Variation of Width and Composition of Grain-Boundary Film in a High-Purity Silicon Nitride with Minimal Silica

Contrary to the widely accepted observation that grain-boundary amorphous films for a given Si₃N₄ composition have common (equilibrium) widths and compositions, a significant variation for both parameters from film to film was observed in an undoped high-purity Si₃N₄ prepared using a hot isostatic pressing method. This material previously has been reported to have an equilibrium film width of 0.6 nm, as measured using a high-resolution electron microscopy (HREM) method; this value is significantly different from that which is typical for other high-purity Si₃N₄ ceramics (1.0 nm). A total of four boundaries were analyzed, using spatially resolved electron energy-loss spectroscopy methods, which can give the chemical width and composition for the film. Widths of these grain-boundary films were substantially different from each other; only the thinnest matches the previous HREM observations. The nitrogen content in the film decreased concurrently as the film thickened. This material had many cavities and complicated configurations at triple pockets, because of the very low total-SiO₂ content (0.55 vol%). They created locally different equilibrium conditions for grain-boundary films, in comparison with other fully densified Si₃N₄, causing such strong variation in both film structure and chemistry. This observation reveals the importance of triple pockets in equilibrium film structures, providing new insight in evaluating the absorption and wetting models. The thinnest film may correspond to the amorphous structure that is required to bind two randomly oriented Si₃N₄ grains under greater local stress.     

不同处理方法对冶金硅系产业回收微硅粉结构组成的影响

为研究不同处理方法对微硅粉结构组成、元素存在状态的影响,以冶金硅系产业回收微硅粉为原料,采用水洗磁选、水流分级、微波酸浸、700℃煅烧自然冷却、700℃水淬急冷、800℃煅烧自然冷却、800℃水淬急冷对微硅粉进行实验处理,得到了不同处理条件下的微硅粉样品.通过XRD、SEM、TEM、XPS对微硅粉样品物相组成、微观形貌和元素存在状态进行了表征分析.结果表明:水洗磁选、水流分级和微波酸浸处理微硅粉只去除了微硅粉中部分Fe3 O4、游离碳和金属氧化物杂质;高温煅烧微硅粉改变了微硅粉结晶状态,在800℃时,微硅粉由无定形的玻璃相转化为方石英相.通过对微硅粉元素拟合分析,发现微硅粉中除含有SiO2外,还有化合物(SiO2)0.694(Na2 O)0.306、(K,Ca)2[Mg4.3 Fe0.7][Si7.2 Al0.8 O22](OH)2、Mg3 H2(SiO3)4,并存在少量CaO、MgO等矿化剂.     

The Reduction of Silica with Carbon and Silicon Carbide

In the presence of carbon or silicon carbide, silica can be reacted to form a vapor of silicon monoxide. The rates of these reactions were explored at 1300° to 1550°C. For mixtures of carbon and silica, evidence supported a two-step reaction: silicon carbide formed prior to reaction between silicon carbide and silica.     

Fabrication of Biogenic Silica Nanostructures from Sorghum bicolor Leaves for Food Industry Applications

Silicon - Due to the large production of sorghum, the generation of associated agricultural residues, which contain high contents of silica, is inevitable. Also, these agricultural residues are not...     

有机硅/二氧化硅溶胶制备超疏水表面

材料超疏水是由其表面的化学组成及微观结构共同作用的结果,使其在工业和日常生活有重要的应用前景。文章用甲基三甲氧基硅烷(MTMS)、丙基三甲氧基硅烷(PTMS)和二苯基二甲氧硅烷(DPDS)与二氧化硅溶胶颗粒共聚,用喷涂法可制得对水接触角高达155°,滚动角低达1°,同时附着力达二级的超疏水材料。     

Potential for use of crushed waste calcined-clay brick as a supplementary cementitious material in Brazil

The Brazilian ceramic industry generates large amounts of calcined-clay waste. This paper examines the factors that influence its potential for use as a partial replacement of Portland cement. Superplasticized mortars of equal workability containing ground crushed waste calcined-clay brick (GCWCCB) in the proportions of 10, 20, 30 and 40% as a cement replacement were analyzed through mechanical tests, pore structure characterization and durability tests. The results indicated the optimal percentages of substitution lies between 10% to 20%. The potential reduction of CO₂ emissions could be as high as 10% of current Brazilian cement industry emissions if this approach were to be fully implemented, and it could be eligible for “Clean Development Mechanism” credits under Kyoto protocol.     

