乙醇-水混合溶液中碳酸钙晶须的合成

不加任何添加剂,在乙醇-水的体积比为V(乙醇):V(水)=1:1、温度50℃、原料浓度0.25mol/L的条件下,利用沉淀法制得了大小均匀、长度为10～30μm、长径比为20～30:1的文石型碳酸钙晶须.同时,实验中还得到了树枝形和稻穗状等特殊形貌的晶体.用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、红外光谱仪(...     

Quantification of chemical and biological calcium carbonate precipitation: Performance of self-healing in reinforced mortar containing chemical admixtures

Cracks increase permeability affecting the durability of concrete. As they develop gradually, it is difficult to determine when to repair them. Self-healing materials can repair themselves gradually as cracks form. In this study, the isolated and combined effect of two self-healing agents for concrete, both based on calcium carbonate precipitation, was studied. Lightweight aggregates were impregnated with chemical and biological solution to be added as healing agents in concrete mixtures. The influence of two common chemical admixtures on the performance of the self-healing agents was also studied. All self-healing agents were able to seal cracks between 0.08 and 0.22 mm in width. The estimated effect of chemical agents on the mean healing was higher than that of biological agents. In addition, thermogravimetric analysis suggests the precipitates are different. Admixtures had no significant influence on the performance of self-healing agents.     

一种基于微生物沉积的水泥砂浆表面改性技术

某些微生物能诱导沉积出具有胶凝和矿化作用的碳酸钙,可以用来修复和密实水泥基材料。但是目前微生物沉积技术工艺复杂,成本高,不利于推广和工程应用。尝试采用水泥砂浆粉作为覆膜载体,利用巴斯德芽孢杆菌对水泥砂浆进行表面处理。研究结果表明,采用该方法能使巴斯德芽孢杆菌在水泥试块表面诱导沉积出碳酸钙,有效减少水泥砂浆的吸水性能。当微生物采用含有尿素的培养基培养时,表面改性后的水泥砂浆吸水系数降低了58%。采用压汞测试仪(MIP)分析了处理前后水泥试块表层的孔隙率以及孔结构特征。发现采用巴斯德芽孢杆菌处理后,样品孔隙率显著降低,大孔的含量显著减少,当微生物采用含有尿素的培养基培养时,总孔隙率降低了40%。X射线衍射仪(XRD)和场发射扫描电镜(SEM)分析表明,经微生物技术处理后水泥试块内部的孔洞和裂缝被球霰石和方解石填充。     

Hydrothermal synthesis of various carbonate containing calcium hydroxyapatites

Carbonate containing hydroxyapatites were prepared hydrothermally between 2000 and 20,000 psi and 250 and 900°C using H₂O or CO₂ pressure. On the basis of IR, x-ray and chemical investigations it is shown that under these conditions the CO₃ triangle can replace both the OH group and PO₄ tetrahedron in the apatite structure. Replacement is possible either in only one of these positions or also combined. The extent of the solid solubility, however, is still unknown.     

Mineralization of calcium carbonate by controlled release of carbonate in aqueous solution

The generation of carbon dioxide from organic precursors in aqueous media in presence of calcium chloride and under conditions where calcium carbonate is formed was investigated. Photochemical decomposition of pyruvic acid, 2-nitro-phenylacetic acid and 4-benzoylphenyl acetic acid gave ill-defined morphologies of calcium carbonate contaminated by organic by-products. Alkaline hydrolysis of dimethyl- and diethyl-carbonate yielded amorphous calcium carbonate in form nanospheres of narrow distribution of radii if the precipitation occurred under quiescent conditions. Addition of a polymer surfactant gave spherical particles as well, however consisting of vaterite.The formation of spherical particles of amorphous calcium carbonate is rationalized in terms of a liquid–liquid phase separation followed by rapid gelation of the droplet phase of high concentration of calcium carbonate. A lower critical solution temperature is postulated and its value was estimated as 10 °C.     

Crystallization of strontium carbonate in alcohol or water solution containing mixed nonionic/anionic surfactants

The crystallization of strontium carbonate is performed in aqueous solution or alcohol/water solution in the presence of mixed nonionic/anionic surfactants Pluronic F127/sodium dodecyl sulfate. With an increase of the volume ratio of ethanol/water, SrCO₃ pancakes transform into flowers, and then to irregular flakes. X-ray diffraction (XRD) pattern reveals that both of pancake-like and flower-like SrCO₃ particles are orthorhombic phases. Larger pancakes with porous structure are produced when the content of ethylene glycol reaches a relatively high value. Results indicate that -OH groups of alcohol play an important role in morphological controlling of SrCO₃.     

Formation of carbonate apatite on calcium phosphate coatings containing silver ions

The prerequisite for bioactive materials to bond to living bone is the formation of biologically equivalent carbonate apatite on their surfaces in the body. Calcium phosphate ceramic surfaces can be transformed to a biological apatite through a series of surface reactions including dissolution–precipitation and ion exchange. In the present work, apatite coatings with different crystallinity, compositions and crystal sizes, including a well-crystallized hydroxyapatite coating, were synthesized electrochemically and doped with silver ions in silver nitrate solution at room temperature. The formation of a new carbonate apatite on the surface of these coatings was investigated in an acellular simulated body fluid with ion concentrations comparable with those of human blood plasma, using scanning electron microscopy and Fourier transform-infrared spectroscopy. The results show that small quantities of silver ions incorporated into apatite coatings may have a strong stimulatory effect on the formation of carbonate apatite without adversely affecting the chemical stability of these coatings.     

