Quantitative Analysis of Composition Change in AZ31 Magnesium Alloy Using CF-LIBS After Laser Material Processing

The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd：YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy （CF-LIBS）. The composition change in AZ31 magnesium alloy under different laser pulse width was also investigated. The experimental results showed that CF-LIBS can obtain satisfactory quantitative or semi-quantitative results for matrix or major elements, while only qualitative analysis was possible for minor or trace elements. Moreover, it is found that the chemical composition of molten metal will change after laser processing. The concentration of magnesium in molten metal is lower than that present in the base metal. The Mg loss increases with an increase of pulse width in the laser processing. This result shows that the selective vaporization of different elements is affected by the pulse width during laser processing.

Self‑Assembly of Binderless MXene Aerogel for Multiple‑Scenario and Responsive Phase Change Composites with Ultrahigh Thermal Energy Storage Density and Exceptional Electromagnetic Interference Shielding

The severe dependence of traditional phase change materials(PCMs)on the temperature-response and lattice deficiencies in versatility cannot satisfy demand for using such materials in complex application scenarios.Here,we introduced metal ions to induce the self-assembly of MXene nanosheets and achieve their ordered arrangement by combining suction filtration and rapid freezing.Subsequently,a series of MXene/K^(+)/paraffin wax(PW)phase change composites(PCCs)were obtained via vacuum impregnation in molten PW.The prepared MXene-based PCCs showed versatile applications from macroscale technologies,successfully transforming solar,electric,and magnetic energy into thermal energy stored as latent heat in the PCCs.Moreover,due to the absence of binder in the MXene-based aerogel,MK3@PW exhibits a prime solar-thermal conversion efficiency(98.4%).Notably,MK3@PW can further convert the collected heat energy into electric energy through thermoelectric equipment and realize favorable solar-thermal-electric conversion(producing 206 mV of voltage with light radiation intensity of 200 mw cm^(−2)).An excellent Joule heat performance(reaching 105℃with an input voltage of 2.5 V)and responsive magnetic-thermal conversion behavior(a charging time of 11.8 s can achieve a thermal insulation effect of 285 s)for contactless thermotherapy were also demonstrated by the MK3@PW.Specifically,as a result of the ordered arrangement of MXene nanosheet self-assembly induced by potassium ions,MK3@PW PCC exhibits a higher electromagnetic shielding efficiency value(57.7 dB)than pure MXene aerogel/PW PCC(29.8 dB)with the same MXene mass.This work presents an opportunity for the multi-scene response and practical application of PCMs that satisfy demand of next-generation multifunctional PCCs.

Controllable thermal rectification design for buildings based on phase change composites

Phase-change material(PCM)is widely used in thermal management due to their unique thermal behavior.However,related research in thermal rectifier is mainly focused on exploring the principles at the fundamental device level,which results in a gap to real applications.Here,we propose a controllable thermal rectification design towards building applications through the direct adhesion of composite thermal rectification material(TRM)based on PCM and reduced graphene oxide(rGO)aerogel to ordinary concrete walls(CWs).The design is evaluated in detail by combining experiments and finite element analysis.It is found that,TRM can regulate the temperature difference on both sides of the TRM/CWs system by thermal rectification.The difference in two directions reaches to 13.8 K at the heat flow of 80 W/m^(2).In addition,the larger the change of thermal conductivity before and after phase change of TRM is,the more effective it is for regulating temperature difference in two directions.The stated technology has a wide range of applications for the thermal energy control in buildings with specific temperature requirements.

Mechanism of Slag Composition Change During Electroslag Remelting Process

The mass loss rate of CaF2-CaO-Al2O3-SiO2-MgO slag system originated from ANF-6 was studied with CaF2, CaO, Al2O3, SiO2 or MgO content as variables. The method of quadratic regression orthogonal design was used for the design and analysis of the experiment. The experimental results indicated that mass loss rate of slag can be increased by 6% with CaF2 changing from 50%to 65%. Mass loss increases with SiO2 , Al2O3 and MgO adding and decreases with CaO content increasing. Because of the reaction between oxide and fluoride in the slag pool, apparent mass loss of CaF2-Al2O3 CaO-SiO2 MgO slag system appears at melting point. This will cause obvious composition change of electroslag. In addition, the segregation occurs in the slag skin forming process. This is another reason causing the composition change of electroslag.

