Cyclic voltammetric study of zinc and zinc oxide electrodes in 5.3 M KOH

The behaviour of zinc and zinc oxide in 5.3 M KOH in the presence of alkaline earth oxides, SnO, Ni(OH)₂ and Co(OH)₂ was examined by cyclic voltammetry. The influence of the alkaline earth oxides was compared with additives of established effects (Bi₂O₃, LiOH, Na₂CO₃ and CdO). The alkaline earth oxide each exhibits a distinct behaviour towards zincate. Whereas, a single process of interaction with zincate was shown by CaO; two modes of reaction were obtained with SrO and BaO. Solid solution formation was noticed with BeO and MgO. The other additives forming solid solution with ZnO were CdO, SnO. The ionic sizes of Ni(OH)₂ and Co(OH)₂ allow solid solution formation with Zn(OH)₂. Both Bi₂O₃ and Na₂CO₃ enter into complexation with zincate. LiOH forms two distinct zincates, of which one is an oxo zincate leaching the `hydroxyl' functionality. Cyclic voltammetry revealed the deposition of the oxide/hydroxide additives as metal prior to the onset of zinc deposition and the potential range for this additive metal deposition is almost the same for different additives (SnO, CdO, Ni(OH)₂). The beneficial action of these additives to zinc alkaline cells is associated with a substrate effect. The implication of this electrocatalytic deposition of metals on a zinc oxide electrode is also discussed.     

The effect of foreign ions on the reactivity of the CaO-SiO2-Al2O3-Fe2O3 system: Part II: Cations

The subject of this paper is the effect of foreign cations on the reactivity of the CaO-SiO₂-Al₂O₃-Fe₂O₃ system. One reference mixture and eighteen modified mixtures, prepared by mixing the reference sample with 1% w/w of chemical grade MnO₂, CuO, V₂O₅, PbO, CdO, ZrO₂, Li₂O, MoO₃, Co₂O₃, NiO, WO₃, ZnO, Nb₂O₅, CrO₃, Ta₂O₅, TiO₂, BaO₂ and H₃BO₃ were studied. The effect on the reactivity is evaluated on the basis of the free lime content in samples sintered at 1200 and 1450 °C. At 1200 °C, the reactivity of the mixture is greatly increased in the presence of Cu and Li oxides. Based on their effect at 1450 °C, the added elements can be divided into three groups. W, Ta, Cu, Ti and Mo show the most positive effect, decreasing the free CaO (fCaO) content by 30-60%, compared with the pure sample. Cr and B cause an increase of fCaO content, while the rest of the elements exhibit a marginal positive effect. According to their volatility at 1450 °C, the added compounds can be subdivided into three groups of low (Ti⁴⁺, Cu²⁺, Mo⁶⁺, W⁺⁶, V⁵⁺, Zn²⁺, Zr⁴⁺), moderate (Cr⁶⁺, Co³⁺, Ni²⁺, Mn⁴⁺) and high volatility (Cd²⁺, Pb²⁺). All burned samples, analyzed by means of X-ray diffraction, have a final mineralogical composition, which corresponds to the structure of a typical clinker.     

New catalytic functions of Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys in the conversions of methanol

Pd and Pt supported on ZnO, Ga₂O₃ and In₂O₃ exhibit high catalytic performance for the steam reforming of methanol, CH₃OH+H₂OCO₂+3HH₂, and the dehydrogenation of methanol to HCOOCH₃, 2CH₃OHHCOOCH₃+2HH₂. Combined results with temperature-programmed reduction (TPR) and XRD method revealed that Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys were produced upon reduction. Over the catalysts having the alloy phase, the reactions proceeded selectively, whereas the catalysts having metallic phase exhibited poor selectivities.     

New polyester resins with reduced flammability and smoke evolution capacity

Smoke evolution [in NBS chamber by the ASTM E-622-(1983) method] and ignitability (by the oxygen-index method) was investigated for glass-reinforced polyester (GRP) laminates obtained with unsaturated polyester (UP) resins containing chlorine and bromine in the chain. In these studies, the effect on the properties of such additives as Sb₂O₃, Al (OH)₃, MoO₃, Mg(OH)₂ and melamine diphosphate in an amount up to 30 mass-% was determined. The most efficient ignition and smoke-evolution retarder of the investigated compounds was Mg(OH)₂, whereas an essential reduction in smoke evolution was observed also with MoO₃. GRP laminates with these additives meet the fire-safety recommendations concerning smoke evolution from materials used in transportation means and in the building industry. © 1998 John Wiley & Sons, Ltd.     

