Virgin Samples Research Articles

Enhancement of Luminescence Behaviour of Colloidal ZnO Quantum Dots Coated with SiO2 Irradiated by Ni+7 Ion

ZnO quantum dots of average size 10 nm are embedded in a matrix (polyvinyl alcohol (PVA)) following chemical route. They are irradiated by 100 MeV Ni7+ ion beam with fluences 1 × 1011, 3 × 1011, 1 × 1012 and 3 × 1012 ions/cm2. The optical absorption edge of irradiated quantum dots reveal negligible red shift with an increase in fluences with respect to that of unirradiated (virgin) ones. This fact clearly indicates no significant change in particle diameter under ion irradiation and is confirmed by high resolution transmission electron microscopy (TEM). AFM study also reveals the r.m.s surface roughness of the particles. It has also been observed that irradiated quantum dots produce similar type of photo luminescence and electroluminescence like virgin samples but the emission intensity increases remarkably after irradiation due to creation of large numbers oxygen vacancies by the ion beam.

Multiscale thermal study of virgin and aged polyphenylene sulfide reinforced by glass fiber

AbstractIn this study, virgin and thermal aged PPS samples were prepared and tested using different techniques such as thermogravimetric analysis (TGA), coupled TGA–Fourier transform infrared spectroscopy (FTIR), and FTIR as well as optical microscopy. Some interesting research results can be summarized as follows: TGA results prove the PPS composite samples aged at 180 and 200°C have been degraded obviously during the aging period in oven. Moreover, accelerated aging leads to the degradation of PPS composite with the observation of increased thermal oxidation layer from outside to inside. There is a plateau standing at about 350 μm for the thermal oxidation layer at oxidation temperature of 200°C. Some thermal decomposition models are applied to clarify the degradation kinetics of PPS composite. According to the activation energy value, it appears degradation more easily at the beginning of the heating process in the atmosphere of oxygen than that of nitrogen. Moreover, the related products of PPS composites during pyrolysis are fully discussed with the combined analysis of TGA–FTIR techniques.

Hygrothermal aging effect on physical and mechanical properties of carbon fiber/epoxy cross-ply composite laminate

Fiber reinforced composites used in aircraft and marine industries lead to critical environmental factors like high temperature and humidity. This work investigates the physical and mechanical response of hygrothermally aged IMA carbon fiber/M21 epoxy CFRP cross-ply composite laminates. The Vacuum assisted resin transfer moulding technique was employed to fabricate two symmetric laminates with a constant fiber volume fraction of 59%. The CFRP laminates with stacking sequence [0, 90, 0, 90]2S and [0, 90]2S were immersed in tap water at 70 °C for more than 6 months up to saturation. The effect of high-temperature submerged environment on the chemical and physical property was determined by the kinetics of moisture absorption rate, FTIR, DSC, and SEM analysis. The mechanical characterization of moisture aged and virgin sample was carried out using tensile test along with post-test failure analysis by SEM micrographs. The moisture absorption followed a typical two-stage model where diffusion rate was increasing proportional to square root of immersion time followed by a sluggish phase up to saturation. The DSC result showed a significant variation in glass transition temperature after aging. SEM micrographs of aged specimen illustrated a matrix dominated failure attributable to fiber-matrix interfacial degradation which finally resulted to a major strength reduction of laminates.

Glass/jute/sisal fiber reinforced hybrid polypropylene polymer composites: Fabrication and analysis of mechanical and water absorption properties

