Showing papers on "Sodium sulfate published in 2017"

Investigations on latent heat storage materials for solar water and space heating applications

Abstract: The present study provides a thorough review on available latent heat storage materials (LHSMs) and their thermophysical properties for low temperature (25–80 °C) solar heating applications The applications are solar water and space heating The best LHSMs have been short-listed for the above applications based on the primary and secondary selection criteria Based on the above two criteria, it is found that lauric acid, palmitic acid, stearic acid, myristic acid, paraffin wax, sodium acetate trihydrate and an eutectic mixture of stearic acid and myristic acid (80:20 wt%) have a great potential to act as the best LHSM for solar water heating system, whereas, calcium chloride hexahydrate, n-eicosane, P116 wax, sodium sulfate decahydrate, disodium hydrogen phosphate dodecahydrate and lithium nitrate trihydrate are the best LHSMs for solar space heating The parameters affecting the life span of a LHSM, namely, thermal stability, corrosion, phase segregation and subcooling have been discussed in detail The present study also includes a list of commercially available LHSMs which can be employed for the solar water and space heating applications

The effects of nano- and micro-particle additives on the durability and mechanical properties of mortars exposed to internal and external sulfate attacks

Abstract: In this study, the effects of micro-silica (MS), nano-silica (NS), class C fly ash (FA), and metakaolin (MK) on the durability and mechanical properties of mortars exposed to internal and external sulfate attacks were investigated. For that purpose, mortars were produced from 3 different sands with different ratios of sulfate ions to generate conditions for an internal sulfate attack. Standard curing procedures were applied to all mortar samples for 23 weeks. Furthermore, mortar samples prepared from Sand A, which had the lowest sulfate content, were kept in sodium sulfate and magnesium sulfate solutions to produce an external sulfate attack. When all test results were evaluated together, the most significant contribution to durability and strength among the admixtures was observed to be from NS, which demonstrated an average improvement of 2–10% over MS, which had the second most significant contribution for mortar samples exposed to the most severe internal and external sulfate attacks. When all mixing ratios and tests were considered, the least significant contribution to durability and strength was determined to be from metakaolin. Additionally, when the test data for all days were compared, magnesium sulfate was found to be approximately 1–10% more destructive in comparison to sodium sulfate.

Combined effects of additives and power levels on microwave drying performance of lignite thin layer

Abstract: The microwave drying performance of lignite thin layer in a bench-scale setup was highlighted in terms of three additives with 10% dosage. The dielectric loss for dried lignite, raw lignite, lignite/coal fly ash, lignite/Na2SO4, and lignite/Na2CO3 at 2,450 MHz were 0.06, 0.13, 0.14, 0.15, and 0.18. In comparison with raw lignite, the average temperature rising of the thin layer at 385 W for lignite blending with sodium carbonate, sodium sulfate, and coal fly ash was about 10, 7, and 2°C. The apparent activation energies of both falling rate periods for lignite blending with three additives were less than that of raw lignite. Sodium carbonate among three additives could be preferable one, followed by sodium sulfate and coal fly ash. The energy efficiency increased with the addition of sodium carbonate, sodium sulfate, and coal fly ash. The required electricity energy for lignite/Na2CO3 blend at 385 W was reduced by about one half compared with the raw lignite.

Enhancement of Methane Concentration by Removing Contaminants from Biogas Mixtures Using Combined Method of Absorption and Adsorption

Abstract: We report a laboratory scale combined absorption and adsorption chemical process to remove contaminants from anaerobically produced biogas using cafeteria (food), vegetable, fruit, and cattle manure wastes. Iron oxide (Fe2O3), zero valent iron ( ), and iron chloride (FeCl2) react with hydrogen sulfide (H2S) to deposit colloidal sulfur. Silica gel, sodium sulfate (Na2SO4), and calcium oxide (CaO) reduce the water vapour (H2O) and carbon dioxide (CO2). It is possible to upgrade methane (CH4) above 95% in biogas using chemical or physical absorption or adsorption process. The removal efficiency of CO2, H2S, and H2O depends on the mass of removing agent and system pH. The results showed that Ca(OH)2 solutions are capable of reducing CO2 below 6%. The H2S concentration was reduced to 89%, 90%, 86%, 85%, and 96% for treating with 10 g of FeCl2, (with pH), Fe2O3, , and activated carbon, respectively. The H2O concentration was reduced to 0.2%, 0.7%, 0.2%, 0.2%, and 0.3% for treating raw biogas with 10 g of silica gel and Na2SO4 for runs R1, R2, R3, R4, and R5, respectively. Thus, given the successful contaminant elimination, the combined absorption and adsorption process is a feasible system for biogas purification.

