四硼酸锶(SrB_4O_7)的制备新工艺及其影响因素

采用液相沉淀法合成两种水合硼酸锶SrB_2O_4·4H_2O和SrB_6O_(10)·5H_2O,将其高温煅烧制备出纯四硼酸锶(SrB_4O_7)相,分析了高温煅烧过程、产物的物相和形貌,研究了煅烧温度和保温时间等因素的影响。结果表明,在加热过程中水合硼酸锶发生脱水→非晶化→晶化过程,且SrB_6O_(10)在800℃左右分解为SrB_4O_7和液态氧化硼;将SrB_2O_4·4H_2O和SrB_6O_(10)·5H_2O在900℃煅烧4 h可制得纯相四硼酸锶;延长煅烧时间可提高产物的晶化程度,但是其晶型没有明显的变化。用该法制备的SrB_4O_7:Eu荧光粉,其发光强度明显比以SrCO_3和H_3BO_3为原料制备的样品高.     

Preparation of Gd2O2S:Pr Scintillation Ceramics by Pressureless Reaction Sintering Method

Fabrication of Gd₂O₂S:Pr scintillation ceramics by pressureless reaction sintering was investigated. The 2Gd₂O _3˙(Gd,Pr)2(SO ₄)_3˙mH₂O precursor was made by hydrothermal reaction using commercially available Gd₂O₃, Pr₆O₁₁ and H₂SO₄ as the starting materials. Then single phase Gd₂O₂SO₄:Pr powder was obtained by calcining the precursor at 750°C for 2 h. The Gd₂O₂SO₄:Pr powder compacts can be sintered to single phase Gd₂O₂S:Pr ceramics with a relative density of 99% and mean grain size of 30 μm at 1750°C for 2 h in flowing hydrogen atmosphere. Densification and microstructural development of the Gd₂O₂S:Pr ceramics were examined. Luminescence spectra of the Gd₂O₂S:Pr ceramic under 309 nm UV excitation and X-ray excitation show a green emission at 511 nm as the most prominent peak, which corresponds to the ³P₀-³H₄ transition of Pr³⁺ ions.     

超临界流体干燥法制备TiO2/ Fe2O3 和TiO2/ Fe2O3/ SiO2 复合纳米粒子及光催化性能

以TiCl₄ 、Fe (NO₃ )₃·9H₂O 和Na₂SiO₃19H₂O 为原料, 采用溶胶凝胶法结合超临界流体干燥法(SCFD)制备了纳米级TiO₂/ Fe₂O₃ 和TiO₂/ Fe₂O₃/ SiO₂ 复合光催化剂。以光催化降解苯酚对所得催化剂的催化活性进行了评价。结果表明, 纳米TiO₂/ Fe₂O₃ 复合粒子与单组分TiO₂ 比较, 复合粒子光催化活性高于单组分的TiO₂, 6h 苯酚降解率高达95.9 %。SiO₂ 的加入可以抑制纳米粒子粒径的长大和晶相的转变, 增强TiO₂ 纳米粒子的热稳定性。复合光催化剂中Fe₂O₃ 最佳掺入量为0.06 %, SiO₂ 最佳掺入量为10 %(摩尔分数) 。并用XRD、TEM 和FTIR 等手段进行了表征。TiO₂ 以锐钛矿型形式存在, SiO₂ 以无定性形式存在。比较了不同制备方法制得的TiO₂/ Fe₂O₃ 复合光催化剂, 得出超临界干燥法制备的光催化剂具有粒径小、比表面积大、分散性好、光催化活性高等特点。采用超临界流体干燥可直接得锐钛型纳米复合光催化剂。     

CuO-TiO_2复合助剂低温烧结氧化铝陶瓷的机理(Ⅱ)