The main objective of the present work is to prepare a glass/jute/sisal fiber (GF/JF/SF) reinforced polypropylene (PP) hybrid composites and analyse the influence of different fiber loadings on its mechanical and water absorption behaviour. The polymer composites of various compositions with different fiber loadings such as 70 wt% PP + 30 wt% GF, 70 wt% PP + 30 wt% JF, 70 wt% PP + 30 wt% SF, 70 wt% PP + 15 wt% GF + 15 wt% JF, 70 wt% PP + 15 wt% GF + 15 wt% SF, 70 wt% PP + 10 wt% GF + 10 wt% JF + 10 wt% SF have been fabricated using compression moulding technique. The fiber loading of different fibers is found to have a significant positive effect on the performance of glass/jute/sisal fiber reinforced polypropylene hybrid composites. Among the hybrid composites one with the composition of 70% PP + 10% GF + 10% JF + 10% SF shows a maximum flexural modulus of 3119.81 MPa which is almost 130% higher than the value obtained for virgin PP. It also shows a maximum hardness value of 100.1 in R/Scale reading. The same composition shows highest impact strength of 44.15 J/m, which is almost 40% higher than the value obtained for virgin sample. Water absorption is also found to be less in all these polymer composites and hybrid composites below 0.3% (by weight).

Free thaw resistance of stabilized and fiber-reinforced soil vulnerable to landslides

The research is undertaken to study the combined reinforcing and stabilizing effect of Eco sand, Metakaolin added with Polypropylene fibers in silty soil obtained from Nilgris district. In this work, an effort is made to obtain the impact of adding polypropylene fibers in fixed ratios (eco sand10%_metakaolin 5%) tandem with two novel stabilizing agents in various proportions (polypropylene fiber 0.1% & 0.2%) is the effects of non-traditional additives on the geotechnical properties of soils have been the focus of much investigation in recent years. It has been well established that the plasticity index and also the size, shape, and arrangement of soil particles will affect the treatment process of natural soils with additives. Stabilization of soils that are subjected to a regular variation in the temperature requires the most probable selection of suitable stabilizers and admixtures to improve the strength of the soil. This study investigates the resistance of the Nilgiris soil over the freeze–thaw reaction. The soil is stabilized with Eco Sand, Metakaolin, and polypropylene fiber (synthetic fiber). The index and engineering properties of the soil were determined in the laboratory. The soil is stabilized with two variants of an equal proportion of EcoSand-10%, Metakaolin-5%, and varying the polypropylene fiber in a proportion of 0.1% and 0.2% with the weight of the soil. UCS test was conducted for the virgin sample as well as the sample after four freeze–thaw cycles. The soil sample is kept at 0° for 24 h and later at 28° for 24 h to complete a cycle. It is determined that the admixtures added has increased the resistance of the soil over the freeze–thaw reaction after the cycles. The polypropylene fiber has increased the bonding of soil, and hence it stabilizes the soil during a large periodical variation in the temperature of the soil.

Structural and Mechanical Strength of Proton Radiation Processed Polyethylene Terephthalate

The change in structural and mechanical behavior of polyethylene terephthalate (PET) due to 2.4 MeV proton has been studied. Radiation processing of PET polymer is carried out using different low doses such as 0.2, 2.0, and 20 kGy. The Physics of microstrain and radiation-induced mesophase formation are analysed. X-ray investigation indicates that proton-induced structural modification takes place in the material. Apart from usual diffraction peaks, a low intensity broad peak is observed at small angle of about 2q =10º, when the fibre axis is mounted parallel to the X-ray direction. Such peak is absent in the diffraction spectrum when the fibre axis is mounted perpendicular to the beam direction. The appearance of the extra peak in a particular orientation confirms that, the phase is 2-dimensionally oriented (mesophase). The Young’s modulus (Y) of this irradiated PET sample is found to be more than that of the virgin sample with the highest value recorded for a dose of 2.0 kGy. The decrease in Y for higher dose (20 kGy) may be due to enhanced ion-induced microstrain in the sample, causing degradation in mechanical strength.

Effects of electrical-hydrothermal aging degradation on dielectric and trap properties of high temperature vulcanized silicone rubber materials.

