and the shift in precipitation phases is even more pronounced in the Tibetan Plateau (TP), a region sensitive to global climate change. The accuracy of precipitation phase discrimination is essential for studying precipitation variability. Based on the observed data from 112 meteorological stations in the study area obtained from the China Meteorological Administration (CMA) and the National Climatic Data Center (NCDC) before 1980, we compared and assessed six methods for distinguishing precipitation phases and the optimal method was determined to complete the precipitation phase data after 1980 in the study area. Subsequently, the changes in precipitation amount, intensity, and frequency were analyzed by classifying them into light, moderate, heavy, and extreme precipitation using the percentile threshold discrimination method. It found that the dynamic threshold temperature method (presented by Ding et al., 2014) was the most effective to distinguish precipitation phases in the TP, and its performance was further improved from 80.9% to 86.1% after using frequency intersection and probability guarantee methods. Precipitation was mainly concentrated in July. Meanwhile, the proportion of snowfall to total precipitation (S/P) was approximately 9%. From 1961 to 2020, the amount of total precipitation, rainfall and snowfall in the TP exhibited increasing trends, while the sleet demonstrated a persistent decline. Spatial and temporal heterogeneity existed in the changes of precipitation of different phases. The average single precipitation amount increased. Moreover, the changes in the amount and frequency of extreme precipitation were more pronounced. Increased frequency and amount of both rainfall and snowfall were distributed in the central and eastern parts of the study area with a more significant proportion. In contrast, the peripheral areas witnessed a decrease. The spatial distribution of frequency and amount of different precipitation intensities was comparable to that of the total precipitation. This study offers novel procedure into changes of precipitation phases at high altitudes, which will inform future research on climate change and water resource management.

Анализ климатических норм в Забайкальском крае

Using observational data from 27 meteorological stations of the Roshydromet network, on average for the territory of the Trans-Baikal Territory and its geoadministrative regions, the values of climatic norms for four operational periods recommended by the WMO (1961–1990, 1971–2000, 1981–2010, 1991–2020) were calculated and analyzed. , and general (1961–2020) for surface air temperature and precipitation. Updated data on climate norms and their dynamics over different time intervals are of particular importance for ensuring the economic sustainability and environmental security of the Russian Federation in the context of current climate trends. The purpose of this study was to assess the regional features of changes in climatic norms of air temperature and precipitation in the territory of the Trans-Baikal Territory. The results of the study showed that the warming observed in the Trans-Baikal Territory led to an increase in the norms, the average annual values of which with each subsequent period are 0.3–0.4 °C higher than in the previous one. On average, over the region, the largest contribution to the increase in climatic norms of average annual air temperatures for the cold season was observed in 1971–2000, for the warm season in 1981–2010. An analysis of air temperature anomalies calculated as deviations from the average value for the base period 1991–2020 shows that positive anomalies on average over the territory of the region began to be recorded only since 1990. Then the mode of precipitation here is characterized by cyclicity. An analysis of precipitation anomalies shows that, in general, their negative values correspond to the dry phases of the cycle, while positive values correspond to wet ones, although wet years are noted in arid years, and dry years in humid ones. The average difference between the sum of atmospheric precipitation of different phases is about 50 mm. The values of climatic norms correspond to their average number for the general period. Precipitation norms do not reflect the climatic situation, and in order to solve applied problems in climate-dependent industries and adopt management strategies, it is more expedient to take into account the cycle phase of the territory's humidification regime.

Inclusions in calcite phantom crystals suggest role of clay minerals in dolomite formation

