Formation and surface properties of electron-emissive coatings III. Thermal decomposition and sintering of some co-precipitated alkaline-earth carbonates

The thermal decomposition of co-precipitated alkaline-earth carbonates, prepared in a manner similar to that used in the manufacture of oxide cathode coatings, has been studied by preparing a calcination series, under vacuum, up to 1200°. Samples were heated in the sorption balance, described previously, up to set temperatures, after which the specific surface and total pore volume of the cooled residue were calculated, using data obtained from the sorption of nitrogen at 77°. The results indicated that the co-precipitated carbonates decompose in several distinct stages.     

Formation and surface properties of electron emissive coatings: X. Sintering of the alkaline-earth formates

The thermal decomposition of calcium, strontium and barium formates has been studied by preparing a calcination series, under vacuum, up to 1100 °C. The results indicate that each major stage of the decomposition process gives rise to a corresponding increase in specific surface. One possible exception is the initial decomposition of barium formate. This substance melts, accompanied by violent evolution of gaseous products and exfoliation of the re-solidified residue, thereby making it impossible to determine accurately the specific surface.     

Formation and surface properties of electron-emissive coatings VI. Structure and decomposition of co-precipitated carbonates

The decomposition, under vacuum, of some co-precipitated alkaline-earth carbonates has been further investigated by applying the techniques of differential thermal analysis (DTA),? electrothermal analysis (ETA) and dilatometry. The results supplement previous work by confirming that decomposition of double and triple carbonates proceeds in two and three distinct stages, respectively. Loss of carbon dioxide from the strontium carbonate component of a double (SrBa) carbonate leads to a breakdown in the crystal structure, forming a mixture of strontium oxide and barium carbonate. Decomposition of the barium carbonate commences before decomposition of the strontium carbonate is complete. With a triple (CaSrBa) co-precipitated carbonate, thermal decomposition of the calcium carbonate component results in a mixture of calcium oxide with the corresponding double carbonate: DTA shows conclusively that the mixture does not contain the single strontium and barium carbonates.     

Formation and surface properties of electron emissive coatings. II. Thermal decomposition and sintering of single alkaline-earth carbonates

The thermal decomposition of ‘Spec-Pure’ calcium, strontium and barium carbonates has been studied by preparing a calcination series up to 1200°. 0·6 g samples were placed in the bucket of a spiral silica spring balance and heated under vacuum, at a rate of rise of temperature of 200 deg c/h. After reaching a set temperature, the specific surface and total pore volume of the cooled residue were calculated, using data obtained from the sorption of nitrogen at 77°k. The results indicated that the extent of the activation which accompanies thermal decomposition depends on the amount by which the Tammann temperature of the resulting oxide exceeds the temperature at which the maximum rate of decomposition occurred. Thermogravimetric and gas evolution studies on strontium and barium carbonates are also discussed in connexion with work reported in an earlier paper.     

Formation and surface properties of electron-emissive coatings IV. DTA,ETA and dilatometry studies on some alkaline–earth hydroxides

The decomposition under vacuum of the hydroxides of calcium, strontium and barium was investigated by differential thermal analysis (DTA), electrothermal analysis (ETA) and dilatometry. The results suggest that the rate of sintering of calcium oxide is initially governed by the formation of a pseudo-hydroxide lattice; rapid sintering occurs only after conversion of this to the true oxide. Compacts of the oxides of strontium and barium show a remarkable resistance to sintering at temperatures up to 1000°. It is proposed that the sintering may have been inhibited by the presence of trace amounts of calcium oxide and strontium oxide formed by decomposition of impurities present in the samples of strontium and barium hydroxides, respectively.     

Formation and surface properties of electron-emissive coatings V. DTA,ETA and dilatometry studies on some alkaline–earth carbonates

The decomposition under vacuum of the carbonates of calcium, strontium and barium was investigated by differential thermal analysis (DTA), electrothermal analysis (ETA) and dilatometry. The results indicate that the rates of sintering of the oxide produced by the decomposition of the corresponding carbonate are in the order predicted by their respective Tammann temperatures, i.e. BaO>SrO>CaO. DTA studies on the decomposition of samples of barium carbonate have shown that great care must be taken to ensure that the decomposition is carried out under the highest vacuum attainable, in order to eliminate the formation of a basic carbonate. Further evidence of the formation of free barium by this decomposition process is also reported.     

