包覆型氧化铁黄颜料微结构与耐热性能研究

氧化铁黄颜料因耐热性差而限制了在塑料加工和卷材涂料中的应用。本研究以氧化铁黄为前驱体, 采用沉淀法合成氢氧化铝包覆氧化铁黄颜料, 采用XRD、FT-IR、TG-DTA、SEM&EDS和TEM等方法表征包覆型铁黄颜料的结构, 探讨了反应pH对复合材料微结构以及耐热性能的影响。结果表明, pH为4时, 铁黄表面包覆层为无定型氢氧化铝; pH提高至6、8和10时, 表面包覆层为晶态薄水铝石相。包覆后氧化铁黄颜料耐热性有了较大提升。特别在pH为8、10时, 铁黄颜料 240℃下耐热处理30 min后色差值较小, 与表面包覆层形成的薄水铝石相密切相关。铁黄包覆前后, 保持了原先的针状结构, 未出现团聚; 当pH为10时, 包覆后铁黄颜料除针状结构外, 还出现了较粗的晶态棒状物, 可能与羟基氧化铝在反应过程中自身成核有关, 解释了DTA图谱上246℃处出现的特殊吸热峰。本研究为耐温铁黄颜料开发提供了理论与实践指导。     

Preparation of ultradispersed magnesium nitride by the electric-arc low-temperature plasma technique

The conditions are investigated for the preparation of ultradispersed magnesium nitride (UDMN) from elemental magnesium and nitrogen by the electric-arc low-temperature plasma (LTP) technique. Thermodynamic calculations are carried out with the objective of finding the values of the equilibrium constant for the synthesis reaction of magnesium nitride from its elements in the temperature range 298–1800 K as a function of the aggregation state of the components. By means of a cold wall (CW) plasma-chemical reactor (PCR), ultradispersed product (UDP) is synthesized with a specific surface of 33 m²g^–1 containing up to 56% of Mg₃N₂; the use of a warm wall (WW) PCR allows the preparation of UDP with a Mg₃N₂ content of up to 73% and a specific surface reaching 184 m²g^–1. The dominant role of the radial temperature gradient in the PCR in the synthesis of UDMN with maximal degree of nitride formation and maximal specific surface values is experimentally demonstrated. The UDMN exhibits a high chemical activity; heat-treatment at 900 K in an inert atmosphere decreases substantially its chemical affinity to water vapour and oxygen in the air.     

Structural,phase and morphological features of plasmachemically synthesized ultradispersed particles

An attempt has been made to characterize and explain some physical and physicochemical, including structural, phase and morphological features, of ultradispersed particles (UDP) of nitrides (Si₃N₄, AIN, TiN), oxides (Al₂O₃, FeO, Fe₃O₄, Fe₂O₃), metals (Fe) and catalysts (catalyst for ammonia synthesis), synthesized under electric arc low-temperature plasma (LTP) conditions. A relative decrease in the value of the crystal lattice period of up to 0.9% has been observed in ultradispersed powders with particle sizes up to 50 nm. For ultradispersed powders with admixtures, the crystal lattice period may decrease under the influence of the Laplace pressure or increase due to the introduction of admixtures in the main phase crystal lattice. The plasmachemically synthesized ultradispersed powders are built up by the respective high-temperature modifications which have minimum free surface energy, i.e. by phases with a maximum compact crystal lattice.     

High chemical activity and passivation of ultradispersed particles synthesized under the conditions of electric-arc low-temperature plasma

Under conditions of electric-arc low-temperature plasma (LTP), various ultradispersed particles (UDP) have been synthesized. UDP are characterized by their specific surface (from several tens to several hundred m²g^–1), particle size (10–100 nm), phase composition, etc. The most efficient passivation agents preventing the high chemical activity of pyrophore, plasmachemically synthesized UDP have been experimentally established. These are: pure nitrogen for manganese, CO for molybdenum, N₂(0.5% O₂) for iron, N₂(0.5%–2% O₂) or CO₂( 2% O₂) for the reduced catalyst for ammonia synthesis, N₂(1% O₂) for the reduced catalyst for natural gas reforming, and N₂(1% O₂) for the reduced catalyst for low-temperature conversion of CO with H₂O. The high chemical activity of AIN and Mg₃N₂ was decreased by slow annealing at about 900–1000 K in a nitrogen atmosphere or by thermal treatment in an inert gas flow. Passivation was enhanced by the ability of some metals to form surface complexes (due to chemosorption of some gases) of composition similar to that of chemical compounds, e.g. metal carbonyls (Fe, Mo, W, etc.). The sorption (chemisorption) of gases on the surface of UDP can only decrease the oxidation rate rather than prevent oxidation.     

