Modification Behavior of Trace Rare Earth on Impurity Phases in Commercial Purity Aluminum

Modifying effect and mechanism of trace rare earth on Fe(Si) rich impurity phases in commercial purity aluminum were studied with the aids of SEM, EDAX, TEM, etc. It is found that Ce rich mixed rare earth (RE) is an effective modifying agent, which makes the coarse Fe rich impurity phases transform into complex compounds of tiny, sphere/short stick form, thus improving mechanical properties of this material; its modifying mechanism is in that RE gathering in front of solid/liquid interface enters into the impurity phases, forming complex (AlFeSiRE) compounds; or is adsorbed in the impurity phases surface, impeding the growth of impurity phases; however, excessive RE will result in the increasing of RE compounds (secondary phases), and plasticity reduction of this material. Therefore, its addition amount should be less than 0 07% (mass fraction).

Effect of mixed rare earth oxides and CaCO_3 modification on the microstructure of an in-situ Mg_2Si/Al-Si composite

The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive spectrum analysis. The results showed that the morphol-ogy of the primary Mg2Si phase particles changed from irregular or crosses to polygonal shape,their sizes decreased from 75 μm to about 25 μm,and the compound of both the oxide and CaCO3 was better than either the single mixed rare earth o...

Modification Mechanism of Rare Earth Elements in ZA27 Casting Alloys

The model of the liquid-phase ZA27 alloys was set up by molecular dynamics theory. The atomic structure of phase, RE-compounds, and the phase-liquid interface in ZA27 alloys were constructed by computer programming. Electronic structures of phase with rare earth elements dissolved and of phase-liquid interfaces with rare earth elements enrichment in ZA27 casting alloys were investigated by using the Recursion method. The ESE energy of RE elements and the structure energy of RE-compounds, phase, and the liquid-phase ZA27 alloys were calculated. The results show that rare earth elements are more stable to be in the phase interface than in phase, which explains the fact of very small solid solubility of rare earth elements in phase, and the enrichment in the solid-liquid growth front. This makes dendrite melt and break down, dissociate and propagate. RE-compounds can act as heterogeneous nuclei for phase, leading to phase refinement. All above elucidates the modification mechanism of rare earth elements in zinc-aluminum casting alloys at electronic level.

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.

Effect of Rare Earth Alloy Modification on High Carbon Equivalent Gray Cast Iron of Automotive Brake Drum

Effect of rare earth alloy modification on properties and microstructure of high carbon equivalent gray cast iron was investigated.The experimental results show that in the way of mechanical property,when the addition of rare earth alloy is 0.2% and 0.3%,the tensile strength of cast iron increases.In the way of microstructure,the addition of rare earth alloy increases the number of primary austenite dendrites,reduces secondary dendritic arm spacing,and changes the eutectic size and quantity.When rare earth alloy is added into gray cast iron,the morphology and quantity of graphite play a major role on the improvement of tensile strength.

SURFACE MODIFICATION ON STEEL BY RARE EARTH AND LASER TREATMENT

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Multiplex modification with rare earth elements and P for hypereutectic A1-Si alloys

The effect of rare earth （RE） elements on the morphologies and sizes of Si phases in the hypereutectic A1-Si alloys modified with P was investigated. The results show that the addition of La element to the hypereutectic A1-Si alloys can enhance the effect of P element on the modification of the primary Si phases. In the multiplex modification of RE-P, the primary Si phase is refiner and the shape of the eutectic Si is changed from long needle-like to short rod-like. Moreover, the agglomeration rate of the primary Si phase is slowed greatly. Even the melt is held for 6 h, the average size of the primary Si phase is still satisfied. The results analyzed by scanning electron microscope （SEM） indicate that La is richer at A1-Si interface than that in α-A1 or primary Si phase. The higher the La content in the A1-Si interface, the smaller the primary Si phase.

Inclusions modification by rare earth in steel and the resulting properties: A review

Rare earth(RE) elements are excellent modifiers for non-metallic inclusions that inevitably appear in steel and affect steel properties. This paper reviews the research status of inclusions modification by RE elements and the changes it cause on steel properties. First, the inclusion changes caused by RE modification are described. Generally, after adding pure RE, the main evolution of inclusions occurs as M →M + RE-Al-O → RE-Al-O + RE_(2)O_(2)S → RE_(2)O_(2)S + RE—S/RE_(2)O_(2)S + RE-O with an increase in the RE content(M represents the inclusions before RE addition). The type of final inclusion obtained after RE modification is related to the relative contents of S and O in the steel. Moreover, fine, regular, and uniformly distributed inclusions can be obtained with appropriate RE addition. However, the effectiveness of inclusions modification by adding both RE and non-RE elements is closely related to the order of their addition. Second, the applications and advantages of thermodynamic calculations in the study of RE-modified inclusions are introduced. Third, the changes in the corrosion resistance, impact properties,and other properties of steel caused by the modification of inclusions by RE are reviewed. Finally, the perspectives and trends of inclusions modified by RE elements in the steel industry are presented.

