Studies concerning charged nickel hydroxide electrodes I. Measurement of reversible potentials

Reversible potentials (E _R) have been measured for nickel hydroxide/oxyhydroxide couples over a range of KOH concentrations from 0·01–10 M. It is shown that the couples derived from the parent- and-Ni(OH)₂ systems can be distinguished by the relative change in KOH level on oxidation and reduction. In the case of couples derived from the-class of materials a dependence of 0·470 moles of KOH per 2e change is found compared with 0·102 moles of KOH per 2e change for the-class of materials. Couples derived from the- and-Ni(OH)₂ systems can be encountered in a series of activated and de-activated forms having a range of formal potentialsE ₀ . Activated. and de-activated-Ni(OH)₂/-NiOOH couples are found to lie in the range 0·443–0·470 V whilst-Ni(OH)₂/-NiOOH couples lie in the range 0·392–0·440 V w.r.t. Hg/HgO/KOH. It is demonstrated for de-activated,-Ni(OH)₂/-NiOOH couples thatE _R is independent of the degree of oxidation of the nickel cation between states of charge of 25% and 70%. SimilarlyE _R is constant for states of charge between 12% and 60% for activated-Ni(OH)₂/-NiOOH couples. The constant potential regions are considered to be derived from heterogeneous equilibria between pairs of co-existing phases both containing nickel in upper and lower states of oxidation. Differences inE ₀ between the activated and de-activated couples are considered to be related to the degree of order/disorder in the crystal lattice.     

Response of two okra (Abelmoschus esculentus L. Moench) varieties to fertilizers: Yield and yield components as influenced by nitrogen and phosphorus application

The response of two okra (Abelmoschus esculentus L. Moench) varieties (White velvet and NHAE 47-4) to fertilization in northern Nigeria was examined using four rates of nitrogen (0, 25, 50 and 100 kg ha^–1) and three rates of phosphorus (0, 13 and 26 kg ha^–1). Nitrogen application significantly increased green pod yield, pod diameter, number of fruits per plant, number of seeds per pod and pod weight. Application of phosphorus also significantly increased green pod yield, pod number and number of seeds per pod. The two varieties responded to nitrogen application differentially with respect to green pod yield. For optimum green pod yield of White velvet 35 kg N ha^–1 is suggested while for variety NHAE 47-4, N fertilization can be increased to 70 kg ha^–1. There was no differential response of varieties to phosphorus fertilization for green pod yield; however, the application of 13 kg ha^–1 enhanced the performance of both varieties.     

Mating behaviour and evidence for a female released courtship pheromone in the signal crayfish Pacifastacus leniusculus

The mating behaviour of the signal crayfish, Pacifastacus leniusculus (Dana), has been categorised into seven distinct stages:; orientation; contact; seizure; turning; mounting; spermatophore deposition; and dismounting. These categories were used in the development of a bioassay to test whether mature females release a sex pheromone during the breeding season to which males respond. Water conditioned by 1) mature females (MF water), 2) immature females (IF water) and 3) freshwater (C water), were injected through standard aquarium air-stones into tanks containing mature males. The behaviour of the male was recorded on video for 15 minutes before and after injection of each test water. The time that the males spent exhibiting the three behavioural categories of quiescent, motile and handling of the air-stone, were recorded. Handling of the air-stone included the mating behaviours of seizure, mounting, and spermatophore deposition onto the surface of the air-stone. Males exposed to MF water exhibited significantly increased levels of motile activity and handling behaviour, than males exposed to C water or IF water. These results demonstrate for the first time the presence of a sex pheromone, released during the breeding season by mature females, that stimulates courtship and mating behaviour in male P. leniusculus.     

