常压干燥法制备铁掺杂二氧化钛气凝胶

以钛酸四丁酯(TRIP)为原料、硝酸铁为掺杂剂、冰醋酸为催化剂、甲酰胺为干燥控制化学添加剂,采用溶胶-凝胶法制备Fe3+掺杂TiO2醇凝胶,并结合常压干燥工艺,实现了Fe3+掺杂TiO2气凝胶的常压干燥法制备.采用XRD、BET、SEM、IR等对样品进行检测.结果表明:制备态Fe3+掺杂TiO2气凝胶密度为0.24 g/cm3,比表面积为529.17 m2/g,平均孔径约为20.10 nm,晶型为无定形;经850℃空气气氛下煅烧2h后,样品转变为锐钛矿型结构,平均孔径增大到22.32 nm,比表面积为136.22 m2/g.通过甲基橙溶液光催化降解实验,相比未掺杂二氧化钛气凝胶,掺入nFe∶nTi=0.05时,样品具有更高的光催化性能.     

介孔SiO2/Fe3O4中空微球孔径调控以及漆酶固定性能研究

以自制的β-FeOOH中空微球为内核,十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,以不同的方式添加扩孔剂癸烷(Decane)和1,3,5三甲基苯(TMB),经水解缩聚反应、焙烧和还原后得到介孔SiO2/Fe3O4中空微球.重点研究了扩孔剂的加入方式对中空微球微观形态和漆酶固定化性能的影响.结果表明,扩孔剂的加入量和加入顺序对扩孔效果产生很大影响,其中先加入癸烷和后加入1,3,5-三甲基苯的复合扩孔方式所制得介孔SiO2/Fe3O4中空微球的扩孔效果最优.当n(TMB+ Decane)/n(CTAB)=2,n(TMB)/n(CTAB)=1时,介孔SiO2/Fe3O4中空微球的介孔层的厚度约50 nm,其比表面积约为855 m2·g-1,孔体积为1.23 cm3 ·g-1,平均孔径为5.72 nm,中空微球对漆酶的固定量达到276 mg/g;固定化漆酶活性较游离漆酶活性有一个更好的pH和温度稳定性.介孔SiO2/Fe3O4中空微球在外加磁场中可实现快速分离.     

HNTs/SiO2复合气凝胶制备及其性能研究

采用正硅酸乙酯(TEOS)为硅原,以硅烷改性的埃洛石纳米管(HNTs)为增强相,利用CO2超临界干燥技术制备具有优良力学和隔热性能的HNTs/SiO2复合气凝胶.利用傅立叶红外光谱、扫描电镜、比表面积与孔径分析仪、万能试验机和导热率测量仪等手段对HNTs改性后的表面状态、HNTs/SiO2复合气凝胶的微观形貌、孔结构、力学和导热性能进行了测试分析.结果表明:改性后的HNTs均匀分散到二氧化硅气凝胶基体中,并与SiO2纳米颗粒实现良好的结合,HNTs/SiO2复合气凝胶呈三维网络结构,当HNTs含量为15wt;时,平均孔径为10.47 nm;随着HNTs含量的增加,复合气凝胶的力学性能不断增强,同时其导热系数也不断增大,当HNTs含量为15wt;时,HNTs/SiO2复合气凝胶的抗压强度为0.85 MPa,导热系数为0.024 W/mK.     

聚氨酯增强二氧化硅气凝胶常压干燥制备及其性能

以正硅酸乙酯(TEOS)为硅源,3-氨丙基三乙氧基硅烷(APTES)为偶联剂,聚氨酯为增强相,经水解缩聚形成凝胶后通过常压干燥工艺制备聚氨酯增强二氧化硅复合气凝胶.采用傅立叶红外光谱对样品的化学结构进行表征,并通过扫描电镜、比表面积与孔径分析仪,万能试验机和接触角仪等对所制得气凝胶的微观形貌、孔结构,力学和疏水性性能进行了分析.结果表明,所制备的气凝胶的孔径分布范围为2.0～25.0 nm,是一种具有三维网状结构的介孔材料,并且具有良好的力学性能,15wt;聚氨酯增强的气凝胶的压缩模量达到4MPa,同时疏水性也得到了提高,其接触角为77.73°.     

介孔氧化锌的微乳液法制备及表征

以十六烷基三甲基溴化铵(CTAB)/苯乙烯/硝酸锌溶液/过硫酸钾组成的聚苯乙烯微乳液为模板,提出一种制备介孔氧化锌的简易方法,研究了煅烧温度对介孔氧化锌结构特性的影响,提出了介孔形成的可能机制.结果表明:煅烧温度较高时,所得介孔氧化锌的孔径较大,比表面积较小;当煅烧温度为 500℃时,所得纳米氧化锌的比表面积为 11.013 m2·g-1,孔容为0.135 cm3·g-1,介孔分布在40.2 nm左右.此外,光催化降解亚甲基蓝的实验表明所制备的介孔 ZnO 具有较高的光催化性能.     

