Chemical Composition Distribution Research Articles

Determination of Short Chain Branching in LLDPE by Rheology

AbstractThe relationship between the structure and the final properties of materials is an important issue in polymer science. In particular, the properties of polyolefins are impacted by their branching contents. A simple rheological method is presented to estimate the degree of short chain branching (SCB) in linear low‐density polyethylene (LLDPE). A range of ethylene‐1‐hexene copolymers is synthetized using a metallocene catalyst to obtain homogenous LLDPE models with various comonomer contents. The polymers are analyzed by size exclusion chromatography, 13C NMR, and crystallization elution fractionation to determine both their molar masses and their chemical composition distributions. Subsequently, they are measured by rheology to assess the impact of SCB. This work provides calibration curves for rheology and proves that it is possible to predict the SCB content in LLDPE from the melt viscosity analysis.

Determination of Chemical Composition and Monomer Sequence Distributions of Methacrylate Copolymers by Multivariate Analysis of NMR Spectra

Determination of Chemical Composition and Monomer Sequence Distributions of Methacrylate Copolymers by Multivariate Analysis of NMR Spectra

Cocrystallization of Polyethylene Blends during TREF–GPC Cross‐Fractionation Characterization

AbstractCross‐fractionation characterization (CFC) between temperature rising elution fractionation (TREF) and gel permeation chromatography (GPC) is a technique developed to determine the bivariate molecular weight and chemical composition distribution (MWDxCCD), a unique and detailed microstructural fingerprint of polyolefin. Like other crystallization‐based characterization techniques, CFC may suffer from cocrystallization effects during analysis, which can mislead the interpretation of polymer microstructures. However, cocrystallization phenomena during CFC analysis are not investigated, especially for industrial polymers. In this study, the cocrystallization effect during CFC analysis is systematically investigated using two series of binary blends based on four individual polyethylene samples. These individual samples have distinct microstructural characteristics, representing polyethylene produced using different polymerization processes and catalytic systems. The effects of microstructural characteristics and blending ratio on cocrystallization level are examined. When the CFC profiles of individual components do not overlap, a high level of cocrystallization can be observed. Furthermore, the behavior of how the blending ratio affects cocrystallization depends on the characteristics of CFC profiles of individual component and their interactions. The level of cocrystallization in binary blends increases with the weight fraction of the component having microstructures eluted in the cocrystallization temperature range.

Study on Microstructure Distribution of Al-Cu-Mg Alloy in Squeeze Casting Process

The squeeze casting process is an advanced technology, which is suitable for a wide range of alloys including Al-Cu-Mg alloys. The high pressure in squeeze casting process both refines the microstructure and enhances the mechanical property of the alloys. The heat transfer and solidification process are complex with the chilling mould and pressure of machine punch. This results in the inhomogeneous microstructure and property in casting alloy. This study focuses on the distribution of microstructure, chemical composition, and hardness of Al-Cu-Mg alloy along the radial direction of casting. The composition and area fraction of eutectic phases are characterized. Moreover, the relationship between the microstructure and mechanical property was also analysed to show the characteristic of microstructure in squeeze casting process.

Enhanced ductility and toughness by tailoring heterogenous microstructure in an ultra-heavy gauge high strength steel with severe centerline segregation

• New approach was offered to greatly enhance ductility and toughness with severe centerline segregation. • Heterogeneous microstructure was homogenized to fine multi-phase microstructure. • Centerline segregation produced more stable retained austenite. • Partitioning during annealing made local fluctuation of Mn concentration. • Similar local fluctuations of Mn concentration led to chemical homogeneity on the whole. A novel two-step intercritical heat treatment was applied to tailor the heterogenous microstructure in an ultra-heavy E500 offshore engineering steel with severe centerline segregation. Compared with the mechanical properties in the center of the studied steel after thermo-mechanical controlled processing, the yield strength of the steel is maintained above 550 MPa, the ductility and low-temperature toughness were greatly improved, the elongation was increased from 18.7% to 29.1%, and the low-temperature impact energy at −40 °C was enhanced from 16 to 163 J. The fundamental basis for the enhancement should be attributed to the more homogenous chemical composition distribution from the overall view and the fine multiphase microstructure with stable retained austenite obtained in the segregation region.

