The Formation Mechanism and Characterization of Al-Si Master Alloys from Sodium Fluosilicate

A modified Al-Si alloy containing up to 15 wt.% Si has been obtained from the reaction of sodium fluosilicate (Na2SiF6) with molten aluminum. This work attempted to estimate the mechanism of the reaction of Na2SiF6 with molten aluminum to produce Al-Si alloys. The effect of temperature, Na2SiF6/Al Wt ratio and reaction time on the formation of Al-Si alloy were investigated. The thermodynamic data, kinetic and rate of the reaction were studied. The results showed the possibility of the reaction between Na2SiF6 and molten aluminum thermodynamically, and that this reaction might be controlled chemically. The current study aims to optimize the factors that affecting the preparation of a modified Al-Si alloy from a reduction of sodium fluosilicate using molten aluminium. Temperature 950 oC, reaction time 20 – 25 min and Na2SiF6/Al Wt ratio related to the applied Si percentage. The prepared alloys could be modified due to the presence of Na2SiF6 in the used material as a source of sodium in response to modifying the produced Al-Si alloys. The microstructure by using LOM, SEM, and EDX proved that the needle-like silicon converts to fine fibrous. The volume fraction of primary Si reduces and the eutectic point moves to a higher silicon concentration. The modification improves the wear characteristics and increases the tensile and hardness.

Effect and Mechanism of Sodium Fluosilicate on Setting Time of Cement

Sodium fluosilicate (Na2SiF6) is prepared from by-product of phosphate fertilizer production. According to a certain percentage of Na2SiF6 mixed in the cement, the influence of different dosages on the setting time of cement under different water-cement ratio was discussed, and the effect of different forms of fluoride compounds on the setting time of cement were compared. The effect and mechanism of sodium fluosilicate on the hydration products of cement were researched by using the X-ray diffraction analysis and micro electron microscope. Experimental results show that the retarding effect of sodium fluosilicate on the coagulation time had a critical effect, and beyond a certain value, it sharply decreased the setting time. The critical dosage increased with the increase of water-cecment ratio. Compared with the retarding effect of Na2SiF6、MgSiF6、NaF and CaF2 on the coagulation time of cement, Na2SiF6 was the best. The incorporation of Na2SiF6 does not change the types of the hydration products, the main function of FN is hydrolyzed with Ca2+ ions to form CaF2 with a very low solubility.

Experimental Study of the Application of Sodium Silicate in the Windbreak and Sand Fixation Engineering

With the accelerated development of land desertification, sudden wind sand disaster, strong dust storm occurrence frequency more and more high.In the desert area where the alkali content in soil is low and there is existence of quicksand, the sand brick was prepared by using sodium silicate as chemical sand fixation adhesive materials and sodium fluosilicate as hardening agent, in order to improve the surface properties of desert land, control the spread of deserts and improve the environment of desert. In this paper, the suitable dosage of sodium fluosilicate and sodium silicate were studied,which have an important effect on compressive strength, flexural strength, block antifreeze and water absorption properties of the mortar test block.

Preparation and Characterization of Activated Sericite Modified by Fluorosilicate and Acid

Although sericite belongs to 2:1 clay minerals, it hardly has intercalation properties because it has high layer charge density, which produces pretty strong electrostatic force. Therefore, the purpose of activation is to permanently reduce the layer charge of sericite and obtain numbers of exchangeable cations. The original sericite (S0) was sintered at 800 °C for 1 h. After that, thermal-treated sericite (S1) was activated with sodium fluosilicate and nitric acid, whose effects were characterized by X-ray diffraction (XRD) analysis, chemical analysis and zeta electric potential analysis. The dissolving-out amount of Al3+ of acid-treated product (S2) reached circa 65 mg/g at the optimal processing conditions. After sodium modification with NaCl, CEC of final resulting product (S3) was increased to 14.34 meq/100g compared with that of original sericite (4.94 meq/100g). The results of chemical analysis and zeta electric potential analysis indicated that acid activation with sodium fluosilicate and nitric acid decreased the layer charge of sericite.

Preparation and Characterization of Activated Sericite Modified by Fluorosilicate

The structure of sericite is stable, and it is hard to prepare polymer layered silicate nanocomposites (PLSN). Therefore, structural modification was employed to activate sericite to reduce the layer charger. The thermal treated sericite (S1) was prepared by thermal modification at 800 for one hour. Then, the resulting product was modified with sodium fluorosilicate, whose effect was characterized by X-ray diffraction (XRD) analysis. The dissolving-out amount of Al3+ of salt-treated product (S2) reached circa 2.55 mg/g at the optimal processing conditions. CEC of S2 was increased to 10.52 meq/100g compared with that of original sericite (4.94 meq/100g). The results of XRD analysis indicated that mica-type phase persisted after salt modification with sodium fluosilicate.

A mathematical approach to rating food acceptance of the harvester termite, Hodotermes mossambicus (Isoptera: Hodotermitidae) and the evaluation of baits for its control

Hodotermes mossambicus (Hagen) is a harvester termite which competes with livestock for natural grazing. Control by baiting is recommended. Field trials in the north-western Orange Free State and south-western Transvaal, Republic of South Africa, showed that the two most commonly used commercial baits, with carbaryl or sodium fluosilicate as the active ingredient, are ineffective in controlling this species. A simple mathematical model was developed to rate the acceptability of grasses as food for the termite colonies. This enabled the attractiveness of the bait carriers as food for termites to be compared with that of the grasses. All five grass species tested had a similar food acceptability value, while both bait carriers were unacceptable as food. Failure of the baits was due to the fact that they were not consumed by the termites. The active ingredients was found to be effective when natural grass was used as the bait carrier. The mathematical model was extended to elucidate the effect of different baits on colony survival. This approach could be further used to rate new baits and their carriers objectively.