In this paper, a new aging platform combined the high voltage electric field and the hydrothermal environment was built. To investigate the aging mechanism, physicochemical, dielectric and trap properties of HTV SR before and after electrical-hydrothermal aging for 24 days were discussed. The results indicated that, compared with hydrothermal aging, more cracks and holes appeared on the surface of HTV SR after electrical-hydrothermal aging, and the content of flame retardant decreased significantly. Due to the main chain and side chain scission of PDMS, lots of low weight molecular (LWM) substances and free radicals were produced. And the tensile strength and elongation at break significantly decreased. Various physical and chemical defects appeared in the HTV SR specimen in the process of electrical-hydrothermal degradation, as a result of which, the dielectric constant significantly increased and the peak trap density increased by about 2.5 times compared to the virgin sample. The increase in trap density in turn accelerated the charge accumulation and enhanced the breakdown probability, resulting in the electric field strength decrease from 21.8 kV mm−1 to 16.1 kV mm−1 and severe degradation of HTV SR.

Virgin olive oil volatile fingerprint and chemometrics: Towards an instrumental screening tool to grade the sensory quality

Sensory quality, assessed following a standardized method, is one of the parameters defining the commercial category of virgin olive oil. Considering the difficulties linked to the organoleptic evaluation, especially the high number of samples to be assessed, setting up instrumental methods to support sensory panels becomes a need for the olive oil sector. Volatile fingerprint by Headspace Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry can be an excellent fit-for-purpose tool as the volatile fraction is responsible for virgin olive oil sensory attributes. A fingerprinting approach was applied to the volatile profile of 176 virgin olive oils previously graded by six official sensory panels. The classification strategy consisted in two sequential Partial Least Square-Discriminant Analysis models built with the aligned chromatograms: the first discriminated extra virgin and non-extra virgin samples; the second classified the latter into virgin or lampante categories. Results were satisfactory in the cross-validation by leave 10%-out (97% of correct classification). For external validation, an uncertainty range was set for the prediction models to detect boundary samples, which would be further assessed by the sensory panels. By doing this, a considerable decrease of the panel workload (around 80%) was achieved, while maintaining a highly reliable classification of samples (error rate <10%).

Closing the textile loop: Enzymatic fibre separation and recycling of wool/polyester fabric blends

Textile waste presents a serious environmental problem with only a small fraction of products from the fashion industry collected and re-used or recycled. The problem is exacerbated in the case of post-consumer waste by the mixture of different natural and synthetic fibres in blended textiles. The separation of mixed fibre waste, where garments are often multicomponent, presents a major recycling problem as fibres must be separated to single components to enable effective recycling. This work investigates the selective digestion of wool fibres from wool/polyester blended fabrics using an enzymatic approach. Complete degradation of wool fibres was achieved by application of a keratinase in a two-step process with addition of reducing agent and undigested polyester fibres were recovered. Electron microscopy showed complete breakdown of the natural fibres in the fabric blends, while spectroscopic and mechanical analysis of the recovered synthetic fibres confirmed that the enzymatic treatment had no significant impact on the properties of the polyester compared to virgin samples. The polyester fibres are therefore suitable to be recycled to polyester yarn and re-used in the manufacture of new garments or other products. The nutrient rich keratin hydrolysate could be used in microbial growth media or incorporated into bio-fertilisers or animal feed, contributing to the development of the circular economy.

Uniformity investigation of pHEMTs in 3-D MMICs for pre and post multilayer fabrication

This study deals with the uniformity investigation and comparison on the typical behaviour of pseudomorphic high electron mobility transistors (pHEMTs) before and after the 3-D multilayer fabrication. There are seven multilayer fabricated pHEMTs compared with the seven virgin pHEMTs based on drain-source input current, output current, transconductance, off state leakage behaviour, threshold voltage, knee voltage, on-resistance, Schottky barrier height, ideality factor, reverse saturation current, small signal gain and current gain. Below 10% changes in performance can be seen after multilayer fabrication compare to virgin samples and apart from these exceptions, the discrepancies are well within the tolerance and less than 3% in terms of Schottky behaviour. We show that, the application of the 3D-MMIC technology does not cause any visible destruction of pHEMTs performance using seven different samples before and after the multilayer fabrication.

