Ab initio calculations of the hydroxyl impurities in BaF2

OH^? impurities in BaF₂ crystal have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. Three different configurations of OH^? impurities were investigated and the (1 1 1)-oriented OH^? configuration is the most stable one. Our calculations show that OH^? as an atomic group has a steady geometrical structure instead of electronic properties in different materials. The studies on band structures and density of states (DOS) of the OH^?-impurity systems indicate that there are two defect levels induced by OH^? impurities. The two superposed occupied OH^?-bands located 1.95 eV above the valance bands (VB) at Γ point mainly consist of the O p orbitals, and the H s orbitals do the major contribution to the empty defect level located 0.78 eV below the conduction bands (CB). The optical absorption due to the doped OH^? is centered around 8.61 eV.     

Radiation effects in natural quartz crystals

Optically clear, as visually observed, natural quartz crystals of Brazilian and Arkansas origins, which exhibit Al–OH^?-centers in their as-received conditions, have been measured for their low temperature ESR spectra to see the presence of Al-hole centers. The ESR spectra revealed the presence of Al-hole centers in their as-received conditions. These centers showed an increase in their strength upon irradiation with a ⁶⁰C0 source. Such observations were exhibited by Al–OH^?-centers as noticed earlier. The crystals were thus noticed to exhibit the presence of Al–OH^?-centers and also Al-hole centers in their as-received conditions. The observations match with the results on cultured quartz where irradiation breaks away the Al-alkali centers into a mixture of Al–OH^?- and Al-hole centers. It is thus concluded that the natural crystals, which exhibit the presence of these centers in their as-received condition, have been irradiated in nature with a low dose.     

Factors influencing chloride-induced corrosion of reinforcement in concrete

The paper presents the results of a corrosion investigation on rebar electrodes embedded in concrete prism specimens which were exposed to cycles of sea-water spray for up to about 600 days (1200 marine cycles). The w/c ratio of the matrix was varied between 0.45 and 0.76 and the cement content ranged between 330 and 530 kg m^?3. Corrosion potential and polarization resistance of the electrodes were monitored at regular intervals by means of electrochemical procedures using a potentiostat apparatus. The Cl^? and OH^? concentrations in the matrix were also determined at the level of rebar electrodes. The results show that cement content has an insignificant influence on rebar corrosion, w/c ratio being the dominant factor which controls corrosion. The Cl^? and OH^? concentrations of the pore fluid are of secondary importance relative to w/c ratio. Acceptable corrosion rates are achieved at a w/c of 0.45, with the pore fluid Cl^?/OH^? ratio reaching a value of 11.     

Impurity-conditioned solid-solid transition in simple halides

Solid-solid transitions are well known for many simple halides. All of the rare earth fluorides, RF₃, with atomic number greater than that of Nd have been reported to crystallize to the hexagonal form at the melting temperature (T_mp), and subsequently invert to the orthorhombic form at some lower temperature (T_ss) (2). The temperature difference T_mp - T_ss = Δt reported in the literature (3) is 300°C for GdF₃, 124°C for DyF₃, and 73°C for HoF₃. Using GdF₃, DyF₃, and HoF₃, DTA measurements show T_ss (and therefore Δt) to be impurity-sensitive. Results indicate that the hydroxyl ion, OH^?, is the impurity. DTA measurements show Δt = 0 when OH^? concentration approaches zero. Moreover, crystal growth from the melt in a reactive atmosphere chosen to minimize OH^? directly yields the orthorhombic phase. Consequently, according to the phase rule, hexagonal orthorhomic is not an equilibrium process involving only one component at constant pressure. By minimizing OH^? concentration, large single crystals (>1 cm in length) of many halides previously thought to exhibit dimorphism have been grown from the melt.     

