Reactions between sodium and silica during gasification of a low-rank coal

Laboratory experiments were conducted on samples of a prepared low-rank South Australian Lochiel coal, viz. Na⁺ ion-exchanged acid-washed and physical impregnation of NaCl samples, to study the influence of gas atmosphere on the reactions between sodium with silica during pyrolysis in nitrogen and gasification with steam or carbon dioxide. Additionally, samples of the reaction mixtures of sodium salts (sodium acetate and NaCl) and silica were made and exposed to the same reaction conditions. The characterisation of products has been quantified in terms of their water solubility in combination with mineralogical analysis (SEM, XRD). Sodium disilicate, Na₂Si₂O₅ was found to be the major reaction product formed under all three atmospheres and this is in agreement with thermodynamic equilibrium predictions. Na₂Si₂O₅ forms in a direct reaction between sodium carbonate (intermediate form of Na present in the coal) and solid silica. Steam is found to be the most important variable as it lowers the melting temperature of sodium carbonate and consequently, the temperature of formation of liquid sodium disilicate. Further silica can dissolve in the formed liquid silicates and increase the total mass of fused silicate glass. The liquid sodium silicates formed at 750 °C in steam, or at 850 °C in carbon dioxide or nitrogen, should be considered as a potential source for bed agglomeration and defluidisation during fluidised bed gasification of coal.     

Preparation and characterization of a porous silicate material from silica fume

A porous silicate material derived from silica fume was successfully prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, Thermogravimetry and Differential thermal gravity (TG-DTG), N₂ adsorption and desorption isotherms, and scanning electron microscopy (SEM). Raw silica fume was analyzed by XRD, FT-IR and SEM. The analysis results of silica fume indicated that SiO₂ in silica fume is mainly determined as amorphous state, and that the particles of raw silica fume exhibited characteristic spherical structure with a diameter of from 50 nm to 200 nm. The preparation of the porous silicate material involved two steps. The first step was the extraction of the SiO ₃ ^2? leachate from raw silica fume. The maximum value of SiO ₃ ^2? extraction yield was obtained under the following conditions: reaction temperature of 120 °C, reaction time of 120 min, NaOH concentration of 15%, and alkali to SiO₂ molar ratio of 2. The second step was the preparation of the porous silicate material though the reaction of SiO ₃ ^2? leachate and Ca(OH)₂ suspension liquid. The optimum preparation conditions were as follows: preparation temperature of 90 °C, preparation time of 1.5 h, Si/Ca molar ratio of 1 : 1, and stirring rate of 100 r/min. The BET surface area and pore size of the porous silicate material were 220.7 m²·g^?1 and 8.55 cm³/g, respectively. The porous silicate material presented an amorphous and unordered structure. The spectroscopic results indicated that the porous silicate material was mainly composed of Si, Ca, O, C, and Na, in the form of Ca²⁺, SiO ₃ ^2? , CO ₃ ^2? and Na⁺ ions, respectively, which agreed with the XRD, TG-DSC, and FT-IR data. The N₂ adsorption-desorption isotherm mode indicates that the porous silicate material belonged to a typical mesoporous material. The porous silicate material presented efficiency for the removal of formaldehyde: it showed a formaldehyde adsorption capacity of 8.01 mg/g for 140 min at 25 °C.     

熔盐法从铁尾矿中制取高纯白炭黑

以铁尾矿和NaOH为原料、NaNO₃为熔盐,在500℃下煅烧3 h,使铁尾矿中的惰性SiO₂转变成活性的硅酸钠相。以浸取硅酸钠溶液作为硅源,利用化学沉淀法成功制备了无定形白炭黑。用X射线衍射仪、红外光谱仪、透射电镜和X射线荧光光谱仪对制取白炭黑的物相结构、粒度形貌和成分含量进行分析。结果表明：白炭黑产品中的SiO₂纯度为99.3%,化学结构为无定形的水合二氧化硅,形貌近似为球状粒子,粒径在100 nm左右。白炭黑的比表面积 (BET)为152 m² •g^-1。     

