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1.
Tailhades P. Brieu M. Mollard P. Rousset A. Chassaigne Y. 《IEEE transactions on magnetics》1990,26(1):63-65
γ-Fe2O3 particles (L ≈0.15 to 0.2 μm, L /D ≈2 to 5) with coercivity up to 400 Oe have been prepared from oxalic precursors. To preserve the particle form, the oxalates were doped with boron. The effects due to this element was studied during the different thermal treatments which effect the pseudomorphous transformation of oxalate particles into spinel ferrite. ESCA spectroscopy, and X-ray measurements could point out the presence of a Fe3BO5 phase at the surface of γ-Fe2O3 particles. In spite of the important mass losses (H2O, CO, CO2) and the important crystallographic structure modifications occurring during the transformation of oxalate into magnetic oxide, γ-Fe2O 3 particles obtained by this method have very good textural characteristics. Boron-doped γ-Fe2O3 particles were used to make 3.5-in diskettes with standard formulation. In these conditions, media properties were comparable to trading diskettes properties 相似文献
2.
In this paper, the remanence properties of Co-Sn, Co-Ti and Co-Ti-Sn substituted Ba-ferrite (BaF) oriented particulate samples are compared with those of some oriented acicular particulate samples. A new parameter, the minor remanence distribution (MRD), is proposed to review the remanence properties of magnetic particles and the capabilities for resisting the recording demagnetization of magnetic recording media. It is shown that the MRD values of the oriented BaF particulate samples were smaller compared to oriented Co-γ-Fe2O3 samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-γ-Fe2O3 samples. It Is the small MRD, SFDr, IRS and large DH r of a medium that can result in a large resistance to the effects of recording demagnetization and therefore in superior characteristics for high density magnetic recording. Since Co-Sn substituted BaF platelet-shaped particles exhibit these characteristics and have a very low temperature coefficient of coercivity, these particles can be expected to be a promising candidate for high density magnetic recording 相似文献
3.
Gougeon M. Leroy E. Tailhades P. Mollard P. Rousset A. 《IEEE transactions on magnetics》1990,26(1):57-59
The cobalt modification of pure γ-Fe2O3 acicular particles by the so-called epitaxial process has been applied to γ-Fe2O3 particles, derived from oxalic precursors. Six elaboration parameters have been taken into account for the slurry heat treatment: cable content, pH, time, temperature, gas flowing into the solution, and surface activation. A thermomagnetic study including in situ annealing treatments and magnetic measurements at various temperatures in the range 20-380°C has been carried out. The results are compared with those of commercial surface-cobalt-modified pigments 相似文献
4.
Experimental and theoretical investigations of dispersion properties of magnetic particles (acicular γ-Fe2O3 ) with an adsorbed epoxy-resin layer are presented. The adsorbed polymer amount was 20-110 mg/g and the adsorbed layer thickness was 6-22 nm, depending on the preparation conditions. Dispersion of γ-Fe 2O3 particles was evaluated by the sedimentation rate and surface roughness of the coated film. It was clarified that dispersion was improved with increasing adsorption, increasing solvent/epoxy-resin solubility, and decreasing γ-Fe2O 3 particle size. Interaction energy, consisting of magnetic attraction, van der Waals attraction, and steric repulsion of the adsorbed layer between two cylindrical magnetic particles, was calculated. The interaction energy curves, which vary with the distance between two particles, had primary minimum, maximum, and secondary minimum. The maximum energy and the secondary minimum energy were strongly related to dispersion stability. Experimental results are explained by the energy curve shapes 相似文献
5.
One of the most direct and sensitive ways of studying pigment surface properties is to measure the enthalpy changes which accompany the immersion of pigments in liquids. Different wetting liquids were used to test for H donor and H acceptor properties as well as to probe the polarity of the pigments' surfaces. The measurements were performed in an isoperibol batch calorimeter. Results are presented for γ-Fe 2O3, CrO2, Co-modified γ-Fe2 O3, and barium ferrite pigments. It is found that Co-modified γ-Fe2O3 pigments are very polar, whereas CrO2 pigments have low polarities: H donor and H acceptor properties are less pronounced. It is found that barium ferrite pigments act very much like γ-Fe2O3 pigments. It is shown that the effects of surface treatment can clearly be monitored by calorimetry 相似文献
6.
Hydrothermal processings to produce magnetic particulates 总被引:1,自引:0,他引:1
α-Fe2O3, γ-Fe2O3 , and α-FeOOH powders were used as starting materials to prepare barium hexaferrite hydrothermally. Since strontium hexaferrite and lanthanum-doped calcium hexaferrite have coercivities similar to that of barium ferrite, the hydrothermal synthesis of strontium hexaferrite and lanthanum-doped calcium hexaferrite were also explored. The reaction products obtained with the various starting materials are described. Electron micrographs showed that α-Fe2O3, γ-Fe2O3, or α-FeOOH dissolved in the solution first, and then barium hexaferrite nucleated and grew from the solution 相似文献
7.
