The Structure of Sinter

Poorly performing sinters exhibit excessive lead silicate phases without the tight matrix of intergrown crystal phases to provide structural support. This allows the sinter to soften and slump as the temperature is raised. 

For a typical sinter containing 46 per cent Pb, five per cent Zn, 11 per cent Fe, nine per cent CaO, and 11 per cent Si02, the glassy matrix will represent close to 40 per cent of the volume of the sinter, the melilite phase is of the order of 30 per cent and the ferrites of the order of 20 per cent. 

The residual level of sulfur in sinter is also important in achieving the most suitable sinter structure as well as meeting maximum limits for the blast furnace, and should generally be less than two per cent. Common levels are around 1.7 per cent but can be as low as 0.7 per cent. 

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Takahashi H, Shinohara N, Uematsu K (1996) Influence of spray-dry slurry flocculation on the structure of sintered silicon nitride. J Ceram Soc Jpn 104 59-62... 

When the structure of a metal changes, it is because there is a driving force for the change. When iron goes from b.c.c. to f.c.c. as it is heated, or when a boron dopant diffuses into a silicon semiconductor, or when a powdered superalloy sinters together, it is because each process is pushed along by a driving force. 

PM steel-processing techniques have not been used for the fabrication of structural parts or critical components because, as stated previously, the properties of sintered steel parts have- not... 

Thus, the whole complex of existing experimental data indicates that the major part of polycrystalline contacts in vacuum sintered polycrystalline oxides are provided by bridges of open type. Moreover, the vacuum sintering at moderate temperatures 300 - 350°C leads to formation of a unified pattern (see Fig. 2.4, b) which cannot be disjoint into specific microcrystals and connecting bridges [37, 40]. The structure of adsorbents obtained presents a complex intertwining of branches of various thickness. 

The ferric oxide, hematite, used in the present work was a high purity powder reagent with a BET surface area of 27 m2/g 30 mg was employed in each run. Some measurements were made on hematite calcined in air to see the effects of sintering the surface on the chemical structure of the adsorbed metal ions. The hematite samples were checked by Mossbauer absorption and powder X-ray diffraction measurements. The Mossbauer absorption spectra consisted of a magnetic sextet with no superparamagnetic component due to fine particles ( ). 

Unfortunately these data do not permit of calculation of the change in adsorption per sq. cm. caused by the gradual readjustment of the atomic positions into the stable configurations, since during the process of sintering the superficial surface undergoes contraction as well as a modification in the structure. Some measure... 

There has been considerable work in the literature on the structure of very small particles and clusters. Interest in this field has been primarily due to Ino s (1966) early experimental studies of normally fee metals prepared by vapour condensation which showed that a sizable portion of the particles exhibited non-crystallographic structures. These non-crystallographic atomic clusters or polycrystalline nuclei have been observed to consist of pentagonal bi-pyramid or icosahedra form of twinned structures and are known as multiply twinned particles (MTPs). EM studies of supported transition metal catalyst systems have indicated that MTPs sinter faster in catalytic reactions leading to the loss of surface area and are not beneficial to catalysis (Gai 1992). We describe the structure and the role of MTPs in catalysis in the following sections. 

The crystal structure and the sintering behavior of hexaaluminates was widely investigated. The relation of sintering resistance to anisotropic ion diffusion in the layered alumina phase was clarified to a large extent. Other evidence suggests that combustion activity is obtained through a redox mechanism associated with reversible variation of oxidation state of the transition metal ions in the structure. Mn was the best and most stable active component. However, fundamental and applied studies are needed to better clarify the redox mechanism of the reaction and how it is related to the chemical and structural features of the Mn-containing layered-alumina phase. This could also provide useful information for the development of an optimum catalyst composition,... 

Peters intentionally changed the structural factors fc and d, and thus A, and found in the material close dependence of the toughness of sintered carbides, calculated from Palmquist cracks, on the free-mean-path (Table... 

Since improvements achievable with bulky electrodes are limited by the structure of the electrode itself, sintered, porous, Teflon bonded, or phosphate-bonded Ni electrodes have been proposed [386, 391, 399, 400]. A mere increase in surface area is observed without any change in Thfel slope. The same is the case with Ni wiskers in spite of their very large surface area and small particle size [401, 402], A decisive modification of the kinetic pattern is indeed obtained as Raney Ni is used [93, 403] (see Fig. 11). This form of Ni is well known also in the field of hydrogenation catalysis. As an electrocatalyst it was proposed by Justi et al. [404] long ago. Raney Ni is obtained by allowing Ni with a component (usually Al or Zn) which is then... 

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