On the Influence of Seed Crystals on the Formation of Calcium Silicates with the Composition 3 CaO · 2 SiO2 The formation of the calcium silicates kilchoanite and rankinite of the composition 3 CaO · 2 SiO2 is facilitated and enabled, respectively, in the presence of appropriate seed crystals. Kilchoanite (Ca6[(SiO4)(Si3O10)]) is formed from mixtures of CaO and SiO2 in the autoclave at 200°C and from C? S? H (di, poly) under normal atmosphere at 700°C by seeding for example with kilchoanite, aluminium compounds, γ-Ca2SiO4. Rankinite (Ca3Si2O7) can be synthesized under the same conditions, when rankinite itself is applied as seed crystal. 相似文献
29Si NMR spectra of polycrystalline Ca6[Si2O7¦(OH)6] and [(CH3)4N] 8Si8O20·69H2O were measured using the cross polarization double-resonance technique. Observed shielding tensors are related to the known Si-O bond systems. The arrangement of the four Si-O bonds in the SiO4 tetrahedra is reflected by the 29Si shielding tensor. The most shielded direction corresponds to the shortest Si-O bond. 相似文献
By means of paperchromatographic, kinetic and X-ray methods it is shown that the tetramethylammonium silicate of the composition 1 N(CH3)4OH · 1 SiO2 · ~8 H2O has not – as hitherto supposed – the constitution of a poly- or phyllosilicate, but that of a tetra-anhydrido-bis-cyclotetrasilicate (double-fourringsilicate), [(CH3)4N]8[Si8O20] · ~69 H2O. Its trimethylsilylation by means of hexamethyldisiloxane gives the corresponding, crystalline trimethylsilyl ester [(CH3)3Si]8[Si8O20], which has been characterised by mass spectroscopy. 相似文献
The phase transformations of Syrian phosphorite upon mechanochemical activation are examined in the present work. The latter is carried out in planetary mill equipped with 20 mm steel milling bodies and duration from 30 to 300 min. The established by means of DTA, DTG, TG analyses transformation of non-activated carbonate fluorine apatite type B into the carbonate hydroxyl fluorine apatite (COHFAp) mixed type A2-B leads to substantial changes in the properties of the activated samples expressed in lowering the degree of crystallinity, strong defectiveness of the structure, and increase of the citric solubility. The thermal analysis gives evidence for the decomposition of the carbonate-containing component within the phosphorite, as from the positions placed in the vicinity of the hexagonal 63 axis (type A2), as well as from the positions of the phosphate ion (type B), and from the free carbonates. The data from the thermal analysis, the powder X-ray analysis and the infrared spectroscopy give also evidence for phase transformations of the activated apatite (with admixtures of quartz and calcite) into Ca10FOH(PO4)6, β-Ca3(PO4)2, Ca4P2O9, Ca3(PO4)2 · Ca2SiO4 and for that one of the quartz—into larnite and wollastonite. The influence of the α-quartz as a concomitant mineral is considered to be positive. The α-quartz forms Si–O–Si–OH bonds retaining humidity in the solid phase thus facilitating the isomorphous substitution OH? → F? with the subsequent formation of partially substituted COHFAp. Calcium silicophosphate and Ca4P2O9 are obtained upon its further heating. The presented here results settle a perspective route for processing of low-grade phosphate raw materials by means of tribothermal treatment aiming at preparation of condensed phosphates suitable for application as slowly acting fertilizer components. 相似文献
