Admixtures of Na2B4O7·10H2O (NB), Ca(NO3)2·4H2O (CN) and Na2SO4·10H2O (NS) are studied to discover how they affect the work performance, hydration-induced increases in temperature and mechanical performance of magnesium potassium phosphate cements (MKPCs). Analytical methods such as X-ray diffraction spectroscopy, eight-channel microcalorimetry and thermogravimetric-differential scanning calorimetry are used to investigate the underlying mechanisms of these changes. Incorporation of a single retarder (NB) results in short MKPC hardening times and low early strengths. Admixture with 1·5% or more NB and CN effectively lengthens the hardening time of MKPC, but greatly decreases its fluidity. Incorporation of NB, CN and NS in the ratios 1·5%:1·5%:5% results in an initial hardening time of 37·02 min and the appearance of two temperature peaks in the hydration temperature curve. The resulting cement mix has fluidity of 115 mm and strength of 52·56 MPa after 12 h of hydration. Reaction between NB and CN creates a calcium borate film that envelopes magnesium oxide particles, preventing dissolution of magnesium oxide and generation of the hydrated product MgKPO4·6H2O (MKP), thus slowing down the hydration process. Incorporation of an appropriate quantity of NS endows fluidity of MKPC that can reach 125 mm, owing to crystal waters released during solvation and changes in phase.

Magnetorheological (MR) grease has advantages of the anti-settlement behavior and excellent sealing property compared with conventional MR materials. However, the rheological behaviors of MR effect and shear yield stress are too small to limit the further applications with MR grease. This paper proposes a composite lithium-based MR grease with boric acid-hydroxyl stearic acid to improve the rheological behaviors. Eight different samples of composite lithium-based MR grease with different ratios of mass between lithium stearate and lithium borate are prepared by the saponification method. The rheological behaviors are tested and discussed with qualitative and quantitative analysis. The experimental results show that the off-state viscosity reduces with the decrement of the ratio of mass under low shear rate which changes from 68.7 Pa·s to 16.5 Pa·s. Lithium stearate content has more effects with off-state viscosity. Based on the Herschel-Bingham model, the shear stress of composite lithium-based MR grease can be improved dramatically by adjusting the ratio of mass which is increased by 170% under the magnetic flux density of 0.2 T. Compared with single lithium-based MR grease, the maximum yield shear stress is increased by 166.7% at off-state and the maximum MR effect is also increased by 19.1%. The MR effect can reach 23,600% with a specific mass ratio of the composite MR grease. The experimental results validate that the feasibility of the performance improvement by the composite lithium-based MR grease.

A new approach to dispersing magnetic particles via an oil organogel formed by a low molecular weight gelator to prepare MRF.