Addition Of NH4F Research Articles

Gelation rate of silica nanoparticles at different supersaturation with and without ammonium fluoride additive

Silica nanoparticles have been synthesised using sol gel technique. The effect of ammonium fluoride NH4F addition on the gelation rate of silica was studied under supersaturation ranging from 8.72 to 13.34. The results showed that the gelation times were decreased by increasing the supersaturation and by addition of NH4F. Surface energy between the formed gel and the solution was calculated as 17.28 and 16.11 mJ/m² with and without NH4F addition. The gelation rate was increased and the Gibbs free energy change for the formation of critical nucleus was decreased by increasing the supersaturation and by addition of NH4F. The critical radius of the nucleus was decreased from 6.42 and 5.60 A without and with addition of ammonium fluoride to 5.70 and 4.85 A when the supersaturation was increased from 8.72 to 13.34. This approach can be used to discuss the effect of any additives on enhancing or inhibition the gelation rate.

Leaching of vanadium from carbonaceous shale

The leaching of vanadium from carbonaceous shale using dilute H 2SO 4 was investigated, and the mechanism of leaching determined. The results showed that higher leaching efficiency of vanadium was obtained by increasing initial concentration of H 2SO 4, raising leaching temperature and prolonging leaching time. Addition of ammonium fluoride also enhanced recovery. A recovery of 92% was obtained using a liquid to solid ratio 4:1, initial H 2SO 4 concentration 18%, NH 4F addition 4.8 wt.% of carbonaceous shale, leaching temperature 95 °C and contact time 8 h; the recovery was only 56% without NH 4F. The presence of NH 4F enhanced the leaching of vanadiferous mica.

Palladium–citric acid–ammonium fluoride as a matrix modifier for overcoming of interferences occurring during the direct determination of Sn in aqua regia extracts from environmental samples by D 2-ETAAS

When tin is to be determined in such a complex matrix like aqua regia extracts of environmental samples by electrothermal atomic absorption spectrometry (ETAAS), spectral interferences occur when deuterium-lamp (D 2) background correction is used, even using high pyrolysis temperature of 1400 °C achieved with palladium with citric acid chemical modifier. We have found that the further addition of NH 4F to palladium with citric acid chemical modifier is essential for overcoming the above-mentioned problems for which aluminium oxide is most probably responsible. It is supposed, that NH 4F enables volatilization of the alumina matrix formed by hydrolysis from the chloride salt and interfering in a gas phase via the formation of AlF 3 which could be, in contrast to aluminium oxide, removed from the graphite furnace during the pyrolysis stage. Using the proposed chemical modifier, the direct and accurate determination of Sn in aqua regia extracts from rocks, soils and sediments is possible even when using matrix free standard solutions. This presumption was confirmed by the analysis of certified reference samples and by the comparison with inductively coupled plasma time of flight mass spectrometry (ICP-TOFMS) method. Characteristic mass and LOD value for the original sample (10-μL aliquots of sample) was 17 pg and 0.055 μg g −1, respectively.

Combustion Synthesis of β-Si<sub>3</sub>N<sub>4</sub> and β-SiAlON with Elongated Prismatic Micro-Crystals by Adding SrCO<sub>3</sub> and NH<sub>4</sub>F

β-Si3N4 and β-SiAlON powders were prepared by combustion synthesis with SrCO3 and NH4F used as additives. The resultant β-Si3N4 and β-SiAlON powders consisted of elongated prismatic microcrystals. By adding SrCO3, the anisotropic growth of β-Si3N4 and β-SiAlON crystals is improved and their aspect ratios increase. The addition of NH4F enhanced nitridation reactions and reduced the residual Si in combustion products. It was proposed that the elongated prismatic β-Si3N4 and β-SiAlON crystals grew from liquid phase and the composition and property of this liquid was affected by the addition of SrCO3.

