Removal Of Silicon Research Articles

Application of Purification Method for Deep Silicon Removal of Ammonium Metavanadate in Chemical Production

Application of Purification Method for Deep Silicon Removal of Ammonium Metavanadate in Chemical Production

Study on silicon removal property and surface smoothing phenomenon by moderate-pressure microwave hydrogen plasma

The Si removal property achieved by a localized microwave hydrogen plasma was investigated. The relationship between plasma generation parameters (input power, H2 gas flow rate, and initial surface roughness) and the removal property (etching rate and surface roughness) was revealed. Stress relief and removal of the affected Si layer by H2 plasma etching were also demonstrated. Moreover, this H2 plasma etching technique presents no etching-rate dependence on the crystal plane orientation. Therefore, even though a multi-crystalline Si sample was etched, a mirror surface could be revealed. In addition, a 100-μm-thick Si sample could be thinned to 5.7 μm by H2 plasma etching without breaking the sample. The surface roughness of the etched Si sample depends on the etching rate. A critical etching rate exists, which determines whether the etched Si surface becomes rough or smooth. When the etching rate is significantly lower than the critical etching rate, large surface roughness is generated owing to the formation of {111} platelet defects induced by H atoms in Si crystal. By contrast, when the etching rate is higher than the critical value, the roughness formation is suppressed, and the Si surface becomes smooth despite the high H flux supplied to the Si surface. The suppression of roughness formation is discussed by comparing the etching rate with the diffusion rate of H atoms into Si. It is important to maintain the Si etching rate higher than the H diffusion rate to obtain a smooth etched Si surface.

Fluoride processing of oil hydrocarbon cracking catalyst with REE concentrate extraction

It is proposed to use a spent cracking catalyst of petroleum hydrocarbons containing 1 wt.% of rare earth element (REE) oxides as an alternative REE feed source. The study covers the process of removing silicon in the form of ammonium hexafluorosilicate (NH4)2SiF6 by sintering an oil cracking catalyst sample with NH4F and subsequent (NH4)2SiF6 sublimation to produce an aluminum-containing concentrate of rare earth elements. The orthogonal central compositional planning of the experiment was used to study the effect of three factors: sublimation temperature (350 to 400 °С), duration (40 to 80 min), and weight of the catalyst fluorinated sintered mass (5 to 10 g) on the (NH4)2SiF6 sublimation completeness. Results obtained in the experiment were used to build a second-order model, which correlate with experimental data. The dynamics of (NH4)2SiF6 sublimation removal was determined for sublimation durations of τ = 10, 20, 40 and 80 min at processing temperatures of 350, 375 and 400 °C. The (NH4)2SiF6 removal degree values calculated based on the second-order model for τ = 44, 48, 52, 56, 60, 64, 68, 72, and 76 min fit well the experimental curves. Spectra of fluorinated catalyst samples before and after sublimation were studied using X-ray phase analysis and IR spectroscopy. The data of IR spectroscopy and X-ray phase analysis are in good agreement and show that (NH4)2SiF6, (NH4)3AlF6 and unreacted NH4F are present in the catalyst with NH4F sintered mass, and only aluminum compounds are detected – NH4AlF4 and AlF3 after sublimation. These data indicate the completeness of the sublimation removal of silicon from the catalyst and NH4F sintered mass with NH4AlF4 and AlF3 aluminum compounds only observed after sublimation. REE concentration is 15 % due to silicon removal.

Atomic-Level Material Removal Mechanisms of Si(110) Chemical Mechanical Polishing: Insights from ReaxFF Reactive Molecular Dynamics Simulations.

