Silicate Formation Research Articles

Transformation and Mobility of Cu, Zn, and Cr in Sewage Sludge during Anaerobic Digestion with Pre- or Interstage Hydrothermal Treatment.

Anaerobic digestion (AD) combined with hydrothermal treatment (HT) is an attractive technology for sewage sludge treatment and resource recovery. The fate and distribution of heavy metals in the sludge during combined HT/AD significantly affect the sludge final disposal/utilization options, yet such information is still lacking. This study systematically characterizes the transformation of important heavy metals Cu, Zn, and Cr in sewage sludge during AD with pre- or interstage HT (i.e., HT-AD or AD-HT-AD, respectively). Complementary sequential chemical extraction and X-ray absorption spectroscopy were used to characterize the speciation and mobility of metals. For the HT-AD system, both Cu and Zn predominantly occur as sulfides in HT hydrochars. Subsequent AD favors the formation of Cu2S and partial transformation of nano-ZnS to adsorbed and organo-complexed Zn species. HT favors the formation of Cr-bearing silicates in hydrochars, whereas Fe(III)-Cr(III)-hydroxide and Cr(III)-humic complex are the predominant Cr species in AD solids. Similar reaction pathways occur in the AD-HT-AD system with some minor differences in metal species and contents, as the first-stage AD changed the sludge matrix. These findings have important implications for understanding the fate and mobility of heavy metals in sludge-derived hydrochars and AD solids.

Геохімічні особливості евапоритових формацій Євразії у контексті еволюції хімічного складу морської води протягом фанерозою

Studies of evaporites provide new data to characterize the seawater chemistry in the Early Paleozoic and Middle Mesozoic. In particular, we studied the fluid inclusions in halite from Ordovician (China) and Cretaceous (Laos) evaporites. The corresponding sections on the plot of Ca/SO4 oscillations curve in the Phanerozoic seawater are updated. The calcium content in seawater concentrated to halite precipitation stage was 45.6 mol %, 485 million years ago and 24.3 mol % 112.2–93.5 million years ago. By analyzing the previously published and new factual material, it is established that in Permian evaporites the sulfur isotopic composition is inversely correlated with the sulfate ion content in evaporite basin brines. Thus, the evolution of seawater chemistry in Permian is confirmed by the evolution of the isotopic composition of dissolved seawater sulfate. According to the generalization of 38 Phanerozoic marine evaporite formations, it was found that the peculiarities of the clay minerals associations correlate with the change of the seawater chemical type. Clay minerals associations precipitated from the SO4-rich seawater are characterized by a larger set of minerals, among which smectite and mixed-layered minerals often occur; Mg-rich clay minerals (corensite, paligorskite, sepiolite, talc) also occur. Instead, in the associations of evaporite clay minerals formed from the Ca-rich seawater are represented by the smaller amount of minerals, and Mg-rich minerals are extremely rare. The increased content of magnesium in seawater of SO4-rich type is the main factor in the formation of Mg-rich silicates in evaporites. The composition of clay minerals associations depends on the evaporate basin brine concentration; with its increase, unstable minerals are transformed, which theoretically leads to a decrease in the number of minerals in the associations. However, it was found that evaporite deposits of higher stages of brine concentration often still contain unstable clay minerals – products of incomplete transformation of a significant amount of pyroclastic material from coeval volcanic activity. The main factor determining the composition of clay minerals associations of Phanerozoic evaporites was the seawater (and basin brines) chemical type. Geochemical studies of scattered organic matter and fluid inclusions with hydrocarbon phase in evaporites of the Upper Pechora Basin (overlying oil and gas deposits) indicate the presence of allochthonous bitumoids and allow to use this method to predict oil and gas potential of other areas. Analysis of the results of oil and gas exploration in a number of areas of the Transcarpathian Trough indicates the presence of fluid-saturated reservoirs and the prospects for the discovery of new accumulations of hydrocarbons. Geochemical studies proved the effectiveness of gas-flow survey method for oil and gas exploration, assessing the prospects for fluid saturation of seismic structures.