Effects of NH 4F on the deposition rate and buffering capability of electroless Ni–P plating solution

The deposition rate and buffering capability of alkaline electroless Ni–P plating solution containing ammonium fluoride (NH 4F) have been investigated. When the NH 4F concentration is below 10 g L − 1 , the deposition rate is improved with the addition of NH 4F, reaching the maximum value at 2 g L − 1 . The buffering capability of solutions is found to be improved with increasing NH 4F concentration. Due to the improvement of buffering capability, refined and compact Ni–P coatings with homogeneous elemental distribution of P have been achieved. Therefore, both the corrosion resistance and microhardness of Ni–P coatings are significantly improved. The mechanism of NH 4F improving the deposition rate and the buffering capability is discussed.

Convenient synthesis of large mordenite crystals

Large mordenite (MOR) zeolite crystals with 60–85 μm in length were easily obtained from the low-water content system without any additives. From nitrogen adsorption, it was found that the as-synthesized MOR(Na +MOR) zeolites obtained with Al(NO 3) 3, Al 2(SO 4) 3 and AlCl 3 as an Al source are the small port type zeolite, whereas the MOR zeolite obtained with Al(OH) 3 is the large port type zeolite. However, Li + cation-exchange rendered the small port type MOR zeolite into the large port one. When NH 4F was employed as a fluoride source and added into the starting synthesis gel, all of MOR zeolites obtained were the large port type zeolite regardless of Al source. The addition of NH 4F did not affect the crystal size very much.

Structural study of C,N‐chelated monoorganotin(IV) halides

AbstractThree monoorganotin(IV) compounds of general formula LCNSnX3, where LCN is a 2‐(dimethylaminomethyl)phenyl‐ group and X = Cl (1), Br (2) and I (3), were prepared and characterized using XRD and NMR techniques. Compound 1 reacts with moisture producing [(LCN)2HSnCl2]+ [LCNSnCl4]−. Compound 3 decomposes to (LCN)2SnI2, SnI2 and I2 when heated. Compound 2 was reacted with NH4F yielding an equilibrium of fluorine‐containing species. The major products were [LCNSnF5]2− and [(LCNSnF3)2(µ2‐F)2]2− (4a). When compound 2 was reacted with another fluorinating agent, LCN(n‐Bu)2SnF, an oligomeric product, [LCNSnF2(µ2‐F)2]n, was observed. Further addition of NH4F led to subsequent formation of 4a. The structure of fluorinated products was investigated by 1H, 19F and 119Sn NMR spectroscopy. Copyright © 2006 John Wiley & Sons, Ltd.

Combustion synthesis of fine AlN powder and its reaction control

Aluminum nitride powder produced by the combustion synthesis (SHS) usually contains coarse particles because of its high reaction temperature. These particles make it difficult to achieve sintering. To improve sinterability, the reaction temperature was controlled by adding hydrogen gas up to 20 vol.% to the reactant gas (nitrogen), and NH 4F up to 1.5 mass% to the reactant mixture. The reaction temperature was lowered by 400 K when 10 vol.% of H 2 and 1.0 mass% of NH 4F were added. As a result, the specific surface area of the final powder increased by 80% compared to the powder obtained without addition. The addition of NH 4F reduced the residual aluminum and oxygen content in the AlN products.

Combustion synthesis of fine AlN powder and its reaction control

Aluminum nitride powder produced by the combustion synthesis (SHS) usually contains coarse particles because of its high reaction temperature. These particles make it difficult to achieve sintering. To improve sinterability, the reaction temperature was controlled by adding hydrogen gas up to 20 vol.% to the reactant gas (nitrogen), and NH 4F up to 1.5 mass% to the reactant mixture. The reaction temperature was lowered by 400 K when 10 vol.% of H 2 and 1.0 mass% of NH 4F were added. As a result, the specific surface area of the final powder increased by 80% compared to the powder obtained without addition. The addition of NH 4F reduced the residual aluminum and oxygen content in the AlN products.

