Characterization of surface properties

Surface area of a powder increases geometrically with decreasing particle size, so that the volume fraction of the outermost layer of ions on the surface increase significantly, which has a significant effect on properties of the powder. With the development of nanotechnology, it is readily to synthesize powders with nanosized particles (1-100 nm). Therefore, characterization of surface properties becomes more and more important. Specifically for ceramics or transparent ceramics, the consolidation of fine ceramic powders with liquid suspensions to produce more uniform green bodies has been shown to play an important role in the fabrication ceramics, especially when special or complex structures are required. Because the quality of microstructure of the consolidated body is determined by the dispersion behavior of the powder and the interaction between the particles in the suspension, which is closely related to the surface properties of the particles, controlling the physical and chemical properties of particles is a critical to ceramics fabrication. 

A growing area of research has focused on the characterization of surface properties of particles however, this has typically being limited to the development of inhalation formulations [55]. Applications of surface techniques to study API/ excipient interactions to understand better the target attribute space for API particle properties are less routine. An area that is often overlooked when considering and nominating critical particle attributes for formulation and process design is the surface structural characteristics of the crystallized particles. The surface properties of crystalline particles will be driven by the crystal structure and chemical surface... 

Because the current chapter focuses on Ag-TiN and Ag-ZrN polyester surfaces active in bacterial reduction in the dark and under light irradiation, we will address the investigation of the polyester—Ag-TaN-mediated bacterial reduction kinetics. Here, we report the polyester-TaN, and poly ester-Ag-TaN bacterial reduction kinetics, the characterization of surface properties by surface science techniques of the polyester— Ag-TaN, and the changes induced in the polyester—Ag-TaN smface during redox catalysis during bacterial interaction and reduction by XPS." ... 

Photoelectrochemistry may be used as an in situ teclmique for the characterization of surface films fonned on metal electrodes during corrosion. Analysis of the spectra allows the identification of semiconductor surface phases and the characterization of their thickness and electronic properties. 

The development of new and improved catalysts requires advances in our understanding of how to make catalysts with specified properties the relationships between surface stracture, composition, and catalytic performance the dynamics of chemical reactions occurring at a catalyst surface the deployment of catalytic surface within supporting microstracture and the dynamics of transport to and from that surface. Research opportmuties for chemical engineers are evident in four areas catalyst synthesis, characterization of surface stracture, surface chemistry, and design. 

Surface forces measurement is a unique tool for surface characterization. It can directly monitor the distance (D) dependence of surface properties, which is difficult to obtain by other techniques. One of the simplest examples is the case of the electric double-layer force. The repulsion observed between charged surfaces describes the counterion distribution in the vicinity of surfaces and is known as the electric double-layer force (repulsion). In a similar manner, we should be able to study various, more complex surface phenomena and obtain new insight into them. Indeed, based on observation by surface forces measurement and Fourier transform infrared (FTIR) spectroscopy, we have found the formation of a novel molecular architecture, an alcohol macrocluster, at the solid-liquid interface. 

Following early ETEM investigations using environmental cells, environmental scanning electron microscopy (ESEM) has been developed for characterization of surface effects of bulk SEM samples in the presence of gaseous or wet environments (111-114). The method has been applied to the examination of food, wool fibers (111), and polymers (112) and in the conservation of cultural properties (113). Recently, fuel cell catalysts have been characterized using a low-voltage ESEM with a resolution capability of 2 nm (114). 

Hohl, H., L. Sigg, and W. Stumm (1980), "Characterization of Surface Chemical Properties of Oxides in Natural Waters The Role of Specific Adsorption Determining the Specific Charge," in M. C. Kavanaugh and J. O. Leckie, Eds., Particulates in Water, Advances in Chemistry Series, ACS 189, 1-31. 

V. Gurau, M. J. Bluemle, E. S. De Castro, et al. Characterization of transport properties in gas diffusion layers for proton exchange membrane fuel cells. 1. Wettability (internal contact angle to water and surface energy of GDL fibers). Journal of Power Sources 160 (2006) 1156-1162. 