Fly Ash/Paraffin Composite Phase Change Material Used to Treat Thermal and Mechanical Properties of Expansive Soil in Cold Regions

Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material was prepared with paraffin as the PCM and 8%Class C fly ash(CFA)as the supporting material.Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash(CFA-PCM)on the thermal properties,volume changes and mechanical properties of expansive soil.The results show that PCM failed to establish a good improvement effect due to leakage.CFA can effectively adsorb phase change materials,and the two have good compatibility.CFA-PCM reduces the volume change and strength attenuation of the soil,and 8 wt.%PCM is the optimal content.CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability.CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale.In addition,CFA-8 wt.%PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles,providing a reference for actual engineering design.

Preparation and Characterization of CA-MA Eutectic/Silicon Dioxide Nanoscale Composite Phase Change Material from Water Glass via Sol-Gel Method

This work mainly involved the preparation of a nano-scale form-stable phase change material（PCM） consisting of capric and myristic acid（CA-MA） binary eutectic acting as thermal absorbing material and nano silicon dioxide（nano-SiO_2） serving as the supporting material. Industrial water glass for preparation of the nano silicon dioxide matrix and CA-MA eutectic mixture were compounded by single-step sol-gel method with the silane coupling agent. The morphology, chemical characterization and form stability property of the composite PCM were investigated by transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, Fourier-transform infrared（FT-IR） spectroscopy and polarizing microscopy（POM）. It was indicated that the average diameter of the composite PCM particle ranged from 30-100 nm. The CA-MA eutectic was immobilized in the network pores constructed by the Si-O bonds so that the composite PCM was allowed no liquid leakage above the melting temperature of the CA-MA eutectic. Differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA） measurement were conducted to investigate the thermal properties and stability of the composite PCM. From the measurement results, the mass fraction of the CA-MA eutectic in the composite PCM was about 40%. The phase change temperature and latent heat of the composite were determined to be 21.15 ℃ and 55.67 J/g, respectively. Meanwhile, thermal conductivity of the composite was measured to be 0.208 W·m^（-1）·K^（-1） by using the transient hot-wire method. The composite PCM was able to maintain the surrounding temperature close to its phase change temperature and behaved well in thermalregulated performance which was verified by the heat storage-release experiment. This kind of form-stable PCM was supposed to complete thermal insulation even temperature regulation by the dual effect of relatively low thermal conductivity and phase change thermal storage-release properties. So it can be formulated that the nanoscale CA-MA/SiO_2 composite PCM with the form-stable property, good thermal storage capacity and relatively low thermal conductivity can be applied for energy conservation as a kind of thermal functional material.

Long-term changes in biological soil crust cover and composition

Introduction:Communities change over time due to disturbances,variations in climate,and species invasions.Biological soil crust communities are important because they contribute to erosion control and nutrient cycling.Crust types may respond differently to changes in environmental conditions:single-celled organisms and bryophytes quickly recover after a disturbance,while lichens are slow growing and dominate favorable sites.Community change in crusts has seldom been assessed using repeated measures.For this study,we hypothesized that changes in crust composition were related to disturbance,topographic position,and invasive vegetation.Methods:We monitored permanent plots in the Columbia Basin in 1999 and 2010 and compared changes in crust composition,cover,richness,and turnover with predictor variables of herbivore exclosure,elevation,heat load index,time since fire,presence of an invasive grass,and change in cover of the invasive grass.Results:Bryophytes were cosmopolitan with high cover.Dominant lichens did not change dramatically.Indicator taxa differed by monitoring year.Bryophyte and total crust cover declined,and there was lower turnover outside of herbivore exclosures.Lichen cover did not change significantly.Plots that burned recently had high turnover.Increase in taxon richness was correlated with presence of an invasive grass in 1999.Change in cover of the invasive grass was positively related to proportional loss and negatively related to gain.Conclusions:Composition and turnover metrics differed significantly over 11 years,though cover was more stable between years.This study can be a baseline for assessing change in crust composition due to anthropogenic influences.

Efficient Preconstruction of Three‑Dimensional Graphene Networks for Thermally Conductive Polymer Composites

Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation.Featured by its exceptional thermal conductivity,graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management.Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities.Compared with conventional composite fabrications by directly mixing graphene with polymers,preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances,enabling high manufacturing flexibility and controllability.In this review,we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites.Subsequently,we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications.Finally,our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites.