Study on Heterogeneous Nuclei in Cast H13 Steel Modified by Rare Earth

The dendrite segregation in cast H13 steel was weakened with RE modification treatment. Grain boundary carbide during quenching was also under control and impact toughness was improved greatly. By thermodynamic calculation, analysis of two-dimensional lattice misfitting and electron probe analysis, it is found that Ce2O3 may act as the heterogeneous nuclei of modified cast H13 steel.

The selective adsorption of rare earth elements by modified coal fly ash based SBA-15

Rare earth elements(REE)are strategic resources and the recycling of REE in alternative resources is urgent and gets increasingly attention.However,the separation of REE in these alternative resources is still a challenge due to the low concentration of REE and multi coexisted ions in acidic system.In this study,the species distribution of REE within the pH 0-8.0 was calculated.The SBA-15 originated from coal fly ash was modified by two steps with(3-aminopropyl)triethoxysilane(APTES)and diethylenetriaminepentaacetic dianhydride(DTPADA)to obtain DTPADA-SBA-15 adsorbent,which was applied to the selective adsorption of REE.The results showed that DTPADA-SBA-15 possessed excellent adsorption performance on the selective adsorption of REE,including Eu,Gd,Tb,Nd and Sm,in acidic solution(pH 2)with multi competing ions.The FT-IR and Zeta potential characterization verified that the chemical adsorption through the coordination of O in DTPADA-SBA-15 with REE was dominant at lower pH value.The study of adsorption kinetics indicated that the adsorption of rare earth metal ions followed pseudosecond-order kinetic,of which the adsorption process followed the Langmuir isotherm model.

Modification mechanism of cerium on the Al-18Si alloy

The effect of the rare earth cerium （Ce） on the hypereutectic Al-Si alloy under different casting states have been studied by optical microscope and quantitative image analysis. It is found that the size and the quantity of primary silicon in castings decrease with the increase of added Ce in the melt. Meanwhile primary silicon changes from branched shape to fine facetted shape. Although the modification on eutectic silicon in castings also improves with the increase of added Ce in the melt, the effect of modification on eutectic silicon away from primary silicon is more obvious than that on eutectic silicon close to primary silicon. The modification mechanism was analyzed in detail by means of scanning electron microscope equipped with energy dispersive analysis of X-ray and thermodynamics analysis, which included the analysis on the change in standard Gibbs energy of reaction and reaction equilibrium.

Modification effect of lanthanum on primary phase Mg_2Si in Mg-Si alloys

The modifying effect of La addition on primary phase Mg2Si in Mg-5Si alloys was investigated. The results showed that a proper amount of La could effectively modify the primary phase Mg2Si, Based on the present experiment, the optimal modification effect was obtained with an addition of about 0.5 wt.% La. The size of the primary phase MgzSi was considerably reduced to 25μm or less and the morphology was modified from a coarse dendritic shape to a polyhedral shape. However, when the addition of La increased to 0.8 wt.% or higher, the primary Mg2Si grew into a coarse dendritic morphology again. Moreover, it was found that some LaSi2 compounds were formed during solidification and the amount of the compounds appeared to increase gradually with increasing La content.

Effects of Rare Earths and Al on Structure and Performance of High Chromium Cast Iron Containing Wolfram

Effects of RE and Al on the structure, impact toughness, hardness, and wear resistance of high chromium cast iron containing wolfram were investigated. The results show that without modification the volume fraction of austenite is high and the carbide appears to be thick lath and the grain size is relatively large; proper modification using RE combined with Al can reduce volume fraction of residual austenite in the as-cast structure obviously, refine grain size of primary austenite notably, and make the morphology of carbide changing from thick lath to thin lath, rosette, and feather-like modification can also increase hardness, wear resistance and impact toughness of cast iron.

Effects of RE,V,Ti and B composite modification on the microstructure and properties of high chromium cast iron containing 3% molybdenum

The effects of RE, V, Ti and B on the microstructure and properties of high chromium cast iron containing 3% molybdenum under as-cast and heat treatment conditions were investigated with the method of comparing experiments. The results show that with the increase of RE content, the primary austenite of high chromium cast iron is obviously refined. The morphology of carbide is changed from netlike and lath to small multiangular isolated blocks or massive blocks, the isolated degree of carbide is improved obviously, and the size is significantly refined. The addition of V and B into high chromium cast iron can refine the microstmcture, reduce coarse columnar crystals and make the carbide smaller and uniform. Through composite modification with RE, V, Ti and B, the hardness, wear resistance and impact toughness of high chromium cast iron are increased conspicuously. After heat treatment, the hardness of high chromium iron is increased significantly, but the toughness and wear resistance do not show great improvement.

