Increasing Curing Temperature Research Articles

CURING CHARACTERISTICS OF POLYURETHANE MODIFIED UNSATURATED POLYESTER RESIN/COLOR PASTE MIXTURES

Viscosity and curing characteristics of polyurethane modified unsaturated polyester( PU-UPES) /color paste mixtures were systematically studied. The results showed that the viscosity of PU-UPES / color paste mixtures tends to increase with the content of the color paste,but the experimental data of viscosity are lower than the theoretical additive data. With the increasing of the color paste content,all of the gelation time,the apparent initial curing temperature and the apparent peak curing temperature increase accordingly,while the apparent final curing temperature and the enthalpy decrease. With the increasing of the heating rate,the curing characteristic temperatures of composite systems shift toward higher temperature values when the composite under the same content of color paste,but the curing enthalpy values are almost constant. Meanwhile,based on the the apparent peak curing temperature at different heating rates,the apparent activation energy and the preexponential factor of PU-UPES / color paste mixture curing reaction can be calculated through the Kissinger equation. The initial curing temperature,the peak curing temperature and the final curing temperature are calculated by the extrapolation method in order to optimize the curing process. Based on the optimum curing process,the adhesion grades of PU-UPES / color paste coatings are above the first level.

Citric acid crosslinking of paper products for improved high-humidity performance

Fibre crosslinking with polycarboxylic acids can be used to improve certain properties of paper products, including wet tensile and compressive strength. In the present work it was proposed that citric acid (CA) crosslinks the cellulosic fibres of linerboard by self-catalysed esterification of cellulosic hydroxyl groups, which makes an additional catalyst unnecessary. An increase in CA dose or curing temperature increased linerboard compressive strength. In CA-treated corrugated board most of the applied CA was esterified with fibres while some CA thermolysis products were also present. A significant portion of the applied CA was unaccounted for. The deficit was attributed to thermolysis to give volatile anhydrides of unsaturated acids. Under cyclic humidity and static compressive loading, CA-treated corrugated boxes showed a greater than three-fold increase in resistance to compressive creep, showing that CA treatment can be used to extend the lifetime of corrugated boxes used for horticultural produce storage.

Hydration kinetics modeling of the effect of curing temperature and pressure on the heat evolution of oil well cement

The heat evolution of Class G and Class H oil well cements cured under different temperatures (25°C to 60°C) and pressures (2MPa to 45MPa) was examined by isothermal calorimetry. Curing pressure was found to have a similar effect on cement hydration kinetics as curing temperature. Under isothermal and isobaric conditions, the dependency of cement hydration kinetics on curing temperature and pressure can be modeled by a scale factor which is related to the activation energy and the activation volume of the cement. The estimated apparent activation energy of the different cements at 2MPa varies from 38.7kJ/mol to 41.4kJ/mol for the temperature range of 25°C to 40°C, which decreases slightly with increasing curing temperature and pressure. The estimated apparent activation volume of the cements at 25°C varies from −23.1cm3/mol to −25.9cm3/mol for the pressure range studied here, which also decreases slightly in magnitude with increasing curing temperature.

Optimization of Gas Adsorption Porosimetry for Geopolymer Analysis

Gas adsorption porosity measurement of geopolymers (GPs) is required for quantitative understanding of such mesoporous structures, but the complex nature of the GP system makes analysis difficult. Previous results in the literature are often ambiguous or contradictory. A systematic investigation of metakaolin GP gas adsorption results was conducted to optimize the use of this measurement technique and verify that results match known theory about GP structure. It was found that GP undergoes structural change upon degassing at 100°C or higher. If and only if this change is prevented by degassing at a lower temperature could it be shown that specific surface area and total gas adsorption increases with both increasing curing temperature and decreased Si:Al ratio. This observation is consistent with previous suggestions of increased zeolitic character under these conditions, where previous gas adsorption investigations had not observed this expected relationship. Hydrogen physisorption is proposed as a substitute technique for micropore isotherms in GPs due to the difficulty of removing trace gasses from GPs and the measurement effect of such gasses at high vacuum. A hydrogen physisorption isotherm qualitatively resembled an equivalent nitrogen micropore isotherm.