The magnetic properties of small BaFe12O19 particles about 50 nm in size have been studied; the emphasis was on small-size effects. The compound formation of the hexagonal structure was made at a relatively low temperature; the small particle size made this result possible. As compared to the bulk value, a significantly reduced saturation magnetization is observed for these particles; this agrees with similar reports made earlier by several authors. To examine these phenomena further, Mossbauer spectra were obtained with high magnetic field applied longitudinally (H ex=16.4 and 50 kOe). The spectra show the presence of recalcitrant spins where the spin configuration has a noncollinear arrangement that even a 50-kOe magnetic field does not remove. This hard-to-saturate component may lie in the surface layer of the Ba-ferrite small particles. The data also provide evidence that the Fe ions in the bipyramidal (2b) sites undergo magnetic-field-induced oscillations at 4.2 K 相似文献
8.
研究了以α-Fe2O3、β-Fe2O3和γ-Fe2O3为催化剂的类Fenton试剂溶液氧化吸收NO的过程,分析了3种Fe2O3的晶相结构和表面性质对NO脱除效率的影响机理。脱硝性能测试结果表明:γ-Fe2O3的活性最好,在H2O2浓度为1.5 mol/L、催化剂浓度为20 mmol/L、pH值为5以及反应温度为55℃等条件下,γ-Fe2O3的脱硝率可达87.5%。机理研究表明:3种Fe2O3催化H2O2分解湿法脱除NO的反应发生在催化剂表面,反应过程中存在氧化还原循环,H2O2催化分解的主要产物是·OH。活性差异分析结果表明:Fe2O3的晶相结构和表面性质对NO的脱除效果具有显著的影响,γ-Fe2O3的活性最高是由于比表面积大、分散性高和表面的Fe2+含量更多,而β-Fe2O3的活性高于α-Fe2O3是由于表面的氧空位含量更多。 相似文献
9.
Fujita M. Hiratsuka N. Ueda T. Sugiyama K. Yamada K. 《IEEE transactions on magnetics》1993,29(4):2129-2133
Acicular α-FeOOH particles coated with barium ions were irradiated with microwaves under an oxygen pressure of 20 torr to prepare fine BaFe12O19 particles by a plasma reaction. The fine acicular particles has an aspect ratio of about 13 and a magnetization of 43.5 emu/g and contained small amounts of α-Fe2O3 and BaFe2O4. The particles were mixed with a binder, and the resulting mixture was formed into a coating under a magnetic field of 7 kOe applied vertically to the surface of the film. The squareness ratio in the direction perpendicular to the surface of the coating film was 0.83 without any correction for the demagnetizing field. Transmission electron microscopy (TEM) showed that the long axes of the BaFe12O19 particles all were aligned parallel to the film base. The cross-sections of the particles were rectangular when observed by TEM. It follows that the easy axes of the particles are perpendicular to their long axes 相似文献
10.
Changes in magnetic properties for Fe3-x□x O4 (x: oxidation degree) thin films made by reactive sputtering and subsequent heat treatments have been examined under room temperature aging and constant temperature annealing. Aging causes variations in coercivity of insufficiently oxidized films which have a specific resistance of less than 1×101 Ω·cm, while the coercivity of γ-Fe2O3 (x=1/3) did not change. This phenomenon did not depend on additive elements or preparation method. Other magnetic properties such as saturation magnetization, residual magnetization, squareness ratio and coercive squareness, were not affected by aging for any Fe3-x □xO4 composition. The activation energy for a coercivity change is 0.72-0.95 eV near room temperature for films with a specific resistance below 1×101 Ω·cm. It was confirmed that only the coercivity varied at 20°C, while both coercivity and the degree of oxidation changed with annealing at 100°C 相似文献
11.
本研究以γ-AlOOH、TiO2和SiC为原料, 通过无压反应烧结制备了Al2TiO5多孔材料, 分析比较了SiC粒度和含量对合成产物的物相组成、显微组织、抗压强度、孔隙率和孔径分布的影响。结果表明: 反应产物的物相组成为Al2TiO5、Al6Si2O13、TiC、SiO2和Al2O3, 还有少量未反应的TiO2。SiC与TiO2反应生成TiC和SiO2, TiC颗粒弥散分布于多孔材料壁面或者骨架中, 而SiO2进一步与γ-AlOOH分解出的Al2O3反应生成Al6Si2O13晶须, 晶须交错分布于Al2TiO5颗粒之间或者孔洞中, 与TiC颗粒一起提高复合材料的抗压强度, 特别是采用小粒径SiC时, 对抗压强度的改善效果更加显著; 添加大粒径SiC后, 改变原有颗粒堆积状态, 可提高复合材料的孔隙率。但当SiC含量超过5wt%时, 因为生成较多低熔点的SiO2, 部分填充于多孔材料的孔隙中, 部分则分布于Al2TiO5晶粒之间, 既减小孔隙率, 又降低晶粒间结合强度和试样的抗压强度。 相似文献
12.
