Features of Preparing Nano-Size Powders of Tetragonal Zirconium Dioxide Stabilized with Yttrium

The effect of wet chemical synthesis parameters on the properties of nano-powders of zirconium dioxide stabilized with yttrium is studied. Features of nano-powder synthesis by the oxalate, hydroxide and thermal hydrolysis of a sol methods are determined. Nano-size zirconium dioxide powder stabilized with 3 mole% yttrium is prepared by hydrothermal coprecipitation from a sol of metal chlorides and urea followed by dispersion and calcination. The possibility of controlling particle morphology by changing synthesis conditions, subsequent treatment and ultrasonic dispersion of the powder, and the calcination temperature-time schedule are studied by experiment. A method is developed for optimizing particle morphology (level of aggregation (agglomeration capacity)) and size. Non-agglomerated zirconium dioxide powder consisting of uniform nanosized (about 45 nm) aggregates of primary crystals is synthesized. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 28–42, May–June, 2005.     

Mechanical behavior of the ceramics based on ZrO2

Conclusions Following a single procedure, we studied the strength, the deformability, and the crack resistance of a number of ceramics based on zirconium dioxide containing stabilizing additives (magnesium oxide or yttrium oxide); their mechanical behavior was found to differ significantly. In particular, zirconium dioxide containing yttrium oxide (a brittle material with X=1) is linear-elastic up to its fracture; on the other hand, zirconium dioxide containing magneisum oxide (a relatively brittle material having <1) exhibits nonlinear behavior. In view of this, the resistance to crack growth, the temperature dependence of the deformation diagrams, and the other specific features of mechanical behavior of these types of ceramics differ significantly.Translated from Poroshkovaya Metallurgiya, No. 10 (346), pp. 51–56, October, 1991.     

Powder bronze with additions of an activated charge

Kinetics of processes of dispersion and agglomeration and the formation of sintered powder materials based on mechanochemically activated (MCA) charges have been studied. Effects of the time of milling on the fractional composition, energy consumption of the milling process, density of the compacts and sintered samples, ultimate strength for radial compression, and the efficiency of strengthening upon the introduction of MCA additions have been shown. A technology of production of a powder antifrictional bronze with additions of MCA charges has been developed, which includes a mechanochemical activation of wastes of compacts, their pressing, and sintering.     

Effect of mechanical activation on the formation of Si3N4-SiC composite powders

The paper examines how the mechanical activation of an initial silicon-carbon powder mixture and the temperature of its subsequent treatment influence the specific surface and phase composition of the end products. It is established that the preliminary mechanical activation of Si-C mixtures significantly increases the nitration rate of silicon and decreases the temperatures of formation of silicon carbide and silicon nitride (1200–1300 °C). The products resulting from the nitration of mechanically activated mixtures consist of α-Si₃N₄ whiskers with an aspect ratio of 10–100, silicon, carbide, and silicon nitride particles to 100 nm in size, and their agglomerates.     

Dispersion strengthening in a hypereutectic Al-Si alloy prepared by extrusion of rapidly solidified powder

When a hypereutectic aluminum-silicon alloy containing 16 wt pct silicon was rapidly solidified into powder using the spinning water atomization process, the individual powder grains were predominantly aluminum that was supersaturated with silicon and also contained well-dispersed 0.02-μm silicon particles. Although the silicon particles grew when the powder was extruded into a bar at temperatures from 673 to 803 K at an extrusion ratio of 4.3 and an extrusion speed of 0.9 mm/s, the average diameter was maintained on a submicron level. When the extrusion temperature was decreased from 803 to 673 K, the average diameter of the silicon particles in the extruded bar decreased from 0.8 to 0.5 μm, while the Vickers hardness (HV) and the ultimate tensile strength of the extruded bar increased from 120 to 160 (HV) and from 330 to 500 MPa, respectively. Both the hardness and the tensile strength of the extruded bars were several times higher than those of conventionally cast bars of the same alloy with cooling rates from 10⁻¹ to 10² K/s. On the other hand, the elongation decreased from 5.5 to 3.1 pct when the extrusion temperature was decreased from 803 to 673 K.     

Synthesis of nanocrystalline zirconium dioxide stabilized with yttrium oxide for low-temperature sintering

Technology for the synthesis of nanocrystalline zirconium dioxide powder stabilized with yttrium oxide by joint deposition is developed. This technology makes it possible to sinter ceramics based on this powder at temperatures below 1400°C. Characteristics of the zirconia powder (depending on the synthesis conditions) are investigated using X-ray diffraction, the thermal desorption of nitrogen, and electron microscopy. It is revealed that the ultrasonic (US) effect achieved when washing the gel-like powder, as well as crushing the powder after drying and calcination, make it possible to decrease the degree of its agglomeration and decrease the agglomerate size. It is established based on the data of the thermochemical analysis that a decrease in the heating rate to the isothermal holding temperature during synthesis can decrease the liability of the ceramics made from the nanocrystalline zirconia powder to zonal sintering.     