Supergénne minerály z U-Cu rudného výskytu Východná-Nižný Chmelienec v Nízkych Tatrách (hronikum, Slovensko)

An association of supergene U-Cu and Y/REE minerals was found in a relic of old ore dump at the abandoned U deposit occurrence Východná-Nižný Chmelienec, the northern slopes of the Nízke Tatry Mts., Slovakia. They have partially recent origin, since exploration of the locality took place between 1965 and 1966. The studied mineral assem- blage is represented by goethite, malachite, uranophane and (meta)zeunerite, in a lesser extent baryte and rare zálesíite. Uranophane appears separately (globular aggregates, thin coatings) and it also forms the main part of the yellow to yellow-green crystalline crusts on the rock cracks. The chemical composition of the uranophane was determined by electron microprobe analyses and it is close to its ideal chemical formula Ca(UO2)2(SiO3OH)2·5H2O. The average chemical composition of the studied uranophane can be expressed by an empirical formula (Ca1.0Mg0.02K0.01Fe0.01Ba0.01)Σ1.05 (UO2)2.08(SiO3OH)1.84·5H2O. The infrared vibrational spectra of the studied uranophane show 3 (UO2)2+ at 850-760 cm-1; the 3 (SiO4)4- antisymmetric stretching vibration at 1000-900 cm-1; the 1 (SiO4)4- symmetric stretching vibration at 1150-1199 cm-1; the  H2O bending vibration at 1800-1600 cm-1 and OH stretching vibrations at 3407; 3408 and 3409 cm-1. The weak bands 2648; 2646 and 2651 cm-1 may be assigned to organic impurities. The calculated U-O bond length 1.83 Å corresponds to short U-O bonds in uranophane. The accessory admixtures of uranophane coatings are (meta)zeunerite and zálesíite. (Meta)zeunerite occasionally forms thin coatings of light green to emerald green tabular crystals (up tu 0.5 mm) on the surface of the rocks. Chemical analyses of (meta)zeunerite correspond to the empirical formula (Cu0.66K0.03Fe0.01Ca0.01)Σ0.71(UO2)2.11[(AsO4)1.96(PO4)0.01]Σ1.97·12H2O. Zálesíite occurs as crystalline aggregates, nests, formed by tiny acicular crystals, up to 100 µm in length. This is the second finding (occurrence) of this mineral in Slovakia. An average zálesíite chemical composition is (Ca0.83REE0.18U0.05Al0.03Ti0.01)Σ1.10(Cu5.81Fe0.06Zn0.02)Σ5.90[(AsO4)2.75 (SiO4)0.21(PO4)0.02(SO4)0.03]Σ3.01(OH)5.10·3H2O. Malachite, which has been also found in the association, is only a minor mineral in the studied locality. The formation of uranyl silicates (uranophane) and minerals of the mixite group (zálesíite), present at the studied locality, points to neutralization of acidic supergene fluids in the mine dumps. Possibly, this environment later (precipitation of baryte) passed to neutral or slightly basic conditions (precipitation of carbonates - malachite). The identified uranyl phosphates/arsenates (zeunerite/metazeunerite), typical of an acidic environment, are therefore rare.