Development and evaluation of green fired clay bricks using industrial and agricultural wastes

Green construction materials have emerged as viable options to cope with the sustainability challenges set by the global communities without compromising the technical merits. Agro-industrial wastes have been utilized as alternative components in manufacturing construction products. In this vein, burnt clay bricks (CBs) is one of the novel and viable waste disposal strategy. Therefore, the primary focus of this research is to examine the impacts of agro-industrial wastes, such as sludge waste (SW), steel slag (SS), wood ash (WA), and banana ash (BA) on various physical, mechanical, and microstructure characteristics. The green CBs were prepared by admixing the wastes at a 5%, 10%, 15%, and 20% dosage. The binary blended CBs were dried under the sun for 7 days before being fired at 900 °C for 3 hrs. The CBs containing SW, WA, and BA exhibited lower compressive strengths of ∼67% than the control and SS blended specimens depending on the chemical composition and particle size distribution of the source material. The microstructural analysis of the CBs incorporating the wastes tented to improve with the addition of waste precursors and governed by the Ca/Si ratio. The outcomes revealed the potential of attaining reduced bulk density for the light-weight and cost-effective constructions with low volume (5%) replacement of studied wastes in the clay mixture. The scanning electron microscopic (SEM) analysis revealed a relatively compact matrix of the control and SS-based specimens which tended to improve the engineering properties of developed CBs.

Differential responses of the properties of soil humic acid and fulvic acid to nitrogen addition in the North China Plain

Humus (HS) is an important component of soil organic matter. Humic acid (HA) and fulvic acid (FA) are two of the most important components of HS, as they substantially affect biogeochemical processes and the migration and transformation of pollutants in soil. Long-term nitrogen (N) addition can lead to changes in soil physical and chemical properties, affect the structural characteristics of soil HS (HA and FA), cause changes in the adsorption and migration of pollutants, and ultimately result in the continuous deterioration of the soil ecological environment. However, few studies have examined the effects of N addition on the structural characteristics of soil HS, including the responses of soil HA and FA to N addition. Here, we conducted a long-term positioning experiment with different levels of N addition (CK: 0 kg N ha−1 yr−1, LN: 100 kg N ha−1 yr−1, and HN: 300 kg N ha−1 yr−1) in typical farmland soils of the North China Plain to study the response of soil HA and FA to N addition. N addition altered the physical and chemical properties of soil (e.g., pH, SOC, TN, and enzyme activity), which affected the responses of the chemical structure, quality indexes, and composition distribution of soil HA and FA to N addition. Differences in the response to N addition between HA and FA were observed. The structural characteristics of FA were stronger in response to HN compared with those of soil HA. As the level of N added increased, soil FA degradation increased, the composition distribution changed, the aromatization degree and molecular weight decreased, and the molecular structure became simpler. The properties of soil HA did not significantly respond to N addition. Given increases in the global N input (N addition and N deposition), our results have implications for agricultural fertilization, soil management, and other activities.

Evaluating wettability of vessels in poplar by Micro-CT imaging

Abstract The wettability of wood affects some natural phenomena and applications in industry, such as the ascent of sap in the plant stem, wood drying, and impregnation processes for wood modification. Wettability is generally evaluated by measuring the contact angle using techniques such as the sessile drop method and the Wilhelmy method. However, these methods are not applicable to phenomena at the micro-scale such as liquid transport in hardwood vessels. In this study, micro-CT was used to measure the contact angle of liquid in a single wood vessel directly at the submicron scale. The wettability of a wood vessel was analyzed using contact angles of distilled water and diiodomethane. Conventional contact angles of the wood surface were measured using a fixed drop technique. The average contact angle in a vessel determined by the direct CT observation was significantly smaller than that on the wood surface measured by the sessile drop technique. This discrepancy is attributable to the higher total surface energy of the vessel compared to the free energy of a flat surface. The difference in surface energy is due to different chemical composition distributions in various cell wall layers, roughness and surface topography between the wood surface and vessels, and moisture state.