Theoretical models based on first principles, such as Langmuir s adsorption model, help us understand what is happening at the catalyst surface. However, there is (still) no substitute for empirical evidence, and most of the papers published on heterogeneous catalysis include a characterization of surfaces and surface-bound species. Chemists are faced with a plethora of characterization methods, from micrometer-scale particle size measurement, all the way to angstrom-scale atomic force microscopy [77]. Some methods require UHV conditions and room temperature, while others work at 200 bar and 750 °C. Some methods use real industrial catalysts, while others require very clean single-crystal model catalysts. In this book, I will focus on four main areas classic surface characterization methods, temperature-programmed techniques, spectroscopy and microscopy, and analysis of macroscopic properties. For more details on the specific methods see the references in each section, as well as the books by Niemantsverdriet [78] and Thomas [79]. 

In general, microprobe analysis methods have been considered semiquantitative, but EPMA has been promising for quantitative studies. With further improvement and investigation, these microprobe techniques will be useful for the characterization of surface and bulkparticle properties. 

In this review, the relationships between structure, morphology, and surface reactivity of microcrystals of oxides and halides are assessed. The investigated systems we discuss include alkali halides, alkaline earth oxides, NiO, CoO, NiO-MgO, CoO-MgO solid solutions, ZnO, spinels, cuprous oxide, chromia, ferric oxide, alumina, lanthana, perovskites, anatase, rutile, and chromia/silica. A combination of high-resolution transmission electron microscopy with vibrational spectroscopy of adsorbed probes and of reaction intermediates and calorimetric methods was used to characterize the surface properties. A few examples of reactions catalyzed by oxides are also reported. 2001... 

The coordinative and/or dissociative adsorption of various probe molecules has been used to characterize the surface properties of Ti02) which finds applications as a catalyst, photocatalyst, and sensor. Among the molecules used as probes, we mention CO (37, 38, 563-576), C02 (563, 565, 577), NO (578,579), water (580,581), pyridine (582,583), ammonia (584,585), alcohols (586, 587), ethers (including perfluoroethers) (588), ozone (589), nitrogen oxide (590), dioxygen (591), formic acid (592-594), benzene (584), benzoic acid (595), and chromyl chloride (596). 

Figure 4 shows that deposition of one layer of PMBQ from solution with pH = 6 resulted in drastic changes of surface properties. This was quantitatively characterized by the shift of surface IEP (isoelectric point) from pH < 3.5 to 6. Since the isoelectric point of the PMBQ solution was higher than 12, it may be assumed that the electrokinetic behavior was still determined by the com-... 

Over the last 20 years, analytical tools have become available that allow for the characterization of the elemental and chemical composition of solid surfaces. The apphcation of these analytical tools has increased our understanding of surface properties and successfully characterized surface layers. 

This complexity determines that investigations on heterogeneous photo-catalytic processes sometimes report information only on dark adsorption and use this information for discussing the results obtained under irradiation. This extrapolation is not adequate as the characteristics of photocatalyst surface change under irradiation and, moreover, active photoadsorption centers are generated. Nowadays very effective methods allow a soimd characterization of bulk properties of catalysts, and powerful spectroscopies give valuable information on surface properties. Unfortunately information on the photoadsorption extent under real reaction conditions, that is, at the same operative conditions at which the photoreactivity tests are performed, are not available. For the cases in which photoreaction events only occur on the catalyst surface, a critical step to affect the effectiveness of the transformation of a given compound is to understand the adsorption process of that compound on the catalyst surface. The study of the adsorbability of the substrate allows one to predict the mechanism and kinetics that promote its photoreaction and also to correctly compare the performance of different photocatalytic systems. 

Characterization of surfaces and thin films has been revolutionized by the invention of scanning probe microscopes, i,e, scanning force microscopy, scanning tunnelling microscopy, and scanning near field optical microscopy [262-264], These methods not only allow imaging of molecular and supramolecular details, but can also be employed to probe and to manipulate chemical properties on a nanoscopic or molecular scale, e,g., mechanical SFM [265], chemical SFM [266], electrochemical STM [267,268],... 

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