固定CuO(0.4%)和TiO₂(4%)的添加量、改变TiO₂(0--32%)和CuO(0--3.2%)的添加量(质量分数, 下同), 研究了CuO--TiO₂复合助剂对氧化铝陶瓷烧结性能、微观结构、物相组成以及烧结激活能的影响, 以揭示复合助剂的低温烧结机理。结果表明, 在1150--1200℃TiO₂固溶入Al₂O₃生成Al₂Ti₇O₁₅相, 并生成大量正离子空位提高了扩散系数, 从而以固相反应烧结的作用机理促进了氧化铝陶瓷的致密化; TiO₂在Al₂O₃中的极限固溶度为2%--4%, 超过固溶极限的TiO₂对陶瓷烧结没有促进作用; 添加适量的CuO(0.4%)可将TiO₂在Al₂O₃中的固溶温度降低到1100℃以下, 并以液相润湿作用促进氧化铝陶瓷的致密烧结。陶瓷烧结激活能的计算结果定量地印证了上述烧结机理; 当在Al₂O₃中添加4%的TiO₂和2.4%的CuO, 可将烧结激活能降低到54.15 kJ ? mol-1。     

共沉淀法合成近零膨胀ZrW2O8/ZrO2复合陶瓷的致密化

采用化学共沉淀法合成前驱体,经1150℃ 烧结3.5 h得到近零膨胀26 wt% ZrW₂O₈/ZrO₂复合陶瓷,并利用X射线衍射仪、扫描电镜和热膨胀仪研究了原料中加入Al(NO₃)₃·9H₂O对26 wt% ZrW₂O₈/ZrO₂复合陶瓷的相组成、致密度和热膨胀性能的影响。研究结果表明,少量添加Al(NO₃)₃·9H₂O可有效提高复合材料致密度,所得复合陶瓷的组分仍为立方结构的α-ZrW₂O₈和单斜的m-ZrO₂,其中添加2.21 wt% Al(NO₃)₃·9H₂O的复合材料的致密度达到理论密度的98.67%,且对复合陶瓷的热膨胀性能影响不大。其促进致密化机制为晶界处低熔点液相物质Al₂(WO₄)₃提高了复合材料的烧结性能,消除气孔促进致密化。     

不同晶核剂对硼硅酸盐钙钛锆石固化体析晶行为及化学稳定性的影响

通过“一步法”热处理制备含24%(质量分数)模拟核废物的硼硅酸盐钙钛锆石固化体,从析晶动力学角度出发,利用Kinssinger法研究不同晶核剂(Fe₂O₃、Cr₂O₃、P₂O₅、CaF₂)作用下固化体的析晶行为及其对化学稳定性的影响。实验结果表明,Cr₂O₃的引入促进了板状CaZrTi₂O₇晶体的析出,析晶活化能E由218 kJ/mol降至128 kJ/mol,并使残留在玻璃基体中的模拟核素进入所析出的晶相,而其他晶核剂对析晶无明显影响。MCC-1标准测试法结果显示,Cr₂O₃作为晶核剂时,模拟核素Ce元素抗浸出性能最为优异,化学稳定性最佳,7 d后归一化元素浸出率小于10-7 g·m-2·d-1。     

NiCo2O4/氧化石墨烯复合材料制备与电化学性能研究

为了研究NiCo₂O₄/氧化石墨烯(NiCo₂O₄/GO)复合材料的电化学性能,本文通过先水热合成前驱体再煅烧的方法制备了一系列NiCo₂O₄/GO复合材料.利用X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学方法对其进行物理表征,其中以GO质量浓度为1 mg/mL悬浊液制备出的NiCo₂O₄ /GO-3复合材料呈类海胆状结构.在1 M KOH水溶液中使用循环伏安法、恒电流充/放电法和交流阻抗法研究了NiCo₂O₄/GO复合材料电化学性能.研究表明,与纯NiCo₂O₄相比,制备的NiCo₂O₄ /GO复合材料的比容量和赝电容性能均有明显提高,这主要是由于NiCo₂O₄ /GO复合材料中NiCo₂O₄与GO纳米片的相互作用形成的高孔隙率复合结构;NiCo₂O₄ /GO-3复合材料在电流密度为0.5~3.0 A/g时,比电容超过650 F/g,具有良好的倍率性能和高比容量.采用本文方法合成的NiCo₂O₄/GO复合材料,既提高了其倍率性能又保证了高比容量,是一种良好的超级电容器电极材料.     

