Periodic Crystallisation of Magnesium Hydroxide in Agar-Agar Gel

Investigations are made to get the experimental conditions for obtaining periodic crystallisation of magnesium hydroxide in agar-agar gel. A detailed study is made on the dependence of the velocity constant (K), the spacing coefficient \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {p = \frac{{x_{n + 1} }}{{x_n }}} \right)'$\end{document} the length of the continuous precipitate and the width of the rings on the concentrations of the inner and outer electrolytes. Using SHINOHARA 's revised coagulation theory, the flocculation value F is calculated. F = Γ + C₃₀, where Γ is the characteristic concentration of the outer electrolyte for which the flocculation starts and C₃₀ is the reduced concentration of the reaction product. The value of the concentration of the outer electrolyte for which the flocculation stops (γ) is calculated. The dependence of F on the concentrations of the reactants is also discussed. Observation of a coneshaped precipitation is also reported.     

Crystal Growth in Gel: Nuclei and Precipitation Distribution in Gel

The investigation of the gel structure and properties influence upon the crystallization processes have been carried out and are reported in this paper. The gel acidity and nucleation centers distribution are chosen as the parameters describing this process. The analytical approximations for the nucleation and precipitation density along the gel column are proposed. It has been shown that in the view of the parameters chosen it is impossible separately to determine the gel structure and proton concentration effects on crystallization processes.     

氢氧化镁晶须的制备及其生长机理探讨

以Mgcl2和NaOH为原料,采用直接沉淀法制备氢氧化镁晶须.研究了添加不同晶控剂对氢氧化镁晶须生成的影响,同时对添加硬脂酸锌制备氢氧化镁晶须的工艺进行研究.采用扫描电子显微镜和粒度分析仪对产品进行表征.结果表明,硬脂酸锌和氯化铁对氢氧化镁晶须的生成具有导晶作用;所得产品为长径比10.7的氢氧化镁晶须.采用负离子配位多面体生长基元理论可以有效地解释氢氧化镁晶须的生成.     

Workshop on Pattern Formation in Liquid Crystals

Abstract

This event marked the 10th anniversary of the first workshop on this topic in Bayreuth, which initiated a bi-annual series on pattern formation in complex systems which took place in Kitakyushu, Santa Fe, Copenhagen and Budapest. Some of the topics discussed are reported below (see also www.phy.uni-bayreuth.de/-ptlc/).     

Effect of Different Parameters on the Liesegang Ring Formation of Lead Carbonate Crystals

Influence of different parameters like concentration of the outer electrolyte, age of the gel and impurities added to the outer electrolyte on the periodic precipitation of lead carbonate crystals in silica gel are presented. Increase of outer electrolyte concentration has the effect of increasing x²/t value while it decreases with increase of the gel age. Impurities added to the outer electrolyte delay the time of formation of the rings. All these observed results are explained.     

人工可控氢氧化镁晶须生长

从负离子配位多面体生长基元模型出发,根据大维度生长基元的结构特性,讨论了人工可控氢氧化镁晶须生长,主要介绍了多元醇法及镁盐过饱和度法.多元醇法的实质是醇中的羟基在一定条件下与大维度生长基元中的羟基发生假联结(即吸附),使得与多元醇发生了假联结的晶面生长速率大大减小或甚至停止生长,而其他晶面仍然保持原有的速率生长以致形成晶须.镁盐过饱和度法就是使得生长基元[Mg-Ax](x-2)-(A≠OH-)的浓度很大,且要远比[Mg-(OH)x](x-2)-组分浓度大4倍以上,以先形成碱式镁盐晶须,碱式镁盐晶须再与适当的碱液反应,即可制备得氢氧化镁晶须.     

Pattern Formation in Interacting Suspensions

The observation of periodic bands and macroscopic deposits, when suspensions of silver and arsenious trisulphide are allowed to interact in a gel medium may be due to a chemical instability of autocatalytic reaction mechanism of colloid growth and nucleation.     

