Collagen/hydroxyapatite composite obtained by electric field orientation

The purpose of this study was to obtain and characterize the oriented collagen/hydroxyapatite (COLL/HA) composite materials, using different kind of electric field. The orientation process takes place due to the dipolar collagen structure. The collagen molecules are electrically charged and can become oriented if an electric field is applied. The composites were obtained by the co-precipitation method starting from collagen gel and hydroxyapatite precursor. The mineralized collagen gel was introduced in an electric field for 1 h, frozen and lyophilized. In order to study the orientation process parameters, two types of electric fields were tested: pulsatory and superposed (both direct and pulsatory). The obtained materials were characterized by XRD, FTIR and SEM. Best results in what it concerns the oriented character of the microstructures, as resulted from SEM images, were obtained for a pulsatory field of 0.93 V/cm, the presence of the direct electric field component decreasing the orientation degree. The average orientation degree, calculated at the magnification of 1000× was about 95%.     

Crystal orientation of non-magnetic materials by imposition of a high magnetic field

From the view point of learning from the nature, the controlling of crystal orientation is accounted to be a major subject for materials processing. This paper reviews the researches on the crystal orientation by use of a high magnetic fieldand belongs to the category of researches for mimicking structures, namely the crystal orientation, which nature or livingbodies are forming. Regarding to the crystal orientation, several methods such as unidirectional solidification and epitaxial growth and so on have been developed hitherto. On the other hand the magnetization force that is familiar with the force to attract iron to a magnet, has been recognized to be effective even in non-magnetic materials when those are placed under a high magnetic field, which has become rather conveniently available by developing superconducting technologies in these days. In this paper, main results obtained when the imposition of a high magnetic field was accompanied to several materials processing such as electrodeposition, vaperdeposition, solidification, baking, slip-casting and precipitation, arereviewed from the view point of crystal orientation of non-magnetic materials.     

Direct Generation of Internse Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing accelerating reaction rate,removing exclusions from molten metals and refining solidifcation structures during metallurgical processing of materials,In the present study ,two electromagnetic methods are proposed to generate intense compression waves directly in liquid metals.One is the simultaneous imposition of a high frequency electrical current filed and a static magnetic field ;the other is that of a high frequency magnetic field and a static magnetic field ,A mathematical model based on compressible fluid dynamics and electromagnetic fileds theory has been developed to derive pressure distri-butions of the generated waves in a metal.It shows that the intensity of compression waves is proportional to that of the high frequency electromagnetic force,And the frequency is the same as that of the imposed electromagnetic force,On the basis of theoretical analyses ,pressure change in liquid gallium was examined by a pressure transducer under various conditions.The observed results approximately agreed with the predictions derived from the theoretical analyses and calculations.Moreover,the effect of the generated waves on improvement of solidification structures was also examined .It shows that the generated compression waves can refine solidification structures when they were applied to solidification process of Sn-Pb alloy ,This study indicates a new method to generate compression waves by imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves can probably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.     

磁/电场约束下钛合金表面羟基磷灰石/TiO_2复合生物涂层的制备

用恒电位阳极氧化法分别以硫酸和磷酸为电解液,在钛合金基体上制备出具有不同孔径大小和不同晶型的TiO2涂层. 外加磁场条件下,在TiO2涂层上电沉积形成纳米羟基磷灰石涂层.当垂直电场方向施加1T磁场时,在洛伦兹力影响下生长成羟基磷灰石生长成长度大约为200nm,直径大约为50nm的棒状晶粒;在磁场平行于电场的条件下,生成直径为50-70nm的粒状晶粒.纳米羟基磷灰石与多孔TiO2涂层之间几何形貌的匹配程度,影响复合涂层与钛合金基体的结合强度.当TiO2涂层的孔径大约为100 nm时,棒状羟基磷灰石晶粒与钛合金基体间的锁合更牢固,结合力更强.     

Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate,removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed to generate intense compression wavesdirectly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a staticmagnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical modelbased on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to thatof the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagneticforce. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure     

Fabrication of mesoporous carbonated hydroxyapatite/carbon nanotube composite coatings by microwave irradiation method

Carbonated hydroxyapatite/carbon nanotube composite coatings (MHCs) with mesoporous structures were fabricated by electrophoretic deposition of nacre powders and carbon nanotubes on Ti6Al4V substrates followed by treatment with a phosphate buffer solution (PBS) by microwave irradiation method. The carbon nanotubes are dispersed uniformly on the whole MHCs. The conversion mechanism of the crack-free nacre/carbonate nanotube composite coatings (NCCs) to MHCs is a dissolution-precipitation reaction. After soaking in PBS, calcium ions are released from the nacre powders and react with phosphate ions to form carbonated hydroxyapatite nanoparticles. These nanoparticles aggregate to form mesopores with the pore sizes of ~ 3.9 nm among them. Simulated body fluid (SBF) immersion tests reveal that MHCs have a good in vitro bioactivity.     

Nucleation kinetics of paramagnetic and diamagnetic metal melts under a high magnetic field

The influence of a high magnetic field (HMF) on the nucleation kinetics of paramagnetic aluminum and diamagnetic zinc melts has been investigated by differential thermal analysis (DTA).It is found that the application of an HMF increases the undercooling of pure aluminum and pure zinc at the same heatingcooling rates.Moreover,the quantitative analysis of activation energy calculated from the DTA results using the Kissinger method manifests that the HMF reduces the activation energy of pure aluminum and pure zinc.Regardless of magnetism,the nucleation frequency under an HMF is higher than that without an HMF.Furthermore,the increase in undercooling under the HMF is mainly attributed to the increase of the contact angle,calculated by the functional relationship between the cooling rate and undercooling.This result is consistent with the increase of the calculated nucleation work for pure aluminum and pure zinc.Additionally,the increase in undercooling caused by the HMF is partly ascribed to the magnetic field-induced suppression of thermal convection in the undercooled melt.     

Cu-Fe合金的强磁场固溶时效行为

将Cu-15%Fe(质量分数)合金在强磁场中进行不同同溶时效处理,研究了合金的时效行为.结果表明,施加10 T强磁场可以促进第二相Fe枝晶的球化,而且Fe枝晶的形貌受强磁场的球化作用与高温缓慢冷却引起的粗化作用的影响.在Cu-15%Fe合金1000℃同溶处理中,施加10 T强磁场使基体中的Fe含量降低了0.39%.这表明,强磁场在一定程度上促进了Fe在Cu基体中的析出,获得与缓冷相类似的效果;施加10 T强磁场固溶处理并在10 T强磁场作用下经500℃时效处理后,基体中的Fe含量较低.其原因是,施加强磁场后Fe原子的析出规律受温度制度和析出相磁性转变的共同影响.施加强磁场改变了原子的激活能,进而影响了原子的扩散行为.     

6.5 wt% Si high silicon steel sheets prepared by composite electrodeposition in magnetic field

A new preparation method of near-net-shape 6.5?wt% Si high silicon steel sheets was proposed by combining composite electrodeposition (CED) and diffusion annealing under magnetic field. The obtained sheets were characterized by scanning electron microscopy, energy dispersive spectrometry, analytical balance and a silicon steel material measurement system. The results show that the surface morphology, the elemental distribution, the cathode current efficiency and the silicon content of coatings were obviously influenced by the micro and macro magnetohydrodynamics (MHD) flows under magnetic field. With the effect of magnetic field, the silicon particles content of coatings showed an increasing trend and the diffusion process showed that an approximately uniform 6.5?wt% silicon steel sheet has been successfully obtained. The magnetism measurement showed that the high silicon steel sheet has the lower iron loss, and the iron loss further decreased under magnetic field. The new method proposed in this article, which is more environmentally friendly and low energy consumption, is feasible to prepare high silicon steel sheets.     