烧成温度对Al2O3/Ni复合材料的致密化、物相组成和显微结构的影响

首先采用非均相沉淀合成出Ni包裹Al₂O₃粉体,然后热压烧结包裹粉体制备了Al₂O₃/Ni复合材料。本文作者主要研究了不同烧成温度对复合材料致密化、物相组成和显微结构的影响。结果表明:在1400℃保温1h,烧结体获得了最大相对密度,而致密度随Ni含量的增加反而降低;高于1350℃时,除Al₂O₃和Ni相外,在烧结体的表层生成一种由Al,Ni,O,C四种元素组成的新相;随着温度的升高,包裹层的纳米Ni颗粒聚合、长大,并退缩至三角晶界处,在适当的烧结温度(1400℃),少数小的纳米Ni颗粒被卷入Al₂O₃晶内,大的位于三角晶界,当烧成温度为1450℃时,不仅观察到Al₂O₃/Ni界面存在空隙,也发现了Al₂O₃晶粒异常长大现象。     

氧化铝纳米晶陶瓷研究进展

Al₂O₃陶瓷由于具有独特的物理化学特性而被普遍应用于结构材料、光学材料、电子材料等领域,但脆性严重限制了其更广泛的应用。近年来,人们对Al₂O₃纳米晶陶瓷的制备进行了不懈探索。Al₂O₃纳米晶陶瓷的制备主要包括α-Al₂O₃纳米颗粒的制备、素坯的烧结两个方面。本文综述了α-Al₂O₃纳米颗粒的主要制备方法,包括喷雾热解法、溶胶-凝胶法、沉淀法和机械球磨法;总结了Al₂O₃纳米晶陶瓷的主要烧结方法,包括放电等离子烧结、微波烧结、热压烧结和无压烧结;归纳了Al₂O₃纳米晶陶瓷力学性能的初步研究进展。最后展望了Al₂O₃纳米晶陶瓷研究的发展趋势。     

氧化石墨烯/H2O2可见光催化性能影响因素

为了研究氧化石墨烯/H₂O₂可见光催化处理含难降解有机物废水影响因素,用改进的Hummers法制备了氧化石墨烯(GO),通过扫描电镜(SEM)、电子能谱(EDS)、拉曼光谱对GO的微观形貌、成分及结构进行了表征.以甲基橙(MO)为难降解有机物代表,通过改变光照、pH值以及GO的量探究了不同条件对GO/H₂O₂复合试剂降解甲基橙的光催化效果.研究表明：GO/H₂O₂复合试剂可以通过光催化产生羟基自由基降解污染物,通过改变光照、pH值及GO的量增加自由基含量可提升催化效果; 采用GO/H₂O₂复合试剂比单独使用H₂O₂在48 h内对甲基橙的降解率可提高79.09%(pH=2).用改良的Hummers法制备GO成本较低,采用GO/H₂O₂复合试剂光催化降解甲基橙时,GO用量较少,且不产生危险废弃物,为实际应用中处理难降解有机物污水提供了一个绿色环保、节能高效的思路.     

Features of strontium tetraborate synthesis by means of borate rearrangement

The results of thermoanalytical and x-ray diffraction measurements show that strontium tetraborate (SrB₄O₇) is formed as the result of crystallization of an amorphous substance at 750°C. The amorphous substance was obtained by dehydration of a mixture of strontium borate crystal hydrates synthesized at 95 ± 5°C via solid-state interaction of orthoboric acid with strontium carbonate. Conditions for reproducible synthesis of single-phase SrB₄O₇ by means of borate rearrangement have been established.     

Low-temperature performance of Al4B2O9 nanowires

In this paper we report on the synthetic investigation of single-crystalline aluminum borate (Al₄B₂O₉) nanowires in large scale by a direct calcination of a precursor powder made of Na₂B₄O₇·10H₂O and Al (NO₃)₃·9H₂O at a low temperature of 850 °C. The nanowires, with the diameter of 20-40 nm and the length up to several micrometers, possess smooth surfaces and uniform sizes along the entire wire. The growth mechanism of the nanowires is attributed to a solid-liquid-solid process, which controls the nanowire morphology.     

