粉末结构形貌控制新方法--生物矿化机理的模拟

介绍了生物矿化作用机理及其主要的生物控制因素,指出了模拟生物矿化机理控制粉末结构形貌的三个途径,展望了其发展趋势.     

YBCO覆膜导体低成本制备研究

报道新近发展的离子束结构改性(ISM)技术以及同步织构(STEX)技术在YBCO覆膜导体制备中的最新进展。采用TFA-MOD工艺成功的在LaAlO_3(100)衬底上制备出了临界电流密度高达6.5 MA/cm~2 (77K,0T)的YBCO超导薄膜,其超导转变温度接近91K;同时还在LaAlO_3(100)衬底上成功地采用溶胶-凝胶工艺制备出了具有高度外延双轴织构取向的SrTiO_3缓冲层材料;在YSZ(100)衬底上采用溶胶-凝胶工艺制备出了具有高度双轴织构取向的CeO_2缓冲层材料。随后在这两种衬底上采用TFA-MOD工艺沉积的YBCO超导薄膜也获得了超过1MA/cm~2(77K,0T)的临界电流密度。作为制备实用化YBCO超导带材的新路线,在数厘米长的IBAD-YSZ/Hastelloy金属基带模板上,采用低成本化学溶液方法依次制备出了高质量的CeO_2缓冲层和YBCO超导薄膜,获得了高达1.2MA/cm~2(77K,0T)的临界电流密度。为长超导带材的制备打下了很好的基础。提出了在金属基带上制备YBCO覆膜导体的新方法一同步织构(STEX)法。用该方法可以有效解决RABiTS方法中的金属基带热处理变软...     

顶部籽晶粉末熔化法制备的超导YBCO单晶畴性能研究

采用顶部籽晶粉末熔化法(TSPMP)制备了30mm×15mm的YBCO单畴样品.在77K、零场冷却条件下获得最大磁悬浮力值43N(NdFeB,0.5T).在2T的静态磁场中场冷充磁后,77K下获得最大的捕获磁通为380mT.金相分析显示211粒子的粒度分布在1～3μm,ac面上的211粒子的分布密度＞ab面上的分布密度.从磁通钉扎角度分析了211的粒度对磁悬浮力和捕获磁通的影响.     

籽晶法YBCO超导块材的制备及其磁化性能研究

以ＳｍＢａＣｕＯ超导晶粒为籽晶，制备了具有大晶粒的ＹＢａＣｕＯ超导块材。磁化强度和交流磁化率表明该材料具有较强的磁通钉扎和良好的晶界妆特性，较强的磁通钉扎使大块样品在磁化后能冻结大量磁通，表现出很好的剩磁性能，经０．５Ｔ永磁体化后，实验测得其表面剩磁场最大值为０．１２５Ｔ，且在短时间内这一剩磁场没有明显的衰减。     

二氧化钛片状粉末制备的研究

研究了二氧化钛片状粉末的制备。将配制的透明氧化钛溶胶涂覆于玻璃基片上,经干燥后形成胶态薄片,然后将胶态薄片剥离并经过高温煅烧,可获得具有明显片状结构、表面光滑平整的二氧化钛薄片。研究结果表明:四氯化钛的浓度、乙醇用量、HCl用量是制备溶胶的主要影响因素。胶态薄片的煅烧温度以600℃、时间3h为宜。XRD检测结果表明,煅烧后获得的二氧化钛薄片以锐钛型氧化钛为主。SEM图象显示其薄片的粒径大多在5～20μm之间,厚度小于1μm。     

爆炸法制备超细金刚石粉末的提纯与性质研究

研究了利用爆炸合成法制备的超细金刚石的提纯工艺；对提纯样品的晶粒尺寸分布和平均晶粒尺寸进行了表征和分析，并对超细金刚石的热稳定性做了研究。     

二代YBCO超导带材的制备及其临界电流测试方法

超导材料在低温下具有零电阻性和抗磁性,在电力传输、交通、医学、国防等领域有着广泛的应用前景。超导材料分为一代超导材料和二代超导材料,     

硝酸盐PAD法快速制备YBCO超导薄膜研究

用硝酸盐高分子辅助沉积法(简称PAD)来制备YB2C3O7-x(YBCO)超导薄膜,有着制备速度快、工艺简单和无环境污染等优点。采用硝酸盐水相前驱液,并加入高分子螯合剂和薄膜改性剂,然后将前驱液涂覆在LaAlO3(LAO)单基晶片上,采用快速低温分解,再经过高温烧结制备出完整的YBCO超导薄膜。在1.0×10-4 O2/N2气氛下制备的YBCO超导薄膜致密,YBCO(00l)峰取向明显,没有其它杂相峰,同时,转变起始温度TC=91K,转变宽度ΔTC=2K;在77K、自场下临界电流密度JC为约1MA/cm2。实验结果表明,采用硝酸盐PAD法的低温分解时间比传统的TFA-MOD法缩短9h左右,而且制备出的YBCO超导薄膜性能优良,该方法为以后的长带生产提供了一种新的制备技术。     