Effect of magnetic field treated water on mortar and concrete containing fly ash

This research investigates the workability and compressive strength of mortar and concrete, which were mixed with magnetic field treated water (MFTW) and contained fly ash. MFTW was obtained by passing tap water through a magnetic field. Test variables included the magnetic strength of water, fly ash content in place of cement, water-to-cementitious material ratio (W/CM) and curing age.Results show that the compressive strength of mortar samples mixed with MFTW is higher than those prepared with tap water. The best compressive strength increase of concrete is achieved when the magnetic strength of treated water is of 0.8 and 1.2 T. The compressive strength increase of concrete prepared with MFTW is more significant at early age.     

Preparation of calcium carbonate microparticles containing organic fluorescent molecules from vaterite

The encapsulation of fluorescent organic molecules into crystalline calcium carbonate was examined using calcium carbonate microcapsule, whose crystalline phase is vaterite as a metastable phase of calcium carbonate. A calcium carbonate microcapsule with impregnated pyrene that is a water insoluble fluorescent molecule was soaked into suitable aqueous solutions to promote the phase transition of vaterite toward calcite as the stable phase of calcium carbonate. When 0.2 M calcium chloride solution was used, the largest amount of pyrene (approximately 0.06 wt%) was encapsulated into the calcite particle. Pyrene thus included was not eliminated even after thorough washing with THF. The calcite particle thus prepared produced the excimer emission of pyrene by UV irradiation. Rhodamine B was also introduced into calcium carbonate by the immersion of the microcapsule into the aqueous solutions of Rhodamine B. The fluorescence of rhodamine B was observed from the calcium carbonate particles by visible light irradiation. Acetaminophen, a common drug poorly soluble in water, was also included in the calcium carbonate particle by the same procedures as the pyrene encapsulation. As acetaminophen thus encapsulated was released by the dissolution of the calcium carbonate particle in acidic solution, the particle is expected to be applied for a dissolution-triggered drug delivery.     

Control the polymorphism and morphology of calcium carbonate precipitation from a calcium acetate and urea solution

Two metastable calcium carbonate polymorphs, rod-like aragonite and spherical vaterite are selectively formed in this study. Aragonite rods were synthesized from a calcium acetate (Ca(AC)₂) and urea (CO(NH₂)₂) solution under a given condition. In contrast, the addition of polyacrylamide (PAM) and oleic acid results in the formation of spherical vaterite. The morphology, size and crystal structure were characterized by means of Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and X-ray diffraction (XRD). The results show that PAM and oleic acid can be used as additives to select the polymorph from aragonite and vaterite. The contact angle of the modified products reached 112.49°. We have succeeded in surface modification of particles in situ at the same time.     

Influence of interactions on the tensile behaviour of polystyrene filled with calcium carbonate

Mechanical properties of filled polymers are dependent on a lot of parameters: matrix properties, particles characteristics (nature, size, shape, size distribution), constituent volume fraction and particle-particle and matrix-filler interactions. In this work, mainly devoted to polymer-filler interactions, the tensile behaviour of calcium carbonate-filled polystyrene is examined for different kinds of filler surface modification: carboxylic acid adsorption and polystyrene or polybutyl acrylate grafting. Experimental relative tensile strength of the composite varies mainly with the matrix proportion in the fracture surface and with the matrix-filler interactions: adhesion level and matrix-particle stress transfer. The model enables the calculation of dewetting angles which are a very good representation of the filler-matrix adhesion level.     

Optimization of process parameters of polymer solution mediated growth of calcium carbonate nanoparticles

With the advent of nanotechnology, many methods of synthesis of nanoparticles have come into practice and the 'polymer mediated growth' technique is among them. In this route, ions of one of the reactants are allowed to diffuse from an external solution into a polymer matrix where the other reactant is complexed and bound. The exact role of ionic diffusion in the formation of nanoparticles was investigated in the current study by studying the patterns of kinetics of nanoparticle formation using UV vis spectroscopy. Typically, calcium carbonate nanoparticles were formed by the aforementioned technique using polyethylene glycol solution. The particle size was calculated using Scherrer's formula on x-ray diffraction plots and was reconfirmed with field emission scanning electron microscope and transmission electron microscope images. Energy-dispersive x-ray analysis was used to study the composition and purity of the nanoparticles formed. The reactant to polymer ratio, reaction temperature and molecular weight of polyethylene glycol affected the size of the particles formed. Through this knowledge we optimized these parameters to obtain particles as small as 20?nm and confirmed that this technique can be used to control the size of nanoparticles.     

