Teflon Vessel Research Articles

Synthesis of polyamide microcapsules and effect of critical point drying on physical aspect

Polyamide microcapsules were synthesized at room temperature by an interfacialpolymerization technique, by reaction of terephthaloyl dichloride with diethylenetriaminein an aqueous medium. Partially hydrolyzed polyvinyl alcohol was used asthe emulsifier and toluene as the organic dispersed phase. For polyamidemicrocapsules, the drying technique has a strong influence on the physical aspectof the resulting microcapsules. In this paper the physical aspect of polyamidemicrocapsules was studied with various drying methods such as air, vacuum andCO2 critical point. It was observed that drying the microcapsules at room temperature underatmospheric conditions or vacuum resulted in an aggregated mass of broken microcapsules, whereasCO2 critical point drying (CPD) in a microfiltration teflon vessel preserved the spherical shapeof polymer microcapsules with high collection efficiency. Similar results were observed onvertically aligned polypyrrole nanowires.

Is microwave digestion using TFM vessels a suitable preparation method for Pt determination in biological samples by adsorptive cathodic stripping voltammetry?

The occurrence of Pt in environmental matrices is increasing since the introduction of automobile catalytic converters. Given that Pt is bioavailable and causes biological effects in plants and animals, respective biomonitoring programs are in high demand. But the analytical methods for conducting such programs have not yet been sufficiently established. Therefore, a study was carried out to develop a microwave digestion of biological samples, which allows a rapid determination of Pt by adsorptive cathodic stripping voltammetry. A high pressure microwave system was used and the digestion was performed in HNO 3 and HCl. After digestion the HNO 3 was evaporated with a microwave assisted vacuum concentration set. The study resulted in a procedural detection limit of 37.5 ng L −1 and a relative standard deviation of 18%. A recovery study resulted in a Pt loss below 5%. The microwave assisted evaporation of HNO 3 performed satisfactorily and up to 500 mL of the sample solution could be used for the voltammetric measurements without any effect on the peak heights. A direct comparison of Pt concentrations conducted after microwave digestion and digestion by high pressure ashing showed similar values. However, these promising results were not persistent throughout the repeated analysis using the same Teflon vessels. The vessels did not endure the harsh conditions and due to aging processes the Pt loss consistently increased until Pt determination in environmental relevant concentrations became impossible. Quartz vessels could not be employed as an alternative to the Teflon vessels, due to a lack of compatibility with the vacuum concentration system. Consequently, the results of this paper show that there is a need for further development of more resistant Teflon materials.

Torus generated by Escherichia coli

The bioluminescence images of unstirred cultures show that lux reporter E. coli (0.10 mg biomass per ml of the broth medium) in 6.4–10 mm diameter circular containers induce center-fluid-rising toroidal convection of ≤1 mm/min. The bioconvective torus is stable in a Teflon vessel and is deformed by 3.2–4.4 mm wavelength azimuthal waves in polystyrene or glass vessels.

TiO2나노분말과 수산화알칼리와의 반응으로부터 티탄산 나노튜브의 형성과 나노구조의 전개

[ <TEX>$TiO_2$</TEX> ] nanotubes for photocatalytic application have been synthesized by hydrothermal method. <TEX>$TiO_2$</TEX> nanotubes are formed by washing process after reaction in alkalic solution. Nanotubes with different morphology have been fabricated by changing NaOH concentration, temperature and time. <TEX>$TiO_2$</TEX> nanoparticles were treated inside NaOH aqueous solution in a Teflon vessel at <TEX>$110^{\circ}C$</TEX> for 20 h, after which they were washed with HCl aqueous solution and deionized water. Nanotube with the most perfect morphology was formed from 0.1 N HCl washing treatment. <TEX>$TiO_2$</TEX> nanotube was also obtained when the precursor was washed with other washing solutions such as <TEX>$NH_4OH$</TEX>, NaCl, <TEX>$K_2SO_4$</TEX>, and <TEX>$Na_2SO_3$</TEX>. Therefore, it was suggested that <TEX>$Na^+$</TEX> ion combined inside the precursor compound slowly comes out from the structure, leaving nanosheet morphology of <TEX>$TiO_2$</TEX> compounds, which in turn become the nanotube in the presence of hydroxyl ion. To stabilize the sheet morphology, the different type of washing treatment solution might be considered such as amine class compounds.

