Waleska Campos Guaglianoni

Comparison between the indirect approach and kriging with samples of different support for estimation using samples of different length

In this paper we compare two estimation methods to deal with samples of different support: (1) the indirect approach using accumulation and (2) kriging with samples of different support. These two methods were tested in a simple example. The estimates of the two methods were compared against a benchmark scenario. The benchmark consisted of kriging using a complete set of samples on the same support. The effects of the nugget effect, variogram range and type on the weight of long samples, the estimate, and the error variance were assessed. Kriging with samples of different support led to lower error variance and to estimates closer to the estimates of the benchmark scenario. Furthermore, in the case of spatially continuous attributes (low nugget effect), the indirect approach assigns greater weight to long samples than kriging with samples of different support. A cross validation study comparing the two methods with a database from a bauxite deposit was performed. The results of the cross validation study showed that kriging with samples of different support resulted in more precise estimates.

SYNTHESIS OF WC-12wt%Co NANOCOMPOSITES BY HIGH ENERGY BALL MILLING AND THEIR MORPHOLOGICAL CHARACTERIZATION

In this work micrometric particles of WC and Co were processed by high energy ball milling in a planetary ball mill. We evaluated the phase formation and changes in microstructure of WC-12wt%Co as a result of the following milling parameters: ball-to-powder weight ratio, milling time and speed. The material was characterized by X-ray diffraction (crystalline phases and crystallite size), particle size analysis (average grain diameter), the BET method (surface area), and scanning electron microscopy (powder morphology). The average particle size (D50) and crystallite size were respectively 1.63μm and 13.8nm, for a surface area of 4.709 m2/g, using a ball-to-powder weight ratio of 1:20, a milling time of 5h and a milling speed of 500 rpm.