Effect of hydrothermal curing on early hydration of G-Oil well cement

G-Oil well cement has been cured under standard and hydrothermal conditions with different steam pressures and temperatures. Compressive strength, pore structure parameters, microstructure, and hydrated products were evaluated after 7 days curing by using SEM, MIP, and simultaneous TGA/DSC. Obtained results showed that 7 days aged sample cured under standard conditions has the highest compressive strength with compact pore structure and hydrated products similar to those found after hydration of Ordinary Portland cement. With increasing temperature and pressure from standard conditions (25 °C, 10125 Pa) to hydrothermal ones (150 °C and 0.3 MPa, 200 °C and 1.2 MPa), compressive strength has drastically decreased from 77.5 ± 2.0 to 20.5 ± 1.0 MPa due to the transformation of original hydrated products (C–S–H) to crystallized α-C₂SH and C₆S₂H₃. The crystallization has led, under hydrothermal curing, to the increase of permeability and pore structure depletion. The final compressive strength after curing for 7 days at 150 °C (51.8 ± 2.0 MPa) and 200 °C (20.5 ± 1.0 MPa), which significantly exceeds the recommended values of 3.45 MPa according to API to hold many casings of oil wells is questionable for application in geothermal ones.     

Effect of additives on the performance of Dyckerhoff cement,Class G,submitted to simulated hydrothermal curing

Stability of Dyckerhoff cement Class G partially substituted (15 mass%) by metakaolin (MK), silica fume (SF) and ground granulated blast-furnace slag (BFS) was investigated after 7 days of curing under standard and two different autoclaving conditions. Mercury intrusion porosimetry, X-ray diffraction analysis and combined thermogravimetric–differential scanning calorimetry were used to evaluate pore structure development, compressive strength and their dependence on the type of additives in relation to the particular phase composition. Hydrothermal curing led to the formation of α-C₂SH and jaffeite, mostly in the case of referential samples and compositions with addition of slowly reacting BFS. Whilst modest hydrothermal curing (0.6 MPa, 165 °C) favoured formation of α-C₂SH, larger amounts of jaffeite were determined after curing at the highest used pressure and temperature (2.0 MPa, 220 °C). Undesired transformation of primary hydration products was prevented especially by addition of highly reactive and very fine SF. Particular composition attained the best pore structure characteristics and compressive strength after curing at 0.6 MPa and 165 °C. Formation of more stable phases with C/S ratio close to 1 was proved by wollastonite formation during DSC analyses. More severe conditions of curing, however, led to the significant deterioration of microstructure and strength of corresponding sample, probably due to the formation of trabzonite, killalaite and zoisite. Considering the values of hydraulic permeability coefficient and compressive strength, replacement of cement by MK improved significantly the properties of cement when compared with the referential as well as with other blended compositions under the mentioned curing conditions.     

Hydration,mechanical properties and durability of high-strength concrete under different curing conditions

The properties of high-strength concrete under standard curing condition (20 °C, 95% RH), high-temperature curing condition (50 °C) and temperature match curing condition were comparatively investigated. The cumulative hydration heat of composite binder containing fly ash and silica fume is lower than that of composite binder containing the same amount of slag. Addition of fly ash and silica fume clearly reduces the adiabatic temperature rise of concrete, but adding slag leads to higher adiabatic temperature rise than Portland cement concrete. High-temperature curing condition and temperature match curing condition lead to the sustainable increase in compressive strength of concrete containing mineral admixture, but they hinder the later-age strength development of Portland cement concrete. For cement–slag paste and cement–fly ash–silica fume paste, the non-evaporable water contents increase significantly and the pore structures are much finer under high-temperature curing condition and temperature match curing condition, which negatively affect the pore structure of Portland cement paste. The differences in properties of concrete among three curing conditions become smaller with time. The properties obtained under standard curing condition can approximately reflect the long-term properties of high-strength concrete in the real structure. The concrete prepared with cement–fly ash–silica fume composite binder has the highest compressive strength, finest pore structure and best resistance to chloride permeability under any curing condition. This composite binder is very suitable to prepare the high-strength concrete with large volume.     

