Chloroform uptake by gutta-percha and assessment of its concentration in air during the chloroform-dip technique
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Abstract:
The use of chloroform as an adjunct to the practice of endodontics has been a matter of debate. In the present study the chloroform uptake of gutta-percha cones was determined by a gravimetric assay for different times of chloroform dip. In conjunction with an assessment of the amount of gutta-percha dissolved during dip, this provided an estimate of the amount of chloroform that patients are exposed to in clinical conditions. An assay was also performed of the chloroform concentration in the air in a dental office. Chloroform uptake was shown to increase with an increasing dipping time. There also seems to be a difference in this uptake between pure chloroform and a chloroform preparation with colophonium. The concentration levels of chloroform evaporated during the practice of chloroform dip within a dental office do not exceed the safety limits.Keywords:
Gutta-percha
Gravimetric analysis
In most studies of exposures to man-made mineral fibres both fibre number and total mass concentration have been measured, but, generally, correlations between these measures were found only for data pooled by plant or activity rather than for individual samples; also, there were differences between fibre types. Gravimetric measurements have practical advantages and suggestions have been made to approach MMMF exposure evaluation either on a dual gravimetric/fibre count basis or by use of a gravimetric screening test. This paper describes Danish experience in the derivation and performance of a gravimetric screening limit value (SLV) as against a ‘correct’ hygienic index which combines both respirable fibre and total mass concentrations. The system is considered to have many advantages, but the adopted SLV should be checked before use under new or changed conditions.
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The aim of this work is to study the suitability and limitations of a new gravimetric hydrogen evolution (HE) collection method for corrosion rate determination on pure Mg. This method, originally developed by Curioni [1], is based on the real-time weight measurement of the H 2 produced during dissolution and exhibits a higher accuracy level as well as better collection efficiency than the traditional volumetric method. The gravimetric HE collection method overcomes some of the limitations exhibited by the traditional volumetric HE method, where hydrogen gas tends to accumulate at the walls of the funnel and the burette, leading to a lower determination of the amount of H 2 produced and thus, an underestimation of the HE rate. The gravimetric HE collection method also exhibits good suitability for the study of Mg alloys with high corrosion resistance and for short experimental times, where the low levels of H 2 produced prevents reliable measurements of the amount of gas evolved by the volumetric HE collection method. The gravimetric HE collection method is also applicable for dynamic measurements, i.e. potentiodynamic and galvanodynamic polarizations. The gravimetric method was evaluated for the study of anodic HE on pure Mg (also termed Negative Difference Effect (NDE)), which is characteristic of Mg and its alloys when they are forced to dissolve at anodic potentials from the E corr . Possible artifacts and experimental limitations of the gravimetric experimental method will be discussed. [1] M. Curioni, The behaviour of magnesium during free corrosion and potentiodynamic polarization investigated by real-time hydrogen measurement and optical imaging, Electrochim. Acta 120 (2014) 284-292.
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정수처리 공정에서 소독 부산물로서 생성되는 THM 성분 중 chloroform의 제거에 TiO2 광촉매 반응을 적용하였다.
TiO2 광촉매에 조사되는 자외선 파장 변화에 따른 chloroform의 제거율은 반응시간 1시간에 UV-C에서 49.6%, UV-B에서 47.6%, UV-A에서 34.8%로 나타났다. 또한 TiO2 광촉매에 의한 순수한 chloroform의 제거율은 UV-A 파장에서 6.3%로 나타났다. Chloroform 초기농도 1mg/L, 10mg/L, 100mg/L에서 제거율은 각각 40.6%, 34.8%, 31.7%로 나타났다. pH 변화에 따른 chloroform의 제거율은 pH가 3, 5, 7, 9, 11에서 각각 25.4%, 33.1%, 34.8%, 40.6%, 46.7%로 나타났다. 따라서 pH 변화에 따른 chloroform의 제거율은 알칼리성이 강할수록 증가하는 경향을 보이고 있다.
온도 변화에 따른 chloroform의 제거율은 온도 10℃, 20℃, 30℃에서 각각 31.8%, 34.8%. 37.7%나타났다. 이것은 광촉매 반응이 광에 의한 활성화 과정이기 때문에 원칙적으로 승온을 필요로 하지 않고 상온에서 수행될 수 있기 때문이다. Chloroform 10mg/L 수용액에 과산화수소를 0mg/L, 50mg/L, 300mg/L, 500mg/L 주입하였을 경우 chloroform 제거율은 각각 34.8%, 41.8%, 31.5%, 30.4%로서 나타났다. 따라서 본 실험의 경우 과산화수소 50mg/L 주입했을 때의 chloroform의 제거율이 가장 높게 나타났다.
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The accurate measurement of adsorbed gas up to high pressures (∼100 bars) is critical for the development of new materials for adsorbed gas storage. The typical Sievert-type volumetric method introduces accumulating errors that can become large at maximum pressures. Alternatively, gravimetric methods employing microbalances require careful buoyancy corrections. In this paper, we present a combination gravimetric and volumetric system for methane sorption measurements on samples between ∼0.5 and 1 g. The gravimetric method described requires no buoyancy corrections. The tandem use of the gravimetric method allows for a check on the highest uncertainty volumetric measurements. The sources and proper calculation of uncertainties are discussed. Results from methane measurements on activated carbon MSC-30 and metal-organic framework HKUST-1 are compared across methods and within the literature.
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On the basis of our modeling of pillared covalent organic frameworks (PCOFs) with pyridine molecules inserted between the COF-1 layers, we propose that the surface area and free volume of storage materials should be balanced to increase the gravimetric and volumetric hydrogen uptake capacities. Density functional theory and grand canonical Monte Carlo simulations show that these PCOFs have significantly improved gravimetric and volumetric hydrogen storage capacities of 8.8–10.0 wt % and 58.7–61.7 g L–1, respectively.
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The thermal chlorination of chloroform has been studied in the range 260–320°C, using chloroform to chlorine ratios from 10 down to ⅙. For high partial pressures of chloroform the reaction is independent of the chloroform and unimolecular with respect to chlorine. At lower chloroform pressures there is a small dependence on the chloroform in addition to the first-order dependence on chlorine. A mechanism similar to one postulated for the photochemical chlorination of chloroform is discussed and a comparison with the thermal hydrogen-chlorine mechanism leads to the significant conclusion that the reaction has a chain mechanism initiated by chlorine atoms originating on the walls. Production of the latter is interfered with by chloroform adsorption and possibly also by adsorption of reaction products. The chains are broken principally in the gas phase.
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The present theories and experimental methods to evaluate the swelling behaviors by gravimetric measurement were experimentally tested for polyvinyl alcohol (PVA) films. It was found that the swelling behaviors and swelling kinetic parameters, such as diffusion exponent n, by gravimetric measurement may be greatly influenced by experimental procedures. In this pa- per, both the continuous (denoted as scheme A) and the separated (scheme B) experimental procedures of the gravimetric method to evaluate the swelling behaviors were presented and the difference between the two schemes were analyzed. The results suggest that the continuous diffusion of water molecules in films during gravimetric determination may be the key factor affecting the swelling behaviors. The advantages and disadvantages of the two schemes were discussed. It was concluded that an appropriate selection of experimental schemes is effective to extend the applicability range of gravimetric methodology and to increase the accuracy of gravimetric measurement.
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Polyvinyl Alcohol
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