AbstractMicro- and nano-inclusions embedded in calcite phantom crystals from Gemerská Ves, Slovak Republic, have been characterized by a combination of Raman spectroscopy, scanning and transmission electron microscopy, X-ray powder diffraction, and C and O isotope analysis. Whereas the outer, colorless part of the phantom crystal is relatively homogeneous and cavity and inclusion-free, the inner terracotta-colored part contains abundant cavities, dolomite, hematite, goethite, titanite, phyllosilicates (mainly kaolinite and illite), and apatite inclusions and nanostructures that have formed on the walls of cavities. The nanostructures comprise hematite and goethite particles sandwiched between either two phyllosilicate crystals or a phyllosilicate and a carbonate (calcite or dolomite) crystal. Our observations suggest that all inclusions in the terracotta calcite originate from the terra rossa (a common soil type in karstic areas) and limestone outcropping adjacent to the calcite crystals. While the micrometer-sized phyllosilicate and hematite particles were likely transported from the terra rossa and attached to the surface of growing calcite, the presence of phyllosilicates that are only a few atomic layers thick and of euhedral hematite, goethite, and dolomite crystals suggests that these particles precipitated along with the phantom calcite in situ, from an aqueous solution carrying terra rossa-derived and limestone-derived solutes. The compositional differences between the terra rossa (e.g., smectite as the only major Mg-rich phase) and terracotta calcite inclusions (e.g., dolomite as the only major Mg-rich phase and the presence of only Mg-free clays) hint that a smectite-illite conversion provides the Mg necessary for the precipitation of dolomite and possibly the Fe associated with the iron oxyhydroxide nanostructures. Phyllosilicate nucleation on calcite and dolomite nucleation on phyllosilicates, as inferred from nanoscale mineralogical associations, suggest that carbonates and phyllosilicates may mutually enhance nucleation and growth. This enhancement may result in the formation of large-scale clay-carbonate successions in aqueous settings, including the enigmatic, pink-colored cap dolostones succeeding late Neoproterozoic “Snowball Earth” deposits. The distribution of inclusions in the terracotta calcite and the preferred nucleation of hematite and goethite on phyllosilicate, rather than on carbonate surfaces, indicates that phyllosilicates have a potential to not only disrupt crystal growth and trigger the formation of cavities in the structure of the calcite host, but also to provide surfaces for the precipitation of different phases in the cavities and to uniformly distribute otherwise incompatible materials in a calcite host crystal. This calls for further exploration of the potential application of phyllosilicates in composite structure development.

Effect of selective-precipitations process on the corrosion resistance and hardness of dual-phase high-carbon steel

It is commonly known that precipitation of secondary phase in non-ferrous alloys will affect the mechanical properties of them. But due to the nature of dual-phase low-alloy high-carbon steel and its high potential of precipitation of cementite, there is limited study on tailoring the mechanical and corrosion properties of this grade of steel by controlling the precipitation of different phases. Predicting and controlling precipitation behaviour on this grade of steel is of great importance towards producing more advanced applications using this low-cost alloy. In this study the new concept of selective-precipitation process for controlling the mechanical and corrosion behaviour of dual-phase low-alloy high-carbon steel has been introduced. We have investigated the precipitation of different phases using in-situ observation ultra-high temperature confocal scanning laser microscopy, image analyser – ImageJ, scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and electron probe microanalysis (EPMA). Volume fraction of each phase including retained austenite, martensite and precipitated phases was determined by X-ray diffraction (XRD), electrochemical corrosion test by Tafel extrapolation method and hardness performance by nanoindentation hardness measurement. The experimental results demonstrated that, by controlling the precipitations inside the matrix and at grain boundaries through heat treatment, we can increase the hardness of steel from 7.81 GPa to 11.4 GPa. Also, corrosion resistance of steel at different condition has been investigated. This new approach will open new possibility of using this low-cost steel for high performance applications.

Microstructural evolution during aging at 800 °C and its effect on the magnetic behavior of UNS S32304 lean duplex stainless steel

Duplex stainless steels are high strength and corrosion resistant alloys extensively used in chemical and petrochemical industries. However, exposition to temperatures in the range 300–1000°C leads to precipitation of different phases having a detrimental effect on the mechanical properties and on the corrosion resistance of the alloy.In this work, the microstructural evolution during aging of a UNS S32304 lean duplex stainless steel was investigated by scanning electron microscopy, transmission electron microscopy and magnetic force microscopy. Formation of secondary austenite as well as Cr2N and Cr23C6 precipitation and, consequently, a decrease of ferrite volume fraction were observed. EDX analysis indicated that secondary austenite is depleted in chromium which is detrimental to the corrosion resistance of the alloy. A variation of magnetic properties and Eddy current measurement parameters during aging was simultaneously detected and can be explained by the decrease of ferrite volume content. Therefore, Eddy current non-destructive testing can be successfully applied to detect the formation of deleterious phases during aging.

