Electrobalances

The Cahn electrobalance is a sensitive, accurate, reliable, and easily operated balance which is based on a D Arsonval galvanometer, with the sample 

The latest versions of the Cahn recording microbalance are the Models 1000 and 2000. The former has a mass capacity of 100 g with a sensitivity of 0.1 jug and is capable of operation at pressures of 10 7 Torr to 50 atm. The Model 2000 is similar, except that the mass capacity is 1.0 or 2.5 g with a mass sensitivity of 0.L or 1.0 xg for the t.O or 2.5 g load, respectively. This microbalance is used in the Cahn 113 TG system. The furnace on ihis system has a maximum temperature of 1100°C with heating rates of 1 -25 C min. 

One of the most important components of a thermobalance is the sample holder. The geometry, size, and material of construction have a rather important effect on the mass-loss curve obtained. A large variety of sample holders have been described, a representative number of which are shown 

A sample holder which is widely used with Cahn Electrobalance is shown in (a). It is 5-9 mm in diameter and is constructed of platinum or quartz with the geometrical shape of a hemisphere. Sample sizes from 1-20 mg 

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Fig. 11-13. Apparatus for measuring the time dependence of interfacial tension (from Ref. 34). The air and aspirator connections allow for establishing the desired level of ftesh surface. IV denotes the Wilhelmy slide, suspended from a Cahn electrobalance with a recorder output.

CAHN RG ELECTROBALANCE/SEDIMENTATION ACCESSORY. This app produces a continuous, visible chart record of the sediment weight collected on the balance pan. It has been evaluated for measuring particle size distributions of the primary expls Lead Styphnate, Lead Azide, Tetracene by Hutchinson (Ref 41). 

Electrobalances suitable for thermogravimetry are readily adapted for measurements of magnetic susceptibility [333—336] by the Faraday method, with or without variable temperature [337] and data processing facilities [338]. This approach has been particularly valuable in determinations of the changes in oxidation states which occur during the decompositions of iron, cobalt and chromium oxides and hydroxides [339] and during the formation of ferrites [340]. The method requires higher concentrations of ions than those needed in Mossbauer spectroscopy, but the apparatus, techniques and interpretation of observations are often simpler. 

Examples of such substances are calcium oxalate CRS employed for the verification of the electrobalance in thermogravimetry and the solvents, trimethylpentane CRS, toluene CRS and methylnaphthalene CRS, employed for verification of the performance of refractometers. 

Chickering, D.E.lll, and Mathiowitz, E., Bioadhesive microspheres. 1. A novel electrobalance-based method to study adhesive interactions between individual microspheres and intestinal mucosa, J. Control. Rel., 34 251-262 (1995). 

Sensitivity can thus be increased by using a very thin plate. The force is, in this way, determined by measuring the changes in the mass of the plate, which is directly coupled to a sensitive electrobalance. 

The monolayer can also be held at a constant surface pressure, which is enabled by a computer-controlled feedback system between the electrobalance and the motor responsible for the movements of the compressing barrier. This is useful when producing LB films, that is, when the monolayer is deposited on a solid substrate. 

A portion (10.2 cm x 17.8 cm) of each RSP sample was sequentially extracted in a Soxhlet apparatus with cyclohexane, di-chloromethane and acetone, (8 hr. for each solvent) in the order given. A more complete extraction of the organic compounds present in particulate matter is achieved and a partial separation of the organic compounds into non-polar, moderately polar and polar fractions is obtained by this method. The volume of each extract was reduced to 10.0 ml using a rotary evaporator. The samples were then stored in a freezer at -15 C until further analysis. Weights of extracts were determined by weighing duplicate 100 yl aliquots of each, taken to dryness on a slide warmer (40 C), on a Cahn Electrobalance. 

The aerosol samples collected by the SFU were analyzed both gravimetrlcally for total suspended particulate mass less than 15pm, and by particle induced x-ray emission (PIXE) for elemental content. The filters were weighed before and after sampling using a Cahn 25 electrobalance sensitive to Ipg. Typical precision of TSP determined by this analytical method is 0.5pg/m for samples collected under conditions of low aerosol concentrations ( ). After weighing, the filters were analyzed for elemental content (elements heavier than Na) using the UC Davis PIXE system. This analysis technique is described in Cahill al ( ). 

Accuracy and precision vary with instrument model and total, initial, sample size, and sample preparation. A 0.05% accuracy and a precision of 0.1 /xg can be achieved with a electrobalance [6]. Reproducibility between runs, except in relatively pure materials, is usually significantly poorer (see Notes section). 

Sorption Properties. Sorption isotherms were determined of n-hexane and 2,3-dimethylbutane on variously pretreated samples of zeolite by a gravimetric method using a Cahn electrobalance. No shape-selective sorption was observed for these sorbates, which bespeaks a pore size greater than about 0.5 nm. The sorption capacity of S2 was appreciably lower than that of zeolite X, Y, or mordenite. Routine sorption capacities were determined by a simple procedure of pore filling with benzene at room temperature after calcination of the samples at various temperatures. 

Samples of BaU03+x were weighed on a Cahn GRAM electrobalance in the dry box and reacted sequentially in the calorimeter in 1M HCl(aq). ... 

Cahn Electrobalance, Cahn Instrument Co., Downey, California. 

Measurements of oxygen in the gas phase are based on its paramagnetic properties. Any change in the mass concentration of 02 affects the density of a magnetic field and thus the forces on any (dia- or para)magnetic material in this field. These forces on, for example, an electrobalance can be compensated electrically and the current can be converted into mass concentrations further conversion into a molar ratio, e.g. % 02, requires the knowledge of total pressure (Fig. 8). 

A recycle electrobalance reactor for the study of catalyst deactivation by coke formation... 

A new reactor concept for the study of catalyst deactivation is presented, it consists of the combination of an electrobalance and a recycle reactor. With the electrobalance, the coke content on the catalyst is measured continuously. The recycle reactor operates gradientlessly at high conversion, with on-line gas chromatographic analysis of the effluent. Thus, the catalyst activity and product selectivities may be coupled directly with the coke content and the coking rate on the catalyst. 

In the electrobalance technique, the coke content on the catalyst is measured continuously. The combination with on-line gas chromatography couples the catalyst activity with its coke... 

The limitation to low conversion is the major disadvantage of differential operation. This is not critical if the influence of the catalyst properties on deactivation is studied. If, on the other hand, one is interested in the mechanism and the kinetics of coke formation and in the deactivation of the main reactions, it is necessary to reach higher conversions. A solution to this problem is to combine the electrobalance with a recycle reactor. The recycle reactor is operated under complete mixing, so that the reactor is gradientless. Since in a completely mixed reactor the reactions occur at effluent conditions and not at feed conditions, a specific experimental procedure is necessary to obtain the deactivation effect of coke. 

A schematic diagram of the recycle electrobalance concept is given in Figure 1. 

The electrobalance (I) is a high pressure Sartorius microbalance (type 4436 MP 81, resolution 1 /Jg). The weight of the catalyst is continuously measured and recorded. Nitrogen blanketing prevents damage of the electrobalance by hydrocarbons. The nitrogen (L Air Liquidc (99.8+)) causes an additional dilution of the reaction mixture, A sensitive differential pressure meter (m) (range from -1 till 4 mm H20) indicates the pressure difference between the balance chamber and the reactor. 

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