Solid solution behavior of Cu-1.0Cr-0.1Zr alloy

Characterization of Ti-based hydrogen absorbing alloys

Deformation behavior of Mg–5Y–2Nd–0.5Zr alloys with different Sm additions

Temperature dependence of the mechanical properties of equiatomic solid solution alloys with face-centered cubic crystal structures

Beitrag zur kenntnis des ausscheidungsverhaltens einiger magnesium-mischkristalle

A new perspective on tensile yield plateau formation in extruded Mg-4.83Gd-2.36Nd-0.21Zr alloy

It is well known that a solid solution forms in the a-SiC (2H)-AIN system over a wide composition range, because both of them have wurtzite (2H) structures [1]. The lattice parameters of the solid solution vary with the composition. It has been reported that their behaviour approximately follows Vegard's law [2]. Although SiC-A1N solid solutions are prepared by hot-pressing of both powders [3], they can also be obtained directly by the carbothermal reduction of oxides having the SiO2-A1203 compositions in nitrogen. In the carbothermal reduction process, the intimate mixing of SiO2, A1203, and carbon is desirable. So far, two attempts at the preparation of solid solutions by carbothermal reduction have been reported; SiC-A1N from the mixture of fumed silica, AI(OH)3, and starch [4, 5], and SiC-A1N-A12OC from acidtreated kaolinite and starch [5]. Aluminosilicate materials, for example kaolinite and zeolite, consist of silicon, aluminium and oxygen, which are mixed at the atomic level. Of these, montmorillonite shows a layered structure and takes up a number of organics in its interlayer space to form "intercalation compounds" [6]. In montmorilloniteorganic intercalation compounds, silicate and organic layers are interstratified alternately. Hence, the intimate mixing between SiO2, A1203, and carbon is expected after their thermal transformation into a nonoxidative atmosphere. We prepared n-alkylammoniummontmorillonite-polyacrylonitrile (PAN) intercalation compounds and applied these to the carbothermal reduction processes for fl-sialon [7-9] and SiC production [10]. In such processes, the intimate mixing and the two-dimensional ordering in the intercalation compounds affected the reactions to a great extent. In the present study, the preparation of a SiC-A1N solid solution from the montmorillonitePAN intercalation compound by carbothermal reduction was attempted. To investigate the effect of the mixing condition on solid solution formation, montmorillonite-carbon mixtures were also converted. The amount of carbon in the mixtures was varied to study its influence on solid solution formation. The method for the preparation of the intercalation compound was described elsewhere [7]. The compound after thermal pre-treatment at 220°C was characterized by X-ray powder diffraction (XRD) analysis (Rigaku, RAD II-A, Mn filtered FeK~ radiation) and thermogravimetry (TG) (Shimadzu, TGA-20); the basal spacing was 1.75nm and the amount of carbon from PAN approximately corresponded to that in the mixture containing 53 wt % carbon. The procedure for the preparation of the mixtures was the same as described elsewhere [10]. The carbon contents were 40, 50, and 60 wt %. These indicate that the calculated C/SiO2 molar ratios were 5.8, 8.2, and 12.0, respectively; the C/A1203 ratios were 21, 37, and 55, respectively. Both kinds of starting materials were placed in a graphite boat, and heated in a nitrogen flow (flow rate: 900 ml min~) for 0 to 10 h. Crystalline phases were identified by XRD analysis after decarbonization at 650 ° C for 6 h. The characterization of 2H compounds was based on the profile and the position of their (1 0 0) lines. The position was precisely measured by using NaC1 as an internal standard and compared with those calculated from the reported d values for a-SiC (2H) [11] and A1N [12] (a-SiC (2H), 42.56°; A1N, 42.13°). The composition was approximately estimated from the lattice parameter, a, which was calculated from the position of the (1 00) lines on the basis of the reported relationship [2]. The Si/A1 ratio in the products was obtained by inductively-coupled plasma emission spectroscopy (ICP) (Nippon Jarrell Ash, ICAP-575 II). The products were dissolved in water by alkali fusion. Details were described elsewhere [8]. The reaction temperature was fixed at 1670 ° C in the present study on the basis of our primary results. The presence of the boundary temperature above which SiC formed instead of Si3N4 was reported at ~ 1400 to 1600°C in the SiO2-C-N2 system [13, 14]. A similar one was observed in the carbothermal reduction process of kaolinite [15]. Hence, the reaction temperature was initially set at 1700°C in our primary runs. When the mixture containing 40% carbon was heated, a large amount of/~-SiC and smaller amounts of the 2H compounds were detected. Two (1 0 0) lines of the 2H compounds were observed and one was ascribed to almost pure A1N (detailed discussion for the assignment was similar to that shown below). As heating time increased, the peak intensity of the (1 0 0) line of A1N remarkably decreased; A1N seemed to decompose at 1700 ° C. Thus, the~eaction temperature was lowered to 1670°C. In the reactions at 1670°C, the peak intensity of the (1 00) line of A1N did not remarkably decrease. In the XRD patterns of the products obtained by heating the intercalation compound for 0 to 10h,