Increased reactivity and in vitro cell response of titanium based implant surfaces after anodic oxidation

In the quest for improved bone growth and attachment around dental implants, chemical surface modifications are one possibility for future developments. The biological properties of titanium based materials can be further enhanced with methods like anodic polarization to produce an active rather than a passive titanium oxide surface. Here we investigate the formation of hydroxide groups on sand blasted and acid etched titanium and titanium–zirconium alloy surfaces after anodic polarization in an alkaline solution. X-ray photoelectron spectroscopy shows that the activated surfaces had increased reactivity. Furthermore the activated surfaces show up to threefold increase in OH^? concentration in comparison to the original surface. The surface parameters S_a, S_ku, S_dr and S_sk were more closely correlated to time and current density for titanium than for titanium–zirconium. Studies with MC3T3-E1 osteoblastic cells showed that OH^? activated surfaces increased mRNA levels of osteocalcin and collagen-I.     

Study on the temperature dependence of the OH− absorption band in Hf-doped LiNbO3 crystals

We study in this paper the temperature dependence of the OH^? absorption band in LiNbO₃ crystals with different Hf-doping concentrations. It is found that the shoulder at 3500 cm^?1 appears in the doping level of 2.6 mol%, becomes more evident at 3 and 4 mol%, and then gradually faints when the doping concentration increases. This result is explained by the non-monotonic change of Nb vacancy density in the three stages of the defect evolution involved in the Hf incorporation of LN lattice. Moreover, the absorption difference analysis of the OH^? bands is consistent with this explanation and reveals that the mobility of H⁺ ions may be reduced by the strong trapping of the highly electronegative Nb vacancies.     

Reactive atmosphere processing of oxides

Concepts of reactive atmosphere process (RAP) are extended to the cleanup of OH^? impurities in Ln₂O₃. Chlorine is unsuitable as this halogen converts Ln₂O₃ to LnOCl quantitatively. Iodine is shown to be suitable for OH^? impurity cleanup of Ln₂O₃.     

Determination de la structure cristalline de la variete a des hydroxycarbonates de terres rares LnOHCO3 (Ln = Na)

A probable model for the structure of the orthorhombic A - type neodymium hydroxycarbonate is presented. It relies on an optical determination of the site symmetry of OH^?, CO^2?₃, and Nd³⁺ atoms from infrared and visible absorption spectra, together with a computation of 50 X-ray diffraction lines intensities of a high resolution Guinier orthorhombic powder pattern ($\text{a}\text{= 4,953}\text{A}\text{?}$, $\text{b}\text{= 8,477}\text{A}\text{?}$, $\text{c}\text{= 7,210}\text{A}\text{?}$; space group Pmcn (n^o62)). The CO^2?₃ groups lies flat between mettalic planes as in the aragonite type of structure and are linked to OH^? by hydrogen bond ($\text{d(CO}{}^{\mathrm{2?}}{}_3\text{?}\text{OH}{}^{\mathrm{?}}\text{) = 2,52}\text{A}\text{?}$). The rare earth coordination is nine fold: two OH^? groups being closer (2,58 Å) than the seven oxygen from the CO^2?₃ groups (2,58 to 2,70 Å).     

Atomic carbon in magnesium oxide Part VII: Infrared analysis of OH-containing defects

The multitude of OH stretching bands in the near IR in arc-fused MgO can be divided into two main groups, a triangular shaped band at 3548 cm^?1 (300K) which strongly shifts and splits to a triplet at 3571, 3566 and 3550 cm^?1 upon cooling to 82 K, a quadruplet at 3297, 3312, 3327 and 3342 cm^?1 (82 K), plus a broad background absorption extending from 3600 – 3300 cm^?1. The H-H band at 4150 cm^?1 points at molecular H formed by charge transfer from [OH^· V″_Ma HO^·]^x = [O^· (H₂)″_Mg O^·]^x. The broad background absorption is assigned to interstitial protons, H^·₁. The 3300 and 3550 cm^?1 groups are assigned to the diamagnetic defects [OH^· V″_Ma]¹ and [OH^· V″_Mg HO^·]^x respectively. Their multiplet structure is explained by interaction of the OH oscillator with near-by C^x₁ atoms on interstitial sites surrounded by an elastic strain halo which causes local lattice expansion.     