On the Coordination of Al in the Calcium Aluminate Hydrates 2 CaO · Al2O3 · 8 H2O and CaO · Al2O3 · 10 H2O By investigations with high-resolution 27Al-NMR in solids it is shown that in the compound 2 CaO · Al2O3 · 8 H2O the Al merely exist in octahedral coordination. According to this and considering its structural relationship with 4 CaO · Al2O3 · 19 H2O the dicalcium aluminate hydrate is proposed to be formulated as [Ca2Al(OH)6][Al(OH)3 (H2O)3]OH. Likewise for the compound CaO · Al2O3 · 10 H2O the octahedral coordination of the Al is proved by 27Al-NMR. This result corresponds with literature according to which a constitution as cyclohexaaluminate Ca3[Al6(OH)24] · 18 H2O is proposed. 相似文献
Pr4S3[Si2O7] and Pr3Cl3[Si2O7]: Derivatives of Praseodymium Disilicate Modified by Soft Foreign Anions For synthesizing both the disilicate derivatives Pr4S3[Si2O7] and Pr3Cl3[Si2O7], Pr, Pr6O11 and SiO2 are brought to reaction with S and PrCl3, respectively, in suitable molar ratios (850 °C, 7 d) in evacuated silica tubes. By using NaCl as a flux, Pr4S3[Si2O7] crystallizes as pale green, transparent single crystals (tetragonal, I41/amd, a = 1201.6(1), c = 1412.0(2) pm, Z = 8) with the appearance of slightly compressed octahedra. On the other hand, Pr3Cl3[Si2O7] emerges as pale green, transparent platelets and crystallizes monoclinically (space group: P21, a = 530.96(6), b = 1200.2(1), c = 783.11(8) pm, β = 109.07(1)°, Z = 2). In both crystal structures ecliptically conformed [Si2O7]6– units of two corner‐linked [SiO4] tetrahedra with Si–O–Si bridging angles of 131° in the sulfide and 148° in the chloride disilicate are present. In Pr4S3[Si2O7] both crystallographically independent Pr3+ cations show coordination numbers of 8 + 1 (5 S2– and 3 + 1 O2–) and 9 (3 S2– and 6 O2–). For Pr1, Pr2 and Pr3 in Pr3Cl3[Si2O7] coordination numbers of 10 (5 Cl– and 5 O2–) and 9 (2 ×; 4 Cl– and 5 O2– or 3 Cl– and 6 O2–, respectively) occur. 相似文献
Hydrothermal reaction of K7H[Nb6O19]·13H2O with Na2SiO3·9H2O (220 °C, 24 h) produces a lacunary siliconiobate [Si4Nb16O56]16?, which was isolated as mixed salt NaK8H6[Na@Si4Nb16O56]·26H2O (1). Changing the silicon source to Ph2Si(OH)2 under the same conditions slightly improves the yield of [Si4Nb16O56]16?, which was isolated as K14H[K@Si4Nb16O56]·26H2O (2). Extending the reaction time leads to rearrangement of [Si4Nb16O56]16? into Keggin-type silicododecaniobate [SiNb12O40]16?, which was isolated and characterized as K8H2(Nb2O2)[SiNb12O40]·20H2O (3). The complexes were characterized by X-ray single crystal analysis, elemental analysis, thermogravimetry, 29Si NMR. 相似文献
Sealing of components for high temperature applications with coefficients of linear thermal expansion (CTE) > 10·10−6 K−1 can be achieved by glasses from which crystalline phases with high CTE are precipitated. Many sealing glasses also contain further components as e.g. aluminium and hence, not only the desired phase is crystallized, but also additional phases. For this purpose, high temperature XRD was performed in order to determine the CTE of BaAl2Si2O8, CaAl2Si2O8, and Ca2Al2SiO7. In the case of BaAl2Si2O8 and Ca2AlSi2O7 the CTEs were 7.8·10−6/K and 7.9·10−6/K, respectively. In the case of CaAl2Si2O8 the CTE is 4.4·10−6/K. Especially the formation of the latter phase should be avoided for a sealing material of high temperature fuel cells. Sintered specimens of the respective compounds were also characterized by dilatometry. 相似文献
