Effect of order-disorder transition on magnetic properties of rapidly soldified high silicon-iron ribbons
The effect of ordering on the soft magnetic properties of 6.5% silicon-iron ribbons obtained by rapid solidification is studied. The atomic order cannot be prevented by the fast cooling. It is shown that isothermal aging at 700 degrees C induces a small decrease in coercive force and hysteresis losses, while aging at 500 degrees C induces an increase in these parameters. The magnetic evolutions are corroborated by Lorentz microscopy observations. The values obtained and the observations suggest a weak individual interaction, which may be due to local variation of exchange and anisotropy energy. >
The B2 and DO3 Ordering Reactions in Iron–Silicon Alloys in the Vicinity of the Curie Temperature
AbstractThe ordering reactions in iron–silicon alloys have been studied by transmission electron microscopy in the composition range 10–17 at.-%Si and the temperature range 535–822°C. It has been found that: The A2 → B2 ordering reaction appears to occur homogeneously (i.e. in the non-classical manner) both above and below the Curie temperature, Te . The magnetic interaction suppresses the A2 → B2 critical temperature by about 100°C in Fe–10 at.-%Si. The B2 → DO3 ordering reaction appears to occur homogeneously above Tc , but by nucleation and growth below Tc . Antiphase boundaries nucleate phases with lower degrees of order than has the matrix but not phases with higher degrees of order. Long-range-order fluctuations occur near the critical points of the homogeneous A2 → B2 and B2 → DO3 transformations.
Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material
Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.