Ammonium Hydrogen Difluoride Research Articles

Development and validation of a microwave-assisted digestion technique as a rapid sample preparation method for the estimation of selenium in pharmaceutical dosage forms by ICP-OES.

Selenium is a class 2B element according to the International Council for Harmonization Q3D guidelines. Selenium sulfide is an anti-infective agent with antifungal and antibacterial properties used to treat dandruff and seborrheic dermatitis. The literature survey revealed that most of the analytical techniques to estimate selenium were time-consuming and/or required high skill levels. The process involved identifying the isotopes, selecting the measurement approach, and optimizing a typical microwave-aided digesting procedure. Ammonium hydrogen difluoride, water, and concentrated nitric acid were added to the samples. The confirmed microwave digestion program was a two-step program where in the initial step, the samples were ramped at 200°C for 20 min and held for 5 min. Later, samples were cooled and neutralized by boric acid, then ramped for 20 min to a temperature of 180°C and held for 10 min. Selenium was estimated at 196.090 nm by inductively coupled plasma optical emission spectroscopy (ICP-OES). System suitability was run before initiating analysis to ensure that system performance was consistent. Analytical validation parameters, such as the specificity of the method, were demonstrated at 196.090 nm, linearity was proven from 10 ppm to 150 ppm of selenium concentration, the detection limit was 1.28 ppm, and the limit of quantification was 3.89 ppm. Robustness was confirmed for small changes to ICP-OES operating conditions. The precision of the method demonstrated by analyzing the percentage relative standard deviation for six injections was found to be less than 2.0%. Accuracy was confirmed from 10 ppm to 150 ppm, and all the samples were observed to be within the range of 95%-105%. A common microwave-assisted digestion technique was developed and validated as well. The precision, specificity, linearity, accuracy, and robustness of the method for estimating selenium in selenium sulfide drug substances and various pharmaceutical dosage forms were demonstrated. This newly developed microwave-assisted digestion technique has optimum sensitivity and is highly reproducible and time-saving than the existing methods This method can be applied to numerous matrices for a finished dosage of selenium sulfide formulations.

Is Ammonium Hydrogen Difluoride a Solution for Zirconia Surface Conditioning?

This research investigated the topographical features and phase transformation of high-translucent monolithic zirconia after different surface conditioning methods. Zirconia slabs were divided into six groups according to surface treatment method. Group I: etched with hydrofluoric acid (HF); Group II: etched with an experimental acid solution (EAS); Group III: melt-etched with ammonium hydrogen difluoride (AHD); Group IV: air abrasion (AB); Group V: etched with EAS after air abrasion (AB+EAS); Group VI: melt-etched with AHD after air abrasion (AB+AHD). Surface topographies of specimens were documented by scanning electron microscopy (SEM). Tetragonal-to-monoclinic phase transformation was detected by X-ray diffraction and surface evaluation of zirconia specimens; surface roughness and contact angle measurements were performed. The data were statistically analyzed by the Kruskal- Wallis test and post hoc tests (P⟨0.05). The acid-etched zirconia groups (Group I, II, and III) showed the lowest contact angle and surface roughness values (P⟨0.05), while the air abrasion groups (Group IV, V, VI) showed the highest. The SEM images also supported these results. Within the limitations of this in vitro study, treating the monolithic zirconia surfaces with EAS or AHD after air abrasion may be recommended to alter the zirconia surfaces.

Development of a YF3:ThF4 membrane for the possibility of determining fluoride

Preparation of yttrium substituted thorium fluoride (YTF) solid solution, YxTh1−xF4−x (x = 0 – 0.15) by fluorinating a stoichiometric ratio of yttria (Y2O3) and thoria (ThO2) with ammonium hydrogen difluoride (NH4HF2) was acheived. The maximum solubility of YF3 in ThF4 was observed to be 15 mol %. All three compositions of YxTh1−xF4−x (x = 0 – 0.15) solid solution showed an enhanced ionic conductivity over ThF4. 5 mol % yttrium substituted ThF4 (5-YTF) had the highest ionic conductivity, almost 2 orders higher than ThF4. The F− ion selective electrode was designed and tested for estimation of fluoride ion in solution (10−1M to 10−5 M). 5-YTF had the highest sensitivity of 40.0 ± 4 mV/decade in the linear range of 10−1 M to 10−4 M. All the three sensors compositions 5, 10 and 15-YTF have sub Nerstian behavior which is attributed to strong OH− ion interefenece.The results were compared with commercial fluoride ISE (Eu: LaF3).

