钛基表面纳米羟基磷灰石涂层的电泳沉积

应用沉淀法合成纳米羟基磷灰石,并以电泳沉积法在粗糙化的钛表面制备纳米结构的羟基磷灰石涂层.纳米涂层有利于保持羟基磷灰石的化学组成和结构,制备的涂层均匀并且无裂缝,烧结后涂层仍保持纳米结构,其烧结温度也明显降低。钛表面经化学处理后,可形成很多微孔和TiO2薄层,增强了涂层和基体之间的结合.涂层的结合力为 18±2. 5MPa,硬度和杨式模量分别为 32. 0和 2. 4GPa.     

Interpolation determination of the lattice energy of ionic crystals within the framework of stereoatomic model

A new method based on graph theory was suggested for interpolation calculation of the lattice energy U of ionic crystals. The method is based on revealing matrix correlation between the ionic radii and U values for MX compounds, where M is a metal and X is halogen, hydrogen, or chalcogen. A new formula was obtained for calculating the lattice energy solely from the ionic radii, without introduction of abitrary factors. The mean error of determining U for alkali metal halides is 0.49%. The lattice energies were calculated for a large group of inorganic substances. The accuracy of the interpolation calculation of the lattice energy of ionic crystals depends on the degree of ionicity of the bond: With an increase in the covalent contribution, the error increases.     

Lattice energy estimation for inorganic ionic crystals

An empirical method based on chemical bond theory for the estimation of the lattice energy for ionic crystals has been proposed. The lattice energy contributions have been partitioned into bond dependent terms. For an individual bond, the lattice energy contribution made by it has been separated into ionic and covalent parts. Our calculated values of lattice energies agree well with available experimental and theoretical values for diverse ionic crystals. This method, which requires detailed crystallographic information and elaborate computation, might be extended and possibly yield further insights with respect to bond properties of materials.     

Mechanical properties of hydrogenated nanocrystalline silicon thin film with different indentation depths

Hydrogenated nanocrystalline silicon thin films were prepared on Corning 7059 glasses by plasma enhanced chemical vapor technique with radio frequency and direct current bias stimulation. The surface topography and microstructure of sample were characterized with atomic force microscopy and X‐ray diffraction. The mechanical properties of the samples were investigated by TriboIndenter nanosystem. The elastic modulus E and hardness H of samples were calculated by means of Oliver and Pharr analysis method. The results show that with increasing the indentation depth from 70 to 180 nm, the maximum applied load P_max increases from 500 to 2000 µN, while the elastic modulus E dives to 25 from 45 GPa, and the hardness H decreases from 4.9 to 3.8 GPa. After complete unloading, some plastic deformations occur on the films' surface and with the increase of the indentation depth, they become more obvious. This phenomenon is mainly connected with the film's growth mechanism. In this paper, we did an investigation and a discussion in detail about this phenomenon. Copyright © 2011 John Wiley & Sons, Ltd.     

Hard ormosils prepared with ultrasonic irradiation

Organically modified silicates (ormosils) of high hardness were prepared by the reaction of TEOS (tetraethoxysilane) and PDMS (polydimethylsiloxane) aided by ultrasonic irradiation, which was chosen as the method for concentration of the solutions. The mechanisms leading to the hard ormosil formation were examined by liquid state ²⁹Si NMR spectroscopy. PDMS chains were found to be broken into shorter chains and/or cyclic D₄ tetramers during the reaction and finally, all the PDMS chains were chemically incorporated as short chains into silica networks. Structural models of the mechanisms are also proposed. Elastic moduli and Vickers hardnesses of the hard ormosils were measured. Vickers hardnesses of the hard ormosils were compared with those of some glasses and the hardest transparent plastics and the hard ormosils were much harder than the plastics and a little softer than soft glasses. Theoretical models have been developed for the calculations of the elastic moduli and Vickers hardnesses and agreed well with the experimental results. Predictions based on these models indicate that even higher elastic moduli and Vickers hardnesses of the hard ormosils can be obtained when Al₂O₃, ZrO₂ and TiO₂ are substituted for SiO₂. 30 mol% TiO₂-containing ormosils of high hardness were also prepared aided by ultrasonic irradiation. TEOS and tetraisopropyltitanate (TIPT) were used as the inorganic components. Dimethyldiethoxysilane (DMDES) was used instead of PDMS as the organic precursor. The reactions among alkoxides were examined by liquid state ²⁹Si NMR spectroscopy. While the reactivity between TIPT and PDMS was much lower than the reactivity between TIPT and hydrolyzed TEOS, the reactivity between TIPT and hydrolyzed DMDES was not so different from the reactivity between TIPT and hydrolyzed TEOS, and thus DMDES was used as the organic precursor instead of PDMS. Elastic moduli and Vickers hardnesses of the hard ormosils of the TEOS/TIPT/DMDES system were measured and even higher elastic moduli and Vickers hardnesses than those of the TEOS/PDMS system hard ormosils were obtained. Also, the calculated results from the theoretical models agreed well with the experimental results.     