Influence of portlandite on Pyrex glass dissolution and the formation of alkali‐silica chemical reaction products

The dissolution behavior of Pyrex glass in a model system consisting of 1‐M NaOH with varying amounts of portlandite, representing the glass dissolution in alkaline environment and alkali‐silica reaction (ASR) in cementitious materials, is studied. The Pyrex glass dissolution and the reaction products were characterized using X‐ray diffraction (XRD), ²⁹Si nuclear magnetic resonance (²⁹Si‐NMR), and scanning electron microscopy with energy dispersive X‐ray (SEM/EDX), and the silica and calcium concentrations in the liquid phase were determined using inductively coupled plasma atomic emission spectroscopy (ICP‐AES). The experimental results show that the dissolution of the Pyrex glass continued until it consumed the portlandite and then reached a constant rate, with a linear relationship with the amount of portlandite. The absence of calcium and reduction of silica concentration in the liquid phase with the increase in portlandite indicate the formation of high‐reaction products with portlandite, confirmed by XRD and ²⁹Si‐NMR. The calcium sodium silicate hydrate (C–N–S–H) and sodium silicate hydrate (N–S–H) are the main ASR products; their composition and proportions strongly depend on the reaction time and the amount of portlandite added. A thermodynamic model, which couples geochemical code (PHREEQC) and the experimental silica dissolution rate, was used to predict ASR products and the remaining portlandite. The simulation results predicted the experimental data fairly well for different portlandite additions. The mechanism for Pyrex glass dissolution in the presence of varying portlandite additions is discussed with regard to experimental data and simulation results.     

High temperature thermochemical and thermophysical transformation of porcellanite

Abstract

Currently there is interest in Trinidad porcellanite as a potential raw material for ceramic applications. Thus, XRD and SEM techniques have been used in the present work to study high temperature thermochemical and thermophysical transformations in powder compacts of the rock type. Mineralogically, XRD showed that in the as mined state the porcellanite studied was comprised mainly of leucite (potassium aluminium silicon oxide), potassium silicate, and silica. On firing in the temperature range 1150-1350°C, the leucite dissociated into mullite and potassium silicate. Further, on firing at or above 1225°C, the compacts fused as a result of fusing of the alkali (potassium) silicate. SEM techniques showed that the resultant microstructure of the fused compacts was comprised predominantly of silica particles embedded in a dense matrix composed of mullite and potassium silicate.     

The chemistry of ‘alkali-aggregate’ reaction

To clarify ideas about the alkali aggregate reaction, the reaction between sodium hydroxide and various forms of silica has been studied. Variations with time in the sodium, hydroxyl and silica concentrations in solution have been followed and the volume change of solid silica immersed in solution has been measured.If the silica is an absorbant and reactive form such as silica gel, there is an immediate drop in both sodium and hydroxyl concentrations. Subsequently, as the silica dissolves, sodium concentration rises again. Both the final concentration of dissolved silica and the volume expansion of solid silicate pass through a maximum at an intermediate total Si0₂/Na₂0 mole ratio.     

Sustainable activation of pumice with partially variable substitutions of metakaolin and/or fumed silica

Sustainable alkali activation of pumice from Turkish origin was studied by a partial replacement of metakaolin and/or fumed silica additives. Following the characterization of as-received pumice by X-ray fluorescence spectroscopy, x-ray diffraction, and nuclear magnetic resonance spectroscopy, a series of powder mixtures were prepared by introducing metakaolin and/or fumed silica (8, 14, and 20 M) into 1 M of the pumice. The mixtures were then dissolved in 11 M NaOH or sodium silicate solutions. The slurries were poured into polyacetal molds to obtain geopolymer samples for mechanical testing and cured in a constant 50°C temperature in a humidity oven for 48 h and then left for 1 week to undergo additional curing at ambient temperature. The microstructural, mechanical, and thermal properties of the final geopolymer samples were determined by XRD, scanning electron microscopy, Weibull analysis of 3-point flexural and compressive tests and thermal conductivity measurements. Results showed that all the Weibull values were best for 14 M of metakaolin and/or fumed silica. The metakaolin-added pumice yielded higher compressive strengths of (53.78 ± 33.30 MPa) than fumed silica (10.87 ± 4.04 MPa) and fumed silica plus metakaolin (41.22 ± 5.16 MPa). Thermal conductivities (0.19–0.46 Wm^–1K^–1) were also comparable to the thermal conductivity of metakaolin-based geopolymers.     

