Anhydrous

About: Anhydrous is a research topic. Over the lifetime, 17632 publications have been published within this topic receiving 163495 citations.

Gaseous process and apparatus for removing films from substrates

Abstract: A process for removing at least a portion of a film from a substrate, such as a wafer of silicon or other similar materials, the film on the substrate typically being an oxide film, maintaining the atmosphere embracing the substrate at near room temperature and at near normal atmospheric pressure, flowing dry inert diluent gas over the substrate, introducing a flow of reactive gas, preferably an anhydrous hydrogen halide gas, namely anhydrous hydrogen flouride gas, for typically 5 to 30 seconds over the substrate and film to cause the removal of portions of the film, flowing water vapor laden inert gas, preferably nitrogen, over the substrate and film from a time prior to commencing flow of the reactive gas until flow of the reactive gas is terminated. In the case of non-hygroscopic film on the substrate, the flow of water vapor continues during the flow of the reactive gas and is terminated shortly after the termination of the flow of reactive gas. In the case of hygroscopic film, the flow of water vapor is discontinued prior to the start of flow of the reactive gas. In carrying out the process, a process chamber is needed to confine the substrate and have a vent, which though restricted, continuously open to the atmosphere.

Ascent-driven crystallisation of dacite magmas at Mount St Helens, 1980–1986

Abstract: We introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system Qz–Ab–Or–H2O in order to relate variations in volcanic glass chemistry to changing pressure (P) and temperature (T) conditions in the sub-volcanic magma system. By this means an important distinction can be made between ascent-driven and cooling-driven crystallisation under water-saturated or undersaturated conditions. In samples containing feldspar and a silica phase (quartz or tridymite), quantitative P–T estimates of the conditions of last equilibrium between crystals and melt can be made. Formation of highly silicic melts (i.e. >77 wt% SiO2) is a simple consequence of the contraction of the silica phase volume with decreasing pressure, such that high silica glasses can only form by crystallisation at low pressure. Resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation. Groundmass and inclusion glasses in dacites from the 1980–1986 eruption of Mount St Helens volcano (WA) span a wide range in SiO2 (68–80 wt%, anhydrous). The compositions of the least evolved (SiO2-poor) inclusions in amphibole phenocrysts record entrapment of silicic liquids with ≤5.4 wt% water, corresponding to a water saturation pressure of ~200 MPa at 900 °C. The compositions of more evolved (higher SiO2) plagioclase-hosted inclusions and groundmass glasses are consistent with extensive ascent-driven fractional crystallisation of plagioclase, oxide and orthopyroxene phenocrysts and microlites to low pressures. During this polybaric crystallisation, plagioclase phenocrysts trapped melts with a wide range of dissolved water contents (3.5–5.7 wt%). Magmas erupted during the Plinian phase of the 18 May 1980 eruption were derived from a large reservoir at depths of ≥6 km. Subsequent magmas ascended to varying depths within the sub-volcanic system prior to extraction. From glass chemistry and groundmass texture two arrest levels have been identified, at depths of 0.5–1 and 2–4 km. A single dome sample from February 1983 contains groundmass plagioclase, tridymite and quartz, testifying to temperatures of at least 885 °C at 11 MPa. These shallow storage conditions are comparable to those in the cryptodome formed during spring 1980. The corresponding thermal gradient, ≤0.2 °C MPa–1, is consistent with near-adiabatic magma ascent from ~8 km. We argue that the crystallisation history of Mount St Helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation. This challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980–1986 eruption. Because the crystallisation process is both polybaric and fractional, it cannot be simulated directly using isobaric equilibrium crystallisation experiments. However, calculation of the phase proportions in water-saturated 910±15 °C experiments by Rutherford et al. (1985) over the pressure range 220–125 MPa reproduces the crystallisation sequence and phenocryst modes of Mount St Helens dacites from 18 May 1980. By allowing for the effects of fractional versus equilibrium crystallisation, entrained residual source material, and small temperature differences between nature and experiment, phase compositions can also be matched to the natural samples. We conclude that decompression of water-saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres.

Crystalline zeolite and method of preparing same

Abstract: A new crystalline zeolite, designated ZSM-35, a method of making same and the use thereof in catalytic conversion of hydrocarbons is the subject of this application. The new zeolite has a composition, in the anhydrous state, expressed in terms of mole ratios of oxides as follows: (0.3-2.5)R.sub.2 O:(0-0.8)M.sub.2 O:Al.sub.2 O.sub.3 :>8 SiO.sub.2 wherein R is an organic nitrogen-containing cation and M is an alkali metal cation, and is characterized by a specified X-ray powder diffraction pattern.