Effect of the fluorine content on the structural and electrical properties of SnO 2 and ZnO–SnO 2 thin films prepared by spray pyrolysis

Transparent conducting oxide thin films of SnO 2 (TO) and of ZnO–SnO 2 binary–binary system (ZO–TO system) have been prepared by the spray pyrolysis method. In this work, we study the influence of fluorine doping concentration on the structural, optical and electrical properties of films above mentioned. Fluorine doped tin oxide (FTO) thin films on glass present resistivity around to 4×10 −4 Ω cm, high optical transmission close to 80% and optical band gap close to 4.5 eV. X-ray diffraction measurements show that the FTO films are highly oriented along the (200) plane parallel to the substrate. ZO–TO films deposited at substrate temperature of 450 °C using alcoholic solutions of ZnCl 2/SnCl 4 with a Zn/Sn=0.40 atomic ratio, presented polycrystalline structures with a mixture of zinc oxide and tin oxide phases (ZO–TO system). These films present a resistivity close to 6 Ω cm and an optical transmission in the visible range of 82%. Further addition of NH 4F to the starting solution lowered the resistivity of ZO–TO thin films to 2.43×10 −1 Ω cm as a consequence of fluorine incorporation. From electrical and optical measurements, the Moss–Burstein effect was found in both TO and ZO–TO thin films.

Nuclear magnetic imaging of an osmotic water uptake and delivery process

The water absorption of NH 4F-doped silicone cylinders was studied by spin-echo Fourier nuclear magnetic resonance imaging, in conjunction with gravimetric (mass uptake) and ionic concentration (release of NH 4F) measurements. The addition of NH 4F greatly increases the water uptake as the inclusions are surrounded by droplets of water when wetted by water diffusing in the polymer. These droplets then expand due to the osmotic pressure difference between the internal droplet and external solution; this expansion is opposed by an elastic restraining force. The rate of ingress into the polymer will depend on the relative chemical potential of water associated with the polymer and the droplet, as well as the diffusion coefficient. Later stages of the absorption process are dominated by the droplets. The dilution of the droplets (from water diffusing into the droplets) slowly reduces the chemical potential driving the process. Hence, the later stages occur without any notable concentration gradient but a slight chemical potential gradient. If the droplet expansion exceeds that which can be restrained by the material, failure around the droplet occurs resulting in the release of the salt and the solution within the droplet.

Some physical properties of F-doped CdO thin films deposited by spray pyrolysis

Transparent conducting cadmium oxide (CdO) thin films have been deposited by chemical spray pyrolysis from a solution of cadmium acetate in distilled water and methanol. The films were doped by addition of NH 4F to the solution whose optimum concentration was determined. As-deposited films show values of Hall mobility , carrier concentration, resistivity, and transmittance (at λ=825 nm) of 25.4×10 −4 m 2/Vs, 3.66×10 26 m −3, 6.72×10 −6 Ω m and 87.1% respectively. The figure of merit Φ= T 10/ R sh (3.35×10 −2 Ω −1 at 825 nm) is the highest reported in the literature for doped and undoped CdO films obtained through such an inexpensive technique.

A Promoting Effect of NH4F Addition on the Photocatalytic Activity of Sol-Gel TiO2 Films

Abstract The photoreactivity of sol-gel (SG)-TiO2 films was enhanced significantly with addition of a small amount of ammonium fluoride (AF) into the SG-starting solution. The rate of the TiO2 photoinduced oxidation of an overlying methylsiloxane monolayer reached a maximum near [AF]/[Ti] molar ratio of 1.35 × 10−2. The apparent rate constant was as much as 8.2 times greater than of AF non-added system. X-Ray diffraction analyses clearly indicated that the principal factor is the improvement in the anatase crystallinity caused by F− ions.

Liquid phase deposition of a film of silica with an organic functional group

The thin films of silica with an organic functional group, –CH 3,–CHCH 2, –C 2H 4CF 3, were produced by a deposition method. In this method, the film was formed on a substrate in a solution above room temperature. The dilute solution containing organotrimethoxysilane (Si concentration 0.03 mol/l) was utilized. The addition of NH 4F promoted the film growth. The deposition film was not formed in the solution containing tetramethoxysilane. Therefore, it is assumed that the role of organic functional group is important in initiating the deposition process.