Atmospheric gaseous aromatic hydrocarbons in eastern China based on mobile measurements: Spatial distribution, secondary formation potential and source apportionment

Monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs) are both well known as hazardous air pollutants and also important anthropogenic precursors of tropospheric ozone (O3) and secondary organic aerosols (SOA). In recent years, there have been intensive studies covering MAHs emission from various sources and their behavior under stimulated photochemical conditions. Yet in-situ measurements of PAHs presence and variations in ambient air are sparse. Herein we conducted large geometrical scale mobile measurements for 16 aromatic hydrocarbons (AHs, including 7 MAHs and 9 PAHs) in eastern China between October 27 and November 8, 2019. This unique dataset has allowed for some insights in terms of AHs concentration variations, accompanying chemical composition, source contributions and spatial distributions in eastern China. In general, AHs showed a clear concentration variability between the south and the north of the Yangtze River Delta (YRD). The concentrations of PAHs were approximately 9% of AHs, but contributed 23% of SOA formation potential. Source apportionment via positive matrix factorization (PMF) model revealed that industrial processes as the largest source (44%) of observed AHs, followed by solvent usage (21%), vehicle exhaust (19%), coal combustion (11%) and coking processes (6%). In the perspective of PAHs sources, coal combustion emissions were identified as the dominating factor of a share of 41%–52% in eastern China. Our findings complemented the simultaneously monitoring information of PAHs and MAHs in eastern China, revealed the importance of PAHs to SOA formation and highlighted the necessity of formulating strategies to reduce emissions from anthropogenic sources and reduce risks to human health.

Computing diffraction patterns of microstructures from phase-field simulations

The diffraction pattern of a material contains information not only on the crystal structures of its constituting phases, but also on its mesoscale spatial distributions of phases, grains, and ferroelastic, ferroelectric, and ferromagnetic domains. While diffraction patterns from experiments such as X-ray diffraction are presented in the reciprocal or Fourier space, mesoscale microstructure models such as the phase-field method naturally produce real-space images of spatial distribution of chemical composition, structural, and ferroic domains. Although one could rather readily compute the Fourier amplitudes of chemical and structural domain distributions generated by mesoscale simulations, they only contain information about the length scale and alignment of the real-space chemical and structure domains. Therefore, a direct comparison between diffraction experiments and mesoscale microstructure simulations is not possible. Here, we develop a theoretical approach to directly compute the crystal diffraction patterns of microstructures predicted by phase-field simulations. In particular, we consider five representative examples of microstructure patterns involving purely compositional domains, a single pair of tetragonal twin structures, multiple twin variants in a hexagonal system, ferroelectric polar vortices, and polycrystalline grains. The results are compared with previous experimental observations as well as X-ray diffraction experiments performed in the present study. The theoretical framework allows one to directly connect material microstructures and diffraction patterns predicted from phase-field simulations and the corresponding diffraction patterns from experiments, and thus providing guidance to experimental diffraction characterization and interpretation of microstructures.

Hydrolysis Behavior and Kinetics of AlN in Aluminum Dross during the Hydrometallurgical Process.

In this study, the hydrolysis behavior and kinetics of AlN in aluminum dross (AD) were investigated in order to better identify the steps controlling the AlN hydrolysis reaction and the factors influencing the hydrolysis rate to enhance the removal efficiency of AlN. The hydrolysis behavior of AlN, including AlN content, phase composition, chemical composition, microstructure, and element distribution, was determined by a leaching test, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and energy dispersive spectroscopy, respectively. The results showed that increasing the leaching liquid–solid ratio as well as the temperature was helpful for the removal efficiency of AlN. When the liquid-–solid ratio was 4:1, temperature was 90 °C, and leaching time was 300 min, the removal efficiency of AlN reached 89.05%. The kinetics were described using the unreacted core model, and when the temperature was 30–40, 50–70, and 80–90 °C, the hydrolysis reaction rate of AlN was controlled by boundary layer diffusion, chemical reaction control, and product layer diffusion control, respectively.

