Lag-ring

The pore structures of various solid are very anfractuous and multifarious, and their lag rings are different from each other. Der Booer considered that it would not exceed the five kinds of a, b, c, d, e as shown in Fig. 7.10. In the study of pore structure of catal3dic materials, the analysis of these five lag rings can help to provide useful information for the understanding of the pore structural characteristics and for the reasonable choice of the pore structural models. 

Type A. Adsorption and desorption branch separate in the medium zone of p/po, and are very steep. This type reflects the pore structures such as the tube-like pores opening at both ends, the little wide tubular pores, tubular pores with both ends narrow and centre wide, wide mouth inkstand-shaped pores with r < rw < 2r and narrow mouth inkstand-shaped pores (Fig. 7.11). Groovy-shaped pores also show the A-t3rpe lag ring. 

Type B. Adsorption branch zooms in the point of the saturated vapor pressure, while desorption branch precipitately drops in the middle p/po- A pore with parallel wall slit-like openings is a typical type B lag ring. Those with special wide-body and... 

Type C. Adsorption branch zooms in the middle p/po zone, while desorption branch grows slowly. It is a typical lag ring formed from uneven distributed pores. Cone-shaped or double cone-shaped capillary pores, and wedge pores are closed at sides and opening at both ends belong to this type. The C-ring is very rare. 

Type E. Absorption branch ascends slowly before achieving a stable state with p/po approaching saturated vapor pressure, while desorption branch moves very slowly to the middle of p/po zone, and then displays a sharp decline. For the pores with the characteristics of A-type lag ring, in which the parts are uneven in pore size result in the adsorption branch of this type, and the others equal in pore size result in the desorption branch. The adsorption isothermal lag ring of Ti02 also shows characteristics of the E-ring. 

The five kinds of lag rings reflect the typical pore structural information. The real catal3dic materials are rarely similar, mostly as superposition-like of various lag rings, which reflects the complexity of the pore structure. This analysis should be used to identify the main types of pore structure. 

The best results are obtained b distillation from a small flask through a short fractionating column a Hempel column tilled with glass rings (Fig. 11,16, 1) and lagged with asbestos cloth or several thicknesses of linen cloth is quite satisfactory. 

At the beginning of the polymerization reaction, the viscosity of the medium is low, and efficient rotation (about the ethylenic double bond and the single bond linking ethylene to the phenyl ring) accounts for the low fluorescence quantum yield. After a lag period, when approaching the polymer glassy state, the fluorescence intensity increases rapidly as a result of the sharp increase in... 

Another example is illustrated in Figure 9 (27). The outer, sap-wood rings of a western redcedar, Thuja plicata Donn, which grew about 50 miles south of Seattle, show an increase in 14C which lags slightly behind the levels of 14C which prevailed in the atmosphere. This lag is attributed to a holdover of food supply from the previous year a sizeable... 

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