海藻酸钠-壳聚糖-粉末活性炭生物微胶囊的制备

制备了海藻酸钠-壳聚糖-粉末活性炭(SA-CA-PAC)微胶囊,研究了添加适量粉末活性炭后对新型SA-CA-PAC生物微胶囊的粒径、机械强度和膨胀度等主要性能的影响.结果表明:适量粉末活性炭的添加对海藻酸钙胶珠和SA-CA-PAC微胶囊其它制备条件的影响不大,但却对SA-CA-PAC微胶囊的机械强度性能有较大的影响.在反应温度为30℃时,向2.0%的海藻酸钠溶液中添加粉末活性炭量为0.75%,氯化钙溶液浓度为4.0%,壳聚糖溶液浓度1.8%,成膜反应时间10 min,覆膜时间10 min,液化时间8 min,控制盐离子浓度为1.5%,所制得的SA-CA-PAC微胶囊具有良好的成囊性能.扫描电镜结果显示,SA-CA-PAC微胶囊具有良好的膜结构.     

Effect of gamma irradiation and silver doping on YBCO superconductor

The effect of -irradiation and silver doping on the properties of YBCO superconductors has been studied by electrical resistance measurements and x-ray diffraction techniques. The zero-resistance superconducting transition temperature of (YBCO)_1–xAg _x systematically increase by about 2 K with an increase of Ag content up tox=0.04. Further increase in Ag content decreases the transition temperature. The normal-state resistance decreases up to a factor of 3.4 with an increase of Ag content. No significant change in the transition width has been observed due to silver addition up tox=0.30. Undoped YBCO and the Ag-doped specimens of (YBCO)_1.96Ag_0.04 were irradiated with-rays up to an integrated-dose of 77 MR. The normal-state resistance of the specimens gradually increases and the transition temperature slightly decreases with increase of-dose. The intensities of the x-ray diffraction peaks of the monolayers of the sample powders decrease with -irradiation without noticeable change of diffraction angles or peak widths. These observations indicate that the high-T _c supconductor YBCO is quite sensitive to-irradiation but drastic lattice expansion does not occur up to a-dose of 77 MR.     

定向凝固法制备YBCO超导棒材研究

为了使高温超导体YBa2Cu3O7-d(简称YBCO)的晶粒取向排列,提高其临界电流密度,利用定向凝固方法生长YBCO棒材.采用光学显微镜、扫描电子显微镜研究了定向凝固工艺(抽拉速率和添加211粒子)对YBCO显微组织及片层生长的影响.结果表明,改变抽拉速率可以改善片层质量,211粒子是显微组织及片层厚度的重要影响因素;较低的抽拉速率有利于高质量定向结构的生长;均匀分布的细小Y211粒子会使片层厚度变薄,晶界连通性改善,有利于YBCO的生长.     

Growth and Characterization of YBCO Thin Films by Sequential Deposition and Annealing

A novel thin film growth procedure, sequential deposition and annealing (SDA), which contains the advantages of both in situ and ex situ procedures, was proposed. Y₁Ba₂Cu₃O_{7 – x} (YBCO) high temperature superconducting thin films were grown and characterized by the SDA procedure. Purely c-axis-oriented YBCO thin films with no foreign phases and other oriented grains were successfully prepared. The superconducting transition properties of SDA-grown YBCO thin films were measured by measurement of inductance and resistance. The inductance measurements gave a T _c ^onset of 85 K and a T _c of 5 K. The resistance measurements gave a T _c ^onset of 90 K and a T _c of 5 K. Atomic force microscopy studies showed that SDA-grown YBCO thin films had micrometer-size grains surrounded by many nanometer-size grains. The nanometer-size grains in SDA-grown YBCO thin films are responsible for degradation of superconducting transition properties.     

