Ag掺杂SmBCO熔融织构单畴生长工艺研究

通过Ag掺杂降低Sm123/Sm211体系熔点,利用Nd123冷籽品技术成功制备出具有理想织构的smBCO/Ag单畴块材.研究了smBco/Ag单畴的生长过程,结果发现,相比于未掺杂坯体,掺入Ag后的smBcO坯体生长速率下降,在所考察的慢冷温区里,生长速率呈不断减小趋势,最终因自发成核而无法继续生长.实验还发现,SmBCO/Ag 单畴生长温度窗口随Ag掺量增加向低温区平移.对样品剖面的观察发现,在最高熔化温度保温阶段大量气体未能排出SmBcO/Ag坯体,这些气体在单畴慢冷生长过程中不断向外侧迁移、合并形成宏观可见的孔洞.在单畴生长过程中,这些位于生长前沿的高密度气孔,一定程度上影响了液相和sm3+离子向生长前沿的供应,是单畴生长速率较低的可能原因.微结构分析表明熔融生长过程中Sm211粒子发生二次晶粒长大现象,长大后的Sm211粒子提供Sm3+离子的能力减弱,导致慢冷生长后期阶段生长速率呈下降趋势.     

同质冷籽晶技术生长SmBCO/Ag超导单畴块材的研究

在前期的研究中,利用NdBCO123冷籽晶技术成功制备出具有理想织构的SmBCO/Ag单畴块材.但由于高质量的Nd籽晶的供应难以得到保证,从而限制了SmBCO单畴块材的批量化制备.Ag可以降低SmBCO坯体的熔点,这为用SmBCO冷籽晶技术引导SmBCO/Ag坯体生长单畴块材提供了可能性.然而,实验中我们发现,坯体里面的Ag容易向籽晶内部扩散,导致籽晶熔融,对单畴块材的生长产生不利影响.为克服这困难,我们通过在坯体和籽晶之间加入一个SmBCO211缓冲层,有效地阻止坯体里面的Ag向籽晶扩散,成功实现了同质冷籽晶技术生长SmBCO超导单畴块材.     

单畴熔融织构YBCO/Ag样品的生长工艺研究

本文研究了用冷籽晶技术制备掺Ag单畴熔融织构YBCO超导块材的工艺.通过引入有效的隔离层避免了籽晶的熔化.使用纯Y1.8粉作为隔离层的材料,并探索出同时施加两个隔离层的方法.对施加隔离层后大块单畴YBCO/Ag样品生长窗口的研究发现,加入隔离层后使慢降温上限温度升高,970℃到955℃是Y123/Ag系单畴生长的主要窗口.制备的直径26mm单畴超导块材的磁浮性能已达到12N/cm2(77K,0.5T).认为如果进一步提高熔化温度或延长保温时间将有助于抑制自发成核.     

MgO粒子掺杂对NdBCO超导块材熔化温度的影响

采用改进后的顶部籽晶熔渗生长(RE+011 TSIG) 工艺, 通过在固相先驱粉中掺杂不同含量的 MgO 来有效地提高 NdBCO 籽晶的熔化温度, 从而成功地制备出直径为32 mm 的大尺寸单畴 SmBCO 超导块材. 结果表明,MgO 的掺杂对 NdBCO 超导块材的熔化温度有着明显的提高, 随着固相先驱粉中 MgO 掺杂量的增加, Mg2 + 离子逐渐进入到 Nd123 相的晶格中, 当掺杂量达到16 wt% 时呈现出饱和状态, 且 NdBCO 超导块材的熔化温度提高近18 ℃ , 可有效地抑制在制备SmBCO 超导块材的过程中出现的 NdBCO 籽晶熔化现象.     

最高熔化温度对GdBaCuO单畴块材生长及磁悬浮性能的影响

采用熔融织构生长工艺结合冷籽晶法,通过调整最高熔化温度,成功制备出直径53mm的GdBCO单畴超导块材.不同高温下淬火坯体的XRD图谱表明,提高最高熔化温度对Gd123相的充分熔解和大单畴的生长具有重要意义.最高熔化温度对块材的磁悬浮性能有重要影响,最高温度偏低不利于熔体中气体排出,制成的单畴存在大量孔洞,使磁悬浮力下降;适当提高最高熔化温度,可减少单畴内部的孔洞,使材料致密从而提高磁悬浮力.     

直径53 mm熔融织构单畴YBCO块材制备研究

实验表明:通过对Y123/Y211前驱粉体粒度的调整以及采用Y123∶Y211=1∶0.3摩尔比的配制方案,在顶部籽晶诱导熔融织构生长条件下,可以提高单畴YBCO块材的起始生长温度Ts,从而有效地抑制了大尺寸单畴高温超导块材生长过程中的非籽晶成核现象. 利用这一技术,我们成功地生长出多块直径53 mm、厚18mm单畴YBCO高温超导块材,其中最大磁浮力达到302牛顿,最小为274牛顿,平均磁浮力密度达到12.9 N/cm2(77K、0.55T),达到和超过了该类材料的实用化国际标准.从宏观形貌上看,样品沿径向呈完全织构生长状态,沿轴向也基本呈完全生长状态. XRD和极图分析结果显示,整块样品具有较理想的织构化程度.这一结果意味着近期有望实现更大直径单畴YBCO超导块材的织构生长.     