High ductility in solution-treated Mg-Sc-Yb-Mn-Zr alloy mediated by<c + a>dislocations

The classification of equilibrium between ionic solid solutions and aqueous solutions by Roozeboom is interpreted as being a result of the ideal or regular behaviour of the ionic solid solutions. Due to the fact that the solubility products of isomorphous compounds which form ionic solid solutions differs in general by several orders of magnitude, it is very unlikely that precipitates differ much from the stoichiometry of one of these compounds. This principle is applied to the problem of biominerals, especially bone mineral. As a result it appears that the first mineral deposited in bone is octocalcium phosphate. Under in vivo conditions this phase is transformed into a mixture of three other calcium phosphates having a much lower solubility. The solubility controlling phase in living bone appears to be octocalcium phosphate which is continuously formed during the turn‐over of bone. This model for bone mineral has lead to the explanation of the formation of renal stones, pathological calcifications and osteoporosis as a consequence of slight chronic magnesium deficiency. The action of magnesium is mediated by the osteocytes.

It is shown that the distribution of ions over the solid phase and an aqueous solution can be interpreted in terms of Roozeboom's classification in the case of ideal ionic solid solutions and regular ionic solid solutions with and without ordering or substitutional disorder. A general relation is derived between the distribution coefficient D of the system and the solubility products of the components of the solid phase. In this way D can be determined experimentally in an independent way. It appears that in practice type II and type III systems are indistinguishable from type I systems, when the distribution coefficient D differs about one order of magnitude or more from unity even in the case of good recryatallization. In those cases distribution diagrams are not suitable to derive the nature of the series of solid solutions involved.

CoCrFeNiX (X=Mn, Cu) high entropy alloys (HEAs) were prepared by powder metallurgy. The effects of milling time and milling speed on the microstructures and properties of CoCrFeNiX (X=Mn, Cu) HEAs were studied. The results show that at high rotational speed, the particle size of the HEA powders is refined and is tended to be uniform, and obvious solid solution phenomenon occurs; the microstructure of CoCrFeNiMn HEA is mainly composed of BCC solid solution, FCC solid solution and CoNiCr intermetallic compound; with the increase of ball milling time, Cr-rich phase and CoNiCr compound decrease. The microstructure of CoCrFeNiCu HEA is mainly composed of BCC solid solution and FCC solid solution; with the increase of ball milling time, Ni-rich FCC solid solution is gradually replaced by Co-rich and Ni-rich FCC solid solution. CoCrFeNiMn and CoCrFeNiCu HEAs have higher compressive strength, compression ratio and hardness, and they are 1300 Mpa and 1100 Mpa, 34% and 33%, 400 HV and 350 HV, respectively; The friction coefficient curve of CoCrFeNiMn HEA is more stable than that of CoCrFeNiCu HEA.

The reduction behaviour of a high surface area CeO2-ZrO2 solid solution is compared with that of a high surface area CeO2. It is shown that, upon sintering induced by repetitive reduction/oxidation processes, the temperature of reduction of the solid solution decreases from 900 to 700 K. In contrast, the reduction at low temperatures of the CeO2 sample is strongly retarded after such treatments. The role of ZrO2 in promoting the reduction at low temperatures is discussed.