采用二次化学共沉淀法制备出六角或近六角片状BaFe12O19,其颗粒径向尺寸和径厚比分别为0.4-2μm和4-20。通过XRD、FTIR、TG/DTA及SEM/EDS分析技术研究了片状BaFe12O19的形成历程。结果表明:前驱体为非晶态BaCO3、低结晶态Fe(OH)3和晶态α-Fe2O3包覆原料BaFe12O19复合物;前驱体在焙烧过程中经过Fe(OH)3脱水、BaCO3分解反应、中间相α-Fe2O3和BaO反应得到终产物BaFe12O19。基于形成历程,六角片状BaFe12O19较原料BaFe12O19表现出显著提高的颗粒径向尺寸和径厚比、较高的纯度和略低的结晶有序程度,进而表现出明显提高的矫顽力、略低的饱和磁化强度和剩余磁化强度。 相似文献
13.
针对传统ZnO光催化活性不高的问题,采用Zn(CH3COO)2和FeCl3作为ZnO和Fe2O3的前驱体,水热条件下采用“一锅法”制备带状γ-Fe2O3/ZnO异质结光催化剂,采用XRD、BET比表面积测量仪、TEM、紫外-可见漫反射、电子顺磁共振(EPR)等对其晶体化学结构进行表征。在可见光光源下,探究了不同γ-Fe2O3负载量时γ-Fe2O3/ZnO异质结光催化剂对四环素的光催化降解的效果。研究表明,ZnO负载γ-Fe2O3后比表面积和光照吸收显著改善,禁带宽度有所减小,可见光光照120 min,n(Zn)∶n(Fe) (原子比)为20∶1的γ-Fe2O3/ZnO异质结光催化剂对四环素的降解率高达97.2%,多次重复使用后四环素的降解率保持在95%以上。 相似文献
14.
通过聚苯乙烯(PS)胶晶球模板法制备出三维有序大孔(3DOM)α-Fe2O3薄膜骨架, 再利用磁控溅射将Al沉积到3DOM α-Fe2O3骨架上得到核/壳结构的Fe2O3/Al纳米铝热复合薄膜。扫描电镜(SEM)测试结果表明: 纳米Al均匀地附着在α-Fe2O3骨架表面, 骨架孔结构由原先的近圆形转变为Al沉积后的类菱形, 孔壁的厚度从32 nm增加到100 nm; 采用X射线能谱(EDS)对Fe2O3/Al纳米铝热薄膜的元素含量进行了分析; 由差示扫描量热法(DSC)分析显示铝热薄膜在490℃开始反应, 经历固-固和固-液两个反应阶段, 总放热量达到1374.7 J/g; 使用激光点火器对铝热薄膜进行点火, 薄膜飞溅出火花并伴有明亮刺眼的亮光, 整个发火时间达2.6 ms, 显示其能被点火并发生自蔓延反应, 可作为一种理想的点火材料。 相似文献
15.
在1400℃和1500℃温度下合成了不同配比的铝酸钙水泥(CMA)。检测结果显示, 当温度升高时镁铝尖晶石的粒径由5 μm生长到15 μm。合成温度达到1400℃时, 镁铝尖晶石晶粒呈团簇状并分布在铝酸钙晶粒周围; 当合成温度升高至1500℃时, 镁铝尖晶石晶粒穿插在铝酸钙晶粒中。另外, 随着水泥中镁铝尖晶石含量的增加, 水泥的凝结时间延长, 同时粘度下降。相应的, 水泥储能模量和流动点的大小分别为0.15 MPa和4.44%。提高镁铝尖晶石相的含量或增大铝酸钙晶粒尺寸会减弱水泥水化时絮凝结构的强度。 相似文献
16.
Nanosize particles of CoFe2O4 have been synthesized by the citrate precursor technique. Considerably higher coercive force (1.68 kOe) than that obtained by the conventional technique (1.00 kOe) is associated with the nanostructure of CoFe2 O4. These nanosize ferrimagnetic CoFe2O4 particles exhibit chainlike clusters indicating strong interparticle interactions and reduced magnetic moment, which is attributed to anisotropy and canted spin structure at the surface of the particle. The magnetization shows a peak just below the Curie temperature Tc during heating in the presence of a small magnetic field (the Hopkinson effect), On the other hand, the magnetization increases monotonically when the system is cooled from T c. This peak is associated with the single domain behavior of nanocrystalline CoFe2O4 particles and explained within the mathematical formalism given by Stoner and Wohlfarth in conjunction with other explanations of Hopkinson effect 相似文献
17.