A fast and simple methodology for determination of yttrium as an inert marker in digestibility studies

The need to develop a fast, simple and low cost methodology for the determination of yttrium in fish diets and faeces using a microwave digestion system and atomic absorption spectrometry with flame atomization analysis was the main aim of this study. The final methodology consisted in the digestion of approximately 300mg of dry fish diet or 100mg of dry fish faeces in teflon vessels using Parr reactor bombs, at high pressure, in a domestic microwave system with nitric acid solution. After digestion, 330μl of a 120mg potassium nitrate/ml solution was added to each solution. Yttrium was determined using a calibration with aqueous standards. Analytical difficulties and problems encountered during the optimizations were overcome and the application of the final methodology to the fish diets and faeces samples was carried out with suitable results.

Fabrication of (Ba,Sr)TiO&lt;sub&gt;3&lt;/sub&gt; Thin Films by Hydrothermal Crystallization of Sol-Gel Precursor

Barium strontium titanate (BST) ferroelectric thin films have been successfully prepared on the single crystal silicon substrates using hydrothermal crystallization of sol-gel precursor, which combined the conventional sol-gel process and the hydrothermal method. The precursor film was deposited by the dip-coating method. The multiplayer BST gel films were hydrothermally treated in a Teflon vessel at low temperature of 160-180 °C for 1-3.5 h. The influences of the reaction conditions on the structure and crystallizing degree of BST thin films were discussed. We find that the temperature of as-dried gel films and post hydrothermal treatment are the critical parameters determining the quality of formation of BST thin films. Under optimized conditions, we can obtain well-developed perovskite BST films with smooth and pinhole-free surfaces. These results reveal that this technique is a promising low temperature process for the fabricating of thin films.

Development of a Three-Dimensional Blood Vessel Searching System by Using the Near Infra-Red Light

In this study, an automatic blood vessel searching system (BVSS) is newly developed, which is built in the Health Monitoring System (HMS) and the drug delivery system (DDS) to extract the blood, evaluate the blood sugar level and inject the insulin for the diabetic patients. Main subjects of this BVSS development are 1) a transmittance photo imaging of the finger by using the LED light as the near-infrared light source with the peak wave length of 870 nm, and 2) an image processing to detect the location of the center of blood vessel. To estimate the depth of blood vessel, the lens focal method was employed in the BVSS. To confirm the availability of this method, we carried out experiments by using a skin tissue phantom having a blood vessel, whose vessel part is made of the teflon tube, and whose skin tissue part is made of the silicone rubber. The teflon blood vessel was 0.6 mm in diameter and wasfilled with the human blood. Experimental results demonstrated that the estimated depth has shown a good agreement with the given depth.

Development of tin-loaded liquid scintillator for the double beta decay experiment

Tin-loaded liquid scintillator offers some advantages as a detector for double beta decay experiment. A research program was carried out with the objective of developing such scintillators. Several organometals were loaded into pseudocumene-based liquid scintillator (LS) and light output variation was studied. Up to 50% of tetramethyltin (32.6% w of tin) was successfully loaded into LS and light output was as high as 57% of unloaded LS. We have studied the characteristics and stability of the one liter tin-loaded LS contained in a Teflon vessel. Several γ -ray radioactive sources were used for energy calibration and calibration data were compared with Monte Carlo simulation. Data-taking at the 700 m underground laboratory in Yangyang is ongoing for the search of 0 ν β β decay of 124Sn.

