Isothermal gravimetry

Curve 5 Bitumen B200/3 Curve 6 PMB/3 Curve 7 Bitumen B80/4 Curve 8 PMB/4 

The three samples which experience weight loss at 165 °C (Q 1) show that this loss is due to evaporation of non-oxidized parts of the sample (Fig. 4-90). At 200 °C there is no such uniformity (Fig. 4-91). For samples B80/1 and PMB/2 Q is permanently 1.0, i.e. their considerable losses are due to volatile oxidation products. The values for the PMB/4 are still higher  

At 200 °C the quotient Q of PMB/1, B80/2, B200/3, and B80/4 increases with increasing test times, but PMB/1 only exceeds Q = 1.0 after 90 minutes test time. 

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Quotient of weight loss in air divided by weight loss in inert gas (Isothermal Gravimetry)... 

Of some interest is the question whether the Noack evaporation loss test could be replaced by isothermal gravimetry. In contrast to the Noack test, which only delivers one value after one hour test time, the weight loss versus the test time is recorded by the thermobalance. The important information is whether the evaporation has already reached its final stage. But there is a significant difference in the ratios of surface to volume S V between the cup of the Noack tester and the pan of the thermobalance (Stanton-Redcroft TG 750) ... 

There is a higher weight loss in the thermobalance experiment than in the Noack test, even at equal test times and temperatures because of this. Therefore the temperature in the thermobalance was reduced to 200 "C, and a heating rate P= 100 K/min was applied in order to attain the final isothermal temperature as rapidly as possible. The gas flow rate had the standard value of 25 cmVmin. The results of the Noack test are listed in Table 4-167, those of isothermal gravimetry in Table 4-168. Since it was difficult to establish an exact final temperature in the TG 750, the correct final temperatures are also listed in Table 4-168. Repeated tests showed that the temperature remained within 0.57 % of the mean during the 90 minutes test time. Comparison between tables 4-167 and 4-168 shows that the losses from the light oils (samples 01, 02, 08-011) in the thermobalance after 10... 

All the samples were tested by isothermal gravimetry in air in order to assess whether the evaporation losses of the additive-treated lubricants could be calculated from the losses of the basic components (Table 4-169). Samples FVAl, FVA2, and FVA3 reach a final value after only 30 minutes test time the others did not reach this stage, even after 90 minutes. Theoretical evaporation losses were calculated for the additive-treated lubrication oils using the data from the basic compounds (Table 4-170). Comparison between Table 4-168 and Table 4-170 shows that the components of a blended lubrication oil influence one another in such a manner that precise prediction is impossible, and only approximate values of their evaporation losses can be given. 

Table 4-169 Evaporation Loss in the Isothermal Gravimetry in Air at 200 °C. Vaccum Distillates, Base Oils, and Additives. 

Temperature-programmed thermogravimetry in inert gas gives a quick survey of the evaporation behavior, as shown in Fig. 4-144 for some polysiloxanes. For comparison, the TGA curves of a polyalphaolefm (sample 1) and of a perfluoroalkylether (sample 29) are also plotted. Those substances evaporate at considerably lower temperatures than the polysiloxanes despite their substantially higher viscosities. Similar behavior was observed in the isothermal gravimetry. For comparison the oven-aged samples (120 days at 220 "C both with and without wood chips) were also tested by thermogravimetry. The index numbers from those experiments are listed in Table 4-185. 

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