相场再结晶储能释放模型与显微组织演变的模拟研究

在相场再结晶模型中提出了形式为 f(η_i^k,η_j^k) = E_s (η_i^de )² (1-(η_j^re)²)的冷变形储能项,并应用该模型模拟了 AZ31镁合金的再结晶过程,模拟结果和实验观测结果符合很好.研究表明, 引入储能释放模型可以实现再结晶形核物理过程的模拟; 模拟结果可以把合金在冷变形后退火的过程按照机理分为再结晶和热晶粒 长大两个阶段,模拟得出的理论再结晶时间是实验再结晶时间的2/3. 考察了冷变形应变大小对形变金属的亚晶粒尺寸和储能的影响机理和 试验结果,并将考察结果代入到改进后的再结晶模拟模型, 成功地再现了一个经典实验结果:随预先应变量的增加, 存在临界应变量对应的一个再结晶晶粒尺寸峰值.同时还给出了 这一经典实验结果的理论解释.     

利用聚乙烯亚胺修饰的CaCO3仿生模板合成3D花朵型二氧化硅微球

利用聚乙烯亚胺(PEI)修饰的碳酸钙仿生模板合成了具有3D花朵型形貌的SiO₂微球.通过调整碳酸钙微粒表面不同浓度PEI的吸附量实现SiO₂微球的形貌控制呈现花朵或刀锋的形状. 用XPS和SEM对制备的SiO₂微粒进行表征. 结果表明,不用浓度的PEI修饰可以较好地控制3花朵型DSiO₂微球的形貌.     

调幅分解及形核对相分离作用机理研究

以SCN-30wt%H₂O, SCN-50 wt%H₂O和SCN-80 wt%H₂O三组透明体系, 在恒温场下实现了形核和调幅分解两种过程; 在此基础上, 施加温度梯度, 研究了第二相液滴的迁移运动规律. 结果表明, 相分离在临界成分体系以调幅分解方式进行, 在另外两种体系中以形核长大方式进行; 调幅分解与形核过程相比, 反应进行得更快, 液滴长大到同一尺寸所需时间仅为形核所需时间的1/3—1/2. 且临界成分体系有更大的不混溶间隙, 所以第二相液滴具有更多迁移时间, 揭示了偏晶体系相分离过程中在临界成分处易获得壳-核组织的内在机理. 在单向温度场中, 测量了不同半径的液滴迁移速率, 并且与理论Marangoni迁移速率值作比较, 发现液滴迁移速率和Marangoni理论迁移速率符合较好. 说明了在较好地抑制自然对流条件下Marangoni迁移对于相分离过程起主要作用.     

聚(N-异丙基丙烯酰胺)模板法制备二氧化硅中空微球

以在50 oC水溶液中析出的聚(N-异丙基丙烯酰胺) (PNI-PAM)聚集体作为软模板,使正硅酸乙酯吸附在PNIPAM聚集体表面进行水解缩合,原位生成二氧化硅包裹PNIPAM的核壳结构微球;进一步冷却至室温使PNIPAM溶解在水中除去内核,从而成功合成出SiO₂中空微球．实验表明,只有在足够的PNIPAM和正硅酸乙酯含量以及正硅酸乙酯水解时间下,才能形成稳定的SiO₂中空微球．用TEM、SEM和FTIR对合成的SiO₂中空微球进行了表征,结果表明,微球尺寸为150 nm左右,并且由于PNIPAM上酰胺基团和正硅酸乙酯水解出来的硅醇间具有静电相互作用,使得SiO₂壳层上依然有PNIPAM残留.     

鼻腔滴入Fe2O3细颗粒在小鼠嗅球中的微区分布及对其他微量元素的影响

用同步辐射X射线荧光(SRXRF)微区扫描分析技术研究了经鼻吸入三氧化二铁(Fe₂O₃)细颗粒后, Fe在小鼠嗅球中的分布及其对Ca, Zn, Cu等其他微量元素分布的影响.研究发现经鼻吸入40 mg/kg体重Fe₂O₃(60—200nm)细颗粒, Fe可以通过鼻粘膜在小鼠嗅球中富集. 小鼠嗅球切片中Fe的浓度比对照组升高了20%.通过SRXRF微区扫描分析发现, Fe在嗅球的嗅神经纤维层(ON)、突触小球层(Gl)和前嗅核外部(AOE)的 浓度比对照组显著升高, 表明Fe₂O₃颗粒已经由初级嗅神经进入到嗅球小球层, 进而沿次级嗅神经进入前嗅核外部(AOE).同时, 吸入Fe₂O₃细颗粒还使小鼠嗅球中Ca浓度比对照组分别升高了12%, Zn的浓度则下降了17%, 而Cu的浓度与对照组接近, 但Cu在嗅球各层中的分布发生了明显变化. 升高的Ca主要分布在嗅神经层和小球层.实验组嗅神经层、小球层和外丛层(EPl)中Cu的浓度与对照组相比有显著升高, 而在前嗅核外侧部(AOL)、前嗅核外部(AOE)、副嗅球颗粒细胞层(GrA)和副嗅球(AOB)层中浓度降低了. 说明进入脑嗅球组织中的Fe已经对脑组织中微量元素的含量和分布产生了影响.     