高性能氮化硅陶瓷凝胶注模成型的研究

凝胶注模成型工艺的关键在于制备低粘度高固相体积含量的陶瓷浆料.本文以四甲基氢氧化铵(TMAH)溶液为分散剂制备氮化硅陶瓷浆料,研究了pH值、分散剂含量、助烧剂含量以及固相体积含量对氮化硅浆料流变性的影响;测定了凝胶注模成型素坯以及烧结体的力学性能.研究结果表明:当pH＝10.5,分散剂加入量为6;(相对于氮化硅固相体积比),助烧剂加入量为10;(质量分数)时,浆料具有最好的流变性.根据以上制备的工艺参数,制备得到固相体积含量大于50;,具有良好流变性的浆料.铸模成型干燥后,素坯的抗弯强度达27MPa;常压烧结后氮化硅陶瓷具有优异的力学性能,其抗弯强度为730 MPa,断裂韧性高达8.8 MPa·m1/2.     

单分散SiO2微球的制备及疏水改性研究

采用改进的凝胶-溶胶法制备了200~800 nm的单分散SiO2微球,并通过真空冷冻干燥法得到不易团聚的单分散SiO2粉体,采用乙醇超临界方法对制备的SiO2微球进行疏水改性.通过扫描电镜和氮吸附-脱附分析仪对SiO2微球的表面形貌、粒径以及孔径分布进行表征;用傅里叶红外变换测试和测量接触角对疏水改性的SiO2微球进行分析.结果表明SiO2微球粒径随二次加入TEOS体积增加呈先增大后减小.经过乙醇超临界处理,SiO2微球表面成功接枝上了疏水烷基,微球尺寸越小,疏水性越好,其接触角高达149°,单次SiO2微球处理量对结果无明显影响.采用本方法可以单次处理12 g以上的SiO2微球,接触角均在140°左右,可充分满足实验室使用需求.经过真空冷冻技术和乙醇超临界技术得到疏水单分散SiO2微球粉体,具有不易团聚及单分散性良好的优点,能够作为胶体晶体原料和三维有序材料(3-DOM)模板剂进行广泛应用.     

提高氧化硅气凝胶耐温性能的研究进展

氧化硅(SiO2)气凝胶是一种高效隔热材料,具有高孔隙率、低导热系数、低密度等优点,在隔热保温领域具有广阔的应用前景.但纯SiO2气凝胶高温时易烧结,严重限制了SiO2气凝胶的使用.本文详细综述了国内外关于提高SiO2气凝胶耐温性能的研究进展,并对未来提高SiO2气凝胶耐温性能的研究提出展望.     

微波辅助水热条件对二乙胺合成SAPO-11晶体结构与性质的影响

以二乙胺为模板剂,利用微波辅助水热合成法制备了SAPO-11晶体,研究了水热温度和时间对合成产物晶体结构性质的影响。采用XRD、FT-IR、SEM、BET和NH3-TPD等手段对SAPO-11晶体的物相组成、骨架结构、微观形貌、孔结构及表面酸性进行了分析表征。研究结果表明,不同水热条件对SAPO-11晶体结构性质影响较大。反应温度低于180℃时,合成样品仅存SiO2物相,无SAPO-11晶相生成;反应温度高于200℃时,部分SAPO-11晶体二次生长致使晶粒均匀度和比表面积大幅下降;反应时间大于1 h时,SAPO-11晶体生长易转晶生成少量AlPO4-5和CFSAPO-1(C)杂晶相;在反应温度200℃,反应时间1 h条件下制备得到的纯相SAPO-11球形晶粒表面具有弱酸特征,比表面积、孔容和平均孔径分别达199.4 m2·g-1,0.15 cm3·g-1和2.92 nm。     

凝胶注模成型Al2O3-ZrO2泡沫陶瓷的制备与表征

采用环保无毒生物高分子明胶作胶凝剂和四甲基氢氧化铵(TMAH)为分散剂,通过凝胶注模工艺制备了相对密度为10;～35;的ZrO2增韧Al2O3(ZTA)泡沫陶瓷,对制备泡沫陶瓷的结构和性能进行了表征.SEM分析表明泡沫陶瓷由相互贯通的球形孔室构成,其孔径分布取决于泡沫陶瓷的相对密度.ZTA泡沫陶瓷抗弯强度随相对密度从10;变化到31;而相应地从3.1 MPa提高至28.1 MPa,渗透系数随相对密度的增大呈指数衰减.     

On the inhomogeneity of the transition surface layer of the solid core of the earth

Different geophysical data and conclusions of theoretical models, which can give information about the behavior of the solid and liquid cores of the Earth as well as about the existence of a transition layer as a temperature-hysteresis region at a relatively weak first-order phase transition, are compared. It is concluded that liquid inclusions inevitably exist in this region; these inclusions are involved (due to the complex convective processes occurring in the liquid core) in the transport of light materials from some areas of the solid-core surface. The porosity and permeability of the transition layer determine the seismic acoustic inhomogeneities in these areas, which contact the convective flows in the liquid core. In particular, this explains the well-known ??east-west?? effect. Obviously, the model of the crystalline core is not the only possible alternative for a model of a core with a metallic glasslike structure.     