Slagment Cement Improve the Cement Resistance Toward Acids Attack During Acidizing Treatment

Acidizing treatment in past experience shows several zonal isolation problems after the treatment. This study presents the effect of the acid treatment toward class G cement and slagment cement as the improvement method to improve the cement resistance toward the acid. Lab experiments were conducted by immerge the respective cement cubes into 12% HCl/3% HF solution for 40 min before several analysis were conducted. Based on the result, the mass loss and compressive strength loss of the cement cubes decrease as the curing temperature and pressure increase due to more evenly distributed cement chemical composition crystal in high curing condition as shown in Scanning Electron Microscopy (SEM) analysis. From X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) analysis, only the first layer of the cement cubes shows chemical component change due to the reaction between the acid. This study found that, replacing class G cement to slagment cement can reduce the mass loss and compressive strength loss up to 72% and 82%, respectively.

A comparison study of Portland cement hydration kinetics as measured by chemical shrinkage and isothermal calorimetry

Two different methods of evaluating cement hydration kinetics, namely chemical shrinkage and isothermal calorimetry tests, are used to investigate the early stage hydration of different classes of oilwell cement at various temperatures. For a given cement paste, the hydration kinetics curves measured by the two methods are proportional to each other at the same curing temperature. The ratio of heat of hydration to chemical shrinkage for different cements used in this study ranges from 7500J/mL to 8000J/mL at 25°C and increases almost linearly with increasing curing temperature at a rate that varies only slightly with cement composition (approximately 58J/mL per °C). A previously proposed scale factor model for simulating the effect of curing temperature and pressure on cement hydration kinetics is further validated in this study for its temperature aspect. The model is shown to be particularly helpful in correcting for slight temperature errors in the experiments.

Study on vulcanization kinetics of constant viscosity natural rubber by using a rheometer MDR2000

Vulcanization kinetics of constant viscosity natural rubber (CVNR) prepared with hydroxylamine hydrochloride was studied by using a Rheometer MDR2000. The results show that the first stage of curing period follows first-order reaction, but the induction period and the end stage of curing period does not. The calculated reaction order n of the end stage of curing period of CVNR is in the range of 0.01–0.52, and that of natural rubber (NR) is in the range of 0.38–0.66. The reaction orders of the end stages of curing periods of CVNR and NR increase with increasing curing temperature, and the reaction order of the end stage of curing period of CVNR is smaller than that of NR at the same temperature. The rate constants of the induction period, the first stage of curing period and the end stage of curing period of CVNR are smaller than that of NR at the same temperature. The activation energies of the induction period, the first stage of curing period and the end stage of curing period of CVNR are greater than that of NR. The activation energy of the induction period of CVNR is increased by13.52%, the activation energy of the first stage curing period of CVNR is increased by 3.95%, and the activation energy of the end stage of curing period of CVNR is increased by 1.60% compared with the activation energies of NR. The time tdis of CVNR is longer than that of NR at the same temperature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synthesis and characterization of low-k films for large area imaging applications

An organic liquid polymer based on methyltriethoxysilane has been synthesized. The material;when spin-coated onto wafers and thermally treated;lead to dielectric films of low permittivity;which can be used in hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) based large area imaging arrays as an inter-level dielectric between the TFT and pixel levels. Fourier Transform Infrared Spectroscopy (FTIR) shows prominent peaks of Si-CH3 stretch and Si-O stretch modes. The dielectric constant (k) of the film was found to decrease with increasing curing temperature (Tcure). However;k values were<3 for Tcure<260^oC;which is the upper limit for our a-Si:H process. Thermogravimetric analysis showed that major weight loss takes place for up to 200^oC;and the film stabilizes thereafter. The stress in the films was found to be compressive;and increased from 50 to 220MPa when Tcure was increased from 250 to 450^oC. The low stress for low Tcure is a desirable property for film integration.

