Green synthesis of ZSM-5 using silica fume and catalytic co-cracking of lignin and plastics for production of monocyclic aromatics

ZSM-5 with hierarchical pore structure was synthesized by a simple two-step hydrothermal crystallization from silica fume without using any organic ammonium templates.The synthesized ZSM-5 were oval shaped particles with a particle size about 2.0 μm and weak acid-dominated with proper Brønsted(B)and Lewis(L)acid sites.The ZSM-5 was used for catalytic co-cracking of n-octane and guaiacol,lowdensity polyethylene(LDPE)and alkali lignin(AL)to enhance the production of benzene,toluene,ethylbenzene and xylene(BTEX).The most significant synergistic effect occurred at n-octane/guaiacol at 1:1 and LDPE/AL at 1:3,under the condition,the achieved BTEX selectivity were 24%and 33%(mass)higher than the calculated values(weighted average).The highest BTEX selectivity reached 88.5%,which was 3.7%and 54.2%higher than those from individual cracking LDPE and AL.The synthesized ZSM-5 exhibited superior catalytic performance compared to the commercial ZSM-5,indicating potential application prospect.

Effect of Different Silica Fumes on Properties of Al_(2)O_(3)-SiC-C Castables for Iron Trough

In order to improve the performance of Al_(2)O_(3)-SiC-C castables for iron trough,samples were prepared using brown corundum,dense corundum,activated alumina micropowder,ball pitch,and silicon as main raw materials,calcium aluminate cement as the binder.Several kinds of silica fumes(93SiO_(2),96SiO_(2),and 99SiO_(2))with different particle size distributions and chemical composition were added to research the effects on the properties of castables.The results show that the sample with 99SiO_(2) fume has high water requirement for molding,but the bulk density is the lowest,the apparent porosity is the highest,the oxidation resistance is the worst,and the permanent linear change on heating is low after firing at 1 450 ℃ for 3 h.The bulk density and the apparent porosity of the sample with 93SiO_(2) fume or 96SiO_(2) fume are equivalent,the hot modulus of rupture of the sample with 93SiO_(2) fume is the lowest,and the slag resistance of the sample with 96SiO_(2) fume is the best.The comprehensive performance of the sample with 96SiO_(2) fume is the best.

On the Combination of Silica Fume and Ceramic Waste for the Sustainable Production of Mortar

The combined use of silica fume(SF)and ceramic waste(CW)for the production of mortar is studied.Sand is replaced by 5%,10%,15%and 20%of CW while a fixed 5%percentage(%wt of cement)of SF is used.The results show that the best results are obtained by using silica fume and ceramic waste sand with 15%weight of sand and 5%wt of cement.With the addition of sand ceramic waste(SCW),the mortar compressive strength and density increase,while the porosity displays an opposite trend.The experimental analysis is complemented with theoretical considerations on the matrix strength and related improvements in mechanical behavior.It is shown that the agreement between the experimental values and the estimated values is good.

Enhancing Concrete Properties Using Silica Fume:Optimized Mix Design

In the current work concrete mixes containing(7.0-33.11)weight%silica fume as fractional substitution of cement with water/cement ratio(0.42-0.48)were formulated conferring to an implemented two factorial central composite design.The samples were water cured for 7,28,56,and 90 days.The samples were tested for compressive strength and density.The experimental results approved that compressive strength and density increase with age and with rising silica fume content up to 11.9 wt.%.Response surface analysis results for samples cured for 28 days confirmed that silica fume concrete with developed compressive strength(53.42 MPa)could be prepared by incorporation of 11.9 wt.%silica fume as a substituent for cement using a 0.42 water/cement ratio.An intensification in compressive strength and density(up to 39.3%and 2.6%)respectively was recorded for silica fume concrete mixes in contrast to Portland cement concrete.Overall,the research findings revealed that silica fume concretes prepared with appropriate silica fume content and water/cement ratio exhibited superior strength and density features candidate them to be used effectively in civil engineering structural applications.