Reactive molecular dynamics (ReaxFF) simulations are performed to explore the atomistic mechanism of chemical mechanical polishing (CMP) processes on a Si(110) surface polished with an a-SiO2 particle. The Si surface is oxidized by reacting with water before the CMP process, and the O atoms of the oxidized Si surface mainly exist in the form of Si-O- dangling bonds and Si-O-Si bonds. In the CMP process, the insertion of O atoms into the surface, the formation of interfacial Si-O-Si and Si-Si bridge bonds, and the adsorption of H atoms on the surface-saturated Si atoms can all cause the surface bond breakage and even the Si atomic removal. The contributions of the four different kinds of tribochemical wear mechanisms to the surface wear decrease in turn and are much larger than that of mechanical wear. The results indicate that the material removal in the actual Si CMP process is the combined results of multiple atomic-level wear mechanisms. Furthermore, we find that the oxide layer of the Si surface plays an important role in the surface wear mainly by providing O atoms to insert into the surface, rather than by providing additional reaction pathways to form interfacial Si-O-Si bridge bonds. This work provides new and further insights into the process and mechanism of silicon removal during CMP.

Investigation of mechanical and thermal activation on metal extraction from red mud

Red mud is an inevitable and under-utilized byproduct of the aluminium industry. The current study evaluates the effect of mechanical and thermal activation on the acid leaching of red mud. The acid leaching of the pretreated product is followed by acid-base treatment to precipitate the dissolved aluminium values from solution and enrich the residue with Fe and Ti values. Mild acid leaching yielded ~76% aluminium dissolution with 81% silicon removal. The direct acid leaching resulted in dissociation of sodium aluminosilicate; meanwhile, gibbsite phase remains in the residue. The mechanical milling for 1 h enhanced the aluminium dissolution to 89.5% with silicon and iron dissolution of 98.5 and 9.6%, respectively. The silica and iron oxide values were separated before HCl leaching by thermal pretreatment step using microwave heating with NaOH and carbon additives respectively. The sodium silicate and sodium aluminate phases formed during alkali thermal treatment resulted in ~33% silicon and ~ 27% aluminium removal by water washing. Meanwhile, HCl leaching of the water wash residue resulted in 82% aluminium dissolution with 70% recovery and residue containing ~52% Fe2O3, and 28% TiO2 is obtained. The carbothermal reduction yielded iron-rich magnetic concentrate having 48% iron grade with 20% metallic iron, and ~ 83% iron recovery. Leaching of the non-magnetic fraction containing hercynite and fayalite as the major aluminium and silicon bearing phases resulted in 81% aluminium dissolution with overall aluminium recovery of only 37%. Mullite formation is also observed in the precipitate with a high Al/Si molar ratio. The carbothermal route was found as an energy-efficient route, whereas the mechanical milling route yielded maximum Al extraction of ~90% with Fe and Ti content of 41.1% and 16.8% in the residue.

Material removal and surface evolution of single crystal silicon during ion beam polishing

The ion beam polishing techniques for silicon wafers play a key role in the fabrication of optical element. However, the dynamical ion beam polishing process at nanoscale time and space is very difficult to be recorded and observed, which most directly affects the quality of the machined surface. Here, the material removal and surface generation process during ion beam polishing are investigated using atomic simulation. In order to reveal the effects of the Ar ion dose, surface roughness, and Ar ion energy on surface integrity and subsurface damage, the surface topography, stress distribution, material removal rate, and radial distribution function are calculated and analyzed. As a result, the higher ion dose would generate the better machined surface quality, but increases the thickness of the amorphous layer. The initial surface roughness, including hill height and diameter, strongly affects the surface quality, due to the ion implantation depth to fall behind the maximum roughness value. Moreover, the average surface roughness, the material removing rate, and amorphous structure are significantly related to the Ar ion kinetic energy. This work demonstrates the potential of reasonable parameter optimization to prepare the ion beam polishing sample with high precision and few defects for optics applications.

