Reaction pathway and phase transitions in Al–Ti–Si system during differential thermal analysis

The present paper mainly studied the phase formation and reaction pathway of the Al–Ti–Si system in detail by thermal analysis combined with XRD and SEM observations. The phase formation sequence in Al–Ti–Si system from starting mixtures to final products with increasing temperature can be described as following: Al_(l) + Ti_(s) + Si_(s) → (Al–Si)_(l) + Ti_(s) + Si_(s) → Ti(Al,Si)_3(s) + Si_(s)Ti₅(Si,Al)₃ + Al_(l). More importantly, the solubility of Si in Ti(Al,Si)₃ decreased gradually while that of Al in Ti₅(Si,Al)₃ increased with temperature increasing, suggesting the transportation of Si atoms from intermediate aluminides Ti(Al,Si)₃ to final stable silicides Ti₅(Si,Al)₃ and hence further confirming the formation of Ti₅(Si,Al)₃ at the expense of Ti(Al,Si)₃.     

Mechanochemical synthesis and high-frequency induction heated consolidation of nanostructured Ti5Si3 and its mechanical properties

Pure Ti and Si powders were milled in a horizontal-rotation ball mill and in a high-energy ball mill to synthesize Ti₅Si₃ powders. The high-energy ball milling produced nanosized single-phase Ti₅Si₃ particles. Meanwhile, no reaction occurred during the horizontal milling. The two milled powders were consolidated using the high-frequency induction heated sintering method. A dense nanostructured Ti₅Si₃ compact was consolidated within 2 min using the mechanically synthesized Ti₅Si₃ powder. The retainment of nanoscale structure during sintering is believed to be the reason for the good mechanical properties of the Ti₅Si₃ compact. In comparison, the horizontally milled powder reacted to form Ti₅Si₃ partially on sintering. It is believed that the enhanced toughness of the horizontally milled samples may be due to the crack-deterring effect of softer Si/Ti grains.     

The Metallic Zintl Phase Ba3Si4 – Synthesis,Crystal Structure,Chemical Bonding,and Physical Properties

The Zintl phase Ba₃Si₄ has been synthesized from the elements at 1273 K as a single phase. No homogeneity range has been found. The compound decomposes peritectically at 1307(5) K to BaSi₂ and melt. The butterfly‐shaped Si₄⁶⁻ Zintl anion in the crystal structure of Ba₃Si₄ (Pearson symbol tP28, space group P4₂/mnm, a = 8.5233(3) Å, c = 11.8322(6) Å) shows only slightly different Si‐Si bond lengths of d(Si–Si) = 2.4183(6) Å (1×) and 2.4254(3) Å (4×). The compound is diamagnetic with χ ≈ −50 × 10⁻⁶ cm³ mol⁻¹. DC resistivity measurements show a high electrical resistivity (ρ(300 K) ≈ 1.2 × 10⁻³ Ω m) with positive temperature gradient dρ/dT. The temperature dependence of the isotropic signal shift and the spin‐lattice relaxation times in ²⁹Si NMR spectroscopy confirms the metallic behavior. The experimental results are in accordance with the calculated electronic band structure, which indicates a metal with a low density of states at the Fermi level. The electron localization function (ELF) is used for analysis of chemical bonding. The reaction of solid Ba₃Si₄ with gaseous HCl leads to the oxidation of the Si₄⁶⁻ Zintl anion and yields nanoporous silicon.     

The Ternary System Nickel/Silicon/Titanium Revisited

The constitution of the ternary system Ni/Si/Ti is investigated over the entire composition range using X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDS), differential thermal analysis (DTA), and metallography. The solid state phase equilibria are determined for 900 °C. Eight ternary phases are found to be stable. The crystal structures for the phases τ₁NiSiTi, τ₂Ni₄Si₇Ti₄, τ₃Ni₄₀Si₃₁Ti₁₃, τ₄Ni₁₇Si₇Ti₆, and τ₅Ni₃SiTi₂ are corroborated. For the remaining phases the compositions are determined as Ni₆Si₄₁Ti₅₃ (τ₆), Ni₁₆Si₄₂Ti₄₂(τ₇), and Ni₁₂Si₄₅Ti₄₃ (τ₈). The reaction scheme linking the solid state equilibria with the liquidus surface is amended to account for these newly observed phases. The discrepancies between previous experimental conclusions and modeling results are addressed. The liquidus surface is dominated by the primary crystallisation field of τ₁NiSiTi, the only congruently melting phase.     

