超级铁精矿提纯与锶铁氧体预烧料试验研究

对武钢金山店的磁铁精矿进行提纯，得到了超纯磁铁精矿（TFe〉71．5％，SiO2〈0．5％）。以该超纯磁铁精矿与分析纯碳酸锶及添加剂为原料，通过对配比、预烧温度、保温时间等条件进行优化得到了性能较好的锶铁氧体预烧料。     

Effects of pre-sintering and annealing on the optical transmittance of Zr-doped Y2O3 transparent ceramics fabricated by vacuum sintering conjugated with post-hot-isostatic pressing

In this work, Zr-doped Y₂O₃ transparent ceramics were fabricated by vacuum pre-sintering at various temperatures ranging from 1650 to 1800 °C combined with a post-hot-isostatic pressing (HIP) treatment. The pre-sintered samples all show black opaqueness mainly due to the formation of oxygen vacancies, which can be removed by post-annealing in air. The HIP treatment can also eliminate the blackness as well as residual pores, giving rise to optical transparency. The in-line transmittance of the samples after HIP was found to depend strongly on the microstructure of the as-sintered samples. The optimal microstructure of these types of samples before the HIP treatment should be fine grained with only intergranular pores, which can easily be removed by HIP. Annealing before HIP was shown to be necessary to enhance the transmittance of the samples. The effects of the pre-sintering heating rate on the optical transmittance of the HIP-treated samples were also studied.     

Micro machining of pre-sintered ceramic green body

Ceramic materials are widely used in industrial products because of their excellent properties such as resistance to erosion, high temperature and wear. Those properties pose difficulty in processing ceramic materials to desired shapes and dimensions, especially in micro machining of ceramics using micro tools because of the low mechanical strength of tiny tools and the extreme hardness of ceramics. The machining of ceramic green body may be a solution to the problem. However, the low strength of ceramic green body results in low machining accuracy such as damage at the edges of micro features. In this paper, the pre-sintering of ceramic materials was used to enhance the material strength, and hence to improve the machining accuracy. Microstructures of pre-sintered ceramic green bodies at different temperatures were observed and analyzed. The mechanical strength of pre-sintered ceramics was measured. It was confirmed that the mechanical strength of ceramics increased with an increase of pre-sintering temperature. There was no obvious shrinkage after pre-sintering at below 850 °C. The edge damage of machined micro features was reduced significantly. The tool wear increased with the increase of pre-sintering temperature. Finally, a 3D micro feature was machined and the fully sintering shrinkage was compensated accurately.     

Microstructure and electrical properties of ‘pre-sintered bismuth ruthenate-glass composite’ based thick film paste for resistor application

Thick film resistors based on a bismuth ruthenium oxide (BRO) and a leadborosilicate glass have been used to study the effect of a ‘pre-sintered glass–ceramic composite’ powder in the paste preparation on the resistor characteristics. Pre-sintered glass–ceramic composite was prepared by heating a physical admixture of leadborosilicate glass frit and BRO as functional material at various temperatures above the softening point of the glass. The microstructural changes associated with ‘pre-sintering’ step were studied using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction, and, were correlated to the electrical characteristics of these resistors. It was observed that pre-sintering at a lower temperature of 600°C helps in restricting the agglomeration of conducting BRO particles and in generating more non-sintered contacts between them, which improves consistency in sheet resistance and hot temperature coefficient of resistance (TCR). At the same time, the pre-sintering step lowers the absolute TCR value, mostly by way of compensation of the high negative TCR of glass by the positive TCR of Pb containing ruthenate phases and/or RuO₂, which have positive TCR. It is explained that the Pb containing BRO phases are formed in situ through the Bi???Pb exchange reaction. The pre-sintering temperature of 600°C was, thus, found to be optimum for the present processing conditions.     

永磁铁氧体“花斑”现象的研究

以铁鳞作为原料是永磁铁氧体预烧料生产经常采用的方法,在永磁铁氧体产品的生产过程中,经常会遇到所谓的跑锶和“花斑”现象,严重影响产品的外观。本文阐述了永磁铁氧体跑锶和“花斑”现象产生的原因和形成机理,并采取有效的预烧工艺控制和二次添加技术,很好地解决了压坯和烧结体的“花斑”与水印现象。     

Effect of the pre-sintering atmosphere on the microstructures and optical qualities of transparent spinel ceramics

The densification process, microstructure evolution, and final optical quality of the transparent MgO?nAl₂O₃ (n = 1.1 and 1.5) ceramics pre-sintered in air and under vacuum were investigated for the effects of pre-sintering atmosphere. The samples pre-sintered in air exhibited uniform microstructure, which was easier to obtain high optical quality at lower HIP temperatures. However, non-cubic precipitates appeared in the samples with a high Al₂O₃/MgO ratio after HIP treatment, resulting in the deterioration of transmittance. For the samples pre-sintered under vacuum, a large-grain layer was formed on the sample surface due to accelerated MgO volatilization. However, non-cubic precipitates did not appear due to the generation of oxygen vacancies. The mechanisms of formation of the large-grain layer, non-cubic precipitates were discussed from the viewpoint of MgO vaporization, Al₂O₃/MgO molar ratio, and oxygen vacancy.     

Manufacturing of a ceramic groove part based on additive and subtractive technologies

Ceramic stereolithography Three-Dimensional (SL-3D) printing has a unique advantage in forming ceramic parts with complex shapes. However, because of the effects of the slicing layer thickness, laser spot diameter, and curing inhomogeneity, its manufacturing dimensional accuracy still lags far behind traditional processing methods. In this study, a manufacturing process based on additive and subtractive technologies was used to prepare ceramic groove parts. The manufacturing process of ceramic groove parts is composed of SL-3D printing, debinding, micro-milling, and sintering processes. In order to improve the dimensional accuracy of ceramic groove parts, a model based on shrinkage compensation and micro-milling was proposed. The dimensional change pattern in the curing phase was modelled and a shrinkage compensation method was established to control the dimensional accuracy of the finished parts. A method to characterize the micro-chipping on machined edges of the workpiece was investigated by applying a micro-milling cutter to process the 3D-printed part pre-sintered at 1150 °C. The effectiveness of the proposed dimensional accuracy control method was verified by the case study of a ZrO₂ ceramic part.     

Dependence of dc and ac conduction on the pre-sintering temperature in sol–gel derived Ba0.5Sr0.5TiO3 thin films

The effect of pre-sintering temperature on the activation energies of dc and ac conduction in sol–gel spin-coated Ba_0.5Sr_0.5TiO₃ (BST) thin films is reported in this paper. Layer by layer coating of BST sol on Pt/TiN/SiO₂/Si substrates was done with varying pre-sintering temperatures (drying temperature for individual layers). Dominant mechanism of dc conduction was identified as Schottky process whereas ac conduction was governed by trap controlled hopping process. The activation energy for dc conduction decreased from 0.45 to 0.38 eV with increase in the pre-sintering temperature from 400 to 600 °C; whereas, that for ac conduction increased from 0.17 to 0.21 eV. The results have been correlated with grain growth phenomena and reduction of oxygen vacancies in the films with increase in the pre-sintering temperature.