PREPARATION OF PEROVSKITE 0.75Pb(Ni1/3Nb2/3)O3-0.25PbTiO3 CERAMICS USING SEMICHEMICAL METHODS AND RELATED REACTION MECHANISMS

This article discusses a mechanism for preparing perovskite powders, 0.75Pb(Ni_1/3Nb_2/3)O₃-0.25PbTiO₃ (PNN-PT), using a semichemical method (SCM).Precursors were prepared by adding aqueous Ni(Ac)₂ solutions to an alcohol slurry of PbO, Nb₂O₅, and TiO₂. The TG-DTG and DSC analysis of the precursors and XRD analysis of the powders at different thermal treatment temperatures showed that the reaction mechanisms in this method differ from those in the conventional mixed-oxide method. The aqueous Ni(Ac)₂ solution reacted with PbO to form Pb(Ac)₂ · Pb(OH)₂ · H₂O and Ni(OH)₂, which decomposed to form nascent PbO and NiO, thereby improving the reactivity and distribution of PbO and NiO. Pb₃Nb₂O₈ and NiNb₂O₆ formed and were easily converted into the perovskite phase during the thermal treatment process. At a thermal treatment temperature of 850°C, the content of the perovskite phase reached 98%. Pyrochlore-free PNN-PT ceramic was obtained after 2 h of sintering at 1100°C, and its dielectric properties were found to be excellent at temperatures ranging between ?55 and 120°C.     

Effects of Atmospheric Chemical and Climate Change on Tropospheric Ozone

Changes in atmospheric levels of certain pollutants (CH₄, CO, NO_X, nonmethane hydrocarbons) have the potential to affect tropospheric O₃ formation and the abundance of the free radical OH on a global scale. Perturbations to stratospheric O₃ and climate (temperature and moisture) also can influence tropospheric O3 and OH. We have used a tropospheric photochemical model with projections of CO, NO_X, and CH₄ to predict tropospheric ozone and OH changes from 1980-2030. The calculations simulate the background chemistry of various global regions and assume that increases in CH₄ and CO will continue at current rates. Predicted changes in tropospheric O₃ and OH are different in urban and nonurban areas, and in marine and continental regions.

Generally, increasing levels of CH₄ and CO at constant NO_X levels will increase O₃ and suppress OH. A rough estimate of possible global changes shows tropospheric O3 increasing ?10% from 1980 to 2030 and OH decreasing ?10% during that period. When calculations are performed assuming that stratospheric ozone depletion and climate warming occur at anticipated rates during the same period, tropospheric O₃ enhancement and OH loss in nonurban areas are both reduced relative to changes assuming that only CH₄ and CO emissions change.

Regional changes in surface-level O₃, OH and the water-soluble oxidant H₂O₂ are estimated for the year 2030. Increases in CO and CH₄ suppress OH and enhance O₃ and H₂O₂ in nonpolluted (low NO_X) areas. In urban environments (background NO_X > 1 ppbv), increases in CO and CH₄ add significantly to all three oxidants, O₃, OH and H₂O₂. Changes in and near urban areas may be of greatest magnitude, but the high levels of OH (and H₂O₂) found in the tropics indicate that perturbations in that region could dominate future global oxidant changes.     

An investigation of inorganic tin flame retardants which suppress smoke and carbon monoxide emission from burning brominated polyester resins

In view of the current demand for novel, non-toxic, flame- and smoke- suppressant systems for synthetic polymers, certain inorganic tin compounds have been evaluated as fire retardants in a series of commercial brominated polyester resin formulations. The results obtained clearly show that zinc hydroxystannate (ZnSn(OH)₆) and zinc stannate (ZnSnO₃) impart beneficial properties to the polyesters in terms of flame retardancy and smoke/carbon monoxide suppression, and the improvements in performance are, in general, superior to those exhibited by tin (IV ) oxide or antimony (III ) oxide. The surface area and degree of dispersion of the fire-retardant additive has been shown to have a marked effect on its efficiency and, in this connection, colloidal tin (IV ) oxide is found to exhibit significantly improved flame-retardant properties compared to powdered SnO₂. Simultaneous thermal analyses (TG/DTG/DTA) and related mechanistic experiments have shown that tin additives markedly increase the amount of char formed during combustion, whereas Sb₂O₃, a vapour-phase flame retardant, has little effect on char formation. The zinc stannates also appear to exhibit a significant vapour-phase activity, and this may account for their flame-retardant superiority to SnO₂ itself.     