Effects of crystallinity and supermolecular formations on the interfacial shear strength and adhesion in GF/PP composites

Aim of this study was to screen the morphological effects on the interfacial shear strength (i) in glass fibre (GF) reinforced isotactic polypropylene (iPP) model composites. i was determined by a modified single fibre pull-out technique. It was established that the relation between i (5–6 MPa) and the yield stress of the iPP (y30 MPa) is at about 1:6 and that the i values were not influenced by the mophological superstructure set under isothermal crystallization conditions. Increased i was only observed when specimens were produced non-isothermally, by quenching (i9 MPa). This improvement could not be related to thermal shrinkage stresses. The enhancement in i was attributed to better wetting and improved adhesion due to the enlarged amorphous PP (aPP)-phase. A schematic adhesion model considering the wetting behaviour of aPP and iPP was proposed.     

Temperature programmed oxidation of Cu/ZnO catalysts with N2O: an attempt for characterization of copper catalysts

For characterization of the surface structure of metallic copper formed on the support, temperature programmed oxidation (TPO) with N₂O was carried out over various Cu/ZnO catalysts. Four peaks of the N₂ formation (, , and ) were observed at 223, 400, 545 and 600 K in the TPO runs. The average copper crystallite size estimated from the sum of the amount of - and -peaks agreed fairly with those determined by X-ray diffraction and transmission electron microscopy. It was concluded that - and -peaks resulted from the oxidation of metallic copper atoms on the steps, corners and/ or defect sites, and on the flat sites of the surface of copper crystallites, respectively, while - and -peaks resulted from the bulk oxidation of copper.     

Properties ofSrMO 3-δ(M=Fe,Co) as oxygen electrodes in alkaline solution

Strontium ferrates and cobaltates with compositions SrFeO_3- (0.060.40) and SrCoO_3- (0.040.30) were synthesized. The dependence of the oxygen electrode properties on the value was examined in 1 mol dm^–3 KOH solution. In the SrFeO_3- series, the samples with 0.24<<0.29, showed the highest activity in both oxygen evolution and reduction reactions. In contrast, no strong dependence on the value was observed in SrCoO_3-, which also showed a high catalytic activity for oxygen evolution.     

Chemical effects in commercial and laboratory mixtures of ‘reactive’ phosphate rock and acidulated fertilisers

The chemical analyses of different size fractions of a variety of commerical and laboratory prepared samples of partially acidulated phophate rocks and mixtures of reactive phosphate rock and single superphosphate (called LONGLIFE in New Zealand) have been studied. Whereas only minor chemical segregation effects have been observed for partially acidulated products quite a large bias has been established for LONGLIFE materials, and more especially commercial samples, where larger proportions of phosphate rock were found in the lower size fractions. This inhomogeneity was considered to arise from poor mixing of components and subsequent inconsistent granulation; more stringent rejection criteria for undersize material would greatly assist in improving the product quality. Chemical deactivation of the phosphate rock residue in LONGLIFE materials was also observed; this can be partially explained by a selective reaction of the reactive phosphate rock component with acid still present at the time of mixing with the single superphosphate component.     

Studies on the response of ‘Tifblue’ and ‘Woodard’ rabbiteye blueberries to fertilizers

A field study was conducted to investigate the effects of three fertilizer placement methods and 11 fertilizer formulations on plant survival, economics of replanting, yield, and fruit size of two rabbiteye blueberry (Vaccinium ashei Reade) cultivars Tifblue and Woodard. Fertilizer rates were either mixed with the soil under plants (before planting), sidedressed, or half-rate was placed under plants with the other half sidedressed. Fertilizers at planting caused a total of 34% Woodard and 12% Tifblue plants to die as compared to 6% for Woodard and none for Tifblue when no fertilizer was applied. Fertilizer formulas 2-1-1 and 5-10-10 oxide ratios placed under Woodard plants caused 100% mortality whereas Tifblue fertilized with oxide ratios 2-2-2 and 5-10-10 under plants reached the maximum 50% mortality. Splitting fertilizer placement under the side of the plants resulted in less Woodard plant mortality (30%) than placing all the fertilizer under plants (54%). However, plant mortality for the side/under group was not different than sidedressing all fertilizer (23%). A planted hectare in this experiment consisted of 1852 Tifblue and 926 Woodard plants, providing one Woodard plant to pollinate two Tifblue plants. Based on the results obtained, the 5-10-10 fertilizer placed under plants would be expected to cause half the Tifblue (926 plants) and all the Woodard (926 plants) to be replanted. Plant costs alone was estimated to be $2315 with additional replanting costs of $93 for Tifblue and much higher for Woodard. Sidedressing 5-10-10 fertilizer eight weeks after planting would have prevented plant mortality. Placement of various fertilizers under Woodard or Tifblue plants resulted in a significant increase in plant mortality as compared to side placement of fertilizers. Yield loss due to plant mortality increased linearly with the N level of the fertilizers (ranging from 0 to 2) for both cultivars. Woodard fruit size was not affected by fertilizer placement but placing fertilizers under Tifblue plants produced smaller yields with larger fruit than sidedressed plants. Blueberry plants in a virgin acidic soil may experience no reduction in yield if fertilization is completely eliminated.     

