共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
The liquidus-solidus relations along the join Ca2 SiO4 -Ca(OH), in the system CaO-SiO2 -H2 O have been determined at 1000 atm up to 1110°C. This join is binary and contains the calcium silicate hydrate, calciochondrodite, Ca5-(SiO4 (OH)2 . Calciochondrodite melts incongruently to Ca2 SiO2 + liquid (composition 23 wt% Ca2 Si04 ) at 955°C. The eutectic between calcium hydroxide and calciochondrodite lies at 13% Ca2 Si04 and 822°C. Preliminary experiments, also at 1000 atm, in the ternary system CaO-Ca2 Si04 -Ca(OH), indicate that the eutectic at which the fields of primary Ca(OH)2 , CaO, and Ca2 (Si04 )2 (OH)2 meet is close to the CaO-Ca. (OH), side of the triangle at approximately 805° C. The ternary reaction point Ca2 SiOl + liquid ⇌Ca5 (SiO4 )2 (OH)2 + CaO + liquid is believed to lie in the low-CaO (<5%) high-Ca(OH)2 (>70%) part of the system. 相似文献
3.
Konstantinos Kyritsis Nicola Meller Christopher Hall 《Journal of the American Ceramic Society》2009,92(5):1105-1111
We have studied the chemistry and the morphology of hydrogarnet crystals produced in cement-based hydroceramic materials at elevated temperatures (200°–350°C) with silica and alumina additions. Such materials lie within the hydrothermal CaO–Al2 O3 –SiO2 –H2 O (CASH) system. Hydrogarnet Ca3 Al2 (SiO4 )3− y (OH)4 y is the dominant aluminum bearing phase formed and its composition is influenced mainly by the curing temperature and to a lesser degree by the addition of silica. The composition parameter y was estimated by Rietveld refinement of X-ray diffraction (XRD) data. Electron probe microanalysis (EPMA) shows that the hydrogarnets incorporate minor elements such as Fe, Mg, and S. EPMA data confirmed the hydrogarnet composition estimated from XRD. Both octahedral and icositetrahedral forms are observed. The icositetrahedral form is associated with higher minor element content. 相似文献
4.
MASAYUKI ISHITSUKA TSUGIO SATO TADASHI ENDO MASAHIKO SHIMADA 《Journal of the American Ceramic Society》1987,70(2):69-71
Aluminum titanate solid solutions with empirical formulas of Al2 Ti1-x Zrx O5 , Al6(2-x)(6+x) Si6x/(6+x) □6x/(6+x) TiO5 , and Al2(1-x) Mgx Ti1+x O5 were synthesized by reaction sintering and annealed at 900° to 1300°C in air to evaluate the thermal stability. Substitution of Al in Al2 TiO5 by Si and 2Al by Mg and Ti ions to form solid solutions such as AI6(2-x)/(6+x)l-Si 6x/(6+x)□6x/(6+x) TiO5 , and Al2(1-x) Mgx Ti1+x O5 was effective in controlling the thermal decomposition, but substitution of Ti by Zr had little effect. 相似文献
5.
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
6.
Dilshat Ubaydullayevich Tulyaganov 《Journal of the American Ceramic Society》2000,83(12):3141-3146
The binary systems Ca5 [PO4 ]3 F–CaAl2 Si2 O8 and Ca5 [PO4 ]3 F–CaMgSi2 O6 have been investigated, via annealing and quenching in the experimental method, direct observation of the melting behavior of the samples, X-ray diffraction analysis, petrography, and transmission electron microscopy. Phase equilibrium in the ternary system Ca5 [PO4 ]3 F–CaAl2 Si2 O8 –CaMgSi2 O6 was determined by combining information from the structure of the binary boundary systems and additional experimental data that were obtained from ternary compositions. The glass-formation region of the fluorapatite–anorthite–diopside system was studied, and the glass compositions for the development of glass-ceramics for technical and medical applications were identified. 相似文献
7.
Mary W. Barnes Maria Klimkiewicz Paul W. Brown 《Journal of the American Ceramic Society》1992,75(6):1423-1429
Compositions along the Ca2 SiO4 –Ca3 (PO4 )2 join were hydrated at 90°C. Mixtures containing 15, 38, 50, 80, and 100 mol% Ca3 (PO4 )2 were fired at 1500°C, forming nagelschmidtite + a 1 -CaSiO4 , A -phase and silicocarnotite and a -Ca3 (PO4 )2 , respectively. Hydration of these produces hydroxylapatite regardless of composition. Calcium silicate hydrate gel is produced when Ca2 SiO4 ≠ 0 and portlandite when Ca2 SiO4 is >50%. Relative hydration reactivities are a -Ca3 (PO4 )2 > nagelschmidtite > α 1 -Ca2 SiO4 > A -phase > silicocarnotite. Hydration in the presence of silica or lime influences the amount of portlandite produced. Hydration in NaOH solution produces 14-A tobermorite rather than calcium silicate hydrate gel. 相似文献
8.