Synthesis of Glass-Ceramic Materials in the BaO–PbO–B2O3–Al2O3–TiO2 System

The influence of PbO, B₂O₃, and Al₂O₃ additives on the glass formation and crystallization of glasses with a high total content of BaO and TiO₂ (65–75 wt % or 76–86 mol %) is investigated. It is shown that glasses of the compositions (wt %) 31–35 BaO, 12–17 PbO, 34–42 TiO₂, 10–13 Al₂O₃, and 2–3 B₂O₃ are promising materials for use in preparing glass-ceramic ferroelectrics based on the melting–molding–crystallization technology. These compounds are characterized by a relatively low melting temperature (1450°C), the absence of spontaneous crystallization during molding, and the possibility of controlling the phase composition of the material through the appropriate choice of the crystallization temperature.     

Synthesis of gallium nitride nanostructures by nitridation of electrochemically deposited gallium oxide on silicon substrate

Gallium nitride (GaN) nanostructures were successfully synthesized by the nitridation of the electrochemically deposited gallium oxide (Ga₂O₃) through the utilization of a so-called ammoniating process. Ga₂O₃ nanostructures were firstly deposited on Si substrate by a simple two-terminal electrochemical technique at a constant current density of 0.15 A/cm² using a mixture of Ga₂O₃, HCl, NH₄OH and H₂O for 2 h. Then, the deposited Ga₂O₃ sample was ammoniated in a horizontal quartz tube single zone furnace at various ammoniating times and temperatures. The complete nitridation of Ga₂O₃ nanostructures at temperatures of 850°C and below was not observed even the ammoniating time was kept up to 45 min. After the ammoniating process at temperature of 900°C for 15 min, several prominent diffraction peaks correspond to hexagonal GaN (h-GaN) planes were detected, while no diffraction peak of Ga₂O₃ structure was detected, suggesting a complete transformation of Ga₂O₃ to GaN. Thus, temperature seems to be a key parameter in a nitridation process where the deoxidization rate of Ga₂O₃ to generate gaseous Ga₂O increase with temperature. The growth mechanism for the transformation of Ga₂O₃ to GaN was proposed and discussed. It was found that a complete transformation can not be realized without a complete deoxidization of Ga₂O₃. A significant change of morphological structures takes place after a complete transformation of Ga₂O₃ to GaN where the original nanorod structures of Ga₂O₃ diminish, and a new nanowire-like GaN structures appear. These results show that the presented method seems to be promising in producing high-quality h-GaN nanostructures on Si.     

Crystallization and Ability of Hydroxyapatite Formation in Some Trivalent Oxides Containing Na-Ca-Silicate Glass-Ceramics

The formation of glass-ceramics based on Na₂O–CaO-silicates containing P₂O₅ with minor additives of some trivalent oxides (e.g. La, In, Ga, and Al), has been investigated. Different crystalline phases including sodium-orthosilicate containing lanthanum, or aluminum were formed together with Na₂Ca₂Si₃O₉, NaInSi₂O₆, and Na₃Ga₂Si₃O₁₀. The nature and mechanism of HA formed in the glass-ceramics are considered. In general, the presence of trivalent oxides in the glass-ceramics progressively reduced the ability to form a calcium phosphate layer on the surfaces of the materials. The addition of In₂O₃ decreased the crystallization of the hydroxyapatite layer. However, in the presence of either Ga₂O₃ or Al₂O₃ only the amorphous calcium phosphate layer was formed after the immersion of the crystallized specimens in the SBF solution.     

The effects of Cr2O3, Cu(OH)2, ZnO and PbO on the compressive strength and the hydrates of the hardened C3A paste

The purpose of this paper is to investigate the effects of Cr₂O₃, Cu(OH)₂, ZnO or PbO on the hydration of C₃A and characterization of its hydrates. C₃A pastes adding the above compound were examined on the basis of the hydration products and their structure, compressive strength and rate of early hydration.     

Acid-Base Properties of Alumina-Supported M2O3 (M=B, Ga, In) Catalysts

The acid-base properties of -Al₂O₃ and alumina-supported B₂O₃, Ga₂O₃ and In₂O₃ have been determined by microcalorimetry of ammonia and sulfur dioxide adsorption. From the adsorption of NH₃, it was found that the addition of B₂O₃ on alumina leads to an increase of the number of acid sites, while Ga₂O₃ and In₂O₃ additives caused a decrease in the acidity of alumina. Using SO₂ as a probe molecule to study the basicity, the number of surface basic sites on alumina was found to be strongly decreased by the addition of boron oxide, while it was only slightly affected by the addition of gallium oxide and decreased by the addition of indium oxide. The differential heats of adsorption are discussed as a function of the coverage by the probe molecules. The electronic properties of the oxides are examined in order to explain the acid-base properties of the supported oxides.     

