Reactivity of lime and related oxides. XVIII. Production of plasters

Conditions for production of plasters are surveyed in relation to variations in phase composition, surface area and crystallite size. The commercially known α- and β-hemihydrate plasters prepared by autoclaving and dry calcination are not two distinct phases—they differ in crystal habit, surface area, crystallite size and lattice perfection. The terminal β-hemihydrate and γ-CaSO₄ produced in vacuo have greater surface areas than samples produced in air. The most active γ-CaSO₄ (Class C plaster) samples are finely porous and rapidly rehydrate in atmospheric water vapour with considerable loss of surface area and porosity. ‘Wet’ rehydration (liquid water) or γ-CaSO₄ causes more rapid development of the 6.01 Å (10.10) spacing, in accord with the c-direction elongation of the ‘α’-hemihydrate crystals prepared by autoclaving or precipitation from 50% HNO₃. The porosity of the γ-CaSO₄ diminishes considerably between 200° and 300°, but remains to a smaller extent up to 500° when the γ-CaSO₄ has changed to β-CaSO₄, anhydrite (Class D plaster). Anhydrite sintered extensively between 500° and 900° before decomposing to lime at temperatures up to 1400° (Estrich Gips plaster). Removal of the SO₂ and O₂ is facilitated by streams of nitrogen or carbon dioxide, which increases the decomposition rate. Calcination at temperatures below 1200° gives anhydrite and lime crystals of more comparable sizes, and avoids complete ‘dead-burning’ of the lime.     

Structure and properties of ethylene—methacrylic acid copolymers and their sodium salts: Dielectric and proton magnetic relaxation studies

Dielectric and proton magnetic relaxation data have been obtained for an ethylene-methacrylic acid copolymer (containing about 4 mole% methacrylic acid units) and its 53% ionised sodium salt. The degrees of crystallinity and percentage ionisation of the samples investigated were estimated by infra-red methods. The dielectric results were obtained principally in the frequency range 100 Hz to 10 kHz and at temperatures ranging from 80° to – 120°. A few results are also reported at frequencies down to 0·1 Hz and up to 100 MHz. For the acid copolymer, two dielectric loss regions are observed and these are correlated with the reported mechanical β′- and γa-processes respectively. The partly ionised copolymer exhibits three dielectric relaxation regions which correlate with the mechanical α-, β- and γa-relaxations respectively. In addition, a dielectric peak appears at about —40° in the presence of absorbed water, a result similar to that found in the polyamides. The proton magnetic relaxation results were obtained by pulse methods which yielded the spin-lattice relaxation times T₁ (at 30 MHz) and T_1p (at kilohertz frequencies) as a function of temperature from ?180° to 100°. Two components were generally observed for T_1p. For the acid copolymer the β′- and γ-processes have been observed from these results, as well as a lower-temperature (δ) process which has not been detected by the mechanical or dielectric methods. For the sodium salt the γ- and δ-processes are also found, in addition to a high-temperature process in the region of the merged α- and β-processes. The present data are consistent with previous assignments for the β′-, α-, β- and γ-processes. The ‘water’ relaxation appears to involve some rotation of water molecules, or of ionic segments to which water molecules are attached, in the proposed ionic domains. The δ-process is ascribed to the rotations of methyl groups present in the methacrylic acid units.     

Preparation of highly porous Al2O3 aerogel by one-step solvent-exchange and ambient-pressure drying

This work presents the preparation of alumina aerogel via sol-gel route utilizing ambient-pressure drying. A novel and efficient solvent-exchange process has been utilized as an alternative to conventional solvent-exchange processes by directly boiling the hydro-gel in solvent. High emphasis has been given in the selection of solvent based on polarity, boiling point, and specific gravity compared with water to facilitate efficient solvent-exchange and reuse of the solvent. The ambient-pressure-dried alumina aerogel was thermally treated at temperature from 300°C-1200°C to study the change in density, porosity, specific surface area, and microstructure along with crystalline properties. The ambient-pressure-dried alumina aerogel showed lower tapped density 0.108 g/cm³, specific surface area 519 m²/g, and total weight loss of 36.94% at 900°C. The degree of crystalline structure from amorphous was observed to increase with increase in thermal treatment temperature above 300°C, dominant above 700°C, whereas the transformation of bayerite γ-Al(OH)₃ to boehmite γ-AlO₂H was observed at 150°C-300°C and to γ-Al₂O₃ phase was observed at temperature of 300°C-1200°C.     