通信光纤原料SiCl4提纯方法

四氯化硅是生产石英通信光纤的主要原料,但粗四氯化硅中含有多种杂质,直接影响光纤的损耗特性。为保证光纤具有低损耗,必须对粗四氯化硅进行提纯,最大限度地脱除这些引起光纤吸收损耗的杂质。介绍了精馏法、吸附法、部分水解法及络合法等多种四氯化硅提纯方法,指出了各种方法的优缺点。     

Silica nanoparticles as a tool for fluorescence collection efficiency enhancement

In this work we demonstrate enhancement of the fluorescence collection efficiency for chlorophyll-containing photosynthetic complexes deposited on SiO₂ spherical nanoparticles. Microscopic images of fluorescence emission reveal ring-like emission patterns associated with chlorophyll-containing complexes coupled to electromagnetic modes within the silica nanoparticles. The interaction leaves no effect upon the emission spectra of the complexes, and the transient behavior of the fluorescence also remains unchanged, which indicates no influence of the silica nanoparticles on the radiative properties of the fluorophores. We interpret this enhancement as a result of efficient scattering of electromagnetic field by the dielectric nanoparticles that increases collection efficiency of fluorescence emission.     

磷肥副产含硅化合物制取高纯二氧化硅的研究综述

高纯二氧化硅属于高性能无机硅材料,已广泛应用于许多高新技术领域。本文简要介绍了国内外磷肥副产物制取高纯二氧化硅的研究情况,着重论述了由氟硅酸和氟硅酸钠制备高纯二氧化硅的具体工艺,并对磷肥副产物制取高纯二氧化硅的前景进行了扼要展望。     

硫酸钠/氧化硅复合定形相变材料的溶胶凝胶法制备和表征简

A sodium sulfate （NaeSO4）/silica （SiO2） composite was prepared as a shape-stabilized solid-liquid phase change material by a sol-gel procedure using Na2SiO3 as the silica source. Na2SO4 in the composite acts as a latent heat storage substance for solid-liquid phase change, while SiO2 acts as a support material to provide structural strength and prevent leakage of melted NazSO4. The microstructure and composition of the prepared composite were characterized by the N2 adsorption, transmission electron microscope （TEM）, scanning electron microscope （SEM）, Fourier transform infrared spectroscopy （FTIR） and X-ray diffraction. The results show that the prepared Na2SOJSiO2 composite is a nanostructured hybrid of NazSO4 and SiO2 without new substances produced during the phase change. The macroscopic shape of the NazSO4/SiO2 composite after the melting and freezing cycles does not change and there is no leakage of Na2SO4. Determined by differential scanning calorimeter （DSC） analysis, the values of phase change latent heat of melting and freezing of the prepared NazSO4/SiO2 （50%, by mass） composite are 82.3 kJ.kg i and 83.7 kJ.kg-1, and temperatures of melting and freezing are 886.0 ℃ and 880.6 ℃, respectively. Furthermore, the Na2SOJSiO2 composite maintains good thermal energy storage and release ability even after 100 cycles of melting and freezing. The satisfactory thermal storage performance renders this composite a versatile tool for high-temperature thermal energy storage.     

Optimal Composition of Zircon–Fused Silica Ceramic Cores for Casting Superalloys

The dependence of flexural strength on crystalline phase content, residual porosity, and sintering temperature has been investigated for ceramic cores based on a mixture of fused silica and zircon. The rule of binary particle mixture, adopted for three particle sizes of fused silica, predicts a critical weight fraction of fine (zircon) particles of 46.9 wt% for the best packing. However, the optimal composition of a 37.8 wt% zircon–fused silica mixture for the flexural strength of ceramic cores found experimentally is lower in zircon content. The content of α-cristobalite +α-quartz crystallized from infilling silica sols exceeds ∼3 wt% when the strength decreases from ∼10 MPa to ∼6 MPa in samples sintered at 899–927°C. The degradation is ascribed to microcracking and the loss of coherency between the fused silica grains and the infilled silica due to β- →α-phase transformation on cooling and differential densification during sintering.     

