THE FORMATION MECHANISM OF PORTLAND CEMENT CLINKER MINERALS IN RAPID BURNING

Cement clinker is burnt at the rapid heating rate has the obvious effect of saving energy due to the low burning temperature and short burning time. This kind of technique is being researched actively in recent years, but the systematical theory investigation about the formation mechanism of clinker minerals under this condition has not been reported. In this paper, the formation mechanism of Portland cement clinker minerals in rapid burning was studied by means of DTA, SEM, EPMA, XRD and other conventional testing methods by using a special burning equipment.

Kinetic transitions and Mn partitioning during austenite growth from a mixture of partitioned cementite and ferrite:Role of heating rate

Austenite formation from a ferrite-cementite mixture is a crucial step during the processing of advanced high strength steels(AHSS).The ferrite-cementite mixture is usually inhomogeneous in both structure and composition,which makes the mechanism of austenite formation very complex.In this contribution,austenite formation upon continuous heating from a designed spheroidized cementite structure in a model Fe-C-Mn alloy was investigated with an emphasis on the role of heating rate in kinetic transitions and element partitioning during austenite formation.Based on partition/non-partition local equilibrium(PLE/NPLE)assumption,austenite growth was found alternately contribute by PLE,NPLE and PLE controlled interfaces migration during slow-heating,while NPLE mode predominately controlled the austenitization by a synchronous dissolution of ferrite and cementite upon fast-heating.It was both experimentally and theoretically found that there is a long-distance diffusion of Mn within austenite of the slow-heated sample,while a sharp Mn gradient was retained within austenite of the fast-heated sample.Such a strong heterogeneous distribution of Mn within austenite cause a large difference in driving force for ferrite or martensite formation during subsequent cooling process,which could lead to various final microstructures.The current study indicates that fast-heating could lead to unique microstructures which could hardly be obtained via the conventional annealing process.

Direct growth of tungsten oxide nanorods from heated tungsten foils

Tungsten oxide （W18O49） nanorods were grown by directly heating tungsten foils covered with potassium bromide （KBr） in low-pressure wet oxygen. The approach featured such advantages as convenient manipulation, low cost and rapid accessibility to high temperatures. A solid-liquid-solid （SLS） mechanism is believed to have dominated the growth process, in which the W18049 nanorods segregated from eutectic droplets of potassium tungstate and tungsten oxide. The ultraviolet photoelectron spectroscopy （UPS） analysis disclosed that the valence band maximum （VBM） of these nanorods was approximately 9 eV be- low the vacuum level. The feasibility of using the such-fabricated nanorods as field emitters was tested and the related mecha- nism was also discussed.