Utilization of new micronized and nano-CoO·MgO/kaolin mixed pigments in improving the properties of styrene–butadiene rubber composites

The present work highlights the role of a new prepared core–shell pigment based on kaolin as the bulk (core) covered with cobalt oxide and magnesium oxide comprising the surface of the pigment (shell). The new pigment was prepared in the micronized and nano-sized particles and its effect on the different properties of styrene–butadiene rubber (SBR) vulcanizates was studied. Incorporation of these two particle sized pigments and their varied content of cobalt oxide to magnesium oxide in the shell of the different pigments in different styrene–butadiene rubber vulcanizates was done, and their effects on the rheological, physical, mechanical and dielectric properties was studied. The study showed that there was a significant effect of these new pigments on SBR properties, and that the optimum micronized pigment loading in SBR was 30 phr, while that of the nano-pigment was 6 phr. The different measured properties were in good agreement with each other.     

Quantitative acoustic microscopy of anodized and coated aluminium at frequencies up to 1 GHz

Quantitative acoustic microscopy (QAM) has been used to measure surface wave velocities on polished, anodized and coated aluminium substrates, these materials being representative of those used for adhesive bonding in the aerospace industry. Good quality acoustic measurements were obtainable at frequencies between 225 and 980 MHz, despite the inhomogeneous nature of the oxide layer produced by phosphoric acid anodization (PAA). Good agreement was obtained between the surface acoustic wave dispersion measured on aluminium coated with 0.2 and 1.0 m PMMA, and that calculated by a simple isotropic layer model. The anodized aluminium was modelled as a transversely isotropic oxide layer on an aluminium substrate. At 0.2 m, the oxide layer was too thin for the comparison between measurement and calculation to be conclusive, but the calculations suggest that a change in porosity of 10% in a 0.6 m oxide layer, as obtained with an industry standard PAA treatment, should be readily detectable. The highly dispersive nature of some of the surface acoustic wave modes makes QAM extremely sensitive to small changes in the material parameters.     

铁氧化物纳米晶自组装空心微球的制备、表征及其应用

铁氧化物纳米材料和纳米结构空心微球分别代表了材料研究中组分和结构的研究热点. 而由铁氧化物纳米晶自组装形成的空心微球的研究则是二者相结合, 具有重要的科学意义和良好的应用前景. 虽然已发展了多种方法制备各种单质及化合物的空心微球, 但铁氧化物纳米晶自组装空心微球的制备方法报道较少. 本文简要介绍了近几年发展起来的多种铁氧化物纳米晶自组装空心微球的一些制备方法, 利用上述方法, 制备出了多种不同组成单元、不同尺寸、不同空心程度的铁氧化物纳米晶自组装空心微球, 对所制备的铁氧化物纳米晶自组装空心微球进行了表征, 并初步介绍了所制备的铁氧化物纳米晶自组装空心微球在药物缓释和环境领域中的应用.     

Titanothermal reduction of oxides on iron and steel under conditions of self-evacuation

We study the process of contactless titanothermal reduction of oxides on Armco iron and Kh18N10T steel. The kinetic curves of oxide films thinning on iron and steel obtained in the work reveal two different mechanisms of these processes. Oxide reduction on iron runs at lower temperatures and the kinetic curves are characterized by a certain incubation period for which no oxide film thinning is observed. The appearance of this period can be explained by two processes that run either in the diffusion mode or in the kinetic mode. The contactless titanothermal reduction of oxide films on steel occurs at higher temperatures and oxide films are not completely reduced. Moreover, as temperature increases, its thinning becomes slower. The data of X-ray analysis indicate the presence of titanium sublimation with subsequent condensation on the steel surface. In this case, the composition of the film on the steel surface does not change.Paton Electrical Welding Institute, Ukrainian Academy of Sciences, Kiev. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 2, pp. 84–90, March–April, 1994.     

