Mixture Of HF Research Articles

Assessment of dissolution techniques for the analysis of ceramic samples by plasma spectrometry

In this study, 13 ceramic samples were subjected to dissolution using three different procedures: (a) acid attack in open PTFE vessels with a mixture of HF–HClO 4, (b) fusion of the sample with lithium metaborate and (c) microwave digestion in PTFE bombs. The samples used in the study had been previously analyzed by neutron activation analysis (NAA), X-ray fluorescence (XRF) and X-ray diffraction (XRD) and they cover a wide range of ceramics fired in different atmospheres and temperatures as well as different mineralogical and chemical compositions. The effectiveness of each procedure is evaluated in terms of its ability to dissolve the various mineralogical phases of the samples, of the number of elements that can be determined and of the time needed for the whole scheme of analysis to be completed.

Determination of trace phosphorus in high purity tantalum materials by inductively coupled plasma mass spectrometry subsequent to matrix separation with on-line anion exchange/coprecipitation.

An on-line matrix separation/inductively coupled plasma mass spectrometry (ICP-MS) method is proposed for the determination of trace amounts of phosphorus in high purity tantalum metal, tantalum (V) oxide, and tantalum pentaethoxide. In the present method, the matrix tantalum in the sample solution was adsorbed on the anion exchange resin, and phosphorus (phosphate ion) was eluted with the carrier solution of HF and HNO3 mixture. Then, the effluent solution was subsequently mixed with bismuth solution and aqueous ammonia solution to coprecipitate phosphate together with bismuth hydroxide. The precipitate formed was collected on the in-line membrane filter to wash out nitric acid with pure water, and then dissolved with hydrochloric acid. The obtained phosphorus sample solution was introduced directly into the nebulizer of ICP-MS for the determination of phosphorus. Phosphorus was determined at the molecular ion signal of 31P16O+ (m/z 47). The detection limit (3sigma) of phosphorus in the present method was 1.3 ng mL(-1) as the sample solution basis, and the relative standard deviation for 30 ng mL(-1) of phosphorus in the standard solution was 4.3% in the replicate measurements (n=11). The present method was applied to the analysis of high purity tantalum materials. The concentrations of phosphorus in tantalum samples were in fairly good agreement with those obtained by glow discharge mass spectrometry (GDMS).

Determination of low-level 54Mn in soils by ultra low-background gamma-ray spectrometry after radiochemical separation

An analytical method was developed for the measurement of low-level 54Mn in soil sample by ultra low-background g-ray spectrometry after radiochemical separation. The method consists of decomposition of sample by a mixture of HNO3 and HF, dissolution by HNO3, precipitation as hydroxide, solvent extraction with diisopropyl ether and anion exchange. Finally, for purification of Mn it was precipitated as MnO2 by adding KClO3. 54Mn in the precipitate was measured by ultra low-background well-type Ge detector at Ogoya Underground Laboratory. Measurements of 54Mn using 30-200 g of soil samples from the JCO grounds were successfully performed by the present method. The minimum detectable activity of 54Mn was about 0.01 dpm (0.2 mBq) for a 7-day counting period.

Application of new physical chemical methods in soil ecological investigations.

The article discusses methodological investigations for the improvement and unification of soil testing in combination with the application of complex physico-chemical methods. An analytical procedure involving different extractions was used in order to determine the total and mobile amount of heavy metals (Cd, Cr, Pb, Ni, Cu, Zn, etc.) by atomic absorption spectrophotometry in soil and its fine-dispersive fraction (< 0.005 mm). The average samples (effected upon by background pollution) of Calcari Epihypogleyic Luvisol, (Lvg-p-w-cc, FAO-Unesco, 1998) has been taken from the rotation field of the experimental station of the Lithuanian University of Agriculture Subsequently, a fine-dispersive fraction was separated by a principle of peptization in distilled water. The investigation results obtained have shown a substantial dependence on the extractor used and the amount of fine-dispersive fraction in soil as well. It was found that the greatest reliability of the mobile heavy metal form is by using 1N CH3 COONH4 extractor and an HCl+HF mixture extractor for their total amount. Additionally, for the first time in Lithuania, the X-ray photoelectron spectroscopy (XPS) it has been applied for the interpretation of soil chemical composition.

Differential etch rates in z-cut LiNbO3 for variable HF/HNO3 concentrations

We report the experimental measurements for etch rates of the +z and -z faces of single crystal lithium niobate immersed in HF and HNO3 acid mixtures of varying ratios. We find that pure HF produces an etch rate that is a factor of 2 higher than the rate obtained for the more frequently used mixture of HF/HNO3 in a 1 : 2 ratio. We further observe that the quality of etching is improved for either pure HF or HF/HNO3 in a 1 : 4 ratio, again by comparison with use of a 1 : 2 ratio. These results lead to a discussion of the etch chemistry involved, and an explanation for the observed high degree of differential etching between the +z and -z crystal faces.