Mechanism of Formation of Cadmium Oxalate Liesegang Rings

Qualitative and semiquantitative study of the Liesegang rings formed by the reaction of oxalic acid and cadmium chloride in the acidic range of pH in silica hydrogel is made. The behaviour of Jablczynski's space constant and Morce-Pierce's time constant at various temperatures, pH and concentration of outer electrolyte is studied. The possible mechanisms for the above observed behaviour are suggested. The deviations from Isemura's general obserations are interprerted by considering two particular aspects, viz., comparatively larger crystals constituting the rings and the irreversibility of inner and outer electrolytes.     

Dendritic Growth of Ammonium Tartrate Single Crystals in Silica Gel

Dendritic growth of Ammonium tartrate single crystals in silica gel at 30 °C is reported. Main stem parallel to the ‘C’ axis is observed. Dendritic growth in initial and final stages with its surface structures are illustrated and described. Growth features are correlated to the growing conditions and reacting components.     

Growth of calcium iodate crystals by Gel method

Synthesis of single crystals of calcium iodate by gel method is described. Fairly transparent crystals of reasonably large size with different habits obtained here are illustrated. Crystals grown are identified and characterized by electron microprobe, chemical, X-ray, thermogravimetric and infra-red analysis.     

砷化锗镉晶体的合成与生长

砷化锗镉(CdGeAs2)晶体是一种重要的中远红外波段非线性光学晶体,非线性光学系数高达236pm/V[1]。此外,晶体的透光波段宽(2.4~18μm)[2],双折射率适中(ne-no=0.1)·K)[3],具有广泛的应用前景。本文采用单温区法合成了CdGeAs2多晶原料。采用可视温梯冷凝法生长了大尺寸,低吸收系     

六角片状氢氧化镁(001)晶面优先生长条件的研究

以常温工业合成氢氧化镁为原料,采用水热法制备六角片状氢氧化镁阻燃剂.研究了水热条件对氢氧化镁(001)晶面生长的影响并从生长基元的角度对其进行了解释.采用SEM、XRD、激光粒度仪和接触角测试仪对水热处理后的氢氧化镁进行表征.结果表明,原料初始粒度越小越有利于(001)晶面生长,当水热介质中碱浓度为6～8mol/L、水热温度为140～180℃时,氢氧化镁(001)晶面的生长速度最快,当氢氧化镁的含量大于15wt;时会明显抑制(001)晶面的生长.     

Effect of Growth Conditions on Formation and Properties of CdS Single Crystals at Dynamic Sublimation

Influence of technological factors on growth and photosensitivity of CdS single crystals prepared by sublimation in an argon flow has been studied. A conclusion is drawn that crystal growth occurs in the non-stoichiometric medium with an excess in Cd.     

CdTe量子点生长速率的参数研究

以NaTeO3为碲源,还原型谷胱甘肽(GSH)为稳定剂,一步合成CdTe量子点.研究了参与反应回流的镉与碲摩尔比和Cd2+浓度对CdTe量子点生长速率的影响,并用荧光光谱、X射线衍射光谱及透射电子显微镜对其性能进行表征.结果表明:GSH稳定的CdTe量子点具有闪锌矿结构、球形形貌;在pH =8.5,n(Cd2+)∶ n(GSH)=1∶1.2,C(Cd2)=0.67 mmol/L,n(Cd)∶ n(Te)=6∶1时,CdTe量子点荧光量子效率最高可达51.53;,并且量子点生长的速率在初期的1h内达到最高点,并随着时间的延长呈下降趋势.     

Growth of Potassium Sulphate Crystals by Silica Gel Technique

Single and transparent crystals of potassium sulphate up to 30 × 3 × 3 mm in size have been grown by silica gel technique, using various methods (two-layers three-layers and hybrid gel technique) which are described. The effects of the three differents alcohols (used as top solutions) upon the quality and nucleation of crystals are also reported. The “growth and equilibrium” morphologies and microstructures of the habit faces are discussed.