Roller drawing of ultrahigh molecular weight polyethylene

The roller drawing of ultrahigh molecular weight polyethylene (UHMW-PE) sheets were carried out in the roller temperature T_r range of 100–140°C. In addition to the roller drawing in the solid state (T_r = 100°C), we attempted to crystallize the molten UHMW-PE sheet under the roller-drawing process (T_r = 100–140°C). The tensile and dynamic viscoelastic properties, the molecular orientation, and the microstructure of the roller-drawn UHMW-PE sheets were investigated. The mechanical properties of UHMW-PE sheets were much improved by crystallization during the roller drawing process at T_r = 140°C. The sheets roller-drawn at T_r = 135 and 140°C exhibited c-axis orientation to the draw direction and (100) alignment in the sheet plane. However, at T_r = 100°C the elastic motion of the amorphous chains induces the twinnings of lattice, which enhances the transition to the (110) alignment in the sheet plane. The dynamic storage modulus below γ-dispersion temperature showed good correlation with crystallinity and orientation functions, while taut tie molecules and thick crystallites play an important role in the storage modulus above γ-dipersion temperature.     

Thermoplastic properties of coals carbonized at elevated pressures: effects of waste inorganic materials (GOB)

Thermal behaviour of coal-derived asphaltenes was investigated under atmospheric pressure by thermogravimetry (TG). The weight loss is rapid from 300 to 500°C and is slow above 500°C. The asphaltene comparatively low in molecular weight shows the greater weight loss. The temperature at which the differential thermogravimetry peak appears, T_m, correlates to the asphaltene aromaticity: the asphaltene comparatively high in aromaticity shows higher T_m. Of the residual asphaltene after heating up to 600°C, the obtained crystallite thickness through the c-axis direction (Lc₀₀₂) has a correlation with the molecular weight of the parent asphaltene: the parent asphaltene comparatively low in molecular weight produces residual asphaltene of larger Lc₀₀₂.     

Durability and failure analyses of a silane treated α-Al2O3/polyethylene joint in wet environment

The durability of the joints, consisting of α-Al₂O₃ primed with γ-aminopropyl triethoxysilane (γ-APS) and polyethylene (PE), in wet environment is investigated as a function of the γ-APS thickness, dehydration of γ-APS prior to joint formation and redrying the joint after a certain exposure. The joint strength measured by 180°s peel is found to decrease with exposure time in wet environment more rapidly in water than in 100 percent RH. With exposure time, the debonded area increases from the edges toward the central area of the joint. Relatively thin γ-APS treatments on α-Al₂O₃ appear to provide a more durable joint than thicker γ-APS treatments resulting in an optimal thickness in the range of 0.3 ～ 1 percent γ-APS concentration level. Dehydration of γ-APS leads to more durable joints with an optimal condition found between 1 ～ 2 days of dehydration at 100°C in vacuum. Regardless of the γ-APS thickness and dehydration history, the failure in the de-bonded area seems to occur by the hydrolysis of γ-APS near the α-Al₂O₃ side and by the deformation of polyethylene (cohesive failure) in the peeled area, as characterized by SEM and ESCA. The debonded area in the dried joint recovers little strength, but in the central bonded areas, the strength is mostly recovered, characterized by cohesive failure of polyethylene. Diffusion of water in γ-APS near the α-Al₂O₃ side rather than the PE side can explain at least qualitatively most of the observed trends. The effects of γ-APS thickness and dehydration on the durability in wet environments are compared with those on adhesion promotion in dry environments as well as on their respective failure mode.     

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.     

The structure of aminofunctional silane coupling agents: 1. γ-Aminopropyltriethoxysilane and its analogues

Gamma-aminopropyltriethoxysilane (γ-APS) and its analogues are studied as aqueous solutions as well as solids by Fourier transform infra-red spectroscopy (FT i.r.) and laser Raman spectroscopy. Emphasis was placed on a determination of the nature of the interaction between the amine groups and the residual silanol groups in partially cured solids. Comparison with γ-aminopropyltrisilanolate and partially cured solids obtained from γ-aminopropylmethyldiethoxysilane and γ-aminopropyldimethylethoxysilane lead us to conclude that the residual silanol groups are strongly hydrogen bonded to the amine groups as SiOH … NH₂ rather than SiO^? … ⁺NH₃. Hydrolysis of γ-APS at concentrations ranging 2–80% by weight showed that the solutions below 40% by weight have a few unhydrolysed alkoxy groups. The amine groups are mutually hydrogen bonded in unhydrolysed silane. However, in an aqueous solution and highly cured solids, the amine groups are either free or are interacting predominantly with water molecules.     

