Al(H2PO4)3/Al2O3复合硬质材料吸湿改性研究

磷酸二氢铝、磷酸铬铝等无机材料作为高温粘结剂具有固化收缩率低、高强度、耐高温等优点,被广泛应用于冶金、化工以及航天航空领域,但其可吸收空气中的水蒸汽,从而降低材料的强度和完整性.为减少无机高温粘结剂在大气环境下的吸湿量,以有机聚合物聚醚砜、无机添加剂氧化锆粉、热辐射屏蔽剂金粉制备出一种具有耐高温、低导热、热辐射屏蔽的复合密封材料,并将其应用在Al(H2PO4)3/Al2O3复合硬质材料的吸湿改性中.通过对比改性前后样品的扫描电镜图、吸湿率曲线,测试复合密封材料对基体材料吸湿性能的改性效果,并为研究喷涂密封材料对基体材料隔热、强度等性能的影响,进一步分析改性前后样品导热系数、弯曲强度的变化.结果表明,聚醚砜可在基体材料表面形成致密的密封膜,不仅可以隔绝空气中的水蒸汽,使吸湿率最高下降68.39％,还可以提升材料的弯曲强度.同时,金粉的添加可以形成辐射屏蔽层,从而降低材料的高温热导率.     

Mechanochemical synthesis of hydroxyapatite from Ca(OH)2-P2O5 and CaO-Ca(OH)2-P2O5 mixtures

Dry grinding of Ca(OH)₂-P₂O₅ and CaO-Ca(OH)₂-P₂O₅ mixtures was conducted by a planetary ball mill to investigate the mechanochemical solid-phase reaction for the synthesis of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp). HAp was synthesized by grinding of the two sets of mixtures. The formation of HAp from the Ca(OH)₂-P₂O₅ mixture was more advantageous than that from the CaO-Ca(OH)₂-P₂O₅ one. This synthesis reaction from the former mixture was almost completed within 30 min of grinding. The presence and amount of H₂O contained in the starting mixtures played a key role to promote the formation of HAp. Especially, in the former mixture, the prolonged grinding assisted the solid-phase reaction of the intermediate DCPD and Ca(OH)₂ to produce HAp more effectively.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Crystallization of AlPo4-5 from a system-1.5 (C3H7)3N.1.0Al2O3.1.0 P2O5. 40.0 H2O : Characterization of the products of crystallization

Crystallization of AlPO₄-5 from a gel of composition 1.5 Pr₃N (tripropylamine)· 1.0 Al₂O₃· 1.0 P₂O₅· 40.0 H₂O has been investigated by carrying out the hydrothermal synthesis of the crystalline aluminophosphate in a closed stainless steel pressure bomb at 423 K for different durations of the crystallization (0–48 h). The solid products obtained during the course of crystallization have been characterized thoroughly for their crystallinity (as AlPO₄-5), crystal size and morphology, N₂-sorption capacity (at 78 K and relative pressure of 0.3), thermal analysis, site energy distribution by TPD of pyridine, acidity by chemisorption of pyridine at 673 K and also for their catalytic activity in cumene cracking and o-xylene isomerization reactions at 673 K. The aluminophosphate formed at the different crystallization periods differ from each other largely in these properties. The optimum crystallization period for the synthesis of AlPO₄-5 is about 24 h.     

Thermal stability and decomposition kinetics of Li2Al4CO3(OH)12·3H2O

The thermal stability of lithium containing hydrotalcite, a material that has potential application for providing atmospheric corrosion protection to aluminium alloys, was investigated. Lithium aluminium carbonate hydroxide hydrate (Li₂Al₄CO₃(OH)₁₂·3H₂O) coatings were prepared by immersion of an 1100 aluminium alloy into a lithium carbonate-lithium hydroxide solution, and the bulk material was prepared by precipitation in the same solution. Thermal stability of the coatings and the bulk material existed to around 150 °C. Above this temperature, interlayer water was expelled, followed by loss of structural water and carbon dioxide. The kinetic parameters for interlayer water loss have been determined, and water loss can be described by a Johnson-Mehl-Avrami rate equation.     