In-Cage Interactions in the Clathrate Superconductor Sr8Si46

The clathrate I superconductor Sr₈Si₄₆ is obtained under high-pressure high-temperature conditions, at 5 GPa and temperatures in the range of 1273 to 1373 K. At ambient pressure, the compound decomposes upon heating at T=796(5) K into Si and SrSi₂. The crystal structure of the clathrate is isotypic to that of Na₈Si₄₆. Chemical bonding analysis reveals conventional covalent bonding within the silicon network as well as additional multi-atomic interactions between Sr and Si within the framework cages. Physical measurements indicate a bulk BCS type II superconducting state below T_c=3.8(3) K.     

The polyoctahedral silsesquioxane (POSS) 1,3,5,7,9,11,13,15‐octaphenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (octaphenyl‐POSS)

Solvent‐free single crystals of 1,3,5,7,9,11,13,15‐octaphenylpentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]octasiloxane (abbreviated as octaphenyl‐POSS), C₄₈H₄₀O₁₂Si₈, were obtained by dehydration/condensation of the tetrol Si₄O₄(Ph)₄(OH)₄. The powder pattern generated from the single‐crystal data matches well with the experimentally measured powder pattern of commercial octaphenyl‐POSS. The geometry of the centrosymmetric molecule in the crystal was compared with that in the gas phase, and had shorter Si—O bond lengths and a broader range of Si—O—Si bond angles. The average Si—O bond length [1.621 (3) Å], and Si—O—Si and O—Si—O bond angles [149 (5) and 109 (1)°, respectively] were within the same range measured previously for octaphenyl‐POSS solvates.     

Synthesis and crystal structure of a new oxychalcogenide La5Ti∼3.25Zr∼0.25S5O9.25

A new phase in the quinary system La/Ti/Zr/S/O was obtained from a mixture of La₂O₃, La₂S₃, ZrO₂, and TiO₂ by a solid-state reaction at 1273 K in a sealed fused-silica tube. The structure of this new phase, La₅Ti_∼3.25Zr_∼0.25S₅O_9.25, was solved by single-crystal X-ray diffraction, with R_(obs)=3.37% for 2764 reflections (I>3σ(I)) and 125 variables. This compound crystallizes with four formula units in the monoclinic space group C2/m with lattice constants , , , and β=106.100(8)°. The structure can be viewed as a 2D building constituted from two-atom-thick slabs of rock salt type (=sulfide part) which are interleaved with double-octahedral chains centered on titanium/zirconium atoms (mixed Ti/Zr sites) and drawing a zigzag arrangement (=oxide part). In addition, EDXS analyses show that a solid solution Ti/Zr exists with a general formulation La₅Ti_3.5−xZr_xS₅O_9.25 (where 0.1?x?0.5).     

Siliciding of titanium carbides with gaseous SiO

Titanium carbides of different stoichiometries were silicided with gaseous SiO at 1350°C. A mechanical mixture of silicon and silicon dioxide was used as a reaction source of SiO. Ti₃SiC₂, TiSi₂, and Ti₅Si₃ were the main reaction products, the phase composition of which strongly depended on the titanium carbide stoichiometry. The siliciding of carbides with a nearly stoichiometric carbon content resulted in the formation of Ti₃SiC₂, on the surface of which the other silicide phases, such as Ti₅Si₃ and TiSi₂, began to form. For titanium carbides with a low carbon concentration, Ti₅Si₃ was the only siliciding product.     