Synthesis of Cerium Tetrafluoride and Cerium Trifluoride Nanoscale Polycrystals from Ammonium Hydrogen Difluoride

This paper reported a dry synthesis and characterization of cerium tetrafluoride (CeF4) and cerium trifluoride (CeF3) nanoscale polycrystals (NPs). The CeF4 NPs were spherical or flaky and approximately 10 ± 2 nm in diameter. The CeF3 NPs were rod-shaped nanorods with a length of about 150 ± 5 nm and a diameter of about 20 ± 2 nm. The first step was to synthesize the intermediate product—(NH4)4CeF8 by mixing CeO2 and NH4HF2 at a molar ratio of 1:6 at 390 K. The structural characterization was analyzed by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Then, (NH4)4CeF8 was heated in an argon gas flow to synthesize the CeF3 and CeF4 NPs. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The properties of CeF3 and CeF4 NPs were further evaluated by transmission electron microscopy (TEM), selected area electron diffraction pattern (SAED), and high-resolution transmission electron microscopy (HRTEM). The findings provided an alternative strategy for the synthesis of nanometer fluorides, which could be a reference for high-performance research on other nanometer fluorides.

Effect of surface treatment with potassium hydrogen difluoride and ammonium hydrogen difluoride on bond strength between layered veneering porcelain and zirconia

ObjectivesThe purpose of this study was to show the effect of surface treatment of potassium hydrogen difluoride (KHF2) and ammonium hydrogen difluoride (NH4HF2) on the bonding of veneering porcelain to zirconia frameworks. Material and methodsTwo types of zirconia (Katana zirconia (3Y-TZP) and KZR-CAD Zr SHT (6Y-TZP)) were used as the adherend material. Cerabian ZR porcelain was fired to each type of zirconia disc (n = 11). Zirconia discs were prepared using the following surface treatment: no treatment (NT), alumina blasting (AB), KHF2 and NH4HF2. Coefficient of Linear Thermal Expansion (CTE) of each type of zirconia and veneering porcelain were measured. The specimens after surface treatment were analyzed with X-ray diffraction analysis (XRD). Shear bond strength was tested after 24 h water storage. The specimens were evaluated under scanning electron microscopy. ResultSignificant differences between CTE values of 6Y-TZP and veneering porcelain occurred as the temperature increased. The XRD analysis of the 3Y-TZP treated with AB, KHF2 or NH4HF2 demonstrated that 3Y-TZP becomes unstable and phase transformation occurs. In 3Y-TZP group, KHF2 and NH4HF2 groups exhibited higher shear bond strengths than AB and NT. In 6Y-TZP group, KHF2 groups showed higher shear bond strengths than NT, AB and NH4HF2. ConclusionHigh bond strength between zirconia and veneering porcelain can be achieved by a surface treatment with selected melted fluoride compounds.

Improving the flame retardancy and mechanical properties of epoxy composites using flame retardants with red mud waste

AbstractIn this study, a novel flame retardant ammonium tetrafluoroborate (ATFB) was successfully synthesized using boric acid (H3BO3) and ammonium hydrogen difluoride (NH4HF2) as the reactants. In addition to ATFB, aluminum hydroxide (Al(OH)3) was used as a flame retardant and red mud (RM) waste was used as a filler to prepare epoxy composite materials with enhanced flammability properties. The appropriate ratio of RM:ATFB:Al(OH)3both in terms of combustion and mechanical properties was found to be 15:10:5 wt%. The tensile strength of the composite in this ratio was obtained as 112 MPa, while the neat ER was 46 MPa. The burnout of the composite with the appropriate RM:ATFB:Al(OH)3ratio decreased in the first 10 seconds, and extinguished in 32 seconds. Moreover, the burned area of this composite was the smallest among all the others. The experimental and estimatedLOIvalues for this composite was found as 26 and 29, respectively.

Phase Formation Processes in Natural Magnesium Silicates of Various Structures by Ammonium Fluoride Treatment

The processes of forsterite, enstatite, and talc treatment by ammonium fluoride have been studied. The phase-formation processes occurring during firing of fluorinated minerals were studied. It was established that structural silica of the minerals reacts with ammonium hydrogen difluoride with the formation of ammonium hexafluorosilicate, sublimation of which leads to removal of structural silica from the minerals with partial destruction of their structure. The firing of fluorinated minerals leads to their structural transformation with formation of magnesium nesosilicates and fluoronesosilicates.

