Gelation of n3p3[nh(ch2)3si(oet)3]6-n [x]n x = nh(ch2)3si(oet)3, nch3(ch2)3cn and oc6h4(ch2)cn, n = 0 or 3 at the liquid/air/interface

Indexación: ScieloThe compounds N3P3[NH(CH2)3Si(OEt)3]6 (1), N3P3[NH(CH2)3Si(OEt)3]3[NCH3(CH2)3CN]3 (2) and N3P3[NH(CH2)3Si(OEt)3]3 [HOC6H4(CH2)CN]3 (3) undergo slow gelation at the interface oil/air at low temperatures to give perfect gels G1, G2 and G3 respective ly. TEM analysis reveals nanoparticles of silica with mean size of about 10 nm. Pyrolysis under air at 800 °C of these gels affords a mixture of mainly Si5(PO4)6O, SiP2O7 and SiO2. Gelation and pyrolysis products were characterized by IR, solid-state NMR, TEM, SEM-EDAX microscopy and X-ray diffraction. The sol-gel process in the interface liquid /air is discussed in comparison with the usual sol-gel solution process.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072010000300031&nrm=is

Tris(trimethylsilyl)silyl stabilized phosphorus and lead clusters

Die Hypersilylgruppe (Me3Si)3Si stellt einen sehr sperrigen, Elektronen liefernden Substituenten dar und kann zur Stabilisierung niedriger Oxidationsstufen sowie ungewöhnlicher Strukturelemente dienen. Durch Reaktionen der base-freien Hypersilanide der Alkalimetalle sowie des Dihypersilylplumbandiyls mit unterschiedlichsten phosphorhaltigen Reagenzien konnten eine Reihe hypersilyl-stabilisierter Phosphor- und Bleicluster-Verbindungen erhalten werden. Kaliumhypersilanid reagiert in Toluol glatt mit weißem Phosphor bei Raumtemperatur in Toluol unter quantitativer Bildung von rotem Kalium-bis(hypersilyl)tetraphosphenid [(Me3Si)3Si]2P4K2 (1), einem Kaliumsalz des Tetraphosphens (Me3Si)3Si-PH-P=P-PH-Si(SiMe3)3. In Benzol oder Toluol steht 1 im Gleichgewicht mit dem dimeren Octaphosphanid [(Me3Si)3Si]4P8K4 (2). Bei längerem Stehen der toluolischen Lösungen zerfällt 1 langsam vermutlich in Folge einer Protolyse zum gelben Pentaphosphanid [(Me3Si)3Si]3P5K2 (4). Aus benzolischer Lösung konnte hingegen ein weiteres Oktaphosphanid, [(Me3Si)3Si]3P8K3 (5), isoliert werden. Führt man die Reaktion Kaliumhypersilanid mit P4 in stärker koordinierenden Lösungsmitteln wie Diethylether durch, so entstehen neben 1 größere Mengen des Triphosphenids [(Me3Si)3Si]2P3K (3); dieses enthält ein Triphosphaallyl-Anion mit partieller P-P-Doppelbindung. Setzt man Lithiumhypersilanid mit weißem Phosphor um, so beobachtet man eine vollständig andere Produktpallette. Als Hauptprodukte lassen Polyphosphane wie beispielsweise [(Me3Si)3Si]2P4 (6) nachweisen, das zu 1 analoge [(Me3Si)3Si]2P4Li2 (7) entsteht nur in vergleichsweise kleinen Mengen. In der Gegenwart von Hexahydro-1,3,5-trimethyl-S-triazin, entsteht aus Lithiumhypersilanid und P4 hingegen im wesentlichen [(Me3Si)3Si]2P3Li (8) neben beträchtlichen Mengen von (Me3Si)4Si. Dessen Bildung erfordert eine Si-Si-Bindungsspaltung im Verlauf der Reaktion. Die Reaktion von Natriumhypersilanid mit P4 verläuft sehr unübersichtlich, das Pentaphosphanid [(Me3Si)3Si]3P5Na2 (9) ist das einzige isolierbare Produkt. Setzt man 1 mit [(Me3Si)2Si]2Sn um, so bilden sich überraschenderweise, je nach verwendetem Solvens [(Me3Si)3Si]3P4SnK (10) oder [(Me3Si)3Si]2[(Me3Si)2N]P4SnK (11). Alle neuen Verbindungen wurden NMR-spektroskopisch charakterisiert, die Phosphenide 1, 7, 8 sowie die Phosphanide 2, 4, 5, 9, 10 darüber hinaus durch Kristallstrukturanalysen. Dihypersilylplumbandiyl und -stannandiyl reagieren bei tiefer Temperatur mit P4, MPH2 (M=Li, K), PMe3, and PH3 zu formalen Lewis-Säure-Base-Addukten. Die Addukte {[(Me3Si)3Si]2PbPH2}M [M = Li (15), K (18)], {{[(Me3Si)3Si]2Pb}2PH2}M [M = Li (19), K (20)], und [(Me3Si)3Si]2EPMe3 [E = Pb (21), Sn (22)] wurden als kristalline Feststoffe erhalten und konnten vollständig charakterisiert werden. Die metastabilen Addukte {[(Me3Si)3Si]2E}4P4 (E = Pb, Sn) und [(Me3Si)3Si]2PbPH3 konnten lediglich NMR-spektroskopisch nachgewiesen werden. Bei Raumtemperatur entstehen in Folge von Ligandenaustausch-Prozessen die kristallographisch charakterisierten Heterokubane [(Me3Si)3Si]4P4E4 [E = Pb (12), Sn (14)], das Diphosphen (Me3Si)3SiP=PSi(SiMe3)3 (13) sowie der Pb2P2-Heterocyclus [(Me3Si)3SiPbP(H)Si(SiMe3)3]2 (17). Bei tiefer Temperatur wird aus einer sehr langsamen Reaktion von Dihypersilylplumbandiyl und PH3 in sehr kleinen Ausbeuten ein weiteres, völlig unerwartetes Produkt gebildet: der Bleicluster [(Me3Si)3Si]6Pb12 (23). Er weist ein