Hydrothermal synthesis and luminescent properties of EuW2O6(OH)3 red micro-phosphors

Red phosphors EuW₂O₆(OH)₃ were synthesized via a facile hydrothermal method at different pH values (1, 2, 3, 4, 5, 6 and 7) at 180 °C for 24 h. The XRD patterns indicate that as-obtained phosphors exhibit monoclinic phase. The SEM results show that the as-obtained phosphors exhibit micro-spherical morphologies. The emission spectra under 394 nm excitation exhibit dominant peaks centered at 617 nm. pH value has a strong effect on the phosphor morphology and the emission intensity. The strongest 617 nm red emission was obtained at pH 6. The influence of morphology and crystal size on the intensity of red emission were discussed. The as-obtained micro-phosphors are potential candidate for red-emitting LED phosphors.     

Geometric isomerism of layered complexes of uranyl selenates: Synthesis and structure of (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)] and (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)](H2O)

New uranyl selenates with organic cations (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)] (I) and (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)](H₂O) (II) were synthesized by evaporation of aqueous solutions and studied. Compound I has monoclinic symmetry, space group C2/c, a = 16.7572(13), b = 11.7239(12), c = 19.0490(13) Å, β = 98.875(6)°, V = 3697.6(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.085 for 2868 reflections with |F _hkl | ≥ 4σ|F _hkl |. Compound II has monoclinic symmetry, space group P2₁/n, a = 10.8252(10), b = 19.0007(10), c = 18.6463(15) Å, β = 100.324(7)°, V = 3773.2(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.084 for 5721 reflections with |F _hkl | ≥ 4σ|F _khl |. The structures of I and II are based on layered complexes [(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)]^3? formed by combination of uranyl pentagonal bipyramids and selenate tetrahedra. H₃O⁺ cations, water molecules, and protonated methylbutylamine cations are located in the interlayer space. Geometric isomerism of two-dimensional complexes [(UO₂)₃(SeO₄)₅(H₂O)] in the structures of uranyl selenates was found and described.     

Crystal structure of a new organic dihydrogenomonophosphate (C6H8N3O)2(H2PO4)2

Chemical preparation, X-ray single-crystal, thermal behavior, and IR spectroscopy investigations are given for a new organic cation dihydrogenomonophosphate (C₆H₈N₃O)₂(H₂PO₄)₂ (denoted IAHP) in the solid state. This compound crystallizes in the orthorhombic space group P2₁2₁2₁. The unit cell dimensions are: a = 7.422(3) Å, b = 12.568(5) Å, c = 20.059(8) Å with V = 1871.1(13) Å³ and Z = 4. The structure has been solved using direct method and refined to a reliability R factor of 0.029. The atomic arrangement can be described as inorganic layers of H₂PO₄⁻ anions between which are located the organic groups (C₆H₈N₃O)⁺ through multiple hydrogen bonds.     

Solid solutions between ettringite, Ca6Al2(SO4)3(OH)12·26H2O, and thaumasite, Ca3SiSO4CO3(OH)6·12H2O

A series of solid solution phases between ettringite, Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O, and thaumasite, Ca₃SiSO₄CO₃(OH)₆·12H₂O, have been prepared and analysed by X-ray powder diffraction and full pattern fitting. Solid solutions were shown to exist with both the ettringite structure (space group P31c) and the thaumasite structure (space group P6₃, c-axis halved). A possible discontinuity was identified, characterised by a gap in the a-dimension of the solid solution phases produced. This discontinuity is believed to correspond to a switch between the ettringite space group and the thaumasite space group. It is suggested that any discontinuity in the solid solution is caused by differences in the hydrogen bonding of the two structures.     

Combustion synthesis and dielectric properties of B4C/Al2O3/CNTs composite powders

Journal of Materials Science: Materials in Electronics - To develop a novel high-temperature microwave absorber, B4C/Al2O3/CNTs composite powders were prepared by a combustion synthesis method. The...     