Effectiveness of rock phosphate, coastal superphosphate and single superphosphate for pasture on deep sandy soils

The effectiveness of coastal superphosphate and two rock phosphate fertilizers was compared with the effectiveness of single superphosphate for pasture production on deep, humic, sandy podzols in high rainfall (> 800 mm annual average) areas of south-western Australia. The pastures were subterranean clover (Trifolium subterraneum) or mixed subterraneum clover and serradella (Ornithopus compressus). Coastal superphosphate was made by adding rock phosphate and elemental sulphur to superphosphate during manufacture, as it came out of the den before granulation. One rock phosphate was a 50% mixture of apatite rock phosphate from Nauru and Christmas Islands, and which was also used to make the single and coastal superphosphate used in this study, and superphosphate made in Western Australia at the time these experiments started. The other rock phosphate was Calciphos, the fertilizer produced by heating (calcining), at about 500 °C, Christmas Island C-grade ore, a calcium iron aluminium rock phosphate. There were two types of experiments. In the three Type 1 experiments, levels of each fertilizer were applied annually. In the two Type 2 experiments, levels of fertilizer were applied once only to new plots in different years. Coastal superphosphate was the most effective fertilizer in the Type 1 experiments, with both rock phosphates and single superphosphate being equally effective. All fertilizers were equally effective in the Type 2 experiments. There were large variations in fertiliser effectiveness values between yield measurements in the same or different years. It is known that P leaches from freshly-applied superphosphate in these soils. The extent of this leaching probably varies between yield measurements affecting effectiveness values determined for all fertilizers because the effectiveness values were calculated relative to the effectiveness of single superphosphate. The humic, sandy podzols remain wet during the growing season, are acidic, and are known from laboratory studies to possess adequate hydrogen ions to cause extensive dissolution of North Carolina rock phosphate so that rock phosphates are equally or more effective than single superphosphate in these soils. When elemental sulphur in coastal superphosphate is oxidized to SO₄ hydrogen ions are produced which in previous studies has been shown to enhance dissolution of rock phosphate in biosuper, a mixture of rock phosphate and elemental sulphur.     

Available nitrogen in soils and its determination by the ‘Nmin-method’ and by electroultrafiltration (EUF)

Excess nitrogen fertilizer rates are an environmental hazard. To avoid excess rates, the level of available nitrogen in the soil must be known and considered for assessing the nitrogen fertilizer rate. In arable soils nitrate and exchangeable ammonium in the rooting depth of a crop are directly available to plant roots. These two nitrogen forms are recovered with the Nmin method and they are considered in assessing the nitrogen fertilizer rate for arable crops.Besides nitrate and ammonium recovered by the Nmin method from soil samples taken in early spring, a considerable amount of organic soil nitrogen may be mineralized during the growth period and contribute to crop nutrition. The nitrogen mineralization potential can be determined in incubation tests. The absolute quantities of mineralized nitrogen thus obtained, however, are much higher than the mineralization rates under field conditions. It is for this reason that incubation tests have not obtained a major importance for assessing nitrogen fertilizer rates.With the electro-ultrafiltration (EUF) method nitrate, ammonium, and a minor portion of organic soil nitrogen are extracted from a soil suspension. There is experimental evidence that this organic nitrogen (=Norg) is easily mineralizable. Based on field experiments with cereals and maize formulae were established by which the nitrogen fertilizer rate can be calculated. In these formulae nitrate, ammonium and organic nitrogen extracted by EUF are considered.Advantages and drawbacks of the Nmin method and EUF method are discussed.     