Compactability of Stabilized Zirconium Dioxide Powder

Features of compacting articles from stabilized zirconium dioxide powder synthesized by the sol-gel method, and also their structure and properties are studied. Compaction parameters are determined. It is shown that the relationship between compact density and extrusion pressure may be described by the Bal'shin equation. It is established that parameters of this equation depend linearly on the duration of zirconium dioxide synthesis.     

液固凝胶反应法制备超细氧化锆粉体

利用有机单体自由基聚合反应机制,采用聚合物网络法制备了超细氧化锆粉体。以八水合氧氯化锆为原料,选取丙烯酰胺和N,N′-亚甲基双丙烯酰胺两种水溶性有机作为单体,在引发剂过硫酸铵的作用下,有机单体发生交联共聚,从而使Zr(OH)4浆料变成凝胶。该凝胶具有三维网络状结构,能够较好地抑制热处理过程中粒子的团聚,700℃下热处理2h获得超细氧化锆粉体。     

Experimental determination of the dependence of starch looseness on the concentration of the silicon dioxide nanopowder (tarcosil) in it

The looseness of starch powder is investigated, depending on the concentration of nanodimensional silicon dioxide powder (tarkosil) in it, by measuring the angle of the natural slope and the consumption of the flow of starch mixed with this powder through calibrated funnels with various diameters. It is found that adding small amounts of tarkosil substantially affects the angle of natural slope and increases the looseness of starch.     

Creep of zirconium and zirconium alloys

Cumulative zirconium and zirconium alloy creep data over a broad range of stresses (0.1 to 115 MPa) and temperatures (300 °C to 850 °C) were analyzed based on an extensive literature review and experiments. Zirconium obeys traditional power-law creep with a stress exponent of approximately 6.4 over stain rates and temperatures usually associated with the conventional “five-power-law” regime. The measured activation energies for creep correlated with the activation energies for zirconium self-diffusion. Thus, dislocation climb, rather than the often assumed glide mechanism, appears to be rate controlling. The common zirconium alloys (i. e., Zircaloys) have higher creep strength than zirconium. The stress exponents of the creep data in the five-power-law regime were determined to be 4.8 and 5.0 for Zircaloy-2 and Zircaloy-4, respectively. The creep strength of irradiated Zircaloy appears to increase relative to unirradiated material. It was found that the creep behavior of zirconium was not sensitive to oxygen in the environment over the temperature range examined.     

Determination of optimal conditions for obtaining a mixture of associated dioxides of zirconium and silicon by sintering of ZrSiO4 with MgO

Obtaining dissociated zircon (a mixture of associated dioxides of zirconium and silicon (ZrO₂, SiO₂) by sintering ZrSiO₄ with MgO and the subsequent leaching of the forming pitch by concentrated hydrochloric acid is studied. The mechanism of sintering of the ZrSiO₄ + MgO mixture is established based on laboratory investigations. The optimal parameters of the process (the molar ratio of components and the temperature and duration of heating at the final temperature) for the maximal transformation of zircon into zirconium dioxide are determined.     

Fractographic study of a tungsten-copper pseudoalloy

Conclusions The addition of silicon has a refining effect on a tungsten-copper pseudoalloy and improves its properties. Some increase in the strength and ductility of the alloy is observed. A silicon addition changes the character of fracture of the pseudoalloy from interto transgranular. The effect of a zirconium addition on the properties of the pseudoalloy is less than that of a silicon addition.Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 101–105, March, 1982.The author wishes to thank Dr. S. A. Firstov' for helpful discussion.     

纳米氧化锆喷涂材料的制备及表征

采用聚合物网络法制备了具有纳米结构的氧化锆粉体,将粉末进行了喷雾干燥球形化制粒及等离子致密化处理。结果表明采用该方法制备的纳米结构的氧化锆粉末松装密度高、流动性好,表面光亮,有利于提高涂层的综合性能。     

Investigation of the treatment process of associated dioxides of zirconium and silicon by an aqueous solution of ammonium fluoride

The process of isolation of zirconium dioxide from dissociated zircon (a mixture of associated ZrO₂ and SiO₂) via treatment by an aqueous solution of ammonium fluoride is investigated. Based on laboratory investigations, the solubility of ZrO₂ and the efficiency of washing SiO₂ out of it in an aqueous solution of ammonium fluoride are determined depending on its concentration, the excess content of the F⁻ ion, and treatment temperature. The optimal conditions of isolation of technical zirconium dioxide of commercial quality are determined.     

Effects of oxide particles on properties of sintered nickel

Conclusions The effect was investigated of the addition of aluminum, zirconium, silicon, and hafnium oxides on the hot hardness and rupture strength of nickel at temperatures of 600–800°C. The rupture strength of nickel is shown to increase with increasing amount of oxide introduced into it and with decreasing oxide particle size. In tests below the temperatures at which transformations take place, the nature of the oxides investigated does not affect the properties of nickel.Translated from Poroshkovaya Metallurgiya, No. 6 (78), pp. 81–86, June, 1969.     