Investigation of structural, microstructural and magnetic properties of YbxY1-xF3 solid solutions

In this investigation, we have synthesized YbxY1-xF3 solid solutions by fluorination of yttrium and ytterbium sesquioxides with ammonium hydrogen difluoride. According to the XRD analysis, all synthesized YbxY1-xF3 samples have an orthorhombic crystal structure belonging to the β-YF3 structural type. The refinement of crystal structure was done by the Rietveld method within the Pnma space group using the TCH pseudo-Voigt function. The anisotropic peak broadening was analyzed, and the average apparent crystallite size is about 50 nm with a small anisotropy of shape, while the significant microstrain that is highly anisotropic is present in all samples. The temperature-dependent magnetic susceptibility was analyzed by applying the model of a free ion perturbed by the crystal field. We have obtained the effective magnetic quantum numbers Mieff of four Kramer's doublets of Yb3+ ion along with the entire crystal field splitting of the 2F7/2 manifold of Yb3+ in YF3. The acquired maximum energy splitting of the ground level is about 150 K in our most diluted samples. The field-dependent isothermal magnetization measurements were carried out at various temperatures and analyzed by classical Langevin function. Results obtained from magnetic measurements show that all YbxY1-xF3 (x ≠ 0) solid solutions exhibit pure paramagnetic behavior in the whole temperature range from 2 to 300 K, with a predominant antiferromagnetic exchange interactions.

Effect of etching with potassium hydrogen difluoride and ammonium hydrogen difluoride on bonding of a tri-n-butylborane initiated resin to zirconia.

The purpose of the current study was to evaluate the effect of etching with potassium hydrogen difluoride (KHF2) and ammonium hydrogen difluoride (NH4HF2) on the bond strength of a self-polymerizing methyl methacrylate resin (MMA-TBB) bonded to zirconia. Zirconia disks were prepared using the following surface treatment: no treatment, alumina blasting, and etching with KHF2 or NH4HF2. The specimens were bonded with the MMA-TBB. The shear bond (Ø=5 mm) strength was measured. The surface free energies of the specimens were determined by measuring contact angles. The KHF2 and NH4HF2 groups exhibited higher shear bond strength and surface free energy than did the alumina blasting and no treatment groups. Compared with alumina blasting, etching with KHF2 and NH4HF2 exhibited superior bonding ability of mechanical retention to zirconia.

Porous LiF layer fabricated by a facile chemical method toward dendrite-free lithium metal anode

Abstract Lithium metal is supposed to be critical material for constructing next-generation batteries due to extremely high capacity and ultralow redox potential. However, the perplexing issue of lithium dendrite growth impedes the commercial application. The initial nucleation and low Li ions diffusion rate in the electrolyte/electrode interface dominate the deposition behavior. Therefore, a uniform and flexible interface is urgently needed. Here, a facile method is proposed to prepare a thin and porous LiF-rich layer (TPL) by the in-situ reaction of small amount of ammonium hydrogen difluoride (NH4HF2) and Li metal. The deposition morphology on Li metal anode with LiF layer is significantly flat and homogeneous owning to low lateral diffusion barrier on LiF crystals and the porous structure of TPL film. Additionally, the symmetrical cells made with such TPL Li anodes show significantly stable cycling over 100 cycles at high current density of 6 mA/cm2. The TPL Li | LiFePO4 full cells keep over 99% capacity retention after 100 cycles at 2.0 C. This approach serves as a facile and controllable way of adjusting the protective layer on Li metal.

Synthesis of thorium tetrafluoride (ThF4) by ammonium hydrogen difluoride (NH4HF2)

Abstract The present study aims to investigate the fluorination of thorium oxide (ThO2) by ammonium hydrogen difluoride (NH4HF2). Fluorination was performed at room temperature by mixing ThO2 and NH4HF2 at different molar ratios, which was then left to react for 20 days. Next, the mixtures were analyzed using X-ray diffraction (XRD) at the intervals of 5, 10, 15, and 20 days, followed by the heating of the mixtures at 450–750 °C with argon gas flow. The characterization of ThF4 was established using X-ray diffraction (XRD) and scanning electron microscopy–dispersion X-ray spectroscopy (SEM–EDX). In this study, ammonium thorium fluoride was synthesized through the fluorination of ThO2 at room temperature. The optimum molar ratio in synthesizing ammonium thorium fluoride was 1.0:5.5 (ThO2:NH4HF2) with 5 days reaction time. In addition, the heating of ammonium thorium fluoride at 450 °C was sufficient to produce ThF4. Overall, this study proved that NH4HF2 is one of the fluorination agents that is capable of synthesizing ThF4.