Increasing the efficiency of water shut-off in oil wells using sodium silicate

Purpose. Substantiation of technology for creation of a water-blocking zone below an oil reservoir and calculation of the proper composition of a gel-forming compound based on sodium silicate, in order to reduce water cut in production wells. Methodology. The goal of the work was achieved by conducting theoretical and experimental studies on technological processes of water blocking in an oil reservoir, and by identifying patterns of gel formation of sodium silicate and hydration of a micro-cement solution in reservoir conditions on full-scale models. The gel compound included sodium silicate (Na2SiO3, also referred to as liquid glass) and an aluminum salt cross-linker (AS-1). The plugging material mixture of Portland micro-cement and sodium silicate contained calcium oxide, to allow expansion, and a GL-1 reaction inhibitor. The criteria for assessing the creation of a reliable water-blocking zone in an oil reservoir are: the mobility of the aqueous solution of the gel-forming compound during its movement from the wellhead to the bottom of the well, the low permeability of the zone following its creation, and the sufficient strength of the non-shrink micro-cement in the annulus of the well. Findings. A new technology is suggested used to create a water isolation zone is a gel-forming compound based on sodium silicate, which provides a significant reduction of water cut in oil production. It is found that perforation of production string below the oil reservoir at the level of the water-saturated zone followed by injection into a well through perforated channels, the mixture of fresh water and the gel-forming compound prevents water inflow to the bottom of the well. Experiments established that with a gelation time of 2 hours at a temperature of 80 C, the viscosity of the gel is in the range of 1.22.9 Pas, and the density is 10801109 kg/m3. These values for the viscosity of the gel allow transportation from the top of the well to the bottom with the least resistance to motion. Following gelation time, the viscosity increases significantly, and after 3 days the gel viscosity reaches a range of 3.46.7 Pas. The values indicated for the viscosity of the gel are much greater than those of oil. Therefore, the proposed gel-forming compound provides a reliable water shut-off zone at the bottom of an oil reservoir, and prevents the influx of water at the bottom of a well. Originality. The proposed sodium silicate compound allows for the creation of a reliable water shut-off zone and an enhanced grouting material, based on the combination of sodium silicate and micro-cement, which together provide a significant reduction in water cut in wells during oil production. Practical value. A method for studying technological processes of oil reservoir water-blocking has been devised and the rational composition of gel-forming compound and micro-cement grout slurry with an expanding additive and a reaction retarder in reservoir conditions on full-scale models has been established. The application of the research results in oil fields allows reduction of water cut in production wells to 010%, against existing values of 7090%, and an increase in flow rate in producing wells by 2030%.

The hydrocarbon potential of the Miocene siliceous formations in Tsugaru Basin, northern Japan, based on the geochemical analyses

The hydrocarbon potential of the Miocene siliceous formations in Tsugaru Basin, northern Japan, based on the geochemical analyses

Silicate Island Formation in Gas Metal Arc Welding

Because formation of silicate islands during gas metal arc welding is undesirable due to decreased productivity and decreased quality of welds, it is important to understand the mechanism of the formation of these silicate islands to mitigate their presence in the weld. The effects of welding parameters on the silicate formation rate were studied. Results showed that the applied voltage and oxidizing potential of the shielding gas were the parameters that most strongly influenced the amount of silicates formed on the surface of the weld bead. High-speed video was used to observe the formation of silicate islands during the welding process, which showed that the silicates were present at each stage of the welding process, including the initial melting of the wire electrode, and grew by coalescence. A flow pattern of the silicate islands was also proposed based on video analysis. An electromagnetic levitation system was used to study the growth kinetics of the silicate islands. Silicate coverage rate was found to increase with increasing oxidizing time, increasing oxidizing potential of the atmosphere, and increasing content of alloying elements except for Ti.

Tuning catalytic performance in Fischer-Tropsch synthesis by metal-support interactions

Metal-support interactions in inverse catalysts prepared by adsorbing tetraethoxysilane (TEOS) on to Co3O4 can be manipulated by varying the solvent mixture, from which TEOS is taken up. Deposition of TEOS on Co3O4 nanoparticles in n-hexane results in the formation of silica oligomers after calcination at 573 K interacting strongly with cobalt(II,III)oxide. Modification of Co3O4 nanoparticles with TEOS in a hydrolysing environment results in a stronger interaction due to the formation of surface cobalt silicate formed through hydrolysis. The presence of surface silicates results in a strong increase in the turnover frequency of carbon monoxide consumption in the Fischer-Tropsch synthesis operating at close to industrial conditions. The obtained activity change is accompanied with a shift to a more paraffinic product.

