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1.
Oludele O. Popoola Waltraud M. Kriven J. Francis Young 《Journal of the American Ceramic Society》1991,74(8):1928-1933
The microstructure of a macrodefect-free (MDF) cement has been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and high-resolution electron microscopy (HREM). The microchemistry of ultramicrotomed samples has been studied by energy dispersive spectrometry (EDS) and parallel electron energy loss spectrometry (PEELS). MDF cement consists of CaAl2 O4 and CaAl4 O7 grains randomly distributed in a polymer matrix. The ceramic/polymer interface contains an amorphous interphase inside of which are distributed very fine crystallites of the metastable hydration product Ca2 Al2 O5 ·8H2 O. PEELS analyses of the interphase revealed the presence of carbon, indicating that Ca2 Al2 O5 ·8H2 O was most likely stabilized by the intercalation of polymeric chains into its basal interlayers. The polymer phase preferably cross-links with Al. In situ environmental cell electron microscopy showed that moisture uptake of MDF cements occurred by polymer swelling and interphase dissolution. The role of the interfacial interphase in dry and wet mechanical properties is discussed. 相似文献
2.
Brian P. Borglum John M. Bukowski J. Francis Young Relva C. Buchanan 《Journal of the American Ceramic Society》1993,76(5):1354-1356
Hexagonal anorthite (CaAl2 Si2 O8 ) has been prepared by hydrothermal processing of monocalcium aluminate and quartz at temperatures as low as 200°C. The successful development of this phase is dependent upon several processing parameters, including the hydration of the calcium aluminate precursor material to the hydrogarnet phase (Ca3 Al2 O6 ·6H2 O) prior to hydrothermal treatment and the use of quartz as opposed to amorphous sources of SiO2 . Quartz has partial solubility in the hydrogarnet lattice for additions up to 40 wt%. Increased SiO2 substitution has been shown to reduce the conversion of hydrogarnet to Ca4 Al6 O13 ·3H2 O, thereby increasing its thermal stability and improving its strength characteristics at temperatures greater than 200°C. Quartz additions greater than 43 wt% lead to the formation of CaAl2 Si2 O8 as the sole reaction product. The moderate temperatures involved in forming this anhydrous material are an order of magnitude lower than those necessary to form this phase by melt crystallization, making it a true chemically bonded ceramic. The reaction can form a bonded matrix with strengths up to 40000 psi (280 MPa). Strengths are limited due to density changes during anorthite formation, but the matrix is thermally stable up to 1000°C. 相似文献
3.
Nakshatra B. Singh Awadhesh K. Singh Shashi Prabha Singh 《Journal of the American Ceramic Society》1990,73(10):3063-3068
Hydration occurring in the system Ca3 Al2 O6 –CaSO4 · 2H2 O–Ca(OH)2 –H2 O has been studied at different temperatures and it was found that the reactions are diffusion controlled. The kinetic data obeyed Jander's equation and the rate of reaction increased with increasing temperature. X-ray diffraction studies and calorimetric measurements show that when gypsum is consumed, ettringite is converted into monosulfate. The rate of this conversion also increased with the increasing temperature and decreased in the presence of citric acid. Spectroscopic studies showed that there was some interaction between citric acid and the cement and that the product of hydration is of colloidal nature. Zeta potential measurements show that retardation of Ca3 Al2 O6 hydration in the presence of gypsum and Ca(OH)2 is not due to SO2− 4 adsorption. Electrical conductivity and thermoelectric potential measurements of solid Ca3 Al2 O6 show that Ca3 Al2 O6 is an n -type semiconductor and contains defects. The retardation of Ca3 Al2 O6 may be due to poisoning of reaction sites by gypsum and Ca(OH)2. 相似文献
4.
