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2O, and Global Warming: How to Stop the Planet from Burning
Published in Abu Zahrim Yaser, Poonam Khullar, A. K. Haghi, Green Materials and Environmental Chemistry, 2021
Francisco Torrens, Gloria Castellano
Teflon was discovered in 1938 by U.S. chemist Roy Plunkett; trying to make a chlorofluorocarbon (CFC) refrigerant, he heated tetrafluoroethylene (cf. Figure 3.6a) in a Fe container under pressure, obtaining a white solid [5]. It transpired that Fe catalyzed the polymerization, leading to PTFE (cf. Figure 3.6b). The strong C-F and C-C bonds cause it to be chemically inert to other chemicals, making it of almost immediate use in the Manhattan project for the construction of the first nuclear bomb. The isotopes 235U and 238U were separated by gaseous diffusion of volatile and reactive UF6; Teflon was vital for making unreactive and leak-proof valves and seals in the plant. Today, Teflon-coated magnetic stirrer bars are widely used in laboratories. Teflon presents an extremely low coefficient of friction and is widely used for a range of nonstick applications [Teflon-coated, nonstick cookware, coatings for machinery parts (gears, bearings), windscreen wiper blades]. Teflon taps in the burettes prevent sticking and require no lubrication. Teflon tape is used as a thread-sealing tape by plumbers, whilst Teflon coatings are used on some armor-piercing bullets (though it is not the Teflon that gives them the armor-piercing property).
T
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[biomedical, chemical, mechanics] Brand name for polytetrafluoroethylene (PTFE), a synthetic fluoropolymer of tetrafluoroethylene; registered trademark from the DuPont corporation, discovered in 1938 by the chemist from the United States Roy Plunkett (1910–1994). The high molecular weight material has a very low coefficient of friction; this will result in an extremely low degree of static and kinetic friction with respect to virtually any material. Teflon has a high stability temperature and is hence used as a nonstick coating for a broad range of industrial and commercial applications (e.g., pots and frying pans). The additional mechanical and chemically inert properties have provided ample applications as tape and gasket material (see Figure T.13).
Sampling procedures
Published in T. R. Crompton, Determination of Metals and Anions in Soils, Sediments and Sludges, 2020
The fact that ‘classical’ systems of dry decomposition still persist in today’s analytical chemistry is due to the traditional thinking of the analytical chemist, who still believes that the most favourable agent for speeding up the process is temperature. For this reason, dry decomposition has now become the greatest drawback in sampling; on the one hand, it has led to the lengthening of the analysis time and, on the other, to increased contamination risks due to the decomposition agents used. Unlike acids, which can now be obtained in a high degree of purity, solid reagents are often of insufficient purity for trace analysis. It is this aspect of trace analysis which has led to the development of some noncontaminant decomposition systems. The simplest way of achieving faster (and non-contaminating) decomposition has been to resort to an additional physical parameter, namely pressure, coupled with an adequate decomposition temperature. As discussed later, the use of high-pressure decomposition vessels requires much lower temperatures for decomposing a sample, than those necessary for dry decomposition at atmospheric pressure. The appearance of the high-pressure decomposition vessels (bombs) is a direct result of the availability of a chemically inert plastic, namely Teflon. Teflon exhibits good thermal stability and offers minimal contamination risks. High-pressure decompositions involve the use of some decomposition agents which can be prepared easily in a high degree of purity (e.g. hydrochloric acid). The great advantage offered by these disintegration systems is that they make use of relatively cheap laboratory apparatus and avoid expensive materials such as platinum. These high-pressure decomposition systems have now become commonplace in the laboratory.
