Über den Einfluß von Kristallkeimen auf die Bildung von Silicaten der Zusammensetzung 3 CaO · 2 SiO2

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.     

High-resoluttin 29Si NMR in solid silicates: Correlations between shielding tensor and Si-O bond length

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.     

Die Konstitution des Tetramethylammoniumsilicats der Zusammensetzung 1,0 N(CH3)4OH 1,0 SiO2 · 8,0–8,3 H2O

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.     

Thermal behavior and phase transformations of nanosized carbonate apatite (Syria)

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.     

Zur Koordination des Aluminiums in den Calciumaluminathydraten 2 CaO · Al2O3 · 8 H2O und CaO · Al2O3 · 10 H2O

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.     

Pr4S3[Si2O7] und Pr3Cl3[Si2O7]: Durch weiche Fremdanionen modifizierte Derivate von Praseodymdisilicat

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 S^2– and 3 + 1 O^2–) and 9 (3 S^2– and 6 O^2–). For Pr1, Pr2 and Pr3 in Pr₃Cl₃[Si₂O₇] coordination numbers of 10 (5 Cl^– and 5 O^2–) and 9 (2 ×; 4 Cl^– and 5 O^2– or 3 Cl^– and 6 O^2–, respectively) occur.     

Formation of Silicon-Containing Polyoxoniobates from Hexaniobate Under High Temperature Conditions

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.     

High temperature thermal expansion of BaAl2Si2O8, CaAl2Si2O8, and Ca2Al2SiO7 studied by high-temperature X-ray diffraction (HT-XRD)

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.     

Chemische,thermoanalytische und röntgenorgraphische Untersuchungen zur Bildung des β-Ca2[P2O7] aus dem Ca2[P4O12] · 4 H2O

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.     

Study of CuCl2 Supported on SiO2 and Al2O3

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.     

BaY2Si3O10: a new flux‐grown trisilicate

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.     

[(CH3)3Si]14Si7O21 – ein neuer cyclischer Kieselsäuretrimethylsilylester

[(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.     

Thermal studies on sodium silicate hydrates. IV. Thermal stability of sodium silicate hydrates Na2[SiO2(OH)2]·nH2O(n = 4, 5, 7, 8). Phase relations and decomposition characteristics under open-system conditions

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 T_mp is followed by condensation at temperatures T_c > 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, [Si_1+nO_2+3n(OH)₂]^(2+2n)?, to be formed in the melts under open-system conditions. From DTA double peak configurations at temperatures T_c 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.     

[TMPA]4[Si8O20] · 34 H2O and [DDBO]4[Si8O20] · 32 H2O are heteronetwork clathrates with 1,1,4,4-tetramethylpiperazinium (TMPA) and 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane (DDBO) guest cations

[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.     

Kristallographische Orientierungsbeziehungen zwischen den Phasen der Reaktionsfolge Ca2[P4O12] · 4 H2O → β-(Ca2[PO3]4)x

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.     

Co(en)3[B4O5(OH)4]Cl·3H2O和[Ni(en)3][B5O6(OH)4]2·2H2O的合成、结构以及热力学性质

利用水热法合成了两种过渡金属配合物为模板剂的含水硼酸盐晶体Co(en)3[B4O5(OH)4]Cl·3H2O(1) 和 [Ni(en)3][B5O6(OH)4]2·2H2O (2),并通过元素分析、X射线单晶衍射、红外光谱及热重分析对其进行了表征。化合物1晶体结构的主要特点是在所有组成Co(en)33+, [B4O5(OH)4]2–, Cl– 和 H2O之间通过O–H…O、O–H…Cl、N–H…Cl和N–H…O四种氢键连接形成网状超分子结构。化合物2晶体结构的特点是[B5O6(OH)4]–阴离子通过O–H…O氢键连接形成沿a方向有较大通道的三维超分子骨架,模板剂[Ni(en)3]2+阳离子和结晶水分子填充在通道中。     

La2Si2O7 im I—Typ: Gemäß La6[Si4O13][SiO4]2 kein echtes Lanthandisilicat

I‐Type La₂Si₂O₇: According to La₆[Si₄O₁₃][SiO₄]₂ not 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.     

Structural links between zeolite-type and clathrate hydrate-type materials: Synthesis and crystal Structure of [N(CH3)4]6[AlxSi8−xO18−x(OH)2+x] · 44H2O (x = 3–4)

A novel tetramethylammonium aluminosilicate hydrate with the approximate composition [NMe₄]₆[Al_xSi_8?xO_18?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 [Al_xSi_8?xO_18?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.     

Preparation of Hydrated Strontium Silicates from Silica Hydrogel Isolated from Serpentines and Their Thermal Transformations

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.     

Die neuen Schichtsilicate Ba3Si6O9N4 und Eu3Si6O9N4

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, R_p = 0.0379, R_F² = 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.