The hydration of two high replacement composite cements (3:1 blast furnace slag:ordinary Portland cement (BFS:OPC), and 3:1 pulverized fuel ash:OPC (PFA:OPC)) with the addition of both SnCl2 and SnCl4 has been investigated and the results from X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) are presented. Adding 5% or 1% SnCl2 ·2H2 O or SnCl4 ·5H2 O to the mix water resulted in the formation of Friedel's salt, Ca3 Al2 O6 .CaCl2 ·10H2 O, and calcium hydroxo-stannate CaSn(OH)6 , which also involved the consumption of calcium hydroxide. After 90 days hydration at lower levels of addition (i.e., 1%) there was no longer evidence for CaSn(OH)6 , indicating that it too had been consumed in the pozzolanic reaction due to the lack of calcium hydroxide present. Results from SEM and EDS showed that bright regions between the BFS or PFA grains were tin containing and they were incorporated into the hydrated cement matrix. The tin was, therefore, localized rather than spread throughout and intimately incorporated into the microstructure. 相似文献
5.
Junying Zhang Zhongtai Zhang Zilong Tang Yuanhua Lin 《Journal of the American Ceramic Society》2002,85(4):998-1000
A (Ce0.67 Tb0.33 )Mn x Mg1− x Al11 O19 phosphor powder was synthesized, using a simple sol–gel process, by mixing citric acid with CeO2 , Tb4 O7 , Al(NO3 )3 ·9H2 O, Mg(OH)2 ·4MgCO3 ·6H2 O, and Mn(CH3 COO)2 . The phosphor crystallized completely at 1200°C, and the phosphor particle size was between 1 and 5 μm. The excitation spectrum was characteristic of Ce3+ , while the emission spectrum was composed of lines from Tb3+ and Mn2+ . The Mn2+ gave a green fluorescence band, and concentration quenching occurred when x > 0.10. The luminescent properties of the phosphor were explained by a configurational coordinate model. 相似文献
6.
Synthesis of Mesoporous Needle-Shaped Ytterbium Oxide Crystals by Solvothermal Treatment of Ytterbium Chloride 总被引:1,自引:0,他引:1
Saburo Hosokawa Shinji Iwamoto Masashi Inoue 《Journal of the American Ceramic Society》2007,90(4):1215-1221
The reaction of rare-earth (RE; Y, Er, and Yb) chloride hydrates in 1,4-butanediol at 300°C for 2 h gave mixtures of RE(OH)2 Cl and RE2 O3 · x H2 O, and the products were composed of irregularly shaped particles. A prolonged reaction (10 h) yielded a mixture of RE(OH)2 Cl and RE2 O3 · x H2 O for Er or Y, but phase-pure RE2 O3 · x H2 O was obtained for Yb. The product for Yb comprised needle-shaped single crystals of Yb2 O3 · x H2 O with a width of 0.2–0.6 μm and a length of 5–15 μm. The Yb2 O3 · x H2 O phase decomposed to Yb2 O3 at 350°–500°C, preserving the needle-shaped morphology; this was maintained even after calcination at 1100°C. Single crystals of Yb2 O3 obtained by the calcination of Yb2 O3 · x H2 O at 500°C had very small voids and the voids were enlarged to 35 Å in diameter by calcination at 800°C. 相似文献
7.
Qingmei Lu Wensheng Dong Haojing Wang Xinkui Wang 《Journal of the American Ceramic Society》2002,85(2):490-492
Yttrium aluminum garnet (YAG, Y3 Al5 O12 ) was synthesized by sol–gel processing from the stoichiometric amounts of aluminum pellets, Y(NO3 )3 ·6H2 O, and Al(NO3 )3 ·9H2 O or AlCl3 ·6H2 O, with suitable kinds of acid (citric acid, acetic acid, etc.) as catalysts. Polycrystalline YAG powder was obtained by drying the YAG precursor followed by calcination at temperatures above 900°C. Thermogravimetry/differential thermal analysis and Fourier transform infrared specotrscopic analyses in air showed an exothermic peak at ∼900°C, attributed to the formation of a polycrystalline YAG phase and weight loss of 60% at 1000°C, caused by the decomposition of hydroxyl and NO3 − , etc. X-ray diffraction analysis showed that YAG can be formed at 900°C, and no other intermediate was observed. In particular, the YAG sol can be used for dry-spinning fibers with the aid of some organic polymer. 相似文献
8.
