摘要:

Equilibrium phase diagrams for the systems NdCl3–CaCl2and NdCl3–NaCl were determined by differential thermal analysis. A simple eutectic was observed at 59 ± 1 mol% CaCl2and 600°± 2°C in the NdCl3–CaCl2system. A compound NaCl.3NdCl3which melts incongruently at 545°± 5°C to NdCl3and a liquid containing approximately 47 mol% NaCl, and a eutectic at 68 mol% NaCl and 439°± 2°C were found in the NdCl3–NaCl system. On the basis of agreements between the activities calculated by the Clausius–Clapeyron equation and Temkin's model using the present data for the NdCl3–CaCl2system and the literature data for the PrCl3–CaCl2system, the melts in the former system consist of Nd3+, Ca2+, and Cl−ions and in the latter system of Pr3+, Ca2+, and Cl−ions. The above approach indicates the presence of Na+, Cl−, and NdCl2‐5ions in the NaCl‐rich melts and Nd3+, Cl−, and NdCl−4in the NdCl3‐rich melts in the NdCl3–NaCl system. Analogous ions were indica

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05601.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Commercial β‐SiAlON ceramics were joined using mixed Si3N4, Y2O3, Al2O3, and SiO2powders. At a joining temperature of 1600°C and a hold time in excess of 10 min, the adhesive was converted to an approximate 60:40 vol% composite of β‐SiAlON–glass‐ceramic. The grain size of the acicular β‐SiAlON grains precipitated in the joint (submicrometer diameter, average aspect ratio of 10) was significantly smaller than those in the adherend ceramic (1–5 μm diameter). Intergrowth of β‐SiAlON grains at the joint interface resulted in high bond strengths. The chemistry and microstructure of the ceramic adhesives

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05602.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Three different diameters (0.50, 1, and 2 μm) of monosized spherical pores were introduced, at different volume percents up to 15%, into two submicrometer commercial Zr(Y)O2powders which exhibited either sluggish (ZrO2–3 mol% Y2O3) or rapid (ZrO2–8 mol% Y2O3) grain growth kinetics. Densification and grain growth behavior was studied as a function of heat‐treatment period at 1400°C and/or 1500°C. Pores in the finer‐grain Zr(3Y)O2densified more rapidly. The grain growth kinetics of the Zr(3Y)O2material were unaffected by porosity, because the pores were always larger than the grains. Consistent with the Zener concept applied to mobile pores on grain junctions, the spherical pores influenced the grain growth kinetics of Zr(8Y)O2once the grain size was greater than the pore size. Measurements indicated that the number of pores per unit volume decreased dramatically during densification, whereas their average size remained approximatel

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05603.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Carbothermal reduction kinetics to synthesize boron carbide are studied under conditions of high carbon/boron oxide precursor heating rates (>103K/s) and intermediate temperatures (1803 K

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05604.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Monoclinic zirconia has been synthesized hydrothermally from zirconium oxychloride in the range 20–100 MPa, 250–650°C, for run duration from 20 to 100 h and in the presence of NaOH, Na2CO3, Na2SO4, NH4F, HNO3, and H2SO4additives. Isometric, platelike, and elongated crystal morphologies were obtained depending on the additive. Both spherulitic and isolated textures were encountered with H2SO4. Growth of isometric crystals follows a general dissolution–precipitation mechanism. For H2SO4, two growth steps were identified: an early spherulitic step followed by an isolated crystals step resulting from Ostwald ripening of preexisting spherulites. The formation of spherulites is consistent with the specific properties of the sulfuric hydrothermal

