Influence of Silicon Carbide on Direct Powder Bed Selective Laser Process (Sintering/Melting) of Alumina

The powder bed selective laser process (sintering/melting) has revolutionised many industries, including aerospace and biomedicine. However, PBSLP of ceramic remains a formidable challenge. Here, we present a unique slurry-based approach for fabricating high-strength ceramic components instead of traditional PBSLP. A special PBSLP platform capable of 1000 °C pre-heating was designed for this purpose. In this paper, PBSLP of Al2O3 was accomplished at different SiC loads up to 20 wt%. Several specimens on different laser powers (120 W to 225 W) were printed. When the SiC content was 10 wt% or more, the chemical interaction made it difficult to process. Severe melt pool disturbances led to poor sintering and melting. The structural analysis revealed that the micro-structure was significantly affected by the weight fraction of SiC. Interestingly, when the content was less than 2 wt%, it showed significant improvement in the microstructure during PBSLP and no effects of LPS or chemical interaction. Particularly, a crack pinning effect could be clearly seen at 0.5 wt%.

Investigation of Weight Fraction and Alkaline Treatment on Catechu Linnaeus/Hibiscus cannabinus/Sansevieria Ehrenbergii Plant Fibers-Reinforced Epoxy Hybrid Composites

The aim of the present work is to develop novel hybrid composites using areca, kenaf, and snake grass fibers as reinforcement and epoxy as the matrix. The areca, kenaf, and snake grass fibers were extracted from Catechu Linnaeus, Hibiscus cannabinus, and Sansevieria Ehrenbergii plants, respectively, and treated with 5% NaOH to improve the interfacial adhesion between the hydrophilic fiber and the hydrophobic matrix. Hybrid composites were developed by the compression molding technique and formulated based on the weight fraction of fibers. Tensile, flexural, and impact strength and hardness samples were prepared as per ASTM D 3039, ASTM D 790, ASTM D 256, and ASTM D 2240, respectively. The effects of alkaline treatment on developed hybrid composites were investigated. The developed hybrid composites with 20% wt. snake grass and 10% wt. areca fiber present interesting mechanical properties with a tensile strength of 58 MPa, flexural strength of 124 MPa, impact strength of 5.24 kJ/m2, and hardness of 88. The results indicate that maximum mechanical properties were obtained for alkaline-treated fiber composites with 20% wt. snake grass fiber compared to untreated fiber composites owing to better adhesion between the treated fiber and the matrix. The effect of alkaline treatment was analyzed by Fourier transform infrared. The fractured surfaces of tested samples were analyzed by scanning electron microscopy.

Molecular-mass distribution of humus acids of taiga soils

Purpose of the study: to reveal the influence of hydromorphism and agricultural use on the molecular-mass distribution (MMD) of humic (HAs) and fulvic acids (FAs) isolated from the soils of the European northeast of Russia. To assess the influence of the acidity of the medium on the MWD of FAs. Place and time of the event. The studies were carried out on the territory of the middle taiga (Maksimovsky station of the Institute of Biology of the Federal Research Center of the KSC UB RAS, located 8 km west of the city of Syktyvkar and the field of the Syktyvkar state farm, 5 km south-west of Syktyvkar, on the watershed of the Sysola and Vazhel-yu rivers) and northern taiga (3 km west of the Troitsko-Pechorsk station). The objects of the study were humic substances isolated from typical podzolic (Eutric Albic Retisol (Loamic)), gleypodzolic (Eutric Albic Stagnic Retisol (Loamic)), peaty-podzolic surface-gleyed (Eutric Albic Stagnic Histic) Retisol (Loamic Eutric Albic Retisol (Loamic)) soils. The soil sampling period is from 1 to 30 August 2014. Methodology. Quantitative analysis of the MMD of HA and FA preparations was performed using liquid size exclusion chromatography (gel chromatography) on Sephadex G-25 and G-100 gels with continuous automatic registration of the optical density of the eluate (λ = 280 nm) in a quartz flow cell, K 9 × 60 cm column (Pharmacia, Sweden). Distilled water, 0.05 M NaOH solution, and Tris-HCl buffer with pH = 8.2 were used as the eluent. Main results. Studies of the MMD of humic substances have been carried out. It was found that HAs contain three fractions with different molecular weights: ≥ 150 kDa, 73–80 kDa, and 13–23 kDa; FAs – two fractions: ≥ 5 kDa, 1–2 kDa. The low molecular weight of FAs, together with a large amount of oxygen-containing functional groups, contributes to their better solubility and migration ability in soils. The HAs of automorphic soils are characterized by a high content of low molecular weight fractions, and the proportion of the high molecular weight fraction in the HAs of the litter is 1.5–2.0 times higher than in the HAs of the podzolic horizon, which may be due to the migration of the low molecular weight fraction down the profile. The high proportion of the acidic low molecular weight fraction in the podzolic horizon promotes the decomposition of soil minerals and their leaching into the illuvial horizon. The influence of agricultural use of soils on the fractional composition of humic compounds is estimated. A sharp increase in the share of the high molecular weight fraction in the preparations of HAs of arable podzolic soil by 2–4 times compared with the HAs of virgin podzolic soils was noted, which is due to the cultivation of the arable horizon, the nature of the incoming plant residues and the increased microbiological activity of the developed soils. The effect of acidity of the medium on the character of chromatograms of FA preparations isolated from the main types of soils of the Komi Republic was studied. It has been shown that in the region of high pH values of the eluent 9–13, the absence of fractionation is associated with the association of FAs, a change in their conformation, and the effect of “over-exclusion”. Elution with distilled water (pH = 6.5) allows the separation of FAs into two fractions with molecular weights ≥ 5 kDa and 1–2 kDa.

