Advanced Materials Research Vol. 1171

Abstract: The synthesis and characterization of spin-coated Al-doped ZnO (AZO) thin films with varying Al concentrations (0%, 5%, 10%, 15% and 20%) onto glass substrates have been demonstrated in this paper. The structural, electrical and optical properties of the spin-coated thin films have been investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) analysis, Van Der Pauw method and UV-visible spectroscopy. The EDX study shows well-defined peaks which confirm the presence of only Zn, O and Al and no other impurities in the films. The increase of Al and decrease of Zn weight percentages with increasing doping level confirms the effective substitution of Zn by Al. SEM of the surfaces of the films shows that undoped ZnO films contain particle agglomeration which is reduced with Al doping and the surfaces of the films gradually became more uniform. The thickness of the AZO films varied from 86 to 699 nm with increasing Al doping concentration. The electrical conductivity of the films increased up to ~ 7 × 10^-2 (Ω.cm)^-1 due to doping with 5% Al concentration. The optical transmittance highly increased above 95% in the visible range with the introduction of Al dopant and it kept rising with the increase of Al concentration. The optical energy band gap of undoped ZnO increased from 3.275eV to 3.342 eV with 5% Al doping.

Abstract: With the development of new energy vehicles, it is necessary to develope new fast charging cathode materials for lithium ion batteries. This paper reports a simple carbon thermal reduction routine to synthesize layered LiMoO₂ cathode for Li-ion batteries. Impurity-free micro-crystalline powders were synthesized by one-step method with a thermal treatment at 800^°C for 5 hrs under N₂ atmosphere. The structural, morphological and electrochemical properties of LiMoO₂ were characterized by using X-ray diffraction pattern (XRD), scanning electronic microscopy (SEM), charge/discharge cycling and electrochemical impedance spectroscopy (EIS). The diffraction results indicate that the prepared sample has a layered hexagonal structure related to α-NaFeO₂. The secondary particles are in order of 2.0 μm length on average with homogeneous distribution. The initial discharge capacity of LiMoO₂ is 110.9 mAh·g^-1 at 0.1 C, and the capacity can still remain 92.8 mAh·g^-1 after 100 cycles. The good cycling performance and high rate discharge performance are attributed to the smaller charge-transfer resistance revealed by EIS results.

Abstract: The strong vacuum ultraviolet (VUV) radiation absorption and energy transfer mechanism is detected in SrF_2: Gd³⁺, Eu³⁺ fluoride phosphor. The phosphor is synthesized by a wet chemical method followed by reactive atmospheric process (RAP). The Powder XRD analysis shows structural purity. The photoluminescence characteristics of SrF₂:Gd³⁺, Eu³⁺ phosphor is studied using the remote access of 4B8 window (VUV beamline) of the Beijing Synchrotron Radiation Facility (BSRF) China. In this paper the mechanism of Energy transfer from the Gd³⁺ to Eu³⁺ through the cross relaxation process is investigated. The down-conversion of energy from VUV (142 nm) to visible with quantum efficiency (QE) around 124% has been detected. The PL excitation and emission characteristics of the prepared phosphor advocates it as a prominent material for the applications in mercury free fluorescent lighting (MFFL) & Plasma Display Panel.

Abstract: The search for new materials that serve as dressings and promote the proper means for wound healing, without yielding toxic waste to the wound bed and at low cost, is currently the subject of research. In this sense, the present study aimed to develop a prototype of a poly(vinyl alcohol) (PVA) polymeric film, sodium carboxymethylcellulose (NaCMC). PVA and NaCMC as miscible polymer blend films for wound dressings was developed using internal mixing chamber processing in a mix torque rheometer (MTR) without the use of binders or crosslinks in different mixing conditions that were investigated by thermal characteristics (differential scanning calorimetry (DSC)) and thermogravimetric analysis (TGA) and crystallinity (X-ray Diffraction Technique (XRD)). The films obtained by pouring from this starting material were characterized by DSC, TGA, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), optical microscopy and swelling assay. All stages of development of this prototype are discussed, from the quality control of the raw materials, through the development of the preparation technique of the blends in 14 different processing conditions. The processed PVA/NaCMC film showed physical crosslinking which may have promoted its ability to resist dissolution in water (unprocessed PVA/NaCMC films’ characteristic). The results demonstrated that the processing of the PVA and NaCMC polymers in the MTR constitutes a viable technique to obtain membranes for use as dressings.

Abstract: Bimetallic nanoparticles (BMNPs) of silver and gold are synthesized by eco- friendly green chemical procedure using leaf extract of Cocculus hirsutus. Under the experimental condition most individual silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) are spherical whereas silver-gold bimetallic nanoparticles (Ag-Au BMNPs) found cloudy and lost their individual shape. Ag-Au BMNPs formed by the co-reduction of Au(III) and Ag(I) ions in aqueous leaves extract solution where the extract act as both reducing and capping agent. NPs were characterized with the help of UV-Vis absorption spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis. UV-Vis spectroscopy exhibit surface plasmon absorption maxima at 435 and 540 nm for AgNPs and AuNPs respectively whereas surface plasmon resonance (SPR) maxima for Au-Ag bimetallic appeared in between the peaks corresponding to pure silver and gold at the same reaction conditions. X-ray diffraction analysis confirmed that crystalline nanoparticles (NPs) are face centered cubic structure. The synthesized bimetallic nanocomposites show stronger scavenging ability, around 67% and 75% on hydroxyl radical and superoxide radicals at the concentration of 400 µg/ml respectively, compared to the mono metallic AgNPs and AuNPs, indicating stronger antioxidant properties of Ag-Au BMNPs.