Syntheses and Molecular Structures of Titanium Derivatives with Polymerizable Ligands. Toward Extended Arrays

The reactions between Ti(OR)₄ and allylacetatoacetate (HAAA) in 1:1 or 1:2 stoichiometry at rt gave Ti₂(OR)₆(AAA)₂ R = Et ( 1 ), iPr ( 2 ) and Ti(OR)₂(AAA)₂ R = Et ( 3 ), iPr ( 4 ) species. A monosubstituted derivative Ti₂(OiPr)₆(AMP)₂ ( 5 ) was isolated with allylmethylphenol (AMPH). 1 and 5 were characterized by single crystal X‐ray diffraction. Their molecular structures consist of dimers with the polymerizable ligands in terminal positions andbridging alkoxide ligands assembling five and six‐coordinated metal atoms, respectively. The Ti‐O bond lengths of 1 are in the range 1.76(1) to 2.11(1) Å with the variation Ti‐OEt < Ti‐μ‐OEt < Ti‐η²‐O (allylacetatoacetate). All compounds were characterized by FT‐IR and ¹H NMR. The possibility to accede to more extended arrays either by hydrolysis or by radical initiated homo‐ or co‐polymerization reactions was investigated for the allylacetato derivatives as well as for Ti(OiPr)₂(AAEMA)₂ AAEMA = [2‐(methacryloyloxy)ethylacetoacetato] for the latter reactions.     

On the hydrolysis of the titanium(IV) ion in chloride media

Determinations of the [Ti(IV)]/[Ti(III) ratio in solutions of titanium(IV) chloride equilibrated with H₂(g), at 25°C in 3 M (Na)Cl ionic medium, have indicated the predominance of the Ti(OH)₂²⁺ species in the concentration ranges 0.5 ? [H⁺] ? 2 M and 1.5 x 10^?3 ? [Ti(IV)] ? 0.05 M. From the equilibrium data the reduction potential has been evaluated Ti(OH)₂²⁺ + 2 H⁺ + e ? Ti³⁺ + 2H₂O, E_oH = (7.7 ± 0.6) x 10^?3 V. The acidification reactions of Ti(OH)₂²⁺ were also studied in 12 M(Li)Cl medium at 25°C by measuring the redox potential of the Ti(IV)/Ti(III) couple as a function of [H⁺]. The potentiometric data in the acidity range 0.3 ? [H⁺] ? 12 M have been explained by assuming Ti⁴⁺ + e ? Ti³⁺, E_o = 0.202 ± 0.002 V Ti⁴⁺ + H₂O ? TiOH³⁺ + H⁺, log K_a1 = 0.3 ± 0.01 Ti⁴⁺ + 2H₂O ? Ti(OH)₂²⁺ + 2H⁺, log K_a1K_a2 = 1.38 ± 0.05.     

Direct Observation of the Binding Mode of the Phosphonate Anchor to Nanosized Polyoxotitanate Clusters

The structures of three newly synthesized phosphonate‐substituted polyoxotitanates are reported. The Ti/O core of [Ti₄O(OEt)₁₂(PhenylPO₃)] ( 1 ) is the building block for two larger phosphonate‐substituted nanoclusters, [Ti₂₅O₂₆(OEt)₃₆(PhenylPO₃)₆] ( 2 ) and [Ti₂₆O₂₆(OEt)₃₉(PhenylPO₃)₆]Br ( 3 ). All compounds exhibit a not previously recognized triply bridging binding mode of the phosphonate anchor with short connecting Ti? O bonds, the average of which is 2.010(7) Å. Comparison with previously reported work suggests that the binding mode of the phosphonate anchor is strongly dependent on the structure of the underlying substrate.     