不同厚度的Nd123片层的2-2复合籽晶对SmBCO样品生长的影响

采用MgO单晶与NdBa2Cu3O7-δ(Nd123)粉体的2-2复合体籽晶可以充分利用MgO与NdBCO籽晶的优势,对SmBCO晶体的生长起到了很好的诱导作用,成功制备出单畴SmBCO超导块材.本文采用不同厚度的Nd123片层和MgO单晶作为2-2复合体籽晶通过顶部籽晶熔渗生长工艺(TSIG)制备SmBCO超导块材,研究了Nd123片层的厚度对SmBCO样品生长的影响.结果表明,随着Nd123片层厚度的增加,样品的单畴形貌逐渐消失,并且出现了随机成核.通过对样品的生长特性和微观结构的研究,阐明了不同厚度的Nd123片层对SmBCO晶体生长形貌的影响机制.     

多籽晶技术生长大尺寸YBCO单畴超导块材的研究

本文利用多籽晶技术成功地生长出直径53mm的大尺寸YBCO单畴超导块材.与传统的单籽晶引导生长相比,该多籽晶技术在大尺寸YBCO单畴生长方面更有效.通过同时使用四个SmBCO籽晶引导生长,大尺寸YB-CO单畴的生长时间得以缩减.实验结果显示多籽晶生长的大尺寸YBCO单畴块材比传统的单籽晶生长的同尺寸块材在超导性能上有所提高.磁通俘获场测量显示多籽晶样品的磁通俘获场比单籽晶样品的峰值更高,均匀性更好.在77K零场冷的环境下,多籽晶的磁悬浮力密度可达到14.6N/cm2,相比单籽晶的12.5N/cm2的磁悬浮力密度有了很大的提高.     

外加电场法制备LiNbO3周期畴的反转电流特性研究

采用外加电场法制备了LiNbO₃单晶周期畴结构. 在对不同尺寸周期畴的反转电流进行比较研究的基础上,提出了一种确定反转畴成核时间和纵向贯穿速率的方法. 根据这一方法,得到在电场强度为25.1kV/mm,脉冲宽度为50 ms的脉冲方波作用下,LiNbO₃单晶反转畴的成核时间约为80ns,纵向贯穿速率约为0.1667m/s. 关键词： 3单晶周期极化')" href="#">LiNbO₃单晶周期极化 反转电流 反转畴成核时间 反转畴纵向贯穿速率     

外加电场法制备LiNbO3周期畴的反转电流特性研究

采用外加电场法制备了LiNbO3单晶周期畴结构.在对不同尺寸周期畴的反转电流进行比较研究的基础上,提出了一种确定反转畴成核时间和纵向贯穿速率的方法.根据这一方法,得到在电场强度为25.1 kV/mm,脉冲宽度为50 ms的脉冲方波作用下,LiNbO3单晶反转畴的成核时间约为80 ns,纵向贯穿速率约为O.1667 m/s.     

Study on single domain growth of Ag-doped Sm–Ba–Cu–O bulk using cold seeding technique

Attempts to prepare single grain SmBCO/Ag using NdBa₂Cu₃O_7?δ (Nd123) cold seeding technique have been performed. As silver decreases the melting temperature of SmBa₂Cu₃O_7?δ (Sm123) to approximately 1028 °C, it becomes possible to texture SmBCO/Ag samples with the Nd123 cold seeding technique, and very well textured mono-domain crystals with 15 mm on a side have been successfully obtained. However, the growth rate of SmBCO/Ag system is severely reduced compared with Ag free sample. A series of samples quenched at various lower limit temperatures of slow-cooling process were fabricated to investigate the single domain growth of SmBCO/Ag system. It is found that mono-domain growth exhibits a suppressed tendency within the slow-cooling temperature window considered, and then is hindered significantly by the spontaneous nucleation. The transversal slides of these samples show that large amount of entrapped gas did not escape from the samples during the dwell time at the maximum superheating temperature. During the slow-cooling process, the entrapped gas continued to move towards the edges of the samples, coalesced with each other and very large pores several millimeters in size were formed, which finally were released from the sample. The SEM analysis reveals that the coarsening of Sm₂BaCuO₅ (Sm211) precipitates has occurred during the growth of mono-domain. Large Sm211 cause decreased ability to supply samarium for the growth of Sm123 crystal, resulting in a gradual decrease in the growth rate.     