Effect of Curing Temperature on Nano-Silver Paste Ink for Organic Thin-Film Transistors

Silver (Ag) metal electrode having 20 microm channel length was printed by reverse offset printing (ROP) using nano-silver paste ink for the source/drain of organic thin-film transistors (OTFT). Specific resistance and surface roughness of printed Ag electrodes with increasing curing temperature were investigated, and surface morphology and grain growth mechanism were systematically verified using a scanning electron microscope (SEM) and atomic force microscope (AFM) in order to obtain an optimized ROP Ag electrode. The Ag electrode was applied to fabricate top-gate/bottom-contact poly(3-hexylthiophene) OTFT devices, which showed reproducible OTFT characteristics such as the field-effect mobility, threshold voltage, and an on/off-current ratio of -10(-3) cm2/Vs, 0.36 V, and -10(2), respectively.

The effect of temperature on the hydration of composite cements containing limestone powder and fly ash

The effect of the curing temperature (5, 20 and 40°C) on the degree of hydration, amount of bound water and calcium hydroxide, porosity and the development of mechanical properties was investigated on pastes and mortars prepared with fly ash (FA)–limestone (L) Portland composite cements. Increasing the curing temperature for ordinary Portland cement (OPC) leads to a more inhomogeneous distribution of hydration products, resulting in an increased coarse porosity and therefore a lower compressive strength after 7 days and longer. In contrast, the FA containing mortars showed higher compressive strength with increasing curing temperature up to 90 days. The reaction of the FA is increased at 40°C and strongly retarded at 5°C. At 20 and 40°C, FA reduces the porosity at later ages. The replacement of 5% of the OPC or FA by L powder did not impair the strength at 5 and 20°C, but lowered strength slightly at 40°C for the FA blended cements. The porosity appears to be the dominating factor regarding the compressive strength, independent of whether part of the OPC is replaced by FA and L powder or not.

Compressive strength and drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement mortars

This paper studies the physical properties, compressive strength and drying shrinkage of multi-blended cement under different curing methods. Fly ash, ground bottom ash and undensified silica fume were used to replace part of cement up to 50% by weight. Specimens were cured in air at ambient temperature, water at 25, 40 and 60°C, sealed with plastic sheeting for 28days. The results show that absorption and volume of permeable pore space (voids) of blended cement mortars at 28day under all curing methods tend to increase with increasing silica fume replacement. The compressive strength of blended cement with fly ash and bottom ash was lower than that of Portland cement control at all curing condition while blended cement with silica fume shows higher compressive strength. In addition, the compressive strength of specimens cured with water increased with increasing curing temperature. The drying shrinkage of all blended cement mortar cured in air was lower than that of Portland cement control while the drying shrinkage of blended cement mortar containing silica fume, cured with plastic sealed and water at 25°C was higher than Portland cement control due to pore refinement and high autogenous shrinkage. However, the drying shrinkage of blended cement mortar containing SF cured with water at 60°C was lower than that of Portland cement control due to lower autogenous shrinkage and the reduced microporosity of C–S–H.

Preparation of a liquid boron‐modified polycarbosilane and its ceramic conversion to dense SiC ceramics

AbstractA boron‐modified ethynylhydridopolycarbosilane (B‐EHPCS) was successfully prepared via the hydroboration reaction of ethynylhydridopolycarbosilane (EHPCS) with 9‐borabicyclo‐[3.3.1]nonane (9‐BBN). The as‐synthesized B‐EHPCS with a branched structure was characterized by means of gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The structural evolution of ceramic conversion of B‐EHPCS was investigated by solid‐state NMR. The 13C magic angle spinning (MAS) NMR results indicated that the CC and CC groups of B‐EHPCS take part in the hydrosilation cross‐linking at a relatively low temperature (170°C). According to the 29Si MAS NMR analysis, the CSiH3 end groups are most reactive hydride functionality involved in the hydrosilation cross‐linking. With increasing curing temperature, the C2SiH2 and CSiH3 units are completely consumed, while C3SiH units remain even after curing at 600°C. The TGA results show the 1200°C ceramic yield of B‐EHPCS reaches 86%, which is 10% higher than that of the parent EHPCS (76%). At high temperatures, the introduction of &lt;1 wt% boron significantly inhibits silicon carbide (SiC) crystallization. The 1800°C ceramics derived from B‐EHPCS are found to be significantly denser than that from EHPCS. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Electrical Properties of Carbon Nanotubes-Based Epoxy Nanocomposites for High Electrical Conductive Plate

