Electronic microbalances

When using a modern thermobalance which incorporates an electronic microbalance requiring small sample weights, the following operating precautions should be noted. 

The development and ready availability of reliable and accurate electronic microbalances [33,122—128] have led to their wide application in kinetic studies of the decomposition of solids. Certain of the disad-... 

Vacuum electronic microbalances and continuous flow instruments provide electronic signals for a permanent record. 

Figure 3. Model AD-2 precision electronic microbalance (capacity 5g sensitivity 0.1 fig)...

Spring balances are still used in certain research investigations when adsorption equilibration is very slow, e.g. for the study of hysteresis phenomena. For this purpose, it is advisable to replace the mercury manometer by a modem pressure gauge. However, in recent years spring balances have been largely superseded by electronic microbalances. The essential features of an electronic, null adsorption microbalance are indicated in Figure 3.11. 

At the other extreme, with materials of specific surface area above 500 m2 g 1 one must be careful not to reduce the mass of sample by too much it must remain representative of the batch of adsorbent and it must be weighed with an accuracy consistent with the accuracy provided by the adsorption measurement. For these two reasons, it is usually unwise to use a sample mass under, say, 50 mg. If the full adsorption-desorption isotherm is to be determined, one can be limited by the capacity of adsorptive reservoir or dosing volume or by the automatic control range of the electronic microbalance (typically, between 50 and 100 mg with sensitivity >1 pg). It therefore often happens that the measurement of one isotherm cannot provide the best determination of the specific surface area and at the same time the best determination of the full adsorption-desorption isotherm. 

Preparing slurries for analysis. Microweighing should be done on an electronic microbalance. An amount of 1-50 mg of ground material can be weighed directly in a Teflon autosampler cup and supplied with 1.0 ml of diluent (5% sub-boiling distilled HNO, containing 0.004% Triton X-100). 

P205 column, 2. capillary flowmeter, 3. three step cock, 4. thermocouple, 5. sample holder with sample, 6. resistance furnace, 7. electronic microbalance, 8. x-t recorder... 

The Model TG-750 thermobalance is illustrated in Figure 3.27. This instrument features a miniature water-cooled furnace in conjunction with an electronic microbalance, with mass sensitivies of 1 -250 mg full-scale deflection on a potentiomeiric recorder. Heating rates of 1-100 C/min are available with a maximum furnace temperature of 1000 C. The furnace will cool from 1000-50 C in about 4 min. 

Instrumentation Adsorption-desorption isotherms of nitrogen were determined with a Cl Electronics microbalance. Infrared spectra were taken with a FTIR Mattson Galaxy instrument. XRD spectra were recorded on a Rigaku X-ray diffractometer. Gas chromatography analyses were carried out in a Konik HRGC 3000-C instrument equipped with a 30 m x 0.25 mm OV-1 column splitter 1/30 Injector temperature 180 C detector FID detector temperature 250 C oven 80 C isothermic by 5 min. rate 6° C/min. carrier H2. 

Figure 4.4.9. Schematic diagram of an isopiestic vapor sorption apparatus using an electronic microbalance PC - personal computer, MB - microbalance, WBl-3 - water bath thermostats with T3>T2>Ti, Vl-3 - valves, WM - W-tube mercury manometer, S - polymer sample/solution, SV - solvent reservoir, MS -magnetic stirrer, CT - cold trap, VP - vacuum pump. [Reprinted with permissitm from Ref. 92, Copyright 1998, American Chemical Society].

TG curves are recorded using a thermobalance. The principal elements of a thermobalance are an electronic microbalance, a furnace, a temperature programmer and an instrument for simultaneously recording the outputs from these devices. A thermobalance is illustrated schematically in Figure 4.2. 

The water vapor sorption experiments were generally performed in a Cahn D-200 electronic microbalance (with a sensitivity of lO g) enclosed in a thermostated reactor (Figure 5). The sample is placed in a pan and dried at 0% humidity. After reaching a plateau, the dry mass is achieved. Thereafter, the sample is exposed to vapor pressure and the mass gain is measured as a function of time until reaching the equihbrium state. The mass equilibrium is obtained at each humidity level tested. 

Before running the DSC, one should weigh the sample to an accuracy of at least 0.2 %, for example, 0.02 mg for a 10-mg sample or 0.002 mg for a 1 -mg sample. For these purposes electronic microbalances are used. The manufacturers may recommend certain balances to the buyer. 

It is very important to accurately weigh the samples for DSC measurements. To achieve an accuracy of better than 1% in heat capacity measurements, for instance, the sample must be weighed to an accuracy of at least 0.1 %. For these purposes the use of electronic microbalances is reconunended. The major... 

The amount of oxygen groups present on the surface was determined by thermogravimetric analysis in a Cl Electronics microbalance (MK2-MC5). The sample was treated under flowing He for 2 h and then heated at a 10 K-min" rate up to 1023 K. 

M, mineral insulated graded heating element N, liquid nitrogen cooling jacket R. four bore ceramic hangdown suspended from electronic microbalance S. flxed compartment divider with gas ports T, side branch gas exit pipe W, water-cooled cold Anger. 

---