Abiotic and Biotic Stresses and Changes in the Lignin Content and Composition in Plants

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route, represented by a metabolic grid for which most of the genes involved have been sequenced in several plants, mainly in the model-plants Arabidopsis thaliana and Populus. Plants are exposed to different stresses, which may change lignin content and composition. In many cases, particularly for plant-microbe interactions, this has been suggested as defence responses of plants to the stress. Thus, understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall. This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.

The present status and future prospects of forest vegetation in part of Nanda Devi Biosphere Reserve(a World Heritage Site),India

We studied forest vegetation at Lata-Tolma- Phagti, a protected area and part of Nanda Devi Biosphere Reserve in the western Himalaya. We analyzed community composition, population structure, regeneration patterns, and projected development of future compositional patterns. We sampled ten 10 x 10 m quadrat for tree species in each of 30 forest stands. We sampled shrubs in ten 5 x 5 m quadrat, and herbs in twenty 1 x 1 m quadrat within each forest stand. We recorded 248 plant species from 8 forest communities. Broadly the demographic profiles at study sites exhibited progressive structures suggesting long term persistence of the communities/species. Density--diameter distribution revealed greater proportions of seedlings and a significant decline （P 〈 0.05） in the proportion of trees in older age/size classes. Of the 23 recorded tree species, 13.0 % showed good, 52.2 % fair, 26.1% poor and 8.7 % no regeneration. Differences in regeneration by species are indicative of future foreststructure and dynamics. Assessment of changes in structure of forest types provides baseline data for development of priorities for conservation of other representative land- scapes in the reserve as well as in the Himalaya.

Preparation and Thermal Properties of a Novel Modified Ammonium Alum/Expanded Graphite Composite Phase Change Material

Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal energy storage(LTES)systems is hampered due to its high supercooling and low thermal conductivity.In this work,modified A-alum(M-PCM)containing different nucleating agents was prepared and further adsorbed in expanded graphite(EG)to obtain composite phase change material(CPCM)to overcome the disadvantages of A-alum.Thermal properties,thermal cycle stability,microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry,thermal constant analysis,scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The cold rewarming phenomenon of CPCM was established and explained.Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54℃,respectively.The supercooling of CPCM decreased by 9.61℃,and thermal conductivity increased by 27 times compared with pure A-alum.Heat storage and release tests indicated that 2 wt%calcium chloride dihydrate(CCD,CaCl_(2)·2H_(2)O)was the optimum nucleating agent for A-alum.The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature.The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.

Preparation and Characterization of KNO3/Diatomite Shape-Stabilized Composite Phase Change Material for High Temperature Thermal Energy Storage

A new potassium nitrate （KNO3）]diatomite shape-stabilized composite phase change material （SS- CPCM） was prepared by the mixing and sintering method. KNO3 served as the phase change material （PCM） for thermal energy storage, while diatomite acted as the carrier matrix to provide the structural strength and prevent the leakage of PCM. It was found that KNO3 could be retained 65 wt% into pores and on surfaces of diatomite without the leakage of melted KNO3 from the SS-CPCM. The calculated filling rate of molten KNO3 that could enter into the disc-like shape pore of diatomite verified the scanning elec- tronic microscopy images of SS-CPCM. X-ray diffraction and Fourier transform infrared spectroscopy results showed that no reaction occurred between KNO3 and diatomite, performing good compatibility. Accord- ing to the differential scanning calorimetry results, after 50 thermal cycles, the phase change temperatures for melting and freezing of SS-CPCM with 65 wt% KNO3 were changed from 330.23 ℃ and 332.90 ℃ to 330.11 ℃ and 332.84 ℃ and corresponding latent heats varied from 60.52 J/g and 47.30 J/g to 54.64 J/g and 41.25 J/g, respectively. The KNO3/diatomite SS-CPCM may be considered as a potential storage media in solar power plants for thermal energy storage.

Biological porous carbon encapsulated polyethylene glycol-based phase change composites for integrated electromagnetic interference shielding and thermal management capabilities

