Xiong Gang Lu

Interaction between the Ceramic CaZrO3 and the Melt of Titanium Alloys

The CaZrO3 complex oxide ceramic was synthesized in the development of the potential refractory for melting of titanium alloy, the crucible ( 40XH40mm) was prepared by the solid sintering of mixture of powder (CaO:ZrO2 =1:1) with a small amount of TiO2 as additive at 1750°C. The melting of TiNi and Ti6Al4V was carried out in the inducting furnace under vacuum or/and Ar atmosphere. The interfacial reaction between the melts of alloys and CaZrO3 refractory was investigated by scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). It is found that, the thickness of interfacial reaction layer between the ceramic CaZrO3 and the melt of titanium alloys (TiNi and Ti6Al4V) is approximately 30-300 μm, there are few elements such as Ca, Zr, Ti, and Ni diffused through the interfacial reaction layer. These results may provide the basement to designing a novel refractory for melting of titanium alloys.

Catalytic Reforming of Model Tar Compounds from Hot Coke Oven Gas for Light Fuel Gases Production over Bimetallic Catalysts

The catalytic reforming of toluene was performed to investigate the possibility for directly converting tar components from hot coke oven gas (COG) with lower steam/carbon (S/C) molar ratio to light fuel gases. The Ni0.25Me0.25/Mg2.5(Al)O (Me=Fe, Cu, Zn, Mn) bimetallic catalysts derived from hydrotalcite showed excellent catalytic activity. The effects of various reaction conditions on the catalytic performance were investigated in detail. Toluene could be completely converted into small gas molecules of CH4, CO and CO2 over the catalyst at S/C=0.7 and 650-750 oC under atmospheric pressure. Lower reaction temperature and higher H2 content in feed gas both could promote the formation of CH4, while higher S/C molar ratio benefited the CO yield.

Hydrogen Production from Coke Oven Gas by CO2 Reforming over Mesoporous La2O3-ZrO2 Supported Ni Catalyst

The CO2 reforming of coke oven gas (COG) for hydrogen production was investigated over mesoporous NiO/La2O3-ZrO2 catalysts. At optimized reaction conditions, the conversions of CH4 and CO2 more than 93%, while a H2 selectivity of 94.7% and a CO selectivity of 98.6% have been achieved at 800 °C. The effect of reaction temperature on the catalytic performance was investigated in detail. The catalysts with appropriate La2O3 content showed better catalytic activity and resistance to coking, which will be promising catalysts in the catalytic dry reforming of COG.

Catalytic Reforming of Model Tar Compounds from Hot Coke Oven Gas over Pd Promoted Ni/Mg(Al)O Catalysts

Pd (0.1-1 wt%) loaded Ni/Mg(Al)O catalysts have been prepared by co-precipitation and impregnation methods, and their catalytic activities were tested in the catalytic reforming of tar components from hot coke oven gas (COG) with lower steam/carbon (S/C) molar ratio. The 0.5%Pd-12%Ni/Mg3(Al)O bimetallic catalyst derived from hydrotalcite showed excellent catalytic activity. The effect of reaction temperature on the catalytic performance was investigated in detail. Toluene could be completely converted into small gas molecules of CH4, CO and CO2 over the catalyst at S/C=0.42 and 600°C under atmospheric pressure.

Steam Reforming of Simulated Coke Oven Gas over Ni/Al2O3-MgO Catalysts for Syngas Production

The steam reforming of simulated coke oven gas (COG) with toluene as a model tar compound for syngas production was investigated over Ni/Al2O3-MgO catalysts. XRD results showed that the catalysts with high calcination temperature and Al2O3 content after calcination formed (Ni,Mg)Al2O4 spinel and Ni-Mg-O solid solution structure. At optimized reaction conditions, toluene and CH4 can be completely converted, while a H2 yield of 71.8% and a CO yield of 76.1% have been achieved at 800 oC. The catalysts with appropriate calcination temperature and Al2O3 content showed better catalytic activity and resistance to coking, which will be promising catalysts in the catalytic reforming of COG.