Regulating Li deposition by constructing LiF-rich host for dendrite-free lithium metal anode

Lithium (Li) metal anode is among the most promising anodes due to its high energy density. However, the long-standing issue of Li dendrites growth hinders the practical application of lithium metal batteries (LMBs) in portable electronics and electric vehicles. Engineering a dendrite-free Li metal anode is therefore critical for the development of long-life batteries. Here, an artificial LiF host with cuboid feature is constructed on Li metal surface by a facial one-step reaction of ammonium hydrogen difluoride (NH4HF2) with bare Li metal. During cycling, Li grows continuously from the bottom gaps to the top of the LiF host and finally cover the surface of the modified anode. Particularly, with the increasing of cycling capacity, the Li metal tend to deposit into scaly morphology which contributes to a dendrite-free anode. The as-obtained smooth Li anodes enabled stable cycling in working batteries with a low overpotential and a high Coulombic efficiency (CE) of 98.5% at the current density of 1 mA cm−2. This work provides a facile approach to prepare LiF-rich Li anode which paves the way to construct high-energy and safe LMBs.

A novel etching technique for surface treatment of zirconia ceramics to improve adhesion of resin-based luting cements

Objectives: Bonding of zirconia crowns and bridges to abutments is important, not only bonding of the thin resin layer to the abutment, but also bonding to the zirconia ceramic is crucial. Both mechanical and chemical adhesion are desired. Mechanical retention of dental porcelain achieved by etching with moderately concentrated hydrofluoric acid is not possible with zirconia ceramics.The purpose of this study was to show that etching is possible with relative low melting fluoride compounds such as ammonium hydrogen difluoride and potassium hydrogen difluoride.Materials and methods: Before melting, the fluorides can be introduced as powders or as aqueous slurries to the contact surfaces of the zirconia. After melting, the yttria-stabilized zirconia surface revealed a surface similar to an HF-etched dental feldspathic porcelain surface. Shear bond testing (n = 10) was performed with zirconia attached to zirconia with the Duo-Link composite luting cement (Bisco) after treatment of the etched zirconia surfaces with Bis-Silane (Bisco) and the Porcelain Bonding Resin (Bisco).Results: Values for adhesive strength (mean ± standard deviation) after melt etching of the surfaces with initially dry powders were for K[FHF], (31.2 ± 7.5) MPa and for NH4[FHF] (31.0 ± 11.8) MPa. When initially aqueous slurries were applied, the values were for K[FHF] (42.7 ± 12.7) MPa and for NH4[FHF] (40.3 ± 10.0) MPa.Conclusion: Good adhesion to zirconia can be achieved by a procedure including etching with selected melted fluoride compounds.

Hydrofluoride decomposition of natural materials including zirconium-containing minerals

Recently, interest in ammonium hydrogen difluoride (NH4HF2) as a versatile fluorinating agent for the decomposition of natural materials resumed. It is considered to be a new and more efficient than hydrofluoric acid (HF) reagent in analytical chemistry. Thermodynamically possible fluorination reactions with NH4HF2 are exothermic and proceed even at room temperature with the entropy reserve. The fluorination products are of high symmetry phases (tetragonal or cubic) with partial substitution of fluoride ion for oxide (or hydroxide). The fluorination of refractory silicate zircon (ZrSiO4) is kinetically hindered, and its complete decomposition requires the use of a Teflon autoclave at 200oC. The fluorination products are cubic (NH4)3Zr(OH)xF7-x (x ≤ 0.3) and tetragonal double salt (NH4)3SiF7, which can be separated due to incongruent sublimation of (NH4)2SiF6. The mechanism of the latter process is proposed.