The development of functional composites with excellent thermal management capabilities and electro-magnetic interference(EMI)shielding has become extremely urgent for keeping up with the continuous improvement of the operating speed and efficiency for electronic equipment.In this study,the biolog-ical wood-derived porous carbon(WPC)was determined as the supporting material to encapsulating polyethylene glycol(PEG),and a series of WPC/PEG/Fe_(3)O_(4) phase change composites(PCCs)with excel-lent shape stability,EMI shielding and thermal management capabilities were prepared via a simple vac-uum impregnation method.The Fe_(3)O_(4) magnetic particles modified PCCs have greatly improved the EMI shielding effectiveness(SE).The EMI SE of WP-4(7.5 wt.% Fe_(3)O_(4) in PEG)can be up to 55.08 dB between 8.2−12.4 GHz,however,the WP-0 without Fe_(3)O_(4) addition is only 40.08 dB.Meanwhile,the absorption ratio of electromagnetic waves(EMW)has also increased from 75.02%(WP-0)to 85.56%(WP-4),which effectively prevents secondary pollution.In addition,after wrapping a thin layer of polydimethylsiloxane resin(PDMS),the obtained WP-4 can maintain a high heat storage capacity(109.52 J/g)and good wa-ter stability.In short,the prepared WPC/PEG/Fe_(3)O_(4) PCCs have great potential application value in the thermal management and electromagnetic shielding requirements for electronic devices.

Endurance characteristics of phase change memory cells

The endurance characteristics of phase change memory are studied. With operational cycles, the resis- tances of reset and set states gradually change to the opposite direction. What is more, the operational conditions that are needed are also discussed. The thilure and the changes are concerned with the compositional change of the phase change material. An abnormal phenomenon that the threshold voltage decreases slightly at first and then increases is observed, which is due to the coaction of interthce contact and growing active volume size changing.

Multifunctional phase change composites based on biomass/MXenederived hybrid scaffolds for excellent electromagnetic interference shielding and superior solar/electro-thermal energy storage

With the rapid development of new generations of miniaturized,integrated,and high-power electronic devices,it is particularly important to develop advanced composite materials with efficient thermal management capability and excellent electromagnetic interference(EMI)shielding performance.Herein,an innovative biomass/MXene-derived conductive hybrid scaffold,cellulose nanocrystal(CNC)-konjac glucomannan(KGM)/MXene(CKM),was prepared by freeze-drying and thermal annealing,and then paraffin wax(PW)was encapsulated in CKM using vacuum impregnation method to obtain CNC-KGM/MXene@PW phase change composites(CKMPCCs).The results show that the obtained CKMPCCs possess considerable reusable stabilities,excellent EMI shielding properties,and thermal energy management capacities.Among them,the CKMPCC-6 with 2.3 wt.%MXene exhibits excellent solar-thermal and electro-thermal conversion capabilities.In addition,the EMI shielding effectiveness value is as high as 45.0 dB at 8.2–12.4 GHz and the corresponding melting enthalpy value is 215.7 J/g(relative enthalpy efficiency of 99.9%).In conclusion,the synthesized multifunctional phase change composites provide great potential for integrating outstanding EMI shielding and advanced thermal energy management applications.

Preparation and Thermal Properties of Grafted CNTs Composites

Oleylamine （G18） and octanol （G8） were grafted onto the surfaces of the multi-walled carbon nanotubes （CNTs）. The grafted CNTs were dispersed into palmitic acid （PA） and paraffin wax （PW） to prepare phase change composites. The heat storage/retrieval experiments showed that the composites kept stable after repeating melting and solidification for 80 times. The structure of the G18-CNT/PA and G8-CNT/PA was homogenous compared with the pristine CNT （P-CNT）/PA. The latent heat capacity （Ls） of solid liquid phase change of G18-CNT/PW was higher than that of PW while those of the G8-CNTI/PW and P-CNT/PW were lower than that of PW. Compared with PA, all PA based composites with both P-CNTs and grafted CNTs decreased Ls evidently. The Ls values of GI8-CNT composites in both matrices were higher than that of the counterparts of G8-CNT. The thermal conductivities of all the PA based composites in the study were higher than that of PA, as well as those of all the PW based composites. However, the thermal conductivities of the GI8-CNT composites in both matrixes were lower than those of the G8-CNT composites in both matrixes at all measured temperatures.

Carbonate-salt-based composite materials for medium- and high-temperature thermal energy storage

This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and a high thermal conductivity material. The ceramic material forms a microstructural skeleton for encapsulation of the PCM and structural stability of the composites; the high thermal conductivity material enhances the overall thermal conductivity of the composites. Using a eutectic salt of lithium and sodium carbonates as the PCM, magnesium oxide as the ceramic skeleton, and either graphite flakes or carbon nanotubes as the thermal conductivity enhancer, we produced composites with good physical and chemical stability and high thermal conductivity. We found that the wettability of the molten salt on the ceramic and carbon materials significantly affects the microstructure of the composites.