Thermogravimetry of ternary cement blends

This study reports the microstructure characteristic and compressive strength of multi-blended cement under different curing methods. Fly ash, ground bottom ash, and undensified silica fume were used to replace part of cement at 50 % by mass. Mortar and paste specimens were cured in air at ambient temperature, water at 25, 40, and 60 °C and sealed with plastic sheeting for 28 days. In addition, these specimens were cured in an autoclave for 6, 9, and 12 h. Results indicated that the compressive strength of multi-blended mixes containing silica fume 10 % by mass cured with plastic sealed and cured in water at 25 and 40 °C was similar to or higher than the corresponding Portland cement control at 28 day. Moreover, the mixes containing silica fume 10 % by mass cured in water at 60 °C had higher compressive strength than Portland cement control. X-ray diffraction and thermogravimetry results confirmed that there was increased pozzolanic reaction with increasing silica fume content which relates to the increasing in strength. For autoclaved curing, the compressive strength of multi-blended cement specimens with silica fume (total of 50 % replacement) was noticeably higher than control Portland cement mix and was highest when autoclaving time was 9 h. X-ray diffraction results showed the pattern of 0.9, 1.1, and 1.4 nm tobermorite crystalline phases as the main product of this curing. Thermogravimetry results showed dehydration of 1.4 nm tobermorite and 1.1 nm tobermorite at about 80–90 and 135–150 °C, respectively. Tobermorite (also shown by scanning electron microscope) thereby as a result lead to significant compressive strength improvement in the short time of autoclaved curing.     

A comparison of early hydration properties of cement–steel slag binder and cement–limestone powder binder

The early hydration properties of cement–steel slag composite binder and cement–limestone powder composite binder were compared in this study by determining the hydration heat of binder within 3 days, the pore structure of paste and the compressive strength of mortar at the age of 3 days. Results show that at the curing temperature of 25 °C, the early hydration heat of the binder containing steel slag is smaller, and the early pore structure of the paste containing steel slag is coarser, but the early compressive strength of the mortar containing steel slag is higher compared with the mix containing limestone powder. Though the early reaction degree of steel slag is low, its chemical contribution to the strength of mortar cannot be neglected. At the curing temperature of 50 °C, the early hydration heat of the binder containing steel slag is larger, and the early pore structure of the paste containing steel slag is finer, and the early compressive strength of the mortar containing steel slag is even higher compared with the mix containing limestone powder. Raising curing temperature can enhance the role played by steel slag more significantly than that played by limestone powder in the hydration and hardening of the composite binder.     

Adsorption properties of ordered mesoporous silicas synthesized in the presence of block copolymer Pluronic F127 under microwave irradiation

Ordered mesoporous silicas (OMSs) were prepared at different temperatures by using tetraethyl orthosilicate (TEOS) as a silica source, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (Pluronic F127) as a structure directing agent and sodium chloride as an additive under acidic conditions and microwave irradiation. The small angle X-ray diffraction patterns of these samples indicate the presence of ordered mesopores, while adsorption studies show that they possess high volumes of pores, bimodal pore size distributions and large pore sizes. There is an interesting change in the hysteresis loop of nitrogen adsorption isotherms with increasing temperature of hydrothermal treatment; a delayed desorption characteristic for cage-like mesostructures is observed for the OMS samples treated at 100 and 120?°C, while the hydrothermal treatment at 140 and 160?°C leads to the samples having hysteresis loops characteristic for channel-like materials.     

A Modified Nanoporous Silica Aerogel as a New Sorbent for Needle Trap Extraction of Chlorobenzenes from Water Samples

In this work, a modified nanoporous silica aerogel was used as a new sorbent for headspace needle trap extraction of chlorobenzenes from aqueous samples. The needle trap extraction is derived from solid-phase microextraction and the sorbent is inside the needle. The thermal stability and functional groups of the sorbent were studied by TG/DTA and FT-IR, respectively. The modified silica aerogels, characterized by field emission scanning electron microscopy, showed a three-dimensional network containing a homogeneous pore structure with pore sizes of a few tens of nm and a sponge-like microstructure. The developed method was applied to the trace level extraction of some chlorobenzene compounds from aqueous samples. The influential parameters on the extraction efficiency, including the extraction temperature, ionic strength and extraction time were investigated and optimized. Under optimized conditions, the detection and quantification limits were in the range of 0.4–0.8 and 1–3 ng L^?1, respectively. The relative standard deviation values for water spiked with chlorobenzenes at 100 ng L^?1 under optimum conditions were 3–7%. The dynamic linear range of the method in the range of 3–3000 ng L^?1 was investigated. Finally, the current method for the analysis of real water samples containing spiked chlorobenzenes was applied and the relative recovery values were found to be in the range of 96–101%.     