Development of an ICP-HRIDMS method for accurate determination of traces of silicon in biological and clinical samples.

An inductively coupled plasma-high resolution isotope dilution mass spectrometric (ICP-HRIDMS) method in combination with a microwave-assisted decomposition technique has been developed for the determination of traces of silicon in biological and clinical samples. A 30Si-enriched spike solution was used for the isotope dilution step. Decomposition of the samples was achieved by use either of HNO3 or a mixture of HNO3 and HF. By application of both methods of digestion to the same sample it was possible to differentiate between a poorly soluble silicate fraction and an HNO3-soluble silicon species. Traces of silicon were determined in different reference materials, which are not certified for this element, and in other biological and clinical samples. A concentration range of 1-600 microgram g(-1) was covered by the different samples. For homogeneous samples relative standard deviations of 2-4% were obtained. The detection limit was strongly affected by the blank. In this connection purification of water, used in the analytical procedure, was especially critical. The blank contribution of the ICP-MS instrument could be minimized by applying a nebulizer and a spray chamber made of PFA, a sapphire injection tube, and a silicon nitride torch. Under these conditions detection limits of 0.15 microgram g(-1) and 0.2 microgram g(-1) were obtained for the HNO3 and HNO3-HF digestion methods, respectively, when a sample weight of 0.5 g was used. With regard to expected silicon content this enables determination in almost all biological and clinical samples. The ICP-HRIDMS results were compared with those recently obtained in an interlaboratory study. This isotope-dilution method is an potential option for certification of silicon in reference materials, a method for which is still required.

On the synthesis of ferrisilicates mesoporous molecular sieves

The initial steps in the formation of ferrisilicate mesoporous molecular sieves in the presence of sodium or tetramethylammonium silicate, cetyltrimethylammonium bromide and an acid (HF, HCl or HNO 3) were followed by X-ray powder diffraction, nuclear magnetic resonance of silicon-29 in the solid state ( 29 Si-MAS-NMR) and electron spin resonance (ESR). The quality of the mesophases obtained (hexagonal or non-parallel mesopores) and even the nature of the phases (mesophases, layered or amorphous) are highly dependent on three factors: the type and polymerization degree of the silicate anions, the presence of iron (III) ions, and the bonding capacity towards CTA + of the other inorganic anions present in the reaction mixture. The acid used controls the relative concentrations of each silicon precursor present in the reaction mixture and through that controls also the concentration of iron effectively incorporated into the framework. For HF and HCl reaction mixtures, Fe(III) is already in tetrahedral geometry in the solid part of the reaction mixture, before aging or hydrothermal treatment, more noticeably for HF derived solids than for HCl ones. For HNO 3, no tetrahedral Fe(III) was observed by ESR in the solid part of the reaction mixture, before aging and hydrothermal treatment.

A simple vapour phase decomposition (VPD) of quartz powder in a polypropylene vessel and determination of phosphorus by spectrophotometry

A simple, low pressure, low temperature vapour phase decomposition (VPD) of quartz powder has been developed for the determination of phosphorus. A platinum dish containing the quartz or silicon powder was placed inside a polypropylene vessel containing 40 ml of 1:1 mixture of HF and HNO 3. After capping the vessel, the entire assembly was heated on a water bath at ∼90 °C for 8 h. The platinum dish was removed from the vessel, the sample solution was treated with 0.5 ml of H 2SO 4 and 0.5 ml of HClO 4 and was heated on a hot plate till HClO 4 fumed out. The resultant solution was diluted to 40 ml (∼0.4N), analysed for phosphorus by spectrophotometry as an ion-pair of molybdophosphate with crystal violet. Phosphorus contamination by reagents has been drastically reduced (around 250 times) compared to the conventional dissolution procedure. The optimum reaction conditions were [H +]=0.42N, [H +]/Mo=62 for the formation of molybdophosphate and its extraction into n-butyl acetate. No interferences due to fluoride, silicate (active silica) and arsenic ( V) upto 6.7×10 3, 2.7×10 3 and 2.0×10 3 times the content of phosphorus, respectively were observed. The LOD was found to be 0.066 μg g −1 (±3 s). RSD is 0.4–2.3% and the molar absorptivity is 2.7×10 5 l mole −1 cm −1.

Alternative sensor materials for light-addressable potentiometric sensors

Ta 2O 5 and porous Si were investigated as alternative sensor materials for the light-addressable potentiometric sensor (LAPS). The Ta 2O 5 LAPS, prepared by the pulsed laser deposition (PLD) technique, showed a high pH sensitivity of 57.5 mV/pH and a good linearity. Porous Si was prepared by anodic etching of Si in a mixture of HF and ethanol. The porous Si LAPS with a Si 3N 4 layer showed a pH sensitivity of 57.3 mV/pH. As an application of the porous Si LAPS, a penicillin LAPS was fabricated by immobilization of penicillinase on the surface. The pH change due to the enzymatic reaction was detected for the penicillin concentration between 250 μM and 10 mM.

