Effect of Adding Co on Crystallization Behavior and Magnetoimpedance Effect of Amorphous/Nanocrystalline FeCuNbSiB Alloy Strips

After one of the B atoms in Fe73.5Cu1Nb3Si13.5B9 alloy was replaced by both 0.7 Si and 0.3 Co, Fe73.5Co0.3Cu1Nb3Si14.2B8 alloy ribbons were prepared by single roll fast quenching method. The obtained alloy ribbons were subsequently wound into ring magnetic cores, and then these magnetic cores were annealed at different temperatures in air. The effects of adding Co on the crystallization behavior and soft magnetic properties of the as-quenched alloy ribbons with and without heat treatment were studied. The results show that the amorphous structure of the prepared Fe73.5Co0.3Cu1Nb3Si14.2B8 alloy ribbons is transformed into the coexistence of amorphous and nanocrystalline structures after heat treatment at 550°C. Comparing with Fe73.5Cu1Nb3Si13.5B9 alloy ribbons, the first initial crystallization temperature (Tx1) and crystallization peak temperature (Tp1) of Fe73.5Co0.3Cu1Nb3Si14.2B8 alloy ribbons were reduced by 1.6 and 1.7°C, respectively, While the second initial crystallization temperature (Tx1) and crystallization peak temperature (Tp2) were increased by 6.5 and 5.7°C, respectively, resulting in that the difference between the first and the second initial crystallization temperatures (∆Tx) are increased by 8.1°C; the initial permeability (μi) and saturation induction density (Bs) of the amorphous/nanocrystalline Fe73.5Co0.3Cu1Nb3Si14.2B8 magnetic cores were reduced by 0.15 H/m and 0.39 T, respectively, while the coercivity (Hc) is increased by 0.34 A/m.

Effects of initial crystallization process on piezoelectricity of PVDF-HFP films

The effects of some important factors in the initial crystallization process of the solution casting method on the piezoelectricity of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) films were extensively explored. The experimental results revealed that there is an optimal initial crystallization temperature at around 90°C. The slow cooling speed can moderately enhance the degree of crystallinity. The most important finding was that a bilayer crystalline structure caused by an asymmetrical heating pattern can enhance the formation of packed micro-fibrillar morphologies after drawing. These three points can increase the piezoelectricity of the PVDF-HFP films, indicating the increase of the extended-chain crystals (β-phase).

The Study of Fe-Based Broad Amorphous Ribbon’s Variable-Temperature Kinetics

Variable temperature kinetics under different heating rates for the Fe-based amorphous ribbons are studied by differential scanning calorimeter (DSC) technology. The results show that imported and domestic amorphous ribbons have the same overheating degree under the same heating rate, and the initial crystallization temperature is proportional to the cube root of the heating rate. The calculation indicate that the crystallization activation energy of imported and domestic amorphous ribbons are about 297~300 kJ/mol and 335~340 kJ/mol, respectively.

Ti50Fe22Ni22Sn6 Amorphous Alloy Synthesized by Mechanical Alloying and Spark Plasma Sintering

Ti50Fe22Ni22Sn6 amorphous alloy is prepared by mechanical alloying and spark plasma sintering. The milling is performed in a high-energy planetary ball mill. XRD shows that after milled 70h, fully amorphous powders can be obtained, under the condition of the milling speed, 300rpm, and the weighs ratio of ball to powder, 10:1. Thermal stability of the as-milled amorphous powder is determined by DSC at the heating rate of 40K/min. The glass transition Tg and the initial crystallization temperature Tx1 is 625K and 770K, respectively. The amorphous alloy powder is compacted by spark plasma sintering at the temperature of 633K, 653K, 673K, 688K and 723K under the compress of 400Mpa. From XRD, it can be seen that near the glass transition temperature, the samples sintered remain completely amorphous, and when the sintering temperature increasing, although not higher than the initial crystallization temperature, the sintered samples have begun to appear crystalline phases.

Crystallization Kinetics of Amorphous Finemet Modified with Co

The aim of this work is to present experimental results of investigation on crystallization process of Co-containing Finemet-type alloys. To different Finemet alloys, there exist different changing trends of the initial crystallization temperature after Co addition. Addition of Co in Fe73.5Cu1Nb3Si13.5B9 alloy reduces the stability of the amorphous phase, and leads to the formation of nanocrystallites at lower temperature. While adding Co increases the stability of Fe76.9Cu0.6Nb2.5Si11B9 amorphous phase, and results in higher nanocrystallites temperature. Using the method of Kissinger, possible reasons were analyzed for the variation of the apparent activation energy of crystallization determined from DSC thermograms.

Synthesis of Nano-Crystalline Magnesium Chromate Spinel by Citrate Sol-Gel Method

Nanocrystalline MgCr2O4 with a crystal size of about 20nm is synthesized by citrate sol-gel process, which is characterized by X-ray diffraction (XRD), thermogravimetry coupled with differential thermal analysis (TG-DTA) and field emission scanning electron microscopy (FE-SEM). The initial crystallization temperature of MgCr2O4 spinel was at about 550°C, whereas that of the fully crystallized magnesium chromate spinel appeared at about 600°C. The crystal grain size increases with the annealing temperature and holding time.

Crystallization and Phase Transformation of ZrO2-SiO2 Gels

ABSTRACTPure SiO2, ZrO2 and SiO2−ZrO2 gels have been prepared by hydrolysis and gelation of tetraethylorthosilicate (TEOS) and zirconium acetate solution. The crystallization and phase transformation of SiO2 and ZrO2 in these gels have been followed up to 1450°C using differential thermal analysis (DTA), thermal gravimetric analysis (TGA) and X-ray diffraction analysis (XRD). The crystallization and phase transformation behavior of SiO2 or ZrO2 is quite different in different gel systems. It was found that in pure SiO2 gel, the cristobalite phase was precipitated out at about 1000°C. In the pure ZrO2 system, tetragonal (t−) phase zirconia was crystallized at about 430°C, t-ZrO2 crystals grew three dimensionally and the activation energy for growth was calculated as about 365 kJmol−1. But in the SiO2-ZrO2 system, the presence of ZrO2 suppressed the crystallization of SiO2 , and SiO2 increased the initial crystallization temperature and the stability of t-ZrO2.