Effect of synthesis procedure on carbonation of calcium‐silicate‐hydrate

Carbonation of synthesized calcium‐silicate‐hydrate (C–S–H) is difficult to avoid and can have significant impact on the molecular structure. Considerable carbonation was observed in C–S–H synthesized from the double decomposition of sodium silicate and calcium nitrate solutions but not in C–S–H synthesized from the direct reaction of fumed silica and calcium hydroxide solution. In order to isolate the cause of the greater carbonation in C–S–H synthesized by double decomposition, carbonation was induced in phase‐pure C–S–H by reaction with four different water‐based solutions containing dissolved CO₂ with varying pH and alkali content. Powder X‐ray diffraction, thermogravimetric analysis, and ²⁹Si nuclear magnetic resonance were used to probe the carbonation and the resulting changes in molecular structure. The pH of the solution was seen to strongly influence the degree of carbonation, while the alkali content had much less effect.     

Alkali Activation of AOD Stainless Steel Slag Under Steam Curing Conditions

Crystalline argon oxygen decarburization slag, in powdery form, was investigated for its hydration potential by alkali activation and curing at 80°C. Na‐silicate and K‐silicate of the same modulus were used as activators. Isothermal calorimetry at 80°C indicated exothermic reactions in the slag pastes. When the slag mortars were cured under steam at 80°C appreciable gain in compressive strength was measured. This was attributed to C–S–H which was detected in TG, FTIR, and ²⁹Si NMR analyses. Upon hydration at 90 d, the amount of crystalline phases decreased, whereas the XRD amorphous content in the slag increased. Electron microscopy showed the formation of different morphologies of reaction products depending on the alkaline activator employed. Presence of reaction rims around the crystalline phases with a major presence of Ca, Si, and O in the reacted matrix was observed in elemental maps.     

白炭黑制备工艺对比表面积和吸油值的影响

利用正交设计安排实验，在超重力旋转床中，采用硫酸沉淀法制备超细白炭黑，研究实验制备工艺条件pH、硅酸钠浓度、温度、电解质和旋转床转数以及不同干燥方式对白炭黑的BET比表面积和DBP吸油值的影响。实验结果表明，反应终止时pH对白炭黑的BET比表面积影响最大，其次是温度、电解质、硅酸钠的浓度和旋转床的转数。干燥方式是影响DBP吸油值的决定性因素，其次是温度、电解质、旋转床的转数、硅酸钠的浓度和反应终止时pH。制得产品的BET比表面积140～351m^2／g，DBP吸油值1．42-4．41mL/g。     

水羟硅钠石的制备与表征

水羟硅钠石（kenyaite）以其良好的离子交换性、吸附性和热稳定性而被广泛应用于催化和吸附等领域。本文以高纯度且价格低廉的沉淀白炭黑为硅源、以碳酸钠（分析纯）和氢氧化钠（分析纯）为碱源,水热法制备了高纯度的单一晶相的水羟硅钠石,考察了反应时间和反应温度对制备的影响。利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、红外光谱仪（IR）、X射线荧光光谱仪（XRF）和同步热分析仪等对样品进行了测试表征。实验结果表明,温度是影响kenyaite制备的主要因素,单一晶相水羟硅钠石的最佳晶化合成条件为晶化温度为180℃,晶化时间为24h,所制备的水羟硅钠石形态为玫瑰花形且其热稳定性在350℃以下。     

