Scanning electron microscopic structure of the prismatic layer in the Bivalvia

The shell structure of the Bivalvia has been observed with the use of optical and electron microscopes since the early 1900’s. The prismatic structure is one of the more attractive shell structures in bivalved mollusks. This structure is composed of the aggregation of polygonal prisms arranged densely. Each prism is made of small calcite crystallites arranged perpendicular to a growth shell surface. Organic materials, named organic sheaths, accumulate around prisms and stain well with heamatoxylin-eosin. The Bivalvia, which make prismatic structures, are divided into two groups. One group has the inner shell layer made up of a nacreous structure, and the other has the inner shell layer made up of a foliated structure. The aragonite prismatic layer and the prismatic layer are closely related to each other, as is the aragonite prismatic layer to the composite prismatic one.     

Scanning electron microscopic structure of the prismatic layer in the Bivalvia

The shell structure of the Bivalvia has been observed with the use of optical and electron microscopes since the early 1900’s. The prismatic structure is one of the more attractive shell structures in bivalved mollusks. This structure is composed of the aggregation of polygonal prisms arranged densely. Each prism is made of small calcite crystallites arranged perpendicular to a growth shell surface. Organic materials, named organic sheaths, accumulate around prisms and stain well with heamatoxylin-eosin.The Bivalvia, which make prismatic structures, are divided into two groups. One group has the inner shell layer made up of a nacreous structure, and the other has the inner shell layer made up of a foliated structure. The aragonite prismatic layer and the prismatic layer are closely related to each other, as is the aragonite prismatic layer to the composite prismatic one.     

Crystallographic alignment of calcite prisms in the oblique prismatic layer of Mytilus edulis shell

The structure and crystallographic orientation of mineral phase in the oblique prismatic layer of Mytilus edulis shell were studied by SEM, XRD and TEM with selected area electron diffraction (SAED). A crystallographic orientation regulation, i.e. the adjacent 1–5 calcite prisms with the same three-dimensional orientation in the oblique prismatic layer, was found for the first time. It is observed that the calcite prisms in the oblique prismatic layer were grown with their (104) parallel to the shell surface.     

Modeling and optimization for a prismatic snapshot imaging polarimeter

Thin birefringent prisms placed near an image plane introduce sinusoidal fringes onto a 2D polarized scene making possible a snapshot imaging polarimeter, which encodes polarization information into the modulation of the fringes. This approach was introduced by Oka and Kaneko [Opt. Express 11, 1510 (2003)], who analyzed the instrument through the Mueller calculus. We show that the plane-wave assumption adopted in the Mueller theory can introduce unnecessary error in a polarimeter design. To directly take prism effects such as beam splitting and deviating into accounts we introduce a geometric imaging model, which allows for a versatile simulation of the birefringent prisms and provides a means for optimization. A calcite visible system is investigated as an example, which essentially shows how each design parameter affects the overall image quality and how to modify the polarimeter design to optimize overall performance. The approach is applicable to any prismatic imaging polarimeter with different prism materials and different working wavelengths.     

三角帆蚌珍珠质层结构和珍珠质涂层的研究

利用扫描电镜和光学显微镜对三角帆蚌贝壳和珍珠的珍珠质层微观结构进行了分析研究, 发现贝壳的珍珠质层中存在异常的结构带, 主要有柱状珍珠质带, 针状晶体带以及棱柱状晶体带. 其中柱状珍珠质带中, 单片文石板片的厚度超过1μm, 是正常珍珠质中文石板片厚度的两倍. 而对正常珍珠的珍珠质层的大量观察却未发现类似的异常结构. 分析认为这可能是因为贝壳珍珠质的矿化微环境与珍珠的珍珠质矿化微环境不同导致的. 并利用圆柱形珍珠囊在钛金属牙种植体表面制备的珍珠质涂层具有沿整个圆周面均匀生长的特点.     

