碳酸化工艺参数对碳酸钙结晶习性的影响

研究了搅拌速度、反应温度和镁钙离子浓度比三种工艺参数对碳酸钙结晶习性的影响．指出反应温度的升高有利于碳酸钙以文石相结晶,但在无镁离子存在的高纯原料情况下,并不能使文石相碳酸钙形成;镁钙离子浓度比是影响碳酸钙结晶习性的决定性因素．     

钙离子镁离子共存的纯无机环境中镁方解石介观晶体的形成及其生物学意义

镁方解石介观晶体广泛分布于具有特殊功能的生物矿物中.至今,在排除有机添加剂的参与后合成镁方解石介观晶体仍是一个很大的挑战,同时海洋中镁方解石的形成机理尚不明确.本工作以纯的无定形碳酸钙(ACC)为前驱体,在钙离子镁离子共存的无机环境中控制结晶条件得到了由许多共同结晶取向的纳米晶组成的玉米状镁方解石.在结晶过程中,ACC...     

矿物基负离子发生材料的结构和组成特征

用X射线粉末衍射仪、X射线能谱仪和等离子体原子发射光谱仪分析了多种矿物基材料的主物相结构和元素组成,并用离子检测仪测定了各材料的负离子发生量.研究表明,具有负离子发生功能的矿物基材料可以由具有明显压电、热电效应的矿物组成,也可以由含有一定量稀土元素和天然原生放射性核素的矿物组成.矿物中适量天然原生放射性核素的存在对于制备高性能的矿物基负离子发生材料是有益的.     

氧化处理时间对Ti6Al4V微弧氧化陶瓷膜的影响

采用交流微弧氧化法于：Na：SiO3-KOH-(NaPO3)6溶液中在％6A14V表面形成了氧化物陶瓷膜．利用扫描电镜、电子探针及X射线衍射研究了陶瓷膜的组织形貌、元素的分布和相组成．研究表明：在恒定的微弧氧化电参数(U =500V，U-=100V和f=600Hz)下，随氧化时间延长，电流密度逐渐降低，膜层厚度不断增加；相对致密均匀的膜分为3层：过渡层、致密层与疏松层．膜层主要由TiO2(锐钛矿和金红石)相组成，延长处理时间，锐钛矿相及金红石相的相对含量发生变化，金红石相TiO2逐渐增多，而锐钛矿相TiO2减小．膜层相的形成过程可分为两个阶段。     

针状碳酸钙制备中氯化镁晶型导向剂的套用研究

以MgCl₂为晶型导向剂制备了形貌规整的文石相针状碳酸钙, 其粒径为2.5~5.0μm, 长径比为10~20. 采用EDTA络合滴定碳化后回收滤液中Ca²⁺、Mg²⁺含量以确定需补加MgCl₂量, 并在相同的碳化工艺条件下逐步改进套用回收液的方法制备针状碳酸钙. 产品用SEM、XRD进行形貌观察和晶型组成分析. 结果表明, 随着套用次数的增加, 碳酸钙产品中文石相的含量逐渐降低, 当文石相的含量低于80%时, 针状碳酸钙的长径比也大幅下降, 同时生成大量微细立方状方解石相碳酸钙, 将不适合继续套用. 直接套用回收液时只能循环使用1次, 而将套用的回收液经补加Mg²⁺、加酸调节pH等优化处理后可使套用次数延长至12次, 这将大幅降低针状碳酸钙的生产成本.     

贝壳资源的深加工利用

以牡蛎壳为原料,对其物相组成、结构等进行分析,然后将牡蛎壳进行煅烧,考察煅烧工艺对于产物氧化钙的活性、有效钙含量、白度以及微观结构等性能的影响,最后将煅烧产物进行消化和碳化,制备纳米碳酸钙.研究结果表明,牡蛎壳中碳酸钙为方解石晶型,含量高达95.87％,是一种优质的海洋生物碳酸钙资源.牡蛎壳煅烧过程中,随着煅烧温度的提...     

