Solid Stearic Acid Research Articles

Effect of high energy ball milling on the structure of iron — multiwall carbon nanotubes (MWCNT) composite

High energy ball milling is employed to produce iron matrix- multiwall carbon nanotube (MWCNT) reinforced composite. The damage caused to MWCNT due to harsh ball milling condition and its influence on interfacial bonding is studied. Different amount of MWCNT is used to find the optimal percentage of MWCNT for avoidance of the formation of chemical reaction product at the matrix - reinforcement interface. Effect of process control agent is assessed by the use of different materials for the purpose. It is observed that ethanol as a process control agent (PCA) causes degradation of MWCNT reinforcements after milling for two hours whereas solid stearic acid used as process control agent, allows satisfactory conservation of MWCNT structure. It is further noted that at a high MWCNT content (~ 2wt.%), high energy ball milling leads to reaction of iron and carbon and forms iron carbide (cementite) at the iron-MWCNT interface. At low percentage of MWCNT, dissolution of carbon in iron takes place and the amount of reinforcement in iron matrix composite becomes negligibly small. However, under the present ball milling condition (ball to metal ratio~ 6:1 and 200 rpm vial speed) iron-1wt.% MWCNT composite of good interfacial bonding can retain the tubular structure of reinforcing MWCNT.

Experimental investigation of beam heating in a soft X-ray scanning transmission X-ray microscope

A variable temperature sample holder with an operational range of 15 to 200 °C and an accuracy of ±1 °C has been fabricated for scanning transmission X-ray microscopes (STXM). Here we describe the device, and use it to image the polycrystalline morphology of solid stearic acid and palmitic acid at temperatures near their respective melting points as a means of checking for possible sample heating caused by the focused X-ray beam. The melting points observed in STXM were identical to those observed by conventional methods within measurement uncertainty, even under the most extreme, high dose rate imaging conditions investigated. The beam-induced temperature rise in the sample is inferred to be below 1 °C for dose rates of up to 2.7 GGy/s.

Photocatalytic degradation activity of titanium dioxide sol–gel coatings on stainless steel wire meshes

Stainless steel wire meshes have been functionalised with multiple titanium dioxide (TiO 2) coatings deposited by the sol–gel technique, using titanium isopropoxide as precursor and titanium dioxide nanopowders dispersed in the colloidal solution. After the thermal conversion of the amorphous fraction of the coating into anatase, the functionalised stainless steel wire meshes were tested for the UV photodegradation of aqueous solutions of methylene blue, solid stearic acid and nitrogen oxides in air. The addition of TiO 2 nanopowders in the colloidal deposition solution enhanced the photocatalytic performance of the deposited TiO 2 layers in all the tested conditions. Moreover, increasing the number of coatings (from 1 to 4) improves the photocatalytic efficiency. The catalyst did not show reduced photoreactivity after four repeated cycles in water decontamination from methylene blue, and after up to 10 repeated cycles in nitrogen oxides photodegradation. Complete regeneration of the catalyst could be achieved by rinsing it with warm deionised water and was observed in the case of experiments for NO x abatement.

Transparent, Well-Aligned TiO2 Nanotube Arrays with Controllable Dimensions on Glass Substrates for Photocatalytic Applications

Transparent, well-aligned TiO(2) nanotube arrays (NTAs) with controllable dimensions are grown on glass substrates via atomic layer deposition (ALD) of TiO(2) onto free-standing porous anodic alumina (PAA) templates. Photodegradation of aqueous methylene blue (MB) solution and solid stearic acid (SA) film using TiO(2) NTAs of various wall thicknesses are investigated. The Pd functionalized TiO(2) NTAs, with a wall thickness of 15 nm and height of 200 nm, has the highest photodegradation efficiency at 76% after 4 h of UV irradiation. These functionalized NTAs are able to photodegrade MB molecules completely as no obvious demethylated byproducts are observed during the process. It also demonstrates excellent photocatalytic activity for solid contaminants such as SA film. By using the ALD technique, the nanotube wall thickness can be precisely controlled so that it is sufficiently thin to be transparent while sufficiently thick for excellent photocatalytic performances. The transparent TiO(2) NTAs on glass substrates with excellent photocatalytic properties might have potential applications in self-cleaning coating, transparent electronics, and solar cells.