Electroconductive membrane ‘Celec’ for application in zinc/air alkaline batteries: An impedance study of oxygen reduction at the interface Pt/Celec

Oxygen reduction was studied at a platinum electrode on a new ceramic membrane named Celec in 6m KOH with a view to application of this ceramic material in Zn/air batteries. Cyclic voltammetry and impedance measurements were carried out on the oxygen electrode to investigate the oxygen reduction mechanism in the presence of the Celec ceramic. The impedance diagrams recorded at low and high overpotentials show different characteristics, which are well interpreted by the proposed mechanisms.     

Studies concerning charged nickel hydroxide electrodes IV. Reversible potentials in LiOH,NaOH, RbOH and CsOH

The variation of reversible potential E_r with log a_moh and has been studied for several nickel hydroxide/oxyhydroxide couples in various alkali hydroxides. Both activated and deactivated -phase couples show only a small dependence ofE _r with log_moh (or where known) in LiOH, NaOH, RbOH and CsOH electrolytes. The change in MOH content on oxidation/reduction is found to be about 0.1 mol MOH per two-electron transfer and is the same as found previously in KOH. These results confirm that the bulk oxidized -phase lattice is devoid of alkali cation although a small quantity may be adsorbed by the surface. On the other hand both activated and deactivated /-phase couples show a marked dependence of 0.45 mol MOH per two-electron transfer in LiOH, NaOH and RbOH (at concentrations > 0.5 m), also in good agreement with earlier data for KOH. On the basis of these results a general stoichiometry can be inferred for the -phase, namely M_0.32NiO₂ · 0.7H₂O where M=Li⁺, Na⁺, K⁺ or Rb⁺. Measurements imply that the Cs⁺ ion or the Rb⁺ ion at low concentration (<0.5 m) do not enter the interlayer structure of the -phase. This behaviour is thought to be related to the low Rb-O and Cs-O bond strengths afforded by the -phase structure.     

Calculation of mean current densities in a two rotating disc electrodes system

A theoretical relationship for mass transfer in the laminar flow region of streaming in a rotating electrolyser was derived by the method of similarity of the diffusion layer for electrodes placed sufficiently far from the rotation axis. The obtained relationship was compared with the known equations valid for systems with axial symmetry. The mean current densities were found from the numerical solution of the convective diffusion equation by the finite-element method and were compared with experimental results.Nomenclature a constant, exponent - c concentration - c ₀ concentration in the bulk phase - C _ij matrix coefficient - D diffusion coefficient - F Faraday constant, 96487 C mol^–1 - h interelectrode distance - j current density - mean current density - J mass flux density - L _j base function - n number of transferred electrons in electrode reaction - n _r outer normal to the boundary - mass flux - N number of nodal points in an element - Q volume rate of flow - mean volume rate of flow - r radial coordinate - r ₀ inner electrode radius - r _l outer electrode radius - r _v radius of inlet orifice - r _d outer disc radius - v _r radial velocity component - v _z normal velocity component - z normal coordinate - thickness of the layer in which the equation of convective diffusion is solved - boundary of the integration domain - thickness of the diffusion layer - _N thickness of the Nernst diffusion layer - v kinematic viscosity - angular velocity - surface Criteria Re _chan channel Reynolds numberQ/hv - Re _loc local Reynolds number,Q/(r + r ₀) - local Reynolds number at mean electrode radius,Q/v(r ₁ +r ₀) - Re _rot rotation Reynolds number, r _d ² /v - modified rotation Reynolds number at mean electrode radius, (r ₁+r ₀)²/4v - Ré _rot modified rotation Reynolds number, (r+r ₀)²/4v - Sc Schmidt number,v/D - Sh _r local Sherwood number,j(r-r ₀)/nFDc _o - mean Sherwood number, - Ta Taylor number,h(/v)^1/2     