香螺壳体的结构特征分析

本文以我国黄渤海地区的香螺为对象,研究了其结构及组织形态特征.研究表明:香螺壳体主要由方解石构成,其次为具有正交晶系结构的文石.香螺壳体的纵截面由外层的柱状晶粒结构层,中间的交错纹片结构层和内层的柱状结构层组成.外层和中间层主要由方解石组成,内层由方解石和文石构成.显微硬度测试结果表明:香螺壳体的硬度从外层到内层是逐渐增加的,说明内层的致密度比中层和外层的高.     

香螺壳的结构和微观力学性能

测量产自黄/渤海海域的香螺贝壳的硬度和弹性模量,研究了贝壳的结构与性能之间的关系.结果表明,香螺贝壳主要由方解石和文石两种矿物镶嵌在有机质中构成,方解石结构为不均匀的柱状晶,文石结构为多级超微的交错纹状结构,其中第三级结构为10-80 nm的纳米级纤维.文石的力学性能优于方解石的性能.贝壳类复合材料的压痕效应主要源于裂纹扩展,而微观裂纹扩展与晶体类型以及晶体结构的排列方式是密切相关的.方解石裂纹形状曲折、不规则且沿着方解石层的边界扩展,抗裂纹扩展能力较差;而文石压痕周围平直清晰,裂纹沿着其二级结构界面扩展,性能较好.     

鲍鱼壳的结构和力学性能

以皱纹盘鲍鱼壳为对象,研究了其结构与力学性能之间的关系.研究表明,鲍鱼壳主要由方解石和文石构成,且外层为方解石,内层为文石.鲍鱼壳的力学性能随其加热温度的升高而明显降低,密度也呈现同样的变化,说明鲍鱼壳中所含有的少量有机质随着加热温度的升高而减少,致使鲍鱼的力学性能明显下降.     

In-vitro study on calcium carbonate crystal growth mediated by organic matrix extracted from fresh water pearls

For the purpose of studying the mediation of organic matrix on the crystallization of calcium carbonate, water soluble matrix (WSM), acid soluble matrix (ASM) and acid insoluble matrix (AIM) were extracted from aragonite pearls and vaterite pearls respectively. Then, in-vitro calcium carbonate crystallization experiments under the control of these six organic matrices were carried out in the present study. Scanning electron microscopy (SEM) was utilized to observe the morphology of CaCO₃ and Raman spectroscopy as a powerful technique was used to distinguish the crystal polymorph. Influences of the six kinds of organic matrices on the calcium carbonate crystal growth are proposed. ASM of vaterite pearls can induce vaterite to crystallize and WSM of aragonite pearls mediates to produce aragonite crystals. The single AIM membranes of the two pearls have no pronounced effect on the CaCO₃ crystallization. Additionally, the crystal size obtained with the additive of WSM of the two kinds of pearls is smaller than that with the additive of ASM. Moreover, self-assembly phenomenon in the biomineralization process and the distorted morphology calcite are observed. Current results demonstrate important aspects of matrix protein-controlled crystallization, which is beneficial to the understanding of nacre biomineralization mechanism. Further study of the precise control of these matrix proteins on CaCO₃ crystal growth is being processed.     

淡水珍珠的生物矿化机理研究进展

碳酸钙广泛存在于生物矿物中, 是地球上最普遍的生物矿物之一。贝壳和珍珠的主要组成部分为碳酸钙无机相。我国淡水养殖珍珠多数品质优异, 具有良好的珍珠光泽。该种珍珠以文石晶型碳酸钙为无机相, 称为文石珍珠。近年来, 在我国淡水养殖珍珠中发现了球文石的存在, 球文石的出现是导致珍珠失去光泽、降低质量的主要原因。本文对比阐述了淡水文石珍珠和球文石珍珠的微观结构与性能, 总结了与珍珠层有关的体外模拟碳酸钙生物矿化的实验结果, 提出了珍珠层生物矿化机理未来的研究方向。     