Thermal behavior of methacrylic acid–ethyl acrylate copolymers

The thermal degradation behavior of copolymers of methacrylic acid (81.5–17.4 mol%) was studied using thermogravimetry (TGA) and differential scanning calorimetry (DSC) and the degradation products were analyzed using mass spectroscopy and DSC–FTIR. From mass spectroscopy, it was observed that in the copolymers the main degradation products obtained below 280°C included water, ethanol, and methanol, whereas at higher temperature (up to 400°C), CO₂, CO, and small olefins were liberated. Elimination of water and ethanol is attributed to anhydride formation, which is believed to result from two routes: (a) anhydride formation involving adjacent acid groups and (b) anhydride formation involving adjacent acid and ester groups. An endothermic transition in the DSC and percent weight loss in the TGA in the same temperature range (140–280°C) support the above proposal. An increase in weight loss with increase in EA content of the copolymer confirms the participation of EA in the anhydride formation. © 1994 John Wiley & Sons, Inc.     

Retardation effect of nanohydroxyapatite on the hydrolytic degradation of poly (lactic acid)

Poly (lactic acid) (PLA) and PLA/nanohydroxyapatite (nHA) composites, containing 2 wt% and 5 wt% of nHA were subjected to in vitro hydrolytic degradation tests in saline phosphate solution at different temperatures (37°C, 48°C, 60°C, and 72°C) to accelerate degradation. Samples were characterized by water uptake, weight loss tests, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and visual analyses. Arrhenius equation was used to describe the behavior of weight loss as a function of time. The PLA activation energy of weight loss showed to be lower than that of the PLA/nHA composites, indicating that the incorporation of nHA retarded the hydrolytic degradation. The rate and percentage of weight loss increased with increasing temperature. All samples presented a decrease in T_g and an increase in degree of crystallinity as a function of time. Incorporation of nHA retarded this behavior that showed to be more expressive in PLA containing 5 wt% nHA.     

Investigations into the thermal stability of sol-gel-derived glasses as models for thermally grown oxides

The thermal stability of sol-gel-derived silica and borosilicate glasses exposed to dry O₂ at 800 and 1200°C for 100 hours was characterized by weight change, thermal transitions, morphology, structure, and composition to investigate suitability as models for thermally grown oxides. Rapid weight loss was observed in the first few hours of isothermal exposure for borosilicate glasses, followed by constant weight loss at a low rate for the balance of the exposure. Weight loss resulted from loss of residual hydroxyl species retained from the sol-gel synthesis, and from oxidation of carbon retained from thermal decomposition of the organic precursors by pyrolysis. Characterization of the sol-gel-derived glasses showed structural similarities to silica and binary borosilicate glasses synthesized by melt or vapor deposition methods, and to thermally grown oxides. Oxygen transport mechanisms through the sol-gel-derived glasses is not thought to be affected by the retained carbon. However, a silica-enriched glass surface resulting from boria volatility, observed from a borosilicate glass exposed dry O₂ at 1200°C, will slow O₂ transport rates. The results show that sol-gel-derived silica and borosilicate glasses can be used as models for thermally grown oxides.     

The effect of soluble cations on the bonding of epoxy resins to aluminum

The bond strength of an amine-cured epoxy resin to etched aluminum washed with, or washed with and immersed in, 10°C tap water was found to be greater than joints similarly pretreated in 10°C distilled water. The higher bond strength was found to be induced by soluble cations of less than 0.8 Å radius; larger cations had no effect. When aluminum is etched in a solution of chromic acid at 65°C, the aluminum surface is oxidized to γ-Al₂O₃. It is possible that the small, soluble cations can occupy the cationic vacancies in the defect spinel structure of the γ-Al₂O₃ and reduce the negative charge on the surface of the aluminum joints. Joints pretreated in 60°C tap water exhibited higher bond strengths than those pretreated in 60°C distilled water, as the growth of a thick, weak layer of bayerite was inhibited by large anions present in the tap water.     