C3S and C2S hydration in the presence of Na2CO3 and Na2SO4

Abstract: This study analyses the behavior of calcium silicates C3S and C2S hydrated in two alkaline media, Na2CO3 and Na2SO4. The silicates were synthesized with laboratory reagents and hydrated in water, to which solid-state alkaline activators with 4 wt% Na2CO3 or 4 wt% Na2SO4 were added. Two- and 28-day mechanical strength values were determined and the reaction products were characterized with XRD, SEM/EDX, and 29Si and 23Na MAS NMR. The findings showed that the presence of Na2CO3 hastened hydration kinetics and stimulated early-age mechanical strength development in both silicates. The most significant effect of sodium sulfate, however, was observed in the 28-day material in both silicates, in which it raised strength by stimulating the precipitation of C–S–H gels with a high percentage of Q2 units.

The Phase Change Process and Properties of Saline Soil During Cooling

Abstract: Detrimental frost heave and salt expansion may occur in saline soils of cold regions. The severity of these processes depends on the amount of salt precipitation and ice crystal growth in the pore solution at different temperatures. By employing nuclear magnetic resonance, the liquid water fractions in different concentrations of sodium chloride and sodium sulfate saline soils were measured at different temperatures. Based on the theory of solution phase diagram and phase change in porous media, the differences and similarities of phase change between pore solution and free solution were analyzed. The phase change sequence and effects of salt on frozen soils are also discussed. The theoretical and experimental results confirm that the phase diagram can reflect the phase change of pore solutions roughly, and pore size distribution is the cause of differences between the pore solution and free solution. Sodium chloride can mitigate the frost heave of soil, and frost heave and salt expansion occur together when the sodium sulfate soil is frozen.

Optimization of Lithium Extraction from Lepidolite by Roasting Using Sodium and Calcium Sulfates

Abstract: The lithium extraction from a lepidolite concentrate using roasting, followed by water leaching, was studied. Several alternative additives were initially tested. The use of sodium and calcium sulfates as additives was evaluated in more detail. The influence of some process variables, namely the roasting time, roasting temperature and the additive/concentrate mass ratio, was studied applying a design of experiments. The lithium extraction was modelled and the fitted and validated model was used to optimize the process response. The increase in the additive/concentrate mass ratio, roasting time and temperature seems to result in solid state reactions and transformations that lead to phase, morphological and particle size distribution modifications, which were assessed by XRPD, SEM, and particle size analyses. In this process, lithium sodium sulfate formation constitutes a crucial step enabling the Li water leaching. High lithium extractions were estimated for several combinations of factors. At 850...

Quantitative analysis for the effect of microstructure on the mechanical strength of frozen silty clay with different contents of sodium sulfate

Abstract: Microstructural transformation is known substantially to be the reason for the differences in mechanical behavior and the failure mechanism of saline soil. The mechanical strength of frozen saline soil decreases by 19.0% initially and then increases by 49.3% with the increasing mass content of sodium sulfate, with the threshold value of 1.5%. To explain the mechanism of this phenomenon, mercury intrusion porosity and scanning electron microscope were adopted to obtain the pore size distributions and microstructural characteristics of silty clay with different mass contents of sodium sulfate at 0.0, 1.5, 2.5 and 5.0%, respectively. The microstructural parameters were calculated by the Image-Pro Plus software based on the threshold of 75 and magnification of 1000× and 2000×. The porosity increases firstly and reduces with the rising salt content, and the fractal dimension is affected slightly ranging from 1.18 to 1.23. As the salt content increases from 0.0 to 1.5%, salts dissolve completely and the thickness of liquid film increases, so does the pore volume, and the friction of soil particles and the mechanical strength decreases. When the salt content is beyond the threshold value, the solution in soil is supersaturated, and salts crystallize and fill the pores and deduce the pore volume. The increasing interlocking abilities between crystals and particles enhance the mechanical strength of frozen saline soil. The results can provide a theoretical guidance to predict the frost and salt heave of frozen saline soil engineering.

Repair Mortars Incorporating Multiwalled Carbon Nanotubes: Shrinkage and Sodium Sulfate Attack

Abstract: This study investigates the effect of multiwalled carbon nanotubes (MWCNTs) on the shrinkage and expansion caused by sodium sulfate attack in repair mortars; repair mortar behavior in the f...