Aqueous phase catalytic hydrogenation of furfural to furfuryl alcohol over in-situ synthesized Cu–Zn/SiO2 catalysts

The aqueous phase catalytic hydrogenation of furfural to furfuryl alcohol is of environmental and technical advantages. In this study, a series of Cu-based catalysts supported on SiO2 were synthesized and used for furfural hydrogenation to furfuryl alcohol. Firstly, the effect of preparation methods of Cu/SiO2 catalysts on the structure and performance was investigated. The results indicate that, different from those by the impregnation and deposition-precipitation, the in-situ synthesized Cu/SiO2-IS catalyst leads to the formation of silicates, increasing the dispersion and surface area of Cu and thus improving the catalytic activity. Furthermore, the addition of Zn species not only promotes the reduction of CuO and improves the dispersion of metal Cu, but also effectively prevents decarbonylation, leading to higher furfuryl alcohol selectivity. Especially, due to its good reducibility and high metal Cu surface area, the Cu–Zn/SiO2-IS catalyst with the Cu/Zn ratio of 2/1 shows an excellent catalytic performance. So, the in-situ synthesized catalyst has a great potential as catalyst for catalytic hydrogenation of furfural to furfuryl alcohol in industry.

Layered silicate formation during chiral acid templated ZSM-5 synthesis

Silicate anion forms four, five and six coordinate complexes with chiral polyhydroxy alcohol and polyhydroxy acids in aqueous alkali media. The chemistry of organosilicate complexes is well established but its effect on zeolite synthesis has not been explored. When chiral acid is used as a template in ZSM-5 synthesis, a new partially crystalline layered silicate is formed whose basal spacing value do not match with any of the known layered silicates. Chiral acids are necessary to induce layered silicate formation and it is not formed in absence of any template or tetrapropylammonium bromide (TPABr) as a template. In presence of chiral acid, layered silicates are not precursors to ZSM-5 formation as observed normally in ZSM-5 synthesis. This method is new and it paves the way for generating layered silicates using simple chiral acids as a template.

Zirconium retention for minimizing environmental risk: Role of counterion and clay mineral

Zr(IV) together with U(IV) are the major components of high-level radionuclide waste (HLRW) and spent nuclear fuel (SNF) from nuclear power plants. Thus, their retention in the waste disposal is of great importance for the environmental risk control. Here, the influence of clay minerals on the retention of Zr(IV), as component of the nuclear waste and as chemical analogues of U(IV), has been evaluated. Three clay minerals, two bentonites and one saponite, were hydrothermally treated with three zirconium salts. A structural study at long-range order by X-ray diffraction and short-range order by NMR was performed to evaluate the generation of new zirconium phases and degradation of the clay minerals. Three immobilization mechanisms were observed: i) cation exchange of ZrO2+ or Zr4+ by clay minerals, ii) the precipitation/crystallization of ZrO2, and, iii) the chemical interaction of zirconium with the clay minerals, with the formation of zirconium silicates.

ТЕРМОДИНАМИЧЕСКОЕ МОДЕЛИРОВАНИЕ ФАЗОВЫХ РАВНОВЕСИЙ В ОКСИДНОЙ СИСТЕМЕ FEO-SRO-SIO2

Oxide systems with strontium oxide as one of the main components are used more and more widely in different industries. The effect of adding SrO on slug, flux, and the properties of glass and even ceramic with magnetic behaviour is intensively studied today. However, there is only a limited amount of data on phase diagrams for oxide strontium-bearing systems in academic literature, in particular for triple and multi-component systems. This research involved a thermodynamic simulation of phase equilibria and further construction of phase diagrams for double oxide systems FeO–SrO, FeO–SiO2, SrO–SiO2, and the calculation of coordinates of the liquidus surface projection of the phase diagram for a triple oxide system FeO–SrO–SiO2. The simulation was conducted using the sub-regular ionic solution theory approximation. The study has identified energy parameters of the theory for every of the researched systems. The estimated data on the position of liquidus lines in double oxide systems are comparable to those published in academic literature, thus confirming that the performed simulation is correct. Information on the phase diagram of the triple oxide system FeO–SrO–SiO2 is not presented in the academic literature and have been calculated for the first time. The present paper also analyses the data on the temperatures, enthalpy and entropy of silicate formation Fe2SiO4, Sr3SiO5, Sr2SiO4, SrSiO3 from the components of oxide melt of systems FeO–SiO2 and SrO–SiO2 respectively. For example, in the case of Fe2SiO4, the enthalpy of the compound formation from the components of the oxide melt was 63600 J/mol; in case of the silicate Sr3SiO5 – 181675 J/mol; in case of the compound Sr2SiO4 – 169576 J/mol; and for SrSiO3 – 155697 J/mol.