Striking Size and Doping Effects of Ti−Si−O Clusters on Methane Conversion Reactions

The size and doping effects in methane activation by Ti−Si−O clusters have been explored by using a combination of gas-phase experiments and quantum chemical calculations. All [Ti_mSi_nO_2(m+n)]^.+ (m+n=2, 3, 8, 10, 12, 14) clusters can extract a hydrogen from methane. The associated energies and structures have been revealed in detail. Moreover, the doping and size effects have been discussed involving generalized Kohn-Sham energy decomposition analysis, natural population analysis, Wiberg bond indexes (WBI), molecular polarity index (MPI) and ionization potential (IP). It suggested that Ti−Si−O clusters with a low Ti : Si ratio is beneficial to adsorbing methane and inclination to the hydrogen atom transfer (HAT) process, while the clusters with a high Ti : Si ratio favors the generation of a terminal oxygen radical and results in high reactivity and turnover frequency. On the other hand, a cluster size of m+n=12 is recommended considering both the ionization potential and the turnover frequency of the reaction. Hopefully, these finding will be instructive for the design of high-performance Ti−Si−O catalyst toward methane conversion.     

Cubic Siloxanes with Both Si−H and Si−OtBu Groups for Site‐Selective Siloxane Bond Formation

Cage‐type siloxanes have attracted increasing attention as building blocks for silica‐based nanomaterials as their corners can be modified with various functional groups. Cubic octasiloxanes incorporating both Si?H and Si?OtBu groups [(tBuO)_nH_8?nSi₈O₁₂; n=1, 2 or 7] have been synthesized by the reaction of octa(hydridosilsesquioxane) (H₈Si₈O₁₂) and tert‐butyl alcohol in the presence of a Et₂NOH catalyst. The Si?H and Si?OtBu groups are useful for site‐selective formation of Si?O?Si linkages without cage structure deterioration. The Si?H group can be selectively hydrolyzed to form a Si?OH group in the presence of Et₂NOH, enabling the formation of the monosilanol compound (tBuO)₇(HO)Si₈O₁₂. The Si?OH group can be used for either intermolecular condensation to form a dimeric cage compound or silylation to introduce new reaction sites. Additionally, the alkoxy groups of (tBuO)₇HSi₈O₁₂ can be treated with organochlorosilanes in the presence of a BiCl₃ catalyst to form Si?O?Si linkages, while the Si?H group remains intact. These results indicate that such bifunctional cage siloxanes allow for stepwise Si?O?Si bond formation to design new siloxane‐based nanomaterials.     

Einige Komplexcarbide und-nitride in den Systemen Ti-{Zn,Cd, Hg}-{C,N} und Cr-Ga-N

Zusammenfassung Die Phasen Ti₃(Ti, Zn)C, Ti₃(Ti, Zn)N, Ti₃(Ti, Cd)C, Ti₃(Ti, Cd)N, Ti₃(Ti, Hg)C, Ti₃(Ti, Hg)N besitzen Perowskitstruktur. Cr₂GaN ist eine H-Phase (Ti₂SC-Typ).

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Some complex carbides and nitrides in the systems Ti-{Zn, Cd, Hg}-{C, N} and Cr-Ga-N

The phases Ti₃(Ti, Zn)C, Ti₃(Ti, Zn)N, Ti₃(Ti, Cd)C, Ti₃(Ti, Cd)N, Ti₃(Ti, Hg)C, Ti₃(Ti, Hg)N have the perowskite structure. Cr₂GaN is a H-phase (Ti₂SC-type).

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Mit 1 Abbildung     

Hydrogen Generation by Water Reduction with [Cp*2Ti(OTf)]: Identifying Elemental Mechanistic Steps by Combined In Situ FTIR and In Situ EPR Spectroscopy Supported by DFT Calculations

A detailed mechanism of hydrogen production by reduction of water with decamethyltitanocene triflate [Cp*₂Ti^III(OTf)] has been derived for the first time, based on a comprehensive in situ spectroscopic study including EPR and ATR‐FTIR spectroscopy supported by DFT calculations. It is demonstrated that two H₂O molecules coordinate to [Cp*₂Ti^III(OTf)] subsequently forming [Cp₂*Ti^III(H₂O)(OTf)] and [Cp*Ti^III(H₂O)₂(OTf)]. Triflate stabilizes the water ligands by hydrogen bonding. Liberation of hydrogen proceeds only from the diaqua complex [Cp*Ti^III(H₂O)₂(OTf)] and involves, most probably, abstraction and recombination of two H atoms from two molecules of [Cp*Ti^III(H₂O)₂(OTf)] in close vicinity, which is driven by the formation of a strong covalent Ti? OH bond in the resulting final product [Cp*₂Ti^IV(OTf)(OH)].     