Microstructure and Fatigue of EA4T Steel in Laser Cladding Remanufacturing

EA4T steel has been widely used in the manufacture of railway axles. Laser cladding remanufacturing technology has been used to repair railway axles, and the failure behaviors of railway axles has been studied. In this work, a class of original FeCrNiMo alloy layers that contain rare-earth elements was successfully fabricated through a laser cladding technique on EA4T steel substrates. The microstructure and elemental distribution of the cladding layers were analyzed through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA). Simultaneously, the microhardness, bond strength and fatigue properties of different samples were determined. The results indicated that the phase composition of the cladding layer was mainly martensite. The grains in the cladding layer were gradually refined with an increase in the distance from the interface, and the chemical composition distribution was more uniform. At the same time, the bonding property of the cladding layer and matrix was good, and the fatigue strength of the sample was improved.

Study on the NiTi shape memory alloys in-situ synthesized by dual-wire-feed electron beam additive manufacturing

In this study, NiTi shape memory alloys were in-situ synthesized by dual-wire-feed electron beam additive manufacturing (dual-wire EBAM), which uses electron beam as energy source working in the vacuum environment, and uses pure Ni and Ti wires as feedstock. Microstructures, chemical composition distribution and mechanical properties of the as-built NiTi alloys were studied. Results showed that the as-built NiTi part exhibited continuous coarse columnar grains all along the building direction. Uniform composition distribution was obtained away from the substrate in the upper and middle regions of the part, which consisted of dominant NiTi phase and exhibited typical one-stage martensitic phase transformation. Good static compressive property with an ultimate compressive strength of 2.9 GPa and a fracture strain of 34.2% were obtained. The as-built NiTi samples also demonstrated good shape memory response, which had recovery rates of 88%, 83%, 81%, 80% and 63% for pre-compressive deformation strains of 2%, 3%, 4%, 5% and 6%, respectively. This study showed that the dual-wire EBAM has great potential to in-situ synthesize NiTi alloys with typical thermomechanical response and to flexibly control the chemical composition and corresponding functional performance of target NiTi alloy components by regulating the feeding speeds of Ni wire and Ti wire independently.

A mini-chemical scheme with net reactions for 3D general circulation models

Context. Growing evidence has indicated that the global composition distribution plays an indisputable role in interpreting observational data. Three-dimensional general circulation models (GCMs) with a reliable treatment of chemistry and clouds are particularly crucial in preparing for upcoming observations. In attempts to achieve 3D chemistry-climate modeling, the challenge mainly lies in the expensive computing power required for treating a large number of chemical species and reactions. Aims. Motivated by the need for a robust and computationally efficient chemical scheme, we devise a mini-chemical network with a minimal number of species and reactions for H2-dominated atmospheres. Methods. We apply a novel technique to simplify the chemical network from a full kinetics model, VULCAN, by replacing a large number of intermediate reactions with net reactions. The number of chemical species is cut down from 67 to 12, with the major species of thermal and observational importance retained, including H2O, CH4, CO, CO2, C2H2, NH3, and HCN. The size of the total reactions is also greatly reduced, from ~800 to 20. We validated the mini-chemical scheme by verifying the temporal evolution and benchmarking the predicted compositions in four exoplanet atmospheres (GJ 1214b, GJ 436b, HD 189733b, and HD 209458b) against the full kinetics of VULCAN. Results. The mini-network reproduces the chemical timescales and composition distributions of the full kinetics well within an order of magnitude for the major species in the pressure range of 1 bar–0.1 mbar across various metallicities and carbon-to-oxygen (C/O) ratios. Conclusions. We have developed and validated a mini-chemical scheme using net reactions to significantly simplify a large chemical network. The small scale of the mini-chemical scheme permits simple use and fast computation, which is optimal for implementation in a 3D GCM or a retrieval framework. We focus on the thermochemical kinetics of net reactions in this paper and address photochemistry in a follow-up paper.

