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Radyo frekans titrasyonu

Radio frequency titrations

  1. Tez No: 66770
  2. Yazar: MUZAFFER ERDOĞAN
  3. Danışmanlar: DOÇ. DR. MUSTAFA ÇETİN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1997
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Fizik Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 63

Özet

ÖZET Elektrolitik çözeltilerin elektriksel davranışları, iletkenliklerine bağlı olarak değişim göstermektedir. Elektriksel davranışların çeşitli yöntemler kullanılarak belirlenmesi ile çözeltinin konsantrasyonu ve iletkenliği hakkında bilgi elde edilebilmektedir. Elektrolitik çözelti radyo frekans (RF) alan etkileşimi, radyo frekanslarda sığasal ya da bobinsel ölçme hücreleri ile sağlanmaktadır. Rezonans yöntemlerinin yanısıra, köprü yöntemi gibi başka yöntemler de kullanılmaktadır [5]. Bu çalışmada bir paralel RLC devresi kullanılmış ve çözelti alan etkileşimi, salınım devresinin rezonans koşullarındaki değişimleri saptanarak incelenmiştir. Çözelti ile alan arasındaki etkileşimi belirlemek amacıyla çözelti, bobin hücresi içersine daldırılmıştır. Rezonans koşulları olarak ölçülen rezonans frekansı ve genliğinin konsantrasyona göre değişiminin incelenmesi amacıyla, kalibrasyon eğrileri elde edilmiştir. Bu eğriler, aynı türden bir çözeltinin konsantrasyonunu belirlemek için kullanılabilmek tedir. Aynı zamanda, bu eğriler farklı türden herhangi bir çözelti türünün iletkenliğini belirlemek için kullanılabilmek-tedir. Konsantrasyon değişimine göre çizilen titrasyon eğrilerinden rezonans genliği ve frekansı değişimi birlikte incelenerek dönüm noktası tayin edilebilmektedir. Dönüm noktasına kadar kullanılan titrant hacmi ve titrantın bilinen mol sayısı kullanılarak incelenen çözeltinin konsantrasyonu belirlenmektedir. vıı

Özet (Çeviri)