The separation of radionuclides and silicon from boron-containing radioactive wastewater with modified reverse osmosis membranes

The ability to reuse boron and minimize the volume of radioactive waste could be accomplished with modified reverse osmosis (RO) membranes. RO membranes were fabricated via polyethylenimine (PEI) grafting to separate silicon and radionuclides from boron-containing radioactive wastewater. The positively charged RO membrane promoted more efficient removal of nuclides and silicon while the rejection of boron declined from 55.88 % to 41.71 % after modification. Compared with virgin RO membrane, the SFB-Si, SFB-Cs, and SFB-Co of the modified RO membranes increased from 6.02, 5.16, and 12.62–29.52, 61.91, and 547.15, respectively. SFB-Si, SFB-Cs, and SFB-Co of the simulated RO system with modified RO membranes further increased to 156.96, 1068.12, and 83617.88, respectively. As a result, permeate water with 433.92mgL−1 boron, 0.04mgL−1 silicon, 1.62μg·L−1 Cs(I), and 0.02μg·L−1 Co(II) was obtained, which could satisfy radionuclide treatment requirements and allow for the reuse of boron. Overall, modified RO membranes would be able to reuse boron and minimize the volume of discharge of radioactive wastewater.

Hydrochemical Structural Patterns of the Lena River–Laptev Sea Mixing Zone in the Autumn Period

This study was based on data obtained during the cruise 63 of the R/V Akademik Mstislav Keldysh in September 2015. We examine the features of the hydrochemical structure of the Lena River–Laptev Sea mixing zone. The studies were carried out in the eastern part of the Laptev Sea on a quasi-meridional transect, with the length of 710 km along 130°30' E. The distribution of dissolved oxygen, pH, alkalinity, major nutrients (phosphates, silicon, nitrate, and ammonium nitrogen), and chlorophyll a was analyzed. The relationship between the main hydrochemical parameters and chlorophyll a was considered. The distribution of hydrochemical parameters is similar to the data of previous studies: significant removal of silicon by waters of the Lena River (66.6 μM) with a moderate nitrate content (3.87 μM) and low concentration of mineral phosphorus (0.08 μM) in the area of strong influence of river runoff (salinity of 3.012 PSU). The presence of a near-bottom stagnant water zone in the part of research area affected by river runoff was detected. It is shown that the influx of mineral forms of nitrogen and phosphorus into the marine region of the Lena River delta occurs mostly as a result of nutrient recycling rather than due to the continental runoff.

Low Power and Compact Silicon Thermo-Optic Switch Based on Suspended Phase Arm Without Support Beams

A low power and compact thermo-optic switch based on $1\times 1$ Mach-Zehnder interferometer structure is demonstrated with the thermal isolation structure fabricated with a new backside etching process. The adjacent SiO2 and underlying silicon around phase arm are removed to suppress the thermal diffusion. Benefiting from the backside anisotropic etching process and front protecting photoresist used in underlying silicon removal, there are no support SiO2 beams in air trenches avoiding about 10% of extra thermal diffusion. At 1550 nm for TE mode, a low switching power (P $_{\pi } $ ) 0.48 mW is obtained with $450~\mu \text{m}$ thermo-optic interaction length ( $\text{L}_{\mathrm {TO}}$ ) representing a $\text{P}_{\pi }\cdot \text {L} _{\mathrm {TO}}$ product of only $0.22~\text {mW} \cdot \text {mm}$ , indicating a high thermal efficiency with a compact footprint. The 10% - 90% response time of the switch is $530~\mu \text{s}$ , including a rise time of 150 $\mu \text{s}$ , and a fall time of $380~\mu \text{s}$ . Compared with the switch without isolation structure, the switching power of the proposed switch is reduced more than 17 times, needing only 5.6% of the original value.

Mechanical wear behavior between CeO2(100), CeO2(110), CeO2(111), and silicon studied through atomic force microscopy

Using atomic force microscopy and scanning electron microscopy, the mechanical removal mechanism of silicon with different exposure surfaces of cerium oxide (CeO2) is studied. It is discovered that the main type of mechanical wear between Si and CeO2 is adhesive wear. The silicon removal rate relationship is RR11RR means removal rate of silicon by CeO2.(CeO2(111))> RR(CeO2(100))> RR(CeO2(110)). Additionally, the relationship of the friction force remains constant: F22F means friction force between silicon and CeO2.(CeO2(111)) > F(CeO2(110)) > F(CeO2(100)). This is consistent with the ceria wear rate relationship of WR33WR means wear rate of CeO2.(CeO2(111)) > WR(CeO2(110)) > WR(CeO2(100)). This paper provides a deeper insight into the mechanical material removal mechanism during chemical mechanical polishing processes; thus, providing a reference for CeO2 particle orientation control.

