La-Co替代的M型永磁铁氧体

对La-Co替代的M型高性能永磁铁氧体进行了详细介绍,包括材料制备的工艺特点,成分,显微结构,材料的内禀参数,技术磁性能以及温度特性等.研究结果表明最优化组分为Sr0.7La0.3Fe11.7Co0.3O19的M型永磁铁氧体的饱和磁化强度Ms(298K)比SrFe12O19永磁铁氧体的大1%～3%,磁晶各向异性场Ha大16.8%,磁晶各向异性常数K1大16.7%,磁性能Br=450mT,Hcj=384kA/m,(BH)max=38.6kJ/m3.     

Cement from magnesium substituted hydroxyapatite

Brushite cement may be used as a bone graft material and is more soluble than apatite in physiological conditions. Consequently it is considerably more resorbable in vivo than apatite forming cements. Brushite cement formation has previously been reported by our group following the mixture of nanocrystalline hydroxyapatite and phosphoric acid. In this study, brushite cement was formed from the reaction of nanocrystalline magnesium-substituted hydroxyapatite with phosphoric acid in an attempt to produce a magnesium substituted brushite cement. The presence of magnesium was shown to have a strong effect on cement composition and strength. Additionally the presence of magnesium in brushite cement was found to reduce the extent of brushite hydrolysis resulting in the formation of HA. By incorporating magnesium ions in the apatite reactant structure the concentration of magnesium ions in the liquid phase of the cement was controlled by the dissolution rate of the apatite. This approach may be used to supply other ions to cement systems during setting as a means to manipulate the clinical performance and characteristics of brushite cements.     

Electrochemistry of carbazolylalkyl substituted polysiloxanes

Carbazolylalkyl-substituted polysiloxanes undergo anodic oxidation to give insoluble electrode supported cross-linked films containing dicarbazolyl groups. The electrochemistry of the immobilized dicarbazolyls can be addressed and the electrochemical switching between the coloured (oxidized) and colourless (reduced) states forms the basis of an electrochromic display. Cyclic voltammetry suggests a model in which virtually all of the pendant carbazole groups are converted into dicarbazolyls. The model is consistent with observation of a range of polymers, and analogous oligomers, and contrasts with earlier reports on the same type of material.     

Electrochemistry of carbazolylalkyl substituted polysiloxanes

Carbazolylalkyl-substituted polysiloxanes undergo anodic oxidation to give insoluble electrode supported cross-linked films containing dicarbazolyl groups. The electrochemistry of the immobilized dicarbazolyls can be addressed and the electrochemical switching between the coloured (oxidized) and colourless (reduced) states forms the basis of an electrochromic display. Cyclic voltammetry suggests a model in which virtually all of the pendant carbazole groups are converted into dicarbazolyls. The model is consistent with observation of a range of polymers, and analogous oligomers, and contrasts with earlier reports on the same type of material.     

Comparison of Ge substituted and Ga substituted garnet for 1.5 μm diameter bubble devices

A comparison has been made of (YSmLuCa)₃(FeGe)₅O₁₂ and (YSmLuGd)₃(FeGa)₅O₁₂ for 1.5 μm diameter bubble devices. The melt composition for film growth, and a summary of magnetic properties, are presented here for each composition.Y_1.1Sm_0.4Lu_0.7Ca_0.8Fe_4.2Ge_0.8O₁₂ has a higher Curie temperature (222°C) and shows a collapse field temperature coefficient (?0.20%/°C) over a wider temperature range (?20 ～ 80°C). Both materials demonstrate nearly the same saturation induction (530 ～ 540 G) and wall mobility (410 ～ 450 cm/sec/Oe) in films with a characteristic length of ? = 0.17 μm and an anisotropy field of Hk = 1900 Oe. It seems that (YSmLuCa)₃(FeGe)₅O₁₂ is more suitable for practical use from the viewpoint of temperature properties.     

Transport properties of trivalent substituted Li-ferrites

The electrical resistivity and thermoelectric power of Li_0.5Fe_2.5–x R _x O₄ (R = Al, La, Sm and Gd; x = 0.0 and 0.1) are studied. The distribution of the substituted ions over the different lattice sites is determined from IR spectra. The electrical resistivity is found to have a direct relation with the ionic radius of the substituted R ions. Meanwhile, the absolute value of thermoelectric power decreased with increasing ionic radius.     