Determination of Mercury in Carbon Black by Cold Vapor Atomic Absorption Spectrometry

Recently, a new color additive, D&C Black No. 2, a high-purity furnace black in the general category of carbon blacks, was listed as a color subject to batch certification by the U.S. Food and Drug Administration. A simple procedure was developed to determine mercury (Hg) in D&C Black No. 2, which is limited by specification to not more than 1 ppm Hg. The method uses partial acid digestion followed by cold vapor atomic absorption and was developed by modifying a method used for other color additives. The carbon black samples are treated with a mixture of nitric and hydrochloric acids and heated by microwave in sealed Teflon vessels. The resulting solutions, which are stable to Hg loss for at least 1 week, are diluted and analyzed for Hg using cold vapor atomic absorption spectrometry. Validation was performed by spiking carbon black samples with inorganic Hg (HgNO3) at levels from 0.1 to 1.5 microg/g, and by analyzing 2 standard reference materials. At the specification level of 1 ppm Hg (1 microg Hg/g), the 95% confidence interval was +/-0.01 ppm Hg (0.01 microg Hg/g). The method developed in this study gave good results for very difficult-to-analyze materials, such as coal standard reference materials and carbon black. By eliminating volatility and adsorption factors through the formation of HgCl4(-2) complexes, one can avoid using extremely hazardous acids such as HF and HClO4.

Preparation of water-soluble and water-swellable starch acetates using microwave heating

Starch acetates of degree of substitution 0.1–1.5 were prepared by heating corn starch, acetic acid and acetic anhydride in sealed, stirred, teflon vessels in a microwave reactor. Reaction efficiencies were typically >90% at reaction temperatures of 150–160 °C for 4–7 min. Starch acetates prepared by reaction at 160 °C to DS values of 0.4–0.9 were >90% soluble in room temperature water. Acetylation rates and water solubilities decreased in the order waxy>normal>high amylose starch. Significant reduction in molecular weights of the starches occurred during microwave reactions. Acetylation occurred preferentially at the C6 position (70%) based on 13C NMR results. Acetylation at lower temperatures (120 °C) gave starches of DS 0.2–0.3 which were water insoluble but highly swellable. These starches retained their native crystallinity, implying that acetate substitution was a block pattern.

High efficiency microwave digestion purification of multi-walled carbon nanotubes synthesized by thermal chemical vapor deposition

Multi-walled carbon nanotubes (MWCNTs) synthesized by thermal chemical vapor deposition (Thermal CVD) have been successfully purified by high efficient microwave digestion purification method. In this paper, microwave digestion method was introduced to purify carbon nanotubes, because that acid can absorb microwave energy rapidly and dissolve metal efficiently in this method. MWCNTs were placed in 100 ml TFM (thermally resistant form of Teflon) vessels with 50 ml 5 M nitric acid. First, the temperature ramped up to 210 °C in 30 min and then kept for 10, 20, 30 to 120 min to digest the catalyst. The efficiency of this method was analyzed by thermogravimetric analysis (TGA) and the results showed that the catalyst content dropped from 10.39% to 1.75% only in 10-min digestion and 1.03% for 120-min treatment. Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) were applied to analyze the property and structure of raw and purified MWCNTs. This study presents a highly efficient and non-destructive purification method for high purity MWCNTs which can be provided in many applications or intrinsic property studies.

Chemical Oxygen Demand Using Closed Microwave Digestion System

A new approach to determine the chemical oxygen demand (COD) using a closed microwave digestion (CMD) system to replace the conventional, time-consuming open reflux (OR) method is proposed. The procedure uses a laboratory-grade closed microwave digestion system (one magnetron) for the digestion of small volume of samples (3.0 mL) in a completely closed (90 mL) Teflon vessel, digesting 10 samples at a time in the range of COD values of 5-1000 mg L(-1). The digestion time required is 15 min as compared to the 2 h required for the conventional OR method. Chloride ion interference can be removed up to 6000 mg of Cl- ions L(-1) as compared to the 2000 mg of Cl- ions L(-1) removed by conventional OR method. The present work reveals that the filtration of effluent samples by membrane filter or homogenization is not essential to obtain reproducible results. The proposed method is cost-effective; saves time, energy, and reagents with providing precise results for both the pure organic compounds and wastewater samples; and is ecofriendly.