某含砷微细粒金矿石浮选-氧化预处理-氰化提金试验研究

某金矿石中的金属矿物主要有黄铁矿、毒砂等,金矿物以自然金的形式存在且颗粒细小,属于微细粒金,大部分被金属硫化矿包裹。试验采用浮选法富集金矿物,获得了金品位63．8g／t,金回收率92．08％的金精矿,并对金精矿进行了常温常压碱性氧化预处理,处理后的精矿金氰化浸出率达到88．56％,该金矿石选冶总回收率达到81．55％。     

非电解盐浴硼硅共渗层组织的研究

研究了在添加还原剂、稀释剂的Na2SiO3-Na2B4O7盐浴中碳钢的硼硅共渗层组织及其形成规律。结果表明，共渗层相受控于盐浴成分，工艺参数对相组成物无明显影响。     

聚酰胺／聚苯硫醚共混物摩擦学性能研究——（I）干摩擦

制备了一系列不同组成的聚酰胺(PA66)和聚苯硫醚(PPS)共混物，对材料的摩擦学性能进行了研究。结果表明，80％φ（PA66)／20％φ（PPS)共混物的摩擦学性能最好。借助扫描电子电镜(SEM)和能量色散谱(EDS)等手段，分析认为，PA66在对偶钢环上形成了不均匀、不连续的牢固转移膜，PPS则不能形成转移膜；共混物中PA66相的存在增强了PPS向对偶面上转移的能力。“摩擦热控制模型”适用于PA66／PPS共混物体系，材料的磨损由其在对偶面上形成转移膜的能力及转移膜的性质控制。     

利用熟料岩相分析提高熟料强度

水泥强度的影响因素主要来自水泥熟料的矿物组成和形态,以及水泥的颗粒组成、颗粒形貌和细度等方面.就熟料矿物而言,硅酸盐相是影响水泥强度的主要因素,硅酸盐矿物的含量是决定水泥强度的主要因素.一般来说,熟料抗压强度越高,抗折强度也越高,在矿物组成对强度的影响方面,往往较多地研究其对抗压强度的影响,本文通过实例对熟料岩相分析提高熟料强度做了简单的分析.     

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.     

Morphology and polymorphic phase changes of calcium carbonate micro/nanocrystals using fruit extracts

This study reveals the morphology and polymorphic phase changes of calcium carbonate crystals into a mixture of calcite and aragonite micro/nanocrystals of interesting morphology at room temperature by a simple reaction with fruit extracts of Tamarindus indica and Emblica officinalis respectively by mixing CaCO3 solutions with their corresponding extracts. The control experiments were carried out to establish the plausible role of tartaric acid from Tamarindus indica and ascorbic acid from Emblica officinalis in this regard. The quantitative determination of CaCO3 phases was done based on the use of intensities obtained from corresponding XRD spectrum. The molar % of aragonite was found to be more in case of TA and AA rather than TI and EO respectively, however the calcite was observed to be the predominant phase in all four reactions. Interestingly, the TI changes the rhombohedral morphology of calcite to elongated rods, whereas EO induces a great polymorphic phase change.     

Transitions of calcium carbonate crystals controlled by self-assembly supermolecule of β-cyclodextrin and sodium dodecyl benzene sulfonate

The transitions from vaterite to calcite and from vaterite to aragonite, were found with the anionic surfactant sodium dodecyl benzene sulfonate and β-cyclodextrin as a template, respectively, when the experimental temperature was controlled at 90 °C. The transition from calcite to aragonite was found when the experimental temperature was controlled at 120 °C. The molar ratio of 1:1 and 1:2 supermolecules composed of sodium dodecyl benzene sulfonate ion and β-cyclodextrin molecule may be formed at 90 and 120 °C, respectively. The possible formation mechanisms of different CaCO₃ polymorphs are proposed based on the “structural correspondence”.     

Monohydrocalcite: a promising remediation material for hazardous anions

The formation conditions, solubility and stability of monohydrocalcite (MHC, CaCO₃·H₂O), as well as sorption behaviors of toxic anions on MHC, are reviewed to evaluate MHC as a remediation material for hazardous oxyanions. MHC is a rare mineral in geological settings that occurs in recent sediments in saline lakes. Water temperature does not seem to be an important factor for MHC formation. The pH of lake water is usually higher than 8 and the Mg/Ca ratio exceeds 4. MHC synthesis experiments as a function of time indicate that MHC is formed from amorphous calcium carbonate and transforms to calcite and/or aragonite. Most studies show that MHC forms from solutions containing Mg, which inhibits the formation of stable calcium carbonates. The solubility of MHC is higher than those of calcite, aragonite and vaterite, but lower than those of ikaite and amorphous calcium carbonate at ambient temperature. The solubility of MHC decreases with temperature. MHC is unstable and readily transforms to calcite or aragonite. The transformation consists of the dissolution of MHC and the subsequent formation of stable phases from the solution. The rate-limiting steps of the transformation of MHC are the nucleation and growth of stable crystalline phases. Natural occurrences indicate that certain additives, particularly PO₄ and Mg, stabilize MHC. Laboratory studies confirm that a small amount of PO₄ in solution (>30 μM) can significantly inhibit the transformation of MHC. MHC has a higher sorption capacity for PO₄ than calcite and aragonite. The modes of PO₄ uptake are adsorption on the MHC surface at moderate phosphate concentrations and precipitation of secondary calcium phosphate minerals at higher concentrations. Arsenate is most likely removed from the solution during the transformation of MHC. The proposed sorption mechanism of arsenate is coprecipitation during crystallization of aragonite. The arsenic sorption capacity by MHC is significantly higher than simple adsorption on calcite.     

