Ammonium Pentaborate Research Articles

Anodic film growth on Al–Li–Cu alloy AA2099-T8

AA2099-T8 aluminium alloy was anodized at a current density of 5mA/cm2 to selected voltages in 0.1M ammonium pentaborate electrolyte at 293K. It was found that the growth of barrier-type anodic film on the alloy was accompanied by oxidation of intermetallics, formation and rupture of oxygen gas-filled voids in the anodic film and healing of the anodic film at the sites of rupture. It was revealed that the formation of oxygen gas-filled voids was related to the oxidation of copper-rich nanoparticles in the copper-enriched layer at the film/alloy interface, and that the oxidation process of copper-rich nanoparticles depended on grain orientation. Further, the significantly reduced Pilling–Bedworth ratio for formation of anodic lithium oxide compared with that for formation of anodic alumina resulted in the formation of fine voids at the alloy/film interface and sequentially, detachment of the anodic film from the alloy surface.

Cotton fabrics treated with novel oxidic phases acting as effective smoke suppressants

Sol–gel processes have been applied to cotton fabrics in order to coat the fibres with a silica film, able to improve their thermo-oxidative resistance and their combustion behaviour under the irradiative heat flow of a cone calorimeter. To this aim, tetramethoxysilane, inorganic precursor of the silica phase, has been employed alone or coupled with species having either smoke suppressant features (namely, zinc oxide, zinc acetate dihydrate and zinc borate) or well known flame retardant properties (like ammonium pentaborate octahydrate, boron phosphate, ammonium polyphosphate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). In addition, the use of barium sulphate, which is a smoke suppressant and, at the same time, a flame retardant, has been investigated. Cone calorimetry turned out to be a suitable technique for assessing the flammability and smoke production of the treated fabrics (particularly when referring to total smoke release, smoke production rate and CO and CO2 yields). The composition and morphology of the deposited coatings, assessed by scanning electron microscopy, have been found to influence their combustion behaviour, as well as their thermal and thermo-oxidative stability evaluated by thermogravimetric analysis in nitrogen and air, respectively.

13C CP/MAS NMR analysis of cure characteristics of phenol formaldehyde resin in the presence of wood composite preservatives and wood: effect of ammonium pentaborate and copper compounds

The effect of typical wood composite preservatives, ammonium pentaborate (APB), nanosize copper oxide and basic copper carbonate, on the cure characteristics of phenol formaldehyde (PF) resin in the presence of wood was evaluated by solid-state 13C nuclear magnetic resonance with cross-polarization and magic angle spinning (CP/MAS). With the introduction of APB the absorption intensity and peak area of PF resin at 129.5 ppm was reduced, and the carbons in methylene bridges shifted from 65.8 to 73.5 ppm, which were the result of hydrogen bond formation between ammonium in APB and oxygen of phenolic hydroxyl, as well as coordination bond between the boron in APB and oxygen in phenolic hydroxyl and/or unreacted hydroxymethyl. In addition, the peak area at 152.7 ppm increased with the addition of poplar powder for the overlap of cellulose, hemicellulose, and lignin chemical shifts with the active groups in PF resin. However, the connection status of critically active chemical groups of condensed polymer structure in cured PF resin such as the existence of phenolic ring, phenolic hydroxyl, methylene bridges, and hydroxymethyl linkage are unchanged. Combined with relative increase in the amount of carbon in methylene bridges from 2.42 to 2.56, drop in number of carbons of unreacted hydroxyls from 1.19 to 1.07, and the reported increase in physical and mechanical properties, the nanosize copper oxide improved the curing degree of PF. Furthermore, the similar analysis indicated that basic copper carbonate delayed the curing degree of PF.