Residual solvent and its diffusion in acrylic fibers

A survey showed that some commercial acrylic fiber products contain small quantities of residual solvent (dimethylacetamide). No diffusion of solvent from these products could be detected on laundering, dry cleaning, or exposure to synthetic perspiration. Acrylic carpets containing residual solvent were enclosed in sealed boxes to simulate a closed room. Air in the boxes was monitored for solvent content over a 14-day period at 24°C (75°F) and 38°C (100°F) at both low and high humidity conditions. In all cases the solvent content of the air was below the detection limit of the best analytical procedure available (below 0.1 ppm). Diffusion rates of sol vent from 15-denier carpel fiber into nitrogen were measured over the temperature range of 25–100°C. There was no detectable diffusion below 60°C measured over a 24-h period. Mass diffusivities ranged from 2.5 × 10^?19 cm²/s at 60°C to 6.4 × 10^?14 cm²/s at 100°C. Under the conditions of expected use, the rate of diffusion of residual solvent from acrylic fibers is very low. Based on the low concentrations of residual solvent and its very low diffusion rate, there is an extremely low probability of any exposure to solvent from the residual solvent present in commercial acrylic fiber products.     

Isothermal pyrolysis of cellulose: Kinetics and gas chromatographic mass spectrometric analysis of the degradation products

Untreated and fire-retardant-treated white α-cellulose samples were isothermally pyrolyzed in a fluidized bath in a nitrogen environment at 298–360°C. Results were reported in terms of volatilization (based on weight loss-time measurements) and the degradation products (based on gas chromatographic–mass spectrometric analysis). The findings products (based on gas chromatographic–mass spectrometric analysis). The findings on untreated cellulose indicate that: (1) pyrolysis occurs in three distinct phases in the temperature range 276–360°C; (2) there is a single activation energy of 42 kcal/mole over this temperature range; (3) the initial rapid weight loss is not due to the desoprtion of water, but primarily to decomposition of the cellulose; molecules: (4) there is little difference in either the quality or relative quantity of the volatiles generated during the three different phases of pyrolysis. The findings on treated cellulose show that the fire retardant, KHCO₃, does not markedly change the types of degradation products having molecular weights below about 110, althought it does change their relative concentrations. Furthermore, the rate of product generation and the quantity of residual char are increased.     

Postfiring stress‐strain hysteresis of concrete subjected to various heating and cooling regimes

This paper reports an experimental investigation involving 90 siliceous aggregate concrete cores (75 mm dia. 175 mm long), which were subjected to 18 different heating and cooling regimes in the temperature range (217°C–470°C). The cores were heated to the point when the centre of the core reached the same temperature as the outer surface, the point of uniformity. Subsequently, the cores were either taken out of the furnace to cool or soaked at the test temperature for 2 h. Cooling was either by spraying the heated core with water for 5 min or by air‐cooling in a controlled environment of 20°C and 65% RH. The extent of damage and internal fracture were assessed using the stiffness damage test (SDT) and the ultrasonic pulse velocity (UPV) as well as petrography methods. Both prolonged duration of thermal exposure and rapid cooling by water quenching resulted in a further loss of stiffness of fire damaged concrete cores. Extending the duration of thermal exposure by 2 h from the point of uniformity resulted in an approximately 10% further reduction in the residual chord modulus (E_c). However, spraying hot concrete with water after reaching the point of uniformity caused more reduction in stiffness than a 2 h extended duration of thermal exposure to temperatures below 320°C. The damage index (DI), which represents the dissipated strain energy in a hysteresis loop, showed a similar effect. The damage index of cores subjected to water quenching was significantly higher than the damage index of cores soaked at temperatures below 320°C. The residual plastic strain (PS), which is measured at the end of a hysteresis loop, showed very similar variation to that of the damage index. The ultrasonic pulse velocity (UPV) test method confirmed that spraying hot concrete with water from the point of uniformity was more damaging than a 2 h extended duration of thermal exposure to temperatures below 320°C. The extended duration of thermal exposure did not seem to affect the degree of non‐linearity of the stress‐strain response of fire affected concrete while water quenching resulted in a more concave response. The results are explained by identifying the various damage mechanisms associated with the various heating and cooling regimes. Copyright © 2002 John Wiley & Sons, Ltd.     

