Papers by Keyword: Pore Structure

Abstract: It is assumed, that the pore content is related to other parameters of CIPP liners such as mechanical properties and service life or durability of pipelines. The article examines the pore structure of two different materials - composites pipes cured with steam and UV light. The pore structure was examined using an optical microscope and X-ray computed tomography (CT). The aim of the work was to verify the applicability of some methods for verifying the volume of air/gas in the cured composite.

Abstract: Titania-modified zirconias with different Ti/Zr ratios were synthesized via thermal treatment of zirconium (IV) tetra-n-propoxide and titanium (IV) tetra-iso-propoxide in 1,4-butanediol at 300 °C. The obtained products were spherical particles composed of nanocrystals with the tetragonal ZrO₂ structure. The products had large specific surface areas, large pore volumes, and relatively narrow pore size distributions in the mesopore region. After calcination at high temperatures, the obtained TiO₂-modified ZrO₂ samples preserved large surface areas and pore structure. Having these superior thermal stability and pore structure, the obtained TiO₂-modified ZrO₂ particles are expected to show high performance as catalytic materials.

Abstract: Surface area and particle size are significant properties of a catalyst that determine the reaction rate of the heterogeneous catalyst. In this research, calcium oxide derived from industrial eggshell waste was synthesized by thermal decomposition method under air-atmosphere. The obtained eggshell waste was washed, dried, and ground to 420 μm followed by calcination of the ground eggshell in different conditions including calcination temperature (800 to 900 °C) and holding time (1 to 4 hours). Changes of pore structure and the median particle size diameter of the obtained calcium oxides were systematically investigated by various scientific instruments. Results from powder X-ray diffractometer (PXRD) indicated that the calcium oxide can be obtained after calcination at both 800 and at 900°C. Laser diffractometer shows that median particle size diameter of calcium oxide significantly decreased by about 76-95 % with increasing of both calcination temperature and holding time. Additionally, specific surface area of calcium oxides determined by N₂ adsorption experiment at-195 °C shows that surface area of calcium oxide dramatically decreased (37-84 %) with increasing both calcination temperature from 800 to 900 °C and calcination time from 1 to 4 hours. These results indicated that both calcination temperature and time play an important role in the shrinkage of pores of calcium oxide. Higher calcination temperature and longer holding time induce more shrinkage of pore leading to smaller particle size diameter and lower surface area of the calcium oxide catalyst.

Abstract: Under the background of shrinkage cracking of cement and concrete, ettringite is regarded as the most effective expansion source because of its outstanding expansion characteristics. In order to study the expansion mechanism of ettringite, the growth process and formation conditions of ettringite in composite cement system were studied by means of SEM, MIP and ICP. The effects of pore structure and ion concentration of pore solution on the morphology and expansion properties of ettringite were also analysed in this paper. The results show that the pore structure of cement paste directly affects the expansion properties of ettringite. It is verified that there is no obvious linear relationship between the expansion rate of ettringite and its quantity. The concentration of SO₄^2- and Al(OH)₄^- in pore solution is the determinant of ettringite formation rate and quantity in composite cement system at the initial stage of hydration reaction. The change of crystallinity of ettringite will be directly caused by pH.

Abstract: Alkylbenzene sulfonates (ABS) is used widely in many industrial and commercial products as surfactants. However, their appearance could cause side effects when released to the environment without treatment. Adsorption method using porous carbon is one of the effective methods to reduce its presence in nature. The aim of this research is to investigate the characters and performances of new type of porous carbon of Jaranan wood carbon (Lannea coromandelica) for ABS removal. Commercial carbon from coconut shell was also used as a comparison. Porous carbons were characterized using scanning electron microscopy SEM and N₂-sorption analyzer. From characterizations, Jaranan wood carbon obtained a higher specific surface area (ca. 1080 m² g^‒1) than the commercial one (ca. 974 m² g^‒1). In the ABS removal test, a lower temperature adsorption is more favorable. The performance of Jaranan wood carbon is comparable to that of commercial porous carbon with uptake capacity up to 3036 mg g^‒1 carbon at 30 °C.