Synthesis of magnetite nanoparticles by surfactant-free electrochemical method in an aqueous system

A simple surfactant-free electrochemical method is proposed for the preparation of magnetite nanoparticles using iron as the anode and plain water as the electrolyte. This study observed the effects of certain parameters on the formation of magnetite nanoparticles and their mechanism in the system, including the role of OH^? ions, the distance between electrodes and current density. We found that OH^? ions play an important role in the formation of magnetite nanoparticles. Particle size can be controlled by adjusting the current density and the distance between electrodes. Particle size increases by increasing the current density and by decreasing the distance between electrodes. Particle formation cannot be favored when the distance between electrodes is larger than a critical value. The magnetite nanoparticles produced by this method are nearly spherical with a mean size ranging from 10 to 30 nm depending on the experimental conditions. They exhibit ferromagnetic properties with a coercivity ranging from 140 to 295 Oe and a saturation magnetization ranging from 60 to 70 emu g^?1, which is lower than that of the corresponding bulk Fe₃O₄ (92 emu g^?1). This simple method appears to be promising as a synthetic route to producing magnetite nanoparticles.     

Potential of the NP(VI)/Np(V) couple in solutions of various alkalis

The formal potentials of the Np(VI)/Np(V) couple E ^f in alkaline solutions were measured potentiometrically. In 1 M LiOH, NaOH, KOH, CsOH, and (CH₃)₄NOH, the potentials are equal to 0.163⊥0.004, 0.125⊥0.005, 0.112⊥0.005, 0.107⊥0.005, and 0.109⊥0.005 V, respectively. In solutions of MOH+MCl [M=Li, Na, K, Cs, and (CH₃)₄N] at the ionic strength of 1, the dependence of E ^f on log[OH^?] is a straight line with a slope of 0.118⊥0.010, i.e., two OH^? ions participate in the electrochemical reaction between Np(VI) and Np(V). Taking into account the well-known structure of Np(VI), it can be stated that Np(V) in solutions with [OH^?]=1 M and less exists in the form of the NpO₂(OH) ₂ ^? anion. In 2–4 M LiOH and 2–11 M NaOH or KOH, the potential decreases with increasing alkali concentration. In these media, the anion NpO₂(OH) ₃ ^2? is formed.     

Measurement and modelling of membrane potentials across OPC mortar specimens between 0.5 M NaCl and simulated pore solutions

This paper reports experimental measurement and theoretical simulations of membrane potentials across OPC mortar specimens between 0.5 M NaCl and simulated pore solutions with various OH⁻ concentrations. The effect of OH⁻ counter transport and cation transport on membrane potentials is discussed. Membrane potentials are found to increase with an increase in OH⁻ concentration. Model simulations are consistent with the measured membrane potentials. This study confirms that cations diffuse much more slowly than anions and that OH⁻ ions diffuse significantly faster than Cl⁻ ions. Membrane potentials across OPC mortar specimens between NaCl and simulated pore solutions are mainly determined by OH⁻ and Cl⁻ transport. A simplified Henderson equation is recommended for membrane potential modelling of thin specimens in diffusion cell tests in which simulated pore solutions are used.     

The lithium and molecular intercalates of FeOCl

Lithium intercalation compounds of the lamellar iron oxychloride have been obtained by means of the butyl lithium technique. Chemical and geometrical considerations suggest that the Li⁺ ions are localized in octahedral sites. Molecular intercalates are formed with amines. Single crystal studies on FeOCl (C₅H₅N)_0.33 show the existence of a superstructure along the a axis. It may be related to an alternate arrangement of the pyridine molecules between the chlorine layers of the host structure. Univalent groups such as OH^?, NH^?₂, (CH₃NH)^? can also be substituted for the chlorine ions in the FeOCl structure.     