A new monoboride phase CrB displaying a δ-MoB-CrB-type transposition (shift) structure has been detected in alloys which were prepared at relatively low temperatures. Furthermore a Cr-rich boride phase not yet characterized was observed. The mutual solubility of the respective Cr-carbides and borides is insignificant for 1000°C. Under the same conditions a phase close to MnB has been found besides the known MnB (FeB-type). The new phase crystallizes with a structure similar to the CrB-type, however some additional clarification is needed. Carbon-boron substitution in Mn23C6 extends to almost Mn23B3C3. Germanium and carbon stabilize γ-Mn solid solutions towards lower temperatures. Besides the ordering phenomenon there is an almost continuous transition between γ-Mn(Ge, C) solid solutions and the perovskite carbide Mn3GeC x . Indications for the existence of derivatives of the perovskite carbides were observed.

Manganese oxide-doped zirconium oxide samples, prepared by heating mixtures of coprecipitated hydroxides at 1073 K in a hydrogen stream (water content 0.2% by volume), were analysed to obtain information on the solid solution formation. The state and the thermal stability of the incorporated species were also investigated. The samples (manganese content up to 14.74 mass%), were studied ‘as-prepared’ and after subsequent thermal treatments in oxygen up to 753 K. The results of several techniques [X-ray diffraction (XRD), Raman spectroscopy, thermogravimetry (TG) and magnetic susceptibility measurements] show that in the ‘as-prepared’ samples (1073 K, H2) a high fraction of manganese is incorporated in the zirconia structure, only a small fraction being present as an MnO separate phase. Most of the manganese in solid solution is present in the +2 oxidation state, the remainder as + 3 and +4. TG experiments and magnetic susceptibility measurements reveal that the Mn3+ and/or Mn4+ are formed both during the cooling in hydrogen by reaction with water present as an impurity in the gas phase, and during the exposure to the atmosphere. As the amount of manganese in solid solution increases, the volume of the zirconia unit cell slightly decreases. The solid-solution formation favours the tetragonal and the cubic modifications at the expense of the thermodynamically stable monoclinic phase. When the samples are heated up to 753 K in oxygen, the Mn2+ in solid solution is partially oxidized to Mn3+ and/or Mn4+. TG and XRD experiments show that the oxidation starts at low temperature and takes place in solid solution without appreciable manganese oxide segregation.

Calcium monoaluminate is the main phase in calcium aluminate cements and participates in the hydration, forming calcium aluminate hydrates. The amount of incorporation of foreign ions influences the hydration behaviour. Strontium aluminate is an important phase in producing phosphorescent materials when doped with rare-earth elements (REE) such as Eu, Dy, and La. These monoaluminates occur in different forms. Monocalcium aluminate forms a monoclinic and an orthorhombic modification, whereas monostrontium aluminate forms a monoclinic low-temperature and a hexagonal high-temperature form. Monoclinic calcium monoaluminate and monoclinic strontium aluminate form a partial solid-solution series. The hydration behaviour of different solid solutions was also investigated using calorimetry. The newly formed strontium aluminate hydrates could be identified while similar strontium aluminate hydrates are formed. Solid solutions of strontium- and calcium-aluminate hydrates will be investigated.

The data of Rau (1967) on the H 2 S/H 2 ratios of gas in equilibrium with high digenite solid solutions permit the calculation of the activity of Cu 2 S as a function of temperature and composition. The activity of Cu 2 S falls to 0.5 when the mole fraction (in the system Cu 2 S-S) drops only to 0.87. These calculations also permit the estimation of the activity of S 2 -temperature curve for the hexagonal chalcocite-high digenite reaction and a revised standard free energy for covellite.New data on the variation of the activity of S 2 in equilibrium with various metal/sulfur ratios for Cu = Fe in the intermediate solid solution permit the calculation of the activity of CuFeS 2 and show that it may drop as low as 0.2 at a mole fraction of 0.90 (system CuFeS 2 -Cu 2 Fe 2 S 2 ). The behavior of the copper-bearing solid solutions closely parallels that of pyrrhotite (Toulmin and Barton, 1964) in which the activity of FeS falls to 0.4 at a mole fraction of 0.9. A phase diagram is given for the CuFe-S join between 400 degrees and 700 degrees C.