Abstract: Chemical admixtures are frequently used to regulate the setting and strength development of concrete materials. In this study, tricalcium silicate (C₃S) was used as a model of the cement system, and the influence of calcium chloride, an extremely useful accelerator, on C₃S hydration and the pore structure of hardened C₃S paste were investigated by the combination of the techniques of differential scanning calorimetry (DSC) and the N₂ adsorption (BET). The results indicated that the addition of calcium chloride would significantly shorten the pre-induction and induction periods and enhance the specific surface area and porosity of hardened C₃S paste. However, the presence of CaCl₂ has little effect on the pores, with a width ranging from 2.5 nm to 5 nm. DSC technique has an advantage of measuring continuously the process of C₃S hydration by changes of free water in hydrated C₃S.

Abstract: Magnesia inorganic lightweight material was prepared by using magnesium cementitious materials as raw materials, sodium silicate solution as modifier, hydrogen peroxide solution as foaming agent, manganese dioxide as activator, calcium stearate as stabilizer and polyacrylamide as thickener in this paper. The effects of sodium silicate addition on the apparent density, mechanical strength, pore structure, crystalline phase and water resistance of magnesia inorganic lightweight material were discussed. The results show that when the content of sodium silicate is 7.5‰, the pore structure presents better morphology and the crystallization contains more 5·1·8 phases (strength phase). At this moment, the compressive strength and bending strength of the composite reached 10.35 MPa and 2.22 MPa, respectively. When the addition of sodium silicate exceeded 7.5‰, SEM and EDS presented that a large amount of sodium silicate and perforation appeared in the pores, meanwhile large number of perforations occurred between pores. XRD showed that the 5·1·8 phases and 3·1·8 phases in the materials changed into Mg (OH)₂ crystals. These results in a significant decrease in material properties. Keywords: Magnesium cementitious material; Sodium silicate; Inorganic light materials; Pore structure

Abstract: Effect of chelating additive on microstructure, hydration products and mechanical property of mortar under different curing conditions was investigated. The microstructure was tested by nuclear magnetic resonance and scanning electron microscope. And the chemical composition of hydration products was analyzed by X-ray diffraction. The compressive strength was measured under different curing conditions at different curing age, including standard curing, water immersion, seawater immersion and salt mist curing. After curing for 28 days in water, compared to control mortar, the reduction ratio of harmful pores whose size larger than 0.1μm in mortar with chelating additive (CA mortar) was 14.6%, followed by 8.9%, 9.2% and 2.9% which was under standard curing, seawater immersion and salt mist curing, respectively. From the scanning electron microscope image, there were more needle-like and bar-like crystals in CA mortar making it more compact, which was mainly calcium silicate hydrate through component analysis. Besides, the raising percentage of compressive strength of CA mortar under water immersion is 28.6% compared to control mortar at the age of 28 days, followed by 26.8%, 21.8% and 16.3% which was under standard curing, seawater immersion and salt mist curing, respectively. The results indicate that chelating additive can enhance compactness and compressive strength of cement-based materials especially under water immersion by promoting the formation of calcium silicate hydrate.

Abstract: In this paper, the extruded precursors were prepared by Powder compact method (PCM),with two different powder AlSi10 or pure Al mixed foaming agent ZrH₂ or TiH₂, then they were foamed to fill the hollow part. L9 (3³) orthogonal test was planned, including three factors, furnace temperature; foaming time; and arrangement mode. The results indicated that the pore structure were effectively improved through adjusting the arrangement mode of precursors. The specimens have been obtained the homogeneous foam expansion when the AlSi10-TiH₂ agent were arranged on the top while AlSi10-ZrH₂ agent precursors at the bottom in the hollow, and foamed 14 min~16 min at 800 °C

Abstract: This research focuses on influence of pore structure on chloride distribution in surface layer of cement paste under cyclic wet-dry condition. The results of chloride distribution reveal that drying and wetting cycles can lead to a peak value of chloride content (C_max) occurring in surface layer of cement paste. C_max increases with the increase of W/C. While the depth (Δx) at which C_max appears does not show a regular change. Moreover, C_max should be used to predict service life of concrete structures when C_max appears in the chloride profiles. For the influence of pore structure, there exists an obvious hyperbolic relationship between chloride diffusion coefficient (D), C_max and pore structure parameters. D and C_max increase with total porosity and the most probable pore diameter, decrease with tortuosity, and stabilize gradually. And the most probable pore diameter has the most significant impact on D and C_max. In addition, XRD and SEM-EDS results indicate that the deposition of Friedel’s salt results in the formation of more inkbottle shaped pores, which may cause the appearance of C_max under cyclic drying-wetting conditions due to hysteretic moisture effect.