Advanced high-density oxide ceramics with a controllable microstructure. Part V. Chemically stable dense ceramics based on yttrium, scandium, and aluminum oxides

Data on sintering of Y₂O₃ ceramics are presented. It is shown that the degree of sample sintering depends on the powder agglomeration, which is determined by the nature of the starting material and the conditions of Y₂O₃ production. Y₂O₃ powder produced from yttrium carbonate exhibits the best sintering characteristics. The samples thus obtained are sintered to a relative density of about 95% even at 1600°C. Dry treatment of various Y₂O₃ powders in a planetary mill equalizes their properties and reduces the sintering temperature substantially. Data on the properties of Y₂O₃ ceramics are presented. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 2–7, January, 1997. For the beginning and continuation of the review see issues Nos. 1,2,4-7,9, and 12 of 1996.     

Modern high-density oxide-based ceramics with a controlled microstructure. Part V. Chemical-resistant high-density yttria-, scandia-, and alumina-based ceramics

A YScO₃-ceramics that is stable with respect to an alkali metal plasma and possesses increased strength and thermal stability, has been developed. The ceramics is obtained by hot pressing at 1450–1550°C. It was established that a 2% Al₂O₃ additive improves the sintering ability and reduces the size of crystallites. The Al₂O₃ additive has proved to be efficient only if introduced in the course of milling hydroxides in an aluminum chloride solution. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 2–10, March, 1997. For the beginning see No. 1 (1996); continued in Nos. 2, 4–7, 9, 12 (1996), Nos. 1 and 2 (1997).     

Modern high-density oxide-based ceramics with a controlled microstructure. Part V. Chemical-resistant high-density yttrium-, scandium-, and alumina-based ceramics

Data on the sintering of Sc₂O₃ ceramics are presented, showing that the degree of densification of the sintered products increases upon dry grinding of the initial Sc₂O₃ powders in a planetary mill. This treatment also equalizes the technological properties of powders from different batches. Properties of sintered Sc₂O₃ ceramics are presented. The strength level of the material can be increased by using certain oxide additives. In particular, introduction of La₂O₃ increases the flexural strength of the ceramics to the level of 250–270 MPa. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp. 2–6, February, 1997. For the beginning see No. 1 (1996); continued in Nos. 2, 4–7, 9, 12 (1996) and No. 1 (1997). (To be continued.)     

Modern high-density oxide ceramics with a controlled microstructure. Part VI. Fabrication of light-transmitting oxide materials

Results obtained in fabrication of light-transmitting ceramics based on yttrium-aluminum garnet are presented. The best optical properties were exhibited by ceramics with HfO₂, ZrO₂, or Sc₂O₃ additives introduced through salts by coprecipitation. The properties of light-transmitting ceramics made of yttrium-aluminum garnet and materials based on them are described and the ceramics are shown to have good prospects in various fields of engineering.     

Modern high-density oxide ceramics with a controlled microstructure. Part VI. Fabrication of light-transmitting oxide ceramic materials

Results obtained in fabrication of light-transmitting Y₂O₃-based ceramics with HfO₂ and ZrO₂ additives are described. The dependence of their sinterability and optical properties on the kind and amount of additives and some process parameters is established. Important physical and engineering properties of the best compositions of Glubor ceramics are compared with the properties of the imported Yttralox counterpart. For the beginning of the series see No. 1 of 1996, for the continuation see Nos. 2, 4–7, 9, 12 of 1996 and Nos. 1–3 and 7 of 1997. Translated from Ogenupory i Tekhnicheskaya Karemika, No. 8, pp. 2–11, August, 1997. (To be continued.)     

Modern high-density oxide ceramics with controlled microstructure. Part I. Effect of aggregation of oxide powders on the sintering and microstructure of ceramics

It is shown that the sintering and microstructure of oxide ceramics are determined by the properties of the powders used for its manufacture and, first of all, by the degree of aggregation of the particles and the characteristics of the aggregates. The aggregation phenomenon is considered for various technological methods. It is established that the structural features are inherited in all stages of the technological process. The highest sintering and homogeneity of the microstructure are exhibited by ceramics prepared from powders with aggregates having a size of fractions of a micrometer.Translated from Ogneupory, No. 1, pp. 5 – 14, January, 1996.     