Novel crosslinked nonlinear optical materials based on cellulose diacetate

Preparation of second‐order nonlinear optical (NLO) materials based on cellulose diacetate and melamine derivatives was attempted. The NLO chromophore DR19 was incorporated into the crosslinking network resulting from the reaction of cellulose diacetate with trimethylolmelamine or hexamethylolmelamine. The poled and cured NLO materials exhibited electrooptic coefficient (r₁₃) values of 1.11 or 1.03 pm/V, respectively, at a laser wavelength of 1550 nm, a modulation frequency of 12.7 kHz. The r₁₃ values decreased to 80 or 81.5% of the initial values after 4 days. The laser transmission loss was 0.50 or 0.44 db. The crosslinking materials showed better temporal stability than that of host/guest type materials, and 73% of the initial r₁₃ value remained after keeping the NLO film at 100°C for 15 h. No evident weight loss was found below 250°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2832–2837, 2006     

Fabrication of low thermal conductivity yttrium silicate ceramic flat membrane for membrane distillation

This paper reports on the successful fabrication of γ-Y₂Si₂O₇ membranes with low thermal conductivity, which is an important membrane property for achieving high performance in membrane distillation process. Single-phase γ-Y₂Si₂O₇ powder was first synthesized by calcination of SiO₂ and Y₂O₃ powders, with 3 wt% LiYO₂ as a sintering aid. The membrane was produced by tape-casting of a suspension of this powder. After sintering at 1300 °C for 4 h, a flat membrane was obtained, which had a thickness of 0.5 mm, 49% porosity, 0.9 μm pore diameter, and low thermal conductivity of 0.497 W/m⋅K at 32 °C, and 0.528 W/m⋅K at 100 °C. The obtained membrane presented hydrophobic features (water contact angle was 132°) after surface modification, which resulted in formation of a strongly adhered robust hydrophobic SiNCO nanoparticle layer on its surface. The resultant hydrophobic membrane was tested in water desalination experiments using a sweeping gas membrane distillation (SGMD) device. High water flux of 10.07 L⋅ m⁻²⋅ h⁻¹ was achieved for a 20 wt% NaCl feeding solution and a temperature at the feed of 90 °C. Stable water flux and rejection rates were recorded in long-term experiments (>400 h).     

Thermal degradation studies of several pyrrone films

The thermal degradation of several polyimidazopyrrolone (pyrrone) films was studied in air and in vacuum over the range of 100–1000°C. by thermogravimetric analysis (TGA), with the use of both isothermal heating and programmed heating rates of 2, 3, 5, and 7.5°C./min. At pressures of 10^?6 torr or less, maximum weight losses average 30% at 800°C. Rates of volatilization and activation energies were derived to provide comparison between these ladder-type polymers. Mass spectrometric analysis of the pyrolysis gases evolved under vacuum conditions showed that CO, CO₂, and H₂O were the primary volatile products and that they were formed throughout the period of weight loss. Approximate correlation between changes in weight and changes in the total pressure for the vacuum tests indicates that mass spectrometric results could provide quantitative as well as qualitative data. The importance of sample history prior to heating and of sample geometry in developing meaningful and reproducible TGA results is aptly demonstrated. The ability of these materials to absorb readily 5–7 wt.-% of water under ambient conditions and the effect of this property upon weight loss measurements are shown.     

Thermal degradation kinetics of rigid polyurethane foams blown with water

The thermal decomposition behavior of rigid polyurethane foams blown with water was studied by dynamic thermogravimetric analysis (TGA) in both nitrogen and air atmosphere at several heating rates ranging from room temperature to 800°C. The kinetic parameters, such as activation energy (E), degradation order (n), and pre‐exponential factor (A) were calculated by three single heating rate techniques of Friedman, Chang, and Coats–Redfern, respectively. Compared with the decomposition process in nitrogen, the decomposition of foams in air exhibits two distinct weight loss stages. The decomposition in nitrogen has the same mechanism as the first stage weight loss in air, but the second decomposition stage in air appears to be dominated by the thermo‐oxidative degradation. The heating rates have insignificant effect on the kinetic parameters except that the kinetic parameters at 5°C/min have higher values in nitrogen and lower values in air, indicating different degradation kinetics in nitrogen and air. The kinetic parameters of foam samples blown with different water level in formulation decline firstly and then increase when water level increases from 3.0 to 7.0 pph. According to the prediction for lifetime and half‐life time of foams, water‐blown rigid foams have excellent thermostability, when used as insulation materials below 100°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4149–4156, 2006     

Creep and recovery of ultra high modulus polyethylene

The creep and recovery behaviour of ultra high modulus polyethylene has been studied over the temperature range 20–70°C. Four types of material were examined; low molecular weight and intermediate molecular weight homopolymer, an ethylene hexene-1 copolymer, and a sample prepared by γ-irradiation of isotropic low molecular weight polymer prior to drawing. With the exception of the low molecular weight homopolymer, the materials showed an apparent critical stress below which there was no detectable permanent creep. It is proposed that the behaviour of all the materials can be described to a good approximation by a simple model, where two activated processes are coupled in parallel. Tentative structural explanations of the results are also given.