Effect of sintering on the catalytic functionalities of MOS2/Al2O3 catalysts

Effect of sintering on physico-chemical and catalytic properties of Mo, Co-Mo, Ni-Mosupported on -Al₂O₃ is reported. Such effects on hydrodesulfurization (HDS), hydrogenation (HYD) and hydrodeoxygenation (HDO) are investigated as a function of sintering temperature. The results indicated that HDS and HYD have different optimum calcination temperatures and these functionalities originate from different sites. The results are discussed in the light of molybdenum sulfide dispersion, promotional effects and phase transformations of active component, promoters and support.     

Processing of mesocarbon microbeads to high-performance materials: Part II. Reaction bonding by in situ silicon carbide and nitride formation

The processing of carbon-ceramic composites by utilizing the unique sintering ability of mesocarbon microbeads (MCMB) is reported. The ceramic constituents (silicon nitride and silicon carbide) are formed in situ by reactions between MCMB and silicon in different atmospheres. In comparison with direct addition of ceramic (SiC, Si₃N₄) phases, in situ formation shows several appealing features. By inducing the reaction of silicon with MCMB, the sintering ability of the composite is enhanced via reaction bonding mechanisms. Similarly, it is demonstrated that composite porosity is limited owing to silicon reaction with nitrogen. The reactive formation of nanoscale ceramic reinforcements via decomposition of the silicon-containing polymer (e.g. poly-carbomethyl-silane) is also reported. This approach results in formation of uniform nanosized (>100 nm) SiC layers strongly bonded to the surface of the carbon particles. The presented results contribute to the development of carbon-ceramic materials with high-operational properties.     

Formation of bed agglomeration in a fluidized multi-waste incinerator

A case study was carried out to investigate the bed agglomeration observed in a fluidized bed incinerator when burning blends of three wastes (carbon soot, biosludge and fuel oil). Several instrumental approaches were employed (i.e. XRF, SEM, XRD, and ICP-AES) to identify the bed materials (fresh sand and degrader sand) and clinkers formed in the full-scale incinerator tests. Several elements (V, Al, S, Na, Fe, Ni, P, and Cl), which normally are associated with the formation of low melting point compounds, were found in the waste blends at high content levels. The clinker bridges were identified to be associated with Al, Fe, V, K, Na, S, Ni, and Si elements.The effects of temperature and blending ratio were investigated in a muffle furnace. Carbon soot is believed to be more susceptible to the clinker formation than the other two fuels. Thermodynamic multi-phase multi-component equilibrium calculations predict that the main low melting point species could be Al₂(SO₄)₃, Fe₂(SO₄)₃, Na₂SO₄, NaCl, Na₂SiO₃ and V₂O₅. This information is useful to understand the chemistry of clinker formation. Also, it helps to develop methods for the control and possible elimination of the agglomeration problem for the design fuels.     

Aerosol deposition of dense lead zirconate titanate thin films at room temperature

Lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) films were grown on silicon 1 0 0 substrate by aerosol deposition, using solid-state reacted powder containing donor oxide Nb₂O₅, while the substrate was maintained at room temperature. The PZT films were simultaneously sintered upon deposition on a highly densified ceramic layer. Crystalline phases of the deposited films have been determined by X-ray diffractometry (XRD), and microstructures analysed by transmission electron microscopy (TEM). The cross-section microstructure consisted of several thin layers, including the PZT film and the platinum electrode and titanium-buffered layers on the substrate. High-resolution images revealed that the PZT layer contained a mixture of randomly oriented grains of nanometre size, which were embedded in an amorphous matrix. In contrast to the conventional liquid-phase sintering mechanism, sintering of the PZT films involved amorphised phases generated by pressure-induced amorphisation (PIA) from plastic deformation when the initial powder particles collided amongst one another upon reaching the silicon substrate during aerosol deposition. An analogy may be drawn to the impact of extraterrestrial meteorites in which diaplectic glass, i.e., amorphised phase, was formed and retained metastably at room temperature. The individual PZT grains were joined with the amorphised phase(s) and sintered to become a dense, thin film on the silicon substrate.     

