Vacuum Microbalance Techniques Research Articles

A vacuum microbalance technique for studies on the wettability of powders.

A vacuum microbalance technique has been used to evaluate the wettability of powders. The rate of uptake, and equilibrium weight of uptake, of water vapour onto outgassed powder samples, of differing wettabilities, were determined at different known temperatures. Standard techniques of data analysis were used to establish the enthalpy, entropy and Gibb's free energy of the activation and adsorption processes. The values obtained appeared to be in the correct order of magnitude and those for activation clearly reflected the relative wettability of the powders. Tests for compensation demonstrated that with the exception of phenobarbitone, there was probably a common mechanism producing the adsorption.

32nd International Conference on Vacuum Microbalance and Thermoanalytical Techniques (IVMTTC32)

32nd International Conference on Vacuum Microbalance and Thermoanalytical Techniques (IVMTTC32)

Inis Jenemann (20.10.1933–19.11.2008)

Inis Jenemann was born as Erna Irene Haubelt on 20th October 1933 at Hirschberg in Sudeten country (today known as Jeleni o. Bruntal, Czech Republic). She died on 19th November 2008 at Hochheim (Main), Germany. In spite of severe illness she was always a cheerful woman and helpful to everybody in her neighbourhood. She left two children. She was married to the chemist Hans Richard Jenemann and both collected several hundred old laboratory balances and restored them. A part of the collection is exhibited in the DECHEMA Institute at Frankfurt am Main, Germany. They sold about 150 balances to the Mettler-Toledo Company. From their salary and own resources they founded the Jenemann Foundation which grants each year a prize for scientific work on historical metrology. After the death of Hans Jenemann in 1996 [J Therm Anal Calorim 55 (1999) 2, 707] she took his place on the Advisory Board. At the Izmir Conference on Vacuum Microbalance Techniques (2007) she was co-author of the introductory lecture [J Therm Anal Calorim 94 (2008) 3, 607–612]. A few weeks before her death she moved all the remaining scales (*100) in her house, the special library and the collection from Mettler-Toledo to the Philipp Matthaus Hahn Museum and Exhibition Riedschule at Albstadt-Onstmettingen (Germany). That museum now houses the world largest collection of scales, in particular those used in laboratories.

31st International Conference on Vacuum Microbalance Techniques (IVMTC31)

31st International Conference on Vacuum Microbalance Techniques (IVMTC31)

IVMTC30, 30th International Conference on Vacuum Microbalance Techniques

IVMTC30, 30th International Conference on Vacuum Microbalance Techniques

The roots of vacuum microbalance techniques and the international conferences on this subject

The balance is one of the earliest measuring instruments of mankind. The oldest balance beam, found in Upper Egypt and exhibited in the Petrie Museum in London, is attributed to the Amratic period (Negade II) B. C. 3000. A wall painting of a standardisation table containing two balance beams and sets of weights and cups was discovered in the tomb of Hesi-re near the Saqqarah pyramids and can be dated rather exactly to B.C. 2650. The history of vacuum techniques, beginning with Evangelista Torricelli and Otto von Guericke covers about 370 years. First in 1861 a kilogram vacuum balance was constructed by Delieul in order to define the mass standards of the newly introduced metric system excluding buoyancy. However, experiments of Henri Victor Regnault were to no avail because of sorption effects. Thermogravimetric techniques were first applied to determine the water content of raw silk in 1833 by Talabot at Lyon. The first vacuum microbalances, already with electromagnetic force compensation, are from G. Urbain and Friedrich Emich, presented both in 1912. Emich constructed also the first helical spring vacuum balance. Propositions for further improvements of vacuum microbalances were developments in the field of electronics, magnetic materials and high-vacuum techniques. Following this an increasing interest in microgravimetry was developed by investigations of the reaction of solids with the gas phase (adsorption, desorption, chemisorption, heterogeneous catalysis) and some analytical methods such as thermogravimetry, surface structure analysis by adsorption, density determination, the measurement of surface tension and of the magnetic susceptibility. Thus, during the 1950s and 1960s many sorption and thermomicrobalances were developed: spring balances, electronic compensating beam balances, magnetic suspension balances and quartz resonators. It was not only necessary to adapt the balance to the vacuum technique, but the vacuum apparatus had also to be modified for the requirements of the incorporated highly sensitive force transducer. Many disturbances (mechanical vibrations, thermally induced