Electroforming and Ohmic contacts in Al-Al2O3-Ag diodes

Electroforming of metal-insulator-metal (MIM) diodes is a non-destructive dielectric breakdown process that changes the diode from its initial high resistance state (HRS) to a low resistance state (LRS). After electroforming, resistance switching memories (RSMs) use voltages to switch from HRS to LRS and back. Many MIM combinations are proposed for use in RSMs. In many cases conduction in the LRS is nearly temperature independent at low temperatures; an Ohmic contact with a barrier to electron injection of ∼0 eV results from electroforming. Electroforming of Al-Al2O3-Ag diodes with amorphous anodic Al2O3 thicknesses between 12 and 41 nm has been studied. Two anodizing electrolytes have been used; 0.1 M ammonium pentaborate (bor-H2O) and a solution of 0.1 M of ammonium pentaborate per liter of ethylene glycol (bor-gly). Polarization of Al2O3 and negative charge in Al2O3 are much larger when Al2O3 is formed in bor-H2O solution than when Al is anodized in bor-gly solution. Electroforming of Al-Al2O3-Ag diodes results in an Ohmic contact at the Al-Al2O3 interface, voltage-controlled negative resistance (VCNR) in the current-voltage (I–V) characteristics, electroluminescence (EL), and electron emission into vacuum (EM) from filamentary conducting channels. Two distinct modes of electroforming occur for Al-Al2O3-Ag diodes. α-forming occurs for 2.5 V ≲ VS ≲ 5 V, where VS is the applied voltage. It is characterized by an abrupt current jump with the simultaneous appearance of EL and EM. β-forming occurs for VS ≳ 7 V. I–V curves, EL, and EM develop gradually and are smaller than for α-forming. Electroforming occurs more readily for diodes with Al2O3 formed in bor-H2O that have greater defect densities. Fully developed I-V curves have similar VCNR, EL, and EM after α-forming or β-forming. A model is proposed in which excited states of F-centers, oxygen vacancies in amorphous anodic Al2O3, form defect conduction bands. Electroforming that results in an Ohmic contact requires injection of positive charge at the Al-Al2O3 interface. α-forming is the result of ionization of F-center recombination centers with energies that are close to the Al Fermi level. Hole injection by high-field ionization of valence band states of Al2O3 causes β-forming.

Growth and field crystallization of anodic films on Ta–Nb alloys

The growth behavior of amorphous anodic films on Ta–Nb solid solution alloys has been investigated over a wide composition range at a constant current density of 50 A m−2 in 0.1 mol dm−3 ammonium pentaborate electrolyte. The anodic films consist of two layers, comprising a thin outer Nb2O5 layer and an inner layer consisting of units of Ta2O5 and Nb2O5. The outer Nb2O5 layer is formed as a consequence of the faster outward migration of Nb5+ ions, compared with Ta5+ ions, during film growth under the high electric field. Their relative migration rates are independent of the alloy composition. The formation ratio, density, and capacitance of the films show a linear relation to the alloy composition. The susceptibility of the anodic films to field crystallization during anodizing at constant voltage increases with increasing niobium content of the alloy.

Synthesis and Photo Catalytic Studies of Nitrogen-Doped ZnO Particles

The decomposition of zinc nitrate hexahydrate with molten ammonium pentaborate octahydrate resulted in nitrogen-doped ZnO particles. The homogenous mixture of nitrogen-doped ZnO particles was prepared by heating the mixture. Samples of increasing ammonium concentrations were synthesized and characterized and showed some increase in absorbency in the visible light region with increasing concentrations leading to an interest and application of more efficient solar cells and substantial advances in practices of the sort.

Dielectric properties of anodic films on sputter-deposited Ti–Si porous columnar films

For electrolytic capacitor application of the single-phase Ti alloys containing supersaturated silicon, which form anodic oxide films with superior dielectric properties, porous Ti–7 at% Si columnar films, as well as Ti columnar films, have been prepared by oblique angle magnetron sputtering on to aluminum substrate with a concave cell structure to enhance the surface area and hence capacitance. The deposited films of both Ti and Ti–7 at% Si have isolated columnar morphology with each column revealing nanogranular texture. The distances between columns are ∼500 nm, corresponding to the cell size of the textured substrate and the gaps between columns are 100–200 nm. When the porous Ti–7 at% Si film is anodized at a constant current density in ammonium pentaborate electrolyte, the growth of a uniform amorphous oxide film continues to ∼35 V, while it is limited to less than 6 V on the porous Ti film. The maximum voltage of the growth of uniform amorphous oxide films on the Ti–7 at% Si films is similar for both the flat and porous columnar films, suggesting little influence of surface roughness on the amorphous-to-crystalline transition of growing anodic oxide under the high electric field. Due to the suppression of crystallization to sufficiently high voltages, the anodic oxide films formed on the porous Ti–7 at% Si film shows markedly improved dielectric properties, in comparison with those on the porous Ti film.

