Silica for sealing

Gd-Pt-Al compounds have been prepared by reacting Gd and Pt in the proper atomic ratio with a 10 fold excess of Al (Lattumer and Kanatzidis 2002). The mixture, placed in a silica tube sealed under vacuum was slowly heated to 1000°C, held at this temperature for several hours and slowly (over a few days) cooled to room temperature. The aluminium flux was removed by soaking the crucible in 5 M NaOH for 1 day. Gdi 33Pt3Al8, Gdo.67Pt2Al5 (and also compounds with Si) have been prepared the main product, however, in all the syntheses was GdAl3. 

Various concentrations (10.00 mL) of Cu2+ or Pb2+ solutions were exposed to 0.0250 g of silica in sealed conical flasks for 16 hours in a wrist action shaker. The slurries were centrifuged, solution aliquots then obtained and analyzed by atomic absorption (AA, Perkin-Elmer 2380). The extent of metal ion adsorption on silica was obtained by subtracting the amount of metal ion present in solution after adsorption from the amount of metal ion in the original solution. 

Metallic lead is used for sealing vacuum-tight quartz glass apparatus, such as cathode-ray tubes and mercury lamps.2 The method is stated to yield highly satisfactory results, and is adopted by the Silica Syndicate in the preparation of scientific apparatus. 

A mixture of pentakis(pentafluoroethyl)pyridine (669 mg, 1 mmol) and perfluoropentane (1 g) in a silica tube sealed under vacuum was irradiated (> 220 nm, Pyrex filter) for 250 h. Fractionation of the products gave 20 mg (3%) of unchanged pyridine and the product as a colorless liquid yield 632 mg (95%) bp 176 °C. 

In spite of some of the disadvantages of silica gel, it is a very useful sorbent. Most of the early work with silica gel use a single U-tube or a train of two or more U-tubes. The U-tubes held at least 10 g of silica gel and sometimes one arm of the tube held a desiccant to reduce humidity effects The commercial tubes now available contain 150 mg to 1.5 g of silica gel sealed in glass tubes. Silica 1 has been used for a wide range of organic solvents halogenated hydrocarbons and nitrogen dioxide Often chemicals collected on silica gel require analysis by HPLC or derivatization prior to analysis. 

Since production of metals by this technique is carried out on a small scale, much of the equipment has been of a laboratory type. The reaction vessels are often made of glass or silica for example, as shown in Fig. 8.1. A reactor contains two electrodes passing through suitable seals and connected to the ends of a loop of wire forming the filament. A side-arm connects to a... 

The crystal structure of the PrRuGe compound was investigated by Welter et al. (1993b). It was found to adopt the PbFCl type, a = 4268, c = 0.6842 (X-ray powder diffraction). The compound was prepared from commercially available high-purity elements. A compacted stoichiometric mixture in a silica tube sealed under argon was heated to 1173K for preliminary homogenization and then melted in an induction furnace. 

Ge-Se glasses were synthesized by introducing the appropriate quantities of germanium (Ge) and selenium (Se) in silica ampoules sealed under vacuum, by further heating this mixture at high temperature, typically between 750 and 950°C, and by subsequent quenching (see ref. 11 for details). The physical and mechanical properties of the studied glasses are reported in Table 2. 

Degussa Corporation, 1979, Synthetic Silicas for Joint Sealing Compounds, Brochure... 

Nano-CaCOs can be used as reinforcing fillers in rubbers as a partial replacement for carbon black or silica. It has been used together with carbon black or other ceramic fillers, such as Ti02 and MgC03 for seals, oil-resistant rubber pipes, shoe components, bicycle tires, car tires, etc. It is particularly suitable for use in light-colored rubber products. 

LiNbOj is prepared by the reaction of LijNb04 and NbO at 1050° as in Kumada et al. Unless otherwise specified, the reactants are heated to the reaction temperature in 1-2 h. The lithium niobium(V) oxide, Li3Nb04, is made as a white powder by heating a 3 1 molar ratio of Li2C03 (6.236 g, 84.41 mmol, Cerac, 99.8%) and Nb205 (7.478 g, 28.13 mmol, Cerac, 99.95%) in an alumina crucible at 900° for 3 days. Niobium monoxide, NbO, is obtained by heating a 3 1 molar ratio of Nb powder (5.118 g, 55.09 mmol, Cerac, 99.8%) and NbjO, (4.882 g, 18.37 mmol) in a fused-silica tube, sealed under vacuum, at 1100° for 3 days. 

Bromo-3-iodo-l-(4-methylphenylsulfonyl)indole (0.476 g, 1.00 mmol), methyl acrylate (0.108 g, 1.25 mmol), EtjN (0.127 g, 1.25 mmol) and Pd(OAc)2 (11 mg, 0.050 mmol) were mixed in a tube, purged with argon and the tube was sealed and heated to 100°C for 1 h. After cooling, it was opened and mixed with CH2CI2 (50 ml). The solution was washed with water and dried (Na SOJ. The residue was purified by chromatography on silica using 1 3 benzene-hexane for elution. The yield was 0.350 g (81%). 

A mixture of 4-bromo-l-(4-methylphenylsulfonyl)indole (88 mg, 0.25 mmol), methyl a-acetamidoacrylate (91 mg, 0.64 mmol), PdCl2(PPh3)2 (16 mg, 0.023 mmol) and NaOAc (82 mg, 0.98 mmol) in EtjN (0.8 ml) and DMF (0.4 ml) was heated to 120°C in a sealed tube for 2 h. The tube was opened and the contents diluted with EtOAc and filtered through Celite. The EtOAc was washed successively with 10% HCl, sat. NaHC03 and brine and then dried (MgS04). The residue was purified by elution through silica gel with 10 1 benzene-EtOAc to give the product as a yellow solid (93 mg, 90%). 

A solution of l-methylpyrano[4,3-b]indol-3-one (1 mmol) and methyl vinyl ketone (5 ml) in toluene (5 ml) containing 5% Pd/C (40 mg) was heated for 48 h in a sealed tube at 110°C. The reaction mixture was evaporated in vacuo and the residue purified by silica gel chromatography to give the product in 80% yield. 

A solution of 3-oxatetracyclo[3.2.0.02 7.04 f,]heptane (941 mg, 10 mmol) in anhyd benzene (10 mL), that had been treated with basic alumina prior to the experiment, was heated in a sealed tube for 4 h at 100 C. After cooling, Et2G (10 mL) was added. The mixture was chromatographed (silica gel, 30 g, Et20/pentane 7 3) to yield benzene as the first fraction and 900 mg (95%) of product. After careful evaporation of the Et20/pentane mixture, the product was purified by distillation to give a light yellow oil. 

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