Advanced Materials Research Vols. 750-752

Abstract: We synthesized Fe₃O₄ nanoparticles using a solvent thermal method and characterized the morphologies, structures, surface properties, thermal stability and magnetism of the products by Field emission scanning electron microscopy (FE-SEM), Powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA) and vibrating sample magnetometer (VSM). The experimental results showed that the Fe₃O₄ nanoparticles have a tunable average size range from 55 nm to 85 nm. Their diameters decreased with increase of precursor FeCl₂4H₂O concentration or increase of the reaction time under other reaction conditions held constant. The XRD pattern confirmed that the Fe₃O₄ nanoparticles belong to cubic structure. Magnetic investigation reveals that the Fe₃O₄ nanoparticles have higher saturation magnetization and negligible coercivity at room temperature.

Abstract: Flower-like ZnO was prepared by using ZnCl₂ and NH₃·H₂O as starting materials employing a simple microwave synthesis method. The result shows that flower-like ZnO microcrystal is obtained with 15mL NH₃·H₂O dropped into ZnCl₂ solution and microwave power of 240W for 20 mins simultaneously. Microstructure and surface morphology were investigated in detail by XRD, SEM. The XRD pattern shows, as-prepared ZnO particles are highly crystallized with a wurtzite structure, SEM result demonstrates that flower structure is closely composed of petaloid unit and consists of a series of the bottom thick and top thin nanorods. By researching on PL properties of ZnO, PL spectra shows it has three emission peaks. Then approximate analysis of the causes of every emission peak was made. A simple analysis of growth mechanism was also made in theory finally.

Abstract: In this work, Core-shell structure palygorskite/nanoCaCO₃ (PnC) composite particles have been synthesized chemically, employing solution precipitation methods. Crystal structure, morphology and thermal stability properties are investigated by means of X-ray diffraction (XRD), transmission electronic microscopy (TEM) and Thermogravimetric (TG) analysis. The results showed that the PnC particles were almost monodispersed microsphere aspect with the size was about 1-3 μm diameter. The nanocomposite particles exhibit the marked thermal stability properties than the palygorskite clay mineral.

Abstract: Arrayed ZnO crystals were fabricated with Zn as raw material by thermal chemical vapor deposition in a tubular reactor. The characterizations indicate the product grown at upstream is the well-arrayed ZnO submicro-column with good crystal properties, that at downstream is well-arrayed nanoneedle with more defects. In combination of mass field analysis with Fluent, it is revealed that the concentration fields at the upstream and downstream positions of Zn source are not identical even in an identical temperature field. It is the diffusion that drives Zn vapor move to upstream position where the O₂ is rich, and the amount diffuse to upstream is rare due to the transportation of working gas. Most of O₂ is consumed when passes the Zn source, leading to more lean O₂ but rich Zn at the downstream position of Zn source. Our results support that lower concentration of Zn and O₂ is in favor of the formation of perfect crystal as happened at upstream, but in such condition that more Zn and rare O₂, defects of O vacancy is liable to form during ZnO growth.

Abstract: A new low-alloy high-carbon steel was designed to obtain the carbide-free bainite under low-temperature austempering. The microstructure, wear resistance under dry sliding friction and the wear mechanism were comparatively studied between samples austempered and low-temperature tempered. Results show that the carbide-free bainitic microstructure composed of bainitic ferrite laths with mean thickness of 120 nm and retained austenite films can be achieved by austempering at 220 °C for 120 h in salt bath after austenitizing at 1000 °C. The wear resistance under dry sliding friction of austempered sample is 19% more than that of low-temperature tempered sample. The wear mechanism of the low-temperature austempered sample is determined as the adhesive wear.

Abstract: The characteristic of structural inheritance for 300M steel was explored and the eliminating effect of normalization was investigated. Then, both the first and secondary normalization process was optimized by comparing eliminate effect. It is known that obvious characteristic of structural inheritance can be shown with the condition of 810°C-840°C×30min/OC after over-heated treatment. The first normalization process whose condition is 950°C~1100°C×2.5h/air cooling has the good effect on eliminating structural inheritance. While, the secondary normalization process whose condition is 960°C~1060°C×2h/air cooling+925°C×2.5h/air cooling owns the better effect on eliminating structural inheritance.

Abstract: Based on the reverse uniaxial loading test, the influences of the plastic deformation on the strength properties are studied. The softening of the X80 pipeline steel is observed which reveals the hardening type is mixed hardening. The expression of mixed hardening factor M and the material parameters of the nonlinear mixed hardening model under different M can be obtained. The results show that, if the pre-strain increases and ranges from 0.55% to 2.5%, the mixed hardening characteristics of the X80 pipeline steel will be more obvious and its M will also increase.

Abstract: As one of the important refining equipments between steelmaking and continuous casting, RH vacuum refining plays an important role in removing the inclusions in the molten steel.RH can improve steel quality largely and meet the demand of mass production of high additional value. On the base of the similarity principle, a water model was developed to study the influence factors of inclusion removal in the molten steel of 180 tons RH vacuum refining device.Liquid steel is simulated by Nacl solution, the air is approximate argon, polypropylene simulate inclusions and NaHCO₃ simulate composite particles. The influence regularity of lift gas flow rate, submersion depth of snorkels and the input amount of NaHCO₃ on the inclusions removal rate have been discussed and the optimal values for each influence factor have been found.

Abstract: The CCT (continuous cooling transformation) diagrams of the Nb-V-Ti without Mo containing microalloyed pipeline steel X70 were investigated. The microstructures observed in continuous cooled specimens are composed of P (pearlite), PF (polygonal ferrite), QF (quasi-polygonal ferrite), and GF (granular bainite ferrite). At low cooling rates between 0.1°C/s and 1°C/s, the microstructure of the steel consisted of banded ferrite and pearlite but higher cooling rates suppressed its formation.

Abstract: Confocal Laser Scanning Microscopy in situ observation of the solidification process of SPHC Steel and SPHC steel solidification structure changes. The results showed that: SPHC steel in the molten state, the surface of the melt flow of black substance; and with the temperature decreasing, SPHC gradually solidified dendrites continue to grow, increasing new nuclear the dendritic structure continue to refine, to δ-Fe and γ-Fe crystalline phase from the melt.