Thermodynamic stabilities of intermediate phases in the Ca–Si system

Vaporization thermodynamics in the binary system calcium–silicon has been studied by Knudsen effusion-mass spectrometry and vacuum microbalance techniques. The equilibrium partial pressure of Ca(g) over the two-phase regions in the composition range 20–75at.% Si has been measured and the standard enthalpy changes for the appropriate vaporization reactions were determined from the temperature dependence of the measured vapor pressures. The standard reaction enthalpy changes were also evaluated by the third-law method using the pressure data in conjunction with estimated Gibbs energy functions. Standard enthalpies of formation of the calcium silicides were derived from the standard reaction enthalpy values at room temperature. The results obtained for Δ f H° 298 were the following: Ca 2Si=−56.1±3.1, Ca 5Si 3=−55.3±3.5, CaSi=−49.6±2.2, Ca 3Si 4=−40.6±1.5, Ca 14Si 19=−44.4±2.3, CaSi 2=−37.8±1.6 all in kJ/mol atoms. The results for Ca 2Si, CaSi and CaSi 2 may be compared with previous measurements, all other results are first determinations.

Criticism on Jäntti's Three Point Method on curtailing gas adsorption measurements

Jantti introduced a method to reduce the time required for the stepwise measurement of adsorption isotherms (Jantti et al., Progress in Vacuum Microbalance Techniques, Vol. 1, Heyden, London, pp. 345–353, 1972). After a pressure change he measured the adsorbed mass three times and calculated its equilibrium value for the new pressure. In the present paper we discuss the applicability of this method in a broader scope (without starting from a single combination of gas and solid adsorbent) and also discuss the influence of measurement inaccuracies. It is shown that the method can serve as an early warning system, which decides whether an improvement of the adsorption model is necessary.

Preface – 28th International Vacuum Microbalance Techniques Conference

Preface – 28th International Vacuum Microbalance Techniques Conference

A Unique Oscillatory Phenomenon Revealed by A Microweighing Method

An earlier study of the interaction between solid urea and n-octane vapour in the presence of noncomplex-forming hydrocarbons by means of a vacuum microbalance technique revealed the oscillatory nature of urea-octane inclusion compound (complex) formation: process damping, occurrence in the reverse direction and repeated renewal without attainment of the complete saturation of the urea with octane.

Water Sorption and Diffusion in Poly-(3-Hydroxybutyrate) Films

For improved understnding of the transport of low-molecular substances' in moderately hydrophobic polymers, the temperature dependence of water vapor sorption and diffusion in poly-(3-hydroxybutyrate) (PHB) was studied for the first time. Equilibrium sorption and diffusion kinetics were determined by a quartz McBain's vacuum microbalance technique in the temperature range 303-333 K. The water molecule interaction with the polymer matrix was analyzed for wet PHB films by the Fourier transform infrared spectroscopy technique. Water sorption isoterms are interpreted as a superposition of free water sorption estimated by the Flory-Huggins equation and water immobilized on car-bony 1 groups of PHB. The immobilization effect was described by a Lmgmuir-type equation. The dependence of diffusivity on water concentration was described in the framework of Fujita's immobilization model in which the growing function D w versus C w characterized the filling degree of carbonyl groups as sites of immobilization in the polymer. Enthalpy of free water sorption (12 kJ/mol) and water immobilization (42 kJ/mol) as well as the activation energy of water diffusion coefficients (71 kJ/mol) in noncrystalline areas of PHB were determined.

Immobilization influence on the water sorption and diffusion in poly(3-hydroxybutyrate)

The temperature dependency of water vapor sorption and diffusion in poly(3-hydroxybutyrate) (PHB) was studied for the first time. Equilibrium sorption and diffusion kinetics were determined by a quartz McBain's vacuum microbalance technique in the temperature range of 303–333 K. A probability of water molecule interaction with the polymer matrix was analyzed for wet PHB films by FTIR spectroscopy technique. Sorption isotherms are interpreted as the solution of free water molecules estimated by the Flory–Huggins equation and the sorption of water molecules immobilized on the carbonyl groups of PHB. The immobilization effect was described by a Langmuir-type equation. The dependency of diffusivity on water concentration was described in the frames of Fujita's immobilization model in which the growing function Dw versus Cw characterized the filling degree of carbonyl groups as sites of immobilization in the polymer. Enthalpy of free water sorption (12 kJ/mol) and water immobilization (42 kJ/mol), as well as the activation energy of water diffusion coefficients (71 kJ/mol), in noncrystalline areas of PHB were determined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 981–985, 1999

Computer-Simulation of Balance Handling

Several decades ago, when working in the field of magnetism, we had to use a balance the sensitivity of which was limited only by Brownian motion. This balance was a very slow one and to calculate the moment of force measured by it we used its equation of motion, T=Jα+kα+Cα, where we measured the values of all the quantities present on the right-hand side of this equation. At the 21st Conference on Vacuum Microbalance Techniques in Dijon, we suggested that, with the help of a computer, this procedure could also be made applicable to the handling of fast balances. The present paper contributes to this topic by presenting a computer simulation of such a fast balance.

