Sintering and Smelting Property Investigations of Ludwigite

In this paper, orthogonal experiments are designed to study the sintering and smelting characteristics of the ludwigite ore. The predominant influencing factors of the optimal ratio, basicity and carbon content on different single sintering indexes, including the vertical sintering speed, yield rate, drum strength and low-temperature reduction pulverization index, are firstly explored by the range analysis method, and the main influencing factors on comprehensive indexes are obtained by a weighted scoring method based on different single index investigation. Considering the sintering characteristics, the primary and secondary influencing factors are: ordinary ore ratio, carbon content and basicity, and the optimal ore blending scheme is: basicity 1.7, ordinary ore blending ratio 60% and carbon content 5%. In terms of the smelting characteristics, the research obtains the order of the influencing factors on the softening start temperature, softening end temperature, softening zone, smelting start temperature, dripping temperature, smelting-dripping zone, maximum pressure difference and gas permeability index of the ludwigite sinters by simply considering various single smelting indexes. On this basis, considering the comprehensive softening-melting-dripping characteristics, the primary and secondary influencing factors are: carbon content, ordinary ore ratio and basicity, and the optimal ore blending scheme is: basicity 1.9, ordinary ore blending ratio 60% and a carbon content of 5.5%. Comprehensively, considering the sintering and smelting property of the ludwigite ore, the primary and secondary influencing factors are: carbon content, ordinary ore ratio and basicity, and the optimal ore blending scheme is: basicity 1.9, ordinary ore blending ratio 60% and a carbon content of 5.5%.

Influence of binder systems on sintering characteristics, microstructures, and mechanical properties of PcBN composites fabricated by SPS

Cubic boron nitride (cBN) with high hardness, thermal conductivity, wear resistance, and chemical inertness has become the most promising abrasive and machining material. Due to the difficulty of fabricating pure cBN body, generally, some binders are incorporated among cBN particles to prepare polycrystalline cubic boron nitride (PcBN). Hence, the binders play a critical factor to the performances of PcBN composites. In this study, the PcBN composites with three binder systems containing ceramic and metal phases were fabricated by spark plasma sintering (SPS) from 1400 to 1700 °C. The sintering behaviors and mechanical properties of the composites were investigated. Results show that the effect of binder formulas on mechanical properties mainly related to the compactness, mechanical performances, and thermal expansion coefficient of binder phases, which affect the carrying capacity of the composites and the bonding strength between binder phases and cBN particles. The PcBN composite with SiAlON phase as binder presented optimal flexural strength (465±29 MPa) and fracture toughness (5.62±0.37 MPa·m1/2), attributing to the synergistic effect similar to transgranular and intergranular fractures. Meanwhile, the excellent mechanical properties can be maintained a comparable level when the temperature even rises to 800 °C. Due to the weak bonding strength and high porosity, the PcBN composites with Al2O3-ZrO2(3Y) and Al-Ti binder systems exhibited inferior mechanical properties. The possible mechanisms to explain these results were also analyzed.

Effects of Cu substitution on microstructures and microwave dielectric properties of Li2ZnSiO4 ceramics

Herein, the influence of Cu2+ substitution on the phase composition, bulk density, microstructures, and microwave dielectric properties of Li2CuxZn1−xSiO4 (0 ≤ x ≤ 0.06) ceramics prepared by a solid-state reaction were investigated. The results of XRD and mapping showed that Cu2+ substitution can avoid the influence of secondary phase on the properties of samples. According to the analysis of bulk density, microstructure and microwave dielectric properties, a proper amount of Cu substitution not only improved the sintering characteristics of Li2CuxZn1−xSiO4 ceramics, reduced the densification temperature from 1250 °C to 950 °C, but also increased the Q×f value. Furthermore, Cu2+ substitution also improved the temperature stability of the samples. Particularly, the Li2Cu0.04Zn0.96SiO4 ceramics sintered at 950 °C for 5 h possessed excellent microwave dielectric properties: εr = 5.624, Q×f = 12,764 GHz, and τf = −77 ppm/°C, exhibiting a potential for the low temperature co-fired ceramic applications.

Sintering characteristics and microwave dielectric properties of 0.5(Ca0.7Nd0.2)TiO3–0.5(Li0.5Nd0.5)TiO3 ceramics with La2O3–B2O3–CaO–P2O5 additive

In this paper, the effects of glass-ceramics sintering aid, La2O3–B2O3–CaO–P2O5 (LBCP), on the sinterability, microstructure, and microwave dielectric properties of 0.5(Ca[Formula: see text]Nd[Formula: see text]TiO3–0.5(Li[Formula: see text]Nd[Formula: see text]TiO3 (CNT–LNT) ceramic have been investigated. The results indicated that LBCP glass-ceramics has good wettability to CNT–LNT (contact angle at 980[Formula: see text]C is 31.9[Formula: see text]), and it can be used as an effective sintering aid to reduce the sintering temperature of CNT–LNT ceramic from 1300[Formula: see text]C to 980[Formula: see text]C. LBCP glass-ceramics did not change the main crystal phase (perovskite structure) of the sample, but a small amount of LaBO3 and LaPO4 phases was precipitated. Since the LaBO3 and LaPO4 phases are low-loss phases, it is believed that the crystal phases can improve the dielectric properties of the sample, especially the dielectric loss. The samples with 10 wt.% of glass additive sintered for 4 h at 980[Formula: see text]C exhibit the optimized properties: a high dielectric constant of 80.8 and a [Formula: see text] value of 2031 GHz. The high [Formula: see text] and [Formula: see text] value, coupled with a relatively low sintering temperature, suggest that the optimized compositions have the potential to be used in microwave low-temperature co-fired ceramics applications.