Peak Maximum Temperature

Onset Onset Onset Weight Loss in the Major Degradation Steps (%) Peak Maximum Temperatures (T ad rC) Rate of Decomposition (div/df) at (%/min) Char Residue at 600°C... 

Another popular method has been developed by Chan, Aris and Weinberg [28], These authors expressed E ( 8) and v(8) in terms of the peak maximum temperature Tmax and the peak width, either at half or at three quarters of the maximum intensity. Their expressions for first order desorption are ... 

The nearest-neighbor interaction is much larger than the other two. It is also much larger than the thermal energy at the temperature of the experiment the peak maximum temperature is about T = 500 K. The other interactions are... 

A relationship between the peak maximum temperature, Tm, and E for data obtained at different heating rates was derived by Kissinger 23) ... 

The TPD spectra of three different adsorbate systems, corresponding to zeroth-, first- and second-order kinetics, are shown in Figure 2.9. Each trace corresponds to a different initial adsorbate coverage, as indicated in the figure. The simplest case in TPD corresponds to first-order desorption kinetics, represented by the CO/Rh(lll) series in Figure 2.9 [17, 18]. For CO coverages up to 0.5 monolayer (ML), the CO molecules do not interact on Rh(lll) and the desorption traces all fall in the same temperature range, all with the same peak maximum temperature. Hence, the rate of desorption is proportional to the surface concentration of CO. Above 0.5 ML, CO starts to populate additional sites (from vibrational spectroscopy studies we know that in addition to on-top sites also threefold hollow sites are occupied see Fig. 8.15), and a faster reaction channel for desorption opens up, as seen by the development of a shoulder at lower temperatures [18]. 

The fact that potassium enhances the adsorption bond of CO with the substrate is revealed by thermal desorption, in a shift of the CO desorption peak to higher temperatures. Figure 9.14 shows thermal desorption spectra (TDS) of CO from potassium-promoted nickel, as reported by Whitman and Ho [53]. On clean Ni(110), CO desorbs in a first-order process with a peak maximum temperature of about 440 K. When potassium is present, CO desorbs out of two states,... 

Discs of paper, %-in diameter, were punched from sheets. The discs were placed in 4-in diameter aluminum foil pans and covered with 80-mesh stainless steel screen to prevent coiling. The samples were then linearly temperature programmed at various rates in a DuPont 990 differential thermal analyzer under a 50-cc/min flow of air or oxygen. The paper reaction peaks were recorded, and the peak maximum temperatures were measured and corrected for thermal resistance, thermo-... 

By applying multiple heating rate DSC measurements and Ozawa s isoconver-sional model free method, an activation energy of 34.2 kcal mol1 and pre-exponential factor of 1.99 1012 s 1 were calculated from the DSC peak maximum temperature - heating rate relationship. 

EO desorbs intact at a peak maximum temperature of 158 K (45 kJ/mol) when dosed on to clean Ag (111) at 80 K. It is held with the molecular plane held perpendicular to the surface [19]. The desorption activation energy of EO increased to 51 kj/mol for EO dosed at 80 K on to oxidised (0o = 0.1) Ag(lll). When EO is dosed on to oxidised Ag(lll) at 300 K, an acetaldehyde species is formed on the surface, the infrared features of which decrease coincidentally with acetaldehyde/EO desorption [19]. 

DFT calculations of the vibrational frequencies of these adsorbed species produced spectra of which those deriving from intermediate 1 more closely resembled the HREEL spectrum of the surface. The authors calculate an activation energy of 55 kj/mol for cyclisation of intermediate 1 from the peak maximum temperature of 300 K for EO desorption using the Redhead equation [35] and an... 

Until Atkins and co-workers published that Cl atoms lowered the O2 desorption peak maximum temperature from 513 K (240 °C) to 481 K (208 °C) [3], there had been nothing published linking the effect of Cl atoms on any measurable physical property of the catalyst. Generally, the comments were nuanced along the lines that, because Cl atoms (which were considered to be on the surface of... 

The effect of reducing the sampling rate from live points per second to one point per second appears to be minimal on the enthalpy calculation. Further reduction in the sampling rate, below one point per second, results in a decrease in the value obtained for the heat of fusion for indium. Other calculated values, such as peak maximum temperature, peak width at half height, and peak height are also affected. 

FIGURE 3.15 Plot showing relationship between heating rate N and peak maximum temperature for water loss (rm) from alkaline-produced magnesium stearate. (Reproduced from Miller, T.A. and York, P., Int. J. Pharm., 23, 55, 1985. With permission.)... 

Peak Maximum Temperatures (°C) from DSC and Derivative TGA (DTG) and Water Loss (moles water per mole drug) from TGA Data for Nedocromil Zinc Hydrates... 

Plots of DSC curves at various heating rates (Fig. 32) showed that the peak maximum temperature (Tp) increased with increasing heating rate (cp). Activation energy (Ea), was evaluated by using the empirically deduced equation [101 — 104] relating Tp and cp, regardless of the reaction order ... 

Curve (a) departs from zero some distance below the 50°C inversion temperature and readies its peak some 20°C above the inversion temperature. In curve b), the sample material surface temperature would correspond to the temperature of the metal block in which the sample and reference cavities are located. This curve starts deviating from the baseline at the inversion temperature, which, if this temperature could be accurately determined, would have useful significance on such a curve. If the differential temperature is plotted against the temperature at the center of the sample material, as shown in curve (c), the peak maximum temperature would be equal to the inversion temperature. 

Langer and Kerr (65) studied the effect of sample mass on the dehydroxyla-tion peak of kaolinite. As shown in Figure 5.30, an increase in sample mass causes an increase in the peak minimum temperature (7 ), all determined at a heating rate of 25°C/min. The phase transition peak maximum temperature was only slightly affected (5°C) in contrast to the change for the dehydroxyla-tion p,eak temperatures (45°C). 

From the curves, the peak maximum temperature, ATmin, was used for the determination of the polymer melting point. Results obtained by DTA were within + 1CC of the reported literature values, although several of them had a 15CC melting-point range, as indicated by the distance between the initial departure from the baseline and the peak. Isotactic polypropylene gave a somewhat broader endothermic peak at A7 in of 169°C. The end point of the transition was somewhere beyond the peak at a point not known exactly. 

Collins and Wendlandt (155) used OL to determine the stabilizer concen-1 tration in polyethylene. The initial deviation of the curve from the baseline1 as well as the peak maximum temperature were both found to be a function of stabilizer concentration in the polymer. The method was compared to those using TG and DSC. 

---