On the role of the porous shell of the solid core of the earth in the anomalous heat and mass flow to the mantle

The model of the pressure-induced first-order phase transition of a metal melt to the metallicglass state considers a thermodynamically nonequilibrium porous near-surface shell of the solid core of the Earth, which contacts cyclonic vortices in the liquid core. Anomalous flows of heat and light-material mass to the mantle from the solid core at these contact points are calculated. These anomalous flows are shown to be comparable with the observed ones under the assumption of a rapid increase in the melt viscosity at pressures of 1–10 Mbar, which is characteristic of a solid core. In this case, the porous layer permeability may be very low.     

Influence of the Crystal Structure of the Nucleus on the Morphology of t-ZnO Tetrapods

Crystallography Reports - A new approach to simulating the morphology of hierarchical nanocrystals has been proposed on the example of ZnO nanotetrapods. Within this approach, twinning is...     

Features of the magnetic state of the layered Fe-V nanostructure of the superconductor-ferromagnet type

The magnetic state of the V(39 nm)/20 [V(3 nm)/Fe(3 nm)] nanostructure has been investigated by polarized neutron reflectometry in the temperature range from 1.6 to 30 K in magnetic fields from 0.2 to 15 kOe. The data obtained indicate that the superconductivity of vanadium layers may affect magnetic ordering both over the depth of the structure and in its plane.     

Study of the influence of the rare-earth elements on the properties of lead iodide

Lead iodide (PbI₂) shows excellent electronic properties for detection of ionizing radiation. We report the introduction of rare-earth elements and other elements as admixtures during synthesis to study their influence on the quality of single crystals. Synthesized material as well as single crystals have been characterized by measurements of electrical resistivity and low-temperature photo luminescence and index of refraction. The structural quality with respect to polytypes was analysed by electron back scatter diffraction. Makyoh topography was applied for surface studies.     

Effect of the temperature on the TMOS sono-hydrolysis and a study of the structure of the resulting aged sonogels

The effect of temperature on the oxalic acid catalyzed sono-hydrolysis of tetramethoxysilane (TMOS) was studied by means of a heat flux calorimetric method. The activation energy of the process was measured as (24.5 ± 0.8) kJ/mol in the temperature range between 10 and 50 °C. The structural characteristics of the resulting sonogels, after long period of aging in saturated conditions, were studied by means of small angle X-ray scattering. The structure can be described as formed by ∼2.7 nm mean size mass fractal-like aggregates (clusters) of primary silica particles of ∼0.3 nm mean size, all imbibed in a liquid phase. The average mass fractal dimension of the clusters was found to be 2.58. The primary particle density was estimated as 2.23 g/cm³, in good agreement with the value frequently quoted for fused silica. The volume fraction of the clusters in the saturated sonogels was estimated as about 28%. The moment in which the meniscus of the liquid phase penetrates into the clusters under rapid evaporation process has been detected by an inflection in the first derivative of the curve of weight loss in a simple thermogravimetric test.     

Ordering of cations in the voids of the anionic framework of the crystal structure of catapleiite

The pseudohexagonal crystal structure of the mineral catapleiite Na_1.5Ca_0.2[ZrSi₃(O,OH)₉] · 2(H₂O,F) from the Zhil’naya Valley in the central part of the Khibiny alkaline massif (Kola Peninsula, Russia) is studied by X-ray diffraction (XCalibur-S diffractometer, R = 0.0346): a = 20.100(4), b = 25.673(5), and c = 14.822(3) Å; space group Fdd2, Z = 32, and ρ_calcd = 2.76 g/cm³. Fluorine atoms substituting part of H₂O molecules in open channels of the crystal structure have been found for the first time in the catapleiite composition by microprobe analysis. The pattern of distribution of Na and Ca atoms over the voids of the mixed anionic framework consisting of Zr-octahedra and three-membered rings of Si-tetrahedra accounts for the pronounced pseudoperiodicity along the a and c axes of the pseudohexagonal unit cell and for the lowering of crystal symmetry to the orthorhombic one. It is shown that part of the hydrogen atoms of water molecules is statistically disordered; their distribution correlates with the pattern of the population of large eight-vertex polyhedra by Na and Ca atoms.     

Investigations of the Chemical Composition of the Metal Finds from the Levadki Necropolis

Crystallography Reports - Copper-based alloy items of the III century A.D., found in Burial no. 182 of the Late-Scythian Levadki necropolis in the submountain Crimea, have been investigated. The...     

Experimental Investigations of the Conditions for the Formation of the Liquid Crystalline State of Polymers

The diagrams of state for concentrated PBG solution in coordinates relating volume fraction-geometric asymmetry and volume fraction-temperature are investigated. The order parameter for macromolecules in the anisortropic phase is dettermined. The experimental data compare with the existing theoretical models for th formation of the liquid crystalline state in solutions of stiff polymer molecule. It is shown that experimental data are in good quantitative agreement with the Flory's lattice model.