Mechanical characterization of Ormosil films on plastics: Young's modulus determination by three points bending

A protective layer has been deposited to improve the scratching properties of polycarbonate organic glasses. The starting solution consists of a mixture of organosilicon compounds, silicon alkoxides or silica colloidal solutions. The deposition is carried out using the dip coating technique. The thickness is about 2–5 µm for the film and 1 mm for the substrate.Young's moduli of the films are obtained by a new three points bending apparatus. Young's modulus of coating depends both on silica content and on the nature of the silica used as a filler.     

Quantum chemical calculation of nickel and copper atomic valencies in crystalline oxides

A new quantum chemical definition is proposed of the full atomic valence, V_A, taking into account both the covalent and ionic parts of the chemical bonds formed by atoms in molecules and crystals. The full atomic valencies, covalencies, and charges on atoms are calculated for nickel–oxygen crystalline compounds in the CNDO band theory approximation. A comparison of the chemical bonding in nickel and copper crystalline oxides is given. © 1994 John Wiley & Sons, Inc.     

Electronegativities of elements in covalent crystals

A new electronegativity table of elements in covalent crystals with different bonding electrons and the most common coordination numbers is suggested on the basis of covalent potentials of atoms in crystals. For a given element, the electronegativity increases with increasing number of bonding electrons and decreases with increasing coordination number. Particularly, the ionicity of a covalent bond in different environments can be well-reflected by current electronegativity values; that is, the ionicity of chemical bonds increases as the coordination number of the bonded atoms increases. We show that this electronegativity scale can be successfully applied to predict the hardness of covalent and polar covalent crystals, which will be very useful for studying various chemical and physical properties of covalent materials.     

Overlapping shells model applied to diamondlike crystals

The model based on the assumption of the existence of an interatomic distance-dependent, local, effective crystal field applied to the alkaline metals (Int. J. Quantum Chem. 52, 321–328 (1994)) is modified and applied to the diamondlike structure crystals (C, Si, Ge, Sn). In the referred to model, a part of the electron density was missed—not included in the calculation (the density in the spaces between the shells). Such an approach could be used for the alkaline metals, but for the covalent crystals, this is a bad approximation. To avoid that problem, we assumed that the atom shells can overlap in such a way that the entire electron density is taken into the calculation. In this case, the electron density is “moved” from the outside of the shells mostly into the interatomic bond region. We applied the modified model to the calculation of the binding energy and the bulk modulus for the diamondlike crystals. The results show that well-chosen parameters allows one to reproduce the proper values of the binding energy at the equilibrium position. The bulk moduli calculated for these crystals are in quite good agreement with ones calculated as (regular crystal structure) B = 1/3(C₁₁ + 2 C₁₂), where C₁₁ and C₁₂ are elastic constants. © 1997 John Wiley & Sons, Inc.     

Calculation of the bulk modulus of simple and complex crystals with the chemical bond method

The relation between the lattice energies and the bulk moduli on binary inorganic crystals was studied, and the concept of lattice energy density is introduced. We find that the lattice energy densities are in good linear relation with the bulk moduli in the same type of crystals, the slopes of fitting lines for various types of crystals are related to the valence and coordination number of cations of crystals, and the empirical expression of calculated slope is obtained. From crystal structure, the calculated results are in very good agreement with the experimental values. At the same time, by means of the dielectric theory of the chemical bond and the calculating method of the lattice energy of complex crystals, the estimative method of the bulk modulus of complex crystals was established reasonably, and the calculated results are in very good agreement with the experimental values.     

