| It is hard for colloidal silica(CS) bonded castables to set or harden and acquire enough green strength, due to the high stability, resulting from the high ζ-potential of CS, of the castables. Therefore, it is still unable to be widely used at present. In order to improve the workability and applicability of CS bonded castables, the problem of its low green strength should be settled first, thus the addition of suitable additives seems to be necessarialy. In this paper, the relationships between dispersants types, addition amount and the flowability, setting behavior of CS bonded castables were investigated, meanwhile, the substance of influence of dispersants on the flowability of castables cured for different time was studied.For these purposes, six dispersants: sodium hexametaphosphate(SHP), sodium tripolyphosphate(STP), citric acid, FS10 and FS20(belonging to polycarboxylate ethers), Polyethylene glycol(PEG400) were chose. Based on this, the change of ζ-potential and apparent viscosity(AV) of CS, AV of mixture slurry(CS + CL370 micropowder), AV of matrix slurry(CS + CL370 + 325-meshes corundum fine) and the flowability of castables, with the dispersants and time, were studied, including the inner relationships of ζ-potential and AV with flowability. Effects of dispersants on the green strength of castables were also discussed.Zeta potential analyzer and rheometer were utilized to(1) measure the ζ-potential and AV of CS with the above dispersants of different additions(%, 0, 0.01, 0.03, 0.05, 0.1, 0.15, 0.2, 0.3) and standing time(0min, 15 min, 30 min, 45 min, 60 min, 90 min, 120min). Moreover, the mechanism for structure, size dimentions and dosages of additives on the stability(ζ-potential) and AV of CS was emphatically discussed.(2) Impacts of dipersants types and dosages(%, 0, 0.1, 0.5, 1, 2, 3, 4) on CL370 slurry and corundum fine slurry, all with a solid contents of 30wt%, was considered, respectively.(3) According to the change of CS viscosity with dipersants, diverse dispersants dosages(wt.%) were selected for mixture slurry(solid loading: 60 wt.%), to study their impacts on AV of mixture slurry(virtually study the effects of CL370 on the curve variation of CS viscosity vs dispersants addition and time).(4) Effects of dipersants on AV of matrix slurry, essentially the effects of 325-meshes corundum fine on the curve variation of CS/mixture slurry viscosity vs dispersants addition and time, were researched. The dispersants dosages(%) for matrix slurry(with a solid loading of 60wt%), were consistant with that of mixture slurry.(5) Researches on the influence of dipersants on the castables flowability were also launched. Along with this, the relationships of the apparent viscosity(AV) variation of CS, mixture slurry, matrix slurry with the variation of flowability of castables were studied. The additions(%) of dispersants were also identical to that of mixture slurry.(6) After the above were finished, we finally conducted an experiment on the influence of dipersants on green strength of the castables that cured at ambient temperature for 24 h. Afterwards, the optimum dispersant and its dosage that making the castables meet both the flowability and green strength of the working requirements were found.The results show that appropriate dosage of these dispersants could reduce the viscosity of CS, mixture slurry and matrix slurry; improve the flowability and green strength of castables. Moreover, the lower the viscosity of CS, the better the flowability of castables, on condition that the absolute value of ζ-potential is greater than 30 m V; if the viscosity increases with time sharply, then the flowability will decrease with time rapidly... |
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