Certain regularities of phase formation and structure evolution during hot-pressing of ultrafine powders

Tkacheva, I. I.

doi:10.1007/bf01283141

Refractories

1993

DOI: 10.1007/bf01283141

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Certain regularities of phase formation and structure evolution during hot-pressing of ultrafine powders

I. I. Tkacheva¹

Abstract: In order to optimize the technological regimes used for obtaining structural ceramics, it is necessa~, to understand the processes of structure evolution of the material and to control them purposefully. In particular, this is important when using ultrafine (highly dispersed) powders because of their peculiar properties.Densification of the powders of silicon nitride requires addition of sintering agents (activators). They interact with Si3N 4 and SiO 2 to form a liquid phase that facilitates the sintering pro… Show more

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1996

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“…2 Powders of PCS-and SHS-Si3N 4 differ in their structure. SHS-Si3N 4 is a powder of a light gray color with particles differing in size and morphology.…”

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Hot-pressed ceramics based on SHS silicon nitride

1996

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The creation of new effective technologies and materials with an optimum ratio of quality and price is a significant achievement. The high cost of ceramics made of silicon nitride is a result of the expensiveness of the initial powder. The present study of the applicability of ct-Si3N4 powder prepared by the method of self-developing high-temperature synthesis (SHS) in hot-pressing technology has shown that although materials based on SHS ct-Si3N4 powders are inferior to materials based on plasmachemical compositions, their high strength, crack resistance, and hardness at a moderate density in combination with the lower cost of the initial raw material make them suitable for operation in aggressive media under moderate temperatures and loads. The materials developed have also shown high armoring properties.The creation of new low-cost technologies and materials with an optimum ratio of quality and price is comparable with the development of high-performance materials. The high cost of ceramics made of silicon nitride is caused by the expensiveness of the initial powder.In this connection, we investigated the possibility of using silicon nitride powder prepared by the method of self-developing high-temperature synthesis (SHS) in hot-pressing technology.For comparison we used hot-pressed materials developed earlier on the basis of ultradisperse silicon nitride prepared by plasmachemical synthesis (PCS) [1,2]. In 1995 prices the cost of 1 kg of silicon nitride prepared by PCS is $55-70 against 55 thousand rubles for 1 kg of silicon nitride prepared by SHS. Additional difficulties arise in customs when the raw material arrives from countries of the former USSR.SHS silicon nitride of ct-modification produced by the SHS Research Center of the Institute of Structural Macrokinetics is a mixture of ~-and [3-Si3N 4 with a content of the a-phase of over 70%. 2Powders of PCS-and SHS-Si3N 4 differ in their structure. SHS-Si3N 4 is a powder of a light gray color with particles differing in size and morphology. In the opinion of the authors of [3] this is connected with the presence of at least two kinds of particles in the synthesized powder, namely, particles with a cotton-like and needle-like morphology. Milling in a planetary mill breaks up both conglomerates and individual parti- cles and thin filaments and needles, causing the appearance of a large number of particles with an approximate size of 0.2 Sam.We conducted mechanical activation of the powders in a ball mill for 100 h with balls made of Si3N 4, which is less effective than milling in a planetary mill. After the activation the mean size of the particles was 1 -2 Sam, the content of the fraction finer than 5 Sam exceeded 91%, and coarser particles (10 -15 sam) were encountered. Particles with an irregular shape were 0.1-0.5 Sam in size, acicular particles had a size of 2 -8 Sam, and broken particles had a size of 4 -8 Sam (Fig. la).The structure of PCS-Si3N 4 powders was uniform and fine-grain, and the particles were 0.05-0.1 Sam in size and had a round shape (Fig....

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“…2 Powders of PCS-and SHS-Si3N 4 differ in their structure. SHS-Si3N 4 is a powder of a light gray color with particles differing in size and morphology.…”

mentioning

confidence: 99%

“…For comparison we used hot-pressed materials developed earlier on the basis of ultradisperse silicon nitride prepared by plasmachemical synthesis (PCS) [1,2]. In 1995 prices the cost of 1 kg of silicon nitride prepared by PCS is $55-70 against 55 thousand rubles for 1 kg of silicon nitride prepared by SHS.…”

mentioning

confidence: 99%

Hot-pressed ceramics based on SHS silicon nitride

1996

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Certain regularities of phase formation and structure evolution during hot-pressing of ultrafine powders

Cited by 1 publication

References 1 publication

Hot-pressed ceramics based on SHS silicon nitride

Hot-pressed ceramics based on SHS silicon nitride

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