Mimicking the biomineralization of aragonite (calcium carbonate) using reverse-micelles under ambient conditions

Reverse micelles have been used, for the first time, to mimic the conditions suitable for the low-temperature (40 degrees C) synthesis of the high temperature and high pressure orthorhombic phase of calcium carbonate (aragonite) normally crystallizing in the sea as abalone shells and as natural pearls. The aragonite phase undergoes morphological changes under higher temperatures with long Y-junctions (at 40 degrees C) to shorter rod-like structures (at 85 degrees C). Pure calcite is obtained at higher reaction temperature. At a lower temperature (5 degrees C) homogeneous and monodisperse spheres of vaterite is obtained. The spherical particles after longer aging (168 h) aggregate to form nanorods and the self assembly is clearly seen at various stages by electron microscopic images.     

Aragonite Nanorods in Calcium Carbonate/Polymer Hybrids Formed through Self‐Organization Processes from Amorphous Calcium Carbonate Solution

Nanostructured inorganic/polymer hybrid thin films comprising aragonite nanorods derived from aqueous suspensions of amorphous calcium carbonate (ACC) are prepared. For the formation of calcium carbonate (CaCO₃)/polymer hybrids, spincoated and annealed films of poly(vinyl alcohol) (PVA) that function as polymer matrices are soaked in aqueous colloidal solutions dispersing ACC stabilized by poly(acrylic acid) (PAA). In the initial stage, calcite thin films form on the surface. Subsequently, aragonite crystals start to form inside the PVA matrix that contains PVA crystallites which induce aragonite nucleation. Nanostructured hybrids composed of calcite thin films consisting of nanoparticles and assembled aragonite nanorods are formed in the matrices of PVA.     

烧水壶水垢矿物组成及成因分析

用XRD、IR、SEM研究了家用烧水壶水垢矿物物相组成、相含量以及矿物形貌,并探讨了各物相成因。研究发现,家用热水壶水垢化学成分主要为碳酸钙,矿物物相主要由文石和方解石组成,以文石相为主,质量占92．8％,方解石占7．2％。文石相主要形成于70～90℃,而方解石则主要形成于较低温度。     

泡沫铝填充多棱管的吸能分析

通过LS-DYNA模拟分析泡沫铝填充多棱管的准静态过程。以柱壳比（R）作为比较具有不同截面形状的泡沫铝填多棱管的依据。通过比吸能、比力和能量吸收率,实现泡沫铝填充多棱管吸能性能的定量化比较分析。研究发现在具有相同柱壳比的条件下,泡沫铝填充四棱管的比吸能最高;泡沫铝填充八棱管的能量吸收率最高（约78%）;四棱管的吸能量占泡沫铝填充四棱管总吸能量的比例最小（约57%）。不同的几何形状和结构对泡沫铝填充多棱管的吸能性能有着显著的影响。同时,对泡沫铝填充多棱管的变形模式和内在机制也做了初步的分析     

Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite

The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy–electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research.     

Self-referenced prism deflection measurement schemes with microradian precision

We have demonstrated several inexpensive methods that can be used to measure the deflection angles of prisms with microradian precision. The methods are self-referenced, where various reversals are used to achieve absolute measurements without the need of a reference prism or any expensive precision components other than the prisms under test. These techniques are based on laser interferometry and have been used in our laboratory to characterize parallel-plate beam splitters, penta prisms, right-angle prisms, and corner cube reflectors using only components typically available in an optics laboratory.     