Microstructural development in the directed melt-oxidized (DIMOX) Al-Mg-Si alloys

Metal-ceramic composites produced via directed melt oxidation (DIMOX) of aluminium alloys are of recent interest. Thein situ composite forming method is based on the reaction of a molten alloy with a gaseous oxidant. In the present study, Al-Mg-Si alloys were subjected to directed melt oxidation and the progressive microstructural evolution was examined by interrupted growth experiments. In the early stages, liquid alloy oxidizes to form a duplex oxide layer (MgO+MgAl₂O₄) on the surface. The openings in these oxide layers allow the liquid alloy to wick through to form small nodules on the surface. When further wicking occurs through these nodules, a cauliflower type of colonies is formed. During the early part of the second stage, spinel growth dominates to form a multi-layered structure. In the final stage, as the magnesium reaches low levels, Al₂O₃ formation dominates the growth, and alumina crystals grow continuously for several tens of micrometres. The oxygen required for alumina formation is expected to come from two sources: (i) from the ingress of oxygen through microcracked oxide layers, and (ii) demixing of magnesium-containing oxides in the underneath layers.     

Effect of kaolin–metal oxides core–shell pigments on the properties of styrene–butadiene rubber composites

This study investigated the effects of core–shell kaolin–metal oxide pigments on the rheological, physico-mechanical and dielectric properties of styrene–butadiene rubber composites. In this way, newly prepared core–shell pigments based on kaolin as the core representing 90% of the whole pigment was covered with different metal oxides (CaO, MgO and CaO⋅MgO) comprising the shell which represents only 10% of the prepared pigments were incorporated with different concentrations in styrene–butadiene (SBR) rubber composites. Studying the different properties of pigmented and unpigmented SBR composites were done. Scanning electron microscopy (SEM) was used to feature out the surface morphology. Addition of the new pigments increased the tensile strength and strain energy, while elastic modulus was decreased. This study revealed that there is a significant effect of the new prepared pigments on SBR properties and the optimum pigment loading was 40 phr for CaO/kaolin, while it was 2.5 phr for MgO/kaolin. The dielectric results also showed that, the values of ε′ (relative permittivity) and ε′′ (dielectric loss) increased with increasing core shell content. Moreover, the samples containing MgO/kaolin and MgO⋅CaO/kaolin showed promising dielectric properties with low relative permittivity and electrical insulating properties. The different measurements showed good agreement in their results.     

The effect of zinc oxide–phosphate core–shell pigments on the properties of blend rubber composites

In this work the rheological, physico-mechanical, thermal and morphology studies were performed on a blend of EPDM/SBR (ethylene propylene diene monomer/styrene butadiene rubber) (50/50) loaded with a new prepared core–shell pigment based on a core of zinc oxide which presents the major component of the prepared pigment (≈90%) covered with a shell of phosphate, this shell comprises only about (≈10%). The new pigments were added in different concentration to the rubber blend and were compared to blends pigmented with commercial zinc oxide and zinc phosphate. The results showed that the new pigments exhibited better rheometric, and physico-mechanical properties. In addition, these prepared pigments showed decrease of equilibrium swelling in toluene solvent and increase in crosslink density for EPDM/SBR blend. The efficiency of prepared core–shell pigments were also evaluated by studying the surface morphology (SEM) and thermal properties TGA (thermal gravimetric analysis). The prepared pigments loading of 10 phr (parts per hundred parts of rubber) showed the optimum properties of EPDM/SBR blend than rubber loaded with higher concentration of the commercial pigments, which indicated that the new core–shell pigment is more economic with better performance than commercial zinc oxide and phosphates individually.     

Growth of γ-alumina on crystallographically distinct aluminium substrates

The growth of-alumina on crystallographically distinct aluminium substrates has been studied using transmission electron microscopy and diffraction and Rutherford backscattering. Oxides grown thermally on single-crystal substrates showed a preferred epitactic orientation relationship with the substrate, while oxides grown by the same technique on polycrystalline substrates did not exhibit a preferred orientation relationship. The grain size of the oxide was found to be at least one order of magnitude smaller than the initial grain size of the polycrystalline aluminium substrate.     

Colour modifiers of zirconium-vanadium pigments on a ZrO2 basis

The synthesis of yellow baddeleyite pigments involves a phase transition of ZrO₂, which facilitates the process of incorporating vanadium chromophore into its lattice, and occasionally also modifiers, such as oxides of trivalent elements, either chromophoric or non-chromophoric. Depending on the type of the modifier used ?? an oxide of indium, yttrium, gallium or thallium ?? the yellow-green colour of the two-component ZrO₂-V pigment may be changed smoothly into yellow or yellow-orange. The temperature of the synthesis of ZrO₂-based pigments ranges from 1050 °C to 1325 °C, depending on the properties of the substrates, such as a non-oxide form of the materials ?? ZrOCl₂, Zr(SO₄)₂, certain additives (e.g. Bi₂O₃). Raising the synthesis temperature over 1400 °C has no visible effect on the colour quality of the pigment, as it depends on the concentration of the vanadium chromophore in the ZrO₂ structure. The article describes the effect of the synthesis temperature and modifying additives on the effectiveness of incorporating vanadium into the ZrO₂ lattice and, consequently, on the colour properties of the pigment.     