Surface Structure of Aged Composite Insulator Studied by Slow Positron Beam

Slow positron beam was applied to study the depth profile structure of the virgin and the aged high-temperature vulcanized silicone rubber (HTV). Scanning electron microscope (SEM) images show that the surface of virgin sample is smooth, while the outdoor aged samples are all rough. According to the S(E) curves obtained by slow positron beam, in a depth of more than 1 μm, the S parameter of the sample aged at low-potential side keeps the same value with the virgin one; while the S values of the highpotential side aged sample remain rather low in a depth of about 5 μm. Thermo gravimetric analysis (TGA) results show that the sample in high potential side contains more inorganic constituents than that of other samples. The results are attributed to the strong electric field induced corona aging at high potential side of the composite insulator.

Effect of laser shock peening on high cycle fatigue characteristics of 316LN stainless steel

The influence of ‘laser shock peening’ (LSP) on fatigue behavior of 316LN stainless steel has been studied at 298 K by conducting fully reversed stress controlled fatigue tests in the range 200–300 MPa. A triangular wave form with a constant frequency of 5 Hz was employed for all the tests conducted below 107 cycles on the virgin and laser shock peened samples. The run out tests at 107 cycles were performed at a frequency of 60 Hz. The studies have clearly revealed that the fatigue life is dependent on surface condition of the material and stress amplitude employed. A comparison is made of cyclic stress-strain hysteresis loops and fatigue lives between virgin and peened material. The peened material showed better fatigue strength and life at low stress amplitudes pertaining to high cycle fatigue regime, and exhibited lower density of surface microcracks. The improved fatigue resistance of peened material is attributed to the presence of residual compressive stresses to a depth of ~100 μm from the surface. The beneficial effect of compressive stresses is perceived both in the reduction in number density of Stage-I microcracks and retarded stage-II crack growth in the initial stages (that revealed striations with lesser spacing compared to un-peened samples).

1 H NMR tests on damaged and undamaged XLPE and SiR samples

Cross-linked polyethylene (XLPE) and silicone rubber (SiR) samples were subjected to a high-voltage AC stress plane–plane configuration and inclined plane test, respectively. The voltage was applied such that discharge was observed across the surface of the XLPE test sample for several hours and for visible damage to occur on SiR samples also after several hours. Selected stressed samples together with virgin samples from the same manufactured batch were tested using nuclear magnetic resonance (NMR) spectroscopy. Specifically, 1 H NMR spin–lattice ( T 1 ) and spin–spin ( T 2 ) relaxation time measurements were employed to examine potential changes in the chemical bonding of undamaged and damaged XLPE and SiR samples. Preliminary results show that there may be a moderate increase in the T 1 and T 2 values of the damaged samples in comparison with the undamaged ones. This raises the possibility that NMR can be a useful additional experimental tool in characterising material degradation.

Carbide precipitation associated with carburisation of 9Cr–1Mo steel in hot CO2 gas

Experimental ferritic 9Cr–1Mo steels exposed at high temperature and pressure to CO2-based gas undergo oxidation and carburisation. Oxidation proceeds initially as a protective phase with parabolic kinetics (stage I). At high temperatures and longer times, more rapid “breakaway” oxidation occurs (stage II). Post-breakaway oxidation follows linear kinetics (stage III). A virgin sample and three oxidised samples were selected for analysis. Precipitates embedded in the matrix with four different morphologies were observed using focused ion beam imaging, X-ray diffraction and electron microscopy techniques. Coarse carbides (M23C6) were observed as the predominant precipitates in all four samples. Fine needles (M2C), large needles (MC) and cored coarse carbide precipitates (M23C6) were also present in stages (I), (II) and (III), respectively. TEM analysis was used to give the lattice types and orientations of the carbides found. Energy-dispersive X-ray analysis was used to obtain compositions. The precipitation is considered particularly with respect to the formation of cored M23C6 carbide precipitates. These data provide a threshold for the matrix composition that defines the onset of breakaway oxidation.