Microstructures and mechanical property of AlCoNiCrFe alloy annealed in high magnetic field

A rapidly solidified high entropy alloy AlCoNiCrFe was annealed at different temperatures with high magnetic field applied up to 4 T. Both precipitation and coarsening of the precipitates were promoted during annealing in a high magnetic field, and nanosized arrayed particles as well as boundary oriented secondary phases were formed with effects of magnetic field. The microstructural features were obtained owing to enhancement of atomic diffusion by applying high magnetic field. It was found that both hardness and yield strength were not strongly dependent on the magnetic field, but the ultimate compression strength is reduced as higher magnetic field is applied due to formation and coarsening of the precipitates on grain boundaries.     

Mössbauer spectrometry study of early stage spinodal decomposition in Fe-Cr-Co alloy under high magnetic field

Local structure in a low-cobalt-type Fe-25Cr-12Co-1Si ferromagnetic alloy spinodal decomposed under an external magnetic field up to 120 kOe was investigated by Mössbauer spectrometry. The high magnetic field was found to significantly affect the local structure in the alloy formed at the early stage of phase decomposition. It was found that high magnetic field favors the acceleration of phase decomposition of ferromagnetic alloy at the early stage, resulting in the enhancement of average hyperfine field. The effect of high magnetic field on spinodal decomposition in ferromagnetic alloy was initially interpreted based on the free energy analyses.     

流延法制备高热导率定向石墨/高分子复合片层材料(英文)

以天然鳞片石墨为原料,PVB为黏结剂,PEG和DBP混合物为增塑剂,通过流延工艺在室温下制备了定向排列的石墨/聚合物片层复合材料。系统分析了不同黏结剂用量和流延刀口高度下复合片层材料的定向排列状况,并探讨了定向排列程度对其热导率的影响。XRD和SEM的结果表明,石墨/聚合物复合片层材料显示了不同程度的定向排列。热导率测试结果表明,片层复合材料的热导率随着定向排列程度的提高而增大。通过优化黏结剂的用量和流延刀口高度制备了具有较高热导率的片层复合材料,其热导率最高可达490 W/(m.K)。     

Synthesis of super-fine L10-FePt nanoparticles with high ordering degree by two-step sintering under high magnetic field

Super-fine L10-FePt nanoparticles (NPs) with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field (HMF) assisted post-sintering processes.The particle size of the L10-FePt NPs was obviously refined by lowering the sintering temperature.By applying the HMF during the post-sintering process,the fine size characteristics of L10-FePt NPs were retained,and the ordering degree was significantly improved.The L10-FePt NPs with sizes of about 4.5 nm,ordering degree of 0.940,and coercivity of 22.01 kOe were obtained by this two-step sintering under a magnetic field of 12 T.The mechanism investigation of HMF enhancing the ordering degree indicates that the HMF enhances lattice distortion and magnetization energy (Zeeman energy).The enhanced lattice distortions cause high stress existing in the lattice,which can effectively promote the disordered-order transition.When the magnetic field reaches to 3 T,the Zeeman energy of the NPs is higher than the thermal disturbing energy of the NPs,and the magnetization effect is stronger.Therefore,the HMF (higher than 3 T) can obviously improve the disorder-order transition by lowering the energy barrier and accelerating the orderly diffusions of atoms.The HMF is a promising assistant to synthesize the L10-phase NPs with both of high ordering degree and super-fine size.     

强脉冲磁场中Al-Cu共晶定向凝固组织的演变

脉冲磁场作用于Al Cu共晶凝固的界面,研究了定向凝固组织的演变.随着脉冲磁场强度的提高,Al-Cu共晶定向凝固组织经历了由规则柱晶到破碎枝晶、粗化枝晶到重新规则化柱晶三个演化阶段;在重新规则化柱晶试样中,共晶片层间距减小,晶团间富铜相析出明显.将感生电势场与溶质扩散场相耦合,分析了脉冲磁场对凝固界面稳定性的影响,发现强脉冲磁场在金属熔体引起感生电势场效应,在凝固界面前沿诱发具有振荡特征的电致迁移,从而促进晶间扩散和减小成分过冷区域.     

