Masatoshi Chikazawa

Infrared spectra of geminal and novel triple hydroxyl groups on silica surface

Abstract We investigated the OH stretching frequencies of geminal and triple hydroxyl groups on silica surface by FT-IR spectroscopy. The geminal and triple hydroxyl groups were individually prepared by the chemical reaction of alkylchlorosilane with surface isolated hydroxyl groups which are separated enough and following hydroxylation of surface chlorine groups. The OH stretching frequencies of these generated geminal and triple hydroxyl groups were observed at frequencies by 2 and 3 cm−1 lower than that of isolated ones, respectively. By heat treatment the triple hydroxyl groups are firstly eliminated, and secondly the geminal hydroxyl groups disappear. Lastly only isolated hydroxyl groups remain on silica surface.

FTIR and TPD studies on the adsorption of pyridine, n-butylamineand acetic acid on calcium hydroxyapatite

Colloidal calcium hydroxyapatite (CaHAP) particles synthesized by a wet method and calcined at different temperatures up to 900 °C have been characterized by various means. The adsorption species and sites on the CaHAP surface for pyridine, n-butylamine and acetic acid were clarified by FTIR and TPD. These molecules were shown to be adsorbed by hydrogen-bonding to the surface P–OH groups. The surface P–OH groups of CaHAP were removed by outgassing above 600 °C to produce surface P–O–P groups. The n-butylamine is hydrogen bonded to the surface P–O–P species.

WETTABILITY OF FINE SILICA POWDER SURFACES MODIFIED WITH SEVERAL NORMAL ALCOHOLS

Abstract The chain length effects of chemical modification with various normal alcohols on the wettability of silica have been studied. The modifications were carried out by chemical reaction of alcohol molecules with surface silanols. The amount of silanols on sample surface was obtained by the Grignard method, and the amount of modifiers was determined by thermal analysis. As a result, surfaces were designed to have various concentrations of normal alkoxyl groups. The wettability of these well-defined samples for water were investigated by water vapor adsorption, heat of immersion and various preferential dispersion tests. The results are summarized as follows: (1) the wettability of samples with modifiers of carbon number above eight markedly changes at the modification ratio of about 20%; (2) the samples chemisorbed alcohol with less than eight carbon atoms, the modification ratios of above 20% are required to give hydrophilic surfaces. Because the bulkiness effect of modifiers on wettability decreases with reduction of chain length; (3) in the cases of hydrophobic samples, cooperative water adsorption takes place at the first stage of adsorption. With the occurrence of multilayer adsorption, a continuous two dimensional water layer is formed at the latter stage of adsorption. In the cases of the hydrophobic samples, the adsorbed amount was less than theoretical monolayer capacity in spite of high relative pressure at about P / P 0 =1. Therefore, such a continuous two dimensional water layer is not formed as a result of the steric hindrance of the modifiers. In this case, multilayer adsorption dose not occur. The surface property is estimated to be hydrophobic; (4) the results of preferential dispersion tests as the evalution of macroscopic wettability are in agreement with the results of water vapor affinity and heat of immersion as the nanoscopic wettability.

Microstructure of Electrodeposited Cu‐Ni Binary Alloy Films

The codeposition of Cu and Ni in the electrodeposition method without a complexing agent is difficult, since the standard electrode potentials of Cu and Ni differ by approximately 600 mV. In this study, the electrodeposited Cu-Ni alloy films with various compositions were obtained using glycine as the complexing agent. Consequently, composition of the deposited Cu-Ni alloy films can be controlled by bath composition and pH, and the crystallographic structure of all the deposited Cu-Ni alloy films consists of a single solid solution and is not influenced by pH.

Effect of geometric structure of flow promoting agents on the flow properties of pharmaceutical powder mixture.

AbstractPurpose. The object of this work was to investigate the mechanism of how the surface geometric structure of flow agents affects on the flowability of pharmaceutical powder mixtures. Methods. Nonporous and porous silicas were mixed with directly compressible fillers as flow promoting agents. The geometric structure of flow agents was investigated by gas adsorption and laser diffraction analysis. Flowability was evaluated with Carrs index measurement. Adhesion force between fillers and flow agents was determined using atomic force microscopy. Results. Flowability was improved with the addition of both nonporous and porous flow agents. In the case of nonporous flow agents, effect to promote flowability decreased with the increase of particle diameter, whereas porous flow agents highly improved flowability independent of particle diameter. Atomic force microscopy measurement found that the adhesion force between a porous agent and filler was smaller than that between a nonporous agent and filler. Conclusions. Enhancement of flowability varies depending on the geometric structure of flow agents. Porous flow agents improve flow properties more than nonporous agents, because porosity is highly contributed to reduction of adhesion force between particles.

