Outgassing temperature

Sample Outgassing temperature/°C > (N2) c Rangef of P/P° Nonane content (mgg l... 

Fig. 4.16 Comparison plots for a microporous sample of y-Mn02 after outgassing at various temperatures, also after pre-adsorption of nonane. The adsorption on the sample is plotted against the adsorption on a reference sample of synthetic MnOOH. (Courtesy Lee and Newnham.) Outgassing temperature (K) Curve A, 9, room B, O, 393 C, , 443 D, A, 493 K. Curve E, pre-treated with nonane.

Fig. 4.18 Plot of log (.x/(mg g" )) against log (p°/p) for the adsorption of nitrogen at 77 K on the samples of manganese dioxide referred to in Fig. 4.16. Outgassing temperature (A) room (B) 393 K (C)443 K (D) 493 K. For the points denoted by V in Curve A, a sample was outgassed at 493 K and charged with nonane before the final outgassing at room temperature. (Courtesy Lee and Newnham.)...

Fig. 4.29 Adsorption isotherms of water vapour on caldte, after being balt-milted for different periods (A, B, C) and on precipitated calcium carbonate (D). Period of milling (A) 1000h (B) ISOh (C) 22h outgassing temperature 2S°C. Isotherms A, B and C (but not D) all showed extensive low-pressure hysteresis, but for clarity the desorption branch is omitted. The amount adsorbed is referred to 1 m of BET-nitrogen area. ...

Fig. 5.20 Adsorption isotherms for water vapour on x-Fe,Oj at 15°C for various outgassing temperatures. Solid points indicate second isotherm after 25°C evacuation of physically adsorbed water. (Courtesy Zettlemoyer.) Outgassing temperature,<, 25°C , I00°C O, 250°C ...

Figure 2 Variations of optical density of vNH band (3390 cm- ) for ZSM-5 (samples 1 and 2) and ZSM-11 (sample 3) vs the outgassing temperature. Wafers of 4.0 mg. cm 2.

Hollabaugh and Chessick (301) concluded from adsorption studies with water, m-propanol, and w-butyl chloride that the surface of rutile is covered with hydroxyl groups. After evacuation at 450°, a definite chemisorption of water vapor was observed as well as of n-propanol. The adsorption of -butyl chloride was very little influenced by the outgassing temperature of the rutile sample (90 and 450°). A type I adsorption isotherm was observed after outgassing at 450°. Apparently surface esters had formed, forming a hydrocarbonlike surface. No further vapor was physically adsorbed up to high relative pressures. 

Wade and Hackerman (302) measured the heats of immersion in water of both anatase and rutile as a function of particle size and outgassing temperature. Apart from the distinct influence of the particle size, a maximum in the heat of immersion was observed after outgassing at 300 to 350°, indicating a rehydroxylation reaction. This is similar to the behavior of silica. Whereas, with silica, the decrease at higher evacuation temperatures is caused by the slowness of the reopening of siloxane bonds (see Section III,A,2), it is very probably caused by a decrease in surface area in the case of TiOj. The maximum in the heat of immersion curves was distinct only with samples of high surface area. Stbber et al. (225) observed a decrease in the surface area of fine particle size anatase already at 450°. 

Figure 3. Area of the X-ray diffraction peak at 22.4 of 20 vs. the outgassing temperature.

The BET method requires that the sample be dried and outgassed to remove adsorbed water. This procedure may, if the outgassing temperature is too high, lead to a phase change at the surface of the oxide hydroxide and hence, an alteration in the specific surface area of the sample. Clausen and Eabricius (2000) recommend that ferrihydrite be outgassed at room temperature, at which temperature, a stable BET surface area is obtained after 19 hr of outgassing. 

Figures 7 and 8 show that n, in most cases increases slowly with temperature owing to the scatter of results, accurate values for the apparent activation energies of this process are difficult to obtain, but in general they lie between 0 and 5 3 kcal./mole. Table I compares values of n, at around 450° with values of monolayer capacity, expressed as nitrogen atoms per gram calculated from the B.E.T. isotherms for the adsorption of N2 at — 196° on the same oxides the same outgassing temperatures were used in both series of experiments. Table I similarly compares the B.E.T. mono-layer capacities and n, values for MgO subjected to various outgassing...

For most purposes the outgassing temperature may be conveniently selected to lie within the range over which the thermal gravimetric curve obtained in vacuo exhibits a minimum slope. 

The properties of lot 34 and the preparation of the Ossar samples have been described by Dry and Beebe (4). Lot 33-43 has been used in an investigation, the results of which are to be published later from this laboratory, dealing with pore size distributions as well as the effect of outgassing temperature on weight loss and specific surface area changes. For reasons discussed elsewhere (4) we have adopted a procedure for dehydration which consists of degassing the samples in vacuo for at least 15 hours at 450°. 

Infrared spectra of Rb-offretite before and after room temperature sorption of pyridine. Outgassing temperatures (a) 100, (b) 200, (c) 400 °C. Curve (d) refers to the Rb-offretite crystals used... 

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