Experimental study on a Nb3Al insert coil under high magnetic field

Nb₃Al is one of the most promising superconductors to replace Nb₃Sn in large scale, high field superconducting magnet. Since the complicated conductor manufacturing process, long and stable Nb₃Al conductor is difficult to acquire in a commercial scale. Based on a 70 m length of Nb–Al precursor conductor, we designed and fabricated a Nb₃Al coil. The coil winding, low temperature diffusion heat treatment and epoxy impregnation are described in detail. The finished Nb₃Al coil is tested as an insert in a background magnet. The test is performed at the background field from 7 T to 15 T. The test results are analyzed and presented in this paper.     

磁场凝固法制备过共晶MnBi/Bi磁性功能复合材料

Bi-Mn过共晶合金分别从3个不同状态凝固．合金中MnBi析出相均在磁场作用下以晶体的C轴平行磁场取向。形成规则排列组织，并且所得材料的剩磁都具有明显的各向异性。合金从低于355℃的固液两相区凝固时，铁磁性MnBi析出相在1．0T磁场中迅速形成均布的织构组织，并能在无磁场条件下保持稳定，材料无需热处理就有很好的剩磁性能。因此，磁场凝固技术能够高效率地、直接制备出性能优良的MnBi／Bi磁性功能复合材料。     

Effect of the simultaneous application of a high static magnetic field and a low alternating current on grain structure and grain boundary of pure aluminum

Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However, when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction (EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field.     

强磁场作用下材料扩散型固态相变的微观机理

为探讨强磁场对物质原子尺度行为(电子运动、离子扩散)的影响,采用光学显微镜研究强磁场作用下Fe-0.12%C合金的扩散型固态相变;采用数字多用表测量强磁场作用下的纯铝板电阻研究其电子分布.结果表明:随磁感应强度增强,Fe-0.12%C合金室温显微组织中,铁素体晶粒平行于磁场方向伸长并呈链状排列的趋势增强,珠光体团的长轴方向平行于磁场方向伸长的程度也增强;纯铝板的电阻在平行于磁场方向放置时减小,垂直于磁场方向放置时电阻有增加趋势.这是由于组成金属晶体的自由电子和排列成晶格状的金属离子在磁场作用下受到洛伦兹力的作用,随磁感应强度增强,沿磁场方向的电子浓度、金属离子扩散有增强趋势,导致磁场作用下材料扩散型相变的室温组织出现形状各向异性.     

Texturing by cooling a metallic melt in a magnetic field

Abstract

Processing in a magnetic field leads to the texturing of materials along an easy-magnetization axis when a minimum anisotropy energy exists at the processing temperature; the magnetic field can be applied to a particle assembly embedded into a liquid, or to a solid at a high diffusion temperature close to the melting temperature or between the liquidus and the solidus temperatures in a region of partial melting. It has been shown in many experiments that texturing is easy to achieve in congruent and noncongruent compounds by applying the field above the melting temperature T_m or above the liquidus temperature of alloys. Texturing from a melt is successful when the overheating temperature is just a few degrees above T_m and fails when the processing time above T_m is too long or when the overheating temperature is too high; these observations indicate the presence of unmelted crystals above T_m with a size depending on these two variables that act as growth nuclei. A recent model that predicts the existence of unmelted crystals above the melting temperature is used to calculate their radius in a bismuth melt.     

Evolution of coating layers during pack alumetizing process induced by high magnetic fields

The application of a high magnetic field during pack aluminization process induced a significant change in the final products at the surface of substrate Cu. Experimental studies demonstrated that the coatings consisted of two layers namely α + γ₂ and α with the magnetic flux density (B) ranging from 0 to 8.8 T, whereas only α layer with Kirkendall voids was observed in case of B ≥ 10 T. With B increasing, the total thickness of coating first increased to a maximum at a field of 6.6 T, and then decreased with further increasing magnetic flux density. These results may be attributed to the contradictory effects of high magnetic fields on chemical reaction and on diffusion.