Electrical properties of carbon nanotubes-based epoxy nanocomposites for high electrical conductive plate were investigated. Dispersion and incorporation mechanism between two conductive fillers with different sizes (CNTs and Graphite) in the polymer matrix are the key factors in the fabrication of high electrical conductivity plate. Different variation of carbon nanotubes (CNTs) (1~10 wt %) and Graphite (G) (60 ~ 69 wt %) loading concentration were added into the epoxy resin. Dispersion of CNTs and G in epoxy resin were conducted by the internal mixer with a Haake torque rheometer. The mixture of G/CNTs/EP was poured into the steel mold, and G/CNTs/EP nanocomposites had been fabricated through compression molding. The electrical conductivity of nanocomposites in terms of variation of G and CNTs concentration were measured by the four point probe for in a plane electrical conductivity. The results revealed that addition of G/CNTs and increasing curing temperature are effective ways to produce high electrical conductive nanocomposites. The highest electrical conductivity was reached on 104.7 S/cm by addition 7.5 wt% of CNTs. Dispersion quality of G and CNTs in the epoxy matrix was observed on the fractured surface by scanning electron microscopic.

Studies about the Initial Curing Conditions on the Carbonation Resistance of Fly-Ash Concrete

Studies about the resistance of carbonation capability of fly-ash (FA) concrete at different initial curing regimes and exposure time through accelerated carbonation experiments were made. Firstly, 30% replacement ratio fly-ash concrete specimens were fabricated and cured in 20°C, 30°C and 40°C water for 3d, 7d, 14d and 28d respectively, and cured in a standard air environment (20±2°C, relative humidity ≥95% ) for 28d. As a comparison, ordinary Portland concrete (OPC) specimens were also made and cured in 30°C water for 7d, and standard curing for 28d. After the initial curing, all the specimens were taken out and placed indoor natural environment. When specimen age reach 30d, 60d and 120d, 2 weeks accelerated carbonation experiments were made and concrete carbonation depth were measured. In addition to this, hydration degrees of fly ash at different initial curing conditions were measured using the selective dissolve method. Results show that the initial curing conditions play an important role in the carbonation resistance of FA concrete. Initial water curing is beneficial to the development of carbonation resistance of FA and OPC concrete. Prolonging initial curing time and increasing curing temperature is beneficial for the carbonation resistance of FA concrete. For the same curing conditions, carbonation rate of FA concrete is usually higher than OPC concrete, but with the increase of initial curing temperature, the difference can be reduced.

HYDRATION OF 3CaO•Al2O3 AND 4CaO•Al2O3•Fe2O3 IN PORTLAND CEMENT

Hydration process of many kinds of cement paste is investigated by powder X-ray diffraction (XRD)/Rietveld analysis. The parameters of the present study are type of cement (Ordinary Portland cement, Low heat cement, and Eco-cement), water to cement ratio (0.50, 0.35), and curing temperature (283, 293, 313K). In this contribution, reaction of aluminate phase (3CaO•Al2O3) and ferrite phase (4CaO•Al2O3•Fe2O3) is focused and evaluated. Experimental results show that the reaction of both aluminate phase and ferrite phase is affected by the temperature and presence of calcite. When system includes calcite, monocarbonate aluminate is mainly produced, rather than ettringite. And in the case of high curing temperature, Al2O3 is reacted as amorphous. Regarding ferrite phase, the reaction degree at the age of 1 year decrease as curing temperature increases, this can be presumed due to dense amorphous phase around cement minerals. Based on these experimental facts, simple hydration model is presented to evaluate development of hydration degree of aluminate phase and ferrite phase.

Electrical Conductivity and Flexural Strength of Graphite/Carbon Nanotubes/Epoxy Nanocomposites

Carbon nanotubes (CNTs) have excellent mechanical and electrical properties. CNTs reported have excellent properties that can replace conventional conductive filler in advanced engineering applications. The polymer matrix was epoxy resin (EP).Conductive fillers were MWCNTs and synthetic graphite (G). Different variation of CNTs (0~10 wt. %) and graphite (60 ~ 67.5 wt. %) loading concentration were added into the epoxy resin. Dispersion of CNTs and G in epoxy resin were conducted by internal mixer with a Haake torque rheometer. The mixture of G/CNTs/EP was poured into the steel mold, and G/CNTs/EP nanocomposites had been fabricated through compression molding. The electrical conductivity of nanocomposites in term of variation of G and CNTs concentration were measured by the four point probe for in plane electrical conductivity. The results revealed that addition of G/CNTs and increasing curing temperature are an effective ways to produce high electrical conductive nanocomposites. Dispersion quality of CNTs and G in epoxy matrix were observed on the fractured surface by scanning electron microscopic.