Equilibria,kinetics and mechanism for the degradation of the cytotoxic compound L-NG-nitroarginine

L-N^G-nitroarginine (LNNA), an analog of L-arginine, is a competitive inhibitor of nitric oxide synthase which causes the selective reduction of blood flow to tumor cells. Despite the potential of LNNA to function as an adjuvant in cancer therapies, its poor solubility and stability have hindered the development of an injectable formulation of LNNA that is suitable for human administration. This work, for the first time, details a systematic study on the determination of equilibrium K_a constants and the rate law of LNNA degradation. The four K_a values of LNNA were determined to be 1.03, 1.10?×?10^?2, 2.51?×?10^?10, and 1.33?×?10^?13 M. From the kinetic and equilibrium studies, we have shown that the deprotonated form of LNNA is the main form of LNNA that undergoes degradation in aqueous media at room temperature. The rate law of LNNA degradation was found to be first order with respect to OH^? concentration and first order with respect to LNNA^? concentration. The rate constant at 25?°C and 1?atm was determined to be 0.04453 M^?1min^?1. A base catalyzed mechanism of LNNA degradation was proposed based on the kinetic study. The mechanism was found to be very useful in explaining the discrepancies and changes of the rate law at different pH values. It is thus recommended that LNNA should be formulated as a concentrated solution in acidic conditions for maximum chemical stability during storage and be diluted with a basic solution to near physiological pH just before administration.     

Enhancing the efficiency of electrochemical desalination of stones: a proton pump approach

Soluble salts are among the most harmful alteration agents affecting the building materials. In recent years, several researches have been devoted to counteract alterations induced by soluble salts using electrokinetic techniques. However, the applicability of these techniques for conservation purposes remains limited due to adverse side effects, such as the extreme pH values occurring near the electrodes, which can affect the stone to be treated. The decrease in efficiency of the treatment caused by the dominant transport of H⁺ and OH^? groups is also an undesired effect. The reduced duration of these treatments due to the drying of the material in contact with the anode also limits their practical use. To overcome these problems, a new electrokinetic design that includes a so called proton pump is presented in this report. This design is based on placing two electrodes in the anodic compartment in order to modulate the net amount of H⁺ produced. The design was applied to desalinate sandstone samples contaminated with several soluble salts. The application of this new approach allowed us to establish an additional electroosmotic process at the anode, which was able to increase the duration of the treatment. Moreover, the new setup provided improved pH buffer ability due to the generation of OH^? in the anodic compartment, which increased the effectiveness of the treatment by hindering the entrance of H⁺ in the porous structure.     

Rapid and Controllable Synthesis of Nanocrystallized Nickel‐Cobalt Boride Electrode Materials via a Mircoimpinging Stream Reaction for High Performance Supercapacitors

Nickel‐cobalt borides (denoted as NCBs) have been considered as a promising candidate for aqueous supercapacitors due to their high capacitive performances. However, most reported NCBs are amorphous that results in slow electron transfer and even structure collapse during cycling. In this work, a nanocrystallized NCBs‐based supercapacitor is successfully designed via a facile and practical microimpinging stream reactor (MISR) technique, composed of a nanocrystallized NCB core to facilitate the charge transfer, and a tightly contacted Ni‐Co borates/metaborates (NCB_i) shell which is helpful for OH^? adsorption. These merits endow NCB@NCB_i a large specific capacity of 966 C g^?1 (capacitance of 2415 F g^?1) at 1 A g^?1 and good rate capability (633.2 C g^?1 at 30 A g^?1), as well as a very high energy density of 74.3 Wh kg^?1 in an asymmetric supercapacitor device. More interestingly, it is found that a gradual in situ conversion of core NCBs to nanocrystallized Ni‐Co (oxy)‐hydroxides inwardly takes place during the cycles, which continuously offers large specific capacity due to more electron transfer in the redox reaction processes. Meanwhile, the electron deficient state of boron in metal‐borates shells can make it easier to accept electrons and thus promote ionic conduction.     