Modification Effects of Lanthanum-Rich Mischmetal on A357 Alloy

A357 alloy was modified with lanthanum -rich mischmetal, and modification effects of the mischmetal on its as-cast and heat-treated structures, mechanical properties and hydrogen content were investigated and compared with that of strontium metal. It is shown that the modification effect of La-rich mischmetal is better than that of strontium in the aspects of refining eutectic silicon, ejecting hydrogen from the melt and improving comprehensive mechanical properties of the alloy. Therefore Al-Si-Mg alloy with high strength and improved toughness can be obtained by modification with La-rich mischmetal.

Recent Developments in Doping and Structural Modification of Ceria-Based Catalysts

Recent development in the modification of ceria-based catalysts for exhaust gas treatment was reviewed with the dependence of redox properties on structural characters of materials. The doping of ceria with different cations such as rare earth or transition metal oxides results in improvement of structural stability, catalytic function and resistance to sintering at high temperatures. Aging and reduction treatment at high temperatures promote ceria reduction and is beneficial for oxygen storage capacity of the three-way catalysts. Chemical filing technique is very effective in modifying the redox property in the low temperature regions.

Anisotropy of rare-earth magnets

Rare-earth intermetallics such as Nd2Fe14B and Sm-Co are widely used as high-performance permanent magnets, because they combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature. The anisotropy is a combined effect of spin-orbit coupling and electrostatic crystal-field interactions. The main contribution comes from the rare-earth 4f electrons, which are well-screened from the crystalline environment but exhibit a strong spin-orbit coupling. In this limit, the magnetocrystalline anisotropy has a very transparent physical interpretation, the anisotropy energy essentially being equal to the energy of Hund＇s-rules 4f ion in the crystal field. The corresponding expression for the lowest-order uniaxial anisotropy constant K1 is used to discuss rare-earth substitutions, which have recently attracted renewed interest due to shifts in the rare-earth production and demand. Specific phenomena reviewed in this article are the enhancement of the anisotropy of Sm2Fe17 due to interstitial nitrogen, the use of Sm-Co magnets for high-temperature applications, and the comparison of rare-earth single-ion anisotropy with other single-ion and two-ion mechanisms.

Microstructure and property modifications in surface layers of a Mg-4Sm-2Al-0.5Mn alloy induced by pulsed electron beam treatments

In this work,surface modification of a Mg-4Sm-2Al-0.5Mn alloy with high current pulse electron beam(HCPEB)under different number of pulses were investigated.The evolution in microstructure,composition and phase components and properties in the surface layer before and after HCPEB treatment were characterized.It was found that the Al 11 Sm 3 and Al 2 Sm phases in the surface layer were gradually dissolved during HCPEB treatment,leading to the formation of a chemical homogeneous melted layers.Besides,deformation bands were formed in the treated layer due to the thermal stress generated during treatment.After 15 pulses treatment,the surface hardness increases to the maximum value of about 62.2 HV,about 61.2%higher than that of the untreated state.Electrochemical results show that the 15 pulses treated sample presents the best corrosion resistance in the 3.5wt%NaCl water solution by showing the highest corrosion potential(E_(corr))of-1.339V SEC and the lowest corrosion current density(I_(corr))of 1.48×10^(-6)A·cm^(-2).The results prove that the surface properties of the Mg-4Sm-2Al-0.5Mn alloy can be significantly improved by the HCPEB treatments under proper conditions.

Study on Preparation and Properties of PVC Film Modified by Rare Ea rth

The transparent PVC films were prepared by tape casting. In the process of prepa ration, rare earth nitrate, as a kind of modifier, was added to th e solution of PVC and THF. These PVC films were tested after being crosslinked b y ultraviolet light. It is found that the mechanical and physical properties of all the PVC films modified by rare earth nitrate are greatly enhanced.

Effect of Surface Modification on Behaviors of Cerium Oxide Nanopowders

Study was made on the effect of surface modification on the behaviors of cerium oxide nanopowders.A surfactant-sodium dodecyl sulfate（C12H25SO4Na）was used to modify the surface of CeO2 powder particles.The unmodified and modified CeO2 powders were characterized by using a powder comprehensive characteristic tester,laser particle size analyzer,specific surface area tester,X-ray diffraction tester,and a scanning electron microscope.The testing and analysis results showed that C12H25SO4Na surface modification might increase the flowability and dispersity,and decrease the specific surface area and agglomeration of CeO2 powders.The mechanism of the surface modification of CeO2 powder particles was also discussed.