羟基聚合铝晶体研究进展

羟基聚合铝的研究在环境化学中具有重要作用。自然条件下存在的无机单核铝本身具有毒性,而多核铝是比单核铝更毒的铝形态,它们很容易进入人体和植物产生毒害作用。因此,水解聚合铝形态研究一直是环境化学、地球化学和材料催化等众多研究领域的前沿热点课题。本文综述了在新环境材料开发中羟基聚合铝晶体研究的进展,对已获得表征的典型羟基聚合铝的结构特点进行了对比与评述,讨论了不同羟基聚合铝晶体的科学意义和应用价值。     

Practical methods to determine hydrogen and hydroxyl contents in quartz crystals

Before manufacturing quartz crystal resonators, it is essential to perform a systematic study of the material which allows a prediction of the behaviour of the resonator. Furthermore, we know that some treatments like sweeping appear as a mean for clearly improving the performance. Unfortunately, up to now, there is no valid method to obtain the hydrogen content which is the major impurity in quartz crystals, sometimes qualified as a poison. The major difficulty lies in the fact that this element is found in several forms. It is just well known that the strength of absorption by hydroxyls in the 3 μm infrared region is frequency dependent. Some sharp bands, attributed to specific impurities like A1-OH or M/OH (where M = K, Li or Na), are superimposed on a broad absorption band. Furthermore, the [1900-2000] nm absorption band has been attributed to the presence of hydrogen in the molecular form H₂O. In this paper we present a review of different methods usually employed to tentatively qualify the H content. We discuss a few of them when they are applied to different kinds of samples issued from synthetic as well as natural quartz and submitted to different combinations of treatments such as sweeping out or into, γ irradiation, high temperature annealings.     

Observations of radiation damage effects in paraffin and polyethylene crystals

Summary Observations by transmission electron microscopy are reported on the lattice defects generated in paraffin and polyethylene single crystals by electron irradiation. The observations suggest that electron irradiation results in the formation of clusters of cross links in the lattice of the paraffin single crystals. It is shown that in the paraffin crystals the clusters of cross links nucleate preferentially in the vicinity of lattice defects (dislocations, interfaces etc.). The formation of the clusters may be due to the strain field interaction between individual cross links.The observations on polyethylene crystals suggest that the cross links formed during electron irradiation are lined up in rows being either parallel to the [100] or [010] direction. The alignment may be due to the elastic interaction of the strain field of the individual cross links.

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Zusammenfassung Elektronenmikroskopische Beobachtungen an n-Paraffin- und Polyäthyleneinkristallen nach Elektronenbestrahlung werden berichtet. Die Beobachtungen zeigen, daß in n-Paraffineinkristallen die Vernetzungen Agglomerate bilden, die bevorzugt in der Nähe von Gitterdefekten entstehen. In Polyäthyleneinkristallen lagern sich die Vernetzungen zu langen Reihen parallel zur [100] oder [010] Richtung zusammen.

     

Distribution of OH in synthetic and natural quartz crystals

The relative intensities of different OH vibration bands have been studied in synthetic quartz crystals with total OH concentration varying by more than a factor of 30 by means of infrared absorption measurements at 78°K. Local variations of OH concentration also have been measured for different directions in these samples and in two crystals of natural quartz from Brazil. Integral absorptions of the different bands in the 3400 cm^?1 region were all found to increase linearly with total OH concentration. Therefore, mechanical Q could be related to any one band of the spectrum as well as to the total OH concentration. Since for natural quartz no relation between total OH concentration and mechanical Q seems to exist, the effect of OH defects characteristic for synthetic quartz must be high, while the OH defects characteristic for natural quartz (i.e., rock crystals and smoky quartz) have a small effect on the mechanical Q.OH concentrations in the Z- and +X-zones were found to be lower near the edge than near the seed. The concentration of OH varies in the order Z < + X ? ?X, suggesting that OH acts as a charge compensator for metal impurities, notably Al⁺³. In natural quartz, the OH concentrations near the edge were also lower than in the interior parts. The overall differences for different directions were much smaller than in the case of synthetic quartz.     