Cathodic behaviour of IrO2 electrodes in alkaline solution Part I: Electrochemical surface characterization

IrO₂ electrodes prepared by thermal decomposition of IrCl₃ on a titanium support at temperatures of calcination between 300 and 500°C have been characterized by cyclic voltammetry and potential steps. Standard voltammetric curves have been recorded between –0.65 and 0.35 V vs SCE (prior to H₂ and O₂ evolution) as a fingerprint of the surface state, and the associated charge,q ^*, has been used to monitor the morphology of the active layer. The effect of hydrogen evolution has been investigated by progressively decreasing the negative potential limit, and by increasingly holding the electrode under hydrogen evolution at a constant potential. Phenomena of proton penetration beneath the outer surface into an inner surface have been quantified by potential step experiments. The effect of storing the electrodes in water rather than in the open air has also been investigated. The thermal oxides lose their typical features at calcination temperature < 350° C. Cathodic load does not appear to cause macroscopic modifications of the surface state.This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribution to electrochemistry.     

Phosphorus efficiency of sugarcane varieties in a tropical alfisol

Varietal differences in P absorption and utilization by sugarcane were studied with the objective of selecting phosphorus efficient varieties which can perform well under conditions of low soil phosphorus availability and at low P application rates. Sugarcane varieties differed significantly in dry matter, cane and sugar yields, P-concentration and P-uptake. Based on the cane and sugar yield phosphorus efficiency indices, varieties were classified as P efficient and P-non-efficient. Phosphorus efficient varieties had low P-concentrations and produced higher dry matter per unit P absorbed.     

Electrochemistry of anodic fluorine gas evolution at carbon electrodes: Part II studies on the ‘CF’ film by the current-interruption,AC impedance,ESCA and auger techniques

The CF films that are formed on the surface of carbon anodes used for the fluorine evolution reaction (FER) in KF·2HF melts at 358 K have been studied by bothin situ electrochemical current-interruption and a.c. impedance methods, and byex situ surface spectroscopy [ESCA (XPS) and Auger] techniques. The surface analysis measurements indicate that a thin CF (CF₂) film, 1.7 nm in thickness is formed on the carbon anodesurface. Results from depth profiling analyses of the film indicate that it is not uniform, higher levels of CF and F components being found towards the carbon anode surface. Thein situ electrochemical measurements demonstrate that an abnormally small interfacial capacitance, (1.6–2.7)×10^–7 F cm^–2, arises in the course of the FER at carbon anodes; this was attributed to the presence of a passive dielectric CF film on the carbon electrodes. The determined interfacial capacitance does not change significantly with potential in the potential range studied, which implies that the thickness of the CF film on the fluorine-evolving carbon anodes may be independent of potential.     

Two-variable periodic perturbation of kinetic oscillations

Using one of the generic models (CO oxidation on Pt with surface-oxide formation) predicting kinetic oscillations in heterogeneous catalytic reactions, we show that the efficiency of two-variable periodic perturbations with respect to converting natural period-1 oscillations to period-l oscillations at the forcing frequency is remarkably sensitive to the kind of perturbations used. Counter-phase perturbations are much more effective compared to in-phase perturbations. The physics underlying these findings is suggestive of their applicability to many other models and/or real systems exhibiting kinetic oscillations.     