Modern high-density oxide ceramics with a controlled microstructure. Part III. Microstructure and recrystallization processes in ceramic oxide materials

It is established that crystal growth in solid solutions depends on the sign of the variation of the lattice parameter. When the lattice parameter decreases, the structure becomes fine crystalline and vice versa. This makes it possible to predict the kind of microstructure of dense oxide ceramics with additives that form solid solutions. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 7, pp. 2 – 7, July, 1996. See the beginning of the article in No. 1, 1996 and its continuation in Nos. 2, 4 – 6, 1996.     

Modern high-density oxide ceramics with a controlled microstructure. Part IV. Technological methods for manufacturing highly disperse oxide powders for multicomponent oxide ceramics

Methods for fabricating highly disperse powders for multicomponent ceramics are discussed. Emphasis is placed on the popular production methods of chemical precipitation and heterophase interaction. Results obtained by a modified method of hydrophase chemical precipitation with spraying of concentrated salt solutions are presented. Problems concerning the production of powders with a specified chemical composition are considered. Special features of other methods used for manufacturing disperse oxide powders are discussed.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 9, pp. 2–10, September, 1996.For the beginning of the article see No. 1 of 1996, and for the continuation see Nos. 2, 4–7, 1996.     

Modern high-density oxide ceramics with controlled microstructure. Part II. Substantiation of the choice of modifying additives that affect the degree of sintering of oxide ceramics

It is established that additives that form solid solutions provide substantial densification of oxide ceramics due to defects of the crystal lattice. The use of combined additives that form solid solutions of isovalent and nonisovalent substitution makes it possible to create oxide ceramics with an exceptionally high density, which may result in the formation of optical transparency.Translated from Ogneupory, No. 4, pp. 2 – 13, April, 1996.The first two articles of the series have been published in Nos. 1 and 2, 1996.     

Modern high-density oxide ceramics with a controlled microstructure. Part II. Substantiation of the principles for choosing modifying additives that affect the degree of sintering of oxide ceramics

The types of solid solutions that additives form with monoxides and oxide compounds are determined. Formulas are suggested for the solid solutions. It is shown that for any type of solid solution formed the materials can be sintered to a very high density up to a transparent state. The main role here belongs to the gaseous medium for firing. Some principles for introducing the additives are formulated and the sinterability of the powders is considered. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 5, pp. 2–9, May, 1996. For the beginning of the article see No. 1, 1996, and for the continuation see Nos. 2 and 4, 1996.     

Modern high-density oxide ceramics. Part III. Microstructure and recrystallization processes in ceramic oxide materials

Recrystallization processes in oxide ceramics at high temperatures are considered. It is established that the microstructure of the ceramics remains equal-size-grained at all heating temperatures. The proportion of crystals with minimum and maximum sizes is controlled by the initial grain composition. The growth of crystals in coarse-crystal structures occurs by the joining of crystals in their rotation due to the stresses that develop. It is established that the degree of crystal growth in solid solutions depends on the sign of the change in the lattice parameter; as the parameter decreases, the structure always becomes fine-crystalline, and vice versa.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 2 – 9, June, 1996.For the beginning of the article see No. 1 of 1996, and the continuation is in Nos. 2, 4, 5 of 1996.     

Phase composition,microstructure, and microwave dielectric properties of non-stoichiometric yttrium aluminum garnet ceramics

A series of Y_3+xAl₅O₁₂ (?0.12 ≤ x ≤ 0.12) ceramics were prepared via a solid-state reaction under a vacuum sintering environment to investigate the impact of variations in different cation composition on the phase composition, microstructure, and microwave dielectric properties of yttrium aluminum garnet (Y₃Al₅O₁₂; YAG) ceramics. X-ray diffraction analyses revealed that Al₂O₃ precipitates in the Al-excess samples. In contrast, the YAlO₃ secondary phase appeared in the Y-excess samples, and variations in the content of both contributed to an increase in lattice parameters. The Rietveld refinement results showed that the lattice parameters and unit cell volume increased as the |x| value increased. The secondary phases of granular Al₂O₃ and YAlO₃ crystallized at the extended grain boundaries in samples with excess Al and Y were visible in the scanning electron microscopy images. The electron diffraction patterns confirmed that a small amount of Y₂O₃ promoted continuous phase boundaries and facilitated the release of internal stresses. Ultimately, after sintering at 1750 °C for 12 h and at x = 0.03, the microwave dielectric properties of the non-stoichiometric YAG ceramic sample were ε_r = 11.18, Q×f = 236936 GHz, and τ_f = ?35.9 ppm/℃.     