Thermal decomposition,structural changes and surface properties of chromium oxide gel

Structural and phase changes of a prepared sample of chromium oxide gel were explored by differential thermal analysis and X-ray diffraction analysis. Dehydration products were obtained at various temperatures up to 740 °C, by heating in air for 3 hours. Samples obtained by heating below 320 °C were amorphous to X-rays whereas those obtained at 320 °C, and between 320 and 510°C proved to be a mixture of α- and γ-Cr₂O₃. However, at temperatures above 510 °C, only one form, the stable α-Cr₂O₃ exists. The glow phenomenon is attributed to the presence of excess oxygen, resulting from the reduction of Cr(VI) to Cr(III), just prior to the conversion of the amorphous gel to the crystalline γ-Cr₂O₃, which is accompanied by a release of energy. Surface area measurements were carried out by cyclohexane, methanol and water adsorption at 35 °C, and the areas were compared with those measured by nitrogen at liquid nitrogen temperature. Pore structure analysis for both micro- and mesopores were carried out. The low temperature samples are characterised by the presence of both types of pores, with the micropore fraction predominating acquiring thus the property of molecular sieves; the pores being accessible to water and nitrogen but not to cyclohexane or methanol. At temperatures above 320 °C, the microporosity collapses with the production of a heterogeneous assembly of mesopores. In the mean time the surface changes to be hydrophobic in nature; accordingly it cannot be measured from water adsorption.     

Design of deicing reagents based on alkali and alkaline-earth metals and ammonium formates, acetates, and nitrates

Phase equilibria in binary, ternary, and quaternary water-salt systems containing sodium, potassium, magnesium, calcium, and ammonium nitrates, formates, and acetates have been studied in the temperature range of 0 to ?70°C, and polytherms of the fusion of ice have been plotted. A series of binary and ternary salt compositions that form low-temperature eutectics with ice, which are promising as deicing reagents, has been determined. The corrosion activity of the most promising compositions relative to metals and alloys, as well as cement concrete pavements, has been determined. Corrosion inhibitors have been chosen.     

Thermal and mechanical properties of crack-designed thick lanthanum zirconate coatings

Vertical cracks are beneficial in thermal barrier coatings due to enhanced thermo-mechanical compliance. Accordingly, an aqueous nitrate based precursor solution was atomized on stainless steel substrates by spray pyrolysis to deposit thick crack-designed lanthanum zirconate coatings. Coatings with designed crack patterns were deposited and characterized by electron microscopy, tribology, Vickers indentation, and thermal diffusivity. The crystallization of the coatings was investigated by in situ high temperature X-ray diffraction. The green coatings crystallized from 600 °C and the pyrochlore structure was formed after heat treatment at 1000 °C. Crystalline lanthanum zirconate multilayered coatings with small crack spacing and crack opening exhibited a higher density, a higher hardness, lower thermal diffusivities, and higher thermal conductivities compared to crystalline monolayered coatings of similar thickness with large crack spacing and crack opening. The thermal diffusivity of the coatings, ∼28 mm²/s at room temperature, was similar to the values reported for yttria-stabilized zirconia plasma sprayed coatings.     

Thermal decomposition of SRC-II middle distillate under surface vaporizing conditions

Decomposition of SRC-II middle distillate under surface vaporizing conditions was studied as a function of temperature (heating rate), vapour phase residence time and oxygen level. The stressed and unstressed fuel was analysed by capillary gas chromatography. Decomposition was found to be greatest at low temperature. Boiling mode did not appear to affect the extent of decomposition. Decomposition was weakly related to chemical class and strongly related to component volatility. The effect of gas phase residence time and oxygen level were negligible at the conditions studied. It is concluded that decomposition occurs primarily within the liquid and at the vaporizer surface.     

