Optical properties of oxynitride powders

International audience(Oxy)nitride materials have attractive properties directly related to the role played by nitrogen. A commonly used synthesis method consists of the thermal nitridation of an oxide precursor in flowing ammonia. As a consequence of the anionic N3-/O2- substitution results an increase in the covalent character, illustrated by a shift of the absorption edge towards higher wavelength values. Thus, oxynitrides offer potentialities as optical materials in the domain of colored pigments, UV absorbers and visible-light photocatalysts

Cation Exchange Properties of Tetratitanic Acid with Interlayer Protons and of Titania with Surface Hydroxyl Protons

Cation exchange properties of tetratitanic acid with interlayer protons were measured and compared to those of titania with surface hydroxyl protons using the Frumkin equation. Tetratitanic acid showed larger ion-exchange capacity and much higher activity than titania. The characteristics of exchangeable protons and intercalated cations are discussed to explain the different ion-exchange properties. The interlayer protons of tetratitanic acid can be regarded as acid functional groups of an oxoacid of TiIV, and acid functional groups dissociate much more easily than the surface hydroxyl groups on titania that are formed by hydration. The cations intercalated into tetratitanate are sandwiched between opposing titanate layers with negative charges and are better stabilized than the cations adsorbed on the outer surfaces of titania owing to better neutralization of cationic charges

Aging Is a Risk Factor for Utricular Dysfunction in Idiopathic Benign Paroxysmal Positional Vertigo

Benign paroxysmal positional vertigo (BPPV) is the most common cause of balance disorders in the elderly. Dislodgement of the otoconia in BPPV might have an association with damage to the otolith organs. The aim of this study was to investigate whether aging is a risk factor for otolith organ dysfunction in idiopathic BPPV. We retrospectively reviewed the medical records of 112 consecutive idiopathic BPPV patients who underwent cervical VEMP testing to air-conducted sound (ACS cVEMP), ocular VEMP testing to bone-conducted vibration (BCV oVEMP), and caloric testing. We performed binomial logistic regression analyses to see whether age, the side affected by BPPV or the canal affected by BPPV have an association with the presence of peripheral vestibular dysfunction in idiopathic BPPV patients. The elderly group (aged ≥65 years) had a significantly positive association with abnormalities in BCV oVEMPs (p = 0.0109), while the side affected by BPPV (p = 0.598) and the canal affected by BPPV (p = 0.576) did not. The odds ratio of the abnormal BCV oVEMPs for the elderly group compared with the non-elderly group (aged < 65 years) was 2.676 (95% confidence interval, 1.254–5.079). The elderly group had no significant association with the abnormalities in ACS cVEMPs (p = 0.0955) or caloric testing (p = 0.488). Dysfunction of the utricle, where the dislodgement of the otoconia mainly occurs, is affected by aging in idiopathic BPPV

Magnetoplumbite and W-type barium ferrites as magnetic mixture with hematite

Magnetic properties were studied on polycrystalline composite mixtures of magnetoplumbite-type BaFe12O19 and W-type BaCo2Fe16O27 ferrites with α-Fe2O3. The respective ferrite mixtures were prepared with hematite in 0 to 70 mol% using solid state reaction. X-ray diffraction (XRD) analysis and magnetic measurement suggested the products were simple mixtures of the ferromagnetic BaFe12O19 or BaCo2Fe16O27 with α-Fe2O3 even after sintering at 1250°C. Their magnetization decreased with the increasing contents of α-Fe2O3. Their electrical resistivities of higher than 102 Ωm were too large to observe their magnetic field dependence, magnetoresistance (MR) effect. Electrical resistivity decreased to 0.36 Ωm by the post annealing of the as prepared BaCo2Fe16O27 with a small amount of α-Fe2O3 in Ar at 1000°C for 5 h. The improved electrical conductivity in 4 orders of magnitude showed the MR effect of 0.86% on the post annealed BaCo2Fe16O27 product

Synthesis, thermal stability, and oxygen intake/release characteristics of YBa(Co1−xAlx)4O7+δ

The YBaCo4O7+d (Y-114) phase has recently attracted interests as a potential oxygen storagematerial due to its oxygen intake/release capability at 200–400 8C. Nevertheless, thermal instability of Y-114 has been an obstacle for future applications, since this compound immediately starts to decompose when the sample is heated at 700–800 8C in oxygen-rich atmosphere. Here we demonstrate that Al-for-Co substitution in Y-114 drastically enhances the thermal stability. Substituting only 10 at.% of aluminum for cobalt in Y-114 essentially suppresses the decomposition reaction seen at 700–800 8C, while well retaining its remarkable oxygen intake/release capability at 200–400 8C. It is also revealed that the addition of aluminum effectively reduces the particle size. The Al-substituted Y-114 products exhibit superior oxygen intake/release response to the Al-free products upon switching the atmosphere between O2 and N2

Iron source effect on BaFe12O19 preparation through citrate route

Both magnetization and coercivity should be controlled on BaFe12O19 for its usage in magnetic recording. Preparation of BaFe12O19 was studied in citrate route by changing the kinds of iron source. Stoichiometric mixtures of iron compounds with Ba(NO3)2 were dissolved in distilled water. They were mixed with citric acid aqueous solution and then condensed on a hot plate to their gelatinous products. Their prefired products below 450°C were pelletized and then fired in a temperature range between 750 and 900°C. The product from iron nitrate was a mixture of α-Fe2O3, BaFe2O4 and a small amount of BaFe12O19. The product from Fe(acac)3 was pure BaFe12O19 fine powder with a crystallite size of < 90 nm. The fine powdered product at 850°C had a saturation magnetization of 58.5 emu·g-1 and a coercivity of 5.5 kÖe