Hydration and Properties of Slag Cement Activated by Alkali and Sulfate

Abstract: In this paper, the results of a study on the influence of sodium hydroxide, calcium hydroxide, aluminum hydroxide, sodium sulfate, calcium sulfate, and calcium sulfate dihydrate as activato...

Experiment Analysis of Concrete’s Mechanical Property Deterioration Suffered Sulfate Attack and Drying-Wetting Cycles

Abstract: The mechanism of concrete deterioration in sodium sulfate solution is investigated. The macroperformance was characterized via its apparent properties, mass loss, and compressive strength. Changes in ions in the solution at different sulfate attack periods were tested by inductively coupled plasma (ICP). The damage evolution law, as well as analysis of the concrete’s meso- and microstructure, was revealed by scanning electron microscope (SEM) and computed tomography (CT) scanning equipment. The results show that the characteristics of concrete differed at each sulfate attack period; the drying-wetting cycles generally accelerated the deterioration process of concrete. In the early sulfate attack period, the pore structure of the concrete was filled with sulfate attack products (e.g., ettringite and gypsum), and its mass and strength increased. The pore size and porosity decreased while the CT number increased. As deterioration progressed, the swelling/expansion force of products and the salt crystallization pressure of sulfate crystals acted on the inner wall of the concrete to accumulate damage and accelerate deterioration. The mass and strength of concrete sharply decreased. The number and volume of pores increased, and the pore grew more quickly resulting in initiation and expansion of microcracks while the CT number decreased.

Na2SO4-Deposit-Induced Corrosion of Mo-Containing Alloys

Abstract: Disk alloys used in advanced gas turbine engines often contain significant amounts of Mo (2 wt% or greater), which is known to cause corrosion under Type I hot corrosion conditions (at temperatures around 900 °C) due to alloy-induced acidic fluxing. The corrosion resistance of several model and commercial Ni-based disk alloys with different amounts of Mo with and without Na2SO4 deposit was examined at 700 °C in air and in SO2-containing atmospheres. When coated with Na2SO4 those alloys with 2 wt% or more Mo showed degradation products similar to those observed previously in Mo-containing alloys, which undergo alloy-induced acidic fluxing Type I hot corrosion even though the temperatures used in the present study were in the Type II hot corrosion range. Extensive degradation was observed even after exposure in air. The reason for the observed degradation is the formation of sodium molybdate. Transient molybdenum oxide reacts with the sodium sulfate deposit to form sodium molybdate which is molten at the temperature of study, i.e., 700 °C, and results in a highly acidic melt at the salt alloy interface. This provides a negative solubility gradient for the oxides of the alloying elements, which results in continuous fluxing of otherwise protective oxides.

An experimental study of salt expansion in sodium saline soils under transient conditions

Abstract: Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.

Measurement of Flow Characteristics for Multiparticulate Bottom Ash-water Suspension with Additives

Abstract: In the present work, Rheological characteristics of bottom ash was studied with and without addition of additives. Two additives were selected as Henko detergent and sodium sulfate. The additive added in bottom ash suspension with proportion of 0.2, 0.4 and 0.6% (by weight). The solid concentration of bottom ash suspension varied from 10 to 60% (by weight). Reduction in apparent viscosity is highly noticeable with addition of sodium sulfate as compared to Henko detergent.The investigation reveals that bottom ash suspension in above manner has a potential to transport in slurry pipeline with minimum energy consumptions.

Sodium sulfate salt weathering of porous building materials studied by NMR

Abstract: Sodium sulfate is known as one of the most destructive salts causing weathering. Many experiments on accelerated weathering tests show that major deterioration effects by weathering are caused by drying and wetting cycles of porous materials saturated with salt solution. In this study we have performed accelerated weathering tests with sodium sulfate in common building materials (fired-clay brick, Indiana limestone and Cordova limestone) measuring the concentration in the materials simultaneously with their expansion. The concentration of sodium sulfate solution is measured non-destructively using Nuclear Magnetic Resonance, while the expansion of the sample caused by crystal growth is measured with a fiber optic displacement sensor. The simultaneous measurement of solution concentration within a material and expansion allow assessment of crystallization pathways most responsible for damage during weathering, i.e., cycles of wetting and drying. It was shown by direct observation, that with rewetting of the partially dried samples, the present thenardite experiences a rapid partial transformation to decahydrate. Simultaneously with this transformation a rapid expansion of the sample was measured in situ.