A Thermoanalytical Study of the Solid State Reactions in the K2CO3-MxOy Systems. Evidence for a kinetic compensation effect

This paper presents the results obtained in the investigation of the reactions of potassium carbonate with some transition metals oxides (TiO₂ , V₂ O₅ , Cr₂ O₃ , MnO₂ , Fe₂ O₃ ). The reactions were carried out under non-isothermal conditions, and thermogravimetric analysis was used to monitor the transformation degree a. Experimental data indicated that the reaction of potassium carbonate and iron(III) oxide occurs in one stage, whereas the reactions of the oxides of titanium, vanadium, chromium and manganese are more complex, involving two-stage processes. Activation energies and pre-exponential factors were determined for all the processes taking place in the investigated systems. For the second stage of the reaction of K₂ CO₃ with Cr₂ O₃ , and V₂ O₅ the obtained values of activation energy were 59.2 and 512 kJ mol⁻¹ respectively. Based on the values of activation energy and pre-exponential factor, the existence of a kinetic compensation effect was postulated for the three homologous series of reactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

X-ray,Thermal and Infrared Spectroscopic Studies on Potassium,Rubidium and Caesium Uranyl Oxalate Hydrates

M₂UO₂(C₂O₄)₂⋅nH₂O compounds (M=K, Rb and Cs)have been prepared and characterized by chemical and thermal analyses as well as by X-ray diffraction and infrared spectroscopy. X-ray powder data show that the compounds belong to an orthorhombic system. Thermal and infrared studies show that the compounds decompose to M₂UO₄ through the formation of alkali metal carbonate and UO₂ as intermediates. K₂UO₂(C₂O₄)₂⋅3H₂O, and Rb₂UO₂(C₂O₄)₂⋅2H₂O gave K₂UO₄, Rb₂UO₄ at 700 and 600°C respectively, while in the case of Cs₂UO₂(C₂O₄)₂⋅2H₂O, the intermediate products of decomposition reacted to yield Cs₂U₄O₁₃ at 1000°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bridgman growth and properties of potassium lithium niobate single crystals

Transparent KLN crystals 10mm in diameter and 25 to 45mm in length have been grown by the modified vertical Bridgman technique from different melts in the range of 3035mol% K₂O, 1723mol% Li₂O and 4350mol% Nb₂O₅. The growth conditions are a growth rate of less than 0.25 mm/hr, temperature gradient in solid-liquid interface of 23 °C/mm and growth direction of <110>. As-grown KLN crystals have tetragonal tungsten bronze structure. Most of the as-grown crystals do not crack when cooling through the paraelectric/ferroelectric phase transition. 180° domain structures are observed after the KLN crystal was etched in boiling 2HNO₃:Hf. Dielectric properties and transmission spectrum of the as-grown KLN crystals are measured.     

甲基丙烯酸3-磺酸丙酯钾盐苯乙烯共聚物负离子与N,N,N-三甲基十六烷基溴化铵相互作用研究

聚电解质与表面活性剂相互作用研究已有很多报道[1～4],由于在很多方面与生物膜中脂质体-蛋白质间相互作用相似,从而近年来备受关注[5～6].作为带电荷的水溶性高分子,聚电解质与带相反电荷的表面活性剂分子可以形成规整性非常好的聚电解质表面活性剂复合物.Ａｎｔｏｎｉｅｔｔｔｉ等报道聚丙烯酸与十六烷基三甲基溴化铵(ＣＴＡＢ)形成规整的介规相(Ｍｅｓｏｐｈａｓｅ)聚电解质表面活性剂复合物结构[7],漆宗能等在同一体系既观察到了热致液晶也观察到了溶致液晶[8].在研究甲基丙烯酸3磺酸丙酯钾盐(ＳＰＭＳ)的苯乙烯(Ｓｔ)共聚物(Ｐ(ＳＰＭ…     

合成钾型丝光沸石的酸改型及对K+的离子交换性

合成出钾型丝光沸石,对其进行了酸改型,测定了其对碱金属离子的饱和交换容量和分配系数、ｐＨ滴定曲线等离子交换性能,并对该沸石进行了Ｘ射红衍射分析和ＦＴ－ＩＲ分析。结果表明,该沸石对钾离子具有较强的交换选择性。     

X射线荧光光谱法快速分析苹果酸·柠檬酸钙中的总钙

文章以粉末压片法制样,顺序式单道X射线荧光光谱仪测定苹果酸·柠檬酸钙中的总钙, 方法快速准确简捷,完成一个样品制备和分析只需10 min;文章还进行了火焰原子吸收光谱法的对比试验, 阐述了两法各自的特点。     

硫酸铜-酒石酸钾钠-头孢克洛体系分光光度法测定头孢克洛

根据头孢克洛在碱性酒石酸铜溶液中能形成棕黄色配合物,建立了分光光度法测定头孢克洛的新方法。头孢克洛的浓度在32.5~175mg/L范围内与吸光度呈良好的线性关系,线性相关系数为0.994,方法的检出限为0.24mg/L,回收率为96.2%~101.0%。该法可用于胶囊和干混悬剂中头孢克洛含量的测定。     

添加剂对硝酸钾结晶习性影响的研究

研究了Fe3+、Bi3+、pb2+、EDTA、柠檬酸、季铵盐和十二烷基磺酸钠共7种添加剂对硝酸钾结晶习性的影响,对不同添加剂在晶体表面的吸附机制进行了初步探讨.结果表明,随金属离子Bi3+、pb2+和EDTA浓度的增高,硝酸钾晶体c轴方向生长速度增大,晶体呈棒状;当柠檬酸添加量为100mg/L时,硝酸钾变为长片状;其他添加剂对硝酸钾结晶习性的影响效果则不明显.尽管某些添加剂可以改变硝酸钾的结晶习性,但粉末衍射和单晶衍射分析进一步证明,添加剂并未改变其晶胞参数及结构.     

共振瑞利散射法测定百草枯的研究

在pH=7.0的NaAc-HAc缓冲溶液中,单独的碘化钾汞试剂或者百草枯溶液的共振瑞利散射(RRS)十分微弱。碘化钾汞试剂和百草枯反应形成疏水性较强纳米微粒,导致RRS急剧增强,从而建立了一个灵敏的测定百草枯的RRS新方法,且对RRS增强的机理进行了初步探讨。实验表明:在λ=497nm处,RRS强度与百草枯浓度有良好的线性关系,线性范围在0.01～13.0mg/L,检出限为8.0μg/L。本法用于大米中百草枯含量的测定,结果满意。