Y. C. Ko

The effect of silica characterization on the microstructure of BaFe12O19 ferrites

The anisotropically formed BaFe12O19 ferrites were prepared from the hot-rolled mill scale and silica was added to the ferrite during fine milling in the range 0.15 to 0.50 wt%. These ferrites were sintered at 1220° C for 2 h. The grain growth of the ferrites is dominantly influenced by the sizes of the silica added. Coarse-grain (≈ 1μm) silica tends to promote discontinuous grain growth, which increases drastically with slightly increasing amounts of silica added, while fine-grain (≈ 0.013μm) silica tends to retain fine grain microstructures with the same increasing amount of silica. The average grain size of the ferrite without silica addition was 8 to 10μm. The size was increased to as large as 30μm on addition of 0.15% coarse-grain silica and the microstructure was full of extremely large grains on the addition of 0.50% coarse-grain silica.

Dependence of magnetic properties of Mn-Zn ferrites on the degree of calcination

Mn0.764 Zn0.187 Fe2.049 O4 and Mn0.687 Zn0.272 Fe2.041 O4 ferrites containing 0.05 wt% CaO, 0.05 wt% SnO2 and 0.05 wt% V2O5 were prepared by conventional methods using manganite (γ-MnOOH) as a source of MnO. The partial-calcined ferrites were made by calcining the mix consisting of total amount of ZnO and one third or half amount of Fe2O3 and MnO required for the formation of the Mn-Zn ferrites and sintering the mix consisting of the previously calcined mix and the remaining two thirds or half the amount of Fe2O3 and MnO. Calcination was conducted at 900 °C for 2 h and sintering at 1335 °C for 1 h. The secondary maximum in permeability (SMP) of uncalcined ferrites was shifted to higher temperature and does not clearly appear in the initial permeability against temperature plot. The values of initial permeability of the uncalcined ferrites increase rapidly with increasing temperature up to 100 °C, then either increased gently or levelled off. In the working temperature range, 80 to 100 °C, the values of all the ferrites, regardless of the degree of calcination were well above 2000. Above 80 °C, the uncalcined and one-third calcined ferrites had the lowest and the second lowest loss factor values (<3 × 10−6), respectively. A dense and homogeneous structure of smaller grains with small pores was prevalent in the uncalcined and one-third calcined ferrites.

The effect of Na2O addition on the magnetic properties of BaFe12O19 ferrites

The effect of Na2O addition on the magnetic properties of isotropic BaFe12O19 ferrites from hot-rolled mill scale was investigated. Na2O was added up to 0.2s%. The values of coercivity and energy product maximum are significantly increased, notably (BH)max from 0.8 to 0.9× 106 OeG, and those of intrinsic coercivity rise drastically from 2500 to 4000 0e when Na2O up to 0.15% is added after calcination. On the other hand, the magnetic properties of the ferrites gradually deteriorate and the values of intrinsic coercivity vary very little when Na2O up to 0.2% is added prior to calcination. The densification of ferrites is slightly decreased in the presence of the Na2O, regardless of the time at which it is added.

Thermal shock resistance test for cast iron used in casting environments

The thermal shock resistance test was conducted for grey cast iron and a compacted cast iron for use in casting environment. The test consisted of a specimen partially immersed in a molten salt bath of 55% Na2C03 and 45% CaC03 at 1000 ° C for 4.5 min, followed by plunging into water. The test results from laboratory and field indicated that the grey cast iron is superior to the compacted cast iron. In the laboratory test, the thermal shock resistance of the cast iron can be judged from the summation of crack length and crack patterns in the specimen after a certain number of thermal shock cycles. The inferior thermal shock resistance of the compacted cast iron is mainly attributed to the more extensive martensite formation after the thermal shock cycling compared with the grey cast iron.

Effect of ZrO2 on the alkali feldspar-aluminosilicate interface

The contact angles of the alkali feldspars containing 0, 4, 8 and 12 vol % ZrO2 on the aluminosilicate substrate were measured by sessile drop method. During the heating from 1350 to 1520° C and the holding at 1350° C, the contact angles were generally increased with increasing ZrO2 content. 8 vol % ZrO2 in the melt drop was very effective to raise the contact angles and 12 vol % ZrO2 was barely sufficient to maintain the contact angles at around 90° or larger at elevated temperatures. The SEM micrographs indicated that ZrO2 particles were scattered throughout the drop and also located in the interface between the drop and substrate. The dissolution of the substrate by liquid feldspar and the diffusion of ZrO2 in the substrate were also observed. The cause of the increase in contact angle with increasing ZrO2 content are discussed.