Toshifumi Sugama Marita Allan Janet M. Hill 《Journal of the American Ceramic Society》1992,75(8):2076-2087
We investigated the characteristics of calcium phosphate cements (CPC) prepared by an exothermic acid–base reaction between NH4 H2 PO4 -based fertilizer (Poly-N) and calcium aluminate compounds (CAC), such as 3CaO · Al2 O3 (C3 A), CaO · Al2 O3 (CA), and CaO · 2Al2 O3 (CA2 ), in a series of integrated studies of reaction kinetics, interfacial reactions, in-situ phase transformations, and microstructure development. Two groups were compared: untreated and hydrothermally treated CPC specimens. The extent of reactivity of CAC with Poly-N at 25°C was in the following order: CA > C3 A ≫ CA2 . The formation of a NH4 CaPO4 · x H2 O salt during this reaction was responsible for the development of strength in the CPC specimens. The in-situ phase transformation of amorphous NH4 CaPO4 · x H2 O into crystalline Ca5 (PO4 )3 (OH) and the conversion of hydrous Al2 O3 gel →γ-AIOOH occur in cement bodies during exposure in an autoclave to temperatures up to 300°C. This phase transformation significantly improved mechanical strength. 相似文献
9.
Fabrication of Translucent Magnesium Aluminum Spinel Ceramics 总被引:5,自引:0,他引:5
Ji-Guang Li Takayasu Ikegami Jong-Heun Lee Toshiyuki Mori 《Journal of the American Ceramic Society》2000,83(11):2866-2868
A precursor for magnesium aluminum spinel powder, composed of crystalline ammonium dawsonite hydrate (NH4 Al(OH)2 CO3 ·H2 O) and hydrotalcite (Mg6 Al2 (CO3 )(OH)16 ·4H2 O) phases, was synthesized via precipitation, using ammonium bicarbonate as the precipitant. The precursor was characterized by differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. Reactive spinel powder, which could be densified to translucency under vacuum at 1750°C in 2 h without additives, was obtained by calcining the precursor at 1100°C for 2 h. 相似文献
10.
Calcium hexa-aluminate (CaO·6Al2 O3 ) has been prepared from calcium nitrate and aluminum sulfate solutions in the temperature range of 1000°–1400°C. A 0.3 mol/L solution of aluminum sulfate was prepared, and calcium nitrate was dissolved in it in a ratio that produced 6 mol of Al2 (SO4 )3 ·16H2 O for each mole of Ca(NO3 )2 ·4H2 O. It was dried over a hot magnetic stirrer at ∼70°C and fired at 1000°–1400°C for 30–360 min. The phases formed were determined by XRD. It was observed that CaO·Al2 O3 and CaO·2Al2 O3 were also formed as reaction intermediates in the reaction mix of CaO·6Al2 O3 . The kinetics of the formation of CaO·6Al2 O3 have been studied using the phase-boundary-controlled equation 1 − (1 − x )1/3 = K log t and the Arrhenius plot. The activation energy for the low-temperature synthesis of CaO·6Al2 O3 was 40 kJ/mol. 相似文献
11.
Phase equilibria have been determined in the system CaO-Al2 O3 -H2 O in the temperature range 100° to 1000°C. under water pressures of up to 3000 atmospheres. Only three hydrated phases are formed stably in the system: Ca(OH)2 , 3CaO·Al2 O3 ·6H2 O, and 4CaO·3Al2 O3 -3H2 O. Pressure-temperature curves delineating the equilibrium decomposition of each of these phases have been determined, and some ther-mochemical data have been deduced therefrom. It has been established that both the compounds CaO·Al2 O3 and 3CaO·Al2 O3 have a minimum temperature of stability which is above 1000°C. The relevance of the new data to some aspects of cement chemistry is discussed. 相似文献
12.