Influence of pre-curing time on the hydration of binder and the properties of concrete under steam curing condition

There is a pre-curing period before the freshly made concrete elements were exposed to steam curing in the steam curing process. In this paper, the influence of pre-curing time on the hydration of binder and the properties of concrete under steam curing condition was investigated. Three binders were used: the pure cement, the binder containing high content of GGBS, and the binder containing high content of fly ash. Three pre-curing times (1, 3, and 6 h) and one steam curing period at 60 °C (over 8 h) were adopted. Results show that pre-curing time has limited influence on the hydration degree of binder, and compressive strength and pore structure of paste. The influence of pre-curing time has limited influence on the compressive strength and chloride permeability of the pure cement concrete and the concrete containing high content of GGBS at whether early or late ages, indicating that the proper pre-curing time can be as short as 1 h for these two concretes. Increasing pre-curing time enhances the late-age compressive strength of the concrete containing high content of fly ash significantly, but it has limited influence on the late-age permeability.     

Phase Transformation of Hydrothermally Stressed Adsorbents

Inorganic materials of zeolite type, silica gel or related materials are used as adsorbents in air conditioning machines. The cooling effect is obtained by evaporation of water thereby the adsorbent acts as pump system. After itôs saturation, the storage must be regenerated by heating. The hydrothermal stress may generate decomposition of their structure accompanied by a loss of sorption capacity. This work describes the hydrothermal stability of AlPO‐5, SAPO‐34, and silica gel in comparison with a newly developed dealuminated Y zeolite DAY. DAY (Si/Al = 3.1) and AlPO‐5 zeolites are hydrothermally stable over a wide temperature range even under harsh condition of maximum water loading of their pore system. DAY exhibits a higher water sorption capacity but becomes amorphous with increasing temperature, whereas AlPO‐5 transforms into a tridymite analogous crystalline phase with an intermediate state at 140 °C. But, both phase transformation processes are not relevant for the application of the compounds in low‐temperature driven heat pumps due to less hydrothermal stressing there. SAPO‐34 decomposes already under mild hydrothermal conditions. In analogy to AlPO‐5 it forms the tridymite analogous structure at high temperature. The silica gel looses the sorption capacity systematically because of the healing of its structure by condensation of free silanol groups, whereby Q² and Q³ groups change into Q⁴ groups.     

大孔硅胶的制备及其在多糖衍生物手性固定相上的应用

为制备孔径为100 nm的大孔硅胶,考察了热液法和焙烧法对球形硅胶（粒径5 μm,孔径10 nm）的扩孔效果。采用热液法扩孔时,在水溶液中加入22 g/L氟化钠,可以有效增强扩孔效果,在高压釜内160℃加热48 h便可扩孔至100 nm,但孔径不均匀。采用焙烧法扩孔时,通过调节焙烧温度、时间以及复盐LiCl-NaCl的加入量可以方便地控制扩孔速度与效果;在每10 g硅胶中加入1.125 g LiCl·H₂O和0.75 g NaCl,于500℃焙烧3~5 h,可得到100 nm大孔硅胶;该方法简单、高效,扩孔后的硅胶孔径分布均匀,表面形态与商品化的Fuji-1000硅胶相似。将两种扩孔方式得到的硅胶经氨基修饰后,涂覆纤维素-三（3,5-二甲基苯基氨基甲酸酯）制得了相应的手性固定相。结果表明,采用焙烧法扩孔得到的硅胶制备的固定相明显具有较好的分离选择性及分离度。     

Influence of cross profile of PE fibers on thermal properties of materials

Molecular sieves MCM-41 were synthesized from rice husk ash (RHA) as alternative sources of silica, called RHA MCM-41. The material was synthesized by a hydrothermal method from a gel with the molar composition 1.00 CTMABr:4.00 SiO₂:1.00 Na₂O:200.00 H₂O at 100 °C for 120 h with pH correction. The cetyltrimethylammonium bromide (CTMABr) was used as a structure template. The material was characterized by X-ray powder diffraction, FTIR, TG/DTG, and surface area determination by the BET method. The kinetics models proposed by Ozawa, Flynn–Wall, and Vyazovkin were used to determine the apparent activation energy for CTMA⁺ species decomposition from the pores of MCM-41 material. The results were compared with those obtained from the MCM-41 synthesized with silica gel. The synthesized material had specific surface area, size, and pore volume as specified by mesoporous materials developed from conventional sources of silica.     