Removal of boron and silicon by a modified resin and their competitive adsorption mechanisms

Boron and silicon are essential trace elements for living organisms. However, these are undesirable in excess amounts owing to the toxic effects of boron on plants, animals, and humans, and the silica scale formation by silicon in water treatment processes. Herein, a new diol-type adsorbent (T-resin) was synthesized by grafting tiron (disodium 4,5-dihydroxy-1,3-benzenedisulfonate) onto an ion-exchange resin (grafting amount is 1.2mmol/gdry) to separate boron and silicon from a solution. The effects of pH, initial concentration, and coexisting anions, particularly, the effect of the coexistence of silicate ion on the adsorption of boron, were investigated. T-resin showed good adsorption properties for both boron and silicon in a wide pH range (pH2-10). The adsorption of boron and silicon was effectively described by the Langmuir isotherm, and the maximum adsorption capacities of boron and silicon were 21.25mg/g and 8.36mg/g, respectively. In a competitive adsorption system, boron and silicon were simultaneously adsorbed on the T-resin, but the adsorption rate of boron was faster than silicon. However, silicon could replace the boron adsorbed on the resin, indicating that the adsorption of silicon was more stable than boron. 11B and 29Si solid state NMR data confirmed the different adsorption mechanisms of the two elements. Boron was adsorbed via two types of complexes, a triangular complex of [LB(OH)], as well as 1:1 tetrahedral complex of [LB(OH)2] and 1:2 tetrahedral complex of [BL2], whereas silicon was only adsorbed via a 1:3 octahedral complex of [SiL3]. Graphical abstract A new diol-type absorbent was synthesized by grafting tiron onto an ion-exchange resin to separate boron and silicon from a solution. Boron and silicon competitively adsorbed on the T-resin, and silicon could replace the boron adsorbed on the resin. 11B and 29Si solid state NMR data confirmed the different adsorption mechanisms of the two elements. Boron was adsorbed via two types of complexes, a triangular complex of [LB(OH)], as well as 1:1 tetrahedral complex of [LB(OH)2] and 1: 2 tetrahedral complex of [BL2], whereas silicon was only adsorbed via a 1:3 octahedral complex of [SiL3].

Effect of biochars, biogenic, and inorganic amendments on dissolution and kinetic release of phytoavailable silicon in texturally different soils under submerged conditions

Extensive cropping leads to higher removal of silicon (Si) from the soils and makes it a limiting element for various crops. Application of silicic acid (H4SiO4) has limited scope due to high cost, low solubility, and high polymerization. The biogenic sources of Si are alternative to silicic acid (H4SiO4) and Si release from these sources is a function of different soil properties like pH, redox potential, texture etc. Kinetics release of plant available Si (PASi) from various organic and inorganic sources was evaluated in texturally different soils such as sandy loam (SL), sandy clay loam (SCL), and clay (CL) under a 60-day incubation study. Our findings suggest that the highest cumulative release of Si (cSi) was observed in SCL (47.6 mg/L) in control sets without any amendments. The highest cSi release among plant residue amendments was observed by bamboo leaves (340 mg/L) and rice husk (RH) (301 mg/L) in SL and SCL soils, respectively. Among biochar amendments, the rice husk biochar (RHB) released the maximum quantity (246.55 and 243.9 mg/L) of Si in SCL and CL soils respectively. Among the ashes, sugarcane bagasse ash had the highest release (316 mg/L) of Si in SCL and RHA which yielded 235.2 Si mg/L in CL soil for 60days. Silicon release kinetics for these sets of systems showed a diffusive behavior of Si being released from amendments primarily dependent on soil type.