Chemical, Thermoanalytical, and X-ray Investigations to the Formation of the β-Ca2[P2O7] from the Ca2[P4O12] · 4 H2O The formation of β-Ca2[P2O7] from Ca2[P4O12] · 4 H2O (modification I) proceeds crystallographically oriented in several steps: In one of these steps an X-ray amorphous phase is formed and simultaneously cyclotetraphosphate reorganizes to polyphosphate. The dehydration proceeds in 2 steps: At 120°C 3 molecules and at 220°C 1 molecule are lost, respectively. The formation of diphosphate from polyphosphate, which is connected with the loss of P2O5, takes place at 850°C according to high temperature Guinier. 相似文献
The nature and stability of surface species of CuCl2 supported on α-Al2O3, γ-Al2O3, and SiO2 were investigated by using X-ray diffraction techniques and reflectance spectroscopy. No specific chemical interaction of CuCl2 is observed on an inert α-Al2O3 support, as opposed to hydrated carriers as SiO2 and γ-Al2O3. On these supports the coordination sphere of Cu2+ consists of surface groups (OH? or O? at drying and activation, resp.), H2O and Cl?, with the H2O ligands decreasing in concentration in the process of impregnation, drying and calcination. γ-Al2O3 samples, calcined at 400°C, show γ-Cu2(OH)3Cl as opposed to CuAl2O4 at higher temperatures. The absence of Cu2(OH)3Cl on SiO2-supported samples is related to the acid-base characteristics of the carriers. The various supports can be arranged in the following order of stability of the complexes formed: γ-Al2O3 > SiO2 ? -Al2O3. 相似文献
BaY2Si3O10, barium diyttrium trisilicate, is a new silicate grown from a molybdate‐based flux. The structure is based on zigzag chains, parallel to [010], of edge‐sharing distorted YO6 octahedra, linked by horseshoe‐shaped trisilicate groups and Ba atoms in irregular eight‐coordination. The layered character of the structure is caused by a succession of zigzag chains and trisilicate groups in planes parallel to (01). The Ba atoms occupy narrow channels extending parallel to [100]. The mean Y—O, Si—O and Ba—O bond lengths are 2.268, 1.626 and 1.633, and 2.872 Å, respectively. The two symmetry‐equivalent terminal SiO4 tetrahedra in the Si3O10 unit adopt an eclipsed conformation with respect to the central SiO4 tetrahedron; the Si—O—Si and Si—Si—Si angles are 136.35 (9) and 96.12 (4)°, respectively. One Ba, one Si and two O atoms are located on mirror planes; all remaining atoms are in general positions. The geometry of isolated trisilicate groups in inorganic compounds is briefly discussed. 相似文献
[(CH3)3Si]14Si7O21 — A New Cyclic Silicic Acid Trimethylsilyl Ester A new silicic acid trimethylsilyl ester was obtained by trimethylsilylation of barium chloride silicate 2 BaO · 3 BaCl2 · 2 SiO2. The ester was investigated by capillary gas chromatography, mass spectrometry, 29Si n.m.r. spectroscopy, and thinlayer chromatography and was found to be a cycloheptasilicic acid trimethylsilyl ester (tetradecakis-trimethylsiloxicyclohepta siloxane) of the formula [(CH3)3Si]14Si7O21. The application of the new compound as a standard substance is discussed. 相似文献
Thermoanalytic studies carried out on hydrate phases Na2[SiO2(OH)2]·nH2O (n = 4, 5, 7, 8) reveal two phase transitions at elevated temperatures under open-system and non-isothermal conditions Congruent melting at temperatures Tmp is followed by condensation at temperatures Tc > 380 K with subsequent formation of solid Na2[SiO3]. Foamingof the melts upon condensation is observed through heating stage microscopy. In situ 29Si NMR experiments proved oligomeric or endless chain-type anions, [Si1+nO2+3n(OH)2](2+2n)?, to be formed in the melts under open-system conditions. From DTA double peak configurations at temperatures Tc the thermal decomposition of the melts is shown to occur in a two-step reaction, uniformly with all four hydrate phases.Isothermal studies below melting temperatures show distinct decomposition of crystalline Na2[SiO2(OH)2]·8H2O to crystalline Na2[SiO2(OH)2]·4H2O whereas all the other crystallinephases within this hydrate series dehydrate to amorphous waterglass-type materials under identical experimental conditions in long-term annealing experiments. This exceptional phase relation between the octa- and the tetrahydrate has also been proved by X-ray powder diffraction heating experiments. 相似文献
