Effect of MgO content in sinter on the softening–melting behavior of mixed burden made from chromium-bearing vanadium–titanium magnetite

The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chro- mium-bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening-melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%-3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening-melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO con- tents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium-titanium magnetite in a blast furnace.

Softening–melting behavior of mixed burden based on low-magnesium sinter and fluxed pellets

A low MgO content in sinter is conducive to reduce the MgO content in blast furnace slag.This study investigated the effect of MgO content in sinter on the softening–melting behavior of the mixed burden based on fluxed pellets.When the MgO content increased from 1.31 wt% to 1.55 wt%, the melting temperature of sinter increased to 1521℃.Such an increase was due to the formation of the high-meltingpoint slag phase.The reduction degradation index of sinter with 1.31 wt% MgO content was better than that of others.The initial softening temperature of the mixed burden increased from 1104 to 1126℃ as MgO content in sinter increased from 1.31 wt% to 1.55 wt%, and the melting temperature decreased from 1494 to 1460℃.The permeability index(S-value) of mixed burden decreased to 594.46 kPa·℃ under a high MgO content with 1.55 wt%, indicating that the permeability was improved.The slag phase composition of burden was mainly akermarite(Ca_(2)MgSiO_(7)) when the MgO content in sinter was 1.55 wt%.The melting point of akermarite is 1450℃, which is lower than other phases.

MELTING BEHAVIOR OF LOW ETHYLENE CONTENT POLYPROPYLENE COPOLYMERS WITH AND WITHOUT NUCLEATING AGENTS

The melting behavior of polypropylene (PP) and low ethylene content polypropylenecopolymer with and without nucleating agent samples crystallized under both isothermal and non-isothermal conditions were studied by Differential Scanning Calorimeter (DSC) and X-raydiffraction. Multiple melting behavior were observed depending on the existence of nucleatingagent and crystallization conditions. The observed phenomena have been discussed by the effect ofnucleating agent on perfection of crystal and the melting and recrystallization of imperfect crystalto a more perfect crystal during the heating process of samples.

Effect of trace calcium on melting behavior of Ag-Cu-Zn brazing alloy by thermal analysis kinetics

The purity of the brazing alloys applied is necessary to be improved with the increasing cleanness of steel. Calcium is easily brought into the widely ased brazing alloy, Ag-Cu-Zn, during the producing process. This paper aims at revealing the effect of calcium on the melting behavior of the brazing alloy. The thermal analysis kinetics of silver alloy with trace calcium was studied by using differential scanning calorimetry （ DSC ） , and the enthalpy peaks were analyzed by differential methods. The rate constant of phase transformation in the probable brazing temperature range goes up with increasing calcium content, according to the values of the apparent activation energy, E, and the frequeney constant, A. It is concluded that the calcium addition could improve the melting performance of Ag-Cu-Zn brazing alloy.

Reduction and melting behavior of carbon composite lateritic bauxite pellets

Direct reduction of low-grade lateritic bauxite was studied at high temperature to recover Fe and beneficiate AlzO3 slag. The re- sults show that a metallization rate of 97.9% and a nugget recovery rate of 85.1% can be achieved when the reducing and melting tempera- tures are 1350 and 1480℃, respectively. Moreover, a higher-grade calcium aluminate slag （A1203 = 50.52wt%） can also be obtained, which is mainly composed of ct-A1203, hercynite （FeAI：O4）, and gehlenite （Ca2A12SiO7）. In addition, high-quality iron nuggets have been produced from low-grade lateritic bauxite. The nugget is mainly composed of iron （93.82wt%） and carbon （3.86wt%）, with almost no gangue （slag）.