The change in the water vapor affinity of fine silica particles loaded with trimethylsilyl groups

Microscopic and macroscopic wettabilities of fine silica powder surfaces loaded with trimethyl-silyl groups (TMS) were studied. The modification was carried out by the chemical reaction of hex-amethyldisilazane (HMDS) molecules with surface silanols and the TMS coverage was determined by elemental analysis of carbon. The microscopic wettability was investigated by water vapor adsorption and IR spectroscopic methods. The macroscopic wettability was examined by various preferential dispersion tests. The results are summarized as follows. (1) HMDS molecules preferentially reacted with free type surface silanols. (2) The macroscopic wettability drastically changed at a TMS coverage of about 40%. (3) The effect of steric hindrance appeared clearly at a TMS coverage above 40%. Hence, a part of the residual surface silanols is shielded by TMS and water molecules will not access these sites. (4) In the case of TMS coverage below about 40%, cooperative adsorption takes place at the first stage of adsorption. Then by the occurrence of multilayer adsorption, a continuous two-dimensional water layer is formed at the latter stage of adsorption. On the other hand, in the case of coverage above about 40%, the adsorbed amount was about 65% of the theoretical monolayer capacity in spite of a high relative pressure at about P/P0 = 1. Therefore, such a continuous two-dimensional water layer is not formed on account of the steric hindrance of the TMS and multilayer adsorption will not occur in this case. The surface property is estimated to be hydrophobic. (5) The results of preferential dispersion tests as the macroscopic wettability are in agreement with the results of water vapor affinity as the microscopic wettability.

Phase transition of capillary condensed liquids in porous silica: effect of surface hydroxyl groups☆

Phase transition temperatures of capillary condensed organic liquids in porous silica were measured using a 1020/DSC system (Perkin-Elmer Ltd.). The amounts and types of hydroxyl groups on the sample surfaces were precisely controlled to discuss the surface effect on the phase transition temperature. The melting point of the solid phase of benzene in the pores decreased with increasing concentration of the surface hydroxyl groups. On the other hand, in the case of n-hexane, such an effect was not observed. From these results, it is assumed that the liquid structure of capillary condensed benzene in the pores changes with the amounts and types of surface hydroxyl groups. This consideration is confirmed from IR spectroscopy.

Modification of amorphous aluminum phosphate with alkyl phosphates

Abstract Synthetic amorphous aluminum phosphate (AlPO4) particles were treated with monohexyl, monooctyl, and monodecyl phosphates in acetone, and the resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric and differential thermal analyses (TG/DTA), and adsorption of N2. XRD patterns of the modified samples showed a strong diffraction peak and two weak ones below 2θ = 15°. The d-values of these peaks linearly increased with elongating of alkyl groups of the phosphates. After the treatment, particle size increased without formation of new particles. These results reveal that a multilayer alternating bimolecular layer of alkyl phosphates and aluminum phosphate phase is formed on the surface of AlPO4 particles by the modification with alkyl phosphates. The layered structure disappeared on outgassing above 300°C, accompanying the removal of alkyl groups, formation of mesopores, and variation of surface structure.

Effect of geometric structure and surface wettability of glidant on tablet hardness

The aim of this study is to investigate the effect of geometric structure and surface wettability of glidant on tablet hardness. Geometric structure is defined, in this work, as three-dimensional structure such as porosity, particle size and specific surface area. A variety of silica was incorporated in direct compressive fillers as glidant and mixed powder was compressed in single punch tablet machine with and without 0.5 wt.% magnesium stearate. Flowability of mixed powder was evaluated with Carrs index measurement. In the case of unlubricated compression, tablet hardness decreased as a function of additional concentration of silica. Reduction rate directly depended on surface coverage of silica over filler surface and hydrophobicity. Since surface coverage is related to geometric structure, it can be concluded that structural influence plays an important role to determine tablet hardness. While, in the case of lubricated compression, either water adsorption amount or geometric structure effects on tablet hardness. Increase of tablet hardness was observed only when hydrophilic porous and small size nonporous silica were added. All the other silica had deleterious effect on tablet hardness and in particular hydrophobicity strongly reduced tablet hardness.

Surface active sites introduced onto calcium carbonate powder by a new surface preparation process

Abstract A new process was proposed to introduce active sites onto calcium carbonate powder. The process consists of three steps: (i) chemical surface modification, (ii) surface oxidation and (iii) surface hydroxylation. Repeating this process can increase the amount of new active sites. IR spectroscopy confirmed the process. The surface density of modifiers was evaluated from measuring the specific surface area and weight loss of the samples caused by the combustion of the modifiers. In one process 1.15 nm −2 modifiers were introduced onto the sample. The process can introduce new active sites quantitatively without influencing the properties of the sample substrate and can also improve its thermostability. Surface acidity increased until four cycles in the repeated modification process; however, it decreased after the fourth cycle. This result was ascribed to a change in the surface binding state by introducing the new active sites and such a conclusion was explained by results of X-ray photoelectron spectroscopy.