Coupled Preparation of Ferronickel and Cementitious Material from Laterite Nickel Ores.

Nickel slags can be produced through ferronickel preparation by the pyrometallurgical processing of laterite nickel ores; however, such techniques are underutilized at present, and serious environmental problems arise from the stockpiling of such nickel ores. In this study, a modification to the process of ferronickel preparation by the direct reduction of carbon bases in laterite nickel ores is proposed. The gangue from the ore is used as a raw material to prepare a cementitious material, with the main components of tricalcium silicate and tricalcium aluminate. By using FactSage software, thermodynamic calculations are performed to analyze the reduction of nickel and iron and the effect of reduction on the formation of tricalcium silicate and tricalcium aluminate. The feasibility of a coupled process to prepare ferronickel and cementitious materials by the direct reduction of laterite nickel ore and gangue calcination, respectively, is discussed under varying thermodynamic conditions. Different warming strategies are applied to experimentally verify the coupled reactions. The coupled preparation of ferronickel and cementitious materials with calcium silicate and calcium aluminate as the main phases in the same experimental process is realized.

A scientific study on the role of organic lime mortars of Padmanabhapuram Palace, Thuckalay, Tamilnadu, India

This research aims at providing the scientific evidence of ancient construction practice and production technology on the use locally available geoearth materials and natural herbs, namely kadukkai (Terminalia Chebula), neelamari (Indigofera tinctoria), hibiscus (Rosa sinensis), palm jaggery (Borassus flabellifer), aloe vera (Aloe barbadenis) as specified in ancient palm leaf texts which were adopted at Padmanabhapuram Palace, India for preparing the traditional lime mortars. Six mortar samples of three different mortar typologies (wall, bedding and floor finish) were taken from the Padmanabhapuram Palace for the study. The sampled mortars were characterized using physiochemical analysis as well as modern analytical techniques including XRD, TG-DTA, FT-IR and FESEM-EDX methods. Different binder-to-aggregate ratios was proportioned for wall plaster (1:3), bedding mortar (1:2) and floor finish (1:1) and was confirmed through acid loss analysis. Wall plaster samples indicated the presence of organic protein and polysaccharide spectral peaks substantiated by FT-IR analysis. Organics have played a significant role in the formation of calcium aluminate silicates and carbonate polymorphs to enhance the crystalline hydrated phases observed through XRD and FESEM analyses. The thermal investigation substantiated that calcite decarbonation mostly occurred between 705 and 730 °C. The results apprised the wide use of hydraulic lime with fine-grained aggregate particles, added with fermented organics to produce an environmentally friendly organic mortar to restore the structure.

Isotopic Composition (δ13C and δ18O) and Genesis of Mn-bearing Sediments in the Ushkatyn-III Deposit, Central Kazakhstan