Anti-icing and anticontamination properties of coatings induced by surface structure

The development of the first model coatings with innovative surface structures, anti-icing, and anticontamination properties could be implemented in the EU-project CleanSky. A porous aluminum alloy structure created by anodization was filled with fluid silicon oil polydimethylsiloxane. At the surface, the silicon oil was modified with vacuum ultraviolet-light to form a thin and solid hydrophobic layer. For further investigations, laser-structured metal surfaces were copied and reproduced with a coating and afterward filled with fluoro-modified oils. Additionally, aluminum alloy AA2024 samples were pickled and treated with hot water to create micro- and nanostructures at the surface. These samples were also filled with different fluoro-modified and nonmodified oils. After application, the surface properties were analyzed with special tests for functionality regarding anti-ice and anticontamination properties.     

Effects of environment and surface coatings on the fatigue properties of polystyrene

The influence of surface condition, environmental media and surface coatings on the fatigue lifetime of polystyrene specimens has been explored. It is shown that surface flaws such as machining marks, are much more detrimental to fatigue lifetime than to static strength. The effect of alcohols on fatigue lifetime is primarily one of plasticization rather than of molecular size and mobility. Hence n-butanol is a more aggressive environment for polystyrene than is methanol. For a wide variety of organic media, a fairly good correlation was found between fatigue lifetime and solubility parameter. Highly polar media, like glycerol and water, are shown to be favourable media, rather than aggressive ones, in that they increase average fatigue lifetimes of polystyrene specimens by about one decade. It is suggested that any media that inhibit or delay crazing, either by increasing surface energy or by blunting flaws and reducing stress concentration, should also be beneficial to fatigue performance. A surface coating that performs this latter function is a 600 molecular weight polystyrene oligomer. It is shown that application of this compatible, viscous coating to polystyrene specimens increases the average fatigue life, for both polished and unpolished specimens by a decade or more.     

Thermal and surface characterization of polyurethane–urea clay nanocomposite coatings

This paper reports synthesis and characterization of polyurethane–urea (PU‐urea) and the nanocomposites derived from the PU‐urea with silicate clays. Organophilic montmorillonite cotreated by cetyl trimethyl ammonium bromide (CTAB) was synthesized and used to prepare PU‐urea/montmorillonite nanocomposites coatings. PU‐ureas were prepared from polyethylene glycol (PEG), polypropylene glycol (PPG), trimethylol propane (TMP), and 4,4′‐diphenylmethane diisocyanate (MDI) by reacting excess diisocyanate with polyether glycols. The excess isocyanate of the prepolymers was cured with atmospheric moisture. The synthesized moisture cured PU‐urea and nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), and angle resolved X‐ray photoelectron spectroscopy (AR‐XPS). The thermal stability of the PU‐urea nanocomposites was higher relative to the mother PU‐urea films. DSC results showed a slight enhancement in the soft segment glass transition temperature after 3 wt % clay loading. The surface properties showed an enrichment of the soft segment toward the surface. An enhancement in the hard segment composition in the nanocomposite coatings has resulted in enhancing the phase mixing process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2393–2401, 2006     

Formation of coatings with tailored properties on polyperoxide-modified polymeric surfaces

Modification (peroxidation) of polymer surfaces, polypropylene, polyethylene, polyethylene terephthalate, nylon 6-6, poly(phenylene oxide), and ethylene–propylene copolymer were affected by the surface grafting of functional polyperoxides (FPPs) such as poly(5-tert-butylperoxy-5-methyl-1-hexene-3-yne-co-octylmethacrylate) (VEP-co-OMA), poly{N-[(tert-butylperoxy)-methyl]acrylamide-co-octyl methacrylate} (PO-co-OMA), and poly(tert-butylperoxy-methacrylate-co-octyl methacrylate) (PEst-co-OMA). The degree of surface modification was shown to be determined primarily by the structure of the polymer substrate. Using a peroxidized surface as an initiator of grafted copolymerization enabled the grafting of functional monomers (acrylic acid, acrylamide, 4-vinylpyridine, and hydroxyethyl methacrylate) and polysaccharides (heparin, dextran, etc.) and thereby imparted adhesive, antibacterial, haemocompatible properties to the polymer surface.     

