Surface properties, radiation

Each body having a temperate above absolute zero radiates energy in the form of electromagnetic waves. The amount of energy emitted is dependent on the temperature and on the emissivity of the material. The wavelength or frequency distribution (the spectrum) of the emitted radiation is dependent on the absolute temperature of the body and on the surface properties. 

The surface of a material exposed to the environment experiences wear, corrosion, radiation, electrical, or magnetic fields and other phenomena. It must have the properties needed to withstand the environment or to provide certain desirable properties, such as reflectivity, semiconductivity, high thermal conductivity, or erosion resistance. Depositing a coating on a substrate produces a composite material and, as such, allows it to have surface property, which can be entirely different from those of the bulk material. 

Radiation Treatment NVP, 2-hydroxyethylmethacrylate (HEMA), and acrylamide (AAm) have been grafted to the surface of ethylene-propylene-diene monomer (EPDM) rubber vulcanizates using the radiation method (from a Co 7 source) to alter surface properties such as wettability and therefore biocompatibility [197]. Poncin-Epaillard et al. [198] have reported the modification of isotactic PP surface by EB and grafting of AA onto the activated polymer. Radiation-induced grafting of acrylamide onto PE is very important... 

The effect of EB-radiation dose intensity on the surface properties of surface and bulk-modified EPDM rubber have been investigated [382]. Predominant chain scission at higher radiation doses... 

TEM observation and elemental analysis of the catalysts were performed by means of a transmission electron microscope (JEOL, JEM-201 OF) with energy dispersion spectrometer (EDS). The surface property of catalysts was analyzed by an X-ray photoelectron spectrometer (JEOL, JPS-90SX) using an A1 Ka radiation (1486.6 eV, 120 W). Carbon Is peak at binding energy of 284.6 eV due to adventitious carbon was used as an internal reference. Temperature programmed oxidation (TPO) with 5 vol.% 02/He was also performed on the catalyst after reaction, and the consumption of O2 was detected by thermal conductivity detector. The temperature was ramped at 10 K min to 1273 K. 

The transfer of heat by radiation in general can be said to occur simultaneously with heat transfer by convection and conduction. Transfer by radiation tends to become more important than that by the other two mechanisms as the temperature increases. It is useful to gain an appreciation of the basic definitions of the energy flux terms, the surface property terms and their relationships while discussing radiative heat transfer. With this objective, reference may be made to Table 3.4 in which these are presented. 

Radiosity J Total thermal radiation energy leaving a surface (emitted and reflected) per unit time per unit area of energy transfer per unit area). The three terms, Absorptivity (a), Reflectivity (p), and Transmissivity (x), are all surface properties... 

In materials such as catalysts where surface properties are of importance it should be possible to alter or enhance activity by use of ionizing radiation. Investigations of the possibility of using radiation to achieve graft polymerizations have recently been initiated. For this application ionizing radiation enjoys some very special advantages. 

Accelerated Tests. Weather resistance in an accelerated test is defined as the resistance of plastics towards changes caused by simulated open-air weathering (simulation of global radiation by means of filtered xenon arc radiation and periodic rain). After the weathering (measured by the product of intensity and duration), defined properties of the test sample are compared with those of an identical unweathered sample. Properties should be considered which are of practical importance, such as color or surface properties. For standards, see Table 1 ( Weathering in apparatus ). Apparatus test chamber, rain and air humidification equipment, air flow equipment, radiation measuring equipment. 

Electrons from the heated tungsten filament are accelerated to the annular anode. Depending on the anticathode material a characteristic fluorescence radiation is emitted, passes through a thin Aluminum window and induces photoelectrons on the surface of the analytical sample. These photoelectrons are deflected in the spherical electrostatic analyzer, double focussed to eliminate stray electrons and finally counted by the electron multiplier. The whole system works under a vacuum of 10-s to 10 7 torr or even 10 10 torr, if surface properties have to be studied. This vacuum is generated by a Titanium... 

Radiation grafting [83, 84, 85, 86, 87, 88, 89] is a very versatile and widely used technique by which surface properties of almost all polymers can be tailored through the choice of different functional monomers. It covers potential applications of industrial interest and particularly for achieving desired chemical and physical properties of polymeric materials. In this method, the most commonly used radiation sources are high-energy electrons, y-radiation, X-rays, U.V.-Vis radiation and, more recently, pulsed laser [90], infrared [91], microwave [92] and ultrasonic radiation [93]. Grafting is performed either by pre-irradiation or simultaneous irradiation techniques [94, 95]. In the former technique, free radicals are trapped in the inert atmosphere in the polymer matrix and later on the monomer is introduced into... 

Furthermore, multiple ionization, which has been postulated as being able to bring about displacements of interior atoms (30), might be extremely effective in leading to surface migrations and thermal patches, in which case surface properties could be more sensitive to electromagnetic radiation than to particle radiation. it was hoped that the present studies would shed some light on what actually happens. 

While the above formulations may appear rather cumbersome at first glance they are easily solved by computer, with either matrix inversion or iteration. For many practical radiation problems, the number of equations is small and programmable calculators may be employed for solution. In most cases one will not know the surface properties (e,) within better than a few percent, so an iterative solution need not be carried out to unreasonable limits of precision. 

During the last decade, there has been considerable interest in studying the interaction between ultraviolet radiation and polymers by the use of pulsed excimer laser (1-41. In fact, some attractive applications in microelectronics and surgery have been successfully implemented (5.), and further informations about the different mechanisms (photochemistry, thermal effect...) involved at the polymer surface have been invoked in order to elucidate their relative contributions. More recently, the attention has been focused on this type of polymer surface modifications to improve some surface properties like the adhesion in metallized polymer structures. 

The difference between the rates of radiation emitted by the surface and the radiation absorbed is the net radiation heat transfer, If the rate of radiation absorption is greater than the rate of radialion emission, the surface is said to be gaining energy by radiation. Otherwise, the surface is said to be losing energy by radialion. In general, the determination of the net rate of heat transfer by radiation between two surfaces is a complicated matter since it depends on the properties of the surface.s, their orientation relative to each other, and the interaction of the medium between the surfaces with radiation. 

To account for the effects of orientation on radiation heat transfer between two surfaces, we define a new parameter called the vieu factor, which is a purely geometric quantity and is independent of the surface properties and temperature. It is also called the shape factor, configuration factor, and angle factor. The view factor based on the assumption that the surfaces are diffuse emitters and diffuse reflectors is called the diffitse view factor, and the view factor based on the assumption that the surfaces are diffuse emitters but specular reflectors is called the specular view factor. In lliis book, we consider radiation exchange between diffuse surfaces only, and ihu.s the term view factor simply means diffuse view factor. 

So fill, we have considered the nature of radiatiou, the radiation properties of materials, and the view factors, and we arc now in a position to consider the rate of heal transfer between surfaces by radiation. The analysis of radiation exchange between surfaces, in general, is complicated because of reflection a radiation beam leaving a surface may be reflected several times, with partial refleclion occurring at each surface, before it is completely absorbed. The analysis is simplified greatly when the surfaces involved can be approximated... 

---