Superacid Catalyst SO42-/ZrO2-La2O3 Prepared by Ultrasonic Co-precipitation and Low Temperature Aging

低温陈化超声波共沉淀法制得SO₄^2-/ZrO^2-La₂O₃前驱体, 经H₂SO₄处理, 在不同温度下焙烧得到纳米晶催化剂SO₄^2-/ZrO^2-La₂O₃;用Hammett指示剂法测定其酸性. 用XRD、BET、TEM、IR和XPS对样品进行表征,其催化活性用醋酸和甘油的酯化反应进行了评价. 结果表明经超声波搅拌和低温(-15 ºC)陈化,650 ºC焙烧4 h得到的固体超强酸表现出较高催化活性.     

沉降介质对单分散SiO2微球重力组装欧泊模板的影响

 以氨水作催化剂、正硅酸乙酯为硅源、乙醇为溶剂,采用改进溶胶-凝胶法制备了系列单分散SiO₂微球,研究了平均粒径为250,280,320 nm单分散SiO₂微球在水、无水乙醇、丙酮等介质中的沉降与自组装过程。还对单分散体系重力沉降组装欧泊模板的形成机理进行了讨论。SEM表明,微球在无水乙醇和丙酮沉降介质中均能组装形成3维有序密堆积结构的欧泊,但在无水乙醇中要优于在丙酮中。沉降速度实验表明,相同粒径的单分散SiO₂微球在水、乙醇、丙酮作为沉降介质中的沉降速度相差并不大,沉降介质对重力水平沉降组装模板的影响主要是由于其表面张力与粘度不同造成的。     

超冷原子向异核四聚物分子A3B的绝热转化

提出了利用Efimov共振辅助的受激拉曼绝热通道(ER-STIRAP) 过程实施超冷原子向异核四聚物分子A₃B转化的理论方案, 得到了转化过程中中间态分别为同核Efimov三聚物A₃和 异核Efimov三聚物A₂B两种途径下系统的暗态解, 证实了ER-STIRAP技术对超冷异核四聚物分子A₃B合成的可行性和有效性. 研究了外场参数, 包括缔合光脉冲的强度、脉宽、磁耦合强度及其失谐量等对A₃B形成的影响. 对两种不同中间态的转化途径进行比较发现, 与中间态为异核Efimov三聚物A₂B的途径相比, 经历中间态为同核Efimov三聚物A₃的途径时系统实现最终四聚物分子A₃B的产率更高. 另外, 还讨论了系统内禀的非线性和中间态的自发辐射损失对异核四聚物分子合成的影响.     

单粒子薛定谔液体和形变核的转动惯量

将单粒子薛定谔液体理论应用于轴对称形变核的集体运动.也给出了一个相反的例子,即在各向异性谐振子势中处于稳定形变的任意数目的独立核子.而且,通过填充与主量子数n_x,n_y和n_z的可能值相应的单粒子态来构成s-d壳偶偶核:²⁰Ne,²⁴Mg,²⁸Si,³²S和³⁶Ar的基态,并计算了作为谐振子参数hω_x,hω_y和hω_z的函数的这些核的推转模型、刚体模型和稳态模型转动惯量.这些谐振子参数用与质量数A、中子数N、质子数Z和形变参数β有关的非形变参数hω00来描述.这些核的推转模型转动惯量的理论计算结果与实验数据符合甚好.而且,所考虑的轴对称形变核可能是扁椭球形的,也可能不是扁椭球形的,其中²⁴Mg是惟一高度形变的.²⁰Ne和²⁴Mg这两个核的刚体模型和稳态模型转动惯量也与实验数据符合甚好.     

傅里叶变换红外光谱法对珍珠粉和贝壳粉的研究

通过FTIR比较研究了淡水养殖珍珠的珍珠粉和贝壳粉样品原样、角壳蛋白以及250、400℃和750℃热处理2h后红外光谱的差异。结果表明,珍珠粉和贝壳粉的主要成分均为文石型碳酸钙,并含有少量有机质和水分。2种粉末角壳蛋白红外吸收峰型基本相似,仅在2113.3cm-1处存在差异。250℃加热后,两者成分结构基本没有变化;400℃加热后2种粉末有机物完全分解,珍珠粉文石碳酸钙的晶型部分转变为方解石型,而贝壳粉碳酸钙已完全转化为方解石型;750℃加热后两者的碳酸钙晶形均已完全转化为方解石型,且有大量碳酸钙分解为氧化钙。     

Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes

The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl₂) and sodium carbonate (Na₂CO₃) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals.     

