Influence of Na_(2)SiO_(3)/NaOH Ratio on Calcined Magnesium Silicate Based Geopolymer——Experimental and Predictive Study

This study aims to investigate the behavior of alkali activated mortar,which is made of naturally available magnesium silicate as source material.For magnesium silicate,ultrafine natural steatite powder(UFNSP)is used as the primary source of binder,and the activation is initiated through the alkali liquid which is proportioned in various combinations of silicate to hydroxide ratio(Na_(2)SiO_(3)/Na OH)ratio,and this ratio in this study varies from 1 to 3.The UFNSP is calcined at two difierent temperatures,700 and 1000℃.The mortar mix is proportioned as 1:3 between powder and the fine aggregate,and the mortar is prepared with hydroxide molarity(M)of 10 M.The mortar is cured for 48 hours at 60℃and the compressive strength was studied.All the mix were studied for its microstructural behavior along with compressive strength.The mix proportion of the mortar,and the results obtained through microstructural characterization were combinedly formed as input for artificial neural network(ANN)predictive modelling.The model is designed to predict the compressive strength,which is trained through Bayesian regularization algorithm with varying hidden neurons of 7 to 10.This experimental and predictive study shows that the strength is influenced by both Na_(2)SiO_(3)/Na OH ratio and calcination process.And the ANN is influenced by mainly calcination temperature and uncorrelation occurs in selected samples of 1000℃calcined UFNSP mix.

Structure, Formation, Properties, and Application of Calcium and Magnesium Silicate Hydrates System—A Review

In order to expand the advantages of strong durability and high compressive strength of calcium silicate hydrates(C-S-H),at the same time to make up for the poor early mechanical strength of magnesium silicate hydrates (M-S-H),we present the features and advantages of C-S-H and M-S-H and a comprehensive review of the progress on CaO-MgO-SiO_(2)-H_(2)O.Moreover,we systematically describe natural calcium and magnesium silicate minerals and thermodynamic properties of CaO-MgO-SiO_(2)-H_(2)O.The effect of magnesium on C-S-H and calcium on M-S-H is summarized deeply;the formation and structural feature of CaO-MgO-SiO_(2)-H_(2)O is also explained in detail.Finally,the development of calcium and magnesium silicate hydrates in the future is pointed out,and the further research is discussed and estimated.

Adsorption of Methylene Blue on magnesium silicate: Kinetics, equilibria and comparison with other adsorbents

Batch adsorption from aqueous solutions in a slightly basic medium of Methylene Blue, up to 2500 mg/L, onto synthetic magnesium silicate （Florisil） of three particle size ranges （mean diameters of 112, 200 and 425 μm） was compared to the corresponding adsorption onto activated carbon and Amberlite XAD-2. The best fit of the kinetic results was achieved by a pseudo second-order equation. The equilibrium data were found to be well represented by the Langmuir isotherm equation. Amberlite XAD-2, an unspecific adsorbent capable of adsorbing exclusively through a surface effect, exhibited a poor dye uptake, confirming that the adsorption mechanism on Florisil was due to electrostatic attraction and ion exchange. Moreover, the comparison between Florisil and the other adsorbents was performed on the basis of the evaluation of the surface area and pore volume occupied by the adsorbed dye.

Synthesis of Long Afterglow Photoluminescent Materials Sr_2MgSi_2O_7∶Eu^(2+), Dy^(3+) by Sol-Gel Method

Long afterglow photoluminescent materials Sr2MgSi2O7 doped with Eu2+, Dy3+ were prepared by sol-gel method. The synthesized samples were characterized by X-ray diffraction. The excitation spectrum, emission spectrum and long decay curve were measured and analyzed. XRD pattern indicates that phosphor is with Sr2MgSi2O7 crystal structure. The wide range of excitation wavelength indicates that luminescent material can be excited by light from ultraviolet ray to visible light. The main peak of emission spectrum is located at 466 nm. Sample excited by visible light can emit bright blue light, and the afterglow time lasts more than 8 h.

The Reaction Mechanism between MgO and Microsilica at Room Temperature

It was proved that MgO and MicroSilica can react at room temperature, giving a hardened product primarily comprised of Mg （ OH ）2 and Magnesium Silicate Hydrate （ M- S- H ）. The reaction ratio and process and the chemical composion of M- S- H were studied and analyzed by QXRD and DTA- TG. The experimental results indicate that much Mg（ OH）2 and less M-S-H were formed at early period. After 7 days there is no change in the quantity of Mg（ OH）2, while M-S-H was increased slowly. The chemical composion of M-S-H would vary with the mix proportion in the hydrution process , but M1.32 SH2.37 is finally the approximute form.

Reaction Products of MgO and Microsilica Cementitious Materials at Different Temperatures

The paste was prepared by mixing MgO, microsilica and H2O in the presence of water reducer at different reaction ratios and temperatures, and characterized by XRD, DTA, TGA, IR, and solid-state 29Si NMR. The experimental results showed that, besides Mg（OH）2, magnesium silicate hydrate （M-S-H） was formed at a low temperature such as 25 and 50 ℃. At a high temperature of 100 ℃, Mg（OH）2 can be further transformed into M-S-H completely, for instance, within ca. 1 month in an excess of microsilica. The average composition and structure of M-S-H was mainly related to the reaction mixture and curing temperature and was discussed in detail.

