Papers by Keyword: Ce

Abstract: The article presents the results of an investigation of microstructural features and mechanical characteristics of Al-5.0Cu-0.5Mg alloy containing up to 0.4 wt. % Ag and up to 0.1 wt. % Ce. The experiment was conducted using optical microscopy, Scanning Electron Microscopy as well as an electron probe micro-analyzer and Differential Scanning Calorimetry. Samples in cast condition and after heat treatment were examined. The melting temperatures of non-equilibrium eutectics (non-equilibrium solidus), equilibrium solidus and liquidus were determined. The optimal temperature of the homogenizing heat treatment was determined, which was 500°C. Using this heat treatment mode resulted in the elimination of dendritic segregation and complete dissolution of silver in aluminum. Injection of cerium into the Al-Cu-Mg-Ag system during crystallization of the melt is accompanied by the formation of a coarse four-component phase, which has the morphology of polyhedrons, is on the grain boundaries. The estimation of the relation between microstructure characteristics and mechanical properties of the alloy has been made.

Abstract: The rare earths are important modifier in copper alloy. This paper did research about the effect of Ce on microstructures and mechanical properties of HMn64-8-5-1.5 brass. The addition of Ce can refine the matrix grain of as-cast and extruded HMn64-8-5-1.5 brass, reduce the size and quantity of big hard phase , and contribute to the extraction of tiny hard phase, such as Mn₅Si₃ phase. When given tensile stress, hard phases can produce crack initiations. The addition of rare earth Ce can increase the number of hard phase and thus produce more crack initiations, so that the mechanical properties of HMn64-8-5-1.5 brass can be reduced.

Abstract: The effect of rare earth element Ce addition on the microstructure and martensitic transformation behavior of Ti₅₁Ni₄₉ shape memory alloy was investigated by scanning electronic microscope (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that the microstructure of TiNiCe ternary alloy consists of Ti₂Ni phase, CeNi phase and the matrix. One-step martensitic transformation is observed in quenched TiNiCe ternary alloys, which is the same as that in quenched TiNi binary alloys. The martensitic transformation temperatures of Ti-rich TiNi alloy hardly increase with Ce addition.

Abstract: In order to develop ignition-proof magnesium alloys, the effect of alloying element Ce on the ignition-proof properties and surface tension of AZ91D-2.5Ca alloy were investigated. The results show that the addition of Ce can significantly raise the ignition temperature and change the structure of surface oxide film as well as the surface tension. When the Ce content increases to 1.2%, the ignition point reaches 1371K. Upon the addition of Ce, the oxide film of AZ91D-2.5Ca melt changes to fine and close structure from the porous structure before the Ce addition. The composite oxide film mainly composed of MgO, Al₂O₃, CaO and Ce₂O₃. The surface tension of AZ91D-2.5Ca decrease with the increasing Ce content, as the active-element Ce enriched at the melt surface.

Abstract: The present work gives a simple precipitation method for preparation of lanthanum oxysulfate and cerium modified lanthanum oxysulfate by using lanthanum nitrate and ammonium sulfate as precursor in the presence of ammonia. The XRD, TEM, XPS, and N₂ sorption measurements have been adopted to characterize those materials. The present work demonstrates that cerium addition can promote the oxidation and reduction process between lanthanum oxysulfide (La₂O₂S) and lanthanum oxysulfate (La₂O₂SO₄). The cerium doped La₂O₂SO₄/La₂O₂S oxygen storage system showed the replacement of cerium for some La site to form a stable structure and no sulfur leakage took place in the process of redox cycle. The oxidation temperatures of Ln₂O₂S to Ln₂O₂SO₄ decrease more than 150 °C for cerium doping samples; and the reduction temperature of La₂O₂SO₄ to La₂O₂S in hydrogen decreases about 50 °C. The redox cycle between Ce³⁺ and Ce⁴⁺ has been considered response to the promotion of the redox cycle.

Abstract: Bit-interleaved coded modulation iterative decoding (BICM-ID) is an excellent bandwidth efficient transmission scheme,which owns remarkable bit-error-rate (BER) performance both in additive Gaussian noise (AWGN) channel and Rayleigh fading channel.But it leads to the increase of computational complexity and decoding delay at the receiver at the same time. In order to decrease the unnecessary iterations ,a variety of the stopping criteria are put forward . This paper presents an improved simplified cross-entropy (CE) stopping criterion based on Simplified-CE criterion, which calculates the value of CE just one time when Signal to Noise Ratio (SNR) is under 2dB to simplified the iterative process. Simulation results show that the improved Simplified-CE criterion can own the least iterative number when the SNR is under 2dB.And when the SNR is from 2.5dB to 4dB, it is about 12% less than CE criterion in the average iterative numbers.

Abstract: The iterative process of bit-interleaved coded modulation iterative decoding (BICM-ID) leads to the increase of computational complexity and decoding delay at the receiver, although it owns remarkable bit-error-rate (BER) performance both in additive Gaussian noise (AWGN) channel and Rayleigh fading channel. A variety of the stopping criteria are put forward to reduce the unnecessary iterations in the process. This paper presents a simplified cross-entropy (CE) stopping criterion based on CE criterion, which sets self-adaptive thresholds for different SNRs to decide whether to calculate the CE in the receiver. Simulation results show that the simplified CE criterion can obtain a better performance and lower computational complexity. The iterative number of the simplified CE criterion is about 12.2% less than the conventional CE criterion.

Abstract: The effects of minor Al and Ce on the microstructures, room-temperature and high-temperature mechanical properties of as-cast Mg-6Zn magnesium alloys were investigated. With the Al addition into Mg-6Zn alloy, the coarse eutectic Mg₅₁Zn₂₀ phases were refined and distributed discontinuously. After adding 0.5wt.% Ce into Mg-6Zn-1Al alloy, a new needle-like Al₂CeZn₂ phase was observed. Meanwhile, the volume fraction of Mg₅₁Zn₂₀ phase decreased and the semi-continuous Mg₅₁Zn₂₀ phase became discontinuous globular morphology. It has been observed that the addition of Ce element coarsens the grains, and 1wt.% Al addition enhanced the yield strength and ultimate strength from 86.35MPa, 229MPa to 90.7MPa, 238MPa, respectively. Moreover, the Ce addition can significantly increase the high-temperature mechanical properties of cast Mg-6Zn-1Al alloy.

Abstract: The paper discussed the effects of Ce, Mn, Cr on the microstructure and properties of high-iron eutectic Al-Si piston alloy using orthogonal design. It has been found that Mn and Cr improved the morphology of β phase (Al9FeSi3), becoming the Fe phase that consists of Mn and Cr; Rare earths Ce has a strong effect on refinement of the eutectic silicon. At a high mass fraction of Ce, Ce enter Fe phase that contains Mn and Ce, which improves its morphology greatly and decreases the size of Fe phase, and is able to replace the position of Ni, becoming high-temperature Al-Ni-Cu-Ce phase. The best additions of Ce, Fe, Mn, Cr would be 0.8%, 1.0%, 0.4% and 0.1% respectively and the tensile strength under room temperature (25°C) and high temperature(300°C) would reach 270.3MPa and 136.7MPa respectively, which fully meet the requirements of the use of novel the piston high temperature load.

Abstract: Ce conversion coating was prepared on the surface of magnesium alloy, and formation of Ce conversion coating was discussed. Structure and resistance to corrosion were measured by scanning electron microscope and electrochemical test system. The results showed the Ce conversion coating was composed of three layers, and it could effectively protect magnesium alloy from corrosion medium.