Analysis of the Solidification and Properties of Plaster Cast Al Based Composites

Analysis of the Solidification and Properties of Plaster Cast Al Based CompositesThe present work deals with aspects related to the solidification and properties of an Al-Si10Mg/SiC20palloy cast in plaster moulds. Several strategies were followed to shorten its solidification time such as embedding copper tubes into the mould to make circulate cooling fluids immediately after the casting step. The analysis of cooling curves provided valuable information on the effect of the particles on solidification events. The precipitation of different phases of the MMC takes place at higher temperatures and earlier than in the case of the non reinforced alloy. Particles affect the solidification pattern of the alloy and play a noticeable role in the precipitation of the phases. This fact should be taken into account to design the filling and feeding systems correctly and for modelling and processing parameters as well as in thermal treatments. Eventually samples were obtained under the highest solidification rate conditions to analyse the microstructure and tensile properties of the MMC material.

Dolostones from Grand Cayman, British West Indies

ABSTRACT Pervasively dolomitized Tertiary strata on Grand Cayman are dominated by heterogeneous dolostones that are composed of both low-Ca calcium dolomite (LCD 55 mol % CaCO3). Homogeneous dolostones, formed of either LCD or HCD, are rare. Some dolostones contain dolomite crystals that are characterized by oscillatory zones (1-10 µm thick) of LCD and HCD, whereas others have rims of LCD surrounding cores of HCD. In some dolostones, bioclasts formed of LCD are embedded in a matrix of HCD. An 1‰ 18O difference between the LCD and HCD can be attributed to the natural covariance that exists between the 18O and mol % CaCO3 in dolomite. There are no significant differences in the 87Sr/86Sr ratios of the LCD and HCD. There is no consistent vertical or lateral pattern to the distribution of LCD and HCD in the Cayman dolostones even in closely spaced sampling sites. Such variability is more consistent with growth of individual dolomite crystals being controlled by processes that operated around the surfaces of individual crystals rather than by large-scale changes in the dolomitizing fluids. This interpretation is consistent with the development of oscillatory zoning, which is attributed to precipitation of different phases or minerals from the same parent fluid because of competition between interface-controlled and diffusion-controlled growth kinetics. Dolomitization of the Tertiary strata on Grand Cayman was probably mediated by seawater or modified seawater. Nevertheless, small-scale intrinsic factors controlled the incorporation of Ca in the dolomite lattice and, accordingly, the geochemical parameters that are intimately linked to the mol % CaCO3. These small-scale intrinsic controls must be factored into any model to explain the formation of Tertiary island dolostones.

Influence of the composition and maximum cycling temperature on the microstructure of Cu-Al-Mn shape memory alloys

The effect of the composition and maximum cycling temperature on the microstructure of Cu-Al-Mn shape memory alloys is investigated. For this purpose, two sets of alloys with constant Al content (close to 10.7 wt%) and Mn (7.0 wt%) were prepared. The influence of the composition on the microstructure of Cu-Al-Mn shape memory alloys was carried out in chill casting alloys, annealed for 5 min at 170°C. The effect of maximum cycling temperature was carried out in a Cu-10.8% wt Al-4.0% wt Mn alloy. The reverse transformation is not detected at temperatures below 400°C. Thermal cycling between 400°C and 510°C produces the precipitation of different phases, which varies the initial martensite composition and their characteristic transformation temperatures.

Embrittlement of maraging steel N18K8M3TYu after slow cooling from high temperatures

1. Steel N18K8M3TYu, like other maraging steels, is subject to embrittlement with slow cooling or isothermal holding at high temperatures, which is due to precipitation of different phases in the grain boundaries. 2. After heating to 1250°C and isothermal holding with cooling, embrittlement develops at 750–1050°C. The embrittlement is greatest around 950°C and is more evident for the steel in the quenched condition. 3. Slow cooling from high temperature after rolling also induces embrittlement, beginning at 1050°C. The degree of embrittlement increases with the temperature. 4. The temperature ranges established for the embrittlement of steel N18K8M3TYu allow measures to be taken to prevent embrittlement of this steel.