Thermal modeling of solid nonfocusing pump-light collectors used for diode-pumped Nd:YAG lasers

We have developed a thermal model for the determination of the temperature distribution of a diode side-pumped Nd:YAG laser in which the laser rod is fixed in a solid nonfocusing (prismatic) pump-light collector. The model permits the temperature to be determined as a function of both spatial and temporal parameters for a wide range of boundary conditions and different collector materials. Interferometric measurements were carried out to obtain the averaged rod temperatures for comparison with results from the model and to fix a convective-cooling rate for ambient air that best fits the experimental results. Two cases were studied both theoretically and experimentally with artificial sapphire and BK7 as prism materials, and good agreement was achieved between model and experimental results. The use of artificial sapphire as the prism material reduces by a factor of ~7 both the rod temperature and the warm-up time compared with BK7 glass. Peltier cooling of the underside of the BK7 glass prism yields thermal Characteristics of the device that are similar to those devices with sapphire prisms. Calculations also show that the thermal properties of the fixant are not critical for moderate fixant thermal diffusivities (i.e., k(f) > 10(-8)-10(-7) m(2) s(-1)), thus the choice of an appropriate fixant can be based on its mechanical and index-matching properties alone.     

On the kinetics of phase transformations of dried porous vaterite particles immersed in deionized and tap water

Calcium carbonate exists in three allotropic forms: vaterite, aragonite and calcite. Metastable vaterite can be easily transformed into calcite and/or aragonite via different routes. We report how dry vaterite particles transform into aragonite and calcite when they are immersed into DeIonized water (DI) or tap water without additives at different temperature (22, 40 and 60?°C) with and without stirring. We show that the transformation rate of vaterite into more stable crystallographic forms is influenced not only by temperature but also by stirring and water purity. Low temperature, absence of stirring and absence of ions in water significantly slow down the kinetics of transformation of vaterite. Additionally, water purity influences the nature of the allotropic phase obtained after transformation. High temperatures and DI water favor the transformation of vaterite into single crystalline nanowires of aragonite, while tap water yields the transformation of vaterite into calcite. The absence of aragonite in tap water at high temperature can be explained by the presence of sulfate ions, which inhibit the formation of this phase. On the contrary, Mg²⁺ ions tend to stabilize vaterite.     

Design and fabrication of a freeform prism array for 3D microscopy

Traditional microscopes have limitations in obtaining true 3D (three-dimensional) stereovision. Although some optical microscopes have been developed for 3D vision, many of them are complex, expensive, or limited to transparent samples. In this research, a freeform optical prism array was designed and fabricated to achieve 3D stereo imaging capability for microscope and machine vision applications. To form clear stereo images from multiple directions simultaneously, freeform optical surface design was applied to the prisms. In a ray tracing operation to determine the optical performance of the freeform prisms, Taylor series was used to calculate the surface shape. The virtual image spot diagrams were generated by using ray tracing methods for both the freeform prisms and the regular prisms. The results showed that all the light rays can be traced back to a single point for the freeform prism, and aberration was much smaller than that of the regular prism. The ray spots formed by the freeform prisms were adequate for image formation. Furthermore, the freeform prism array was fabricated by using a combined ultraprecision diamond turning and slow tool servo broaching process in a single, uninterrupted operation. The slow tool servo process ensured that the relative tolerance among prisms is guaranteed by the precision of the ultraprecision machine without the need for assembly. Finally 3D imaging tests were conducted to verify the freeform prism array's optical performance. The principle of the freeform prism array investigated in this research can be applied to microscopy, machine vision, robotic sensing, and many other areas.     

Comparative study on nano-mechanics and thermodynamics of fish otoliths

Fish otolith is a kind of typical natural biomineral, which is composed of calcium carbonate and organic matrix. In fresh water carp otolith, the inorganic phase of lapillus is pure aragonite, and for asteriscus it is pure vaterite. In this research, the phase composition, phase transformation, mechanical property and solubility of lapillus and asteriscus were studied. And results showed that, the organic content of lapillus was higher than that of asteriscus; the phase-transition temperature of lapillus (aragonite–calcite) and asteriscus (vaterite–calcite) both happened between 520 and 640 °C; the nano-mechanical property of lapillus was better than that of asteriscus; the solubility of asteriscus powder was higher than that of lapillus powder.