Silica-Supported Cobalt Catalysts for Fischer–Tropsch Synthesis: Effects of Calcination Temperature and Support Surface Area on Cobalt Silicate Formation

Cobalt silicate formation reduces the activity of the catalyst in Fischer–Tropsch synthesis (FTS). In this article, the effects of calcination temperature and support surface area on the formation of cobalt silicate are explored. FTS catalysts were prepared by incipient wetness impregnation of cobalt nitrate precursor into various silica supports. Deionized water was used as preparation medium. The properties of catalysts were characterized at different stages using FTIR, XRD and BET techniques. FTIR-ATR analysis of the synthesized catalyst samples before and after 48 h reaction identified cobalt species formed during the impregnation/calcination stage and after the reduction/reaction stage. It was found that in the reduction/reaction stage, metal-support interaction (MSI) added to the formation of irreducible cobalt silicate phase. Co/silica catalysts with lower surface area (300 m²/g) exhibited higher C₅₊ selectivity which can be attributed to less MSI and higher reducibility and dispersion. The prepared catalysts with different drying and calcination temperatures were also compared. Catalysts dried and calcined at lower temperatures exhibited higher activity and lower cobalt silicate formation. The catalyst sample calcined at 573 K showed the highest CO conversion and the lowest CH₄ selectivity.     

粉煤灰碱溶脱硅液碳化法制备白炭黑的实验与硅酸聚合机理研究

以陕西某热电厂粉煤灰碱溶脱硅液为原料,采用碳化法工艺制备白炭黑.通过正交实验和单因素实验,得到了碳化的优化条件为:实验反应温度85℃,CO2通气速度500 ml·min-1,偏硅酸钠滤液的浓度17.8°Bé,搅拌速度100 r· min-1,反应时间2.5h.采用普通干燥方法,制备了白炭黑制品BTH-01,达到GB10...     

Synthesis of hexagonal and cubic mesoporous silica using power plant bottom ash

An alkali fusion method was adopted to extract silicate species from coal bottom ash in a power plant and the supernatant solution was used for the synthesis of MCM-41, SBA-15, and SBA-16 mesoporous silica materials. The minor impurities present in the bottom ash were not found to be detrimental to the successful formation of mesoporous silica phases. Additional silica from sodium metasilicate was introduced to improve the textural properties for SBA-15 and SBA-16. According to SEM analyses, particle morphology of the samples gradually approaches those prepared using pure chemical as the amount of external silica source increases. XRD analyses confirmed well-ordered mesostructures in all of these silica materials. N₂ adsorption–desorption isotherms of MCM-41 prepared using bottom ash showed a type IV isotherm with a region of steep increase due to capillary condensation, whilst SBA-15 and SBA-16 showed type IV isotherm with H1 and H2 hysteresis loops, respectively. ²⁷Al MAS NMR analysis of MCM-41 synthesized from the supernatant solution reveals that the extracted Al species from bottom ash were tetrahedrally incorporated in the framework. TEM clearly showed the uniform pore structure of the materials prepared using the industrial waste.     

Transformation of silica fume into chemical mechanical polishing (CMP) nano-slurries for advanced semiconductor manufacturing

Silica nanoparticles have been synthesized from silica fume using alkali dissolution–precipitation process. The dissolution efficiency of 99% at a temperature of 80 °C and a time of 20 min was achieved. Sodium silicate solution was obtained by dissolving the fume with NaOH solution. Then, silica nanoparticles were precipitated using sulfuric acid. Silica nanoparticles (175 nm) were achieved using 12% sulfuric acid at pH 7 and 200 ppm sodium dodecyl sulfate (SDS). The silica morphologies appeared as a spherical shape with narrow particle size distribution. The silica samples were used for the formulation and testing of chemical mechanical polishing (CMP) slurries. The morphology of the polished wafer surface and its roughness were examined by atomic force microscope (AFM).The results indicated that the surface roughness was greatly improved after application of CMP. It was found that the surface roughness of the polished wafer is 0.226 nm at an applied pressure of 7 psi. The removal rate was found to be 1200 Å. These values confirm the quality of polished wafers.     