Mechanical properties of anodized coatings over molten aluminum alloy

A method to measure interfacial mechanical properties at high temperatures and in a controlled atmosphere has been developed to study anodized aluminum surface coatings at temperatures where the interior aluminum alloy is molten. This is the first time that the coating strength has been studied under these conditions. We have investigated the effects of ambient atmosphere, temperature, and surface finish on coating strength for samples of aluminum alloy 7075. Surprisingly, the effective Young's modulus or strength of the coating when tested in air was twice as high as when samples were tested in an inert nitrogen or argon atmosphere. Additionally, the effective Young's modulus of the anodized coating increased with temperature in an air atmosphere but was independent of temperature in an inert atmosphere. The effect of surface finish was also examined. Sandblasting the surface prior to anodization was found to increase the strength of the anodized coating with the greatest enhancement noted for a nitrogen atmosphere. Machining marks were not found to significantly affect the strength.     

Features of the valence electron charge distribution in LiB<Superscript>II</Superscript>X<Superscript>V</Superscript> crystals

Total, difference, and deformation electron densities are calculated from the first principles using the density functional theory and the sublattice method for LiBX (B = Mg, Ca, Zn; X = N, P, As) crystals with the sphalerite structure. The nature and formation features of the chemical bonding caused by a change in the chemical composition are revealed. A weak bond between Li⁺ ions with X anions enables their displacements in the space between crystal-forming tetrahedral (BX)^– groups. It is found that Ca–X bonds are mainly ionic and in a series of crystals the ionic covalent Li–B bond is traced.     

Mechanical and electrical properties of the phosphor‐doped nano‐silicon film under an external electric field

The mechanical and electrical properties of the phosphor‐doped nano‐silicon film (nc‐Si:H) prepared by the plasma‐enhanced chemical vapor deposition (PECVD) method under electric field have been studied by Tribolab system, which is equipped with nano‐electrical contact resistance (ECR) tool. During indentation, different voltages and loads were applied. The topography of the sample surface was studied by atomic force microscopy (AFM). The experimental results show that the roughness of the film is 5.69 nm; the electric current was measured through the sample/indenter tip with different loads at a fixed voltage, and it increased nonlinearly during the indentation. The maximum current value depth was shallower than the maximum depth of each indent due to the plasticity of the film. When the loading speed is increased to 250 µN/s, the microcrack occurred on the film; the hardness (H) and elastic modulus (E) changed with the voltage applied both in open circuit and in short circuit case, which resulted in different values of H/E rate from 0.082 to 0.096. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanical Properties of SiO2-PMMA Based Hybrid Organic-Inorganic Thin Films

Nano-indentations using a Berkovich indenter were performed in order to analyze the mechanical properties of hybrid organic-inorganic coatings. This technique allows to measure low load deformations and therefore to estimate quantitatively mechanical properties of the coatings. The elastic modulus and the hardness were determined on the basis of the load-displacement curve. We report results obtained for class II hybrid coatings based on SiO₂-PMMA prepared by sol-gel process. The effects of coating composition were investigated.     

A new method of calculation of the melting temperatures of crystals of Group 1A metal halides and francium metal

A new method of calculation of melting temperatures of binary ionic crystals has been suggested. The method is based on finding a matrix relation between the ionic radii (the lattice energy U) and melting temperature of ionic crystals of the MX type, where M is a Group 1A metal, and X is a halogen. From the equation for the lattice energy U, a new equation has been derived for calculation of the melting temperature of ionic crystals with the use of only the ionic radii and the degree of bond ionicity ?: T _m = f(U, ?). The average error of determination of T _m for alkali-metal halides is 2.80%. The melting temperatures of francium halides and alkali-metal astatides (including FrAt) have been calculated. It has been shown that the accuracy of calculation of the melting temperature of ionic crystals depends on the degree of bond ionicity: the error increases with an increase in the covalent contribution. On the basis of the melting temperatures of metal halide crystals, a method has been developed for the calculation of the melting temperatures of corresponding metals. The melting temperature of francium has been calculated to be 24.861 ± 0.517°C.     