Ultrasonic-assisted production of precipitated calcium carbonate particles from desulfurization gypsum

This study aimed to investigate the effect of ultrasonic application on the production of precipitated calcium carbonate (PCC) particles from desulfurization gypsum via direct mineral carbonation method using conventional and venturi tube reactors in the presence of different alkali sources (NaOH, KOH and NH₄OH). The venturi tube was designed to determine the effect of ultrasonication on PCC production. Ultrasonic application was performed three times (before, during, and after PCC production) to evaluate its exact effect on the properties of the PCC particles. Scanning electron microscope (SEM), X-ray diffraction (XRD), Atomic force microscope (AFM), specific surface area (SSA), Fourier transform infrared spectrometry (FTIR), and particle size analyses were performed. Results revealed the strong influence of the reactor types on the nucleation rate of PCC particles. The presence of Na⁺ or K⁺ ions in the production resulted in producing PCC particles containing only calcite crystals, while a mixture of vaterite and calcite crystals was observed if NH₄⁺ ions were present. The use of ultrasonic power during PCC production resulted in producing cubic calcite rather than vaterite crystals in the presence of all ions. It was determined that ultrasonic power should be conducted in the venturi tube before PCC production to obtain PCC particles with superior properties (uniform particle size, nanosized crystals, and high SSA value). The resulting PCC particles in this study can be suitably used in paint, paper, and plastic industries according to the ASTM standards.     

Group Theoretical Analysis of the v 1 (CO 3 2-) Vibration in Crystalline Calcium Carbonate

A group theoretical analysis, based on the correlation method, is presented for the symmetric stretch vibration of the carbonate ion in three crystalline forms of calcium carbonate: calcite, aragonite and vaterite. Numbers of Raman and infrared active components are calculated and compared with experimental data, including those from a recent Raman study of vaterite. It is shown that the splitting observed for v _l in vaterite is compatible with two of the proposed crystal structures for this compound.     

Amorphous,nanocrystalline and crystalline calcium carbonates in biological materials

Raman spectroscopy is a powerful tool in identifying different calcium carbonate polymorphs. Here, the method is applied to cultured pearls from freshwater (genus Hyriopsis) and marine bivalve species (Pinctada maxima) as well as to shells of Diplodon chilensis patagonicus bivalves. Raman spectra for vaterite, detected for the first time in an adult shell, and amorphous calcium carbonate (ACC) are discussed. Results for ACC are compared with those of synthetically produced ACC and with the Raman spectroscopic features of stable biogenic ACC from the crustacean Porcellio scaber. Decomposition of the most intense signal of all calcium carbonate polymorphs—the ν₁ symmetric stretching mode of the carbonate ion—leads to the identification of two polymorphs within the ACC areas: a mixure of an amorphous and a crystalline fraction. The amorphous phase is characterised by a broad peak in the region of the lattice modes, which is composed of two distinct lattice modes with very high full‐widths at half‐maximum (FWHMs). The FWHMs of most of the crystalline fractions (in the range of 6.3–10.7 cm⁻¹) are too high for well‐crystallised materials and support reports of nanocrystalline calcium carbonate polymorph clusters in ACC. Crystallinity indices of different samples are calculated and found to be useful to describe roughly the state of crystallisation in the ACC areas. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of amplitude and frequency of ultrasonic irradiation on morphological characteristics control of calcium carbonate

We have previously reported on the morphological control of calcium carbonate by changing synthetic conditions such as temperature, pH and degree of supersaturation in liquid reaction. The present study reports the effect of amplitude and frequency of ultrasonic irradiation on the particle size of calcium carbonate using a horn type ultrasonic apparatus at two different frequencies. The calcium carbonate precipitated by mechanical stirring had a particle size of about 20 μm. By contrast, the particle size of vaterite formed under ultrasonic irradiation was about 2 μm, with a specific surface area of 25–30 m²/g. The major polymorph of calcium carbonate formed by ultrasonic irradiation was vaterite with some calcite present. For 40 kHz ultrasonic irradiation, the specific surface area of the calcium carbonate increased with increasing amplitude. The particle size of vaterite formed at this frequency was about 2 μm, and its distribution was sharper than that obtained at 20 kHz. The mode diameter of the synthesized vaterite was found to decrease with increasing amplitude at 40 kHz.     