Synthesis of Titanate Derivatives Using Ion-Exchange Reaction 总被引:3,自引:0,他引:3
Chul-Tae Lee Myeong-Heon Um Hidehiro Kumazawa 《Journal of the American Ceramic Society》2000,83(5):1098-1102
Two types of titanate derivatives, layered hydrous titanium dioxide (H2 Ti4 O9 · n H2 O) and potassium octatitanate (K2 Ti8 O17 ) with a tunnellike structure, were synthesized using an ion-exchange reaction. Fibrous potassium tetratitanate (K2 Ti4 O9 · n H2 O) was prepared by calcination of a mixture of K2 CO3 and TiO2 with a molar ratio of 2.8 at 1050°C for 3 h, followed by boiling-water treatment of the calcined products for 10 h. The material then was transformed to layered H2 Ti4 O9 · n H2 O through an exchange of K+ ions with H+ ions using HCl. K2 Ti8 O17 was formed by a thermal treatment of KHTi4 O9 · n H2 O. Pure KHTi4 O9 · n H2 O phase was effectively produced by a treatment of K2 Ti4 O9 with 0.005 M HCl solution for 30 min. Thermal treatment at 250°–500°C for 3 h resulted in formation of only K2 Ti8 O17 . 相似文献
13.
Takeshi Shiono Koji Shiono Kazuyo Miyamoto Giuseppe Pezzotti 《Journal of the American Ceramic Society》2000,83(1):235-37
A precursor was synthesized from a heterogeneous alkoxide solution that contained fine MgO powder, which allowed the preparation of MgAl2 O4 spinel powder with high sinterability characteristics. The precursor consisted of a mixture of boehmite (AlO(OH)) and a mixed hydroxide (Mg4 Al2 (OH)14 · 3H2 O). The spinel phase formed through two steps: (i) decomposition of the mixed hydroxide at low temperature and (ii) solid-state reaction between MgO and γ-Al2 O3 at higher temperatures. Dense polycrystalline spinel could be obtained from the calcined powders at sintering temperatures as low as 1400°C. 相似文献
14.
In this communication, we describe an inexpensive and feasible method for the preparation of hexagonal boron nitride (h–BN) nanorods in the absence of metal catalyst. Tertiary calcium phosphate (Ca3 (PO4 )2 ) and ammonium biborate hydrate (NH4 HB4 O7 ·3H2 O) were selected as starting materials where calcium phosphate was used as a diluting agent to prevent the formation of bulk B2 O3 during the thermolysis of ammonium biborate hydrate. The mixture was nitrided at 900°C in the flowing ammonia and was transformed into h–BN nanorods after subsequent crystallization. After crystallization at 1650°C for 2 h, the unique microstructure of h–BN nanorods was observed. 相似文献
15.
FREDRIK P. GLASSER ERIC E. LACHOWSKI DONALD E. MACPHEE 《Journal of the American Ceramic Society》1987,70(7):481-485
A compositional model based on available structural evidence is proposed for amorphous calcium silicate hydrogel. It is applicable to gels in the (Ca/Si),solid range 1.0 to 1.4 and is formulated to take account of dimeric silicate species in the solid. Its composition is represented by Ca x H6−2 x Si2 O7 · z Ca(OH)2 · n H2 O where x and z are not independently obtainable; x + z , however, is evaluated from the Ca/Si ratio. The model is applied to representative solubility data; Ksp and free energies of formation for C-S-H's in this composition range are evaluated. 相似文献
16.
The crystal structure of hydrothermally formed Al-substituted tobermorite-1.1nm (Ca4.9 Si5.5 Al0.5 O16.3 (OH)0.7 ·5H2 O) has been analyzed using synchrotron radiation powder diffraction data. Crystallographic positions of a zeolitic Ca atom and three water molecules in the channel of the framework were determined by the Monte Carlo method and subsequent Rietveld refinement. The Ca atom splits into two sites at a distance of 0.161 nm apart, and it is coordinated with the three water molecules and the three oxygen atoms belonging to the framework. Al atoms preferably substitute a part of the Si atoms at the "bridging SiO4 " tetrahedra rather than at those of the "chain middle group SiO4 " tetrahedra. 相似文献
17.
