Synthesis and modification of porous materials such as charcoal, silicagel, zeolite are nothing but a kind of nanotechnologies. Zeolites have three-dimensional pore structure like a cage, and FSM-16 has one-dimensional pore structure like a tube. On the other hand, derivatives of clay have two-dimensional pore structure and have an ability of various applications such as adsorbent, molecular sieve, catalyst and catalytic support. They are expected to have different characteristics that are not recognized for three-dimensional and one-dimensional porous materials. Clays are made by layers composed of tetrahedral sheets and octahedral sheet, and are able to exchange ions between layers, to expand gallery height, to pillar between layers, and to modify surface hydroxyl groups, etc. Clays are thus expected to be starting materials for new porous or inorganic-organic hybrid materials.
This review deals with the effect of surface geometric structure and wettability of glidants on the flowability and compressibility of pharmaceutical powder mixture from microscopic aspects. For improving flowability, porous or fine non-porous structure is effective, independent of the surface wettability, and adhesion force between glidants and pharmaceutical filler dominate flowability. Therefore, if glidants having the same particle diameter are added, porous structure is more effective to enhance the flowability, as porosity highly contributes to reduce the contact area and adhesion force due to rougher surface structure. As respect to compressibility, only porous and fine nonporous hydrophilic glidants can increase the tablet hardness when tabletted with lubricant. In particular, hydrophobic glidants have a deleterious effect and weaken tablet hardness. These trends indicate that microscopic structure and wettability are decisive factors to determine the macroscopic properties. This means that desired flowability and compressibility can be obtained by choosing the optimum microscopic structure and wettability of glidants.
Recently, preparation of nano-sized particles and construction of nano-structure on particle surfaces have been vigorously studied. The effects of surface and interface on nano-sized particles are emphasized, and surface modification is useful to control the characteristics of particles. Information of structure and properties of particle surfaces is necessary to design the surfaces. In this review, characterizations of particle surfaces, especially oxide surfaces, has been discussed. Evaluations of functional groups on the surfaces, mainly hydroxyl groups, and adsorption properties observed by FT-IR have been reviewed. The problems in the specific surface area measurement by gas adsorption have been noted. Fractal analysis of solid surface that is a new concept of surface morphology has been explained.
The surface structure and properties of synthetic colloidal calcium hydroxyapatite, Ca10(PO4)6(OH)2 (abbreviated as CaHap), were investigated. The CaHap surface possesses three kinds of P-OH groups acting as adsorption sites for H2O, CO2, CH3I, CH3OH and so on. The number of surface P-OH groups was ca. 2.6 groups nm−2. When the CaHap was outgassed above 400oC, the surface P-OH groups were dehydroxylated to form surface P-O-P groups. Based on the results obtained, the surface design of CaHap by modifying it with various inorganic and organic molecules was made. The hydrophilic CaHap surface turned into a hydrophobic surface by modification with monoalkyl phosphates and hexamethyldisilazane. The surface P-O-Si(CH3)3 groups of CaHap modified with hexamethyldisilazane were combusted at 500oC in air to form surface P-O-Si(OH)3 groups. The number and types of surface P-OH groups of the CaHap could be controlled by treating with pyrophosphoric acid.
A precise surface design of particle, based on the quantitative evaluation between micro physical and macro physical properties on particle surface, is paid to attention in the background of the demand of preparing the high performance material in recent year. In this paper, the knowledge and the method for preparing the particle surface which had aimed physical properties were reviewed. The basic knowledge concerning a real particle surface was introduced at first. Some cases of preparing the functional particle surface by a precise surface design were shown. The positive use of the particle surface such as photo catalysis was also introduced.
Recent progress of solid acidity investigation using temperature programmed desorption (TPD) of ammonia is described with an emphasis of application to the catalytic science and technology. In order to analyze the solid acidity exactly, a water vapor treatment method and theoretical analysis have been developed. Principles on generation of the acidity on zeolites were clarified; one aluminum atom substituting the framework position generates one acid site, and the strength is determined by the crystal structure. The findings on the acidities of metallosilicates and zeolites with extra-framework aluminum species are also introduced. The ammonia TPD was applied to mesoporous solid acids and acidic oxide overlayers covering the surfaces of basic metal oxides in order to clarify the origin of catalytic activity.
An ab initio-based approach was made to understand the influences of temperature and beam equivalent pressure (BEP) on the structural stability of GaAs surfaces. The theoretical approach incorporates free energy of vapor phase; therefore we can calculate how structural stability of GaAs surfaces depends on the temperature and beam equivalent pressure. By the theoretical investigations, temperature and BEP dependences of the stability of GaAs(001)-(4×2) β 2 were predicted. The results agree with experimental results, and feasibility of the theoretical approach was confirmed. Furthermore, the relative stability of Ga adatom among the case of that on GaAs(001)-(2×4) β 2 and (11n)A (n = 2, 3 and 4) surfaces were studied. The results imply that Ga on (113)A is the most stable amongst (001) and all (11n)A surfaces. This is because the strain around the Ga adatom on (113)A is the smallest in the systems.
Technique of a newly developed in-situ electron-spin-resonance (ESR) is introduced for understandings of microscopic mechanism of dangling-bond creation and annihilation in Si oxidation processes as well as in deposition and plasma treatments of hydrogenated amorphous silicon (a-Si: H). 1) Dynamic changes of surface states during the Si oxidation process have been observed; ad-atom dangling bonds in Si(111)7×7 structure, termination of ad-atom dangling bonds due to oxidation, and creation of interface dangling bonds between Si and SiO2 thus formed. 2) Dynamic changes of the Si dangling-bond signal intensity were observed during and after the a-Si: H deposition, which confirms the existence of a subsurface region with a quite high spin density (1013cm−2) only during the deposition process. 3) During hydrogen plasma treatments on a-Si: H hydrogen atoms create dangling bonds, rather than terminate them. These dangling bonds are not confined to the film surface but are spatially distributing to the deeper layers from the top-surface (around 100 nm), whose depth decreases with the increase in the treatment temperature.