Crack resistance of modern ceramics and ceramic composites. II. EF method

The procedure and test results are for crack resistance are presented for various monolithic and composite oxide and nonoxide ceramics by chipping the rectangular edge of a polished specimen. The main difference of the test method suggested (EF method) with an arbitrary point of fracture for a specimen edge from the well-known similar method with a fixed point of fracture is demonstrated. Tests are performed with Rockwell, Vickers and Knoop indenters, and the Rockwell indenter is chosen as the optimum. On the basis of statistically reliable experimental data a direct relationship is established between edge toughness and critical fracture toughness determined in the same ceramic specimens based on scandium oxide, aluminum oxide, zirconium dioxide, silicon carbide and silicon nitride. The EF method, whose use does not require special equipment, may be used effectively in a normal metallurgy test laboratory, particularly when specimens for evaluating ceramic breaking resistance may only be prepared in smaller sizes than those required for standard crack resistance tests. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 39–49, July–August, 2006.     

微波加热与常规加热硅锰粉固相脱硅动力学比较

采用微波加热和常规加热对硅锰粉和巴西粉锰的脱硅反应进行了动力学行为研究,以巴西粉锰为脱硅剂,与硅锰粉中的硅发生氧化还原反应.微波加热和常规加热分别加热到不同温度并保温一定时间,测定产物中硅含量并计算固相脱硅反应的表观活化能.实验表明:单一和混合料均可在微波场中快速升温.随着温度的升高和保温时间的延长,两种加热方式脱硅率均随之提高,在相同实验条件下,微波加热的脱硅率和反应速率均高于常规加热,微波加热可以提高固相脱硅率;微波加热固相脱硅反应的限制性环节为扩散环节,其表观活化能为102.93 kJ·mol-1,常规加热脱硅反应的表观活化能为180 kJ·mol-1,说明微波加热能改善固相脱硅的动力学条件,提高固相脱硅反应速率,降低脱硅反应的活化能.      

Effect of the method of introduction of Y2O3 into NiAl-based powder alloys on their structure: II. Mechanical activation

Effect of mechanical activation of NiAl powders produced by calcium hydride reduction in an attritor and a ball mill on the specific surface, the oxygen concentration, the strain hardening, and the coherent domain size (CDS) of the powders is studied. It is found that the powder specific surface milled in the attritor for 10–15 h is larger by a factor of 1.7–1.8 and the oxygen concentration in a powder is lower by a factor of 1.35 as compared to the its milling in the ball mill for 150 h. The powders milled in the attritor for 15 h have the level of microstresses higher by a factor of ～2.4 and the CDS smaller by a factor of 2 as compared to the powder treated in the ball mill for 150 h. When milling a powder in the attritor, the milling time decreases by a factor of 10 and the degree of powder refinement increases, which improves the technological characteristics of the powders. As a result of the combination (in one operation) of mechanical activation of an NiAl intermetallic matrix powder in the attritor and the introduction of dispersed particles of a refractory oxide Y₂O₃ powder, the produced composite alloy has a density close to the theoretical one and has no aggregates of dispersed oxide particles at grain boundary junctions. Submicro- and nanosized oxide particles are homogenously distributed in the intermetallic matrix volume, which is characterized by a homogeneous distribution of nickel and aluminum.     

Structure and properties of rapidly solidified 7075 P/M aluminum alloy modified with nickel and zirconium

Aluminum alloy 7075 was modified by additions of 1.1 wt pct nickel and 0.8 wt pct zirconium, rapidly solidified by ultrasonic gas atomization, canned, cold compacted, hot extruded, and evaluated in terms of structure and properties. Significant improvements in tensile strength (627 MPa YS and 680 MPa UTS) and crack growth rates were realized, along with a decrease in fracture toughness (23.7 MPa√m) while maintaining ductility (10 pct elong.) as compared to nominal I/M 7075 behavior. The stress for 10⁷ cycles fatigue life was greater than 275 MPa, which represents a 73 pct increase over that of I/M 7075. A variety of experiments was performed to evaluate effects on strength, ductility, and on structure. The variables were: powder size distribution, extrusion ratio, extrusion profile, different size fractions from the same lot of powder, and different locations of test bars in the several extrusions. Tensile properties, toughness, and fatigue properties were not importantly influenced by the location of test bars in the cross section or length of rectangular extruded bars. A comparison of mechanical properties from extruded bars prepared from ?53 μm powdersvs 53 to 250 μm powders showed a small loss of ductility and fatigue stress for 10⁷ cycles for the fine powder product. Higher extrusion ratios were beneficial for mechanical properties.     

Reduced top-down influence in auditory perceptual organization in schizophrenia

Implants made form zirconium dioxide exhibit higher specific radionuclide activities of the uranium-radium and thorium series than metallic and aluminum implants. This study presents data on activity measurements performed on different samples of ZrO2 raw material (powder) and on the ceramic joint heads belonging to it to formulate a correlation between the specific radionuclide activities of the uranium-radium and thorium series in the raw material, the flux density of the alpha particle leaving the implant surface, and the annual dose of the tissue surrounding the implant. Based on this experimental study, an equation for defining the limits of the specific activities in raw material is proposed, taking into account the long-lived radionuclides (key nuclides) of the uranium-radium and thorium series weighted with their relative dose contributions from alpha emitters.