Sex pheromone components of corn stalk borerSesamia nonagriodes (Lef.) isolation,identification, and field tests

Z-11-Hexadecenyl acetate (Z11–16OAc), dodecyl acetate (12OAc),Z-11-hexadecenal (Z11–16Aid), andZ-11-hexadecenol (Z11– 16OH), were found in pheromone gland extracts of femaleSesamia nonagriodes (Lef.) [Lepidoptera: Noctuidae]. These four components were also present in airborne volatiles collected from calling virgin females in a 651889 ratio. Hexadecyl acetate (16OAc) was also detected but found to be inactive. The identification was based on multicolumn GC analysis, mass spectrometry, and field activity.Z11–16OAc is the major sex pheromone component; the addition of the secondary components individually decreased male captures. The blend of the four synthetic components in 691588 ratio was highly attractive to males; 200 g per trap was the most effective concentration in field tests.Lepidoptera: Noctuidae     

Physicochemical properties of electrodepositedβ-lead dioxide: Effect of deposition current density

The influence of current density on the coulometric efficiency of -PbO₂ deposition in 0.5 M cM lead nitrate, the nonstoichiometry, impurity of -PbO₂ and voltammetric double layer capacitance have been studied. While the coulometric efficiency is about 95% at current densities less than 30 mA cm^–2, it decreases at higher current densities. The oxygen deficiency, , in -PbO_2- has been found to be invariant with the current density. X-ray diffraction studies provide a linear decrease in the weight percent of -PbO₂ as an impurity in the -PbO₂ with increase in current density, and the -PbO₂ is found to be absent at 100mA cm^–2 or higher. The estimated double layer capacitance from the cyclic voltammograms recorded in the potential range 0.70–1.10V, increases with deposition current density, indicating enhanced surface area.     

Effects of partial acidulation on chemical and mineralogical characteristics of residual phosphate rocks

Original phosphate rocks (PR) and water insoluble residues (WIR) from mixtures of reactive PRs and single superphosphate, known commercially as longlife single superphosphate (LLSSP), and from partially acidulated PRs (PAPR), were compared in terms of their elemental content, chemical reactivity as indicated by the apatite unit cell a dimension and solubility. Phosphate rock reactivity is known to be inversely related to the a dimension. Partial acidulation (20%) with commercial grade phosphoric acid resulted in an increase in aluminium (Al), iron (Fe) and fluoride (F) concentrations in the WIRs. The apatite a dimensions of WIRs from LLSSPs were greater than those of the respective original North Carolina (NC), Khouribga (KR), Jordan (JR), Sechura (SE) and Arad (AR) PRs added to single superphosphate (SSP), made from Nauru PR (NR)) to produce the LLSSPs. This was attributed to the presence of the less reactive NR in the WIRs left-over from the SSP. Partial acidulation with phosphoric acid increased the apatite a dimensions of NC and ElHassa (EH) PRs. The increase in apatite a dimension of NC and EH was probably due to selective dissolution of a more reactive fraction of the PRs during partial acidulation. Changes in the apatite a dimension following partial acidulation with phosphoric acid were not significant for the other PRs studied, e.g. Gafsa (GF), KR and AR, although differential X-ray diffractograms (DXRD) indicated that the material dissolved during partial acidulation was more reactive than the WIRs and the original PRs. The apatite a dimension of NC PR was not affected by pretreatment with 2% or 4% citric acid (CTA). The contrasting response in a of NC PR to acidulation with phosphoric and citric acids may be related to differences in the strength of these acids, and/or to the differing environments under which the reactions took place.The 2% CTA and formic acid (FMA) solubilities of the WIRs from LLSSPs and PAPRs were markedly lower than those of the original PRs. This reduction in solubility of PRs following partial acidulation was probably related to changes in mineralogical and chemical composition of the WIRs as indicated by the increases in apatite a dimension of some residual PRs and shifts in peak positions in DXRD, to increases in the concentrations of Fe, Al and F compounds, and to coating effects of PR particles by Fe, Al and F compounds. This, in turn, may reduce the agronomic value of the residual PR component of PAPR and LLSSP fertilizers, particularly over the short-term.The solubility of residual PRs following pretreatment with 2% or 4% CTA was slightly lower than that of the original PRs. The pretreatment caused no significant change in the apatite a dimension of NC PR. The complexing effects of CTA and its lack of Fe and Al impurities may have prevented the formation of Fe, Al and F compounds. The effect of citric acid on PR reactivity is thus quite different from that of the mineral acids used to prepare LLSSPs and PAPRs.