Utilization of Cement Kiln Dust (CKD) with Silica Fume (SF) as a Partial Replacement of Cement in Concrete Production

This research aimed to clarify the role of by-product materials, such as CKD with SF as partial replacement by weight of cement in concrete manufacturing and inclusion on different characteristics of concrete. Concrete test specimens were mixed with 0%, 5%, 10%, 15%, 20% and 25% (CKD) with 15% (SF) as partial replacement by weight of Cement (CEM I-52.5N). Fresh concrete properties have been evaluated by workability measurement slump test. While hardened concrete properties have been evaluated by compressive, split tensile and flexural strengths tests at ages 7, 28 and 56 days, but evaluated for bond strength, modulus of elasticity and chemical composition measurement with X-Ray Fluorescence at age of 28 days. The test results have revealed that the increase of CKD amount with fixed amount of SF in concrete mixtures as partial replacement by weight of cement leads to gradual decrease of fresh concrete workability. In concrete mixtures, 20% CKD in the presence of 15% SF as partial replacement by the weight of cement are the optimum ratios which can be used without any negative effect on mechanical properties compressive, indirect tensile, flexural and bond strength at all the ages of concrete. Also modulus of elasticity and bond strength increased by 8.81% and 0.69% respectively at the age 28 days compared with control mixture.

A Comparative Study on the Pozzolanic Activity between Nano-SiO_2 and Silica Fume

The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction （ XRD ） , differential scanning calorimetry （DSC）, scanning electron micrascopy （SEM） and the compressive , bond and bending streugths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca（OH）2 and nano-SiO2, the reaction rate of Ca（ OH）2 with nano- SiO2 and the velocity of C-S-H gel formation from Ca （ OH）2 with nano-SiO2 showed marked increases over those of Ca（ OH）2 with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% .NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO2 was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO2, the Ca（ OH）2 crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.

Effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete

The effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete （SCGC） was investigated in this paper. The work focused on the concrete mixes with a fixed water-to-geopolymer solid （W/Gs） ratio of 0.33 by mass and a constant total binder content of 400 kg/m3. The mass fractions of silica fume that replaced fly ash in this research were 0wt%, 5wt%, 10wt%, and 15wt%. The workability-related fresh properties of SCGC were assessed through slump flow, V-funnel, and L-box test methods. Hardened concrete tests were limited to compressive, splitting tensile and flexural strengths, all of which were measured at the age of 1, 7, and 28 d after 48-h oven curing. The results indicate that the addition of silica fume as a partial replacement of fly ash results in the loss of workability; nevertheless, the mechanical properties of hardened SCGC are significantly improved by incorporating silica fume, especially up to 10wt%. Applying this percentage of silica fume results in 4.3% reduction in the slump flow; however, it increases the compressive strength by 6.9%, tensile strength by 12.8% and flexural strength by 11.5%.

Influence of Fly Ash and Silica Fume on Water-resistant Property of Magnesium Oxychloride Cement

By incorporation of fly ash or silica fume into magnesium oxychloride （MOC） cement, a high water resistance material can be formed for successful industrial applications. The influences of fly ash and silica fume on water-resistant property were investigated by SEM and EDS. It is found that the incorporation of fly ash or silica fume can improve the water-resistance of the MOC. The improvement of the water resistance of the MOC incorporated with fly ash or silica fume may be attributed to the alumino-silicate 5·1·8 gel or silicate 5·1·8 gel.

Analysis of the Damping Behavior and Microstructure of Cement Matrix with Silane-treated Silica Fume

The surface treatment of silca fume with silane coupling agent prior w incorporation in a cement mortar resulted in composites exhibiting increuses in loss tangent by 5%-200% and storage modulus by 10%-20% , relative to the value obtained by using as-received silica fume. The scanning electron microscopy （SEM） images iindicate that there is a morphological difference in the cement paste with treated and as-received silica fume, The, X-ray diffraction （XRD）, infrared （IR） spectrum analyses and mercury intrusion porosimetry （ MIP ） have provided evidence to understand the reaction mechanism between treated silica .fume and the hydrate product of cement. This has led to the establishment of an initial microscopic model describing the damping behavior of cement matrix.

Replacement of alkali silicate solution with silica fume in metakaolin-based geopolymers

A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.

THE PROPERTIES OF SILICA FUME-MAGNESIUM OXYCHLORIDE CEMENT MATERIALS

The properties of a new magnesium Oxychloride cement (MOC) material formed by silica fume uniformly mix in MOC paste was presents. The influence of silica fume on the water resistance and compressive strength of MOC paste was invesigated in this study. It is shown that when 30 weight percent of silica fume is added to the MOC paste, a high strength and water resisting new material with 112MPa compressive strength and 1 00 water resisting coefficient could by obtained.