[TMPA]4[Si8O20] · 34 H2O ( 1 ) and [DDBO]4[Si8O20] · 32 H2O ( 2 ) have been prepared by crystallization from aqueous solutions of the respective quaternary alkylammonium hydroxide and SiO2. The crystal structures have been determined by single-crystal X-ray diffraction. 1 : Monoclinic, a = 16.056(2), b = 22.086(6), c = 22.701(2) Å, β = 90.57(1)° (T = 210 K), space group C2/c, Z = 4. 2 : Monoclinic, a = 14.828(9), b = 20.201(7), c = 15.519(5) Å, β = 124.13(4)° (T = 255 K), space group P21/c, Z = 2. The polyhydrates are structurally related host-guest compounds with three-dimensional host frameworks composed of oligomeric [Si8O20]8? anions and H2O molecules which are linked via hydrogen bonds. The silicate anions possess a cube-shaped double four-ring structure and a characteristic local environment formed by 24 H2O molecules and six cations (TMPA, [C8H20N2]2+, or DDBO, [C8H18N2]2+). The cations themselves reside as guest species in large, irregular, cage-like voids. Studies employing 29Si NMR spectroscopy and the trimethylsilylation method have revealed that the saturated aqueous solutions of 1 and 2 contain high proportions of double four-ring silicate anions. Such anions are also abundant species in the saturated solution of the heteronetwork clathrate [DMPI]6[Si8O18(OH)2] · 48.5 H2O ( 3 ) with 1,1-dimethylpiperidinium (DMPI, [C7H16N]+) guest cations. 相似文献
Crystallographic Orientation Relations between the Phases in the Reaction Ca2[P4O12] · 4 H2O → β-(Ca2[PO3]4)x The dehydration of Ca2[P4O12] · 4 H2O modification I proceeds over several intermediate phases to β-(Ca2[PO3]4)x crystallographically oriented. One of the intermediate phases is X-ray amorphous. It is of special interest, that this amorphous phase does not interrupt the oriented course of the reaction. The β-polyphosphate transforms to β-Ca2[P2O7] connected with the loss of P2O5 at further heating. The crystallographic orientation relations between educt and product were determined for all steps of the reaction. The unit cells of the phases were determined too. 相似文献
I‐Type La2Si2O7: According to La6[Si4O13][SiO4]2not a Real Lanthanum Disilicate In attempts to synthesize lanthanum telluride silicate La2Te[SiO4] (from La, TeO2, SiO2 and CsCl, molar ratio: 1 : 1: 1 : 20, 950 °C, 7 d) or fluoride‐rich lanthanum fluoride silicates (from LaF3, La2O3, SiO2 and CsCl, molar ratio: 5 : 2 : 3 : 17, 700 °C, 7 d) in evacuated silica tubes, colourless lath‐shaped single crystals of hitherto unknown I‐type La2Si2O7 (monoclinic, P21/c; a = 726.14(5), b = 2353.2(2), c = 1013.11(8) pm, β = 90.159(7)°) were found in the CsCl‐flux melts. Nevertheless, this new modification of lanthanum disilicate does not contain any discrete disilicate groups [Si2O7]6‐ but formally three of them are dismutated into one catena‐tetrasilicate ([Si4O13]10‐ unit of four vertex‐linked [SiO4]4‐ tetrahedra) and two ortho‐silicate anions (isolated [SiO4]4‐ tetrahedra) according to La6[Si4O13][SiO4]2. This compound can be described as built up of alternating layers of these [SiO4]4‐ and the horseshoe‐shaped [Si4O13]10‐ anions along [010]. Between and within the layers the high‐coordinated La 3+ cations (CN = 9 ‐ 11) are localized. The close structural relationship to the borosilicates M3[BSiO6][SiO4](M = Ce ‐ Eu) is discussed and structural comparisons with other catena‐tetrasilicates are presented. 相似文献