In the search for new fluorescent materials among lanthanoid-activated Ca2 SnO4 compounds, a parallel solution-based synthesis approach was applied and a new blue-emission Ca2 SnO4 :Ce phosphor was discovered; its emission intensity reaches 80% of the intensity of one of the best commercial Y3 Al5 O12 :Ce3+ phosphors. Among 14 lanthanoid-activated materials, three categories could be distinguished with respect to the effect of the dopant ion on the excitation and emission properties of the phosphor. In addition, potential phosphors in the A–Sn–O (A=Mg, Ca, Sr, and Ba) systems were investigated and Ca2 SnO4 was found to be the most suitable host compound for the lanthanoid-activated phosphors. 相似文献
9.
Shinichi Kikkawa Namie Kato Noriko Taya Masakazu Tada Fumikazu Kanamaru 《Journal of the American Ceramic Society》1995,78(5):1387-1390
Both NaCuO2 -type Ca0.85 CuO2 and infinite-layered (Ca1- x Sr x )CuO2 could be prepared much more easily by firing the dried solids from mixed acetate aqueous solutions titrated with tartaric acid than by normal calcination. The presence of a narrow solid-solution composition range of 0.10 < x > 0.16 was confirmed in infinite-layered (Ca1- x Sr x )CuO2 in the preparation using the tartrate route. The calcium could also be substituted by sodium in a range of y > 0.15 in NaCuO2 -type (Ca1- y Na y )0.85 CuO2 using the same route. Further substitution of Ca2+ with Y3+ might also be possible in infinite-layered (Ca1- x Sr x )CuO2 , but resulted in the NaCuO2-type compound in the substitution with Na+ . 相似文献
10.
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
11.
KIMIHIRO YAMASHITA HITOSHI OWADA HIROSHI NAKAGAWA TAKAO UMEGAKI TAKAFUMI KANAZAWA 《Journal of the American Ceramic Society》1986,69(8):590-594
Synthesis of stable oxy- and oxyhydroxyapatkes [(Ca,M)-Ap] was attempted by substitution of Ca2+ with M3+ (M = Al, Y) assuming the composition Ca10-x Mx (PO4 )6 (OH)2-x Ox . Yttrium-calcium oxyhydroxyapatite was successfully obtained. Its structure was analyzed and confirmed by X-ray diffraction and infrared spectroscopy. Dielectric dispersion and absorption were not so distinct in (Ca,Y)-Ap as in hydroxyapatite (Ca-Ap). The ac electrical conductivity of (Ca10-x ,Yx )-Ap was found to decrease with increasing x. These results are discussed in terms of a proposed charge transport mechanism. 相似文献
12.
Raúl García Carrodeguas Antonio H. De Aza Xavier Turrillas Pilar Pena Salvador De Aza 《Journal of the American Ceramic Society》2008,91(4):1281-1286
The transformation β→α in Mg-substituted Ca3 (PO4 )2 was studied. The results obtained showed that, contrary to common belief, there is, in the system Mg3 (PO4 )2 –Ca3 (PO4 )2 , a binary phase field where β+α-Ca3 (PO4 )2 solid solutions coexist. This binary field lies between the single-phase fields of β- and α-Ca3 (PO4 )2 solid solution in the Ca3 (PO4 )2 -rich zone of the mentioned system. In the light of the results and the Palatnik–Landau's Contact Rule of Phase Regions, a corrected phase equilibrium diagram has been proposed. The practical implications of these findings with regard to the synthesis of pure α- and β- Mg-substituted Ca3 (PO4 )2 powders and to the sintering of related bioceramics with improved mechanical properties are pointed out. 相似文献
13.
Three types of dicalcium silicate (Ca2 SiO4 –calcium zirconate (CaZrO3 ) composites were fabricated and their microstructures correlated with their mechanical properties. In the first type, Ca2 SiO4 was added as a minor phase. The second type consisted of a 50 vol% Ca2 SiO4 -50 vol% CaZrO3 mixture, while in the third type, CaZrO3 constituted the minor phase. Pure CaZrO3 was also studied as a control and found to have a toughness which depended on its grain size. In composites with Ca2 SiO4 as the minor phase, a toughness increase was observed and found to be a function of matrix grain size. The composite with the second type of microstructure had the highest toughness of about 4.0 Mpa. m1/2 , which was about double that of the monolithic CaZrO3 . No evidence was found for transformation toughening by the orthorhombic (β) to monoclinic (γ) transformation in Ca2 SiO4 . The main toughening mechanisms identified were crack deflection and crack branching. Microstructural observations indicated the existence of weak grain boundaries in CaZrO3 agglomerates as well as weak interfaces between the two phases. 相似文献
14.