Ce2Ti2SiO9 – das erste Titanat‐Silicat mit Cer – Präparation,Charakterisierung und Struktur

Ce₂Ti₂SiO₉ – the First Titanate‐Silicate with Cerium – Preparation, Characterization, and Structure Ce₂Ti₂SiO₉ was synthesized by chemical vapour transport in a temperature gradient (1050 °C → 900 °C) using Ce₂Ti₂O₇ as precursor and ammoniumchloride as transport agent. SiO₂ was provided from the wall of the used silica tubes. The chemical composition of the crystals was determined by EDX and EELS analysis. The structure of Ce₂Ti₂SiO₉ was determined and refined to R1 = 0.025, _wR2 = 0.067, respectively. The monoclinic phase crystallizes in the space group C2/m (No. 12) with a = 16.907(3) Å, b = 5.7078(8) Å, c = 7.574(2) Å, β = 111.38(2)° and Z = 4. Ti is octahedral, Si is tetrahedral surrounded by oxygen. Ce(1) is coordinated by eight, Ce(2) by ten oxygen atoms. There are edge connected chains of Ti(1)–O‐octahedra parallel [010] which are connected along [001] with each other by Ti(2)–O‐octahedra‐pairs and Si–O‐tetrahedra.     

Phosphaniminato-Komplexe des Titans. Synthese und Kristallstrukturen von CpTiCl2(NPMe3), [TiCl3(NPMe3)]2, [Ti2Cl5(NPMe2Ph)3] und [Ti3Cl6(NPMe3)5][BPh4]

Phosphoraneiminato Complexes of Titanium. Synthesis and Crystal Structures of CpTiCl₂(NPMe₃), [TiCl₃(NPMe₃)]₂, [Ti₂Cl₅(NPMe₂Ph)₃], and [Ti₃Cl₆(NPMe₃)₅][BPh₄] The title compounds are formed from Cp₂TiCl₂ and titanium tetrachloride, respectively, and the corresponding phosphane imino compounds Me₃SiNPMe₃ and Me₃SiNPMe₂Ph. The tetraphenyl borate salt yielded from the reaction of [Ti₃Cl₆(NPMe₃)₅]Cl with NaBPh₄. All compounds form yellow crystals which are sensitive to moisture. They were characterized by IR-spectroscopy and crystal structure analyses. CpTiCl₂(NPMe₃) ( 1 ): Space group Pbca, Z = 8, solution of the structure with 1632 observed independent reflections, R = 0.037. Lattice dimensions at 19°C: a = 1202.6, b = 1224.2, c = 1766.7 pm. The molecules of the compound are monomeric with the (NPMe₃)^? ligand in almost linear array (bond angle Ti? N? P 170.7°). [TiCl₃(NPMe₃)]₂ ( 2 ): Space group Pbca, Z = 8, structure solution with 698 observed independent reflections, R = 0.030. Lattice dimensions at ?60°C: a = 1140.5, b = 1112.2, c = 1589.4 pm. In 2 the titanium atoms, which occur in trigonal bipyramidal coordination, are linked by the N atoms of the (NPMe₃)^? groups to form a centrosymmetric dimer with Ti? N bond lengths of 184.3 and 208.2 pm. [Ti₂Cl₅(NPMe₂Ph)₃] · CH₂Cl₂ ( 3 ): Space group Pca2₁, Z = 4, structure solution with 8477 observed independent reflections, R = 0.051. The lattice dimensions at 20°C are: a = 1221.0; b = 1407.5, c = 2139.3 pm. 3 can be understood as a reaction product of TiCl₂(NPMe₂Ph)₂ and TiCl₃(NPMe₂Ph). In the resulting, heavily distorted Ti₂N₂-four-membered ring the Ti? N bond lenghts are 1804., 194.4, 199.2, and 234.6 pm. The longest Ti? N bond is in trans-position to the N atom of the terminal (NPMe₂Ph)- ligand, in which the Ti? N distance is 175.6 pm. .[Ti₃CL₆(NPMe₃)₅][BPh₄] (4): Space group P2₁/n, structure solution with 2846 observed independent reflections, R = 0.062. The lattice dimensions at 20°C are: a = 1495.2, b = 2335.4, c = 155,8 pm, β = 93.28°. In the cation of 4 the three titanium atoms along with three (NPMe₃)- groups with μ2- N functions and two (NPMe₃)- groups with μ3- N functions form a nation number 6 with two terminal chlorine atoms.     