A novel tetramethylammonium aluminosilicate hydrate with the approximate composition [NMe4]6[AlxSi8?xO18?x(OH)2+x] · 44H2O (x = 3–4) has been identified by powder X-ray diffraction as a component in a polyphasic solid mixture which crystallized at room temperature from an aqueous NMe4OH? Al2O3? SiO2 solution. Large crystals of the novel hydrate phase could be mechanically selected from that mixture. The crystal structure has been determined from 1 196 unique MoKα diffraction data measured at 180 K: Tetragonal crystal system, cell constants a = 16.181(4) and c = 17.450(4) Å, space group P4/mnc with Z = 2 formula units per unit cell, R = 0.072. The host-guest compound is of polyhedral clathrate type with a mixed three-dimensional, (mainly) four-connected network composed of oligomeric aluminosilicate anions [AlxSi8?xO18?x(OH)2+x]6? and H2O molecules linked via hydrogen bonds O? H …? O. The aluminosilicate anions possess a cube-shaped (double four-ring) structure. Orientationally disordered cationic guest species NMe4+ are enclosed in the large [4668] and [4151067] polyhedral voids of the host framework; the small [46] cages (i.e. the double four-ring anions) and [4356] cages are empty. The hydrate is a further member in a recently discovered series of clathrates with mixed tetrahedral networks, which provides a structure-chemical link between zeolite- and clathrate hydrate-type host-guest compounds. 相似文献
Interaction between silica hydrogel isolated from serpentines (Mg(Fe))6[Si4O10](OH)8, sodium hydroxide NaOH, and strontium chloride SrCl2 in aqueous medium was studied by DTA and X-ray powder diffraction (XRD). Stirring of the boiling aqueous suspension prepared from these reagents under the atmospheric pressure for 2 h yields hydrated strontium silicate species: Sr3Si2O7 · 4H2O and Sr3Si2O7 · 3H2O or their mixtures, whose heating to 810–825°C is accompanied by some phase transformations: strontium metasilicate Sr3Si3O9 or strontium orthosilicate Sr2SiO4 is formed after bound water is removed in the range 250–350°C, and strontium silicate SrSiO3 is formed at higher temperatures. Sr2SiO4 single phase is observed upon heat treatment to 700–750°C. The optimal molar ratio of the reagents was found to favor Sr2SiO4 formation. 相似文献
The New Layer‐Silicates Ba3Si6O9N4 and Eu3Si6O9N4 The new oxonitridosilicate Ba3Si6O9N4 has been synthesized in a radiofrequency furnace starting from BaCO3, amorphous SiO2 and Si3N4. The reaction temperature was at about 1370 °C. The structure of the colorless compound has been determined by single‐crystal X‐ray diffraction analysis (Ba3Si6O9N4, space group P3 (no. 143), a = 724.9(1) pm, c = 678.4(2) pm, V = 308.69(9)· 106 pm3, Z = 1, R1 = 0.0309, 1312 independent reflections, 68 refined parameters). The compound is built up of corner sharing SiO2N2 tetrahedra forming corrugated layers between which the Ba2+ ions are located. Substitution of barium by europium leads to the isotypic compound Eu3Si6O9N4. Because no single‐crystals could be obtained, a Rietveld refinement of the powder diffractogram was conducted for the structure refinement (Eu3Si6O9N4, space group P3 (no. 143), a = 711.49(1) pm, c = 656.64(2) pm, V = 287.866(8) ·106 pm3, Rp = 0.0379, RF2 = 0.0638). The 29Si MAS‐NMR spectrum of Ba3Si6O9N4 shows two resonances at ?64.1 and ?66.0 ppm confirming two different crystallographic Si sites. 相似文献