Adsorption of silane coupling agent on Co-γ-Fe2O3 a nd its effect on dispersibility

The adsorption of a new type of silane coupling agent containing polyethylene oxide (EOS) on cobalt-modified iron oxide (Co--Fe₂O₃) particles and its effect on dispersibility are examined by measuring the surface chemical properties. The EOS is adsorbed on Co--Fe₂O₃ in the form of a monolayer and reduces the hydrophilicity of the surface of the particles with the adsorption. The surface hydrophilicity of EOS-treated iron foil (the iron foil has an ideal iron oxide surface) becomes lower with the increasing heat-treatment temperature. Heat treatment at 80°C or higher is required to achieve chemical bonding between EOS and the iron foil. By the same heat treatment, EOS polymerizes on the iron foil resulting in the formation of a polysiloxane network. The dispersibility of the particles in vinyl chloride-vinyl acetate-vinyl alcohol copolymer solution is improved dramatically by the surface treatment with EOS. The improvement in dispersibility is explained by considering the increase of the wettability of Co--Fe₂O₃ for the solvent due to EOS treatment.[/p]     

Aluminium oxide grafted on silica gel surface: Study of the thermal stability, structure and surface acidity

The synthesis of aluminium oxide grafted on silica gel surface was carried out by the reaction of a suitable aluminium precursor with the surface hydroxyl groups, SiOH, of the oxide support in non-aqueous solvent. The advantage of this preparation method, compared to the conventional ones (impregnation or precipitation and calcination), is that the oxide is highly dispersed on the surface (monolayer or submonolayer). The resulting material, SiO₂/Al₂O₃, was heat treated at temperature range of 423 to 1573 K. The Al/Si atomic ratios, determined by X-ray photoelectron spectroscopy (XPS), showed that aluminium is less mobile up to heat treatment of 1173 K and above this temperature part of it diffuses to the interior of the matrix. ²⁷Al solid state nuclear magnetic resonance spectroscopy (NMR) showed two different environments, tetrahedral and octahedral for sample calcined up to 1023 K and above this temperature, aluminium in a trigonal bipyramidal environment was also detected. Pyridine adsorbed on a Lewis acid sites were observed for samples calcined up to 1023 K, and above this temperature they were not detected.     

Shrinkage in compacts of iron oxides and ores

Compacts have been pressed from (i) four, finely ground, iron ores and (ii) mixtures of subsieve ferric oxide with up to 40 wt % of either lime, alumina, silica, or water, and have been sintered in oxygen at temperatures in the range 1000 to 1400 C. Shrinkage, macro- and micro-appearance were recorded at each sintering stage.The iron ores were classified into two groups: one was characterised by the red ferric oxide appearance and by significant shrinkage at 1000 C; the other was predominantly black and required a temperature of 1200 C to initiate shrinkage in 1 h. The shrinkages of the ores are discussed in terms of the presence of black ferric oxide, particle size, lime content, and dilution of the iron-bearing grains with inert oxides.The mixtures were used to study the effect of inert oxides on the sintering of ferric oxide. The reduction in shrinkage in the case of alumina and silica is shown to be largely a consequence of dilution; the abnormally high shrinkage at 1000 C induced by 5 wt % of lime is probably due to the presence of low-melting-point ferrites.     