NiTi substituted hexaferrites for magnetic recording

In order to obtain hexagonal ferrites with improved characteristics for application in the field of the magnetic recording, the ferrimagnetic Sr(NiTi)_x Fe_12-2xO₁₉ system is studied. Preliminary investigations suggested that NI is more effective than Co in reducing the magnetic anisotropy of hexaferrites. The system was analyzed as a function of the degree of substitution x and of the reaction temperature T_R and time τ. The reactivity of the mixtures and their magnetic characteristics (σ, H_c, H_A, T_c) were measured, and from the _χT(H) data it was possible to distinguish between single-domain or polydomain particles. The results are presented. The influence of the extraneous magnetic phases on the coercive field value was also studied and a preliminary investigation of the relation between coercive and anisotropy fields was carried out     

Phenol and substituted phenols AOPs remediation

The oxidation of phenol and two substituted species (4-nitrophenol and 4-chlorophenol) has been carried out by means of the O3, UV-vis, O3+UV-vis, TiO2+UV-vis, O(3)+UV-vis+TiO2 and O3+TiO2 systems. From UV-vis experiments, the quantum yield of these organics has been calculated (0.018, 0.005 and 0.017 mol per Einstein for phenol, 4-nitrophenol and 4-chlorophenol, respectively). Broadly speaking, the addition of titania powder results in a slight inhibition of the parent compound degradation rate, although a positive effect is experienced when measuring the chemical oxygen demand (COD) and total organic carbon (TOC) removals. Amongst the technologies investigated, those combining ozone and radiation show the best efficiency in terms of phenols elimination and also COD and TOC decay rates. A simple economy analysis of the processes illustrates how the combinations O3+UV-vis and O3+UV-vis+TiO2 are the most attractive technologies, although some additional considerations have to be taken into account.     

Neutron diffraction of chlorine substituted fluorapatite

Fluorapatite, chlorapatite and a mixed apatite synthesised by a high temperature solid state reaction route were analysed using time-of-flight neutron diffraction of the series Ca₅(PO₄)₃F_1 − xCl_x, where x = 0.0, 0.5 and 1.0. Fluorapatite and the mixed apatite were found to be hexagonal in crystal structure. The chlorapatite was monoclinic in structure. The lattice parameters a and b increased with chlorine addition while c decreased. The unit cell volume increased linearly with chlorine content and the density decreased. The Ca(1)O₆ metaprism twist angle (φ) decreased with chlorine addition indicating a tendency towards ideal hcp packing.     

Characterization of a natural substituted pyromorphite

Pyromorphite (Pb5(PO4)3Cl) which occurs in the oxidation zone of a polymetallic Pb–Zn–Ag–Au vein in Paramillos de Uspallata, Mendoza, Argentina, was studied by scanning electron microscopy (including energy dispersive analysis of X-rays (EDAX) electron microprobe), i.r. and Raman spectroscopies and X-ray powder diffraction analysis. The substitution of Pb by Ca and Ba and Cl by OH, respectively, have been detected. In addition, i.r. absorption bands for the CO2-3 ν3-mode have been clearly identified. They are attributed to the CO2-3 for PO-34 substitution in the structure. The composition is regarded as an indication of the paragenesis of the host rocks and the mineralogy of the deposit. This revised version was published online in November 2006 with corrections to the Cover Date.     

Conduction in Mn substituted Ni-Zn ferrites

The d.c. electrical resistivity ‘ρ’ and thermoelectric power ‘α’ are studied as a function of temperature for Mn substituted ferrites with general formula Zn_0·3Ni_0·7+x Mn _x Fe_2−2x O₄. At lower Mn concentrations, the increase in d.c. resistivity is attributed to the hindering of Verwey mechanism Fe²⁺ ⇌ Fe³⁺ due to stable bonds of Mn³⁺ + Fe²⁺ pair. The decrease in resistivity at higher Mn concentrations (i.e. whenx > 0·15) is attributed to the formation of Mn³⁺ cluster and Ni²⁺ ⇌ Ni³⁺. The activation energy values show one to one correspondence with resistivity values. The compositional variation of thermoelectric power showsn-type behaviour for the samples withx < 0·2 whereasp-type behaviour for the samples withx ⩾ 0·2. Thep −n transition is attributed to the formation of Ni³⁺, Fe²⁺ + vacancies which act asp-type carriers. The temperature dependences ofα, ρ, and mobility clearly confirm the conduction mechanism to be due to polaron hopping.     

Cadmium substituted high permeability lithium ferrite

Polycrystalline Li_0.5-x/2Cd_xFe_2.5-x/22O₄ ferrites wherex = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were prepared by a double sintering ceramic technique and characterized by X-ray diffraction and scanning electron microscopy (SEM). The lattice parameter is found to increase monotonically with the cadmium content. It is explained in terms of the sizes of component ions. The grain size of the samples increases up tox = 0.3 and then it decreases for higher values ofx. A similar trend is observed in the variation of Ms with Cd²⁺ content. The initial permeability (μ_i) is however found to increase continuously withx. The increase in μ_i is attributed to decrease of anisotropy constant K₁ and higher grain size of the samples.     