Influence of Silica Fume on the Reflectivity and Transmission Efficiency of Cement-Based Materials

As a kind of mineral admixture, silica fume has low permittivity, which will affect the electromagnetic properties of cement-based materials. To study the effect of silica fume on the properties of cement-based materials, the reflectivity, transmission efficiency and pore structure were analyzed by using the vector network analyzer and mercury injection apparatus. Results show that silica fume can make the mortar more compact and the porosity of sample with 9% silica fume is only 17.8%, which is far lower than the control sample;With the increase of the silica fume content, the peak of reflectivity curve increases from -23.2 dB to -16.0 dB, and then decreases from -16.04 dB to -28.7 dB in the frequency range of 6 – 18 GHz. Reflectivity of sample with 3% content of silica fume is lower than other samples within 26.5 - 40 GHz;Transmission efficiency of samples shows the trend of increase with silica fume content increases from 0% to 6% within 8.2 - 12.4 GHz, 12 - 18 GHz and 26.5 - 40 GHz, but when the content increases from 6% to 9%, the transmission efficiency of samples reduces.

Effect of Silica Fume on Compressive Strength of Oil-Polluted Concrete in Different Marine Environments

In the present research, effect of silica fume as an additive and oil polluted sands as aggregates on compressive strength of concrete were investigated experimentally. The amount ofoil in the designed mixtures was assumed to be constant and equal to 2% of the sand weight. Silica fume accounting for 10%, 15% and 20% of the weight is added to the designed mixture. After preparation and curing, concrete specimens were placed into the three different conditions： fresh, brackish and saltwater environments （submerged in fresh water, alternation of exposed in air ＆ submerged in sea water and submerged in sea water）. The result of compressive strength tests shows that the compressive strength of the specimens consisting of silica fume increases significantly in comparison with the control specimens in all three environments. The compressive strength of the concrete with 15% silica fume content was about 30% to 50% higher than that of control specimens in all tested environments under the condition of using polluted aggregates in the designed mixture.

Rheological behavior of fumed silica suspension in polyethylene glycol

The rheological behavior of fumed silica suspensions in polyethylene glycol(PEG) was studied at steady and oscillatory shear stress using AR 2000 stress controlled rheometer. The systems show reversible shear thickening behavior and the shear-thickening behavior can be explained by the clustering mechanism. The viscosity and the degree of shear-thickening of the systems strongly depend on the mass fraction of the silica, the molecular weigh of PEG and the frequency used in the rheological measurement. The silica volume fraction of the systems is 1.16% 3.62%, corresponding to the mass fraction of 4%9%. The shear-thickening taking place in the low volume fraction may contribute to the fractal nature of the silica. At oscillatory shear stress, when the shear stress is less than the critical stress, the storage modulus decreases significantly, meanwhile the loss modulus and the complex viscosity almost remain unchanged; when the shear stress is larger than the critical stress, the storage modulus, the loss modulus and the complex viscosity increase with the increase of shear stress. The loss modulus is larger than the storage modulus in the range of stress studied and both moduli depend on frequency.

Packing Density Improvement through Addition of Limestone Fines, Superfine Cement and Condensed Silica Fume

Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To obtain a high packing density, powders with different particle sizes, including limestone fines (LSF), superfine cement (SFC), condensed silica fume (CSF), were added to the cement paste and the resulting packing densities were measured directly by a newly-developed wet packing test. Results demonstrated that addition of powders with a finer size would more significantly improve the packing density but the powders should be at least as fine as 1/4 of the OPC to effectively improve the packing density. Packing density and voids ratio relationship showed that a small increase in packing density can significantly decrease the voids ratio, which could allow the W/P ratio to be reduced to improve the strength and durability of the concrete without compromising the flowability.

