Papers by Keyword: Substitution

Abstract: The aggregates factory consumes a big quantity of energy; by consequence, it costs money, in the other hand it produces a lot of waste material or SCM (sustainable concrete material). The main aspects which guide this study is the current tendency to make mortar based on a very abundant material which are crushed limestone aggregates and naturals dunes sand. The results obtained in this study summarize up the importance of SCMs aggregates on behavior of the mortar, this different kind of SCM aggregate offered different behavior at the fresh state of the batch and by consequence its result with different mechanical behavior at the hardened state of mortar. This study focus also on the behavior of the new kind of chemical admixture, which is acrylic superplasticizer. The principal aim of adding rolled or crushed SCM is makes a mortar, which can resist to exhaustive environment (at curing temperature).

Abstract: Within the research presented in this article the attention was paid to the study of microstructure of lightweight and decorative renders. The composition of these renders was modified using alternative raw materials in amount of 5 % substituting the finest aggregate fractions. For evaluation of microstructure and its changes the combination of three methods SEM, XRD and DTA was used. Samples for the analysis were prepared from 90-day old specimens. The reason was the evaluation of material structural changes within the mid-term scale because considering the character and amount of used raw materials including the results of physical-mechanical tests no more significant changes were assumed in a short-term period. The performed analyses showed only inessential changes in microstructure of modified materials in comparison with the results of physical-mechanical tests.

Abstract: In this paper, a new color image encryption mechanism based on multiple chaotic systems is proposed. In the proposal, two modules are achieved by mixing the features of horizontally and vertically adjacent pixels with the help of adopted multiple chaotic systems, respectively. Then, substitution/confusion is accomplished by generating an intermediate chaotic key stream image based on the adopted chaotic maps. Experimental results show that the proposed scheme is able to manage the trade-offs between the speed performance and security requirements.

Abstract: In this paper, the characteristics of melted and annealed Co-free AB₃-type hydrogen storage alloys in low-temperature condition were investigated by electrochemical tests. A series of Co-free AB₃-type hydrogen storage alloys were synthesized with vacuum melting method, and be annealed by low-temperature heat treatment. The structures of alloys are simply discussed through SEM and XRD results. And discharge ability and cycle ability of alloys were tested. Experiment results indicate that characteristics of different AB₃-type hydrogen storage alloys are affected by low-temperature obviously, and heated treatment could increase the discharge capacity of hydrogen storage alloy effectively, and improve the charge-discharge stability of alloy. Furthermore, non-metal element substituted alloy shows better Low-temperature applicability due to its weak crystallization. The discharge capacity of La_0.7Mg_0.3Ni_2.9B_0.05 alloy remains 91.2% after 30 cycles at 273K. And discharge capacity of heated La_0.7Mg_0.3Ni_2.9(FeB)_0.1 alloy could reach to 250mA·g^-1.

Abstract: In this paper, First-principles calculation were used to investigate the effect of Fe substituted Co-free AB₃-type hydrogen storage alloys. (La₃Mg₆Ni₂₇)_1/3 alloy (Hex structure) and (La₃Mg₆Ni₂₆Fe₁)_1/3 alloy's crystal structures were build by Material studio software, Bond structure and DOS results were calculated. To compare with the calculated results, (La₃Mg₆Ni₂₇)_1/3 alloy and (La₃Mg₆Ni₂₆Fe₁)_1/3 alloy were synthesized by vacuum melting method. The effect of Fe on such alloys are discussed according to calculate results and experiment results, as a first-principle investigation.

Abstract: Polycrystalline Ti-Co co-substituted M-type ferrites Ba (TiCo)_xFe_12-2xO₁₉ (x=0.25,0.5, 0.75, 1.0 ) samples were prepared by the citrate precursor method. The particle structure and morphology of the products were characterized by X-ray powder diffraction (XRD) and Field Emission Scanning Electron Microscope (FE-SEM). The effects of the substitution rate on the magnetic properties of samples were analysed by magnetic measurement with the Vibrating Sample Magnetometer (VSM) of Physical Properties Measurement System (PPMS). The XRD patterns show that only one type of crystalline phase can be detected and the substitution did not change the crystal structure. The SEM micrographs of Ba (TiCo)_xFe_12-2xO₁₉ calcined at 450 °C for 5h, and then 950°C for 5h show that the M-type ferrite particles were homogeneously shaped and the grain sizes had no obvious differences when the substitution rate changed. The magnetic hysteresis loops illustrate that the coercivity (Hc) decreased rapidly with the increasing of Ti-Co substitution, while the saturation magnetization (Ms) changed slowly.

Abstract: In this paper we report the microstructure and magnetic properties of Ti⁴⁺-Mn⁴⁺ ions substitued barium hexaferrites (BHF) with formula of BaFe_12-2xMn_xTi_xO₁₉ (x = 0.2, 0.4, 0.6 and 0.8) which prepared by mechanical alloying and successive sintering at 1100 °C. Ti⁴⁺-Mn⁴⁺ ions were obtained from TiO₂ and MnO precursors which were mechanically alloyed together with BaCO₃ and Fe₂O₃ precursors. X-ray diffraction patterns for sintered samples confirmed that the materials are consisted with single phase BHF structure. Unit cell volume and crystallite size was found increase with increasing x. The crystallite size for all samples was below 70 nm, but microstructure observation shown that the particle size is in range of 200 - 400 nm, which concluded that the grains are polycrystalline. The saturation magnetization is increases up to x = 0.4 and decrease for higher x values, while the coercivity remain decreases monotonically. These results were interpreted in terms of the site preferential occupation of Ti²⁺ and Mn⁴⁺ at low level substitution.

Abstract: A novel and efficient method for the synthesis of 4-hydroxy-6-substituted-pyrazolo [3,4-d] primidines with acetic acid via phenol esters intermediate has been developed. Compared to the results obtained from the base substituted conditions, acetic acid catalyzed synthesis afforded target products in good yields.

Abstract: Pure Ca_2.6Bi_0.4Co₄O₉ Ceramic compound were successfully prepared by adopting a facile solution combustion synthesis method. The crystallinity, morphology were characterized by XRD, FE-SEM. The thermoelectric properties of Bi-doped Ca₃Co₄O₉ were also systematically investigated. The results indicate the prepared samples are p-type semiconductors. Both the electrical conductivity and the Seebeck coefficient increase with the increasing of temperatures. Bi substitutions at Ca site enhanced carrier mobility and resulted in a marked increase in thermoelectric properties. The power factor of as-prepared Ca_2.6Bi_0.4Co₄O₉ sample can reach 2.67×10^-4W/mK² at 1000 K. The synthesized Ca_2.6Bi_0.4Co₄O₉ ceramic materials have potential application for high-temperature thermoelectric energy conversion.

Abstract: Crystal structure and microstructure of La_0.7-xHo_xSr_0.3MnO₃ (x=0.2,0.6) prepared by usual ceramic techniques and grinding procedure were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). When doping amount x equals to 0.2, incorporation of Ho atoms contributed to phase separation and coexistence of rhombohedral (La_0.7Sr_0.3MnO₃) and hexagonal (HoMnO₃) phases. La_0.7Sr_0.3MnO₃ phase is of typical perovskite structure, whereas, HoMnO₃ phase is non-perovskite structure. As x reaches 0.6, the volume fraction of HoMnO₃ phase was significantly increasing. Meanwhile, an orthorhombic lattice with perovskite structure and space group Pnma can be observed. It prevented from partial substitution of La ³⁺ or Sr²⁺ by Ho³⁺ and the distortion of Mn-O octahedra.