Powder contact angle

Provides measuring techniques of contact angle, surface tension, interfacial tension, and bubble pressure. Suitable methods for both static and dynamic inteifacial tension of liquids include du Nous ring, Wilhelmy plate, spinning drop, pendant drop, bubble pressure, and drop volume techniques. Methods for solids include sessile drop, dynamic Wilhelmy, single fiber, and powder contact angle techniques. 

Powder contact angle This procedure allows the measurement of average contact angle and sorption speeds of powders and other porous species. The change in the weight as a function of time is measured. 

Figure 17 The influence of contact angle on nuclei size formed in fluid-bed granulation of lactose/salicylic acid mixtures. Powder contact angle determined by goniometry and percent lactose of each formulation are given in parentheses. (From Ref. 31.)...

Single fiber Wilhelmy Powder contact angle... 

The contact angle for water on single-crystal naphthalene is 87.7° at 35°C, and ddjdT is -0.13 deg/K. Using data from Table III-l as necessary, calculate the heat of immersion of naphthalene in water in cal/g if a sample of powdered naphthalene of 10 m /g is used for the immersion study. (Note Ref. 135.)... 

This description is traditional, and some further comment is in order. The flat region of the type I isotherm has never been observed up to pressures approaching this type typically is observed in chemisorption, at pressures far below P. Types II and III approach the line asymptotically experimentally, such behavior is observed for adsorption on powdered samples, and the approach toward infinite film thickness is actually due to interparticle condensation [36] (see Section X-6B), although such behavior is expected even for adsorption on a flat surface if bulk liquid adsorbate wets the adsorbent. Types FV and V specifically refer to porous solids. There is a need to recognize at least the two additional isotherm types shown in Fig. XVII-8. These are two simple types possible for adsorption on a flat surface for the case where bulk liquid adsorbate rests on the adsorbent with a finite contact angle [37, 38]. 

These values make it evident that the contact angles must be observed rather carefliUy to obtain a value close to 90°. The following experimental procedure is practical to obtain good stabiUty. A container with the particles is placed on the bottom of an ofl-filled vessel with parallel walls, and a drop of the aqueous phase is placed on the powder. The shape of the droplet decides the action to be taken. 

Methods of Measurement Methods of characterizing the rate process of wetting include four approaches as illustrated in Table 20-37. The first considers the ability of a drop to spread across the powder. This approach involves the measurement of a contact angle of a drop on a powder compact. The contact angle is a measure of the affinity of the fluid for the solid as given by the Young-Dupre equation, or... 

FIG. 20 66 Contact angle on a powder surface, where y ", are the sohd-... 

Increase adhesion tension. Maximize surface tension. Minimize contact angle. Alter surfactant concentration or type to maximize adhesion tension and minimize Marangoni effects. Precoat powder with wettahle monolayers, e.g., coatings or steam. Control impurity levels in particle formation. Alter crystal hahit in particle formation. Minimize surface roughness in milhng. 

In processes where new powder feed has a much smaller particle size than the smallest granular product, the feed powder can be considered as a continuous phase which can nucleate to form new granules [Sastry Fuerstenau, Powder Tech., 7, 97 (1975)]. The size of the nuclei is then related to nucleation mechanism. In the case of nucleation by spray, the size of the nuclei is of the order of the droplet size and proportional to cos0, where 0 is binder fluid-particle contact angle (see Fig. 20-67 of Wetting section). 

The measured contact angle of mercury on various samples can range from 112 to 170° [39], but for most applications the average value of 140° is used. It should be noted, however, that the accuracy of the pore radii measurement is limited by the accuracy of the contact-angle measurement [40]. Contact angles can readily be measured on flat surfaces or compacts of powders [6], and the measurement of contact angles with powder systems has also been reported [41]. 

The adsorption of alkyl and aryl isocyanides on Au film [26, 32, 33], powder [36, 37] and nanoparticles [39, 41, 42] has been studied using several different techniques IR methods (RAIR, ATR-IR, DRIFT), Raman methods (SERS), X-ray methods (NEXAFS), ellipsometry (OE, SWE) and contact angle measurements (ACA). The gold surface is not oxidized under normal conditions consequently, the experiments were performed in air at room temperature. The gold film was obtained by physical vapor deposition of 100-200 nm of gold on different substrates glass [28, 33], mica [33], silicon [25, 27, 31, 32], ZnSe crystal [26]. A... 

Contact angle measurements are of fundamental importance in a range of industrial and everyday processes such as flotation, painting (i.e. the paint must wet the substrate) and weather-proofing. In the flotation process a solid block of the powdered mineral to be floated is often studied using a wide range of collector (i.e. surfactant) solutions to determine optimum flotation conditions. 

A mercury contact anglometer that measures the contact angle on powders, meets the above requirements and gives highly reproducible results is shown in Fig. 20.5. A cylindrical hole of known radius is made in a compacted bed of powder. A press is used to compact the powder around a precision bore pin, which upon removal, produces a cylindrical open-ended pore. 

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