The Ushkatyn-III deposit is located 300 km west of Karaganda (Central Kazakhstan). It is classified as a weakly metamorphosed Atasu-type hydrothermal-sedimentary ore deposit. Stratiform iron, manganese, and barite–lead orebodies occur in the Upper Devonian (D3fm2) carbonate sequence of this deposit. The Fe- and Mn-bearing rocks were studied. Iron ores are composed of hematite, calcite, and quartz. Manganese ores are divided into two (braunite and hausmannite) types. Braunite ores are composed of braunite, calcite, quartz, and albite; hausmannite ores are composed of hausmannite, rhodochrosite, Mn-calcite, tephroite (sometimes with sonolite and alleghanyite), and friedelite. The mineral composition of ores was formed during the burial of metal-bearing sediments containing oxides of Fe3+ and Mn3+/Mn4+. The nature and intensity of the postdepositional processes was controlled by the content of organic matter (OM) in initial rocks. Braunite ores formed under oxidizing conditions; hausmannite ores, under reducing conditions. The initial presence of OM is indicated by the carbon isotope composition in carbonates. High δ13Ccarb values (from –0.3 to 2.1‰) in hematite ores, braunite ores, and host limestones are close to those in the seawater bicarbonate precipitated as a part of biogenic calcite (e.g., shell fragments). At the same time, low δ13Ccarb values (average –12.3‰) in rhodochrosite and Mn-calcite from hausmannite ores indicate the influence of carbon from the OM buried in sediments. The general oxygen isotope composition in iron ores, manganese ores, and host rocks was determined by variations of the isotope ratio in the initial precipitates of 18O-rich calcite and 16O-rich Fe/Mn oxides. Conversion of the primary sedimentary Fe3+ and Mn3+/Mn4+ oxides to hematite, braunite, and hausmannite slightly changes the oxygen isotope composition of Fe–Mn minerals. Average values of δ18Otot determined in the hematite (1.7‰), braunite (14.8‰), and hausmannite (12.7‰) ores are close to those in the sedimentogenic iron (0‰) and manganese oxides (11.5‰). The oxygen isotope composition suggests that initial manganese oxides did not participate in the formation of carbonates in braunite ores. Average oxygen isotope composition of carbonates in these ores (δ18Ocarb 19.1‰) is close to that in host limestones (20.8‰). During the formation of hausmannite ores, in contrast, manganese oxides reacted with OM leading to the formation of rhodochrosite and silicates. Consequently, the light isotope oxygen in the starting oxides was fixed in carbonates (δ18Ocarb 15.9‰) and rocks in general (δ18Ototal 12.7‰). The oxygen isotope composition was not averaged during the formation of hausmannite ores even in the mineralogically similar aggregates in the adjacent rock layers.

Studies on the formation and hydration of tricalcium silicate doped with CaF2 and TiO2

The comprehensive utilization of wasted pickling sludge in the cement kiln would be a promising practice, but the calcination process of cement clinker became complicated due to the simultaneous introduction of titanium and fluorine. In this paper, the formation and hydration of tricalcium silicate (C3S) doped with CaF2 and TiO2 were discerned by XRD, FT-IR, XPS and isothermal calorimetry. The results revealed that the addition of CaF2 more than 1.5% would promote the appearance of CaTiO3 as the indicator of the solution limit of TiO2, and the formation of CaTiO3 and β-C2S was a concomitant process as the solution limit of TiO2 reached. The addition of 0.5% TiO2 and some addition of CaF2 (≤1.5%) would reduce the polymorph symmetry of C3S, while more addition of CaF2 and TiO2 would actualize the higher polymorph symmetry from M1 to R form. The IR spectra for the polymorphs (T3, M3, R + M3, R) became broader with the increase of the polymorph symmetry of C3S. The replacement of O2− by F− would not be interfered by the simultaneous introduction of titanium, a Ti2p 1/2 peak at 463.39 eV reflected the solution of titanium in the structure of C3S, and the defect reactions of the doped C3S with CaF2 and TiO2 were proposed. The doped C3S had a higher heat flow than the undoped C3S in the initial period, the more addition of CaF2 inhibited the initial hydration activity of C3S, while the addition of TiO2 improved the effect. The incorporation of TiO2 into the doped C3S aggravated the retardation effect caused by CaF2 on the hydration in the acceleration period. The dopant types displayed a more distinct effect than the types of C3S polymorphs on the hydration activity of C3S.

Hafnium silicate formation during oxidation of a permeable silicon + HfO2 powder composite system

Silicon bond coats, applied to silicon carbide composites used in gas turbine engines as a part of an environmental barrier coating (EBC) system, arrest the transport of oxidizing species to the SiC composite by forming a SiO2 thermally grown oxide. Above 1200°C, a crystalline ß-cristobalite SiO2 phase is formed that subsequently undergoes a large thermal contraction during its ß→α-cristobalite transformation upon cooling, leading to oxide layer cracking and eventual EBC delamination. A model system of silicon particles in a highly porous HfO2 particle matrix is used to investigate the rate and mechanism by which ß-cristobalite SiO2 is dynamically converted to hafnium orthosilicate (HfSiO4; Hafnon) when oxidizing silicon is in contact with m-HfO2. The study compares the net rate of SiO2 formation in the model silicon + HfO2 system with that on only silicon particles, and finds that the thickness of the SiO2 layer that forms during high temperature (1250–1316°C) oxidation can be greatly reduced by the hafnon formation reaction. The study also investigates the mechanism by which hafnon forms, and reports a SiO2 rumpling process when its outward (radial) growth is locally constrained by HfO2 particles. Since hafnon is phase stable over the temperature range of EBC interest, and has a thermal expansion coefficient similar to silicon, the dynamic conversion of SiO2 to hafnon provides a promising approach for controlling the delamination of EBC systems that use silicon bond coats.