verzerrt ikosaedrisches, zentrosymmetrisches Pb12-Gerüst auf. Nach jetzigen Erkenntnissen läuft seine Bildung über das nicht fassbare Hydridoplumbandiyl HPbSi(SiMe3)3, das intermediär durch Substituentenaustausch zwischen Pb[Si(SiMe3)3]2 and PH3 entsteht. Der Ersatz des Phosphans durch andere Hydridquellen wie (Ph3PCuH)6, (iBu)2AlH, and Me3NAlH3 führt ebenfalls zur Bildung von Bleiclustern, allerdings ist jetzt der Cluster [(Me3Si)3Si]6Pb10 (24) das Hauptprodukt. Beide Cluster, 23 und 24, gehorchen den Wade-Regeln.Hypersilyl (Me3Si)3Si behaves as a very bulky, electron releasing substituent and can be utilized for stabilizing low oxidation states and unusual structural fragments. By reactions of base-free alkali metal hypersilanides and dihypersilyl plumbylene with various phosphorus containing reagents, a series of hypersilyl stabilized phosphorus and lead clusters have been obtained. Potassium hypersilanide readily reacts with white phosphorus in toluene at room temperature to yield red-violet potassium bis(hypersilyl)tetraphosphenide [(Me3Si)3Si]2P4K2 (1), a potassium salt of the tetraphosphene (Me3Si)3Si-PH-P=P-PH-Si(SiMe3)3, quantitatively. In toluene or benzene solution there exists an equilibrium between 1 and its dimer, octaphosphanide [(Me3Si)3Si]4P8K4 (2). In toluene 1 decomposes slowly through protolysis to give yellowish pentaphosphanide [(Me3Si)3Si]3P5K2 (4). In benzene, most probably also by partial protolysis of the dimer 2, another octaphosphanide [(Me3Si)3Si]3P8K3 (5) is obtained. By using coordinating solvents such as diethyl ether, the reaction of potassium hypersilanide with P4 yields 1 and blue triphosphenide [(Me3Si)3Si]2P3K (3), which comprises a triphosphaallyl anion with a partial P-P double-bond. Replacing potassium for lithium, i.e. reacting lithium hypersilanide with white phosphorus in toluene dramatically changes the type of products obtained. Several polyphosphanes such as [(Me3Si)3Si]2P4 (6) could be found in the resulting mixture and [(Me3Si)3Si]2P4Li2 (7) could be isolated only in low yield. In the presence of hexahydro-1,3,5-trimethyl-S-triazine, lithium hypersilanide reacts with P4 to give [(Me3Si)3Si]2P3Li (8) along with considerable amounts of (Me3Si)4Si, suggesting that cleavage of Si-Si bonds took place during the reaction process. The reaction of sodium hypersilanide with P4 gives no clean reaction and leads directly to the formation of [(Me3Si)3Si]3P5Na2 (9). The treatment of 1 with [(Me3Si)2Si]2Sn affords the unexpected compounds [(Me3Si)3Si]3P4SnK (10) and [(Me3Si)3Si]2[(Me3Si)2N]P4SnK (11), instead of [(Me3Si)3Si]2P4Sn, depending on the solvent used. All the new compounds are identified by NMR spectroscopy and the structures of the phosphenides 1, 7, 8, and the phosphanides 2, 4, 5, 9, 10 are established by X-ray diffraction studies. When dihypersilyl plumbylene or stannylene is allowed to react with P4, MPH2 (M=Li, K), PMe3, and PH3 at low temperature, the formal Lewis acid-base adducts are formed, respectively. The adducts {[(Me3Si)3Si]2PbPH2}M [M = Li (15), K (18)], {{[(Me3Si)3Si]2Pb}2PH2}M [M = Li (19), K (20)], and [(Me3Si)3Si]2EPMe3 [E = Pb (21), Sn (22)] are obtained as pure compounds and were characterized by NMR spectroscopy and X-ray diffraction studies. However, the metastable adducts {[(Me3Si)3Si]2E}4P4 (E = Pb, Sn) and [(Me3Si)3Si]2PbPH3 could only be detected by NMR spectroscopy at low temperature. They undergo ligand exchange at room temperature yielding [(Me3Si)3Si]4P4E4 [E = Pb (12), Sn (14)] along with (Me3Si)3SiP=PSi(SiMe3)3 (13) and [(Me3Si)3SiPbP(H)Si(SiMe3)3]2 (17), respectively. X-ray analyses reveal a heterocubane core for 12 and 14 a monocyclic Pb2P2 skeleton for the 17. Dihypersilyl plumbylene also reacts very slowly with PH3 at low temperature in pentane to give the totally unexpected lead cluster compound [(Me3Si)3Si]6Pb12 (23) in very low yields. It comprises a still centrosymmetric icosahedron Pb12 core. It is suggestive that the formation of the lead cluster proceeds via the elusive hydridoplumbylene HPbSi(SiMe3)3, which has been initially formed by ligand exchange between Pb[Si(SiMe3)3]2 and PH3. Replacing PH3 by other hydride sources, such as (Ph3PCuH)6, (iBu)2AlH, and Me3NAlH3, another molecular lead cluster, [(Me3Si)3Si]6Pb10 (24), is isolated as main product. Both molecular clusters, 23 and 24 match the predictions made by Wade’s rules