Electron migration in hydrated DNA and collagen at low temperatures. Part 2.—The effect of additives

The effects of various additives on the transient conductivity signals seen on pulse irradiation of hydrated DNA and collagen have been investigated over the temperature range 135–250 K. The additives studied were ethanol, H2O2, NH4F, HF, misonidazole and ethidium bromide with DNA and NH4F with collagen. The observed reductions in signal height on addition of NH4F or ethanol to the hydrated biopolymers were very similar to the reduction seen in the signal due to dry electrons in ice on addition of these impurities. However, ethidium bromide, which intercalates into the DNA helix, showed no measurable effect on the conductivity transients seen in the hydrated polymer. These observations strongly support the proposition that the signals observed on pulse radiolysis of hydrated DNA and collagen are due to the unsolvated electron migrating in an ice-like matrix around the biopolymer.

Effect of the addition of NH 4F on anodic behaviors of DSA-type electrodes in H 2SO 4-(NH 4) 2SO 4 solutions

The effect of NH 4F addition on the high-anodic behaviors of various DSA-type electrodes was investigated in a mixture of sulfuric acid and ammonium sulfate. The pronounced effect of NH 4 addition was observed on DSA-type Ti/RuO 2, Ti/IrO 2−TiO 2 electrodes, but not observed on the other electrodes studied. The close relationship was found between the increment of the electrode potential caused by the NH 4 addition and the quantity of F − adsorbed on the electrode surface. The effect of NH 4F addition was considered to be resulted from the adsorption of F − on the electrode surface, and the presence of adsorbed F − was directly proved.

Anodic processes on a titanium-supported Ruthenium dioxide electrode at high potentials in a mixture of sulfuric acid and ammonium sulfate

The anodic polarization behaviours of Ti-supported RuO 2 electrode at high potentials and the electrode reactions, especially oxygen evolution and peroxydisulfate ion formation, were investigated in H 2SO 4(NH 4) 2SO 4 mixed aqueous solutions. The effects of NH 4F addition to the solutions on the anodic processes were also examined. The anodic polarization curve is clearly divided into three parts: in the first linear region only oxygen evolution occurs and in the second one peroxydisulfate ion formation takes place, accompanied by oxygen evolution. The transitional region lies between these two linear regions. However, the oxygen evolution reaction proceeds predominantly in all regions in H 2SO 4(NH 4) 2SO 4 mixed aqueous solutions. The current efficiency for peroxydisulfate ion formation depends on the concentration of (NH 4) 2SO 4 and the current density. The current efficiency is greatly increased by adding NH 4F to the mixed solutions. The formation reaction of peroxydisulfate ion in the NH 4F-containing solutions is controlled by the step of the primary discharge of sulfate ion or hydrogensulfate ion.

ESR Study of Complex Formation and Electronic Relaxation of Fe3+ in Aqueous Solutions

ESR measurements of aqueous solutions of Fe3+ containing various electrolytes were made at X- and Q-band frequencies. It was found that the line shape and integrated intensity depend on the pH and on the type and concentrations of counteranions in the solution. Addition of LiCl and NH4NCS result in reduction in the integrated intensity and subsequent disappearance of the ESR signal. This is interpreted in terms of the formation of monosubstituted complexes which give signals too broad to observe. From the results, formation constants have been calculated. Successive addition of NH4F results in the formation of complexes of the type [Fe(H2O)6−nFn]3−n having different ESR linewidth ranging from 10 to 1000 G. There is a strong reduction in the linewidth on going from X- band to Q-band frequencies. The results are explained in terms of electronic relaxation via the modulation of the zero field splitting (zfs) parameter. From the analysis of the data it was possible to derive values for the zfs interactions and the associated correlation times. The results indicate that the modulation of the zfs interaction is due to collisions between complex and solvent molecules rather than diffusional tumbling.