Formation and dielectric properties of anodic oxide films on Zr–Al alloys

Zr–Al alloys containing up to 26 at.% aluminum, prepared by magnetron sputtering, have been anodized in 0.1 mol dm−3 ammonium pentaborate electrolyte, and the structure and dielectric properties of the resultant anodic oxide films have been examined by grazing incidence X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, and AC impedance spectroscopy. The anodic oxide film formed on zirconium consists of monoclinic and tetragonal ZrO2 with the former being a major phase. Two-layered anodic oxide films, comprising an outer thin amorphous layer and an inner main layer of crystalline tetragonal ZrO2 phase, are formed on the Zr–Al alloys containing 5 to 16 at.% aluminum. Further increase in the aluminum content to 26 at.% results in the formation of amorphous oxide layer throughout the thickness. The anodic oxide films become thin with increasing aluminum content, while the relative permittivity of anodic oxide shows a maximum at the aluminum content of 11 at.%. Due to major contribution of permittivity enhancement, the maximum capacitance of the anodic oxide films is obtained on the Zr–11 at.% Al alloy, being 1.7 times than on zirconium at the formation voltage of 100 V.

A Mechanism of Barrier Film Formation in 0.1 M Ammonium Pentaborate Electrolyte

not Available.

Crystal structure and thermal expansion of ammonium pentaborate NH4B5O8

Anhydrous ammonium pentaborate NH4B5O8 has been synthesized by thermal dehydration of larderellite NH4[B5O7(OH)2] · H2O at a temperature of 290°C for 7 h. The crystal structure has been determined from the X-ray powder diffraction data: a = 7.58667(5) A, b = 12.00354(8) A, c = 14.71199(8) A, R p = 6.23, R wp = 7.98, R B = 12.7, R F = 8.95, and β-KB5O8 structure type. The double interpenetrating framework is formed by pentaborate groups, each consisting of a boron-oxygen tetrahedron and four triangles, in which all oxygen atoms are bridging. The thermal behavior of the NH4B5O8 compound has been investigated using thermal X-ray diffraction. As for other pentaborates of this type, the thermal expansion of the NH4B5O8 compound is anisotropic and reaches a maximum along the a axis. The thermal expansion coefficients are as follows: α a = 39 × 10−6, α b = 6 × 10−6, α c = 20 × 10−6, and α V = 65 × 10−6 °C−1.

Some mechanical properties and decay resistance of wood impregnated with environmentally-friendly borates

This study was made to determine some mechanical properties such as compression strength parallel to grain, modulus of rupture, and decay resistance of wood treated with some environmentally-friendly borates. Sodium tetrafluoroborate (SFB), ammonium tetrafluoroborate, (AFB), and ammonium pentaborate octahydrate (APB) were used as borates. Wood specimens were prepared from Oriental beech ( Fagus orientalis L.) and Scots pine ( Pinus sylvestris L.). Before tests, wood specimens were impregnated with aqueous solutions (0.25%, 0.50%, 1.50%, and 3.00%) of borates according to ASTM D 1413-76. Results showed that compression strength parallel to grain (CSPG) and modulus of rupture (MOR) of wood specimens treated with borates were lower compared to untreated control specimen. In general, our results showed that the higher concentration levels of borates, the lower mechanical properties of wood resulted. Borate treated wood showed considerable resistance to the decay fungus compared to that of untreated control specimen.

Electronoptical Observations of Reanodized Film in 0.1 M Ammonium Pentaborate Electrolyte after Anodizing in Molten Melts

not Available.

Amorphous-to-crystalline transition of silicon-incorporated anodic ZrO2 and improved dielectric properties

Sputter-deposited zirconium and Zr–16 at.% Si alloy have been anodized to various voltages at several formation voltages in 0.1 mol dm−3 ammonium pentaborate electrolyte at 298 K for 900 s. The resultant anodic films have been characterized using X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy, and electrochemical impedance spectroscopy. The anodic oxide films formed on Zr–16 at.% Si are amorphous up to 30 V, but the outer part of the anodic oxide films crystallizes at higher formation voltages. This is in contrast to the case of sputter-deposited zirconium, on which the crystalline anodic oxide films, composed mainly of monoclinic ZrO2, are developed even at low formation voltages. The outer crystalline layer on the Zr–16 at.% Si consists of a high-temperature stable tetragonal phase of ZrO2. Due to immobile nature of silicon species, silicon-free outermost layer is formed by simultaneous migrations of Zr4+ ions outwards and O2− ions inwards. An intermediate crystalline oxide layer, in which silicon content is lower in comparison with that in the innermost layer, is developed at the boundary of the crystalline layer and amorphous layer. Capacitances of the anodic zirconium oxide are highly enhanced by incorporation of silicon due to reduced film thickness, even though the permittivity of anodic oxide decreases with silicon incorporation.