Electrocoagulation with Polarity Reversal for Treatment of Produced Water

Electrocoagulation (EC) is a cost-effective and reliable technology to treat water and wastewater and has the ability to remove many types of contaminants. Studies have shown that EC operated with aluminum or iron electrodes exhibits higher treatment efficiencies than traditional chemical coagulation with aluminum sulfate or ferric chloride salts [1], [2]. EC involves the in-situ generation of metal hydroxide coagulant by the electrochemical dissolution of sacrificial metal anodes using a direct current, combined with generation of hydroxide ions at the cathode. However, material precipitation on the electrodes associated with long term operation is a major problem hindering the scale up of EC [3]. The growth of electrode surface layers increases passivation, which reduces the treatment efficiency and increases operating costs [4]. Polarity reversal during electrocoagulation, i.e. intermittently changing the direction of the current, is a method that can remove passivation layers on the electrodes formed during direct current operation [5]. The main goal of this study was to investigate the effect of polarity reversal on the reaction and electrode fouling mechanisms as well as the performance of electrocoagulation for the treatment of SAGD produced water.Total organic carbon and silicon removal efficiencies were measured to evaluate treatment performance. Laser scanning confocal microscopy was used to monitor the pH distribution close to electrodes as well as the formation of solid products in an electrocoagulation cell. Customized polycarbonate bench scale reactors were used to study the relationship between coagulant production, polarity reversal frequency, solution composition, and flowrate. The cycle time of the polarity reversals was varied from 5 to 600 s, and the Reynolds numbers was varied between 30 to 200. The Faradaic efficiencies for the coagulant dissolution at different operating conditions were determined by digesting the solid products followed by elemental analysis.The evolution of pH during polarity reversal revealed that at higher frequencies or higher flow rates, the thickness of the interfacial pH boundary layer was lower. The quantification of pH was used to study the effect of pH on passivation layer stability. It was found that at higher frequencies, Faradaic efficiencies were lower for EC with iron electrodes, whereas increased efficiencies were observed for aluminum electrodes due to increased susceptibility to non-Faradaic corrosion. EC using aluminum electrodes (Al-EC), employing polarity reversal at all frequencies led to a reduction in cell voltage and therefore a reduction in the required energy for treatment.

Role of mechanically-driven distorted microstructure in mechanochemical removal of silicon

Ultra-precision of nanomanufacturing process down to subnanometer level is actually to achieve controllable removal of atomic material, however, which would be strongly impacted by the preconditions of manufactured surfaces. Here, the atomic structures, chemical and mechanical properties of mechanically-driven distorted microstructures on silicon formed in pre-treated process were characterized and their roles in atomic attrition dominated by mechanochemical reactions were revealed at atomic scale. Mechanically deformed silicon depending on applied stress physically behaviors protrusion forming and material removal (groove), which play opposite contributions to the mechanochemical reactions, i.e., atomic attrition suppressed on the protrusion surface but facilitated on the groove surface. Analyzing the mechanochemical reactions with the stress-assisted Arrhenius-type kinetics model and the DMT contact mechanics implies that, compared to the limited effect of the amorphous structure, the enhanced oxide layer at the protrusion surface that increases the energy barrier for mechanochemical reactions plays a more important role in the mechanochemical removal process. The results may help gain a profound insight into the mechanochemical removal mechanism of silicon and provide a wider cognition for regulating the mechanochemical reactions widely existing in scientific and engineering applications.