An Excursion from Normal to Inverted C?C Bonds Shows a Clear Demarcation between Covalent and Charge‐Shift C?C Bonds

What is the nature of the C? C bond? Valence bond and electron density computations of 16 C? C bonds show two families of bonds that flesh out as a phase diagram. One family, involving ethane, cyclopropane and so forth, is typified by covalent C? C bonding wherein covalent spin‐pairing accounts for most of the bond energy. The second family includes the inverted bridgehead bonds of small propellanes, where the bond is neither covalent nor ionic, but owes its existence to the resonance stabilization between the respective structures; hence a charge‐shift (CS) bond. The dual family also emerges from calculated and experimental electron density properties. Covalent C? C bonds are characterized by negative Laplacians of the density, whereas CS‐bonds display small or positive Laplacians. The positive Laplacian defines a region suffering from neighbouring repulsive interactions, which is precisely the case in the inverted bonding region. Such regions are rich in kinetic energy, and indeed the energy‐density analysis reveals that CS‐bonds are richer in kinetic energy than the covalent C? C bonds. The large covalent–ionic resonance energy is precisely the mechanism that lowers the kinetic energy in the bonding region and restores equilibrium bonding. Thus, different degrees of repulsive strain create two bonding families of the same chemical bond made from a single atomic constituent. It is further shown that the idea of repulsive strain is portable and can predict the properties of propellanes of various sizes and different wing substituents. Experimentally (M. Messerschmidt, S. Scheins, L. Bruberth, M. Patzel, G. Szeimies, C. Paulman, P. Luger, Angew. Chem. 2005 , 117, 3993–3997; Angew. Chem. Int. Ed. 2005 , 44, 3925–3928), the C? C bond families are beautifully represented in [1.1.1]propellane, where the inverted C? C is a CS‐bond, while the wings are made from covalent C? C bonds. What other manifestations can we expect from CS‐bonds? Answers from experiment have the potential of recharting the mental map of chemical bonding.     

SiO2纳米粒子对溶胶凝胶涂层性能的影响

在高强钢表面制备了防护性溶胶凝胶涂层,并研究了不同浓度二氧化硅纳米粒子的加入对于涂层形貌、耐蚀性和硬度的影响。采用扫描电子显微镜(SEM)和电子能谱(EDS)观察了涂层的微观结构和成分;采用显微硬度计测试了涂层的硬度;采用电化学方法研究了二氧化硅纳米粒子的浓度对于涂层耐蚀性能的影响;采用傅里叶红外光谱研究涂层的化学结构,进而探讨了二氧化硅纳米粒子对于涂层的强化机理。结果显示涂层加入二氧化硅纳米粒子的最佳浓度为500 mg.L-1,此条件下的涂层表面均匀致密,有较高的硬度并且在3.5%NaCl溶液中体现出较好的耐蚀作用。纳米粒子在溶胶中反应形成活性羟基基团并与硅烷发生反应生成空间网状结构,从而强化涂层。     

High Precision Diamond Machining of Hybrid Sol-Gel Coatings

Flexible and economic production of complex reflective optical elements is achieved by high-precision machining of aluminum and copper with diamond tools. There is also an increasing demand for complex refractive optical elements like micro lens arrays, Fresnel lenses or prismatic surfaces on silicon wafers or metallic surfaces. For the production of these optical elements, hybrid sol-gel coatings based on methacryloxypropyltrimethoxysilane (MATMS) and zirconium (IV) tetra n-propoxide (ZTP) were deposited on aluminum substrates by spin-coating. The influence of the rotational velocity and the chemical sol composition on the coating thickness was determined. The hardness and elastic modulus of these coatings was measured as a function of the chemical composition. The machining characteristics of these coatings were investigated by high precision turning and fly cutting with diamond tools of different geometry. The resulting surface finish obtained was determined as a function of the machining parameters.     

Comparison of Young's modulus and specific heat anomalies at the magnetic transition in α′-NaV2O5

We have measured Young's modulus (using a vibrating reed technique) and the specific heat (using ac calorimetry) on the same crystals of α′-NaV₂O₅ at its T_c=34 K magnetic phase transition. Both properties exhibit large, unsymmetrical, and sample-dependent anomalies. While the specific heat results suggest tricritical behavior of the transition, large fluctuation effects are observed in the modulus above T_c. Fits of the modulus in terms of the specific heat, entropy, and free energy suggest that fluctuations are strongly stress- and sample-dependent.