Effect of Silica Fume on the Thaumasite Form of Sulfate Attack on Cement-based Materials

Thaumasite form of sulfate attack（TSA） can be observed in cement containing limestone under sulfate condition at low temperature. Mixing with suitable mineral admixture could be a good choice to improve the TSA resistance performance of cement-based materials. We investigated the durability performance of limestone-cement mortars reinforced with silica fume（SF） in 5% MgSO_4 solution at 5 ℃. The mortars, which were immersed in aggressive condition, were prepared with 2%, 4%, 6%, 8%, and 10% cement replacement by SF at a fixed water-to-binder ratio. Appearance, compressive strength, change of length and mass and corrosion products were investigated to evaluate the TSA resistance performance of SF based specimens. The results showed that specimens in the absence of SF almost disintegrated. Increasing SF dosage can reduce the degree of deterioration of SF mortars in TSA environment. Mortar mixtures with more than 6% SF merely show slight degeneration in relation to macroscopic and microscopic tests and characterizations.

Effect of Fly Ash and Silica Fume on Hydration Rate of Cement Pastes and Strength of Mortars

The effect of fly ash and silica fume on hydration rate and strength of cement in the early stage was studied. Contrast test was applied to the complex cementitious system to investigate the hydration rate. Combined with mechanical strength, the influence of fly ash and silica fume during the hydration process of complex binder was researched. The peak of the rate of hydration heat evolution and the mechanical strength decreased as the ratio of fly ash increased, however, as the ratio of silica fume increased, the peak of the rate of hydration heat evolution and the mechanical strength increased obviously. When the ratios of fly ash and silica fume are 10% and 5%, the peak of the rate of hydration heat evolution is the highest. At the same time 7 days of flexural and compressive strength are the highest as 8.89 MPa and 46.52 MPa, respectively. Fly ash and silica fume are the main factors affecting the hydration rate and the mechanical property.

Hydration Mechanism of Silica Fume- sulphoaluminate Cement

Setting time and strength of sulphoaluminate rapid hardening cement （SAC） incorporated in the presence and absence of silica fume （SF） were determined. Combined with the techniques of＂ isothermal calorimeter, XRD and FSEM, the hydration kinetics of the two systems and the effect mechanism of SF on SAC were investigated. The experimental results showed that SF was proved to be beneficial for SAC system, in terms of setting time and late strength gain. Evidence of accelerator effect of silica fume was found during the first 8 hours of hydration. The formation of AFt was accelerated and the microstructure of the hydration products grew denser with incorporation of SF. SF was proved to play the role of dispersion and setting control at early age and had a greater contribution to later strength due to the increment of crystal nucleation point and the pozzolanic activity. Therefore, SF can be used to not only control the hydration kinetics of SAC, but also develop the late strength and improve the microstructure.

Reactivity of Fine Quartz in Presence of Silica Fume and Slag

Dune sand is a very abundant material in south of Algeria. Its high silica content gives a partial pozzolanic reactivity due to its crystalline state. This paper investigates the evolution of cement hydration based on a binary addition particularly the reactivity of dune sand finely ground in the presence of an amorphous addition: silica fume or blast furnace slag. Thus, four combinations of binary additions by substitution have been chosen. The X-ray diffraction analyses performed on cement pastes containing additions have shown the importance of the mineralogy and silica content of additions on their pozzolanic reactivity. Dune sand becomes reactive at long term, especially when associated up to 10% of amorphous addition (blast furnace slag or silica fume). It results an increasing in mechanical strength of Ultra High Performance Concrete (UHPC) and an improvement of the microstructure.

Microstructure and Mechanical Properties of Poly (Vinyl Chloride) Modified by Silica Fume /Acrylic Core-Shell Impact Modifier Blends

This research explored replacing acrylic core-shell impact modifier （AIM） by silica fume to toughen PVC. 100%, 75%, 50% and 25% of AIM （8 phr） were substituted by silica fume in PVC respectively, and then processed by dry blending and twin-screw extrusion. Severe silica fume agglomeration was observed by scanning electron microscope （SEM） in the PVC matrix when 8 phr pure silica fume was used and processed by screw speed of 20 rpm. Its tensile strength was thereby reduced by 38% comparing to unmodified PVC. The silica fume was successfully dispersed while the screw speed was slowed down to 10 rpm to give a stronger screw torque and a longer melt residential time in the extruder. The tensile strength was ’recovered’ to a level comparable to unmodified PVC. Impact test were performed on all formulations extruded at 10 rpm screw speed and synergetic toughening effect was found with 50% substitution and it had the impact strength that was comparable to 8 phr pure AIM toughened PVC.