Spectral Properties of Doped Glasses of the 35Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> · 40PbO · 25Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> Composition Synthesized in a Quartz Crucible

A glasslike material of the 35Bi₂O₃ · 40PbO · 25Ga₂O₃ composition is investigated. Quartz glass is used in the synthesis as the crucible material. It is shown that, compared to the platinum crucible, the high-energy transmission cutoff shifts from 650 to 500 nm, which has enabled us to study the upconversion luminescence spectra of the glass of the 35Bi₂O₃ · 40PbO · 25Ga₂O₃ composition doped by Er³⁺ ions in the range 500–700 nm. The upconversion luminescence spectra for the glass doped by Er³⁺ and codoped by Nd³⁺ and Yb³⁺ ions are obtained.     

Spectroscopic investigation of samarium-doped lead oxyflouroborate glasses using photo and cathode luminescence

Samarium-doped lead oxyflouroborate glasses of 60 B₂O₃- xPbO- (40-x)LiF where (x=0-30 mol%) with 3×10²⁰ ions/cm³ of Sm₂O_3, were prepared by melt quenching. UVVis absorption, photo luminescence (PL) and cathode luminescence (CL) spectroscopies were used to study the effect of varying PbO content on the spectroscopic properties of these samarium-doped glasses. The absorption of the UV-edge shifts toward higher wavelengths, not only because of higher polarizability of lead ions, but also because of the strong allowed s-p transition of Pb²⁺. Judd-Ofelts parameters were determined and indicate that the asymmetry around Sm³⁺ ions increases with increasing PbO content. Ω₂ probes the asymmetry by the ratio of intensity of the hypersensitive transition (⁶H_9/2) to that of purely magnetic (⁶H_5/2) transition. Furthermore, an increase in the spectroscopic quality factor (Ω₄/Ω₆) was observed with increasing PbO content which indicates that these glasses have the potential to be used as efficient active laser glasses. The calculated energy transfer parameter increases with increasing PbO content. Also, stark splitting increases with increasing PbO concentrations. FWHM of the CL emission peaks and stark splitting, are found to be much larger than that in PL. This was explained by the high electric field generated from the exciting electron pulses.     

New ecological polyester resins with reduced flammability and smoke evolution capacity

Smoke evolution in a smoke chamber 750 × 750 × 1000 ± 5 mm (Polish Standard PN‐91/K‐02501 equivalent to UIC 561‐OR 1991) was studied in, and the oxygen index flammability test (Polish Standard PN‐76/C‐89020) was carried out for, glass‐reinforced polyester (GRP) laminates obtained with unsaturated polyester (UP) resins containing chlorine and bromine in the chain. In these studies, the effect on these properties of such additives as ZnSnO₃ (ZS), ZnSn(OH)₆ (ZHS), Al(OH)₃, or Mg(OH)₂ and Sb₂O₃ in up to 30 mass % was determined. The most efficient ignition and smoke‐evolution retarder from among the investigated compounds were ZS and ZHS, and an essential reduction in smoke evolution was also observed with Sb₂O₃. GRP laminates with these additives meet the fire safety recommendations concerning smoke evolution for materials used in transportation and in the building industry. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 379–382, 1999     

The effects of several heavy metal oxides on the formation of ettringite and the microstructure of hardened ettringite

The study was conducted on the effects of Cr₂O₃, Fe₂O₃, Cu(OH)₂, ZnO and Pb₂O(OH)₂ on the formation of ettringite and microstructure of hardened ettringite. The cement samples were prepared by mixing C₃A synthesized and CaSO₄·2H₂O and adding 5 % by weight of above additives. The heavy metal oxides and hydroxides promote the crystal growth of ettringite and produce some changes in microstructure and Cr₂O₃ and Cu(OH)₂ exert a considerable influence.     