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.     

Monohydrocalcite: a promising remediation material for hazardous anions

Abstract

The formation conditions, solubility and stability of monohydrocalcite (MHC, CaCO₃·H₂O), as well as sorption behaviors of toxic anions on MHC, are reviewed to evaluate MHC as a remediation material for hazardous oxyanions. MHC is a rare mineral in geological settings that occurs in recent sediments in saline lakes. Water temperature does not seem to be an important factor for MHC formation. The pH of lake water is usually higher than 8 and the Mg/Ca ratio exceeds 4. MHC synthesis experiments as a function of time indicate that MHC is formed from amorphous calcium carbonate and transforms to calcite and/or aragonite. Most studies show that MHC forms from solutions containing Mg, which inhibits the formation of stable calcium carbonates. The solubility of MHC is higher than those of calcite, aragonite and vaterite, but lower than those of ikaite and amorphous calcium carbonate at ambient temperature. The solubility of MHC decreases with temperature. MHC is unstable and readily transforms to calcite or aragonite. The transformation consists of the dissolution of MHC and the subsequent formation of stable phases from the solution. The rate-limiting steps of the transformation of MHC are the nucleation and growth of stable crystalline phases. Natural occurrences indicate that certain additives, particularly PO₄ and Mg, stabilize MHC. Laboratory studies confirm that a small amount of PO₄ in solution (>30 μM) can significantly inhibit the transformation of MHC. MHC has a higher sorption capacity for PO₄ than calcite and aragonite. The modes of PO₄ uptake are adsorption on the MHC surface at moderate phosphate concentrations and precipitation of secondary calcium phosphate minerals at higher concentrations. Arsenate is most likely removed from the solution during the transformation of MHC. The proposed sorption mechanism of arsenate is coprecipitation during crystallization of aragonite. The arsenic sorption capacity by MHC is significantly higher than simple adsorption on calcite.     

自石灰石矿粉中直接提取CaCO3晶须的碳化-分解法研究

提出一种自石灰石矿粉中直接提取CaCO_3晶须的碳化-分解方法。该方法能够以天然石灰石矿粉为原料,通过水溶性碳酸的作用溶解出Ca(HCO_3)_2,进而在升温条件下通过Ca(HCO_3)_2的分解反应得到形貌规整的棱锥状CaCO_3晶须。扫描电镜观测与X射线衍射分析显示,Ca(HCO_3)_2分解温度对CaCO_3晶须微观形貌的影响显著,晶须长度与长径比随分解温度的升高均呈上升趋势,但分解温度超过80℃会导致文石晶相向方解石晶相转化。实验结果表明,80℃、2h条件下,Ca(HCO_3)_2分解产物中文石晶相含量较高,晶须几何形貌更为合理,其平均长度为14.61 μm、长径比为8.10。     

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.     

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 observed in the prismatic layer of seawater-cultured pearls

The prismatic layer is obviously different from the parallel layer in seawater-cultured pearls. X-ray diffraction (XRD), optical microscopy (OM) and micro-infrared (IR) spectroscopy have been applied to characterize the crystallized layers of high- and low-quality seawater-cultured pearls produced in South China. The result shows that the prismatic layer is not only composed of calcite as reported in previous researches. Three types of prisms were found in seawater-cultured pearls: calcite prism, aragonite prism and calcite and aragonite prism. Therefore, we have a new understanding of the biomineralization of the prismatic layer in seawater-cultured pearls. The result makes us review the traditional viewpoint that the increased content of aragonite improves the quality of pearls. We discovered that some seawater prismatic pearls almost completely composed of aragonite have the worst quality. We thought that the thickness and the spatial distribution of prisms are the main factors that can affect the quality of seawater-cultured pearls.