Ultrafine Grinding Of The Coal Based Carbon Powders

The Coal Based Carbon studied in the paper was made from anthracite by purification, graphitized calcinations and ultra-fine grinding in steps. Among them, the last section, ultra-fine grinding plays an important role in the process, and directly affects the performances of the product. In this paper, the structure and properties of Coal Based Carbon were analyzed, technological parameters of ultra-fine grinding optimized, grinding aid and the mechanism discussed.The physi-chemical properties of Coal Based Carbon, including particle size distribution, morphology structure, surface elements and functional groups and degree of graphitization, were characterized by laser particle analyzer, scanning electron microscope, transmission electron microscope, etc. The characterization results show: the median particle size D50 of Coal Based Carbon is 5.14μm; the morphology structure of Coal Based Carbon particles mostly present irregular polygon shape; the surface chemical structure of Coal Based Carbon is mainly aromatic C-C surrounded by several function groups, that is, phenolic hydroxyl group, carbonyl group and carboxyl group; the carbon structure contains a large number of disordered amorphous carbons and a small number of graphite crystallite.In order to investigate the influence of technological parameters on ultra-fine grinding of Coal Based Carbon powders in dry condition, the ultra-fine grinding experiments were carried out varying grinding time, rotational speed of mill, diameter of grinding media, combination of grinding media, ball-to-powder weight ratio and filling ratio in a planetary ball mill. The experimental results show that the median particle size decrease with increasing the grinding time, but the aggregation of Coal Based Carbon particles occur beyond the limit of grinding time 30 min. The smaller grinding ball has the greater specific surface area, and the contact efficiency with powders is improved, so that the median particle size reach at minimum 3.11μm by 5mm diameter grinding ball. The median particle size reduces relatively with raising the rotational speed of the mill. The median particle size falls down 2.45μm with an increase of ball-to-powder weight ratio up to 50:1. The filling ratio of grinding media is not clearly correlated with the median particle size. Therefore, it points out that ball-to-powder weight ratio, diameter of grinding media and grinding time have a considerable influence on ultra-fine grinding of Coal Based Carbon. The optimum parameters: 3mm diameter of grinding media, 30min’s grinding time, 260r/min’s rotational speed of mill, 20:1ball-to-powder weight ratio and 10.25%filling ratio of grinding media.On the basis of the strength weakening theory and the analysis of surface properties of Coal Based Carbon, the surface modification agent altered the surface chemical structure to prevent the agglomeration and enhanced the fluidity of Coal Based Carbon particles, and the high hardness aid weakened the strength of Coal Based Carbon particles. The aid-grinding experiments results show that the harder quartz has higher efficiency than surface modification agent on improvement of ultra-fine grinding. The median particle size drops the lowest value on dosage of quartz 1.4 g. The quartz sand added before the grinding process has a better effect on the ultra-fine grinding of Coal Based Carbon than the other methods which quartz sand is divided into five equal and divided into five unequal, then added every 10 minutes during the grinding process, respectively.