SUMMARY RADIO FREQUENCY TITRATIONS Electrolytic solutions consist of ions which carry net electrical charges and which can move freely within the solution. Electrical behaviours of an electrolytic solution depend on the density (concentration) and characteristics of the ions it carries. It is possible to observe the behaviours of a solution filled between electrodes by using direct current and electrodes placed inside the solution vessel. In such measuring systems, electrodes used as anode and cathode are directly in touch with the solution, therefore some undesirable outcomes called electron polarization, which can affect the result of the measurement, occur and make it difficult to explain the solution's behaviour [4, 11]. One can obtain information about the electrical behaviours of a solution by letting electrolytic solutions interact with the radio frequency (RF) electromagnetic fields, with regard to the solution's reaction against this interaction [1, 3, 5, 9, 11]. In this method, the solution-field interaction occurs within elements called measuring cell. For RF interactions capacitive and inductive measuring cells are widely used [1, 2, 8, 11]. Examination of interactions of solutions with electromagnetic fields were begun in the 1940s. Characteristics of electrolyte solutions were rather studied through the capacitive method than the inductive method. Although some models were developed for the interaction between electromagnetic field and solution in the inductive method, the interaction mechanism could not be thoroughly understood [2, 3, 6, 7, 11]. The failure vmof studies conducted by means of both the capacitive and inductive methods to reveal the RF field-solution interaction mechanism and to explain common properties of both methods caused a vacuum in this subject [6, 7, 11]. The earliest studies of interaction of electrolyte solutions with radio frequency fields were carried out by Forman and Crisp [9, 10]. These studies were made by using a capacitive measuring cell, and a maximum was observed in the concentration energy absorption curve plotted [4, 9, 10, 11]. This result was also found out after using the resonance method. The measuring cell that we used for examining the interaction between solution and radio frequency field in our experiments was an inductive one. Resonance conditions of oscillation circuit are determined by the interaction between solution and field. Therefore, resonance conditions were provided for the circuit for every measurement we performed. Calibration graphics were plotted for six different coils at different inductances by using the resonance frequency and amplitude data measured for solutions having various concentrations. The curves plotted can be used for determining the concentration of a solution of the same species. The coil to be used for examining the solution must be the one used for developing the calibration curve utilized. When solution is not inserted in the cell, its resonance state can be set by means of the variable capacitor of the measuring circuit. After inserting the solution in the cell, the changing resonance state of the circuit was reset by adjusting the signal generator to the resonance frequency, so that the resonance frequency and amplitude were recorded for each concentration. Dependence of the solution-field interaction on concentration and conductivity in experiments carried out by means of capacitive measuring cells caused radio frequency titration to emerge. Titration is used for IXdetermining conductivity and concentration of a solution [1, 3, 5, 8, 9, 10]. Titrimetric methods employed for this purpose can be classified from different viewpoints. Titrimetric methods are divided into four basic classes in terms of the titration reaction's character, namely the acid-base titrations, reduction titrations, compleximetric titrations, and redox titrations. Another classification is based on the method employed for determining the end point of titration: colour titrations, electrometric titrations, photometric titrations, volumetric titrations, potantiometric titrations, and conductometric titrations. Furthermore, a classification can be made in terms of the quantity of the sample taken: macro, semi-macro, micro or sub-micro. All of these classifications can be valid at certain places, therefore selection of one of them depends on the purpose of utilization [5]. In potantiometric titrations, a convenient indicator's potential is used for determining the end point. A potantiometric measurement made directly through this method can yield different results. On the other hand, in order to achieve neutralization for the potantiometric titration of two acids of the same volume, a standard base of the same volume is needed. Potantiometric end point can be used for a wide range of applications, and it inherently yields more precise data than other, indicator-based methods. However, it takes a longer time than other titration methods employing an indicator. Although some methods are available for determining the end point, the easiest way is to use the curves plotted for the electrode's potential versus volume of the titrant added [1, 14]. Neutralization titrations yield good results to determining the end point thanks to the higher conductivity given to the solution by the hydrogen and hydroxide ions. Conductometric titration provides a convenient method to determine the end point. A sufficient number of measurings must be carried out (three- four times before and after the end point) for obtaining titration curves. Insuch a titration, conductivity of the solution is measured every time when the titrant is added, and the date collected are marked versus the titrant's volume on the curve. The end point corresponds to the intersection, and is obtained by extrapolating the two linear portions of the curve. Conductivity of the solution corresponds to the total contribution of all existing ions. Ions not contributing to the titration reaction have a constant conductivity that does not affect the conductivity changes arising from the reactions. This constant value will not prevent a conductometric titration unless it is too large to make it impossible to determine the conductivity changes. Therefore, it is not desirable to have a very high concentration of inert electrolytes in conductometric titrations. In order to avoid measuring mistakes arising from temperature changes in this titration method, the temperature must be kept stable during the entire process [1, 5]. When an acid and a base are made to titrate by means of the conductometric titration, the below reaction occurs: (H+ + CI') + (Na+ + OH-) -> Na+ CI' + H20 where ions initially existing in the solution and being highly conductive disappear, and CI“ ions with a lesser conductivity appear. Therefore, as alkali is added into the solution, the total conductivity decreases down as the end point is approached. After that conductivity increases as the base is added, because the OH”ions are not used anymore, and have higher conductivity. Conductivity is minimum at the end point, therefore the minimum sharp point of the curve plotted for conductivity vs. titrant is end point. Conductometric titration method is especially used for opaque and colourful solutions whose end poinds can not be detected through an indicator. XIIn addition, in strong and weak acid mixtures, the component amounts can be determined individually. Neutralization titrations are particularly well adapted to the conductometric end point because of large ionic conductances of hydrogen and hydroxide ions compared with the conductances of the species that replace them in solution. Voltammetric methods can be employed to estimate the equivalence point of titrations, provided at least one of the participants or products of the reaction involved is oxidized or reduced at a microelectrode. In amperometric titrations, the current at some fixed potential is measured as a function of the reagent volume (or of time if the reagent is generated by a constant-current coulometric process). Plots of the data on either side of the equivalence point are straight lines with differing slopes; the end point is established by extrapolation to their intersection. An amperometric titration is inherently more accurate than voltammetric methods and less dependent upon the characteristics of the microelectrode and the supporting electrolyte. Furthermore, the temperature need not be fixed accurately, although it must be kept constant during the titration. Finally the substance being determined need not be reactive at the electrate; a reactive reagent or product is equally satisfactory. In our study we used volumetric titration method. The changes of interaction between the solution being studied and the radio frequincy(RF) field applied were investigated and resonant amplytude and frequincy (Vr and fr) against the reagent volume as titration curves were plotted. As the reagent is added in the solution, the varying resonance conditions Vr and fr were measured. Each time the oscillation circuit is set up to the resonance by tracing the resonance frequincy through the variable generator. xnTo see the relation between concentration and resonant conditions for certain species, we obtained calibration curves that are plotted by using solution series having various concentrations. Fig 3.4, 3.8, 3.12 and 3.14 show four radio frequency titration curves obtained with different concentrations. The differences in curve shapes are apparent. A general interpretation of these curves is based on the calibration curves shown in fig 3-5 and 3-9. The shape of the titration curves depend on where the titration starts in the calibration curves X1U

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