In Situ Liquid SAXS Studies on the Early Stage of Calcium Carbonate Formation

Calcium carbonate is a model system to investigate the mechanism of solid formation by precipitation from solutions, and it is often considered in the debated classical and nonclassical nucleation mechanism. Despite the great scientific relevance of calcium carbonate in different scientific areas, little is known about the early stage of its formation. Therefore, contactless devices are designed that are capable of providing informative investigations on the early stages of the precipitation pathway of calcium carbonate in supersaturated solutions using classical scattering methods such as wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) techniques. In particular, SAXS is exploited for investigating the size of entities formed from supersaturated solutions before the critical conditions for amorphous calcium carbonate (ACC) nucleation are attained. The saturation level is controlled and kept constant by mixing four diluted solutions (i.e., NaOH, CaCl₂, NaHCO₃, H₂O) at constant T and pH. The scattering data are collected on a liquid jet generated about 75 s after the mixing point. The data are modeled using parametric statistical models providing insight about the size distribution of denser matter in the liquid jet. Theoretical implications on the early stage of solid formation pathway are inferred.     

Bio-vaterite formation by glycoproteins from freshwater pearls

A 48 kDa acidic and putative calcium-binding glycoprotein was isolated from pearls of the freshwater mussel Hyriopsis cumingii. This protein was compared with a related 46 kDa polypeptide, obtained from the nacreous shell of the same species. Separation by two-dimensional gel electrophoresis revealed that the difference in molecular weight is due to the higher extent of glycosylation of the 48 kDa protein existing in pearls. Evidence is presented that the sugar moieties of the protein contribute to crystal growth, starting with the nucleation step. In in vitro precipitation experiments, the 48 kDa glycoprotein of pearls directed the formation of round-shaped vaterite crystals while the 46 kDa glycoprotein of shells promoted formation of small irregular calcite particles. Furthermore, both proteins, 48 kDa/46 kDa, comprised carbonic anhydrase activity that has been implicated in CaCO₃ formation. Thus, a function of the isolated glycoproteins in biomineralization is proposed together with the mechanism by which they can stabilize different calcium carbonate polymorphs.     

High Loading Efficiency and Controlled Release of Bioactive Immunotherapeutic Proteins Using Vaterite Nanoparticles

Nanoparticles may limit off-tumor/on-target ubiquitous activation of signaling by protein-based drugs. However, many challenges still exist in the design of a nanoparticle for protein delivery. In this study, conditions to establish vaterite nanoparticles as a pH-sensitive drug delivery system (DDS) for encapsulated protein drugs are comprehensively evaluated. Low coprecipitation pH of vaterite and protein prevents protein denaturation and yields high loading efficiency. Unprotected vaterite recrystallizes in aqueous solutions within 3 h to calcite and releases the loaded protein completely, but surface-modified particles with carboxyl groups containing polymers prove stable for more than 5 months. Notably, modification of vaterite with sulfonated polymers increases the loading of cationic proteins by a multiple. A system is developed for vaterite exposure to (pH) conditions under body-like-flow rates, with the dissolution of vaterite and simultaneous release of active proteins at tumor microenvironmental pH reaching up to 80% and only 20% at physiological pH within 2 h. Importantly, the immunomodulatory protein tumor necrosis factor preserves its native structure and fully retains functional activity in vitro after release from the particles. In conclusion, the studies described here provide a framework for the development of vaterite-based DDS as a carrier for bioactive protein-based therapeutics.     

Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing

Droplets of several micrometers in size can be formed in aqueous solution by atomization under ultrasonic irradiation at 2 MHz. This phenomenon, known as atomization, is capable of forming fine droplets for use as a reaction field. This synthetic method is called SARM (sono atomization for reactive mixing). This paper reports on the synthesis of a novel amorphous calcium carbonate formed by SARM. The amorphous calcium carbonate, obtained at a solution concentration of 0.8 mol/dm³, had a specific surface area of 65 m²/g and a composition of CaCO₃•0.5H₂O as determined using thermogravimetric/differential thermal analysis (TG-DTA). Because the ACC had a lower hydrate composition than conventional amorphous calcium carbonate (ACC), the ACC synthesized in this paper was very stable at room temperature.     

The Nanosecond Laser Flash Photolysis (LFP) Transient Spectra of Aqueous CCl4 Solution

Abstract

The Raman spectrum of polycrystalline vaterite is presented and compared to spectra of calcite and aragonite, the other two common CaCO₃ polymorphs; Raman spectroscopy easily distinguishes between these three polymorphs. An important feature of the Raman spectrum of vaterite is splitting of both the ν₁ and ν₄ peaks. The splitting of the ν1 peak implies two distinct site symmetries for the CO₃ ^?2 groups. A definitive crystal structure determination of vaterite is not yet available, but none of the three proposed structures for vaterite show such a feature.