Melt Processing of YBCO Thick Films Fabricated by Sol Gel Route Powder on YSZ

It is evident that the microstructure and superconducting properties of YBa₂Cu₃O_7−σ (YBCO) thick films are highly dependent upon the route of the precursor. The precursor which was used in the preparation of YBCO thick films was produced using sol gel route technique. The screen printing technique was used in the fabrication of YBCO superconducting thick films on yttria stabilized zirconia (YSZ) substrates. The effect of slow cooling rate and slow cooling window on texturing, microstructure and superconducting properties of the melt processed films was carried out. Optimizing the melt processing program was effective in increasing the molten viscosity, keeping the liquid and hence relatively large grain size that has been obtained. Moreover, grain morphologies like which was found in YBCO bulk materials was observed.     

Identification of the effect of grain size on levitation force of well-textured YBCO bulk superconductors

The levitation forces of samples with different grain size have been directly investigated and identified in well-textured YBCO bulks. A single-domain YBCO bulk of ∅30 mm was prepared by a top seeded melt growth process, then divided into two, three and four parts to acquire the levitation forces of samples with different grain size but with completely the same grain orientation. The maximum levitation force for the single-domain sample is about 1.68, 2.05 and 2.4 times higher than that of the samples with two, three, and four grain domains. It is directly confirmed that the levitation force of a single-domain YBCO bulk is much superior than that of samples with multiple domains. It is found that the levitation force is inversely proportional to the total length of grain boundaries of the corresponding sample.     

A new type of biepitaxialc-axis tilted YBCO Josephson junction

A novel fabrication procedure of high critical temperature superconductor Josephson junctions (HTCSJJ) has been developed by a 90° rotation of YBa₂Cu₃O_7–x c-axis around an in-plane direction, on the basis of concepts of the biepitaxial technique. YBa₂Cu₃O_7–x grows oriented along (001) direction on a MgO seed layer deposited on a (110) SrTiO₃ substrate and along (110) direction on the bare substrate. Josephson junctions of good quality were obtained exhibiting RSJ behavior and features characteristic of HTCSJJ phenomenology. Even if not uniform, in some samples, the nature of the critical currentI _c is completely Josephson, as resulting from theI _c dependence on the applied magnetic field. The maximum measuredI _c R _N value atT=4.2K is 2mV.     

阴极沉淀法制备纳米Al_2O_3粉体及表征

采用阴极电化学沉淀方法制备氧化铝纳米粉体,对得到的纳米粉体进行了光吸收性能测试,并对其形成机理进行了初步的探讨。利用阴离子交换膜为隔膜的电解槽,在不添加分散剂的情况下,控制阴极的电流密度在150～500 A/m~2范围,电解一定浓度的硝酸铝溶液,在阴极室内得到Al(OH)_3沉淀,在500℃下焙烧2 h,得到不同粒度的Al_2O_3颗粒。用TEM和XRD分析表明：当阴极的电流密度为300 A/m~2时,得到的Al_2O_3粒度尺寸在30～40nm左右,晶型为γ-Al_2O_3,对波长为370 nm左右的紫外光有一定的吸收能力。     

阴极沉淀法制备纳米AlO3粉体及表征

采用阴极电化学沉淀方法制备氧化铝纳米粉体．对得到的纳米粉体进行了光吸收性能测试．并对其形成机理进行了初步的探讨。利用阴离子交换膜为隔膜的电解槽，在不添加分散剂的情况下。控制阴极的电流密度在150～500A／m^2范围．电解一定浓度的硝酸铝溶液，在阴极室内得到Al（OH）、沉淀，在500℃下焙烧2h．得到不同粒度的Al2O3颗粒。用TEM和XRD分析表明：当阴极的电流密度为300A／m^2时，得到的Al2O3粒度尺寸在30-40nm左右，晶型为γ-AlO3，对波长为370nm左右的紫外光有一定的吸收能力。     

YSZ超细粉末的溶胶——凝胶法制备

应用溶胶－凝胶方法合成了ＹＳＺ（Ｚｒ０２＋９ｍｏｌ％Ｙ２Ｏ３）超细粉末。对凝胶形成超细粉末的热分解及晶化过程用ｘ射线衍射（ＸＲＤ）和热重一差热（ＴＧ－ＤＴＡ）等分析方法进行了研究。试验表明，溶胶－凝胶法制备ＹＳＺ超细粉末的反应过程分为：水份和有机溶剂的挥发；有机基团的燃烧和无定形Ｚｒ０２的形成；无定形Ｚｒ０２向立方要Ｚｒ０２的转变三个阶段。在４７０℃时，凝胶转变为ＹＳＺ固溶体，形成立方相Ｚｒ０２结