Collection efficiency of metallic contaminants on si wafer by vapor-phase decomposition-droplet collection.

The collection efficiency of metallic contaminants on four different types of silicon wafers was investigated. P, p+, n and n(+)-type polished silicon wafers were used for the substrate, and 14 metallic elements (Na, Mg, Al, K, Ca, Cr, Fe, Mn, Co, Ni, Cu, Zn, Mo and Ti) were contaminated on silicon wafer surface. Vapor-phase decomposition-droplet collection (VPD-DC) was employed as the sample preparation procedure. For the collecting solution, HNO3, HF and a mixture of HF and H2O2 were used, respectively. A liquid droplet collecting metallic contaminants during VPD-DC was analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). As a result, it was found that HNO3 and HF were not suitable for collecting Cu. Copper was not collected completely in HNO3 and HF. A mixture of HF and H2O2 is the most effective to collect all of the tested metallic elements, regardless of the dopant concentration and type of substrate.

Formation mechanism of silicon based luminescence material using a photo chemical etching method

A photo chemical etching method to form a silicon based luminescence material on crystalline silicon has been studied. An n-type Si wafer (100) having resisitivity of 0.22–0.38 or 35–45 Ohm/cm was photo chemically etched in a mixture of HF and H 2O 2 (HF:H 2O 2=100:17∼250), and He–Ne laser (633 nm) was irradiated onto the wafer surface through the solution. A photoluminescence spectrum from the photo chemically etched silicon under a He–Cd laser excitation (325 nm) was measured. Rutherford back scattering spectroscopy measurement was carried out to calculate the thickness of the photo chemically etched silicon. Additionally, an electroluminescence device using etched silicon was fabricated. In this paper, we have proposed a schematic chemical reaction model and a chemical formula of the etching process to discuss the photochemical etching mechanism. As a result, it was found that the etching time presenting a maximum intensity of photoluminescence can be explained and calculated by the etching velocity of the photochemical etching process. Additionally, we demonstrated a yellow electroluminescence from photochemically etched silicon in order to develop the future opto-electronic device on a crystalline silicon substrate. We have exhibited here the usefulness of a photochemical etching method.

Use of the ASPEN Plus Process Simulator in Modeling Systems Containing Hydrofluoric Acid

Nonideal association in the vapor phase of HF poses a challenge in modeling. In this paper, a hybrid HF equation in the ASPEN Plus process simulation software and an equation of Anderko and co-workers are compared. Lencka and Anderko used a general framework to combine a simple association model with a cubic equation. This formulation helps to represent the phase behaviors of HF and halocarbon mixtures, especially for systems containing two liquid phases.

Comparison of dissolution methods for multi-element analysis of some plant materials used as bioindicator of sulphur and heavy metal deposition determined

Most analytical methods for trace element determination in plant material require decomposition of the sample. Sample decomposition procedures play an important role in ensuring that chemical analysis gives correct results. This is especially im por- tant in the determination of trace elements in plant material for environmental studies because, as a rule, plant material is not homogeneous and usually contains variable matrices. In this paper microwave digestion procedures using HNO 3, HNO3+H2O2, HNO3+HClO4, HF mixtures and dry ashing + HF were investigated for the analysis of Al, Ca, Cr, K, Mg, Mn, Zn, S, Pb, V, Cu, Cd, Co and Ni by ICP-AES or ICP-MS from pine needle samples. Reference samples BCR CRM 100 (Spruce Needles), BCR CRM 101 (Beech Leaves) and HUMH2 (Organic surface soil) were used to test the dissolution methods. The results showed that the sample digestion procedure is critical step for obtaining accurate results. Losses of volatile metals were notable in many cases when dry ashing was used.

Latency effects and periodic structures in light-induced frustrated etching of Fe:doped LiNbO3

Single crystals of z-cut 0.05% Fe:doped lithium niobate (Fe:LiNbO3), have been etched in a mixture of HF and HNO3 acids, under simultaneous illumination from a ∼100 mW 488 nm wavelength Ar ion laser light source, focused to power densities of ∼50 W cm−2 at the crystal surface exposed to the etchant. Etching is partially inhibited in illuminated regions, and the degree of inhibition shows a systematic latency: sites illuminated early in the etch run resist further etching even after the light is removed. Etched structures additionally exhibit regular periodic features of ∼0.5 μm scale length. Details of these structures are shown, and the latent etching effect is discussed.