烧结助剂对反应烧结氮化硅陶瓷的影响

以Si粉和C粉为主要原料 ,在氮气流量为1.2L·min- 1,氮化温度为 1380℃ ,保温时间为 2 0h的条件下 ,研究了分别以 10wt%的MgO、Al、Al2 O3和Al2 O3+Y2 O3粉为烧结助剂对反应烧结氮化硅陶瓷的影响。结果表明 :以MgO粉作烧结助剂时 ,试样的主要成分是MgSiO3,另外还有Si2 N2 O ,但没有Si3N4 生成 ;以Al粉作烧结助剂时 ,试样的主要成分是SiO2 ,仅有少量Si3N4 存在 ;以Al2 O3作烧结助剂时 ,试样的主要成分是β Si3N4 和α Si3N4 ;以 2wt%Al2 O3+8wt%Y2 O3作烧结助剂时 ,试样的主要成分为 β Si3N4 ,同时含有少量α Si3N4 。     

烧结气氛对合成MgAl2O4-Ti(C,N)复合陶瓷的影响

以金属铝粉、钛白粉和轻烧MgO细粉为原料,通过设计100%焦炭粒(简称C气氛),10%钛白粉 90%焦炭粒(简称TC气氛),以及10%硅微粉 90%焦炭粒(简称SC气氛)3种埋粉条件下的高温烧结还原性气氛,采用X射线衍射仪(XRD)、扫描电镜(SEM)和微区电子探针分析(EPMA)等手段,研究了铝热还原氮化法(1600℃3h)制备MgAl2O4-Ti(C,N)复合陶瓷在不同烧结气氛下的相组成和显微结构的变化。结果表明在不同气氛下,烧后试样的主要物相均为MgAl2O4和Ti(C,N),Ti(C,N)可能会固溶氧,气氛对Ti(C,N)的影响较大。和单纯埋炭气氛下相比,在TC气氛下有助于Ti(C,N)的生成,但晶粒细小;在SC气氛下不利于Ti(C,N)的生成,且有玻璃相存在。     

Effects of the sintering atmosphere on Nb-based dielectrics

The effects of a forming atmosphere on the stability, the sintering and the dielectric properties of Ba₅Nb₄O₁₅, BaNb₂O₆, ZnNb₂O₆ and Zn₃Nb₂O₈ ceramics were investigated, because of the primary importance of the sintering atmosphere in relation to copper sintering. These Nb-based materials were sintered in air and in Ar/H₂10%. Zn-containing samples are very sensitive to the reductive atmosphere. ZnO volatilises at 800–850 °C and the resulting compound does not exhibit the expected properties. BaNb₂O₆ and Ba₅Nb₄O₁₅ are more stable in term of relative weight loss. Nevertheless, the phase analysis reveals a modification of the BaNb₂O₆ phase, what induces the degradation of the dielectric property stability versus temperature. The properties of Ba₅Nb₄O₁₅ are not modified by a sintering in reductive atmosphere. A relative permittivity of 38.8, a permittivity temperature coefficient of −150 ppm °C⁻¹ and an insulating resistivity of 10^10.9 Ω cm were obtained for this latter.     

尖晶石质浸入式水口内衬的研究

以77%的电熔尖晶石(粒度≤1mm和≤0.074mm)、20%的α-Al2O3(≤2μm)和3%的电熔镁砂(≤0.074mm)为原料,分别在1000℃、1200℃、1500℃保温3h的条件下,研究了SiO2微粉外加量(分别为0、0.5%、1.0%、1.5%)对尖晶石材料烧结性能的影响,并在1450℃的还原性气氛下进行了尖晶石内衬材料与铝碳本体材料的复合试验。研究结果表明:在不过多增加尖晶石材料高温液相量的情况下,SiO2微粉的外加量为1.0%较为适宜;在尖晶石试样中同时添加1%SiO2微粉和3%电熔镁砂细粉能很好地降低其烧结温度,而且其热膨胀率与铝碳材料的热膨胀率较为接近,而尖晶石材料与铝碳材料的复合试验结果也表明,内衬和本体材料结合完好,且无裂纹出现。