Electrochemical synthesis of nanocrystalline SrNb2O6 powders and characterization of their photocatalytic property

Nanocrystalline SrNb₂O₆ powders were successfully prepared by a simple electrochemical method for the first time, and the influences of electrolytic solution ingredients, electrolyte concentration, and applied electric current intensity on electrochemical process and products were systemically studied. It was found that the formation of strontium niobates strongly relied on the basic or acidic condition of electrolytic solution. When Sr(OH)₂·8H₂O or mixed Sr(OH)₂·8H₂O with SrCl₂·6H₂O was used as electrolyte, Sr₅Nb₄O₁₅ and SrNb₂O₆ phases could simultaneously form, and the relative ratio of Sr₅Nb₄O₁₅ phase to SrNb₂O₆ declined with the increase of SrCl₂·6H₂O content in electrolytic solution. The higher the basicity of electrolytic solution, the more favored the crystallization and development of Sr₅Nb₄O₁₅ phase. Only monoclinic phase SrNb₂O₆ was obtained in neutral SrCl₂·6H₂O solution or acidic solution of SrCl₂·6H₂O with adding hydrochloric acid solution, and a lower concentration of SrCl₂·6H₂O (≤0.50 M) was beneficial to the formation of SrNb₂O₆ phase and stable anodic sparks could be observed. Moreover, the crystallization and development of the nanocrystalline SrNb₂O₆ powders seem to be not sensitive to the applied electric current intensity, their similar particle size and morphology ultimately result in the resemblance in UV-vis absorption and photodegradation. They show a slight red shift of light absorption onset and better photocatalytic performance compared with that prepared by the solid-state reaction.     

Hydration of ZrW2O8 nanopowders under ambient conditions

We report hydration of ZrW₂O₈ under ambient conditions, and its effect on the negative coefficient of thermal expansion (CTE) of ZrW₂O₈. On storing under ambient conditions for six months, about 66% of the outer annular volume was hydrated to ZrW₂O₈·0.35H₂O, while after one year of storage the sample was hydrated to ZrW₂O₈·0.72H₂O. The CTE was determined by in-situ high temperature X-ray diffraction (XRD) measurements in the temperature range from 25 to 200 °C. XPS and TGA were used to characterize the nature of bonding of the water in the ZrW₂O₈ structure. The negative CTE behavior of partially hydrated ZrW₂O₈·0.35H₂O remained intact, while on further hydration to ZrW₂O₈·0.72H₂O, negative CTE was not observed. The bonding of the water molecules to the ZrW₂O₈ structure were stronger than those of adsorbed water molecules but weaker than those of the structural hydroxyl ions.     

X-ray diffraction and Ir-absorption characteristics of lanthanide orthophosphates obtained by crystallisation from phosphoric acid solution

Powders of LnPO₄ · H₂O (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) prepared by crystallisation from boiling phosphoric acid (2 M H₃PO₄/1) solution were characterised by X-ray diffraction and FTIR-spectroscopy. Hexagonal LnPO₄ · H₂O (La Tb), tetragonal (Ho Lu and Y) and orthorombic DyPO₄ · H₂O crystalline modifications were identified. Ir-spectra of the hydrated hexagonal, anhydrous tetragonal LnPO₄ · H₂O (Dy, Ho, Er, Tm, Yb, Lu and Y) and anhydrous monoclinic (La Tb) are consistent with those reported in the literature. However, the hydrated tetragonal LnPO₄ · H₂O (Ho, Er, Tm, Yb, Lu and Y) display a surplus band (625 cm^–1) in the region of ₄, which was not reported in the literature. The band disappears after ignition at 950°C, while the tetragonal structure is still maintained, which may imply that it is attributed to hydrogen bonding of H₂O molecules to the phosphate oxygen in hydrated salts. Some of the phosphates, after ignition at 950°C, display additional P₂O₇ ^4– band at 1265–1267 cm^–1. That may be resulted from HPO₄ ^2– for PO₄ ^3– substitution in the phosphates crystallised in acidic (2 M H₃PO₄/1) solution.     