Structure of single-molecule single crystals of isotactic polystyrene and their radiation resistance

The structure of single-molecule single crystals of isotactic polystyrene (i-PS) was investigated by electron diffraction (ED). The nanoscale single-molecule single crystals were found to be more resistant to electron irradiation when compared to the larger crystals of many molecules, as indicated by both observation of ED and high-resolution electron microscopy with increasing radiation dose. It is proposed that since the single-molecule single crystals are very small, the secondary electrons escape more frequently from the crystal so that the radiation damage is reduced. Lattice imaging was achieved at room temperature in the case of single-molecule single crystals because of their stability to electron irradiation. Published 1998 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

J Polym Sci B: Polym Phys 36 : 105–112, 1998     

A brief radiological survey and associated occupational exposure to radiation in an open pit slate mine in Kashan,Iran

Journal of Radioanalytical and Nuclear Chemistry - A comprehensive radiological survey was carried out in an open-cut slate stone quarry. The activity of 226Ra, 228Ra and 40&nbsp;K in the ore...     

Curvature and defects in nematic liquid crystals

ABSTRACT

The use of nematic liquid crystals for directed assembly of particles and for the creation of multistable systems depends on the ability to control the topological defects and the distortions of the director field. These are not only driven by topological constraints and by anchoring energies but also by the curvature field created by the bounding surfaces. This review explores the interaction between defects, topology, inclusions and curvature in nematics. I will introduce the relationship between curvature and the Frank elastic energy in nematics, and then I will give an overview of specific examples that show how this coupling can create unexpected behaviours, such as lock-and-key interactions, anchoring transitions on curved surfaces and memory effects.     

Impedance and frequency characteristics of electrode-separated piezoelectric quartz crystals in liquids

The electrical equivalent circuit parameters of an electrode-separated piezoelectric quartz crystal (PQC), where the gaps between the electrodes and the crystal plate were filled with various liquids, were evaluated from admittance measurements and were compared with those of a normal PQC with Au electrodes adhering to the crystal plate. The resistance parameter in the equivalent circuit of the electrode-separated PQC was more sensitive to the specific conductivity, density and viscosity of liquids than was that of the normal PQC. This parameter, unlike that of the normal PQC, was also affecteded by the permittivity of the liquid. The effect of the liquid properties on the other parameters in the equivalent circuit and the series resonant frequency are also discussed.     

Analysis of apatite crystals and their fluid inclusions by synchrotron radiation X-ray flourescence microprobe

Chemical composition analysis of apatites and their fluid inclusions from Yu'erya granite was carried out by synchrotron radiation X-ray fluorescence (SRXRF) microprobe. The result shows that all these apatite crystals have a similar chemical signature, with Ca, P, Cl, Mn, Fe, K, S, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu, Sr, Y, Zr, U, Th, etc. The rare earth elements chondrite-normalized pattern indicates that these apatites are derived from S-type granite. It is shown by the SRXRF analysis that Zn, Cu and Cl are main components of fluid inclusions in apatites. It is the first time that SRXRF analysis is successfully applied in determination of composition of single fluid inclusions in apatite crystals. This technique was proved to be suitable for crystals with homogenously distributing components and thin covering layer would help to determine the composition of fluid inclusions.     

Wireless excitation of quartz crystals immersed in an aqueous fluid

A novel toroidal coil geometry able to induce remote acoustic waves in quartz crystals has been evaluated for the development of (bio)sensors. Remote acoustic generation in air was obtained for two alternative toroidal coils, with corresponding electrical impedance changes of 40 Omega for a PDMS- and 140 Omega for a ferrite-supported toroid respectively. It was found that the range of remote acoustic generation relative to the spiral coil standard was much improved, increasing the axial separation of their resonant sensing element from 0.1 mm to 20 mm, thereby allowing electromagnetic wave penetration across glass walls and fluid media to be utilised. Consideration of the transduction mechanism, along with measured cyclic changes in acoustic signal as a function of rotation, indicated that the large PDMS toroidal coil produced an asymmetric electric field. It was shown for the first time that a quartz crystal blank fully immersed in an aqueous fluid could support chemically sensitive shear acoustic standing waves that were excited and detected remotely. A signal to noise ratio of 30 ratio 1 at 20.13 MHz was achieved by placing a ferrite supported toroidal coil on the lower side of a glass beaker containing a 12 x 0.25 mm AT crystal blank and 1 mL of water. This discovery allows wireless shear acoustic wave measurements to be performed with total separation between the electronic detection system and assays undertaken in fluidic systems.     