实现结构可控、均匀包覆是制备核-壳复合材料的关键。采用离子交换法完成了磺化聚苯乙烯(PSS)表面Na+与溶液中Fe2+和Fe3+的交换,于碱性条件下制备了PSS表面负载Fe3O4(PSS@Fe3O4)的磁性复合颗粒。通过称重法计算了Fe3O4最大包覆率;通过振动样品磁强计(VSM)测试了不同负载含量下PSS@Fe3O4复合颗粒的磁性能;通过XRD、衰减全反射-FTIR (ATR-FTIR)、SEM-EDS分析了PSS@Fe3O4磁性复合颗粒的化学组成和微观结构。结果表明,随着Fe2+/Fe3+浓度增加,PSS@Fe3O4磁性颗粒的饱和磁化强度也随之增大,最大饱和磁化强度为7.51 emu/g,并具有明显的磁响应性;Fe3O4均匀包覆在PSS表面,最大包覆率为8.3 wt%。PSS@Fe3O4磁性复合颗粒有望用于磁流变、医学及水处理领域。 相似文献
18.
Rheological characterizations were made for various types of magnetic particles (rod-like -Fe2O3, CrO2, and plate-like Ba-ferrite) and nonmagnetic (rod-like -Fe2O3) suspensions, in terms of particle concentration and shear rate. Shear rate dependence on viscosity was accurately described by the Casson equation. The highest yield stress for Ba-ferrite among the four types of particles represents the sensitive flocculation characteristics of Ba-ferrite with respect to concentration. The effect of non-magnetic -Fe2O3 and magnetic -Fe2O3 particle mixtures on suspension viscosity was also examined, and a negative deviation from the tie line of individual particle viscosities was observed. 相似文献
19.
Al2O3 coating is deposited using a low power plasma torch with a novel hollow cathode through axial powder injection under a plasma power up to several kilowatts. The effects of the main processing parameters including plasma arc power, operating gas flow and spray distance on particle velocity during spraying, and the microstructure and property of the coating are investigated. The microstructure of the Al2O3 coating is examined using optical microscopy and X-ray diffraction analysis. The property of the coating is characterized by dry rubber wheel abrasive wear test. The velocity of in-flight particle is measured using a velocity/temperature measurement system for spray particle based on thermal radiation from the particle. The dependency of the microstructure and property of the coating on spray particle conditions are examined by comparing the particle velocity, and microstructure and abrasive wear weight loss of subsequent coating deposited by low power plasma spray with those of the coating by conventional plasma spray at a power one order higher. X-ray diffraction analysis of the coating revealed that Al2O3 particles during low power plasma spraying reach to sufficiently melting state prior to impact on the substrate with a velocity comparable to that in conventional plasma spraying. The experiment results have shown that processing parameters have significant influence on the particle conditions and performance of deposited Al2O3 coating. The coating of comparable microstructure and properties to that deposited by conventional plasma spray can be produced under a power one order lower. From the present study, it can be suggested that a comparable coating can be produced despite plasma power level if the comparable particle velocity and molten state are achieved. 相似文献
20.
以海藻酸钠为原料,采用液滴聚合法将其与Al(Ⅲ)离子交联并引入甘氨酸和Fe3O4,制备出磁性氨基酸功能化海藻酸铝凝胶聚合物(Gly/Al/SA@Fe3O4),使用扫描电镜(SEM)、X射线能谱仪(EDS)、傅里叶红外光谱仪(FT-IR)、X射线衍射仪(XRD)和振动样品磁强计(VSM)等手段对其表征,研究了这种凝胶聚合物对偶氮染料的吸附性能。结果表明,Gly/Al/SA@Fe3O4是一种表面具有花式褶皱结构的三维网状聚合物颗粒,其磁响应能力良好。Gly/Al/SA@Fe3O4对水体中直接黑19(DB 19)和直接棕2(DB 2)染料的吸附性能超强,吸附速率极高,吸附15 min和60 min达到动态平衡的吸附量分别为2500和3126 mg/L。吸附过程可用拟二级速率方程描述,等温吸附数据符合Langmuir模型。吸附剂与染料分子间的相互作用通过静电吸附、氢键作用、配体交换和化学吸附协同实现。Gly/Al/SA@Fe3O4颗粒绿色环保,对高浓度偶氮染料废水有超强的净水性能,并可用磁场进行快速固液分离。 相似文献