Composite Fouling Characteristics on Ni-P-PTFE Nanocomposite Surface in Corrugated Plate Heat Exchanger
Published in Heat Transfer Engineering, 2021
Zuodong Liu, Zengchao Chen, Wei Li, Zhikou Ding, Zhiming Xu
In light of the disadvantages of fouling in heat exchange equipment, many attempts have been made to reduce fouling by coating the heat transfer surface with various coatings. Since the 1980s, electroless plating has been treated as an operational technology of surface modification, attracting widespread attention [33, 34]. Some reports reveal that fouling could be effectively inhibited by the electroless Ni-P based coating [35, 36]. Several recent studies have investigated the performance of different anti-fouling coatings. The primary contention is that surfaces with low surface energy can attenuate the deposition of fouling substance. Balasubramanian and Puri [37] conducted fouling experiments in a pilot-scale PHE system, using the plate surfaces of SS-316 and coating surfaces of three different kinds of commercially available food-grade materials. All the three tested coated plates had anti-fouling performance, among which Lectrofluor-641TM was the most effective, showing a reduction percentage of about 16% in thermal energy consumption at the same flow rate. All the different coated plates, due to their low surface wettability, were also easier to clean relative to uncoated ones. Anti-fouling has been attributed to the hydrophobic and oleophobic effects of the heat transfer surface, which can be accomplished with electro-polished and polyurethane-coated plates as well [38]. More recently, Li et al. [24] carried out fouling tests on SS-304 plates coated with Teflon in PHEs. The Teflon coated plates showed good anti-fouling performance, of which the asymptotic fouling resistance had a maximum of 33.8% decrease compared with uncoated plates. As Teflon has extremely low surface energy, it has excellent nonstick property. However, the poor thermal conductivity, poor abrasion resistance and poor adhesion to metal substrate of the Teflon coating currently inhibit its commercial use.
Potential health risk of heavy metals via consumption of rice and vegetables grown in the industrial areas of Bangladesh
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Ram Proshad, Tapos Kormoker, Md. Saiful Islam, Krishno Chandra
All chemicals were analytical grade reagents; Milli-Q water (Elix UV5 and Milli-Q, Millipore, Boston, MA, USA) was used for the preparation of solutions. The Teflon vessel and polypropylene containers were cleaned, soaked in 5% HNO3 for more than 24 h, then rinsed with Milli-Q water and dried. For metal analysis, 0.3–0.5 g of the food sample was treated with 6 mL 69% HNO3 (Kanto Chemical Co, Tokyo, Japan) and 2 mL 30% H2O2 (Wako Chemical Co, Tokyo, Japan) in a closed Teflon vessel and was digested in a Microwave Digestion System (Berghof speedwave1, Eningen, Germany). The digested samples were then transferred into a Teflon beaker, and a total volume was made up to 50 mL with Milli-Q water. The digested solution was then filtered by using syringe filter (DISMIC1–25HP PTFE, pore size = 0.45 mm; Toyo Roshi Kaisha, Ltd., Tokyo, Japan) and stored in 50-mL polypropylene tubes (Nalgene, New York, NY, USA). After that, the digestion tubes were then cleaned using blank digestion procedure following same procedure of samples. For heavy metals, samples were analyzed using inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7700 series, Santa Clara, CA, USA). Instrument operating conditions and parameters for metal analysis are done. The detection limits of ICP-MS for the studied metals were 0.7, 0.6, 0.8, 0.4, 0.06, and 0.09 ng/L for Cr, Ni, Cu, As, Cd, and Pb, respectively. Multi-element Standard XSTC-13 (Spex CertiPrep®, Metuchen, NJ, USA) solutions were used to prepare calibration curves. Internal calibration standard solutions containing 1.0 mg/L of indium (In), yttrium (Y), beryllium (Be), tellurium (Te), cobalt (Co), and thallium (TI) were purchased from Spex Certi Prep® (Metuchen, NJ, USA). During the procedure, 10 mg/L internal standard solution was prepared from the primary standard and added to the digested samples. Multi-element solution (purchased from Agilent Technologies, Japan) was used as tuning solution covering a wide range of masses of elements. All test batches were evaluated using an internal quality approach and validated if they satisfied the defined Internal Quality Controls (IQCs). Before starting the analysis sequence, relative standard deviation (RSD, <5%) was checked by using tuning solution purchased from Agilent Technologies. The certified reference materials INCT-CF-3 (corn flour) bought from the National Research Council (Canada) were analyzed to confirm analytical performance and good precision (relative standard deviation bellow 20%) of the applied method.