Thermogravimetric microbalance

To compare the corrosion behavior of coated and uncoated samples, several oxidation/ sulfidation tests were performed at 700 to 1000°C in a thermogravimetric microbalance. Test results for oxidation of various samples in flowing air and sulfidation in 498-ppm H S/H gas mixture for one month are shown in Figure 8. 

When heated, many solids evolve a gas. For example, most carbonates lose carbon dioxide when heated. Because there is a mass loss, it is possible to determine the extent of the reaction by following the mass of the sample. The technique of thermogravimetric analysis involves heating the sample in a pan surrounded by a furnace. The sample pan is suspended from a microbalance so its mass can be monitored continuously as the temperature is raised (usually as a linear function of time). A recorder provides a graph showing the mass as a function of temperature. From the mass loss, it is often possible to establish the stoichiometry of the reaction. Because the extent of the reaction can be followed, kinetic analysis of the data can be performed. Because mass is the property measured, TGA is useful for... 

The equipment consisted of a microbalance suitable for thermogravimetric analysis (TGA), with an integral sample collector and an on-line gas chromatograph (GC) see Figure 1. Details of the apparatus have been presented before see e.g., Ref. 

Details can be found in Bdlare (ref. 3). The experimental equipment consists of a cumene reservoir, a thermogravimetric analyzer (TGA) and a gas chromatograph (GC). The hdium-cumene mixture enters the TGA, a Cahn System 113DC with a Cahn 2000 Recording Electrobalance, a quartz tubular reactor, and an external split-shell furnace. The catalyst is placed in the sample pan of the microbalance inside the quartz reactor, kept at a controlled temperature in the center of the split-shell furnace. The incremental weight due to coke deposition on the catalyst is monitored by an IBM PC. The reactor exit stream is injected into a Varian 3700 GC using FID. 

Figure 4. Comparison of the CP (thermogravimetric Curve G) with DCP (deformation Curve L) obtained on the linear heating of NiC, prepared by mixing. Both curves relate to the common axis y. X = 6.5 K/min. The microbalance and dilatometer specimens have been cut from the same NiC pellet.

The thermogravimetric measurements were performed in microbalance systems (CAHN TG-121 and Sartorius 4433). The experimental conditions were the following sample mass 100-150 mg, sample temperatures 300°C to 700°C, temperature ramps 2 and 5 K/min. The relative error of the thermogravimetric results was <10%. 

Surface acid densities were estimated using pyridine adsomtion monitored by combined thermogravimetric and infi-a-red spectroscopic techniques. Thermogravimetric analyses were carried out using a PC controlled Cl microbalance attached to a conventional vacuum line fitted with rotary and diffusion pumps. Approximately 100 mg of sample as a fragmented disc (prepared as per FTIR experiments, see below) was outgassed for 2 h at 573 K, then exposed to 1 Torr pyridine and cooled to 373 K. A further... 

While the properties just described are utilized in specific kinds of experiments, the two most common properties studied as temperature is increased are mass and enthalpy. The change in mass as the temperature increases is produced by the loss of volatile products. Therefore, this technique is referred to as thermogravimetric analysis (TGA). Although the design of instruments will not be reviewed here, the basic components are a sensitive microbalance and a heat source that surrounds the sample and allows it to be heated at the desired rate. 

In concluding this section we want to emphasize that gas adsorption experiments also can be done at elevated temperatures. Preferently they should be carried out gravimetrically using a highly sensitive microbalance. These so-called thermogravimetric measurements can be used to monitor surface and structural changes of the sorbent material caused by physical or chemical modifications [1.3]. 

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. 

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