Simple expressions of activities, as functions of composition, were developed from structural models for some borosilicate melts. Their applicability was tested with data from the liquidus curves of phase diagrams. If the heat of fusion is known, a value of the activity-composition function can be calculated for each temperature of the liquidus curve. These values are compared with activities computed from the structural model. Calorimetric heats of fusion were available for the calcium borates studied. Experimental data from published phase diagrams for the systems Ca3 (BO3 )2 –Ca2 SiO4 , Ca2 B2 O6 –Ca2 SiO4 , Ca3 (BO3 )2 –CaSiO3 , Ca(BO2 )–CaSiO3 , Ca2 B2 O5 –CaSiO3 , CaSiO3 –BaSiO3 , and CaSiO3 –K2 SiO3 were used. Simple ionic models seemed to be applicable in most cases, except for melts of highly polymerized mixed ions (metaborate-metasilicate), for which the so-called "group" model appeared to be useful. A value for the heat of fusion of CaSiO3 was calculated from this work (13,200 cal. per mole). 相似文献
15.
Robert S. Roth Nong M. Hwang Claudia J. Rawn Benjamin P. Burton Joseph J. Ritter 《Journal of the American Ceramic Society》1991,74(9):2148-2151
New data are presented on the phase equilibria of the binary systems CaO-CuO and CaO-Bi2 O3 . Corrected compositions are reported for Ca.Bi6 O13 and Ca2 Bi2 O5 and a new metastable high-temperature phase is reported for a composition near Ca6 Bi7 O16.5 . The composition and decomposition temperatures for Ca1–x .CuO2 are given for both air and 1 atm of oxygen at 755 ± 5° and 835 ± 5°C, respectively. 相似文献
16.
Chun-Hsu Shen Cheng-Liang Huang Chuan-Feng Shih Chih-Ming Huang 《International Journal of Applied Ceramic Technology》2009,6(5):562-570
The microstructure and microwave dielectric properties of a (1− x )(Mg0.95 Ni0.05 )TiO3 − x Ca0.6 La0.8/3 TiO3 ceramics system have been investigated. The system was prepared using a conventional solid-state ceramic route. In order to produce a temperature-stable material, Ca0.6 La0.8/3 TiO3 was added for a near-zero temperature coefficient (τf ). With partial replacement of Mg2+ by Ni2+ , the dielectric properties of the (1− x )(Mg0.95 Ni0.05 )TiO3 − x Ca0.6 La0.8/3 TiO3 ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. An excellent Q × f value of 118,000 GHz can be obtained for the system with x =0.9 at 1325°C. For practical application, a dielectric constant (ɛr ) of 24.61, a Q × f value of 102,000 GHz, and a temperature coefficient of resonant frequency (τf ) of −3.6 ppm/°C for 0.85(Mg0.95 Ni0.05 )TiO3 −0.15Ca0.6 La0.8/3 TiO3 at 1325°C are proposed. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance. 相似文献
17.
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
18.
T.M. BESMANN 《Journal of the American Ceramic Society》1986,69(1):69-74
A thermodynamic analysis of the chemical vapor deposition of the composite ceramic (Si3 N4 (BN) ⋆ was performed using a general computer program for the calculation of heterogeneous equilibria. Reactants assumed were (H2 SiCl2 ), (BCI3 ), and (NH3 ). The equilibrium conditions for the deposition of condensed phases in the B-Si-N system wire determined as a function of the variables temperature, total system pressure, and gram-atomic reactant gas fractions B/(Si + B) and N/(CI + N). The phase assemblage (Si3 N4 )-〈BN〉 was found to be stable over a large region. Predominant gaseous species at equilibrium were (HCI), (N2 ), (H2 ), and the silicon chlorides. Deposition efficiencies at equilibrium for (Si3 N4 ) and (BN) were high, particularly in the presence of excess (NH3 ) and at temperatures below 1600 K. 相似文献
19.
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
20.
Koichiro Fukuda Ken-ichi Matsunaga Takahiro Bessho Hideto Yoshida 《Journal of the American Ceramic Society》2005,88(4):954-962
The phase stability in part of the P2 O5 -bearing pseudoquaternary system CaO–SiO2 –Al2 O3 –Fe2 O3 has been studied by electron probe microanalysis, optical microscopy, and powder X-ray diffractometry. At 1973–1653 K, the α-Ca2 SiO4 solid solution [α-C2 S(ss)] and melt coexisted in equilibrium, both chemical variations of which were determined as a function of temperature. The three phases of melt, calcium aluminoferrite solid solution (ferrite), and C2 S(ss) coexisted at 1673–1598 K. On the basis of the chemical compositions of these phases, a melt-differentiation mechanism has been, for the first time, suggested to account for the crystallization behavior of Ca3 Al2 O6 solid solution [C3 A(ss)]. When the α-C2 S(ss) and melt were cooled from high temperatures, the melt would be induced to differentiate by the crystallization of ferrite. Because the local equilibrium would be continually attained between the rims of the precipitating ferrite and coexisting melt during further cooling, the melt would progressively become enriched in Al2 O3 with respect to Fe2 O3 . The resulting ferrite crystals would show the zonal structure, with the Al/(Al+Fe) value steadily increasing up to 0.7 from the cores toward the rims. The C3 A(ss) would eventually crystallize out of the differentiated melt between the zoned ferrite crystals in contact with their rims. 相似文献