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05605.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Transparent lead lanthanum zirconate titanate (PLZT) ceramics were fabricated from fine powders using an inexpensive two‐stage sintering technique. The powders were prepared by hydrolysis from low‐cost inorganic precursors. In the two‐stage sintering method, uniaxially pressed green pellets were densified to nearly theoretical values in an oxygen gas atmosphere during the first‐stage sintering, at 1000°C for 1 h, and then residual, free lead oxide in the pellets was removed by second‐stage sintering at 1100°C for 12 h. Transparent ceramic with an average grain size of 1.6 μm and a porosity of 1.3% was obtained. The transparency and dielectric characteristics of the present samples were compared with those of hot‐pressed samples: The study of the polarization–field hysteresis loops of the present samples yielded a remanent polarization of 6.8 μC/m2and a coercive field of 1.6 kV/cm. The low coercive field of PLZT ceramics could potentially reduce the driving voltage of electrooptic devices in

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05606.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Grain growth of ZnO during the liquid‐phase sintering of binary ZnO–Bi2O3ceramics has been studied for Bi2O3contents from 3 to 12 wt% and sintering from 900° to 1400°C. The results are considered in combination with previously published studies of ZnO grain growth in the ZnO–Bi2O3system. For the Bi2O3contents of the present study, the rate of ZnO grain growth is found to decrease with increasing Bi2O3. Activation analysis, when combined with the results of similar analyses of the previous studies, reveals a change in the rate‐controlling mechanism for ZnO grain growth. Following a low‐Bi2O3‐content region of nearly constant activation energy values of about 150 kJ/mol, further Bi2O3additions cause an increase of the activation energy to about 270 kJ/mol. consistent with accepted models of liquid‐phase sintering, it is concluded that the rate‐controlling mechanism of ZnO grain growth during liquid‐phase sintering in the presence of Bi2O3changes from one of a phase‐boundary reaction at low Bi2O3levels to one of diffusion through the liquid phase at about the 5 to 6 wt%

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05607.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Grinding effects on the synthesis and sintering of cordierite were investigated. The grinding of a precursor gel derived from colloidal processing promoted the homogeneous distribution of elements in the gel, resulting in improved reactivity for the formation of cordiertie. Grinding the calcined powder enhanced the homogeneity of the resulting powder and caused the accumulation of internal energy as crystal strain; consequently, the densities of the sintered bodies increased and the optimum temperature range for sintering widened.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05608.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The effect of curing temperature (40°, 60°, 80°C) on the hydration behavior of β‐dicalcium silicate (β‐C2S) was investigated. The β‐C2S was obtained by decomposition of hillebrandite, Ca2(SiO3)(OH)2, at 600°C, has a specific surface area of about 7 m2/g, and is in the form of fibrous crystals. The dependence of the hydration reaction on temperature continues until the reaction is completed. The hydration is completed in 1 day at 80°C and in 14 days at 14°C. The hydration mechanism is different above and below 60°C, but at a given temperature, the reaction mechanism and the silicate anion structures of C‐S‐H do not change significantly from the initial to the late stages of the reaction. High curing temperature and long curing times after completion of reaction promote silicate polymerization. The Ca/Si ratio of C‐S‐H shows high values, being almost 2.0 above 6

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05609.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Controlled‐geometry voids were introduced into Mg‐implanted and Ca‐implanted sapphire substrates using microfabrication techniques and ion beam etching, and were subsequently transferred to an internal interface by hot‐pressing. The morphological evolution of cracklike and channel‐like defects in response to anneals at 1700°C was studied. The healing behavior of defects in the Ca‐ and Mg‐ion‐implanted samples differs significantly. Mg additions appear to reduce the directional dependence of the healing characteristics and thus homogenize the evolution. Destabilization of the basal plane by Ca may contribute to the rapid healing of cracks oriented parallel to the basal plane. The healing characteristics of pore channels in Ca‐implanted samples indicate a strong residual energetic barrier to healing stemming from surface energy anisotropy. Despite this, defects in Ca‐implanted sapphire healed more rapidly than crystallographically and geometrically identical defects in Mg‐implanted sapphire. Thus, the results suggest that Ca additions increase transport rates sufficiently to more than compensate for the relatively higher energetic barriers t

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05610.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY