BET transformed

Figure 1.7 shows the physisorption isotherm, obtained using the non continuous volumetric technique, of a mesoporous alumina (type IV isotherm) and the results of analysis procedures (BET transform, /-curve, BJH porous distribution). This solid presents a specific surface area of approximately 200 m /g with the narrow pore size distribution at around 10 nm. The shape of the /-curve shows that it does not contain any micropores. 

Figure 1.7 Isotherm of a alumina (A), BET transform (B), BJH porous distribution (C) and r-curve (D).

This equation is based on the assumption that the absorbed species (N in units of gm/gm) are immobilized at sites with concentration M (in units of gm/gm) at first in a monomolecular form and then subsequently in the form of multilayers. The BET transformation is convex with respect to the axis P/P for keratin but linear for the case of rat-tail collagen (figure 7). 

Martensitic phase transformations are discussed for the last hundred years without loss of actuality. A concise definition of these structural phase transformations has been given by G.B. Olson stating that martensite is a diffusionless, lattice distortive, shear dominant transformation by nucleation and growth . In this work we present ab initio zero temperature calculations for two model systems, FeaNi and CuZn close in concentration to the martensitic region. Iron-nickel is a typical representative of the ferrous alloys with fee bet transition whereas the copper-zink alloy undergoes a transformation from the open to close packed structure. ... 

In the tetragonal transformation, the bcc structure is not the local maximum of the D parameter. Although the bcc stracture has a higher density if it is compressed along the tetragonal axis, many elements take this structure. On the other hand, the bet structure is the local maximum of the D parameter in the tetragonal distortion but no metal takes this structure. These results indicate that density is not an important factor for the choice of crystal stracture. 

ABSTRACT The kinetics and mechanisms of the phase transformation of 2-line ferrihydrite to goethite and hematite are being assessed as a function of pH, temperature and Fe/As, Fe/Se, Fe/Mo molar ratios using batch experiments, BET analyses, XRD, and XANES. Initial results from XRD analyses show that ferrihydrite is stable at high pH ( 10) for up to seven days at 25°C, but considerable crystallization occurs at elevated temperatures. Specifically, XRD data show that ferrihydrite is transformed to a mixture of hematite and goethite at 50°C (-85% hematite and -15% goethite) and 75°C (-95% hematite and -5% goethite) after 24 hours and these ratios remain constant to the end of the experiments (seven days). 

Measured surface areas (11-point BET analyses) for pure phases such as ferrihydrite, goethite and hematite are in the range as proposed by Cornell Schwertmann (2003) (Table 1). Preliminary XRD analyses showed that temperature impacts the kinetics of phase transformation of ferrihydrite. Data indicated that after seven days, the rate of transformation from ferrihydrite to more crystalline forms, if it was occurring, was too slow to be measured at 25°C (Fig. 1). In contrast to the 25°C experiment, significant, transformations were observed at 50 (Fig. 2) and 75°C (Fig. 3) after 24... 

When the synthesis is carried out at room temperature for 3 days, a solid containing only disordered mesoporous phase with a BET surface area of over 1000 m2/g is obtained. Its XRD pattern displays only a single [100] peak at low 20 angle. But if the crystallization time is prolonged to about 22 days, [100], [110] and [200] peaks except the absence of [210] peak can be distinctly resolved. This result shows that the synthesis time is important in transforming the ill-defined disordered mesoporous silica framework into integrated hexagonal MCM-41 framework. 

D. Horton and T. Usui, Transformation of nnsatursted acyclic sugars into enantkxnerically pare notbomene derivatives, Carbohydr Bet. 2/6 51 (1991). 

Figure 17 obviously shows that the distribution function of adsorption site energies, /(e), is very similar to BET distribution transform, at low coverage (e > e/(g)=i/2), and behaves similarly to Langmuir s adsorption [178] towards surface monolayer at high coverage. 

FIG. 16 BET distribution transform on the untreated carbon fibers (supplied by Soficar, T-300), measured at 30 °C. 

---