Modification of CaO Refractory for Melting Titanium Alloys and its Hydration Resistance

CaO is a promising refractory for melting TiNi shape memory alloys, the carbon contamination can be avoid by using CaO crucible instead of carbon crucible. However, its industrial application is limited by the easy hydration of CaO in the air. In this study, the hydration resistance of CaO is modified by the addition of ZrO2, the powder of CaO adding 6.0 to 15.0mol% ZrO2 and 2.0mol% TiO2 is ball- milled, the mixture is shaped into the chip by the isostatic pressing method (IP), then the samples are sintered at 1750°C. The X-ray diffraction analysis reveals that the sintered samples consist of CaO dissolved with ZrO2 and CaZrO3. The anti-hydration property is described by the weight addition of samples, which are stored at the room temperature and atmosphere. It is shown that the sample with 12% ZrO2 of additive possesses the good hydration resistance, its weight addition stored after 56-days is less than 0.6wt%. Therefore, the powder of CaO with 12.0% ZrO2 additive are used to prepare the crucible by IP, the green crucible is sintered at 1750°C. This home-made crucible is used for melting TiNi alloy by means of the induction method at 1500~1800°C temperature and the vacuum environment, it is found that, the internal and external surface of crucible were almost kept unchanged after melting, this refractory did not obviously react with titanium melts, this result may provide a support for searching a new refractory with the good hydration resistance for melting of titanium alloys.

INFLUENCE OF TEMPERATURE AND PRESSURE ON THE KINETICS OF Mg-6mol%LaNi PREPARED BY HYDRIDING COMBUSTION SYNTHESIS

A new model to study the hydriding/dehydriding (H/D) kinetic mechanism has been applied in the two-phase (α-β) region of the Mg-6mol%LaNi composite at temperature and pressure ranging from 523 to 623K and 0.256 to 0.992MPa H 2 , respectively. The coincidence of the theoretical calculation with the experimental data indicates that the rate-limiting step is hydrogen diffusion in the β phase for hydriding process and the diffusion of hydrogen in the α solid solution for hydrogen desorption with activation energies 89500 and 87900J/mol H 2 for H/D processes, respectively, which were much smaller than those of MgH 2 and can be attributed to the La and Ni additions.

Carbon deposition on iron surfaces in CO–CO2 atmosphere

Thermodynamic calculations and thermogravimetric (TG) analysis were performed in order to understand the mechanism of carbon deposition on the surfaces of iron particles during the reduction of iron ore in a CO–CO2 atmosphere. The results of the thermodynamic equilibrium phase analysis indicate that the phases of the carbon deposition process can be predicted on the basis of the carbon potential, reaction temperature and gas pressure. The optimal thermodynamic conditions for carburisation are a low temperature (Tu2009<u2009Tm) and a high carbon potential (αc>1). TG analysis is performed in a gas mixture of 65 vol.-% CO and 35 vol.-% CO2 at 650, 706 and 750°C. Cementite (Fe3C) is generated as an intermediate product, which acts as a catalyst for carbon deposition. Carbon deposition is inhibited at high temperatures (T>791°C) owing to the high stability of Fe3C. When the reaction temperature is higher than the thermodynamic limit for the formation of Fe3C, carbon deposition cannot occur. A mechanism for carbon deposition is proposed based on the experimental results.

Catalytic Partial Oxidation of Coke Oven Gas to Syngas over Ni/SiO2 Catalyst Modified by Rare Earth Metal Oxide in a Membrane Reactor

The performance of Ni/SiO2 Catalysts modified by La2O3, ZrO2 and CeO2 were tested in a BaCo0.7Fe0.2Nb0.1O3-δ (BCFNO) membrane reactor by catalytic partial oxidation of coke oven gas (COG) under atmospheric pressure. The results show that the oxygen permeation flux increased dramatically with Ni/RxOy/SiO2 (R = La, Zr or Ce) catalysts by adding the element of rare earth especially the La during the reforming reaction. At optimized reaction conditions, the dense oxygen permeable membrane had an oxygen permeation flux around 16.4 ml/cm2•min and a CH4 conversion of 99.2% have been achieved at 900 oC.

Improving Performance of BaCo0.7Fe0.2Nb0.1O3-δ Ceramic Membrane by a Surface-Coating Layer for Partial Oxidation of Coke Oven Gas

The BaCo0.7Fe0.2Nb0.1O3-δ (BCFNO) membranes combined with Ce0.8Re0.2O2-δ (Re=La, Y) layer on the permeation side were used for hydrogen production by partial oxidation reforming of coke oven gas (COG). The Ce0.8Re0.2O2-δ improved the oxygen permeation flux of the membrane by 11–28% at 750 oC. The high oxygen permeation flux achieved using the Ce0.8Re0.2O2-δ surface-coating layer in this work are quite encouraging with a maximum value reaching 19.7 ml/cm2•min at 900 oC, which will be promising surface modification materials in the catalytic partial oxidation reforming of COG.