Synthesis of phosphatidylcholine: An improved method without using the cadmium chloride complex of sn-glycero-3-phosphocholine

An improved safe method that does not contaminate the environment with cadmium chloride, a toxic heavy metal salt, was developed for the synthesis of phosphatidylcholine (PC). PC was synthesized from sn-glycero-3-phosphocholine (GPC) and fatty acid in one step under mild conditions without the use of cadmium chloride. GPC was prepared from egg yolk PC and adsorbed by kieselguhr in a Teflon vessel. The GPC on kieselguhr was acylated with fatty acid in the presence of two reagents, dicyclohexylcarbodiimide for synthesis of fatty acid anhydride and 4-dimethylaminopyridine as an acylating catalyst, at 30 °C overnight. The PC thus produced was purified by silica gel column chromatography. The yield of dioleoyl PC was 90% based on the starting material, GPC.

Comparison of alkaline fusion and acid digestion methods for the determination of rhenium in rock and soil samples by ICP-MS

A simple acid digestion method was studied in order to analyze many samples at once to understand Re behavior in the terrestrial environment, because, under normal laboratory conditions, digestion methods generally used, such as Carius tube digestions, Teflon vessel digestions and alkaline fusions, can handle only a small number of samples at one time to ensure complete sample digestion. In this study, the Re results for reference materials (RMs) obtained by the acid digestion method were compared with those by the alkaline fusion digestion method to get applicability of the acid digestion method for Re determination in soil by inductively coupled plasma mass spectrometry. Alkaline fusion was chosen for the comparison because it is known to have the highest capability to dissolve Re in geological materials among digestion methods. The average total Re recoveries measured using the 185Re spike for RMs, such as rock, soil and sediment, were 90.6 ± 4.0% for alkaline fusion and 92.2 ± 7.3% for acid digestion, showing no differences between them. However, Re results obtained by the acid digestion method were usually slightly lower than those by the alkaline fusion (Student's t-test, P < 0.05); the concentration ratio of acid digestion to alkaline fusion was 0.85 on average. When the total Re content was higher than 0.2 ng g −1, the acid digestion method could dissolve about 80% of the sample Re. Although the acid digestion method is unable to dissolve all Re in the sample, however, the Re discharged to soils could be more extractable than the Re in the dissolution-resistant part; thus, the acid digestion method could be useful for obtaining Re levels in soil samples.

Enhanced selenium content in buckwheat (Fagopyrum esculentum Moench) and pumpkin (Cucurbita pepo L.) seeds by foliar fertilisation

The fruit and thin-husked seeds of the pumpkin (Cucurbita pepo L.) and buckwheat grain (Fagopyrum esculentum Moench), both grown in Slovenia, were analysed for selenium (Se) content following foliar application of Se(VI) solution during the period of blooming. Samples were digested by a H2SO4-HNO3-H2O2-V2O5 mixture and Se determined, based on hydride generation atomic fluorescence spectrometry. The whole procedure from weighing to measuring was carried out in the same Teflon vessel. The detection limit of the method was 0.14 ng g−1 solution. Buckwheat seeds from untreated plants contained 47 ng g−1 of Se and 394 ng g−1 from plants after foliar fertilisation with Se. Pumpkin seeds from untreated plants contained 108 ng g−1 of Se, and 381 ng g−1 of Se from Se-treated plants, all per lyophilised sample. Se content in lyophilised pumpkin fruit was 15 ng g−1 in untreated plants and 20 ng g−1 in Se-treated pumpkin plants. It is thus feasible to enhance Se content in buckwheat and pumpkin seeds by foliar fertilisation, making them a rich source of dietary Se and useful as a raw material for enriched food products.

Characterization of the formation of NaA zeolite membrane under microwave radiation