Rheology,fiber distribution and mechanical properties of calcium carbonate (CaCO3) whisker reinforced cement mortar

Calcium carbonate (CaCO₃) whiskers are a new kind of microfiber used in cementitious composites and have proved to provide excellent effect on strengthening and toughening. In order to further improve the mechanical properties of CaCO₃ whisker-reinforced cementitious composites, rheological properties of fresh mixtures and the CaCO₃ whisker distribution in the hardened matrix were investigated. The yield stress and plastic viscosity increased with an increasing content of CaCO₃ whisker and a decreasing water-cement ratio. Also, the rheological properties were affected by the distribution of CaCO₃ whisker in the matrix. The largest increments in flexural and compressive strength were 27.59% and 12.60% for the mortars with CaCO₃ whisker contents of 2.0% and 1.5%, respectively. The properties responsible for the mechanical response were explained in terms of the effects of CaCO₃ whisker reinforcement, the distribution of CaCO₃ whiskers, and the porosity as well as pore size distribution.     

Synthesis and mechanical characterization of polymer-matrix composites containing calcium carbonate/white cement filler

With a view to develop polymer-matrix composites of high mechanical strength, composites containing 0.5% to 5.0% of each of calcium carbonate or white cement were prepared by uniformly mixing polystyrene and inorganic materials followed by casting in an aluminum mold. The values of fracture toughness, flexural strength and elastic modulus were found to increase with increasing amount of the inorganic component in the polymer. In addition, for a given percentage of inorganic components, the values of mechanical strength of white cement containing composites were found to be more than those of calcium carbonate containing composites. The optical microphotographs of the composites show that there is uniform distribution of filler in the polymers.     

Fracture behavior dependence on load-bearing capacity of filler in nano- and microcomposites of polypropylene containing calcium carbonate

The fracture toughness and deformation mechanism of PP/CaCO₃ (15 wt.%) composites were studied and related to load-bearing capacity of the particles. To alter the load-bearing capacity of the particles, different particle sizes (0.07–7 μm) with or without stearic acid coating were incorporated. The fracture toughness of the composites was determined using J-Integral method and the deformation mechanism was studied by transmission optical microscopy of the crack tip damage zone. It was observed that the load-bearing capacity of the particles decreased by reduction of particle size and application of coating. A linear relationship between normalized fracture toughness and inverse of load-bearing capacity of particles was found. The crack tip damage zone in composites, which consists in massive crazing, further grows by reduction in load-bearing capacity.     

Effect of the formation conditions of a carbonate film in sea water on corrosion of nonpassivating steels

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 4, pp. 32–35, July–August, 1990.     

In vitro study investigating the mechanical properties of acrylic bone cement containing calcium carbonate nanoparticles

A successful total hip replacement has an expected service life of 10-20 years with over 75% of failures due to aseptic loosening which is directly related to cement mantle failure. The aim of the present study was to investigate the addition of nanoparticles of calcium carbonate to acrylic bone cement. It was anticipated that an improvement in mechanical performance of the resultant nanocomposite bone cement would be achieved. A design of experiment approach was adopted to maximise the mechanical properties of the bone cement containing nanoparticles of calcium carbonate and to determine the constituents and preparation methods for which these occur. The selected conditions provided improvements of 21% in energy to maximum load, 10% in elastic modulus, 7% in bending strength and 8% in bending modulus when compared with bone cement without nanoparticles. Although cement containing nanoCaCO(3) coated in sodium citrate also enhanced the energy to maximum load by 28% and the elastic modulus by 14% when compared with control cement, it is not recommended as a factor in the production of nanocomposite bone cement due to reduction in the bending properties of the final bone cement.     

脲解型微生物诱导碳酸钙沉积研究

研究了钙源种类对脲解型微生物诱导碳酸钙沉积的生物-化学过程的影响。利用电位分析法实时测试了沉积过程中钙离子、铵离子及pH值的变化,并利用显微计数对细菌浓度进行了监测。采用扫描电镜(SEM)、X射线衍射(XRD)和分析红外光谱(IR)对沉积产物进行了研究。结果表明,不同钙源环境下脲解型微生物诱导矿化沉积都存在化学沉淀、微生物诱导矿化沉积和沉淀完全3个阶段;有机钙源环境下细菌的产矿动力比在无机钙源中高,且两种钙源所获得的方解石晶体沉积物在形貌上差异显著。     

Constant-distance mode scanning potentiometry. 1. Visualization of calcium carbonate dissolution in aqueous solution

Constant-distance mode scanning potentiometry was established by integrating potentiometric microsensors as ion-selective scanning probes into a SECM setup that was equipped with a piezoelectric shear force-based tip-to-sample distance control. The combination of specially designed micrometer-sized potentiometric tips with an advanced system for tip positioning allowed simultaneous acquisition of both topographic and potentiometric information at solid/liquid interfaces with high spatial resolution. The performance of the approach was evaluated by applying Ca(2+)-selective constant-distance mode potentiometry to monitor the dissolution of calcium carbonate occurring either at the (104) surface of calcite crystals or in proximity to the more complex surface of cross sections of a calcium carbonate shell of Mya arenaria exposed to slightly acidic aqueous solutions. Micrometer-scale heterogeneities in the apparent calcium activity profiles have successfully been resolved for both samples.