无毒有机硅低表面能防污涂料表面性能研究

制备了不同组分的无毒低表面能有机硅防污涂料,并就其表面性能进行了研究.结果发现,颜基比能够显著影响低表面能防污涂料的表面性能;高苯基含量的PDMDPS硅油能够渗出到涂层的表面,并能够改变其表面性能;低表面能有机硅防污涂料在海水中具有良好的稳定性,经过海水的冲刷作用,污损海生物能够轻易脱落.     

The formation and surface properties of electron emissive coatings VIII. Structure of strontium-barium double carbonates

The double carbonates of strontium and barium Sr_xBa_2-x(CO₃)₂ have been shown to undergo, on heating, a transition from an orthorhombic to a hexagonal crystal form. The temperature at which this phase change occurs, and the heat required for the transition, are dependent on the value of x.     

Thermal decomposition of cyclotriphosphazenes. I. Alkyl-aminoaryl ethers

1,3,5-Triisopropoxy-1,3,5-tris(4-aminophenoxy)-cyclotriphosphazene-[CTP (I)], 1,3,5-trineopentoxy-1,3,5-tris(4-aminophenoxy)-cyclotriphosphazene [CTP (II)], and 1,1,3,5-tetraneopentoxy-3,5-bis(4-aminophenoxy)-cyclotriphosphazene [CTP (III)] were prepared from hexachlorotricylophosphazene. Thermal decomposition of the crude CTP (I), CTP (II), and CTP (III) was studied by thermogravimetry, differential scanning calorimetry, and thermal volatilization analysis. Solid, gaseous, and high boiling degradation products were collected at different steps of thermal decomposition and identified by using infrared and gas chromatography mass spectrometry. On heating to 600°C, CTP (I) shows three main steps of weight loss, whereas both CTP (II) and CTP (III) show two overlapping steps. The first step of thermal decomposition of CTP (I) is observed at 150–200°C, where elimination of part of the aliphatic substituents and polymerization of the CTP (I) occurs. The opening of tricyclophosphazene rings at 220–370°C provokes further elimination of aliphatics and ammonia and formation of crosslinked structures. Phosphorus oxynitride structure bonded with carbonized polyaromatics is formed in the third step of thermal decomposition, accompanied by the elimination of aromatics and chain fragments at 400–500°C. In the case of CTP (II) and (III), simultaneous evaporation of virgin CTPs, opening of the phosphazene ring, and elimination of aliphatic substituents with the formation of crosslinked polymeric structures occur at 210–350°C. A phosphorus oxynitride-aromatic carbonized structure similar to that from CTP (I) is formed at 350–600°C. The process is accompanied by the elimination of aromatics and chain fragments. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 461–472, 1998     

Thermal decomposition of polystyrene

Kinetic studies on the decomposition of polystyrene samples with molecular weights ranging from 900 to 1.8 × 10⁶ have been carried out making use of the differential thermogravimetric and differential scanning calorimetric techniques. Changes in molecular weight distributions with decomposition, at different temperatures or times, have been studied by gel permeation chromatography. This technique was likewise used to carry out component splitting of the undecomposed polymer samples. These components have been shown to break down statistically primarily by a process of random scissions yielding lower molecular weight products. The major portion of the observed weight loss, by the volatilization of small chain segments, is attributed to a rapid and complete depolymerization of chains. These interpretations are based on changes in polydispersity occurring during the decompositions. Similar components, decomposing in a different manner but under identical operating conditions, are suspected of being different stereoregular forms of the polymer. The order of reaction as computed from the method of Freeman and Carroll has been found to be zero for random scissions and one for the process of depolymerization. The activation energy computed by the method of Coats and Redfern was found to increase with molecular weight reaching a maximum value in the 10⁵ molecular weight range.