Recycling gradient-elution liquid chromatography for the analysis of chemical-composition distributions of polymers

Synthetic polymers typically show dispersity in molecular weight and potentially in chemical composition. For the analysis of the chemical-composition distribution (CCD) gradient liquid chromatography may be used. The CCD obtained using this method is often convoluted with an underlying molecular-weight distribution (MWD). In this paper we demonstrate that the influence of the MWD can be reduced using very steep gradients and that such gradients are best realized utilizing recycling gradient liquid chromatography (LC↻LC). This method allows for a more-accurate determination of the CCD and the assessment of (approximate) critical conditions (if these exist), even when high-molecular-weight standards of narrow dispersity are not readily available. The performance and usefulness of the approach is demonstrated for several polystyrene standards, and for the separation of statistical copolymers consisting of styrene/methyl methacrylate and methyl methacrylate/butyl methacrylate. For the latter case, approximate critical compositions of the copolymers were calculated from the critical compositions of two homopolymers and one copolymer of known chemical composition, allowing for a determination of the CCD of unknown samples. Using this approach it is shown that the copolymers elute significantly closer to the predicted critical compositions after recycling of the gradient. This is most clear for the lowest-molecular-weight copolymer (Mw = 4.2 kDa), for which the difference between measured and predicted elution composition decreases from 7.9% without recycling to 1.4% after recycling.

Structure–property relationship in film and blow molding type high‐density polyethylene polymers from a slurry‐process industrial plant

AbstractIn this study, the microstructural, flow, and mechanical properties of two commercially available high‐density polyethylene (HDPE) samples with different particle sizes were quantified. Specifically, two different blow molding and film grade HDPEs produced by the same catalyst under different conditions were acquired in powder form after dryer section of an industrial plant. They were fractioned according to their particle sizes into six samples: ≤125, 125–200, 200–315, 315–400, 400–500, and ≥ 500 μm. According to sieve analysis, the film grade (D50 = 304 μm) had larger particle sizes related to the counterpart injection sample (D50 = 289 μm). A peak value in density, bulk density, viscosity molecular weight (Mv), melt flow index (MFI), and comonomer content characteristics was found in the particles with the diameter of 125–200 μm in both samples, indicating extremely non‐homogeneity of these HDPE samples. Chemical composition distribution (CCD) of the as received polymers as well as sieved fractions was surveyed via SSA or TREF analyses. The film sample represented lower MFI and density and higher Mv and comonomer content in all fractions, originated from different reactor conditions during the samples synthesis, which translate into improved mechanical properties comparing with the blow molding sample.

High temperature oxidation and hot corrosion behaviors of Fe65.7Ni11.7Ti1Mo6.6Co15 high entropy alloy

Understanding the surface oxidation and hot corrosion properties of the Fe65.7Ni11.7Ti1Mo6.6Co15 high entropy alloy (HEA) at high temperatures and hot corrosion media could provide useful insights into designing the high performance of the metallic materials, which is indispensable for its wide applications. Herein, at about 1923 K, the HEA was prepared by vacuum induction melting with five principal metals (Fe, Ni, Ti, Mo, and Co) in the solid-solution form. The high temperature oxidation tests at 823 K, 923 K, and 1023 K, and the hot corrosion tests using mixtures of NaCl and Na2SO4 as the hot corrosion media at 923 K were carried out, respectively. High temperature oxidation and hot corrosion behaviors were investigated via surface and cross-section morphologies observation, oxidation and corrosion products tests, and chemical composition distribution maps analysis. The effect of temperature on the oxidation resistance, as well as the effect of the content of NaCl in the mixed salt medium on the hot corrosion resistance were revealed. The results show that the HEA exhibited good high temperature oxidation resistance at 923 K according to mass gain and products after oxidation. The higher content of NaCl in the mixed salt medium can bring more intense hot corrosion. In addition, more oxygen and molten salts can be migrated via cracks and dense pores, which is not conducive to enhancing the high temperature oxidation resistance and hot corrosion resistance.