Crystallization Characteristic of Periclase in Clinker and Effect of Mg2+ on Hydrate of Cement Pastes

Crystallization characteristic of periclase in clinker and effect of Mg^2+ on hydrate of cement pastes were investigated. Morphologies and relative content of periclase were characterized with scanning electron microscopy and X-ray diffraction. Derivative thermogravimetry analysis and backscattered electron imaging were used to characterize the effect of Mg^2+ on hydrate of cement pastes. The experimental results show that in ample space, periclase forms octahedron structure, and subhedral or anhedral crystal is formed in limited space. Due to the accelerated burning temperature and prolonged holding time, coarse pericalase crystals are formed. Mg(OH)2 particle thickness increases due to faster crystal growth rate along c axis at later age. Mg^2+can substitute Ca^2+ in C-S-H or C-A-H to form magnesium silicate hydrate(M-S-H) or magnesium aluminate hydrate(M-A-H), and the substitution extent for C-A-H is higher than that for C-S-H. Cured in 80 ℃ water, the decalcification rate of C-A-H in pastes is higher than that cured in 50 ℃ water. M-A-H with an atomic Mg/Al ratio of 2 is formed through substitution of Ca by Mg in C-A-H.

Thermodynamics of clayedrug complex dispersions: Isothermal titration calorimetry and high-performance liquid chromatography

An understanding of the thermodynamics of the complexation process utilized in sustaining drug release in clay matrices is of great importance.Several characterisation techniques as well as isothermal calorimetry were utilized in investigating the adsorption process of a model cationic drug(diltiazem hydrochloride,DIL)onto a pharmaceutical clay system(magnesium aluminium silicate,MAS).X-ray powder diffraction(XRPD),attenuated total reflectance Fourier transform infrared spectroscopy(ATRFTIR)and optical microscopy confirmed the successful formation of the DIL-MAS complexes.Drug quantification from the complexes demonstrated variable behaviour in the differing media used with DIL degrading to desacetyl diltiazem hydrochloride(DC-DIL)in the 2 M HCl media.Here also,the authors report for the first time two binding processes that occurred for DIL and MAS.A competitor binding model was thus proposed and the thermodynamics obtained suggested their binding processes to be enthalpy driven and entropically unfavourable.This information is of great importance for a formulator as care and consideration should be given with appropriate media selection as well as the nature of binding in complexes.

Surface roughness affects metastable non-wetting behavior of silicate melts on thermal barrier coatings

Airborne silicate pollutants in flight corridors pose a serious threat to aviation safety whose severity is directly linked to the wettability of molten silicates on thermal barrier coatings(TBCs)at high temperatures(1200–2000℃).Despite its importance,the wettability of silicate melt on TBCs has not been well investigated.In particular,the surface morphology characteristics of TBCs can be expected to have a first-order effect on the wettability of silicate melt on such TBCs.Here,a series of atmospheric plasma spray(APS)yttria-stabilized zirconia(YSZ)TBCs with varying surface roughness were generated through the application of mechanical polishing.The metastable nonwetting behavior of three representative types of airborne silicate ash(volcanic ash,fly ash and a synthetic calcium–magnesium–aluminum–silicates(CMAS)powder)on these TBCs with varying surface roughness was investigated.It was observed that the smoother the surface of TBCs was,the larger the contact angle was with the molten silicate melts,and consequently,the smaller the area of damage was on the TBCs.Thus,the reduction in TBCs surface roughness(here via mechanical polishing)led to an improvement in the wetting and spreading resistance of TBCs to silicate melts at high temperature.In support of these observations and conclusions,the surface morphology of the TBC(both before and after polishing)had been characterized,and the mechanism of the surface roughness-dependence of wettability had been discussed.These results should contribute to reducing the deposition rate of silicate melt on TBCs,thus extending the lifetime of turbine blades and reducing maintenance costs.

Antibacterial forsterite (Mg_(2)SiO_(4)) scaffold: A promising bioceramic for load bearing applications

In the current work,forsterite samples with different surface area were investigated for its antibacterial activity.Dissolution studies show that the lower degradation of forsterite compared to other silicate bioceramics,which is a desirable property for repairing bone defects.Forsterite scaffold shows superior compressive strength than the cortical bone after immersion in simulated body fluid.Bactericidal tests indicate that the forsterite had inhibition effect on the growth of clinical bacterial isolates.Forsterite may be a suitable candidate material for load bearing applications with enhanced mechanical properties and lower degradation rate.

Assembly of SPS/MgSi assisted by dopamine with excellent removal performance for ciprofloxacin

In this work,magnesium silicate-based sulfonated polystyrene sphere composites(SPS/MgSi)were synthesized by one-step(SMD1)and two-step(SMD2)methods.For SMD1,MgSi particles were densely assembled on the surface of SPS,assisted by complexation between Fe^3+and hydroxyl phenol.For SMD2,SPS/SiO2 was firstly obtained by the same method as SMD1,and then SPS/SiO2 was transformed directly to SPS/MgSi under hydrothermal conditions.Therefore,MgSi obtained by the two-step method had an interwoven structure.Compared to SPS,MgSi and SMD1,SMD2 presented a larger specific surface area and more negative surface charges.Therefore,SMD2 showed superior adsorption performance toward CIP with concentrations of 5,10 and 50 mg/L,and for 50 mg/L,the equilibrium adsorption capacity could reach 329.7 mg/g.The adsorption process is fast and can be described by the pseudo-second-order kinetic model.The relationship between pH value and Zeta potential demonstrated that electrostatic interaction dominated the adsorption process.In addition,competitive adsorption showed that the effect of Na^+was negligible but the effect of Ca^2+was dependent on its concentration.Humid acid(HA)could slightly promote the absorption of CIP by SMD2.After five rounds of adsorption-desorption,the equilibrium adsorption capacity of SMD2 still remained at 288.6 mg/L for 50 mg/L CIP.Notably,SMD2 presented likewise superior adsorption capacity for CIP with concentrations of 10 and 50 mg/L in Minjiang source water.All the results indicated that this synthesis method is universal and that SMD2 has potential as an adsorbent for CIP removal from aquatic environments.