Density Of Silanol Groups Research Articles

Surface chemistry of silicon nitride powders: Electrokinetic behaviour and ESCA studies

The surface chemistry of silicon nitride powders was investigated using ESCA and studies of the electrokinetic properties. The results show that the composition of the surface layer can be altered by leaching in water or annealing in vacuum.The results also show that the pHiep of Si3N4 powders is determined by the relative site density of acidic silanol and basic amine groups. The ratio of Si2NH groups over SiOH groups was calculated and found to vary from a few percent to equal amounts in the pHiep range 4.2–7.6. The theoretical ratios have been correlated to N/O ratios obtained by ESCA.

Basic characteristics and applications of aerosil: 30. The chemistry and physics of the aerosil Surface

With the aid of special measuring techniques, it was possible to determine the molar absorptivity ϵ of the OH-stretching vibration band of the free silanol groups at 3750 cm −1 and the total silanol group density of hydrophilic Aerosil. In most cases the silanol group density is independent of the BET surface area (exception: Aerosil OX 50); the density of the free silanol groups decreases as the BET surface area increases (a deviation from the linear course occurs with Aerosil OX 50 and Aerosil 380). A temperature increase up to 600°C results only in the elimination of bridged silanol groups; higher temperatures are required before the isolated silanol groups are eliminated. Freshly manufactured Aerosil has a high content of isolated silanol groups; during storage, this content of isolated silanol groups decreases, and the silanol group density increases. The bonding of dimethylsilyl groups on the surface of Aerosil R 972 is discussed and the temperature stability of the surface groups of Aerosil R 972 and Aerosil R 812 is demonstrated.

Analysis of Surface of Porous Glass

The density of surface silanol groups in three kinds of porous glasses with different pore structures was determined by using CH3Mgl, (CH3)3SiCl(TMS), (CH3)2Cl2(DMS) and CH3OH. The density ranged from 2.3 to 7.7μmol/m2. The density determined by TMS was about 3μmol/m2 regardless of the pore structures. The surface of porous glasses was boron-rich after exposure to air for a long period. But, washing with acid solution removed boron, and the surface contained only silicon. The number of silanol group of single type was dominant in all types of silanol groups and occupied 50-80% regardless of the pore structures. Geminal type comes second. But, when pore was small, the number of geminal type was almost the same as that of paired type.