Magnetic properties of Cu substituted Co-ferrite

Copper substituted Co-Cu ferrites Co_1 − xCu_xFe₂O₄ (0 ≤ x≤0.5) have been studied with Mössbauer spectroscopy, x-ray diffraction, and vibrating sample magnetometer (VSM). The Co-Cu ferrite toroidal core samples were sintered at 860-940 °C for 2 h and the initial permeability, quality factor, density and shrinkage were also measured. The crystal structure was found to be an inverse cubic spinel with the lattice constant a₀ = 8.390 Å and a₀ = 8.386 Å for Co-ferrite and Cu²⁺ substituted Co-ferrite, respectively, by Rietveld profile analysis using the FULLPROF program. Hyperfine field was decreased with increasing Cu²⁺ concentration. The saturation magnetization (Ms) of the Co-Cu ferrite annealed at 900 °C decreased drastically and the coercivity, Hc, dropped dramatically from about 1419 to 455 Oe as copper concentration x decreased from 0.0 to 0.5. This shows that Ms, Hc can be controlled using Cu content, and initial permeability and quality factor Q is nearly constant in Cu²⁺ substituted Co-ferrite. The toroidal core data showed that the density and shrinkage of Co_1 − xCu_xFe₂O₄ (0≤x ≤ 0.5) ferrites increased with increasing quantity of Cu ions.     

New transition metal substituted cadmium tellurides

While crystal growth and physical phenomena in the Mn_xCd_−xTe system have been extensively investigated, little is known about the substitution of other transition metals in cadmium telluride. We have examined the substitution of Fe, Co, and Ni for Cd in CdTe. We find that Co and Ni have very low solubilities in CdTe less than a percent while Fe can be substituted to ≈ 10%. Magnetic susceptibility shows that the iron sites couple antiferromagnetically and gives evidence for clustering at higher Fe concentrations. The lattice constant is observed to decrease with increasing iron concentration, behavior similar to that observed in Mn_xCd_1−xTe. Manganese cadmium tellurides have shown interesting magneto-optical properties. Investigations of this newly formed analog. Fe_xCd_1−xTe, may reveal interesting behavior in this system as well.     

Initial mechanisms involved in substituted magnetite oxidation

The oxidation kinetics of slightly-substituted and pure magnetites, at low conversion ratio is controlled, both by diffusion and surface reaction. However, for highly-subtituted magnetites, diffusion is the sole regulating process. The results are related to the semiconducting properties of the compounds.     

Preparation and characterization of selenite substituted hydroxyapatite

Selenite-substituted hydroxyapatite (Se-HA) with different Se/P ratios was synthesized by a co-precipitation method, using sodium selenite (Na₂SeO₃) as a Se source. Selenium has been incorporated into the hydroxyapatite lattice by partially replacing phosphate (PO₄^3 ?) groups with selenite (SeO₃^2 ?) groups. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) techniques reveal that substitutions of phosphate groups by selenite groups cause lower carbonate groups occupying at phosphate sites and change the lattice parameters of hydroxyapatite. The powders obtained are nano-crystalline hydroxyapatite when the Se/P ratios are not more than 0.1. The particle shape of Se-HA has not been altered compared with selenite-free hydroxyapatite but Se-incorporation reduces the crystallite size. The crystallinity was reduced as the Se/P ratios increased until amorphous phase (Se/P = 0.3) appeared in the Se-HA powder obtained, and then another crystal phase presented as calcium selenite hydrate (Se/P = 10). In addition, the sintering tests show that the Se-HA powders with the Se/P ratio of 0.1 have thermal stability at 900 °C for 2 h; hence they have great potential in the fabrication of bone repair scaffolds.     

Mn掺杂快淬NdFeB永磁体磁性能研究

在前期研究工作的基础上,从热磁重(TMA)测量出发对快淬Nd9Fe85-xMnxB6(x=0～2)的相关磁性能及交换耦合效应作了进一步的研究.发现在最佳的热处理条件下,一定的Mn掺杂能提高快淬NdFeB的磁性能,特别是矫顽力最大能提高20%左右,但是更高的Mn掺杂量会导致矫顽力和最大磁能积的明显下降.XRD显示快淬态的NdFeB样品的晶化程度随Mn掺杂量提高而提高,但在最佳的热处理条件下所有的快淬NdFeB样品都包括硬磁性相Nd2Fe14B和软磁性相α-Fe.热磁重(TMA)测量显示一直随着Mn掺杂量提高到2%(原子分数),硬磁性相Nd2Fe14B的居里温度(Tc)在不断下降,但是α-Fe的Tc却随Mn掺杂量提高而提高.认为磁性能和居里温度改变是因为形成了δ-Mn和R2Fe23B3相.当Mn掺杂量较低时高温下有δ-Mn形成并和α-Fe产生交换耦合作用导致α-Fe的居里温度升高,而当Mn掺杂量提高到2at%时形成的R2Fe23B3相固溶δ-Mn相才导致α-Fe的居里温度下降.