Evaporation Of Silica Research Articles

Rigorous silica solubility estimation in superheated steam: Smart modeling and comparative study

One of the main issues of wastewater treatment is the silica deposition in steam turbines. Evaporation of silica with the steam in adequate concentration is one of the main sources of scale formation in steam turbines. In this study, the authors introduce the utilization of a genetic‐based approach—gene expression programming (GEP)—for solubility prognostication of the silica in superheated steam of boilers with respect to water silica content and pressure. The result of GEP mathematical approach is a new algebraic formula to achieve our goals. Developed model predicts the silica solubility in the range of 0.8–22.1 MPa and 1–500 mg/kg for pressure and boiler water silica content, respectively. The results show that the constructed model outperforms pre‐existing method and provides acceptable predictions with average absolute relative deviation (AARD%) of 9.46% and determination coefficient (R2) of 0.98. Outcomes of the performed sensitivity analysis reveal that the effect of pressure is more pronounced than the impact of the boiler water silica content on the estimation of the silica solubility. Moreover, an outlier analysis based on Leverage approach was performed confirming the validity of the used database in this study. Finally, it can be concluded that the recommended tool in this study can be a suitable candidate for prognosticating the silica scaling in industries dealing with steam. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13089, 2019

Vacuum arc on the polycrystalline silica cathode

Thin films of silica and its compounds are used in modern technology to produce Li-ion batteries, wear-resistant and protective coatings, thin-films insulators, etc. This coating is produced with CVD methods, with magnetron sputtering systems or with electron-beam evaporation. The vacuum arc evaporation method, presently, is not used. The paper demonstrates a possibility for a long-term operation of vacuum arc evaporator with polycrystalline silica-aluminum alloy (90% of silica) cathode and with magnetic system to create a variable form of arch-like magnetic field on the cathode surface. It was shown that archlike configuration of magnetic field provides a stable discharge and uniform cathode spots moving with the velocities up to 5 m/s with magnetic fields induction about 10 mT. Thus, there is no local melting of the cathode, and this provides its long-term work without chips, cracks and destruction. Cathodes spots move over the cathode surface leaving t big craters with melted edges on its surface. The craters size was 150-450μm. The cathode spot movement character and the craters on the cathode surface were like the spots movement, when working on the copper or aluminum cathodes. With the magnetic field induction less than 1 mT, the cathode spots movement was the same as that of on the silica mono-crystal without magnetic field. Thus, the discharge volt-ampere characteristics for different values of magnetic fields were obtained. Voltampere characteristics were increasing and were shifted to the higher voltage with increasing magnetic field. The voltage was 18.7-26.5 V for the arc current 30-140 A. So, it was confirmed that vacuum arc evaporation method could be used for effective evaporation of silica and silica-based alloys and for thin films deposition of this materials.

Facile formation of nanoparticle patterns by water induced flow of a polymer thin film

In general, techniques of particle arrays on polyelectrolyte multilayers involve complex and inefficient steps. Here, we present a simple yet robust method for fabricating ordered two-dimensional nanoparticle arrays on polyelectrolyte multilayers via water induced flow of multilayer films. The process is easy and repeatable without the requirement of complicated surface preparation or chemical modification. By droplet evaporation of silica or other functional nanoparticle solutions on a patterned PDMS stamp, nanoparticle arrays on polyelectrolyte multilayer film surfaces will occur when the PDMS stamp contacts with polyelectrolyte multilayers. This work provides a facile and efficient approach to fabricate colloidal nanoparticle or other functional nanoparticle arrays on polyelectrolyte multilayers which are potentially useful for sensor materials, biomaterials and so on.

A new method to investigate the intense pulsed ion beam ablation of silica

Based on the energy conservation law and the Fourier law, a concise method is employed to build 2-dimensional difference heat conduction equations with appropriate boundary conditions. This method is useful in heat conduction simulation. A formula of the evaporation yield is derived to investigate the ability of every incident ion to evaporate silica through the heat effect. Then, using an argon ion beam as an example, the temperature and evaporation yield evolution of silica is simulated using the new heat conduction model and the evaporation yield formula. Under the calculated conditions of this work, when the evaporation of silica occurs, the evaporation yield increases continuously because the number of incident ions per second during one pulse decreases. At a given time, the evaporation yield decreases with the incident ion beam density because the increase of the number of evaporated silica molecules lags behind the increase of the incident ion number. The calculated results also show that the evaporation yield increases with incident ion beam diameter for a given time and ion beam density. In addition, the corresponding physical mechanism is analyzed theoretically.