Growth and investigation of SmBCO/Ag single grain bulk for batch production of Sm123 seed crystals

Using NdBa₂Cu₃O_y (Nd123) bulk material as a seed, we report a success in the melt-textured growth of SmBCO/Ag bulks by cold-seeding melt-growth process. Very well-textured single domain bulks of SmBCO with 5 wt% Ag₂O addition can be fabricated reproducibly under ambient atmosphere. Microstructure analysis of the obtained SmBCO/Ag bulk sample reveals that no silver particle is trapped within the mono-domain region, where the peritectic decomposition temperature goes back to the one of the Ag-free SmBCO sample. This c-axis oriented mono-domain region can be easily separated into a large amount of Sm123 seeds. Therefore, a new approach to preparation of Sm123 seed crystals in high quantity and quality can be achieved in an uncomplicated way, which exhibits significant advantage in comparison with the conventional method for Sm123 seed fabrication by MgO cold-seeding process. Experimental results show that a batch of well-textured YBCO bulks has been grown successfully by using these new Sm123 seed crystals.     

BaO掺杂对单畴GdBCO超导块材性能的影响(二)

为了有效地抑制Gd BCO超导块材在生长过程中出现的Gd/Ba替换现象,在前期工作的基础上,本文采用顶部籽晶熔渗生长工艺,通过在固相先驱粉中添加不同含量的Ba O粒子成功地制备出了一系列高性能的单畴Gd BCO超导块材,并且对样品的微观形貌以及临界电流密度进行了研究和分析.结果表明,随着BaO掺杂量的增加,样品中的Gd_(1+x)Ba_(2-x)Cu_3O_(7-δ)固溶体(Gd123ss)相呈现出减少的趋势,并生成了纳米量级的Gd123ss,这对GdBCO超导样品中存在的Gd/Ba替换起到了很好的抑制作用,使得样品中的GdBa_2Cu_3O_(7-δ)(Gd123)超导相有所增加;同时当样品中BaO的添加量在2 wt%—4 wt%之间时,样品的临界电流密度在一定程度上得到了有效提高.     

开式单喷嘴喷雾冷却均匀性实验研究

针对高热流密度激光介质高效散热与均匀冷却技术需求，设计并搭建了以去离子水为冷却工质的开式单喷嘴喷雾冷却实验平台，实验研究获得了不同热流密度（16～110 W/cm2）、不同冷却工质流量（200～300 mL/min）以及不同喷雾高度（15～25 mm）下单相喷雾冷却换热系数及其冷却均匀性效果。结果表明:该实验工况下，不同热流密度条件下喷雾高度及工质流量对于单相喷雾冷却换热效率及温度均匀性影响显著；喷雾高度15 mm、工质流量200 mL/min时获得最大对流换热系数为5.93 W/（cm2·K）；喷雾高度15 mm、工质流量250 mL/min时面积20 mm×20 mm的热源表面温度均匀性最佳可优于0.6 ℃。     

Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED

The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30° surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30° surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer.     

Improvement of microstructure and mechanical properties of large single domain GdBaCuO superconductor with low void density

We fabricated large single domain of GdBaCuO (Gd-123) densified superconductor with a seeding and temperature gradient method in oxygen at the melt stage then in air at the growth stage for future applications such as a superconducting flywheel for energy storage system, magnetic separation, motor, current lead, and a bulk magnet. The innovative melt-textured single domain of Gd-123 system superconductor with low void density was about 46 mm in diameter and 15 mm in thickness. Gd-123 densified superconductors are expected to have high J_c and trapped magnetic field properties with higher mechanical strength. In this paper, we discuss processing, superconducting and mechanical properties of the densified Gd-123 bulk for improving the microstructure and strength of the RE-123 bulk. The relation between the microstructure and the flexural strength of the Gd-123 bulk was clearly shown.     

A study of Sm-substituted SrM magnets sintered using hydrothermally synthesised powders

Anisotropic SrM magnets with Sm substitution, which is observed to have the largest beneficial effect both on the coercivity and on the inhibition of grain growth at high temperature among the other elements such as La, Nd and Pr, were investigated. The average grain size of the samples decreases with increasing Sm/Sr ratio. All the magnets with Sm additions exhibit a bigger coercivity and remanence than those of the SrM magnet without Sm and the coercivity of the magnets increases with increasing Sm/Sr ratio. EDX quantitative analysis suggests that the solubility of Sm³⁺ in the SrM-type structure is very small and that the Sm³⁺ preferably goes into SrFeO_3−x, which is probably located around the SrM grain boundaries. The coercivity mechanism of the magnets is nucleation controlled. The formation and the distribution of the SrFeO_3−x phase around the SrM grain boundraies probably provides the inhibition of SrM grain growth, the reduction of the reverse domain nucleation at the grain surface and the isolation of the SrM grains. All these factors would contribute to the improvements of the coercivity of the magnets with Sm additions.