Determination of trace elements in high-purity quartz samples by ICP-OES and ICP-MS: A normal-pressure digestion pretreatment method for eliminating unfavorable substrate Si

The analysis of siliceous matrix samples may adopt a two-step pretreatment, which includes melting with ammonium hydrogen fluoride and redissolving with nitric acid. However, the residual of substrate silicon unfavorable to the determination of trace elements in the samples due to serious matrix effects. Here, a new digestion method using simultaneously both ammonium bifluoride and nitric acid under normal pressure was developed for high-purity quartz sand sample. The digestion pretreatment is a two step process: melting/dissolving with both ammonium bifluoride and nitric acid at 200 °C for 2 h, and evaporating the solution at 250 °C to dryness. As confirmed by XRD analysis, silicates in the sample were converted to (NH4)3SiF6NO3 in the melting/dissolving step. TGA analysis shows that the generated (NH4)3SiF6NO3 could be decomposed and evaporated completely at 250 °C, which ensured a complete removal of silicon by the followed evaporation of the solution at 250 °C. As a result, the followed ICP-OES and ICP-MS analysis needed a solution dilution of only 100 times for the determination of Ca, Mg, Al, Rb, Ba, REE and other trace elements. The new method was applied to the analysis of three certified reference materials, and the results were well consistent with the standard value with RSD% values between 0.62% and 9.73%. Therefore, this method can be applied to the analysis of trace elements in high purity silica-based samples, with the advantages of time-saving, small dilution factor (only 100 times) and low detection limit.

Fabrication and application of flexible AlN piezoelectric film

A fabrication method for high quality flexible aluminum nitride piezoelectric thin films based on micro-nano fabrication technology is reported in this paper. Molybdenum (Mo)/aluminum nitride (AlN)/aluminum (Al) structure was prepared on silicon(100) by sputtering. Then, deep-reactive ion etching technology was used to remove the silicon material used for support, then the Mo/AlN/Al flexible sandwich film was obtained. The full-width at half-maximum of the AlN film (002) peak before and after removal of silicon was only 1.47° and 1.49°, respectively. No obvious cracks in the film under bending conditions were observed with a scanning electron microscope. Capacitance–voltage (C–V) test results showed that the capacitance curve of the sandwich structure was consistent with that of the double-sided Schottky junction. The flexible piezoelectric film with an active area of 2 × 2 mm2 exhibited an average peak-to-peak generated voltage of 0.6 V in energy harvesting tests, which indicates that the method could be used to fabricate high quality flexible energy collectors based on AlN film. The preparation scheme in this paper is compatible with integrated circuit processes and simple to implement, which lays a foundation for the wide application of flexible piezoelectric devices.

Local removal of silicon layers on Si(1 0 0)-2 × 1 with chlorine-resist STM lithography

We report the realization of STM-based lithography with silicon layers removal on the chlorinated Si(1 0 0)-2 × 1 surface at 77 K. In contrast to other STM lithography studies, we were able to remove locally both chlorine and silicon atoms. Most of the etched pits have a lateral size of 10–20 Å and a depth of 1–5 Å. In the pits in which the STM image with atomic resolution is obtained, the bottom is mainly covered with chlorine. Some pits contain chlorine vacancies. Mechanisms of STM-induced removal of silicon and chlorine atoms on Si(1 0 0)-2 × 1-Cl are discussed and compared with the well-studied case of STM-induced hydrogen desorption on Si(1 0 0)-2 × 1-H. The results open up new possibilities of the three-dimensional local etching with STM lithography.

Improved lipid production in oleaginous brackish diatom Navicula phyllepta MACC8 using two-stage cultivation approach.