The effect of MgAl2O4 on the formation kinetics of Al2TiO5 from Al2O3 and TiO2 fine powders

The formation of Al_2(1–x)Mg _x Ti_(1+x)O₅ solid solutions from Al₂O₃-TiO₂-MgAl₂O₄ powder mixtures of 1 m particle size and moderate purity has been studied at 1300°C for different final composition values: x=0 (pure Al₂TiO₅), 10^–3, 10^–2 and 10^–1. Analysis of the kinetic data and microstructural observation indicates that MgAl₂O₄ affects the mechanism of Al₂TiO₅ formation by providing active nuclei for the growth of the new phase. These nuclei are probably constituted by Mg_0.5AlTi_1.5O₅, i.e. the equimolar Al₂TiO₅-MgTi₂O₅ solid solution, and are formed by reaction between MgAl₂O₄ and TiO₂ at temperatures above 1150 °C. As the value of x increases, the number of titanate particles per unit volume accordingly increases and the conversion of the original oxides is faster. At values of x10^–2, the prevailing mechanism is the nucleation and growth of Al₂TiO₅ nodules for fractional conversion up to 0.8. Further conversion of the residual Al₂O₃ and TiO₂ particles dispersed into the titanate nodules is slower and controlled by solid-state diffusion through Al₂TiO₅. At x=0.1, a large number of nucleation sites is present, and solid-state diffusion through Al₂TiO₅ becomes important even in the initial stage of reaction, as the diffusion distances are strongly reduced. The study of Al₂TiO₅ formation under non-isothermal conditions in the temperature range 1250–1550°C shows that reaction proceeds between 1300 and 1350 °C for x=0.01 and between 1250 and 1300 °C for x=0.1. Densification of the titanate becomes important at temperatures above 1300°C for x=0.1, but only above 1450 °C for x=0.01.     

Nucleation studies in supersaturated aqueous solutions of (NH4)H2PO4 doped with (NH4)2C2O4·H2O

Induction periods were measured for various supersaturated aqueous solutions of ammonium dihydrogen orthophosphate doped with ammounium oxalate monohydrate by the direct vision method. Various critical nucleation parameters were calculated based on classical theory for homogeneous crystal nucleation and the results reported and discussed. The critical nucleation parameters increased with increase in doping concentration.     

Non-aqueous synthesis of water-dispersible Fe3O4-Ca3(PO4)2 core-shell nanoparticles

The Fe(3)O(4)-Ca(3)(PO(4))(2) core-shell nanoparticles were prepared by one-pot non-aqueous nanoemulsion with the assistance of a biocompatible triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO), integrating the magnetic properties of Fe(3)O(4) and the bioactive functions of Ca(3)(PO(4))(2) into single entities. The Fe(3)O(4) nanoparticles were pre-formed first by thermal reduction of Fe(acac)(3) and then the Ca(3)(PO(4))(2) layer was coated by simultaneous deposition of Ca(2+) and PO(4)(3-). The characterization shows that the combination of the two materials into a core-shell nanostructure retains the magnetic properties and the Ca(3)(PO(4))(2) shell forms an hcp phase (a = 7.490 ?, c = 9.534 ?) on the Fe(3)O(4) surface. The magnetic hysteresis curves of the nanoparticles were further elucidated by the Langevin equation, giving an estimation of the effective magnetic dimension of the nanoparticles and reflecting the enhanced susceptibility response as a result of the surface covering. Fourier transform infrared (FTIR) analysis provides the characteristic vibrations of Ca(3)(PO(4))(2) and the presence of the polymer surfactant on the nanoparticle surface. Moreover, the nanoparticles could be directly transferred to water and the aqueous dispersion-collection process of the nanoparticles was demonstrated for application readiness of such core-shell nanostructures in an aqueous medium. Thus, the construction of Fe(3)O(4) and Ca(3)(PO(4))(2) in the core-shell nanostructure has conspicuously led to enhanced performance and multi-functionalities, offering various possible applications of the nanoparticles.     

Synthesis of Macroscopic Zr（C6H5PO3）2 Tubes

A new method of infiltration-diffusion is used to synthesize macroscopic α-Zr（C6H5PO3）2 （α-ZrBP） tube. Compared to the routine method, no HF was used and a fiberlike product with several millimeters in length was obtained. SEM （scanning electronic microscopy） result indicates that these fibers are tubes. The wall of the tubes is composed of the flake of α-ZrBP overlapped with each other. As we know, it is the first report on the synthesis of millimeter-scale supramolecular assembly of α-ZrBP.