Zeolite membranes have gained much attention in recent years, due to their potential application in various fields such as catalysis, gas separation, pervaporation, etc. [1–4]. There are many reports on the synthesis, characterization and applications of zeolite membranes [1–4], but literatures about the formation mechanism of zeolite membrane are fewer [5–7]. To prepare zeolite membranes, many methods have been developed, including hydrothermal crystallization [8], vapor phase synthesis [9], and microwave heating [10, 11]. It was reported that microwave heating and crystal seeding could help the formation and improve the performance of zeolite membranes [10]. It was proposed that the formation of zeolite membranes included the following three stages: sol or gel adhesion on the substrate to form the gel layer, the nucleation and crystallization stage, and the dissolving stage [10, 12, 13]. However, there are few reports on the direct observation of these stages, especially under microwave radiation. In this report, by using scanning electron microscopy (SEM), the formation stages of zeolite NaA membrane in microwave radiation environment were observed and confirmed with the results from X-ray diffraction (XRD) and gas permeation measurements. The disk shaped substrates (30 mm in diameter, 3 mm in thickness) used were porous α-Al2O3 made by casting, with pore radius of 0.3–0.5 μm and ca. 50% porosity. The precursor of the gel was prepared by mixing sodium hydroxide, sodium aluminate, water glass and water, and aging for 24 h with vigorous stirring. The final molar composition of the gel was 3Na2O: Al2O3: 2SiO2: 200H2O. After one face of the substrates was rubbed with zeolite NaA crystals as seeds, the substrates were put vertically in Teflon vessels containing 120 ml gel. Then the vessels were transferred into a microwave oven, heated up to 90 ◦C within 1 min, and reacted for a range of specified times. After the reaction, the membranes were vigorously ultrasonically vibrated in water for 10 min to remove the species physically absorbed on the substrates, washed by de-ionized water to pH = 7.0 and dried at 150 ◦C for 3 h. The membranes were characterized by scanning electron microscopy (SEM) on a JEM-1200E scanning electron microscope and Xray diffraction (XRD) using Cu Kα (λ = 0.154 nm) radiation operating at 40 kV and 100 mA on a Rigaku D max /b powder diffractometer. The integrity of the membrane was evaluated with gas permeation tests.

COMPARATIVE STUDY ON TANNINS, FLAVONOIDS, TERPENES AND MINERAL ELEMENTS OF SOME SALVIA SPECIES

COMPARATIVE STUDY ON TANNINS, FLAVONOIDS, TERPENES AND MINERAL ELEMENTS OF SOME SALVIA SPECIES

Microwave Irradiation Technique for Synthesis of Dialkyl Dithiophosphoric Acids

Microwave heating technique was applied to the preparation of dialkyl dithiophosphoric acids from the reaction of alcohol with phosphorus pentasulphide. A microwave oven (CEM-MDS 2000) was utilized to determine the preparation conditions for the best yield of dialkyl dithiophosphoric acids under atmospheric pressure at various times and power. Six different (C 4 -C 9 ) chain-length of dialkyl dithiophosphoric acids were studied. All experiments were performed in an open Teflon (poly-tetrafluoroethylene) vessel. The results obtained showed that the reaction of dialkyl dithiophosphoric acids can be achieved more rapidly using microwave heating than using conventional procedures.

Biotitization of vermiculite under hydrothermal condition

Hydrothermal experiment was carried out reacting vermiculite with K- and Si-bearing solutions in a Teflon vessel at 150°C for 14, 51, and 71 days to demonstrate biotitization of vermiculite. Our results revealed that biotite is formed within 71 days. High-resolution transmission microscopy and energy dispersive X-ray spectrometry showed that biotite is formed by precipitation directly from solution, domain formation in vermiculite, layer-by-layer transformation of vermiculite, or combination of the three. Our results clearly indicate that biotitization of vermiculite occurs under hydrothermal condition when K is available. Our study suggests that vermiculite formed during weathering is altered progressively to biotite by diagenesis as well as metamorphism after burial.

Determination of Lead, Cadmium and Mercury in Surface Marine Sediments and Mussels

Lead, cadmium and mercury were determined in sediments and mussels, and the ability of these indicators to record metal variations in coastal marine environment is described in this work. The results of an extended investigation of the status of three gulfs at Northern Greece are given, regarding the content of these metals in surface sediments and Mytilus galloprovincialis. The samples were collected during a four-year period. The total concentration of the above heavy metals was determined after digestion of the samples by suitable mixtures of acids, including nitric, perchloric and hydrofluoric acid. The digestion was carried out in a steel pressurised bomb with closed teflon vessels. Lead and cadmium were determined by means of electrothermal atomic absorption spectrometry (ETAAS), and mercury by cold vapour atomic absorption spectrometry (CVAAS). The results were statistically evaluated by analysis of variance, and emphasis was given to annual, seasonal and spatial sources of variation. The annual changes during the last four years and the spatial distribution of heavy metals load is also discussed.