Metallic nickel supported on mesoporous silica as catalyst for hydrodeoxygenation: effect of pore size and structure

Catalytic hydrodeoxygenation (HDO) of anisole, a methoxy-rich lignin-derived bio-oil model compound, was carried out over a series of Ni-containing (5, 10, 20, and 30 wt%) catalysts with commercial silica and ordered mesoporous silica SBA-15 as support. Both supports and catalysts were characterized by N₂ adsorption–desorption isotherms, X-ray diffraction, CO chemisorption, and transmission electron microscopy (TEM). Catalytic reaction was performed at 250 °C and 10 bar H₂ pressure. Depending on the catalyst support used and the content of active metal, the catalytic activity and product distribution changed drastically. Increase of the nickel loading resulted in increased anisole conversion and C₆ hydrocarbon (benzene and cyclohexane) yield. However, loading more Ni than 20 wt% resulted in a decrease of both conversion and C₆ yield due to agglomeration of Ni particles. In addition, Ni/SBA-15 samples exhibited much stronger catalytic activity and selectivity toward C₆ hydrocarbon products compared with Ni/silica catalysts. The differences in catalytic activity among these catalysts can be attributed to the effect of the pore size and pore structure of mesoporous SBA-15. SBA-15 can accommodate more Ni species inside channels than conventional silica due to its high pore volume with uniform pore structure, leading to high HDO catalytic activity.     

Strong cellulose nanofibre–nanosilica composites with controllable pore structure

Flexible nanocellulose composites with silica nanoparticle loading from 5 to 77 wt% and tunable pore size were made and characterised. The pore structure of the new composites can be controlled (100–1000 nm to 10–60 nm) by adjusting the silica nanoparticle content. Composites were prepared by first complexing nanoparticles with a cationic dimethylaminoethyl methacrylate polyacrylamide, followed by retaining this complex in a nanocellulose fibre network. High retention of nanoparticles resulted. The structural changes and pore size distribution of the composites were characterised through scanning electron microscopy (SEM) and mercury porosimetry analysis, respectively. The heavily loaded composites formed packed bed structures of nanoparticles. Film thickness was approximately constant for composites with low loading, indicating that nanoparticles filled gaps created by nanocellulose fibres without altering their structure. Film thickness increased drastically for high loading because of the new packed bed structure. Unexpectedly, within the investigated loading range, the level of the tensile index on nanocellulose mass basis remained constant, showing that the silica nanoparticles did not significantly interfere with the bonding between the cellulose nanofibres. This hierarchically engineered material remains flexible at all loadings, and its unique packing enables use in applications requiring nanocellulose composites with controlled pore structure and high surface area.     

Influences of pore size on production of 2-methylpyrazine over bifunctional CuO/ZnO/meso-SiO2 catalysts

Controllable crystallite size of CuO in CuO/ZnO/meso-SiO₂ catalysts was successfully realized by impregnation method using mesoporous silica with different pore diameters as support. Characterization techniques such as N₂ adsorption/desorption, X-ray diffraction, H₂ temperature-programmed reduction, and potentiometric titration were employed to investigate the influences of pore size on textural properties, crystalline phases, reducibility, and acidity. Catalytic evaluation of synthesis of 2-methylpyrazine was carried out at 380 °C under atmospheric conditions. The best catalytic performance was achieved over catalyst CZ/S1 supported on the carrier with smallest pore size.     

Strength and elasticity of bimodal porous silica prepared from water glass

The bending strength and the Young’s modulus of bimodal porous silica gels having different porosity were evaluated. The porosity of the gel increased by aging the gel under basic conditions, and decreased with increasing the calcination temperature. The mesopores disappeared on calcination at 1,050 °C, whereas continuous macropores retained their morphology up to 1,050 °C for all the samples. Both the bending strength and the Young’s modulus of the bimodal porous silica gels were expressed as power-law functions of the bulk density, and no effect of bimodal pore structures on mechanical properties was observed. We also found linear correlation between the bending strength and the elasticity. The bimodal porous silica had higher strength and elastic modulus compared with other porous materials at the same porosity probably due to the presence of homogeneous micrometer-scale macropores.     