Cloud condensation nucleus activity of internally mixed ammonium sulfate/organic acid aerosol particles

The ability of mixed ammonium sulfate/organic acid particles to act as cloud condensation nuclei (CCN) has been studied in the laboratory using a continuous flow, thermal-gradient diffusion chamber operated at supersaturations between 0.3% and 0.6%. The organic acids studied were malonic acid, azelaic acid, hexanoic acid, cis-pinonic acid, oleic acid and stearic acid, and the particles were largely prepared by condensation of the organic vapor onto a dry ammonium sulfate core. For malonic acid and hexanoic acid, the mixed particles activated as predicted by a simple Kohler theory model where both species are assumed to be fully soluble and the droplet has the surface tension of water. Three low-solubility species, cis-pinonic acid, azelaic acid and oleic acid, are well modeled where the acid was assumed to be either partially or fully insoluble. Interestingly, although thin coats of stearic acid behaved in a manner similar to that displayed by oleic and cis-pinonic acid, we observed that thick coats led to a complete deactivation of the ammonium sulfate, presumably because the water vapor could not diffuse through the solid stearic acid. We observed no CCN behavior that could be clearly attributed to a lowering of the surface tension of the growing droplet by the presence of the organic constituents, some of which are highly surface active.

Atomic Layer Deposition of Photocatalytic TiO2 Thin Films from Titanium Tetramethoxide and Water

AbstractTitanium dioxide thin films were grown by atomic layer deposition (ALD) at 200–400 °C from a new titanium precursor, titanium tetramethoxide, and water. As compared with other titanium alkoxides studied earlier, titanium methoxide shows the highest stability with respect to thermal decomposition, and can thus be used over the widest range of temperatures. The films deposited at 250 °C and above were polycrystalline with the anatase structure, whereas those deposited at 200 °C were amorphous. Except for the film deposited at 200 °C, the films contained only minor amounts of carbon and hydrogen residues. The crystalline films were shown to have photocatalytic activity in decomposing both methylene blue in aqueous solution, and solid stearic acid coated on the film surface.

Formation of multilayers on silica surfaces of a cationic polyelectrolyte and dissolved and colloidal substances originating from mechanical wood pulp-Adsorption and influence on adhesion

By measuring adsorption using a stagnation point reflectometer, it was shown that multilayers consisting of cationic polymers and dissolved and colloidal material released from wood fibres into process waters are formed on an anionic silica surface. The similarity of this experiment to the papermaking process was established. It was established using the “JKR-method” that this multilayer adsorption had a profound effect on the adhesion, in air, of an elastic polydimethyl siloxane (PDMS) probe to these surfaces. The adhesion of PDMS to a bare silica surface showed a large hysteresis, with a much stronger adhesion measured upon the separation of the two surfaces compared with the value obtained from gradually pressing them together. It was suggested that this hysteresis was due to specific interactions (hydrogen bonding) that develop over time. The first adsorbed layer, a cationic poly(dimethyldiallylammoniumchloride) (polyDMDAAC), decreased the magnitude of the hysteresis and gave a relatively low adhesion, which may be due to the fact that these specific interactions were blocked. The subsequent build up of layers of lipophilic wood extractives in the form of colloidal particles and cationic polymer increased the adhesion. This was interpreted as being due to the build up of a soft layer on the stiff mineral surface causing additional energy dissipation upon separation, even though the molecular adhesion was still decreased compared with the bare silica. This was supported by the fact that none of the individual components of the multilayer increased the adhesion when applied in a relatively thin layer on the silica, and by the fact that a thick deposition of cast coated wood extractives gave a very high adhesion. Stearic acid was chosen as a model substance for extractives and deposited onto silica from vapour phase. This resulted in a partial coverage of the surface where the stearic acid was present as patches of different size. This gave a significant reduction of the adhesion. The solid stearic acid melted and was redistributed when confined between the PDMS and the silica. This gave a thinner and more uniform layer. The application of a “monolayer” of C 18-tails covalently bound to the silica by siloxane links, gave a very significant reduction of the magnitude of the adhesion hystersis. It is concluded that the distribution of the contaminants over the surface is very significant for the adhesion properties. This is relevant to practical papermaking with respect to: (i) the build up of deposits on process equipment and its effect on adhesion to these surfaces; (ii) fibre–fibre adhesion and thereby paper strength, a phenomenon that can never be studied without directly measuring the adhesion, which makes specific solutions to the practical problems possible.