Formation d'Oxocomplexes du Titane(IV) à Partir de Derives “Alkoxo”

Oxotitanium Complexes Formation from Alkoxo Derivates Five oxotitanium(IV) complexes with the NCS ligand = {Ti₃O₄(NCS)₄(AA)₃}, {Ti₂O(NCS)₂(BB)₄} et M₂[TiO(NCS)₄}] (AA = phen, bpy; BB = acac, dbm) have been prepared and characterized in the solid state on the basis of their analytical and infrared spectral data. In all the compounds, the Ti? O stretching frequency lies at 770–630 cm^?1, which is suggestive of oxygen bridges.     

Synthese und Kristallstruktur von Ti12Sn3O10 – einem niedervalenten Oxid des Titans mit oxidischem Gerüst und intermetallischen „Inseln”︁

Synthesis and Crystal Structure of Ti₁₂Sn₃O₁₀ – a Low Valent Oxide of Titanium with an Oxidic Network and Intermetallic ”︁Islands”︁”︁ The new ternary compound Ti₁₂Sn₃O₁₀ is obtained by the reaction of Ti, TiO₂ and Sn at 1500 °C. According to the single crystal structure analysis (cubic, space group Fm3m, a = 13.5652(9) Å, Z = 8, wR₂(I) = 0.048, R₁(F) = 0.020) the air stable compound represents a new structure type combining structural features of oxides and intermetallics. While tin is surrounded only by titanium the five different Ti atoms have oxidic and metallic coordination spheres as well, explaining the quite low averaged oxidation number. The crystal structure is characterized by a threedimensional net of Ti₄O‐tetrahedra and trigonal bipyramides Ti₅O. In the voids there are intermetallic ”︁islands”︁”︁ of a composition Ti₃₃Sn₆ with a diameter of about 10 Å.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXI. Zum Verständnis des chemischen Transports von Ti4O7, Ti5O9 und Ti6O11 in Gegenwart der Transportmittel HgCl2 und TeCl4

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXI. On the Understanding of the Chemical Transport of Ti₄O₇, Ti₅O₉, and Ti₆O₁₁ in the Presence of the Transporting Agents HgCl₂ and TeCl₄ Transport experiments starting with a phase Ti_nO_2n?1 (e.g. Ti₄O₇) and with HgCl₂ as transporting agent show, that in a temperature gradient at the lower temperature T₁ the neighbour phase with a higher oxygen content Ti_n+1O_2n+1 (e.g. Ti₅O₉) is deposited. As we know from previous investigations, results of experiments with TeCl₄ as transporting agent are comparable. Now on the basis of thermodynamical calculations it could be proved that in dry systems Ti/O/HgCl₂ and Ti/O/TeCl₄ (O/Ti < 2,0) a measurable transport of a TiO_x phase resulting in the deposition of a higher phase cannot take place. Observed and calculated results agree, if small amounts of H₂O are present resulting in the formation of HCl from HgCl₂ or TeCl₄ added as transporting agent. The refinement of the model now makes it possible to calculate the composition of the compound deposited at the temperature T₁ also in systems with numerous closely neighbouring phases and for given experimental conditions.