Powder Metallurgical Processing of MMC Pressure Springs Based on Zirconia and TRIP Steel

A novel powder metallurgical fabrication technology for the development of springs based on metastable austenitic steel and magnesia partially stabilized zirconia is introduced. The developed gel casting technique uses the gelation of alginates in contact with bivalent ions and allows the variation of fabrication parameter such as composition of the starting slurry, wire thickness, coil number, and distance between the single coils. The starting slurry contains 16‐7‐3 (Cr–Mn–Ni) steel and zirconia powders as well as sodium alginate and is subsequently injected into a hardener solution to form rubbery strands that are subsequently coiled around a mandrel to form a spring element. Afterward a two‐stage thermal process is performed. The sintered spring elements are characterized by a homogeneous microstructure, and the formation of manganese silicate is registered. In comparison to commercially available coil springs, the developed spring elements show similar deformation behavior up to a deformation of 50%. The composition which contains 10 vol% zirconia and 90 vol% steel particles shows an improved energy absorption capability with 0.19 kJ kg−1 compared with commercially available springs with 0.11 kJ kg−1, and therefore offers the potential for further investigations in the planned application in the area of crash absorbing structures.

Investigation of synergy and inhibition effects during co-gasification of tire char and biomass in CO2 environment

This study investigates the co-gasification of tire char (TC), as a low-quality side-product of scrap tire pyrolysis, and rambutan peel (RP). The objective of this study was to comprehend any synergistic/antagonistic effects during the co-gasification of TC/RP. For this, co-gasification of TC and RP (85:15, 70:30, 50:50, 30:70, and 15:85 wt% of TC:RP) was conducted in CO2 environment by non-isothermal thermogravimetric method. The samples were heated (15 K/min) under N2 to 923 K and then under CO2 to 1400 K. Comparison of the observed and theoretical results indicated the incidence of antagonism in blends with high proportion of TC (e.g., 85%TC–15%RP and 70%TC–30%RP), possibly attributing to the high content of acid oxides (SO3 (30.1%) and SiO2 (24.8%)) in the TC-ash which could inhibit the gasification by formation of inactive silicates in the presence of alkali/alkaline earth metal-rich biomass. In blends with higher content of biomass (e.g., 30%TC–70%RP and 15%TC–85%RP), the actual gasification rates were higher than the theoretically predicted ones showing the presence of a synergism associated with the natural catalysts (K2O (40.6%) and CaO (42.3%)) in RP-ash. Activation energy and thermodynamic studies confirmed the profound effect of biomass on enhancing the reactivity of TC in reaction with CO2. These promoting effects of biomass were associated with its considerably higher alkali index (133.4) than tire (5.6), its less graphitic structure with more structural defects, and imperfections compared with TC. According to the results, the inherently low reactivity of TC in gasification can be accelerated by co-feeding of biomass with TC.