Free vibration analysis and post-critical free vibrations of nanocomposite rotating beams reinforced with graphene platelet

Treatment of the first natural frequency of a rotating nanocomposite beam reinforced with graphene platelet is discussed here. In regard of the Timoshenko beam theory hypothesis, the motion equations are acquired. The effective elasticity modulus of the rotating nanocomposite beam is specified resorting to the Halpin–Tsai micro mechanical model. The Ritz technique is utilized for the sake of discretization of the nonlinear equations of motion. The first natural frequency of the rotating nanocomposite beam prior to the buckling instability and the associated post-critical natural frequency is computed by means of a powerful iteration scheme in reliance on the Newton–Raphson method alongside the iteration strategy. The impact of adding the graphene platelet to a rotating isotropic beam in thermal ambient is discussed in detail. The impression of support conditions, and the weight fraction and the dispersion type of the graphene platelet on the acquired outcomes are studied. It is elucidated that when a beam has not undergone a temperature increment, by reinforcing the beam with graphene platelet, the natural frequency is enhanced. However, when the beam is in a thermal environment, at low-to-medium range of rotational velocity, adding the graphene platelet diminishes the first natural frequency of a rotating O-GPL nanocomposite beam. Depending on the temperature, the post-critical natural frequency of a rotating X-GPL nanocomposite beam may be enhanced or reduced by the growth of the graphene platelet weight fraction.

Chemical Recycling of Mixed Plastics in Electronic Waste Using Solvent-Based Processing

Currently, less than 20% of electronic waste (E-waste) produced in the U.S. is recycled. To improve the recycling rate of E-waste, the study aimed to: (1) identify the major plastics found within electronic shredder residue (ESR), (2) design solvents and processing conditions capable of separating out 90% of the plastic in ESR, and (3) estimate the energy efficiency of the solvent-based process developed. Preliminary screening showed 25 wt.% of the ESR was composed of plastics, with two polymers dominating the sorted plastic fraction—polystyrene (PS, 40 wt.%) and acrylonitrile butadiene styrene (ABS, 25 wt.%). Subsequently, solvents and anti-solvents were screened using Hansen Solubility Parameter Theory for PS, ABS, and ESR dissolution. The pre-screening results showed dichloromethane (DCM) and tetrahydrofuran (THF) as the most effective solvents for PS and ABS, with methanol (MeOH) and ethylene glycol (EG) as the most effective anti-solvents. By optimizing the dissolution time and the solvents used, the highest polymer dissolution yield (99 wt.%) was achieved using DCM for 48 h. Both MeOH and EG precipitated 71 wt.% of the polymer fraction of ESR. EG removed more phosphorus containing flame retardants (94 wt.%) than MeOH (69 wt.%). Energy analysis indicated that the solvent-based processes could save 25–60% of the embodied energy for PS and ABS. Characterization showed that the solvent-based processing could preserve the high molecular weight fraction of the polymers while removing flame retardants at the same time. The results from this study prove the potential of solvent-based processing to produce secondary plastic materials from E-waste for cross-industry reuse.