Effect of metal oxides on electrochemical performances of La–Mg–Ni-based alloys

Metal oxides (TiO₂, Er₂O₃ and ZnO) were added to La–Mg–Ni-based hydrogen storage alloy electrodes and their effects on the structural and electrochemical properties were studied. The charge efficiency, especially at high charge current density was greatly ameliorated, and the high rate charge capability at 1440 mA g⁻¹ increased from 85.1% (blank) to 94.1% (TiO₂), 93.3% (Er₂O₃) and 90.5% (ZnO). The high temperature dischargeability was also improved in case of TiO₂, Er₂O₃ and ZnO additives. These additives suppressed formation of Mg(OH)₂ and La(OH)₃ during charge/discharge process and therefore the cycling stability was improved. The discharge capacity retention at the 200th cycle increased from 72.9% (blank) to 79.6% (TiO₂), 87.5% (Er₂O₃) and 77.9% (ZnO).     

Color-tunable up-conversion luminescence of Zn(AlxGa1-x)2O4:Yb3+,Tm3+,Er3+ powders

Color-tunable up-conversion powder phosphors Zn(Al_xGa_1-x)₂O₄: Yb³⁺,Tm³⁺,Er³⁺ were synthesized via high temperature solid-state reaction. Also, the morphological and structural characterization, up-conversion luminescent properties were all investigated in this paper. In brief, under the excitation of a 980?nm laser, all powders have same emission peaks containing blue emission at 477?nm (attributed to ¹G₄→³H₆ transition of Tm³⁺ ions), green emission at 526?nm and 549?nm (attributed to ²H_11/2→ ⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transition of Er³⁺ ions respectively), red emission at about 659?nm and 694?nm (attributed to ⁴F_9/2→⁴I_15/2 transition of Er³⁺ ions and ³F₃→³H₆ transition of Tm³⁺ ions, respectively), which are not changed after the doping of Al³⁺ ions. However, the doping of Al³⁺ ions can enhance the up-conversion luminescent intensity and efficiency, while the emission color of as-prepared powder phosphors can be tunable by controlling the doping amount of Al³⁺ ions. Taking Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er as the cut-off value, the emissions have clear blue-shift firstly and then show obvious red-shift with the increasing doping of Al³⁺ ions. Stated thus, pink emission in ZnAl₂O₄:Yb,Tm,Er, purplish pink emission in ZnGa₂O₄:Yb,Tm,Er and Zn(Al_0.9Ga_0.1)₂O₄:Yb,Tm,Er, purple emission in Zn(Al_0.1Ga_0.9)₂O₄:Yb,Tm,Er and Zn(Al_0.3Ga_0.7)₂O₄:Yb,Tm,Er, purplish blue emission in Zn(Al_0.7Ga_0.3)₂O₄:Yb,Tm,Er, blue emission in Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er can be observed, which confirm the potential applications of as-prepared Zn(Al_xGa_1-x)₂O₄:Yb³⁺,Tm³⁺,Er³⁺ powder phosphors in luminous paint, infrared detection and so on.     

Electrochemically deposited gallium oxide nanostructures on silicon substrates

We report a synthesis of β-Ga₂O₃ nanostructures on Si substrate by electrochemical deposition using a mixture of Ga₂O₃, HCl, NH₄OH, and H₂O. The presence of Ga³⁺ ions contributed to the deposition of Ga₂O₃ nanostructures on the Si surface with the assistance of applied potentials. The morphologies of the grown structures strongly depended on the molarity of Ga₂O₃ and pH level of electrolyte. β-Ga₂O₃ nanodot-like structures were grown on Si substrate at a condition with low molarity of Ga₂O₃. However, Ga₂O₃ nanodot structures covered with nanorods on top of their surfaces were obtained at higher molarity, and the densities of nanorods seem to increase with the decrease of pH level. High concentration of Ga³⁺ and OH^- ions may promote the reaction of each other to produce Ga₂O₃ nanorods in the electrolyte. Such similar nature of Ga₂O₃ nanorods was also obtained by using hydrothermal process. The grown structures seem to be interesting for application in electronic and optoelectronic devices as well as to be used as a seed structure for subsequent chemical synthesis of GaN by thermal transformation method.     

Evaluation of the fraction of fourfold-coordinated boron in oxide glasses from their composition

A model for evaluating the fraction of fourfold-coordinated boronN ₄ in the oxide glasses of different systems has been proposed. The model involves simplified equations of hypothetical chemical equilibria between structural groups. The calculated N₄ values are compared with the NMR experimental data obtained by different authors for ∼350 glasses containing Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, Tl₂O, SrO, PbO, ZnO, A1₂O₃, Ga₂O₃, Fe₂O₃, In₂O₃, B₂O₃, and SiO₂ oxides. The mean deviation between the calculated and experimental values ofN ₄ is equal to about 0.05.