Abstract: In continuous casting, the cooling rate, casting speed, and molten metal temperature significantly affect the quality of cast steel billets. Appropriate casting parameters can minimize quality problems such as surface, subsurface and interior crack, rhomboidity, oscillation mark depth, and central porosity. This research determines the relationship between defects and three significant factors temperature, cooling rate, and casting speed. The work has been performed on the two-strand continuous casting machine to investigate the billet (BS-4449 steel grade) cross-section of 150 x 150 cm². The defects analysis through macro examination at different tundish temperatures (1510 °C to 1560 °C), varying cooling rates, and casting speeds (0.9 to 1.6 m/min). The present study provides detailed insight into the three parameters mentioned earlier, which directly affect the quality of cast steel billets.

Abstract: Lotus-type porous materials (LTPMs) are considered as a new category of engineering materials. They are porous materials characterized by long, straight, unidirectional cylindrical pores, and are obtained via unidirectional solidification from a melt under hydrogen and argon atmospheres. The anisotropic pore morphology of lotus-type materials results in the anisotropy of their mechanical and physical properties. This study aims at investigating the effect of cross-sectional pore shapes on the effective Young's modulus (EYM) of LTPMs. The representative volume element-based finite element homogenization method was used to compute the effective bulk and shear moduli. Subsequently, the EYM was deduced from the effective bulk and shear moduli. The numerical results of the circular pores were validated by comparing them with experimental results. Because the results indicated that the EYM is extremely sensitive to the variation in the pore shapes, a formula for estimating the EYM of LTPMs by considering the pore shapes was developed and validated.

Abstract: The gravel geometry (shape and size of aggregate), and water to cement ratio affect the constitutive law of concrete. In concrete technology, it is intended to increase the failure stress and strain for enhancing the seismic performance during the earthquake. The aim of the present study is to propose mathematical equations that the independent variables are aggregate size and water to cement ratio. These equations evaluate the failure stress and strain of plain concrete in compressive behavior. The samples were prepared to cover a varied range of compressive strength from 17 to 37 MPa. Two sets of samples were selected, the rounded and sharp aggregates with a variety of sizes (9.5, 12.5, 19, and 25 mm) and water to cement ratios (0.35, 0.42, 0.54, and 0.76). Error analysis shows that the proposed relations are intolerable agreement with the test results and the models suggested by the other researchers, especially regarding failure stress.

Abstract: Researchers in the field of concrete technology with the application of different admixtures are always in search of suitable admixtures to improve the workability as well as the strength of any concrete grade. An attempt was made in the present research to use chemical admixtures (superplasticizers) like sulphonated naphthalene based Apple Chemie AC-MENT-ALPHA-X5, polycarboxylic ether based Fosroc Auramix 350, sulphonated naphthalene based Fosroc Conplast SP 430, modified polycarboxylate based Du-bond DUPLAST PC P 2 and modified lignosulphate based Sika PLASTIMENT BV 40 for concrete grades M30 and M40. A literature survey revealed that all identified chemical admixtures are used for 20–25% reduced water content. A study was done to compare M30 and M40 grade concrete in both fresh and hardened states, taking water reduction into account. Experimental results showed that all admixtures demonstrate good paste-up consistency of up to 1%. As the percentage of admixtures increases, there is an increase in surface pores due to more significant air entrainment. Compressive strength results of 1% admixture content for Apple Chemie, Fosroc, and Du-bond were observed to be close to their characteristic compressive strengths for both grades, but Sika and Fosroc Auramix 350 have good compressive strength with less than 1%. As the grade of concrete improves, Conplast's effect reduces, but the Du-bond and Fosroc Auramix 350 perform excellently for split tensile strength. As the grade rises, all admixtures show increasing flexural strength levels. However, Auramix 350, with a 1.5% content for M30 grade, consistently outperforms Sika, which has a 1% content. It helped to employ up to 1% of all admixtures, but Sika reveals a cost increase of 2.5 to 7.3% for 1% and 1.5% admixture additions. The study found that Fosroc Auramix 350 could be used for both grades and still have good workability and strength.

Abstract: In Algeria, the calcined dam's mud is a local renewable waste that proved its use as a supplementary cementitious material (SCMs) with similar mechanical performances and better resistance to several physical and chemical attacks than Portland cement. In the same context, the main objective of the work is to evaluate the effect of this calcined mud on thermal conductivity, which was never tested. To concretize this goal, one mortar based on control cement (CEMI) and three others based on modified cement by replacing CEMI by 10% to 30% Wt rates with the calcined mud of Chorfa dam have been prepared and cured before being put to the test procedure. Compressive strength, apparent density, water absorption after immersion, and thermal conductivity at three degrees of saturation state (saturated, outdoors, and dried state) were tested. The results show that using 10% to 20% replacement rate is characterized by good free lime and calcium hydroxide consumption that produces C-S-H gel, fills pores, decreases porosity, and increases density. The thermal conductivity of mortars based on the calcined mud in all states was lower compared than the control mortar, at saturated state by 16.28%, 17.83%, and 18.60% for the mortars 10%, 20%, and 30% (of cement replacement) respectively, at outdoors state by 5.5%, 4%, and 17.5% and dry state with 8.39%, 20.65%, and 38.07%. 10% to 20% mud replacement is beneficial for use in masonry and plastering wall applications of a building's envelope. 30% replacement rate can be developed and used in environments with minimal class expositions.