Chemical preparation, crystallographic characterization, thermal behavior and IR studies of a new cyclotriphosphate SrTlP3O9·3H2O

Chemical preparation, crystallographic characterization, thermal behavior and IR studies are given for two new cyclotriphosphates SrTlP₃O₉·3H₂O and SrTlP₃O₉. SrTlP₃O₉·3H₂O is orthorhombic, space group Pnma, with the following unit-cell dimensions: a=9.147(7) Å, b=8.180(7) Å, c=15.458(2) Å and Z=4. The total dehydration of SrTlP₃O₉·3H₂O leads between 300 and 650°C to its anhydrous form SrTlP₃O₉. SrTlP₃O₉ is monoclinic, space group P2₁/m or P2₁, with the following unit-cell dimensions: a=14.544(2) Å, b=8.639(1) Å, c=7.727(1) Å, β=102.05(1)° and Z=4. The thermal behavior has been investigated and interpreted in agreement with IR absorption spectrometry and X-ray diffraction experiments. We calculated the 30 normal frequencies of the P₃O₉ ring with Cs symmetry and proposed the interpretation of the vibrational spectrum of SrTlP₃O₉·3H₂O. The vibrations were assigned and precised to each frequency for different atoms of the ring on the basis of the results of the theoretical isotopic substitutions and in the light of the crystalline structure of the isotypic compounds, SrM^IP₃O₉·3H₂O (M^I=Rb⁺, K⁺ and NH₄⁺), of SrTlP₃O₉·3H₂O.     

Synthesis, characterization and photoluminescence properties of (Gd0.99,Pr0.01)2O2S sub-microphosphor by homogeneous precipitation method

Homogeneous precipitation method for synthesizing (Gd_0.99,Pr_0.01)₂O₂S sub-microphosphor was developed, using the commercially available Gd₂O₃, Pr₆O₁₁, H₂SO₄ and (NH₂)₂CO (urea) as the starting materials. It was found that the as-synthesized precursor is mainly composed of (Gd_0.99,Pr_0.01)₂(OH)₂(CO₃)(SO₄)·nH₂O. Pure quasi-spherical shaped (Gd_0.99,Pr_0.01)₂O₂S particles can be synthesized by calcining the precursor at a temperature higher than 700 °C for 1 h in flowing hydrogen. The (Gd_0.99,Pr_0.01)₂O₂S particles have a narrow size distribution with a mean grain size of about 300-400 nm. Photoluminescence spectra of (Gd_0.99,Pr_0.01)₂O₂S under 303 nm UV excitation show a green emission at 515 nm as the most prominent peak, which corresponds to the ³P₀ → ³H₄ transition of Pr³⁺ ions. Decay study reveals that the ³P₀ → ³H₄ transition of Pr³⁺ ions in Gd₂O₂S host lattice has a single exponential decay behavior.     

Luminescence of Sm2+ in strontium haloborates

The luminescence properties of Sm²⁺ in Sr₂B₅O₉R (R=Cl, Br) have been studied and compared with those in SrB₄O₇. In the range from 80 to 300 K the emission of Sm²⁺ in Sr₂B₅O₉R is predominantly due to the 4f⁵5d → 4f⁶ transition, while SrB₄O₇ : Sm²⁺ shows a very efficient emission of the 4f⁶ → 4f⁶ type. Differences in the luminescence of Sm²⁺ in the strontium haloborates and tetraborate are discussed.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

Heat capacity and thermodynamic properties of crystalline SrB<Subscript>4</Subscript>O<Subscript>7</Subscript>

The heat capacity of a strontium tetraborate (SrB₄O₇) single crystal has been determined in the temperature range 55–300 K by adiabatic calorimetry, and its Debye characteristic temperature, entropy change, enthalpy increment, and phonon mean free path have been calculated as functions of temperature.