Application of reaction synthesis principles to thermal spray coatings

Reaction synthesis principles have been extended to plasma spraying to obtain coatings consisting of mixed oxide phases and iron aluminides. Elemental powders of iron and aluminium were fed through a d.c. plasma torch to deposit intermetallic coatings on carbon steel substrates. Carbon steel substrates were also pre-heated with a plasma flame to create an iron oxide surface on the substrate such that an exothermic thermite reaction takes place when molten splats of aluminium impinge the pre-heated substrate at sub- or supersonic velocities. A thermite reaction between iron oxide and aluminium allowed the formation of alumina, FeAl2O4, iron, and iron aluminide phases. The presence of FeAl2O4 and Al2O3 increased the surface hardnesses of the coating, and the hardnesses of the coatings are significantly higher than the hardnesses of steel substrate, and aluminium particles. X-ray analysis of the coatings, microstructural observations, and microhardness measurements suggest that plasma spraying conditions can be tailored to obtain coatings with high hardness values with in situ synthesized reinforcements (spinel and alumina) or iron aluminide phases. Aluminium-rich phases were observed in the as-deposited coatings when a mixture of aluminium and iron or aluminium and nickel were fed through the plasma gun in ratios equivalent to Fe3Al, FeAl, Ni3Al, and NiAl. In some cases, annealing allowed the formation of iron-rich or nickel-rich aluminide phases. High solidification rates of molten splats allowed very limited diffusional reactions between the splats of aluminium and iron, or aluminium and nickel because the available diffusional time for exothermic interfacial reactions is limited to a fraction of a second at best. Oxidation of part of the aluminium led to the formation of alumina in the as-deposited coatings, and therefore, a vacuum plasma spraying technique is desirable to obtain intermetallic phases. The results suggest that reactive spraying will allow deposition of coatings by utilizing the heats of reaction between the constituents, and reactive spraying will broaden the engineering applications of reaction synthesis techniques.     

Cyclic oxidation of Haynes 230 alloy

The cyclic oxidation of Haynes 230 alloy (Ni-Cr-W-Mo alloy) was investigated in air at three different temperatures, 871, 982 and 1093 °C. Studies indicated that during cyclic oxidation, protective scales formed which were predominantly Cr₂O₃, with Kirkendall voids formed both at the scale/alloy interface and grain boundaries. Intergranular oxides were observed at temperatures above 982 °C while internal oxide particles were found above 1093 °C. Both intergranular and internal oxides were identified as aluminium oxide. A 50 m chromium-depleted zone developed after 70 h exposure at 1093 °C and was accompanied by disastrous scale spalling. The lowest chromium concentration within the depleted zone was 14 wt% which still provided a sufficient supply of chromium for development of a continuous Cr₂O₃ rich scale. Decarburization was observed at the higher temperature of 1093 °C, and a carbide-free zone developed. Also, it was found that Haynes 230 is subject to a sensitization process. At the lower exposure temperature of 871 °C, large amounts of chromium carbide formed preferentially at the grain boundaries. While at the surface region chromium carbide precipitation occurred at the twin boundaries.     

Synthesis and characterization of composites of mixed oxides of iron and neodymium in polymer matrix of aniline-formaldehyde

Nanocomposites of mixed oxides of iron and neodymium in polymer matrix of aniline-formaldehyde are reported. The composites have been obtained by treating the aqueous solution of aniline, hydrochloric acid and formaldehyde with halide of iron and neodymium oxide. The infra-red spectra show broad peaks at ～ 590 cm^?1 and at ～ 610 cm^?1 due to the presence of oxides of both iron and neodymium. In heated samples, the absorption peaks due to metal oxides are better resolved. A broad and strong peak in XRD spectra at 2θ value of 35.69920 corresponds to spinel γ-Fe₂O₃. ⁵⁷Fe Mössbauer spectrum for unheated sample gives Mössbauer parameters, i.e. isomer shift (δ), quadrupole splitting (ΔE) and effective magnetic field (H_eff). Transmission electron microscopy (TEM) micrographs reveal well dispersed particles at different magnifications. Vibrating sample magnetometry (VSM) studies indicate that the ferrite nanoparticles exhibit characteristics of ferromagnetism.     

Physico-chemical characterisation of native air-formed oxide films on Al-Mg alloys at low temperature. Influence of water

Natural oxide films on two cold-rolled Al-Mg alloys were studied using several techniques (XPS, SIMS, ToF-SIMS, GDOS, SEM, TEM, Wetting measurements). The aim was to characterise and compare the oxide layers formed on the two materials in order to better understand the influence of the thermomechanical history. The experimental tools used allowed the determination of the influence of the annealing process on the nature and structure of the oxides. The hydration and Brönsted behaviour were also investigated. The thickness of the layer, the amount of magnesium oxide and its dissolving resistance in water are strongly modified by the annealing. The oxide film formed on the annealed material is twice as thick as the one on the non-reheated material. The layer on the annealed material contains more magnesium oxide and contains the crystalline forms:-Al₂O₃ and bayerite (Al(OH)₃). On the contrary, the oxide film formed on the as-rolled material seems to be amorphous. The magnesium oxide is less soluble in water in the annealed film than in the non-reheated one. Furthermore, aluminium and magnesium oxides were found to be hydroxylated on both alloys, and the layer surfaces to behave like a Brönsted meaning base.