Isothermal Crystallization Kinetics and Melting Behavior of POE-g-MAH Compatibilized PA11/POE Blends

A new Nylon 11（PA11）/polyethylene-octene（POE） blends compatibilized by maleic anhydride grafted mixture polyethyleneocten（POE-g-MAH） was prepared through melt blending method.The isothermal crystallization kinetics and melting behaviors of PA11/POE blends were investigated in detail by differential scanning calorimetry（DSC） and polarized optical microscope.The n values of PA11 blending with POE or POE-g-MAH are almost similar with pure PA11,which indicates that the effect of POE and POE-g-MAH on nucleation and growth of PA11 crystal is slight.The overall crystallization rate of PA11/POE blends are higher than ones of pure PA11 at the same crystallization temperatures,but they decrease significantly when POE-g-MAH is added into PA11/POE blends.DSC heating curves of both PA11 and its blends exhibit two melting peaks,but the two melting peak become weaker when POE-g-MAH is add into PA11/POE blend systems.And the spherulite size is reduced significantly by the addition of POE-g-MAH compared with pure PA11 and PA11/POE blends.

Effects of Molecular Weight on the Crystallization and Melting Behaviors of Poly(L-lactide)

In this study, a series of monodispersed poly（L-lactide）（PLLA） were synthesized by the ring-opening polymerization with Schiff base aluminum catalyst, and the effects of the number-average molecular weight（Mn） on the crystallization and melting behaviors of PLLA were investigated by differential scanning calorimetry（DSC） and wide-angle X-ray diffraction（WAXD）. The total crystallization rate of PLLA was Mn-dependent, which reached the maximum value for PLLA with Mn of 18.6 kg/mol. In addition, when Mn of PLLA was 18.6 kg/mol, the melting enthalpy（ΔHm） showed a maximum value（87.1 J/g）, which was the highest reported value till now. The critical temperature for change of crystal formation from ？-form to ？-form crystals increased in the isothermal crystallization process with Mn increasing. In the reheating procedure, high-Mn PLLA demonstrated a small exothermal peak prior to the dominant melting peak, corresponding to crystal transition from ？- to ？-form, but low-Mn PLLA didn＇t show the peak of crystal transition. These different crystallization and melting behaviors were attributed to the different chain mobility of PLLA with different Mn.

Atomistic simulations of the tensile and melting behavior of silicon nanowires

Molecular dynamics simulations with Stillinger-Weber potential are used to study the tensile and melting behavior of single-crystalline silicon nanowires（SiNWs）.The tensile tests show that the tensile behavior of the SiNWs is strongly dependent on the simulation temperature,the strain rate,and the diameter of the nanowires.For a given diameter,the critical load significantly decreases as the temperature increases and also as the strain rate decreases.Additionally,the critical load increases as the diameter increases.Moreover,the melting tests demonstrate that both melting temperature and melting heat of the SiNWs decrease with decreasing diameter and length,due to the increase in surface energy.The melting process of SiNWs with increasing temperature is also investigated.

Investigation on multiple-melting behavior of nano-CaCO_(3)/polypropylene composites

The multiple melting-peak behavior of polypro-pylene(PP)in nano-CaCO_(3)/PP composites and modified nano-CaCO_(3)/PP composites were investigated under the con-dition of isothermal crystallization and nonisothermal crystal-lization.The result indicated that the addition of nano-CaCO_(3) markedly increased the crystallization temperatures of PP and induced the formation of the b-crystal of PP.The crystalliza-tion temperatures of nano-CaCO_(3)/PP composites modified by reactive monomers were further increased,but the melting-peak intensity of the b-crystal of PP was not greatly influenced.While in the presence of dicumyl peroxide,nano-CaCO_(3)/PP composites modified by reactive monomers led to the significant increase in the melting-peak intensity of the b-crystal of PP.The double melting-peak of PP was observed,which was attributed to the formation of two kinds of different crystallization forms of a-crystal or b-crystal during the crystallization of PP.With the increase of crystallization tem-peratures,the double melting-peak moved toward the high-temperature side.The intensity of high-temperature melting peak was higher than that of low-temperature melting peak in nano-CaCO_(3)/PP composites.While in modified nano-CaCO_(3)/PP composites crystallized at higher temperature,the inten-sity of high-temperature melting peak was lower than that of low-temperature melting peak.The isothermal crystallization time had little effect on the melting temperatures.