The Impact of Control on the Development of Recording Balances

I am honored by the invitation to give a lecture at this Conference on Vacuum Microbalance Techniques. I have very good memories of such meetings over 35 years, first in the USA, and then alternating in Europe and Africa. Those who have participated in several conferences of this series know that major developments from manually operated to automated balances have been presented there and documented in the Proceedings of these Conferences. I would like to give a few examples from my own work.

Optimizing of Balances of the Second Generation

At the 3rd Conference on Vacuum Microbalance Techniques in Los Angeles in 1962, we suggested the use of the equation of motion of a balance T=J+α+kα+Cα for the calculation of the unknown torque T, and the measurement for that purpose of the values of all the other quantities in this equation. The present paper discusses the consequences of two sources of error relevant for this method. First, the errors caused in the first and second derivatives of the deflection are considered, deduced from two or three deflection measurements separated by small time intervals. Secondly, the consequences of the errors caused by the uncertainties in the deflection measurements are discussed. Consideration of the two errors together leads to an optimal set of values of parameters for the balance handling.

Water Sorption and Diffusion in Poly(S-hydroxybutyrate) Films

The temperature dependence of water vapour sorption and diffusion in poly-(3-hydroxybutyrate) (PHB) was investigated. Equilibrium sorption and diffusion kinetics were determined by a quartz Mac Bain's vacuum microbalance technique in the temperature range of 303–333 K. The water molecule interaction with the polymer matrix was analyzed for wet PHB films by FTIR spectroscopy technique. Water sorption isotherms are interpreted as a superposition of free water sorption, estimated by the Flory-Huggins equation and water immobilized on carbonyl groups of PHB. The immobilization effect was described by a Langmuir type equation. The dependence of diffusivity on water concentration was described in the framework of Fujita's immobilization model in which the growing function Dw vs Cw . characterized the filling degree of carbonyl groups as sites of immobilization in the polymer. Enthalpy of free water sorption (12kJ/mol) and water immobilization (42kJ/mol) as well as the activation energy of water diffusion coefficients (71kJ/mol) in noncrystalline areas of PHB were determined.

27th International Conference on Vacuum Microbalance Techniques

27th International Conference on Vacuum Microbalance Techniques

A New Zr-Based Alloy for Tritium Recovery from Tritiated Water

The dissociation of tritiated water and the recovery of tritium is an important issue for the future thermonuclear fusion device. Various solutions have been proposed including chemical dissociation on active beds. The results of H{sub 2}O sorption tests performed on different possible candidate alloys, by means of vacuum microbalance technique at a pressure of some hundreds Pa and at temperatures ranging from 300 to 400{degree}C, are presented. From these tests a ternary Zr-Mn-Fe alloy appears to have promising features, combining good dissociation characteristics for H{sub 2}O with low hydrogen pick up. The basic properties of this material are discussed, including structural aspects and sorption characteristics vs. other gases. 14 refs., 11 figs., 1 tab.

Diesel particulate characterisation by vacuum microbalance techniques

The physical and chemical character of diesel particulate (DP) has been determined. Electron microscopy (EM) and a gravimetric BET method (BET) determined particle size and specific surface area (SSA). Two different diesel engine types (direct injection (DI) and indirect injection (IDI)) were run at similar operating conditions and DP was collected by filtration of the exhaust gas at temperature without dilution. An in-vacuo gravimetric thermal degassing (TD) apparatus has been constructed to extract adsorbed hydrocarbon volatiles from the DP during a slow heating program. The desorbed volatiles were trapped and analysed by gas chromatography (GC). The carbons were fuel- and oil-derived unburnt hydrocarbons (UHC), trapped within the slit-shaped micropores and ‘ink-bottle’-shaped mesopores/surface of the aggregated diesel particles.

Some comments on the history of vacuum microbalance techniques

Based on the reviews of Behrndt, Iwata, Duval, Jenemann and Gast, we present a chronology of vacuum microbalance techniques in table form. The earliest discoveries of weights and balances are dated to about 3000 B.C. In the 19th century, balances were operated in vacuum for meteorological purposes. Thermogravimetry began with Talabot who, in 1833 in Lyon, equipped a laboratory with thermobalances for quality control of Chinese silk. At the beginning of the 20th century, microbalances were placed in high-vacuum apparatus.