폴리카르복시산 가교제를 이용한 고흡수성 PVA 필름의 제조

PVA films were crosslinked with dimethylol dihydroxy ethylene urea (DMDHEU) and three polycarboxylic acids of butanetetracarboxylic acid (BTCA), citric acid and malic acid Different factors influencing the crosslinking treatment with BTCA were investigated including BTCA and sodium hypophosphite (SHP) concentration, curing temperature and time. The cured films was extracted with boiling water and gel fraction was calculated based on weight change of the PVA films. The gel fraction of PVA films increased with increasing curing temperature and time. And the resistance to water and thermal stability of the crosslinked PVA films improved with the BTCA crosslinking treatment. While crosslinking with citric acid gave the highest gel fraction among the crosslinkers, crosslinking with malic acid showed the highest absorbancy in 0.9% saline solution, which was attributed to lower crosslink density and high number-average molecular weight between crosslinks. The superabsorbent PVA films could be prepared by adjusting the crosslinking condition of PVA with polycarboxilic acids.

Transfer printing with disperse dyes on cotton fabric modified with an aqueous tolylene diisocyanate derivative

Transfer printing with disperse dyes on cotton fabric modified with an aqueous tolylene diisocyanate derivative (TDD) was discussed in this paper. The effect of the degree of substitution (DS) on color strength (K/S value) of the modified and transfer printed fabric was investigated. The DS of the cotton fabric increased with increases in TDD concentration and curing temperature and time, while the sample whiteness decreased with the increasing curing temperature and time. And the change of structure of the modified cotton fabric was characterized by FT-IR spectra, DSC curves, and SEM images. All of the factors, such as the concentration and molecular weight of poly(ethylene glycol), the DS of the modified fabric, the transfer printing temperature and time would affect the K/S value of the sample. After transfer printing with disperse dye, the K/S value and printing fastness of TDD-modified cotton fabric were higher than those of cotton control fabric, the change of chromatic difference was not obvious, but the tensile strength of the modified fabric was lower than that of original cotton.

Succinic Acid 처리면포의 역학 특성 - 인열강도 -

Polycarboxylics acids are used as crosslinking agents for cotton cellulose to produce durable finished press cotton fabric. It has been observed that the strength of the cotton fabric treated with polycarboxylic acids showed significant reduction as a result of the crosslinking process. The effect of acid-catalyzed depolymerization on the tear strength of cotton fabric is investigated by evaluating the cotton fabric treated by succinic acid, which does not crosslink cotton cellulose and form little ester on the cotton fabric. We find that the tear strength of cotton fabric treated with succinic acid decreases at elevated temperature due to acid-catalyzed depolymerization of cellulose. The magnitude of fabric strength reduction increases as the acid concentration increases. At a constant acid concentration, it increases as the curing temperature and time increases. It decreases as the pH of the acid solution increases. We also find that the dissociation constant of an acid also has a significant effect on the fabric strength reduction. The magnitude of fabric tear strength reduction increases as the acid dissociation constant decreases.

Curing behavior of epoxy asphalt

The curing process of epoxy asphalt was analyzed by Fourier transform infrared (FT-IR) spectroscopy. Effect of curing temperature on viscosity of epoxy asphalt, and changes of mechanical properties with curing time were investigated. The evolution of concentration of epoxy band was followed as a function of the applied curing process. The experimental results indicate that the curing reaction rate of epoxy asphalt is invariable before 70 min at 120 °C, and it decreases when curing time exceeds 70 min. The viscosity of epoxy asphalt increases slowly with curing time at initial curing stage. But it increases quickly after initial curing stage and the initial curing time decreases as the curing temperature increases. The tensile strength increases slowly at incipient curing stage and increases rapidly when curing time is form 20 min to 70 min. The elongation at break shows a decrease with curing time, but it exceeds 200% after cured.