Macrodefect-Free Materials: Modification of Interfaces in Cement Composites by Polymer Grafting

MDF materials are chemically bonded ceramic materials free of the macrodefects typical of hydraulic cement-based materials. MDF materials arising through reactions of sulfo-aluminate-ferrite belitic (SAFB) clinkers and/or Portland cements (PC) with two types of water-soluble polymer (hydroxy-propylmethyl cellulose {HPMC}, polyphosphate glass {poly-P}) are discussed. Mixes of low energy SAFB clinkers with Portland cement, HPMC and, especially poly-P comprise promising cross-linked compositions additional to the better known MDF materials formed from high alumina cement with polyvinylalcohol/acetate. The principles of co-ordination of P and C atoms (of the polymer) with Al and Fe atoms (originating from the cement) are highlighted from spectroscopic information on next-nearest-neighbour interactions, along with the effects of second co-ordination spheres. Polymers modify the interface through functional bonding/grafting of polymer chains onto the surfaces of cement grains. Both the cross-linked atomic structure and the interface coincide well with the model of functional polymers and represent a new type of atomic-level structure in polymer-modified cements. Interpretation is based on previous magnetic resonance and thermal analysis studies. The compactness of Al(Fe)-O-P cross-links reduces transport through the interfaces, increasing the interfacial interactions and resisting the unfavourable uptake of moisture and carbonation.     

The role of variable surface charge and surface complexation in the adsorption of humic acid on magnetite

The ionic strength dependence of humic acid (HA) adsorption on magnetite (Fe₃O₄) was investigated at pH 5, 8 and 9, where variable charged magnetite is positive, neutral and negative, respectively. The adsorption studies revealed that HA has high affinity to magnetite surface especially at lower pH, where interacting partners have opposite charges. However, in spite of electrostatic repulsion at pH 9 notable amounts of humate are adsorbed. Increasing ionic strength enhances HA adsorption at each pH due to charge screening. The dominant interaction is probably a ligand-exchange reaction, nevertheless the Coulombic contribution to the organic matter accumulation on oxide surface is also significant under acidic condition. The results from size exclusion chromatography demonstrate that the smaller size HA fractions enriched with functional groups are adsorbed preferentially on the surface of magnetite at pH 8 in dilute NaCl solution.     

Lanthanum nitrate decomposition by both temperature programmed heating and citrate gel combustion

Thermal decomposition of lanthanum nitrate to lanthanum oxide was carried out by both temperature programmed heating (TPH) and citrate-gel combustion. The temperature programmed heating was carried out under flow of oxidizing (air), neutral (nitrogen) and reducing (25 vol.% hydrogen+argone mixture) gases, and the processes were controlled by simultaneous thermogravimetry and differential thermal analysis. It was shown that hydrogen atmosphere helps to reduce temperatures of all decomposition steps. The results of TPH were utilized to check the nature of residues in the products of lanthanum nitrate-to-oxide conversion performed via citrate-gel combustion technique.     

Photoemission study of the modification of the electronic structure of transition-metal overlayers on TiO2 surfaces II. Cr on TiO2(0 0 1)

The electronic states of the Cr overlayers on TiO₂(0 0 1) surfaces have been investigated using angle-resolved and resonant photoemission spectroscopy with synchrotron radiation. At lower coverages, Cr deposition on TiO₂(0 0 1) creates two well separated in-gap emissions due to the formation of surface Ti³⁺ (3d¹) ions and Cr³⁺ (3d³) ions. At higher coverages, the in-gap emission is developed into the 2-peak-structure emission of Cr 3d character. The corresponding state is considered to be of metallic nature from the viewpoint of the high ability of oxygen adsorption, but has no Fermi edge, indicating a possibility of forming small Cr clusters on TiO₂(0 0 1) at this stage.     

MgO在Mg-hBN体系中对合成cBN晶体的影响

 以金属镁粉为触媒，以六角氮化硼为原料，其中加入适量比例的氧化镁，在国产六面顶压机上，在约5.0 GPa压力、1 500～1 800 K温度条件下，合成出了颜色均匀、晶形完整的黄色立方氮化硼单晶体。实验结果表明，在Mg-hBN体系中，氧化镁对合成cBN晶体的颜色及合成温度有很大的影响。     

ESR方法研究高TC氧化物的超导电性

用电子顺磁共振方法研究了一些高温超导氧化物样品的零场非共振吸收信号和正常的ＥＳＲ共振信号。认为这种方法可以作为鉴别样品进入超导态的实验判据之一。利用零场非共振吸收实验给出的下临界磁场Ｈｃ１（Ｔ）很好地遵多Ｈｃ１（Ｔ）＝Ｈｃ１（０）（１－Ｔ＆＾２／Ｔｃ＾２）。     

Multibody dynamics of aircraft occupants seated behind interior walls

To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA, incorporating a dynamic model of the human body with a finite element model of the seat structure was used. Modifications were performed in the program for reconstruction of an occupant's head impact with the interior walls or bulkhead. A viscoelastic-type contact force model was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft.     

四溴双酚A锑铝双金属化合物的合成及其阻燃性能

以四溴双酚Ａ（ＴＢＡ）合成了在水和空气中稳定的四溴双酚Ａ合锑铝双金属化合物（ＴＢＡＳＡ）．通过ＩＲ、１ＨＮＭＲ和元素分析予以表征，并研究了其对聚乙烯（ＰＥ）和聚环氧乙烷（ＰＥＯ）的阻燃性能．结果表明，这种分子中含有溴、锑和铝的化合物，对聚乙烯和聚环氧乙烷等高聚物材料有高的阻燃性能与消烟效果．     

On a model of electromagnetic field propagation in ferroelectric media

The Maxwell system in an anisotropic, inhomogeneous medium with non-linear memory effect produced by a Maxwell type system for the polarization is investigated under low regularity assumptions on data and domain. The particular form of memory in the system is motivated by a model for electromagnetic wave propagation in ferromagnetic materials suggested by Greenberg, MacCamy and Coffman [J.M. Greenberg, R.C. MacCamy, C.V. Coffman, On the long-time behavior of ferroelectric systems, Phys. D 134 (1999) 362-383]. To avoid unnecessary regularity requirements the problem is approached as a system of space-time operator equation in the framework of extrapolation spaces (Sobolev lattices), a theoretical framework developed in [R. Picard, Evolution equations as space-time operator equations, Math. Anal. Appl. 173 (2) (1993) 436-458; R. Picard, Evolution equations as operator equations in lattices of Hilbert spaces, Glasnik Mat. 35 (2000) 111-136]. A solution theory for a large class of ferromagnetic materials confined to an arbitrary open set (with suitably generalized boundary conditions) is obtained.