Potassium bromide for infrared laser windows: Crystal growth,chemical polishing,and optical absorption

Potassium bromide single crystals have been prepared with 10.6-μm bulk absorption coefficients smaller than the intrinsic value for potassium chloride. Of several halogen-producing vapors studied, that of carbon tetrachloride is most effective in decreasing infrared absorption. Water-grinding, followed by polishing with HBr solutions, produces non-absorbing and etch-pit-free surfaces on planes remote from (100). Hydroxyl lines are absent from infrared absorption spectra of all crystals. Vacuum-ultraviolet absorption at 215 nm shows presence of between 0.01 and 4.0 OH^? ions per million anions. Incomplete removal of metaborate (BO^?₂) by iodine monobromide or by hexabromobenzene is evident in infrared absorption spectra.     

Engineering 2D Nanofluidic Li‐Ion Transport Channels for Superior Electrochemical Energy Storage

Rational surface engineering of 2D nanoarchitectures‐based electrode materials is crucial as it may enable fast ion transport, abundant‐surface‐controlled energy storage, long‐term structural integrity, and high‐rate cycling performance. Here we developed the stacked ultrathin Co₃O₄ nanosheets with surface functionalization (SUCNs‐SF) converted from layered hydroxides with inheritance of included anion groups (OH^?, NO₃^?, CO₃^2?). Such stacked structure establishes 2D nanofluidic channels offering extra lithium storage sites, accelerated Li‐ion transport, and sufficient buffering space for volume change during electrochemical processes. Tested as an anode material, this unique nanoarchitecture delivers high specific capacity (1230 and 1011 mAh g^?1 at 0.2 and 1 A g^?1, respectively), excellent rate performance, and long cycle capability (1500 cycles at 5 A g^?1). The demonstrated advantageous features by constructing 2D nanochannels in nonlayered materials may open up possibilities for designing high‐power lithium ion batteries.     

Defect Complexes and Optical Properties of Doubly Doped Lithium Niobate Crystals

The effect of defect complexes related to the presence of protons on the optical properties of LiNbO₃:Y(0.24):Mg(0.63) and LiNbO₃:Gd(0.25):Mg(0.75) (wt %) crystals has been studied using IR absorption spectroscopy, photoinduced light scattering, and laser conoscopy. The results indicate that the absorption bands at frequencies of 3483 and 3486 cm^–1 correspond to vibrations of a V _Li ^- –OH^? defect complex. To a Mg _Li ⁺ - Mg _Nb ^3- –OH^?defect complex in the LiNbO₃:Gd(0.25):Mg(0.75) crystal correspond bands at frequencies of 3526 and 3535 cm^–1. In the LiNbO₃:Y(0.24):Mg(0.63) crystal, we have detected an anomalous opening of the speckle structure of the photoinduced light scattering indicatrix.     

The ?NHx Group Induced Formation of 3D α‐Co(OH)2 Curly Nanosheet Aggregates as Efficient Oxygen Evolution Electrocatalysts

Recently, the curly structure attracts researchers' attention due to the strain effect, electronic effect, and improved surface area, which exhibits enhanced electrocatalytic activity. However, the synthesis of metastable curved structures is very difficult. Herein, a simple room temperature coprecipitation method is proposed to synthesize 3D cobalt (Co) hydroxide (α‐Co(OH)₂) electrocatalysts that consist of curly 2D nanosheets. The formation process of curly nanosheets is elaborated systematically and the results demonstrate that the ? NH_x group has great effect on the formation of curly structure. Combining the advantage of 2D curly nanosheet and 3D aggregate structure, the as‐prepared α‐Co(OH)₂ curly nanosheet aggregates show the best water oxidation activity with an overpotential of 269 mV at j = 10 mA cm^?2 in 1.0 m KOH. The electrocatalytic process studies demonstrate that the formation of Co^IV?O species is the rate‐determining step. Theoretical calculations further confirm the beneficial effect of the bent structure on the conductivity, the adsorption of OH^? and the formation of OOH* species.