Ordered mesoporous silica with large cage-like pores: structural identification and pore connectivity design by controlling the synthesis temperature and time

FDU-1 silicas with large cage-like pores (diameter about 10 nm) were synthesized under acidic conditions from tetraethyl orthosilicate in the presence of a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer template B50-6600 (EO(39)BO(47)EO(39)). High-resolution transmission electron microscopy and small-angle X-ray scattering provided strong evidence that FDU-1 silica synthesized under typical conditions is a face-centered cubic Fm3m structure with 3-dimensional hexagonal intergrowth and is not a body-centered cubic Im3m structure, as originally reported. Samples synthesized in a wide range of conditions (initial temperatures from 298 to 353 K; hydrothermal treatment at 333-393 K) exhibited similar XRD patterns and their nitrogen adsorption isotherms indicated a good-quality cage-like pore structure. The examination of low-pressure nitrogen adsorption isotherms for FDU-1 samples, whose pore entrance diameters were evaluated using an independent method, allowed us to conclude that low-pressure adsorption was appreciably stronger for samples with smaller pore entrance sizes. This prompted us to examine low-pressure adsorption isotherms for a wide range of samples and led us to a conclusion that the FDU-1 pore entrance size can be systematically enlarged from about 1.3 nm (perhaps even lower) to at least 2.4 nm without an appreciable loss of uniformity by increasing the temperature of the hydrothermal treatment or the initial synthesis. Further enlargement of pore entrance size was achieved for sufficiently long hydrothermal treatment times at temperatures of 373 K or higher, as seen from the shape of nitrogen desorption isotherms. This allowed us to obtain samples with uniform pore sizes, high adsorption capacity, and with pore entrances enlarged so much that their size was similar to the size of the pore itself, resulting in a highly open porous structure. However, in the latter case, there was evidence that the pore entrance size distribution was quite broad.     

A Direct and Rapid Route to Synthesize Pd/Si‐MCM‐41 at Room Temperature

The pure silica mesoporous molecular sieve MCM‐41 was synthesized under hydrothermal conditions. Pd/Si‐MCM‐41 was prepared by the incipient wetness impregnation of pure silica MCM‐41 with mixed solution of PdCl₂, ethanol and CH₂Cl₂. The samples were characterized by x‐ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption–desorption isotherms at 77 K. The XRD and TEM results reveal that Pd is actually anchored inside the pores of Si‐MCM‐41 and the Si‐MCM‐41 structure is clearly maintained after impregnation.     

A Comparison of Silica C and Silica Gel in HILIC Mode: The Effect of Stationary Phase Surface Area

In order to assess the effect of silica gel structure on retention in hydrophilic interaction chromatography, a test system was developed which used quaternary ammonium ions as probes with tetramethylammonium acetate (TMAA) as the counter-ion competing against the interaction of the test probes with ionised silanols in the stationary phase. Four silica gel columns and a silica hydride column were examined. Retention times were obtained for the test probes at 20, 40, 60, 80 and 90 % acetonitrile (ACN) with all the mobile phase mixtures containing 10-mM TMAA buffer at pH 6.0. All phases gave “U”-shaped plots for log k against percentage of ACN with the steepest rise in retention occurring between 80 and 90 % ACN. Benzyltrimethylammonium, the smallest quaternary ammonium ion, was the most strongly retained probe at 90 % ACN and was most retained on a high surface area 60 Å Kromasil column and least retained on a 300 Å ACE silica gel column. The ionic strength of the mobile phase was varied at 80 and 90 % ACN and plots of log k against the inverse of buffer strength followed by fitting of second-order polynomial curves allowed an assessment of the contribution from HILIC to the mixed HILIC/ion-exchange retention mechanism. Toluene and pentylbenzene were used to assess the decrease in accessible pore volume due to water absorption in HILIC mode.     

Fabrication and characterization of hexagonal mesoporous silica monolith via post-synthesized hydrothermal process

Large-sized, optical transparent mesostructured Brij 56/silica monolith has been fabricated using a lyotropic liquid crystal of Brij 56 (C₁₆EO₁₀) as a template and TMOS as a silica source, combined with a optimizing sol-gel process and a hydrothermal aging process. By programmed temperature drying and calcinations, translucent mesoporous silica monolith with two-dimensional hexagonal structure (P6mm) has bee obtained. The ordered mesoporous silica monoliths have been characterized by small-angle X-ray diffraction, transmission electron microscopy (TEM), and nitrogen adsorption, which shows that the materials have a highly ordered two-dimensional hexagonal mesostructure with the high specific surface area of 837 m² · g⁻¹ and narrow pore distribution with a mean BJH pore diameter of 2.73 nm. Based on calculations and differential scanning calorimetry and thermogravimetric analyses, the action mechanism of the hydrothermal aging process has been proposed: the 100°C hydrothermal conditions and autogenous 2.3 atm pressure promote the condensation and dehydration of silanol groups, with the result that cross-linking degree, the flaws and moisture content in gels are reduced notably. Those processes guarantee the integrity of gels in the following drying process.