Determination of heavy metals in soils and sediments by microwave-assisted digestion and inductively coupled plasma optical emission spectrometry analysis

The determination of the total content and the leachable aliquot by aqua regia dissolution of eight heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) in soils and sediments was developed by microwave digestion technique combined with inductively coupled plasma atomic emission spectrometry. A complete digestion of soils and sediments was achieved by using an acid mixture of HF–HCl–HNO 3 (1:3:1); the microwave-irradiated closed vessel system used for the determination of aqua regia leachable quota, proved to be a viable alternative to the traditional reflux system. The experimental study was conducted using five BCR standard reference materials (CRM 141R ‘Calcareous Loam Soil’, CRM 142 ‘Light Sandy Soil’, CRM 143 ‘Sewage Sludge Amended Soil’, CRM 277 ‘Estuarine Sediment’ and CRM 320 ‘River Sediment’) in two laboratories with different microwave ovens and ICP-OES. Calculated recovery, repeatability, and reproducibility confirm the good performance of the procedures adopted. A Nested Design statistical analysis was carried out for both procedures and showed that the major source of variability in the analysis was due to ICP-OES measurements rather than microwave-assisted dissolution.

Ion-chromatographic assay of chromium(VI)-containing semiconductor etchants: Statistical comparison of two columns

Semiconductor etchants are concentrated-acid mixtures that are prepared under tight specifications. Assay procedures are needed to ensure that the proportion of each component is within a small percentage (usually 10 relative percent or less) of the target concentration. One such etchant class contains chromium trioxide, usually in combination with HF and HNO 3. While several ion-chromatographic columns can be used to analyze most mineral acids, chromium(VI) presents a problem. This latter species is highly retained by many separators and may also degrade the resins. This paper compares two columns that showed potential for success with these assays: the AS11 and the AS16 separators (both from Dionex). These columns permit elution of chromium(VI) as chromate in 25 min or less. A representative mixture of HF, HNO 3 and CrO 3 was used in the research. Simultaneous calibration studies were conducted and the data sets analyzed statistically. Also investigated was the effect on the columns of repeated exposure to chromate.

Modification of optoelectronic properties of porous silicon produced in an electrolyte based on heavy water

The methods of infrared spectroscopy, electron spin resonance, and photoluminescence were used to study the porous-silicon layers formed by electrochemical treatment of Si in an HF: D2O solution. In contrast with the samples prepared in a conventional electrolyte (HF: H2O), a steady increase in the photoluminescence intensity in the course of routine oxidation of the sample was observed, with the hydrogen coverage of the silicon-skeleton surface retained. A mechanism for anomalous oxidation of the layers of porous silicon obtained in a mixture of HF and heavy water is suggested.

Analysis of plutonium in soil samples

Procedures for analysis of plutonium in soil samples were developed using anion exchange as a purification technique. Special attention was paid to removing impurities of 228Th which interferes in 238Pu determination by alpha spectrometry. Two anion-exchange methods were compared. The determination of plutonium in soil involves the conversion of soil samples to acid-soluble form. Two methods for the extraction of plutonium from a natural reference soil were compared. The first method (a direct digestion in nitric acid) is suitable for the determination of plutonium in large amounts of sample. The second method involves microwave digestion of soil (5 g) with a mixture of HNO3, HCl and HF, and is suitable for saving time in routine determinations. Activities calculated with a reference soil matrix were in good agreement with the reference value. The microwave digestion method was applied in a study of different soil samples, and recoveries ranged between 20% and 50%.

Determination of heavy metals in sewage sludge by microwave acid digestion and inductively coupled plasma atomic emission spectrometry

A description is given of a method for the determination of metals in sewage sludge samples using an acid mixture of HNO3, HClO4 and HF and a microwave oven in open vessel. The elements Al, Cd, Co, Cu, Cr, Fe, Mn, Mo, Hg, Ni, Pb, Ti and Zn were measured by inductively coupled plasma atomic emission spectrometry. The results for the analysis of three reference materials (sewage sludge CRM 145R, sewage sludge from domestic origin CRM 144R and sewage sludge from industrial origin CRM 146R) after microwave acid digestion showed close agreement with the state values for all the metals studied (except Hg). The proposed method was applied to the analysis of Al, Cd, Co, Cu, Cr, Fe, Mn, Mo, Ni, Pb, Ti and Zn in a conventional sewage treatment work to the east of Seville.

Refinement of .BETA.-Si3N4 Single Crystal Grown from Silicon Melt.

Silicon powder in a reaction-sintered silicon nitride crucible was heated at 1600°C in a nitrogen atomosphere. Clustered β-Si3N4 single crystals were obtained in residual silicon metal after cooling. The silicon residuals were dissolved by chemical purification using a mixture of aqueous HF and HNO3, and subsequently treated and with H2SO4. Scanning electron microscopy observation showed that large β-Si3N4 crystals without Si residuals could be successfully separated by this process.