A highly refractory material based on zirconia stabilized with yttrium and aluminum oxides

Conclusions With combined additives (Y₂O₃ + Al₂O₃), zirconium dioxide forms solid solutions which resist thermal decomposition.A material was synthesized containing from 90–93 mol. % ZrO₂, from 3.5 to 5 mol.% Y₂O₃, and from 3.5 to 5% mol Al₂O₃, possessing an average coefficient of thermal expansion which is lower, and a thermalshock resistance which is higher, than the double solid solutions in the system ZrO₂-Y₂O₃ and ZrO₂-CaO.Translated from Ogneupory, No. 4, pp. 42–45, April, 1973.     

稀土氧化物对钛酸铝陶瓷显微结构和力学性能的影响

研究了添加稀土氧化物Y2O3和Y2O3+Nd2O3对钛酸铝陶瓷的烧结温度、力学性能和显微结构的影响.结果表明,添加1%的稀土氧化物可以降低钛酸铝陶瓷的烧结温度,改善其显微结构,提高其力学性能,尤其是添加1%的复合稀土氧化物(Y2O3+Nd2O3)后,钛酸铝陶瓷的抗折强度和断裂韧性是未添加的试样的1.96倍和1.82倍.其性能提高的主要原因是由于稀土元素的细晶强化、净化界面、固溶强化、自增韧补强等作用.     

Optically transparent ceramics based on yttrium oxide using carbonate and alkoxy precursors

Methods for producing optically transparent ceramic materials based on Y₂O₃ using carbonate and alkoxy precursors are considered. It is established that ceramic synthesized from yttrium isopropylate has better optical parameters than ceramics based on yttrium carbonate under equal heat treatment and firing regimes. __________ Translated from Steklo i Keramika, No. 8, pp. 17–19, August, 2006.     

Corundum ceramics based on aluminum oxide obtained by a plasma chemical method

Problems of sintering aluminum oxide consisting of highly disperse α-Al₂O₃ prepared by the plasma chemical method are considered. It is shown that this material possesses high sinterability even in the case of considerable pressing pressures. The introduction of MgO improves sintering of plasma chemical aluminum oxide and the addition of partially stabilized zirconia increases the ultimate strength of the ceramics in three-point bending to 450 MPa.     

Effect of different contents of zirconia and yttrium oxide on microstructure and properties of high alumina ceramics

The effects of zirconia and yttrium oxide addition on microstructure, bulk density, microhardness, flexural strength, and wear resistance of high alumina ceramics (>97 wt% Al₂O₃, MSA ceramics) composed of MgO–SiO₂–Al₂O₃ system have been investigated. The results show that the addition of zirconia makes the mechanical properties and wear properties of ceramics composed of MgO–SiO₂–Al₂O₃–ZrO₂ (MSAZ ceramics) system have been greatly improved compared with MSA ceramics. In addition, the ceramics composed of MgO–SiO₂–Al₂O₃–ZrO₂–Y₂O₃ (MSAZY ceramics) system have better mechanical properties and wear properties than MSAZ ceramics. With the contents of zirconia and yttrium oxide increase, the bulk density, microhardness, and flexural strength of MSAZ and MSAZY ceramics increased at first and then decreased. However, the wear rate shows the opposite. When 0.4 wt% ZrO₂ and 0.6 wt% Y₂O₃ were added to the matrix, the wear rate of MSAZY ceramics reached a minimum of 0.042%, and the wear resistance was improved by about 73.8% compared with MSA ceramics with a wear rate of 0.16%. In addition, the optimum additions of zirconia and yttria are 0.4% and 0.6%, respectively.     

Advanced ceramics based on aluminum,silicon, chromium,and lanthanum oxides: Preparation and applications (an overview)

Overviewed is the state-of-art in the synthesis and applications of advanced Al₂O₃-Cr₂O₃, SiO₂-Cr₂O₃, and Cr₂O₃-La₂O₃ composite ceramics.