Regression Analysis for the Two-Step Growth Kinetics of Crystals in Pure Solutions

The overall growth kinetics of ammonium pentaborate, borax decahydrate, and boric acid crystals in pure solutions were analyzed using a two-step mass transfer model. Four different linear expressions of the two-step mass transfer model (TSM), which include the widely used expressions of Sobczak and Karpinski, were discussed. The influence of linearization for an assumed second-order reaction kinetics on the mass transfer and reaction steps was studied for various crystallization systems with overall growth kinetic order ranging from 1 to ≥2. The overall growth kinetics of ammonium pentaborate and borax decahydrate were used to study the effect of linearization as a function of temperature and seed size. The complexities in using the linearized TSM expression to predict the mechanism of the crystal growth process in pure solutions were discussed. A Type 3 expression of Karpinski that successfully represents the overall crystal growth kinetics was determined to be successful in representing two-step growth ...

Improved electrical properties of silicon-incorporated anodic niobium oxide formed on porous Nb–Si substrate

In the present study, porous Nb–Si alloy films with isolated nano-column morphology have been successfully developed by oblique angle magnetron sputtering on to aluminum substrate with concave cell structure. The deposited films are amorphous with the 15 at% silicon supersaturated into niobium. The porous Nb-15 at% Si films, as well as niobium films with similar morphology, are anodized at several voltages up to 50 V in 0.1 mol dm −3 ammonium pentaborate electrolyte. Due to the presence of sufficient gaps between neighboring columns, the gaps are not filled with anodic oxide, despite the large Pilling–Bedworth ratio (for instance, 2.6 for Nb/Nb 2O 5) and hence, a linear correlation between the reciprocal of capacitance and formation voltage is obtained for the Nb-15 at% Si. From the comparison with the anodic films formed on porous niobium films, it has been found that silicon addition improves the thermal stability of anodic niobium oxide; the change in capacitance and increase in leakage current become small for the Nb–Si. The findings indicate the potential of oblique angle deposition to tailor porous non-equilibrium niobium alloy films for high performance niobium-base capacitor.

Formation of anodic films on sputtering-deposited Al–Hf alloys

The growth of barrier-type anodic films at high efficiency on a range of sputtering-deposited Al–Hf alloys, containing from 1 to 95 at.% Hf, has been investigated in ammonium pentaborate electrolyte. The alloys encompassed nanocrystalline and amorphous structures, the latter being produced for alloys containing from 26 to 61 at.% Hf. Except at the highest hafnium content, the films were amorphous and contained units of HfO 2 and Al 2O 3 distributed relatively uniformly through the film thickness. Boron species were confined to outer regions of the films. The boron distributions suggest that the cation transport number decreases progressively with increasing hafnium concentration in the films, from ∼0.4 in anodic alumina to ∼0.2 for a film on an Al–61 at.% Hf alloy. The distributions of Al 3+ and Hf 4+ ions in the films indicate their similar migration rates, which correlates with the similarity of the energies of Al 3+–O 2− and Hf 4+–O 2− bonds. For an alloy containing ∼95 at.% Hf, the film was largely nanocrystalline, with a thin layer of amorphous oxide, of non-uniform thickness, at the film surface. The formation ratios for the films on the alloys changed approximately in proportion to the hafnium content of the films between the values for anodic alumina and anodic hafnia, ∼1.2 and 1.8 nm V −1 respectively.

Inhibition of field crystallization of anodic niobium oxide by incorporation of silicon species

The present work demonstrates effective inhibition of field crystallization of amorphous anodic niobium oxide by incorporation of silicon species from substrate. The field crystallization, detrimental for capacitor application of niobium, occurs during anodizing of magnetron sputtered niobium at 100 V in 0.1 mol dm −3 ammonium pentaborate electrolyte at 333 K, while amorphous structure of the anodic oxide is totally retained during anodizing of magnetron sputtered Nb–12 at%Si. Even after prior thermal treatment in air, which accelerates field crystallization of anodic oxide on niobium, no crystallization occurs on the Nb–12 at%Si. Through examination of the crystallization behaviours of anodic films formed on a thin Nb–12 at%Si layer superimposed on a niobium layer as well as on a thin niobium layer superimposed on an Nb–12 at%Si layer, it has been confirmed that air-formed oxide or thermal oxide becomes a nucleation site for crystallization. Modification of the air-formed or thermal oxide by incorporation of silicon species inhibits the nucleation of crystalline oxide. The modification, however, does not influence the growth of crystalline oxide. The growth is suppressed by continuous incorporation of silicon species into anodic film from the substrate during anodizing.