Biomass in an industrial boiler: characterizing and reducing waste from the burning process

Ashes constitute a waste produced in the heat generation process from bioenergy. This study aimed to improve the biomass energy efficiency used in an industrial boiler. The physicochemical analysis was used to perform improvement in the quality of the biomass for solid fuel. Four biomass types (eucalyptus bark, wood chips, sawdust, and recycled wood waste) were analyzed. The material (ash) was collected every two months over one year. All samples were characterized regarding proximate analysis, chemical composition (macro and micronutrients), morphological characterization (via scanning electron microscopy [SEM] coupled with dispersive energy spectroscopy [EDS]), and particle size distribution. The four biomass types presented significant differences in moisture content and proximate analysis. The bark showed a high percentage of impurities with an ash content of 26.99%. It was possible to reduce the ash content of the biomass inserted into the boiler in half, by separating the bark in the granulometric strata and excluding the smallest particle size (<0.84 mm). The results regarding the ashes showed that chemical composition and physical attributes were similar in all samples over the year. The chemical components were the same, although they varied in quantity. It is possible to improve the biomass energetic performance by excluding the smallest particles prior to the boiler insertion.

Screening of optimum composition of superparamagnetic nanocomposite microparticles modified with various layered double hydroxides for phosphorus removal

Superparamagnetic nanocomposite microparticles (NCMPs) modified with various layered double hydroxides (LDHs) (MgFe, MgAl and their Zr-doped equivalents) were investigated for phosphorus (P) removal. Screening of optimum composition was performed based on the P removal performance of NCMP@LDH particles as well as their magnetic separability in a flow-through column as a function of NCMP content (100–1000 mg) and stability as a function of LDH content (20–100%). The results showed that except for NCMP@MgFe-Zr, all the other particles exhibited a partial dissolution of LDH components at each of the examined LDH contents. However, NCMP@MgFe-Zr showed no dissolution up to a LDH content of 60% at all, whereas a partial dissolution occurred at a LDH content of 80 and 100%. Results of magnetic separability test revealed that the NCMP@MgFe-Zr composed of 500 mg magnetic particle (NCMP) and 60% LDH was separated from the solution with a separation efficiency of 96.9%, while lower NCMP contents resulted in lower separation efficiencies. P removal efficiency and specific removal capacity of the NCMP@MgFe-Zr with the optimized composition was found to be 18.5% and 53.1 mg/g, respectively. The crystal structure, chemical composition, surface morphology, crystallite size and particle size distribution, functional groups and magnetic properties of the NCMP and NCMP@MgFe-Zr particles were confirmed by various characterization analysis. The observed results clearly demonstrates that the NCMP@MgFe-Zr with the optimized composition remained stable during the removal experiments and enabled the removal of P under the conditions of acidic pH and relatively high P concentration without LDH dissolution.

Robust photothermal self-healing superhydrophobic coating based on carbon nanosphere/carbon nanotube composite

In this study, a photothermal superhydrophobic surface based on carbon nanospheres/carbon nanotubes (CNSs/CNTs) composite was fabricated, and the self-healing effect of its superhydrophobicity under solar irradiation was demonstrated. To investigate the chemical composition and elemental distribution of the coatings, infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS) mapping analyses were performed. The morphology, roughness and wetting properties of the coatings were characterized using field emission scanning electron microscopy (FESEM), confocal laser scanning microscopy (CLSM) and contact angle measuring instrument, respectively. The results showed that CNSs and CNTs synergically constructed peak-like microstructures and villi-like nanostructures with the assistance of polydopamine (PDA) and epoxy resin (EP), and the obtained superhydrophobic coating had a water contact angle (WCA) of 160.7° and sliding angle (WSA) of 4.0°. The coating can convert light energy into heat energy (T230s = 189 °C) in a short time under the irradiation of simulated sunlight (I = 20 A). The photothermal self-healing mechanism was analyzed by X-ray photoelectron spectroscopy (XPS). When the coating became superhydrophilic under the treatment of O2 plasma, the hydrophobic long chain provided by dodecyltrimethoxysilane (DTMS) migrated to the upper layer of the coating under the thermodynamic drive, thus realizing the self-healing of superhydrophobic properties.