Optical and dielectric properties of antiferroelectric liquid crystals and their surface effects

Abstract

A detailed study of the dielectric and optical properties of the ferroelectric liquid crystal material (R)-4′-(3-methoxycarbonyl-2-propoxycarbonyl)phenyl 4-(4-(n-octyloxy)phenyl)benzoate (3MC2PCPOPB) has been carried out. It has been found that an anomalous temperature dependence of the dielectric constant in 3MC2PCPOPB is due to the antiferroelectric and ferrielectric properties. A T(temperature)-E(electric field) phase diagram has been obtained on the basis of the apparent tilt angle measurements. In a thin cell (< 3 μm), both ferroelectric and antiferroelectric domains are simultaneously observed over a wide temperature range, and the complete antiferroelectric phase does not appear even at low temperature. A characteristic texture in which boundary focal conics are aligned parallel to a smectic layer has been observed. The movement of the zig-zag defect line caused by the application of the voltage is also observed.     

Frequency shifts of piezoelectric quartz crystals immersed in organic liquids

A piezoelectric quartz crystal oscillates in organic liquids. The frequency change (ΔF) depends on the density (d) and viscosity (η) according to ΔF = ad^1/2 + bη^1/2 — c, where a, b and c, are constants depending on the crystal.     

Binding and degradation of DNA on montmorillonite coated by hydroxyl aluminum species

Adsorption, desorption and degradation by DNase I of DNA on montmorillonite (M) and different hydroxyaluminum-M complexes (Al(OH)_x-M) containing 2.5, 10.0 and 20.0 mmol coated Al/g clay (AM_2.5, AM₁₀ and AM₂₀) were studied. The adsorption isotherms of DNA on montmorillonite and Al(OH)_x-M complexes conformed to the Langmuir equation. The amount of DNA adsorbed followed the sequence of montmorillonite > AM₂₀ > AM₁₀ > AM_2.5. A marked decrease in the adsorption of DNA on montmorillonite and Al(OH)_x-M complexes was observed with the increase of pH from 4.0 to 9.0. Calcium ion significantly promoted DNA adsorption. The adsorption enthalpy of DNA on montmorillonite was endothermic, whereas that on Al(OH)_x-M complexes was exothermic. The percent desorption of DNA from clays was in the order of montmorillonite > AM_2.5 > AM₁₀ > AM₂₀, suggesting that OH–Al loading on montmorillonite surface increased the binding affinity of DNA. Fourier transform infrared (FTIR) spectra showed that the binding of DNA on AM₁₀ and AM₂₀ changed its conformation from the B-form to the Z-form. The presence of montmorillonite and Al(OH)_x-M complexes provided protection for DNA against degradation by DNase I. The higher level of protection was found with Al(OH)_x-M complexes compared to montmorillonite. The higher stability of DNA in the system of Al(OH)_x-M complexes seemed to be attributed mainly to the conformational change of bound DNA and their greater adsorption capacity for DNase I. The information obtained in this study is of fundamental significance for understanding the behavior of extracellular DNA in soil environments.     

Textures and defects in lyotropic liquid crystals of ethyl-cyanoethyl cellulose

Textures and defects in ethyl-cyanoethyl cellulose [(E-CE)C]/dichloroacetic acid (DCA) cholesteric liquid crystalline solutions and in (E-CE)C/polyacrylic acid (PAA) composites were observed and studied by polarizing microscopy and electron microscopy. The existence of χ, λ and τ disclinations were observed in the mesophase with disk-like and band-like textures. Pairs of disclinations with different signs were also found in the mesophase with the band-like texture. Domain walls were observed in (E-CE)C/PAA composite films with cholesteric order by TEM. The orientation of polymer chains in the vicinity of the core of the disclinations is discussed.