Distribution of lanthanides during treatment of high-carbon rocks with ammonium hydrogen difluoride

Distribution of lanthanides during treatment of high-carbon rocks with ammonium hydrogen difluoride

Activation and Fluoride-Assisted Phosphating of Aluminum-Silicon-Coated Steel

Phosphating is a crucial process in the corrosion protection of metals. Here, activation and fluoride-assisted tricationic phosphating is investigated on aluminum-silicon (AS) coated steel surfaces. Dynamic light scattering results from the activation bath show a bimodal size distribution, with hydrodynamic radii of ~400 nm and ~10 μm. For the smaller particle fraction, static light scattering results are consistent with the interpretation of disklike particles as scattering objects. Particles of the larger fraction sediment with time. In the presence of electrolyte, the scattering intensity from the larger particle fraction increases. Coagulation with time is suggested to be related to the decrease in activity of the activation bath. Scanning Auger microscopy (SAM) shows a higher phosphorus concentration after titanium phosphate activation in the Al-rich areas compared to the Si-rich areas of the AS coatings. There is no correlation between the size of the species in the activation bath, and the size of the phosphate-containing regions on the activated surface. Phosphating was performed in the presence of hexafluorosilicic acid, H2SiF6, ammonium hydrogen difluoride, NH4HF2, and both, at an initial pH of 2.5. The absence of crystals after phosphating with H2SiF6 is an indication that SiF6(2-) is the final product of the oxide dissolution in the presence of fluoride. In the presence of NH4HF2, the Si-rich regions of the surface are phosphated before the Si-poor (Al-rich) regions. Hence, the phosphate distribution after activation and after phosphating are opposite. These results show that a high surface concentration of phosphate after activation is not sufficient for a high coverage with phosphate crystals after phosphating.

Effect of Nanoadditives with Surfactant on the Surface Characteristics of Electroless Nickel Coating on Magnesium-Based Composites Reinforced with MWCNT

An experimental investigation has been carried out on optimizing process parameters of electroless nickel-phosphorous coatings on magnesium composite reinforced with carbon nanotube. A comprehensive experimental study of electroless Ni–P coatings on magnesium composite reinforced with multiwalled carbon nanotube under specific coating conditions was performed. The electroless coating bath consists of nickel sulphate (26 g/L), sodium hypo-phosphite (30 g/L) as reducing agent, sodium acetate (16 g/L) as stabilizer, and ammonium hydrogen difluoride (8 g/L) as the complexing agent. The surfactant SLS was added in the solution for better wetting and spreading of coating on substrate. The stabilizer thiourea (1 ppm) was added in the bath to prevent decomposition of bath. Different nanoadditives such as ZnO, Al2O3, SiO with various concentrations were used in the bath and their influence on coating process characteristics were studied The nano additives such as ZnO, Al2O3, SiO were added at concentrations of 0.1%, 0.5%, 1%, and 2% in the EN bath. The output parameters such as surface roughness, microhardness, specific wear rate, and surface morphology were measured. Surface morphology was studied using scanning electron microscope. The results showed that the proposed method resulted in significant improvement on the quality of the coatings produced.

Structure of ultradispersed powders obtained by thermal decomposition of ftoroplast-4 in presence of ammonium hydrogen difluoride

Study of the structure of ultradispersed powders of polytetrafluoroethylene (PTFE) obtained by thermal decomposition of ftoroplast-4 in the presence of ammonium hydrogen difluoride is performed. Using methods of electron microscopy, IR and NMR spectroscopy, TGA and DSC, and others, the peculiarities of the molecular and morphological structure of the powders and their thermal properties are established, and a comparison with the structure of other ultradispersed PTFE powders is performed.

Fluoride Processing of Titanium-Containing Minerals

Fluoride processing of natural ilmenite with the use of ammonium hydrogen difluoride (NH4HF2) as an effective fluorinating agent is suggested. Chemistry, composition, structure, thermal and hydrolytic properties of fluorination products were investigated. Ammonium fluoro- and oxofluorotitanates are suitable for preparing of titanium dioxide as pigmentary product or as doped by nitrogen and fluorine.

Preparation and examination of the properties of complex scandium fluorides

Precipitation of scandium with sodium fluoride from an ammonium hydrogen difluoride solution was examined at the molar ratios of Na to Sc within 1–14 and different initial concentrations of scandium in solution. The composition of the resulting precipitate was determined by X-ray phase analysis method. The solubility of the scandium compounds synthesized was examined.