A Short-Cut Data Mining Method for the Mass Spectrometric Characterization of Block Copolymers

A new data mining approach as a short cut method is given for the determination of the copolymer composition from mass spectra. Our method simplifies the copolymer mass spectra by reduction of the number of mass peaks. The proposed procedure, namely the selection of the mass peaks, which is based on the most abundant peak of the mass spectrum, can be performed manually or more efficiently using our recently invented Mass-remainder analysis (MARA). The considerable reduction of the MS spectra also simplifies the calculation of the copolymer quantities for instance the number- and weight-average molecular weights (Mn and Mw, respectively), polydispersity index (Đ = Mw/Mn), average molar fraction (cA) and weight fraction (wA) of the comonomer A and so on. These copolymer properties are in line with those calculated by a reference method taking into account all the mass peaks of the copolymer distribution. We also suggest a highly efficient method and template for the determination of the composition drift by processing the reduced mass spectra.

Wear and Morphological Analysis on Basalt/Sisal Hybrid Fiber Reinforced Poly lactic acid Composites

The investigation was undertaken to evaluate the wear behavior of basalt fiber and sisal fiber reinforced polylactic acid PLA composites. Basalt saline-treated chopped fiber and treated sisal chopped fiber were alloyed with polylactic acid and the samples were obtained using an injection mold in a twin-screw extruder. Three weight fraction samples were prepared, namely PBSi-1 (90% by weight polylactic acid, 5% by weight basalt and 5% by weight sisal), PBSi-2 (85% by weight polylactic acid, 7.5% by weight basalt and 7.5% by weight sisal) and PBSi-3 (80% by weight polylactic acid, 10% by weight basalt and 10% by weight sisal). The wear behavior of the prepared specimen were determined using a Pin-on-disc. The wear loss was measured at four different loads (10 N, 20 N, 30 N and 40 N) and four different sliding speeds (100 rpm, 150 rpm, 200 rpm and 250). The wear mechanism map was generated based on the wear regime nature using the Fuzzy Cluster C-means algorithm. The PBSi-3 composite showed a more mild wear regime than the severe and ultra-severe wear, due to the increase in the basalt and sisal fiber content within the composite that results in an increase of hardness and wear resistance. The predominant mechanism observed in the SEM image of PBSi-3 composite is ironing, which indicates the lesser wear occurrence in the composite.

Evaluation of Physicothermal Properties of Silicone Oil Dispersed with Multiwalled Carbon Nanotubes and Data Prediction Using ANN

The researchers wanted to see whether MWCNTs changed the physicothermal properties of solar thermal working fluids. Assessing thermal properties is vital for solar thermal efficiency. Lubricant contains silicone oil resurfaced. It contains 0.25, 0.5, 0.75, and 1.0% multiwalled carbon nanotubes. Before dispersion in thermic fluids, nanomaterials must be properly surface modified. Between 100°C and 300°C, a fluid’s thermal conductivity and specific heat physical characteristics like viscosity and density may be inferred from data collected between 50°C and 150°C. Thermal conductivity increases by 15% to 20% when carbon nanotubes are dispersed. The pressure drop is minimal at 0.5 percent weight fraction, demonstrating the suitability of nanofluids in closed loop systems. The characteristics are forecasted using feed-forward backpropagation method and GRNN, and the best of them is selected for prediction. In this research, hidden layer neurons and factors are examined.

Isolation and Characterization of Polysaccharides from the Ascidian Styela clava

Styela clava is an edible sea squirt farmed in Korea that has gradually invaded other seas, negatively impacting the ecology and economy of coastal areas. Extracts from S. clava have shown wide bioactivities, and ascidians have the unique capability among animals of biosynthesizing cellulose. Thus, S. clava is a relevant candidate for valorization. Herein, we aimed at surveying and characterizing polysaccharides in both tunic and flesh of this ascidian. To this end, we enzymatically hydrolyzed both tissues, recovering crystalline cellulose from the tunic with high aspect ratios, based on results from microscopy, X-ray diffraction, and infrared spectroscopy analyses. Alkaline hydroalcoholic precipitation was applied to isolate the polysaccharide fraction that was characterized by gel permeation chromatography (with light scattering detection) and NMR. These techniques allowed the identification of glycogen in the flesh with an estimated Mw of 7 MDa. Tunic polysaccharides consisted of two fractions of different Mw. Application of Diffusion-Ordered NMR allowed spectroscopically separating the low-molecular-weight fraction to analyze the major component of an estimated Mw of 40–66 kDa. We identified six different sugar residues, although its complexity prevented the determination of the complete structure and connectivities of the residues. The two more abundant residues were N-acetylated and possibly components of the glycosaminoglycan-like (GAG-like) family, showing the remaining similarities to sulfated galactans. Therefore, Styela clava appears as a source of nanocrystalline cellulose and GAG-like polysaccharides.