Friction Characteristics of Polymeric Nanofiber Arrays against Substrates with Tailored Geometry

We present a study on macroscale friction of polyethylene nanofibrillar arrays against patterned rough surfaces with various asperity heights, spacings, and area fractions. These surfaces are prepared by utilizing colloidal lithography and silica evaporation, which allows the independent control of geometric parameters. While the nanofiber arrays exhibit high friction on a smooth surface, much lower friction is observed when the asperity height becomes larger than can be compensated by fiber compliance, or when the asperity spacing becomes small enough to prevent fiber penetration for contact. The observed behavior is discussed with simple mechanical models and summarized to provide some criteria to maintain high friction against rough surfaces.

Nanoparticle formation through solid‐fed flame synthesis: Experiment and modeling

AbstractThe preparation of silica nanoparticles through solid‐fed flame synthesis was investigated experimentally and theoretically. Monodispersed submicrometer‐ and micrometer‐sized silica powders were selected as solid precursors for feeding into a flame reactor. The effects of flame temperature, residence time, and precursor particle size were investigated systematically. Silica nanoparticles were formed by the nucleation, coagulation, and surface growth of the generated silica vapors due to the solid precursor evaporation. Numerical modeling was conducted to describe the mechanism of nanoparticle formation. Evaporation of the initial silica particles was considered in the modeling, accounting for its size evolution. Simultaneous mass transfer modeling due to the silica evaporation was solved in combination with a general dynamics equation solution. The modeling and experimental results were in agreement. Both results showed that the methane flow rate, carrier gas flow rate, and initial particle size influenced the effectiveness of nanoparticle formation in solid‐fed flame synthesis. © 2009 American Institute of Chemical Engineers AIChE J, 2009

An approach to the genesis of palygorskite in a Neogene-Quaternary continental basin using principal factor analysis

AbstractThe Carrión lacustrine basin (≈10 km2), central Spain, is filled with Neogene-Quaternary sediments (20–25 m thick) rich in palygorskite. Two clay units of ∼15 m thick are of particular interest in the basin. The lower one contains over 75% phyllosilicates (palygorskite up to 90%, smectites and illite) in marginal areas (facies A), and it is laterally bound by a distal facies (B) also rich in clay minerals (smectites and illite, and some palygorskite) and gypsum, and includes dolomitic marl intercalations. The composition at the top is primarily marly, with some gypsum (C). The upper clay unit, mainly clay-size material, (D) is rich in smectites, palygorskite and sepiolite, and contains carbonate intercalations near the top. A statistical treatment of the mineralogical and chemical composition data from 120 samples, using principal factor analysis, suggests that: (a) illite and smectite are detrital in origin; (b) palygorskite was formed by transformation of illite and smectite involving reaction with Mg; and (c) sepiolite was a neoformation product favoured by evaporation of silica- and Mg-bearing waters.

Determination of boron in high-purity silica using direct current plasma emission spectrometry

The method involves decomposition with hydrofluoric acid-nitric acid in the presence of mannitol in a simple closed Teflon PFA vessel and subsequent evaporation of silica without detectable losses of boron. The boron is determined by direct current plasma emission spectrometry. The detection limit is 0.76μg g −1. The possible losses of boron resulting from evaporation of the solution to dryness were investigated.

Evaporation of silica

Evaporation of silica

On the Mechanism of Evaporation in Vacuum. I. Evaporation of Silica Gel

Abstract The evaporation of silica is facilitated by the use of silica gel, instead of quartz. The silica film thus obtained is available as replica for the electron microscopy. The difference of the easiness of evaporation between quartz and silica gel is atributed to molecular constitutions. Under the assumption, that quartz consists of three dimensional net work of covalent linkage, while silica gel is constructed by linear chain having some oxygen bridges between, chains, vapor pressure is calculated, and the ease of evaporation is accounted for by the comparison to some usual metals.

Preparation and Uses of Silica Replicas in Electron Microscopy

A detailed description of the preparation of silica replicas and substrates and their many and varied uses is presented with photographs and electron micrographs. A method of preparing silica replicas of specimens which cannot be subjected to the temperatures and pressures of the ordinary technique is described. It consists of applying a polystyrene lacquer to the specimen surface in place of the conventional molding. The question of ``up and down'' in stereo pictures of silica replicas is definitely settled by adding a metal oxide smoke (MgO) to the polystyrene replica before the silica evaporation. A successful powder dispersing technique consists of dispersing the powder in an ethyl cellulose lacquer and depositing upon a silica substrate. Several other techniques are also included.

On the Silica Replica Method of Surface Examination with the Electron Microscope

An essential step in the making of a silica replica by the Heidenreich technique consists in the evaporation of silica in a high vacuum. An alternate method for depositing silica has been investigated and is discussed in this paper. This method consists in the chemical deposition of silica from the compound SiCl4.