Growth, structural, optical, thermal and mechanical properties of ammonium pentaborate single crystal

Nonlinear optical single crystals of ammonium pentaborate (APB) were grown by the slow cooling method from aqueous solution. Grown crystal was characterized by powder X-ray diffraction (PXRD) and FT-IR spectral analysis. Perfection of the grown crystal was evaluated by high-resolution X-ray diffractometry (HRXRD). The effect of nylon threading on the perfection of the grown bigger crystal was also studied by HRXRD. The range and percentage of optical transmission was ascertained by recording UV–vis–NIR spectrum. Thermal properties were investigated by TG–DTA and DSC analyses. Its mechanical hardness was estimated by Vickers microhardness tester.

Electrolyte effects on charge, polarization, and conduction in thin anodic Al2O3 films II. Temperature dependent conduction and a Meyer-Neldel relation

The effect of anodizing electrolyte on the temperature dependence of current-voltage (I-V) curves of Al–Al2O3–Au diodes is reported. Two aqueous electrolytes, 0.1M ammonium pentaborate (bor-H2O) and 0.1M ammonium citrate (citrate), and one nonaqueous electrolyte, 0.1M ammonium pentaborate per liter of ethylene glycol (bor-gly), have been used. Al2O3 thicknesses are between 12 and 54nm; temperatures are between 100 and 320K. Maximum currents for the applied voltage for VA>0V (IMX+) and for VA<0V (IMX−), and the rectification ratio RR (IMX+∕IMX−) depend on the electrolyte. RR(bor-H2O)>RR(citrate)⪢RR(bor-gly) at 300K; at 100K, the rectification ratios are approximately equal. I-V curves for decreasing VA>0V are reproducible and nearly independent of previous history. They are due to Fowler-Nordheim tunneling, J=CF2exp(−B∕F), where J is current density, F is the electric field, and B and C are constants. B is used to obtain an effective barrier height for tunneling, ϕE. ϕE is 1.3–1.5eV at 300K for all three electrolytes. ϕE increases as temperature decreases. If ΔϕE=[ϕE(100K)−ϕE(300K)], then ΔϕE=1.3–1.5eV for Al2O3 formed in bor-H2O and ΔϕE∼0.5eV for Al2O3 formed in bor-gly. The pre-exponential tunneling factor C increases by orders of magnitude as temperature decreases from 300to100K. There is a Meyer-Neldel relation between C and B, C=r+sB where r and s are constants that depend on the anodizing electrolyte. A model is proposed in which ϕE depends on temperature dependent occupation of defect states in anodic Al2O3. Defect states, in turn, depend on the anodizing electrolyte.

Electrolyte effects on charge, polarization, and conduction in thin anodic Al2O3 films. I. Initial charge and temperature-dependent polarization

A sequence of three current-voltage (I-V) curves of Al–Al2O3–Au capacitors has been used to study the effect of anodizing electrolyte on Qin, the initial charge introduced into Al2O3 during anodization and the temperature dependence of polarization of anodic Al2O3. The first I-V curve, with VA<0V, polarizes the Al2O3 film; the difference between the next two I-V curves is a measure of polarization induced by the negative voltage. Two aqueous electrolytes, 0.1M ammonium pentaborate (bor-H2O) and 0.1M ammonium citrate (citrate), and one nonaqueous electrolyte, 0.1M ammonium pentaborate per liter of ethylene glycol (bor-gly), are used for anodizing; Al2O3 thicknesses are between 12 and 54nm. The galvanostatic anodizing rate is the same for anodizing in bor-H2O and bor-gly electrolytes after initial transients. The anodizing rate in citrate electrolyte is constant but is 0.7 times the rate in the other two electrolytes. Qin for Al2O3 films formed in bor-H2O and bor-gly is proportional to Al2O3 thickness; it is distributed throughout the film. The magnitude of Qin is ∼100 times greater for Al2O3 films formed in the aqueous electrolyte. Qin for Al2O3 films formed in citrate is nearly constant with thickness. Qin anneals out when I-V curves are measured. Two quantities are measured that depend on polarization of anodic Al2O3, QPK, and Qmax. QPK is due solely to polarization produced by negative bias. Both polarization and conduction currents contribute to Qmax. Both QPK and Qmax depend exponentially on the polarizing field. Maximum values of QPK for samples anodized in bor-H2O or citrate are ∼13 times larger than for Al2O3 formed in bor-gly; maximum values of Qmax are more than 100 times larger for anodic Al2O3 formed in aqueous electrolytes. The temperature dependence of Qmax is also less for Al2O3 films formed in bor-gly than for Al2O3 formed in bor-H2O or citrate.