Characterization of 167 MeV Xe ion irradiated n-type 4H-SiC

The nitrogen-doped, n-type 4H-SiC with 6 μm thick epitaxial layer was irradiated at the perpendicular incidence and room temperature by 167 MeV Xe+26 ions to a fluence of 5 × 1012 cm−2. The Monte Carlo simulation code, Stopping and Range of Ions in Matter (SRIM) was used to simulate the Xe26+ ions irradiated in SiC. The Rutherford backscattering spectrometry (RBS) analysis with 3.5 MeV He++ ions which have a projected range of ~9 μm in SiC (SRIM prediction) did not detect implanted Xe. Raman spectroscopy and imaging depth profiles clearly showed three distinct parts of the swift heavy ion (SHI)-irradiated 4H-SiC, i.e. 5.6 μm irradiated epitaxial layer, 6.9 μm damaged irradiated layer and non-irradiated 4H-SiC bulk. Raman spectroscopy showed new broad bands of crystalline SiSi and distorted SiC in the damaged irradiated layer. The new SiSi bands were attributed to the ordering in the SiSi homonuclear bonds without crystal amorphization. The scanning near-field optical microscopy (SNOM) results of the SHI-irradiated 4H-SiC sample displayed a very low signal counts (transmission) compared to the virgin sample, and this difference in the optical absorption could be correlated with the defects energy levels created within the bandgap of the sample upon irradiation.

Micro-Raman investigations on zirconium oxide film during swift heavy ion irradiation to study crystalline-to-crystalline phase transformation kinetics by cascade overlap model

In situ micro-Raman studies are reported to monitor the evolution of the tetragonal phase in a monoclinic zirconium oxide thin film under swift heavy ion irradiation with increasing ion fluences. Structural changes in the irradiated film are observed as compared to the virgin sample, evident from an evolution of the tetragonal phase beyond critical ion fluence. The interpretation of experimental data allows for an in-depth understanding of irradiation induced stiffening of phonon and crystalline-to-crystalline phase transformation in ZrO2 thin films. Irradiation induced peak broadening and uniform shifting of fundamental Raman modes are observed mainly in the anion (i.e., oxygen atom) dominant frequency region and give a direct indication of the accumulation of structural disorder in the oxygen sublattice of the ZrO2 film. A qualitative approach is followed to understand the kinetics of such a crystalline-to-crystalline phase transformation. Experimental results reveal that the cascade overlap model with the requirement of about six multiple ion impacts provides an excellent fit to data, and the same is further confirmed by x-ray diffraction data. Thus, this study suggests that such in situ studies envisage a better and more authentic insight into the kinetics of phase transformations under similar nonequilibrium conditions.

Screening Method for Argan Oil Adulteration with Vegetable Oils: An Online HPLC Assay with Postcolumn Detection Utilizing Chemometric Multidata Analysis

This study is focused on examining the tocopherol isomers (α-, γ-, and δ-) fingerprinting by online RP-HPLC analysis with post column detection using CUPRAC (cupric reducing antioxidant capacity) methodology for argan oil authenticity. The proposed online assay was validated with good precision, reproducibility, and linearity. Sixteen argan oil samples (100% pure-certified and other commercial argan oils), possible adulterating vegetable oils (i.e., olive, sunflower, corn, and soya oils), and virgin argan oil blended with olive, sunflower, corn, and soya oils at levels of 5%, 10%, 15%, and 20% were analyzed. Spectrophotometric CUPRAC, DPPH, and ABTS assays were applied. Discrimination of fraudulent argan oils from virgin samples was performed by utilizing orthogonal partial least-squares discriminant analysis (OPLS-DA) regression modeling with good sensitivity and specificity. We suggested [γ-toc/α-toc] value as a new first screening adulteration factor (AF) that could be used to assess fraudulent argan oil samples. The distinct decrement in AF value was observed by the increase of adulteration rate. The AF values for virgin argan oils were ranged from 11.8 (lower limit) to 18.6 (upper limit). The presence of β-sitosterol detected in commercial argan oils (with AF values out of limit values) was evaluated as fraudulent which was in accordance with the proposed assay. Our method enabled the detection of argan oil samples at adulteration levels of >5% in the case of sunflower, olive, and soya oils, >15% in the case of corn oil. This method may be an alternative and specific assay for the authentication and quality detection of commercial argan oils.