The use of a densitometer as a detector for gel permeation chromatography

A commercially available densitometer, DMA 60 (Anton Paar, Austria), in combination with a Model DMA 602-W flow cell was used as a detector in a Waters Model 200 GPC equipped with differential refractive index and ultraviolet absorbance detectors. The density measuring cell was thermostatted to ±0.004°C and the sample injection concentration was 1.5 mg/mL. Polystyrene samples of molecular weights ranging from 9000 to 860,000 were used. The optimum period was found to be 10,000 oscillations, a setting which gave good resolution and a sufficient number of data points to define the chromatogram. The molecular weight averages calculated using the density outputs compared well with those obtained through the conventional UV detector. A sliding average technique was applied to the densitometer data for reducing the baseline noise. It was found that concentrations as low as 1.0 mg/mL (≈0.114%) could be used to obtain densitometer chromatograms that yield molecular weight averages comparable to those obtained from the ultraviolet detector. This densitometer thus appears suitable to be used as an additional GPC detector for routine analyses.     

Potential use of natural perlite powder as a pozzolanic mineral admixture in Portland cement

This paper investigates the effect of incorporating natural perlite powder (NPP) as a cement replacement on cementitious materials properties. For this purpose, cement pastes and mortars were prepared by replacing 5, 10, 15, and 20% of NPP by mass of the Portland cement. Physicomechanical performances of pastes and mortars based NPP were inspected using normal consistency, setting times, heat of hydration, and compressive strength testing. Resistance against sodium sulfate attack and sulfuric acid attack were also assessed to investigate the durability characteristics of different mortar mixes. Experimental results show that cement pastes and mortars incorporating up to 20% of NPP demonstrate satisfactory physical and mechanical properties with very comparable results to cementitious materials without NPP. In addition, improved sulfate and acid attacks resistance with increased NPP content were demonstrated. The X-ray diffraction analyses confirm that NPP can be considered as a good pozzolanic material that can be used satisfactorily as a mineral admixture in cement production.     

Preparation and Application of Faujasite-Type Y Zeolite-based Catalysts for Coal Pyrolysis using Sodium Silicate Solution and Colloidal Silica as Silicon Source

Using zeolites as catalysts of coal pyrolysis for production of valuable chemical compounds such as aromatics is being widely investigated and has shown promising results. In this study, pure faujasite-type Y zeolite crystals were successfully synthesized by a direct hydrothermal method with sodium silicate solution and colloidal silica as the silicon sources, without any seeding gel. A novel approach was adopted to directly synthesize zeolites impregnated with nickel oxide. Moreover, a batch reactor was designed to increase the silica/alumina ratio (SAR) of the zeolites by dealumination process without causing significant damage to the zeolite structure. The various analysis methods were employed to characterize the parent and modified zeolites, and the fabricated zeolites were applied in coal pyrolysis experiments. The results are presented in order to show the catalytic performance of the faujasite-type Y zeolites for application in coal pyrolysis process.     

The Effect of Silica and Reducing Agent on the Contents of Impurities in Silicon Produced

Silicon - Petroleum coke, soft coal and silica are the main raw materials used to produce silicon, and impurities in them remarkably influence the purity of silicon products. Two different furnace...     

Isotope labelling as a probe for free-radical reactions during dibenzyl ether thermolysis

Pyrolysis of dibenzyl ether (DBE) in tetralin-d₁₂ allowed discrimination between possible free radical and concerted reaction mechanisms. Pyrolysis product spectra contained both α-deuteriotoluene and perprotiotoluene, relative fractions of which were determined, by complementary ¹H and ¹³C n.m.r. analyses, to vary with the initial ratio of tetralin-di₁₂ to DBE. Mathematical extrapolation to DBE pyrolysis at infinite dilution indicated that its thermolysis in tetralin-d₁₂ was entirely via free radical mechanisms.     

The use of calcined serpentine as a cement

Calcined serpentine rock, a magnesian silicate hydrate, when ground to cement fineness will act as a hydraulic binder. Tests on 1:3 cement sand mortars showed that the strength development was slow and low; at one year the strength was 3.3 Pa. Mineralogical analyses have shown that heating to 640°C produces a disorganised semi-amorphous material which reacts with water to form a new magnesium silicate hydrate akin to saponite which acts as the binding agent.