Multiphase ceramic composites derived by reaction of Nb and SiCN precursor

In this work multiphase Nb(C,N)/Nb₅Si₃ ceramic composites containing niobium silicide, nitride and carbide phases were designed by using the polymer derived ceramic (PDC) route to avoid the complicated shaping of refractory metal compounds. Starting from polycarbosilazane (PCSZ) precursor powder and metallic niobium as reactive filler green compacts were manufactured by uniaxial warm pressing and stabilized by subsequent crosslinking. Due to the reactivity of both the Nb and the rearrangements within the forming amorphous SiCN phase a porous ceramic material is generated via solid-state reaction during thermal treatment. Depending on the amount of PCSZ as well as on the pyrolysis conditions the particles within this network reveal a core/rim structure containing submicron-sized Nb₂CN, NbC as well as coarse-grained Nb₂N phases in the core and Nb₅Si₃ or alternatively metastable Nb₅Si₄C phase at the particle surface.     

活性石灰回转窑用耐火砖损坏原因及其解决办法

回转窑耐火砖质量直接影响到窑的正常运转、产品的质量、产量、生产成本。本文对回转窑耐火砖损坏的原因进行了分析,并提出解决办法和预防措施。     

Characteristics and Application of Andalusite Material and Andalusite-Based Refractory

Andalusite material and Andalusite-based refractory are very popular in Europe and Japan, but its applications are restrained because of its low quality and misunderstanding in China. The paper introduced in detail the characteristics of andalusite material and andalusite-based refractory based on the authors‘ research work in recent years and on some references. Some information is illustrated clearly by figures and microstructure photographs. It is concluded the property of raw material and refractory is not determined by alumina content but by type and quantity of the impurities and microstructure.Mullitisation provide andalusite-based refractories more excellent macro and micro properties that guarantee itspopular application.     

Thermophysical properties of molten refractory metals measured by an electrostatic levitator

Thermophysical property measurements of molten refractory metals, which are very difficult and hardly conducted with conventional methods due to their high melting temperature and risk of reaction with container walls, have been conducted using noncontact diagnostic techniques in an electrostatic levitator. This paper first briefly summarizes the procedures and methods adopted by the Japan Aerospace Exploration Agency to enable the measurements of density, surface tension, and viscosity on molten refractory metals. Typical data of superheated and undercooled liquids that would have been impossible to obtain without the use of these techniques are then reported. Specifically, density, surface tension, and viscosity of Ti, Zr, Nb, Mo, Ta, and W were successfully measured over a wide temperature range, including the undercooled region.     

Conditions for fabricating single-phase (Ta,Zr)C carbide by SHS from mechanically activated reaction mixtures

The process parameters for the fabrication of binary carbide (Ta, Zr)C using MA–SHS were optimized. After MA processing in air, the SHS product was the virtually single-phase binary carbide (Ta, Zr)C with a ZrO₂ content less than 3%. Activation of the exothermic mixture in argon or under vacuum did not give rise to the single-phase product because the TaC and ZrC phases were present in addition to (Ta, Zr)C.Introduction of excess carbon, an increase in the combustion and post-reaction temperatures, and an increase in the duration of thermal relaxation using a “chemical oven” yielded the single-phase (Ta, Zr)C solid solution with lattice parameter a=0.4493 nm, which corresponds to 17.5 at% of dissolved ZrC. Dense samples were fabricated from submicron-sized carbide powder via hot pressing and spark plasma sintering; their properties were studied.     

多金属难选钼矿综合回收试验研究

针对某多金属难选钼矿矿石氧化严重以及各主要矿物互含高、嵌布关系密切等特点,研究先采用混合浮选工艺流程,获得混合精矿钼含量为4.21%,金含量为48.86g/t,银含量为84.80g/t;由于用常规物理选矿方法将钼从混合精矿中分离出来难度很大,故对混合精矿进行化学处理,最终获得的钼浸出率为86.6%,使钼与其他有价金属有效分离。     

Possible use of waste serpentine from Abdasht chromite mines into the refractory and ceramic industries

There are approximately 20.5 million tons of waste rocks in Abdasht chromite mines which might cause considerable environmental problems in the near future. Serpentine is one of the most important rocks that can be abundantly found in this mine. In this work, the waste serpentine was processed by dry magnetic drum separator. Chemical analysis showed high content of MgO in the non-magnetic fraction (NMF) serpentine that reached to 47.85% after calcining at 1050 °C. The XRD result revealed that antigorite was the main phase of the NMF-serpentine while the major phase of the samples fired at 1050–1650 °C was forsterite. Considerable water absorption after 2 h dwell time at 1650 °C, indicated high refractoriness and high sintering temperature of the waste serpentine from Abdasht mines. These results proved the potential capability of waste serpentine from Abdasht mines as a raw material to be used in high temperature refractory and ceramic products.     

不定形耐火材料在步进梁式加热炉上的应用

加热炉采用不定形耐火材料进行整体浇注，明显提高了炉体的整体性和气密性，延长了加热炉的使用寿命。本文总结了加热炉使用不定形耐火材料的实践经验，供同行们参考。     

Incipient plasticity and activation volume of dislocation nucleation for TiZrNbTaMo high-entropy alloys characterized by nanoindentation

With instrumented nanoindentation, incipient plasticity of two as-cast BCC TiZrNbTa and TiZrNbTaMo high-entropy alloys(HEAs) are investigated in terms of pop-in events during loading, to characterize the dislocation behavior in these solid-solution alloys. It is shown that the maximum shear stress (max)required for dislocation nucleation is determined to be 1/16-1/12 and 1/18-1/14 of shear modulus for the TiZrNbTa and TiZrNbTaMo HEAs, respectively, which is nearly comparative to the theoretical shear stress of these alloys. The activation volumes of dislocation nucleation the TiZrNbTa and TiZrNbTaMo HEAs are determined to be 1.2 b3 for and 1.3 b3, respectively, which is substantially irrespective of alloying with Mo. Furthermore, activation volumes of these two HEAs are on the order of cubic burger's vector and only one-third of the value for TiZrHfNb HEA, suggesting that a heterogeneous nucleation of dislocation took place in a way of direct atom-vacancy exchange, rather than of the cooperative motion of several atoms. These findings reveal the unique feature in deformation of BCC solid-solution complex alloys.     

Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering

The MoNbTaTiV refractory high-entropy alloy(RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying(MA) and spark plasma sintering(SPS).The microstructural evolutions,mechanical properties and strengthening mechanisms of the alloys were systematically investigated.The nanocrystalline mechanically alloyed powders with simple bodycentered cubic(BCC) phase were obtained after 40 h MA process.Afterward,the powders were sintered using SPS in the temperature range from 1500 ℃ to 1700 ℃.The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic(FCC) precipitation phases.The bulk alloy sintered at 1600℃ had an average grain size of 0.58 μm and an FCC precipitation phase of 0.18 μm,exhibiting outstanding micro-hardness of 542 HV,compressive yield strength of 2208 MPa,fracture strength of 3238 MPa and acceptable plastic strain of 24.9% at room temperature.The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening.It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.