A two-stage cultivation method involving the initial growth in optimized conditions for biomass production followed by those for lipid production in oleaginous brackish diatom Navicula phyllepta MACC8 resulted in a proportional increase of lipid concentration along with biomass production. The diatom was further subjected to stress conditions by altering the nutrient components such as nitrate, phosphate, silicate, and temperature. Silicon deprivation resulted in the highest lipid percentage of 28.78% of weight at the end of the 18th day of the second stage. A significant increase in lipid content was observed on the complete removal of the nutrients silicon and urea one at a time, while the biomass showed a considerable reduction. The application of multiple nutrient stress conditions had a profound influence on the increased rate of lipid production. A combination of phosphate deprivation, silicate limitation and temperature reduction resulted in a significant increase in lipid percentage of 32.13% at the cost of reduced biomass (1.1g L-1), whereas phosphate deprivation, urea limitation, and temperature reduction resulted in lipid percentage of 27.58% with a biomass of 1.44g L-1 at the end of the second stage. Further, the results were supported by Nile red staining, FTIR, fatty acid profile and oxidative stress marker analyses. The changes in biochemical composition and oxidative stress parameters within the various stress conditions demonstrated the profound influence of the selected stress factors on the biodiesel productivity of the diatom, besides its stress tolerance. A two-phase culturing system, with multifactor stress application, especially nitrogen limitation along with phosphate starvation and temperature stress, would be the suitable method for gaining maximum biomass productivity and lipid content in diatom Navicula phyllepta MACC8 towards biofuel production.

The genesis of the Mesozoic alkaline intrusions of the Khokhoi ore field (Upper Amga gold-mining district, Aldan Shield, North Asian Craton)

The article discusses petrography and features of the chemical composition of the Mesozoic alkaline intrusions of the Khokhoi ore field located within the Upper Amga gold-mining district in the Aldan Shield. This gold-mining district is located in the Aldan-Stanovoy Province rich in gold. Tectonic position and magmatic events of this Province are close to those positions and events of Shandong Gold Province of Sino-Korean Craton. The investigation of the genesis of the magmatic rocks and comparison of the Provinces can shed light on the genesis and regularity of location of the gold deposits in them. Intrusions of the Upper Amga gold-mining district passed through the metamorphic rocks of the Precambrian and intruded into the Cambrian carbonate rocks and the Jurassic sandstones. Petrographic observations found that large intrusive massifs of the ore field consist mainly of potassic feldspar and plagioclase. Mineral composition, structure and texture of the rocks correspond to syenite and monzonite. Blocks of melanocratic rocks – presumably tephrites are rare on the surface. Several generations of feldspar and dark-colored minerals are observed within all these rocks, indicating melt fractionation. High Sr and K contents were identified in the rocks. Contents decrease in the series of tephrite-syenite-monzonite. This feature, judging by other petrochemical data, can be associated not only with magmatic differentiation, but also with the melting and interaction of the lithosphere. In sienites, ovoids of quartz and the first-generation potassic feldspar melting margin were found. It could be possibly resulted from the capture of surrounding rock material and changes in the thermodynamic conditions of crystallization. It is found out that potassium and silicon contents in rocks depend inversely on calcium content. Interaction of melts and the host carbonate rocks with removal of silicon and potassium and formation of gold-bearing sericite-quartz and feldspar-quartz metasomatites is assumed. The loss of potassium probably has led to potassium metasomatism at the contacts of intrusions. This metasomatism produced the gold ores.

Influence of alumina precursor on silicon capacity of NiMo/γ-Al2O3 guard bed catalysts for gas oil hydrotreating

Abstract The influence of alumina precursors on NiMo/γ-Al2O3 catalysts for silicon removal from gas oil have been studied. Alumina precursors were prepared by hydrothermal treatment of gibbsite, precipitation of aluminum nitrate by ammonia and precipitation of aluminum nitrate in autoclave. Alumina precursors, supports and catalysts were studied by XRD, nitrogen adsorption-desorption, IR spectroscopy, UV–vis, XPS, SEM, HRTEM. Series of NiMo/γ-Al2O3 catalysts differed in preparation method of alumina precursors was tested in hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane as a model silicon compound. It was shown that prepared alumina precursors were boehmites and dawsonite, which had different particle size. The supports prepared from these alumina precursors were γ-Al2O3 with different particles size. It was shown that there was a dependence of the surface area of the support on the size of primary particles measured by XRD. The higher surface area results in the higher content of OH groups and silicon sorption capacity. Morphology of the sulfide active component also depends on the size of primary particles. The higher length of the particles, the higher slab length of NiMoS phase. The catalyst with the lowest particle size of alumina and highest length of active component had the highest HDS activity.