Multiple Melting Endotherms of Syndiotactic Polystyrene in β Crystalline Form

A series of syndiotactic polystyrene (SPS) samples in β crystalline form were prepared by cooling from the melt at various cooling rates. The effects of cooling rate from the melt, and DSC heating rate on the multiple melting behaviors of β crystals were investigated by differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), from which the nature.of the multiple melting behavior was ascribed to the occurring of a recrystallization process.

Rheological Behavior for Polymer Melts and Concentrated Solutions——Part Ⅶ: A Quantitative Verification for the Molecular Theory of Non-linear Viscoelasticity with Entanglement Constraints in Polymer Melts

Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between. eta((gamma) over dot), psi (10)((gamma) over dot) and shear rate ((gamma) over dot), and topologically constrained dimension number n ' and a were derived. Linear viscoelastic parameters (eta (0) and G(N)(0)) and topologically constrained dimension number (n ' a and <(<upsilon>)over bar>) as a function of the primary molecular weight (M-n), molecular weight between entanglements (M-C) and the entanglement sites sequence distribution in polymer chain were determined. A new method for determination of viscoelastic parameters (eta (0), psi (10), G(N)(0) and J(e)(0)), topologically constrained dimension number (n ', a and v) and molecular weight (M-n, M-c and M-e) from the shear flow measurements was proposed. It was used to determine those parameters and structures of HDPE, making a good agreement between these values and those obtained by other methods. The agreement affords a quantitative verification for the molecular theory of nonlinear viscoelasticity with constrained entanglement in polymer melts.

Microstructure and Fracture Behavior of 316L Austenitic Stainless Steel Produced by Selective Laser Melting

Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g. pores and incompletely melted particles. In this work, the microstructure and texture of 316L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples.

Temperature-induced Evolution of Micro-structure and Chain Dynamics in Thermoplastic Polyurethane with Low Hard Segment Content as Studied by In Situ Synchrotron SAXS and Time-Domain NMR Experiments

The microstructural evolution of a thermoplastic polyurethane(TPU)with low hard segment content has been monitored utilizing in situ real-time synchrotron small angle X-ray scattering(SAXS)and time-domain nuclear magnetic resonance(NMR)measurements.The TPU is composed of 23 wt% of[4,4-methylenediphenyl diisocyanate(MDI)]-[1,4-butanediol(BD)]chain segments,which form hard domains,as[polytetrahydrofuran(PTHF)]forming soft domains.The number and distribution of monomer units in hard blocks is determined by the successive self-nucleation and annealing thermal fractionation technique.In situ SAXS method reveals heating-induced increase in the spacing of hard and soft domains,while time-domain ^(1)H-NMR characterizes the changes in the phase composition and chain dynamics in these domains.A glassy fraction of short MDI-BD chain segments in hard domains passes through T_(g) above ambient temperature.At higher temperatures,MDI-BD nanocrystals start to melt.Sequence length distribution of MDI-BD chain segments causes a distribution in crystal sizes and wide melting temperature range.The melting is accompanied by the mixing of MDI-BD with PTHF segments in soft domains,and by increase in segmental mobility in these domains.Above 180℃,the TPU melt is homogeneous on the scale above nanometers according to SAXS data.

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene γ Form

The crystallization behavior of syndiotactic polystyrene（s PS） γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl＇s crystallization theory. On the basis of the differential scanning calorimetric results, it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness, which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization. Further temperature dependent small-angle X-ray scattering（SAXS） measurement revealed the evolution of the γ form lamellae upon heating until phase transition, involving three different regimes： lamellae stable region（25-90 °C）, melt-recrystallization region（90-185 °C） and pre-phase transition region（185-195 °C）. As a result, recrystallization line, equilibrium recrystallization line and melting line were developed for the s PS γ form crystallization process. Since the melt of γ form involved a γ-to-α/β form phase transition, the melting line was also denoted as the phase transition line in this special case. Therefore, the equilibrium crystallization temperature and melting（phase transition） temperatures were determined at around 390 and 220 °C on the basis of the thermodynamic phase diagram of the s PS γ form.