Temperature effect on stearic acid monolayers on water

Measurements are described for the force-area curve of stearic acid on pure water at temperatures of 1.6, 3.0, 5.0, 10.0 and 20.0°C. The A0 values for both solid and liquid films increase with temperature at the same rate, which is greater than for the corresponding cross-sectional areas in the B and C states of solid stearic acid. There are minima in the compressibilities of both solid and liquid films around 5°C. Taken together, these data point to an interaction between water molecules and the stearic acid head groups, related to the water structure as manifested in the temperature of maximum density of 4°C.

Shear Strength of Lubricant Monolayers

THERE is considerable evidence that the friction of boundary lubricated surfaces is largely attributable to the force required to shear the lubricant layer itself1,2. It might be expected therefore that for plastically deformed contacting metal surfaces, with load bearing area which is inversely proportional to hardness, the coefficient of friction should also vary as the inverse of the hardness. This is, however, not observed; for metals covering a wide range of hardness the coefficient varies only slightly, suggesting that the shear strength of the lubricant is not constant but varies in almost direct proportion to the contact pressure1. A similar conclusion has been reached by Bowers and Zisman3 from their observation that the coefficient of friction of solid stearic acid only slightly exceeds that of hard surfaces lubricated by a thin film of stearic acid. In view of the steep increase of bulk shear strength with increasing pressure observed by Bridgman4 for a solid paraffin this type of behaviour is not entirely unexpected.

Creep Properties of Oily Gelatinous Preparations

Shear creep properties of oily gelatinous preparations were studied using a double-sandwich type apparatus. The specimens were the pasty stuffs obtained by cooling hot solutions of liquid petrolatum(LP) and solid stearic acid(SA).The instantaneous compliance (Jg)and the equilibrium compliance (Je) first decrease with the increase of temperature, and then after passing through a minimum, increase again.The compliances change in proportion to the reciprocal of 2.8 th power of the SA concentration, and this behavior was interpreted with van Dongen's model.Temperature dependence of the creep viscosity was examined and the activation energy of flow was calculated from the data as a function of SA concentration.The initial anomalous decrease of J, that is the apparent hardening of the substance, with the increase of temperature, was interpreted as an effect of voids contained in the system. ' The voids are gradually replaced by the thermally expanded LP. The scaffolding structure of SA crystals is impregnated with viscous and incompressible LP and hardened to gel.The proposed idea was tested by the examination of the thermal expansion behavior of LP, SA, gels, etc.

Extraction of Metals with Stearic Acid Involving Radioactive Nuclides

For the separation of metallic ions, stearic acid was introduced as a new extraction reagent. Solid low-melting point reagent such as stearic acid was expected to simplify the procedure of solvent extraction of metallic elements especially of radioactive isotopes and to do the disposal of radioactivity in the wastes. The extraction can be carried out by adding a solid stearic acid to the sample solution heated above its melting point (71 un. Concent 85% C) and by separating the solid stearic acid after being vigorously shaken with the solution and being left standing to solidify at room temperature. The extractabilities of fission products such as Sr/sup 90/-Y/sup 90/ Ce/sup 144/-Pr/sup 144/, Ru/sup 106/ -Rh/sup 106/, and al so of nonactive ferric iron and cupric copper were investigated as functions of pH. It was concluded that the above elements except Ru were extracted almost completely from the solution at pH around 7. (auth)