Electrical Characteristics of Atomic Layer Deposited Y-Silicate Dielectrics

Introduction High k dielectric materials are widely used for scaling the equivalent oxide thickness (EOT) of various very large integrated devices. Rare-earth silicates maintain their amorphous structure within the temperature range of typical semiconductor processes [1] , making them suitable for high-k dielectrics. Rare-earth silicates are easily formed by thermal processes, but their formation consumes Si at the interface. The consumption of Si at the interface is disadvantageous for micro-structured devices such as three-dimensional structures. One of the methods to suppress Si consumption at the interface is to supply Si atoms in the deposited film to form silicates without reacting with the channel material. In this work, we focused on the formation of yttrium silicate (Y-silicate) dielectrics, a typical rare-earth silicate [2] , so that the formation process can be easily extended to other rare-earth silicates, including La-silicate [3] .Y-silicate films were formed by cyclic deposition of Y2O3 and SiO2 based on atomic-layer deposition (ALD). Experiments Firstly, Y2O3/SiO2 multi-stacked layer（call it stacked-layer from now on）with a thickness of 16 nm without annealing process was analyzed by x-ray photoelectron spectroscopy (XPS) to confirm forming of Y-silicates. Next, MOS capacitor was fabricated by stacked-layer with a thickness 5 nm were deposited on the n-Si substrates by ALD at 200oC. Fig. 1 shows the schematic structure of the fabricated MOS capacitors. The cycles are determined to have the Y/Si atomic ratio of the stacked-layer to be 1:1. Then, W gate electrodes and TiN layer are deposited by RF sputtering. Al contact layers were deposited on the backside of the samples by thermal evaporation. The capacitors were then annealed at 800oC in forming gas (N2: H2=97%:3%) ambient for 30 min. [4] Finally, the metal-insulator-metal (MIM) capacitor, 10-nm-thick stacked-layer were also fabricated aim to no interfacial layer. Result Fig.2 shows the results of XPS analysis. The shift in the binding energy indicates that most of the Y atoms are in the form of silicate. Suggesting that the stacked layer is readily transformed in the form of Y-silicate during ALD process. The bandgap of the stacked-layer was estimated to be 6.4 eV. Fig. 3 shows the XPS depth profile of the stacked-layer obtained by Ar etching. The atomic ratio of Y, Si and O remained constant throughout the film at almost 2:2:7 until the Si substrate appeared. From the results, it is confirmed that a uniform Y2Si2O7 layer can be obtained by the multi-stacking of Y2O3/SiO2 ALD process. Fig. 4 shows the C-V characteristics of the n-Si capacitors with a 5-nm-thick Y-silicate layer. After annealing, the capacity of Y-silicate layer capacitor doesn’t increase. This result indicating little reaction at Y-silicate/Si interface. Finally, from the C-V and J-V measurements of MIM capacitor, A k-value of the stacked-layer is calculated to be 8.5, break down field of MIM capacitor is 6.6MV/cm. The k-value of the Y-silicate layer is also reasonable considering the k-values of SiO2 of 3.9 and Y2O3 of 13. [5] Conclusion Low temperature formation of Y-silicate layer has been confirmed by cyclic deposition of stacked-layer of Y2O3 and SiO2 ALD layers. The target composition of Y2Si2O7 and the formation of Y-O-Si bonds have been confirmed by XPS. Bandgap, breakdown field and k-value of Y-silicate dielectrics were determined to be 6.4eV, 6.6MV/cm, 8.5 respectively.

Effect of calcium to silica ratio on the synthesis of calcium silicate hydrate in high alkaline desilication solution

AbstractHigh alkaline desilication solution (DSS), a high volume byproduct from the pretreatment of high‐alumina fly ash, was used as low‐cost mother liquor for the synthesis of calcium silicate hydrate (C‐S‐H). Through the combined analysis of X‐ray diffraction, thermogravimetric analysis, X‐ray fluorescence, 29Si MAS NMR, and Brunauer‐Emmett‐Teller, the relationship between chemical composition and structure of C‐S‐H synthesized under Ca/Si of 0.83:1 to 2.0:1 was investigated. Silicon conversion and yield of product have a positive correlation with Ca/Si. Sodium uptake in C‐S‐H is inhibited as Ca/Si increases. The formation of sodium in C‐S‐H transfers from “bound Na” to “mobile Na” and aluminum from tetrahedrally coordinated Al (IV) to octahedrally coordinated Al (VI). The increase of Ca/Si leads to shortening of silicate chain and formation of more dimers, which causes more water bound in C‐S‐H. The mechanism of calcium addition on silicate chain obtained from DFT calculation primarily results from more interlayer calcium occurrence to affect bridging tetrahedron and cationic bounding states reorganization. Reasonable control for Ca/Si momentously contributes to the adjustment for composition and structure of C‐S‐H synthesized in DSS.