Diesel-induced transparency of plastically deformed high-density polyethylene

High-density polyethylene becomes optically transparent during tensile drawing when previously saturated with diesel fuel. This unusual phenomenon is investigated as it might allow conclusions with respect to the material behavior. Microscopy, differential scanning calorimetry, density measurements are applied together with two scanning X-ray scattering techniques: wide angle X-ray scattering (WAXS) and X-ray refraction, able to extract the spatially resolved crystal orientation and internal surface, respectively. The sorbed diesel softens the material and significantly alters the yielding characteristics. Although the crystallinity among stretched regions is similar, a virgin reference sample exhibits strain whitening during stretching, while the diesel-saturated sample becomes transparent. The WAXS results reveal a pronounced fiber texture in the tensile direction in the stretched region and an isotropic orientation in the unstretched region. This texture implies the formation of fibrils in the stretched region, while spherulites remain intact in the unstretched parts of the specimens. X-ray refraction reveals a preferred orientation of internal surfaces along the tensile direction in the stretched region of virgin samples, while the sample stretched in the diesel-saturated state shows no internal surfaces at all. Besides from stretching saturated samples, optical transparency is also obtained from sorbing samples in diesel after stretching.

Enhancing electrical strength of acrylate polymer by using fluorinated monomer as surface modifier

A novel method using ultraviolet (UV) cured fluoralkene to realize surface fluorination of acrylate polymer is proposed to enhance its insulation performance. Doping small amount of dofluoroheptyl methacrylate C11H8F12O2 (DFHMA) in UV acrylate resin formulation as modifier can assemble a fluorinated monomolecular layer on the surface whenas bringing little change to its morphology. The influences of the modifier on molecular structure, surface free energy, elemental composition and electric properties of acrylate polymer are investigated by attenuated total reflection infrared (ATR-IR), water contact angle, X-ray photoelectron spectroscopy (XPS), and electrical performance characterizations, respectively. Experimental results indicate that DFHMA is segregated to the surface of acrylate polymer, leading to an increase of its surface hydrophobicity. Surface flashover tests reveal that fluorinated samples have a higher degradation or tracking resistance in comparison with virgin samples. In addition, strong CF bonds also can enhance bulk breakdown characteristics by increasing charge injection barrier.

Jamming analysis on the behaviours of liquefied sand and virgin sand subject to monotonic undrained shearing

It is well documented in the experimental literature that liquefied sands behave differently from virgin sands without a shearing history. In this study, undrained DEM simulations were performed on both a virgin sample and samples liquefied by cyclic loading. An identical critical state was reached regardless of liquefaction history. The fundamental mechanisms underlying the difference in the stress–strain responses between the liquefied sands and virgin sand were interpreted within the framework of jamming transition. The virgin sample was jammed throughout the simulation, characterised by a fully-percolated force transmission network of increasing resilience and mechanical stability. In contrast, the initially liquefied samples experienced an apparent phase transition from unjammed to jammed states. A fully-percolated force transmission network did not exist, and thus the unjammed samples flowed during the initial stage of loading. As loading proceeded, the force transmission network became fully percolated, and its resilience and mechanical stability developed. All of the micro-scale parameters reflecting the resilience and mechanical stability of the force transmission network reached identical values at the critical state independent of liquefaction history. Finally, a micro-scale approach based on the degree of indeterminacy was proposed to identify the four-stage post-liquefaction behaviour.