Sol-gel incorporation of organometallic compounds into silica: useful precursors to metallic nanostructured materials

Indexación: Web of Science; ScieloLa inclusión del MLN organometálica = HOC 6 H 4 CH 2 CN • Mo (CO) 5 (6) en sílice amorfa con los precursores TEOS gelificante y N 3 P 3 {NH [CH 2 ] 3 Si [OEt] 3 } 6 permitirse los geles (MLN) ( SiO 2 ) n . Los nanocompuestos híbridos inorgánicos-orgánicos se piroliza bajo aire a 800 º C para dar óxidos nanoestructurados metálicos y / o pirofosfatos de metal (fosfatos) incluidos en las matrices de sílice. La morfología de los nanocompuestos monolíticas exhiben una fuerte dependencia con el precursor del gel utilizado es principalmente laminar para aquellos preparados utilizando N 3 P 3 {NH [CH 2 ] 3 Si [OEt] 3 } como gelificante. Las imágenes de TEM muestran la forma y tamaño diferentes, tales como nanopartículas circulares, nanocables y aglomerados en algunos casos con tamaños de 20 nm para las nanoestructuras circulares y de diámetro aproximadamente 25 nm para los nanocables.Inclusion of the organometallic MLn = [HOC5H4N•Cp2TiCl][PF6] (1), HOC5H4N-W(CO)5 (2), HOC5H4N•Mo(CO)5 (3), [HOC6H4CH2CN•Cp2TiCl][PF6] (4), HOC6H4CH2CN•W(CO)5 (5) and HOC6H4CH2CN•Mo(CO)5 (6) into amorphous silica using the gelator precursor TEOS and N3P3{NH[CH2]3Si[OEt]3}6 afford the gels (MLn)(SiO2)n. The inorganic-organic hybrid nanocomposites were pyrolyzed under air at 800°C to give nanostructured metal oxides and/or metal pyrophosphates (phosphates) included in the silica matrices. The morphology of the monolithic nanocomposites exhibited a strong dependence on the gel precursor used being mainly laminar for those prepared using N3P3{NH[CH2]3Si[OEt]3} as gelator. TEM images show different shape and size such as circular nanoparticles, nanocables and agglomerates in some cases with sizes of 20 nm for the circular nanostructures, and diameter about 25 nm for the nanocables.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072012000200021&nrm=is