A. Cüneyt Tas 《Journal of the American Ceramic Society》1998,81(11):2853-2863
The binary compounds Ca3 Al2 O6 (C3 A), Ca12 Al14 O33 (C12 A7 ), CaAl2 O4 (CA), CaAl4 O7 (CA2 ), and CaAl12 O19 (CA6 ) in the CaO-Al2 O3 system have been synthesized as high-compound-purity ceramic powders by using the self-propagating combustion synthesis (SPCS) method. Materials characterization of the above-mentioned phases was performed via powder X-ray diffractometry (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The structural characterization of the C12 A7 phase has been performed via Rietveld analysis on the powdered XRD samples. It has hereby been shown that, by using this synthesis procedure, it should be possible to manufacture high-purity ceramic powders of CA, CA2 , and C12 A7 at 850°C, C3 A at 1050°C, and CA6 at 1200°C in a dry-air atmosphere. 相似文献
18.
The phase diagram for the ternary system MgO─P2 O5 ─H2 O at 25°C has been constructed. The magnesium phosphates represented are Mg(H2 PO4 )2 · n H2 O ( n = 4, 2, 0), MgHPO4 ·3H2 O, and Mg3 (PO4 )2 · m H2 O ( m = 8, 22). Because of the large differences in the solubilities of these compounds, the technique which involves plotting the mole fractions of MgO and P2 O5 as their 10th roots has been employed. With the exception of MgHPO4 ·3H2 O, the magnesium phosphates are incongruently soluble. Because incongruency is associated with a peritectic-like reaction, the phase Mg2 (PO4 )3 · 8H2 O persists metastably for an extended period. 相似文献
19.
Arno Kaiser Burkhard Sommer Eduard Woermann 《Journal of the American Ceramic Society》1992,75(6):1463-1471
The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states >3+ (Ca5 Cr3 O12 , Ca3 (CrO4 )2 , and Ca5 (CrO4 )3 ) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite, δ -CaCr2 O4 , is observed. In the CaO-rich section of the CaO–Al2 O3 –Cr2 O3 system a ternary intermediate phase, chrome-haüyne, Ca4 [(Al,Cr3+ )6 O12 ](Cr6+ O4 ), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca6 Al4 Cr2 O15 , coexists with CaO, CaCr2 O4 , chrome-haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al2 O3 system is insignificant. 相似文献
20.
Stephen Kwan Judith LaRosa Michael W. Grutzeck 《Journal of the American Ceramic Society》1995,78(7):1921-1926
Strätlingite (2CaO·Al2 O3 ·SiO2 ·8H2 O) is a complex calcium aluminosilicate hydrate commonly associated with the hydration of slag-containing cements or other cements enriched in alumina. Strätlingite can coexist with the hydrogarnet solid solution [hydrogarnet (3CaO·Al2 O3 ·6H2 O)-katoite (3CaO·Al2 O3 ·SiO2 ·4H2 O)] and calcium silicate hydrate (C-S-H). Since Strätlingite is present in many blended cements, the knowledge of strätlingite's characteristic silicate anion structure and how aluminum is accommodated by the structure is important. Phase pure Strätlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate cement, CaO, NaOH, and water. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) and then further examined using 29 Si, with and without cross-polarization (CP), and 27 Al solid-state magic angle nuclear magnetic resonance spectroscopy (MASNMR). For the most part, NMR data for these strätlingites corroborate structural information available in the literature. The aluminum atoms are both tetrahedrally and octahedrally coordinated, and the silicon atoms exist predominantly as Q2 , Q2 (1Al), and Q2 (2Al) species. The presence of alkali affects the structure of strätlingite in subtle ways, significantly reducing the AlIV /A1VI ratio. 相似文献