Microstructure and mechanical properties of ductile aluminium alloy manufactured by recycled materials

The present paper introduces the microstructure and mechanical properties of the Al-Mg- Si-Mn alloy made by recycled materials, in which the impurity levels of iron are mainly concerned. It is found that the increased Fe content reduces the ductility and yield strength but slightly increases the UTS of the diecast alloy. The tolerable Fe content is 0.45wt.%, at which the recycled alloys are still able to produce castings with the mechanical properties of yield strength over 140MPa, UTS over 280MPa and elongation over 15%.The Fe content is steadily accumulated in the alloy with the increase of recycle times. However, after 13 cycles, the recycled alloys are still able to produce ductile alloys with satisfied mechanical properties.The TSB (UK

Physical-mechanical characterization of biodegradable Mg-3Si-HA composites

Purpose Porous implant surface is shown to facilitate bone in-growth and cell attachment, improving overall osteointegration, while providing adequate mechanical integrity. Recently, biodegradable material possessing such superior properties has been the focus with an aim of revolutionizing implant's design, material and performance. This paper aims to present a comprehensive investigation into the design and development of low elastic modulus porous biodegradable Mg-3Si-5HA composite by mechanical alloying and spark plasma sintering (MA-SPS) technique. Design/methodology/approach This paper presents a comprehensive investigation into the design and development of low elastic modulus porous biodegradable Mg-3Si-5HA composite by MA-SPS technique. As the key alloying elements, HA powders with an appropriate proportion weight 5 and 10 are mixed with the base elemental magnesium (Mg) particles to form the composites of potentially variable porosity and mechanical property. The aim is to investigate the performance of the synthesized composites of Mg-3Si together with HA in terms of mechanical integrity hardness and Young's moduli corrosion resistance and in-vitro bioactivity. Findings Mechanical and surface characterization results indicate that alloying of Si leads to the formation of fine Mg2 Si eutectic dense structure, hence increasing hardness while reducing the ductility of the composite. On the other hand, the allying of HA in Mg-3Si matrix leads to the formation of structural porosity (5-13 per cent), thus resulting in low Young's moduli. It is hypothesized that biocompatible phases formed within the composite enhanced the corrosion performance and bio-mechanical integrity of the composite. The degradation rate of Mg-3Si composite was reduced from 2.05 mm/year to 1.19 mm/year by the alloying of HA elements. Moreover, the fabricated composites showed an excellent bioactivity and offered a channel/interface to MG-63 cells for attachment, proliferation and differentiation. Originality/value Overall, the findings suggest that the Mg-3Si-HA composite fabricated by MA and plasma sintering may be considered as a potential biodegradable material for orthopedic application

Kinetics of silicide formation by thin films of V on Si and SiO_2 substrates

The reaction rate of vacuum‐evaporated films of V of the order of 1000 Å thick is investigated by MeV He backscattering spectrometry. On substrates of single‐crystal Si and for anneal times up to several hours in the temperature range 570–650°C, VSi_2 is formed at a linear rate in time. The activation energy of the process is 1.7±0.2 eV. The presence of oxygen in amounts of 10% can significantly decelerate the reaction. On substrates of SiO_2 in the temperature range 730–820°C and anneal times of several hours or less, V_3Si is formed at a square‐root rate in time. The activation energy of this process is 2.0±0.2 eV

The Traveling Salesman Problem: Low-Dimensionality Implies a Polynomial Time Approximation Scheme

The Traveling Salesman Problem (TSP) is among the most famous NP-hard optimization problems. We design for this problem a randomized polynomial-time algorithm that computes a (1+eps)-approximation to the optimal tour, for any fixed eps>0, in TSP instances that form an arbitrary metric space with bounded intrinsic dimension. The celebrated results of Arora (A-98) and Mitchell (M-99) prove that the above result holds in the special case of TSP in a fixed-dimensional Euclidean space. Thus, our algorithm demonstrates that the algorithmic tractability of metric TSP depends on the dimensionality of the space and not on its specific geometry. This result resolves a problem that has been open since the quasi-polynomial time algorithm of Talwar (T-04)

Development of ductile cladding for TD-nickel turbine vane applications Final report, 5 Jul. 1967 - 31 Dec. 1968

Slurry technique for applying NI-CR-AL-SI coatings to TD-N