The effects of hydrothermal and thermal treatment on structure of Ni (or Co)-mesoporous molecular sieves

Ni (or Co)-mesoporous molecular sieve was hydrothermally synthesized from sodium silicate, nickel chloride or cobalt chloride. Cetyltrimethyl ammonium bromide (CTAB) was used as a template. The samples were characterized by means of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature programmed reduction (TPR), Fourier transform infrared spectrosocopy (FT-IR) and N₂ physical adsorption. The results show that the long-range ordered Ni (or Co)-mesoporous molecular sieve was synthesized. The as prepared Ni-mesoporous molecular sieve has a specific surface area of 753 m²/g and an average pore size of 3.23 nm, and the pore structure of the as prepared Ni-mesoporous molecular sieve still existed after calcination at 750°C for 3 h or hydrothermal treatment at 100°C for 5 days. On the other hand, the as prepared Co-mesoporous molecular sieve has a specific surface area of 744 m²/g and an average pore size of 4.44 nm. The as prepared Co-mesoporous molecular sieve was transformed into wormhole-like mesoporous structure after calcination at 650°C or hydrothermal treatment at 100°C for 5 days and the mesoporous ordering became very poor after calcination at 750°C for 3 h.     

原位法制备沉淀白炭黑／NR纳米复合材料的研究

以硅酸钠为前驱体,在天然胶乳凝固制备天然橡胶（NR）的过程中,原位生成沉淀白炭黑来制备沉淀白炭黑／NR纳米复合材料,扫描电镜（SEM）研究表明该方法可以成功得到沉淀白炭黑／NR纳米复合材料,物理机械性能研究表明沉淀白炭黑对NR有较好的补强作用,在纳米沉淀白炭黑用量为8份时复合材料的综合性能最好。     

竹浆厂除硅工艺技术的探索

为解决竹材在硫酸盐法蒸煮过程中硅与氢氧化钠反应生成硅酸钠而进入蒸煮黑液,导致碱回收系统一系列的“硅干扰”问题,通过在硫酸蒸煮过程中添加偏铝酸钠、氧化钙、硫酸铝留硅剂和在预苛化过程中添加铝盐除硅剂可降低或解决“硅干扰”对竹浆制浆的影响。     

赤泥制备水玻璃工艺研究

为了提取利用赤泥中的硅元素,实现赤泥的资源化,同时为水玻璃的制备寻找一种新原料。本文以中铝山西新材料有限公司两组分赤泥为研究对象,通过化学分析法、XRD对赤泥进行了化学组成及矿物组成分析。表明该赤泥中二氧化硅含量较高且都为非晶态,反应活性高,为制备水玻璃的理想硅源。对赤泥进行酸浸可得到纯度为92%的硅胶。硅胶湿法制备水玻璃最佳工艺参数为NaOH质量浓度15%,液固质量比3,体系温度95 ℃,反应时间为15 min。经实验验证,最佳参数下的二氧化硅溶出率可达91%,对该赤泥中硅的利用率达84.6%。该研究可为赤泥资源化和水玻璃原料选取提供新的思路和依据。     

Nostoc calcicola Immobilized in Silica-coated Calcium Alginate and Silica Gel for Applications in Heavy Metal Biosorption

The present study reports the preparation and characterization of silica-based immobilization matrices for the purpose of metal accumulation using immobilized cyanobacterium Nostoc calcicola. Silica gel was prepared using aqueous sodium silicate and colloidal silica. Calcium alginate (CAG) beads were coated with silica using sodium silicate solutions. Microscopy observations and TTC tests confirmed that the immobilized cells were intact and viable. Ultrastructural studies with electron microscopy revealed a membrane thickness of approximately 10 μm around the CAG and the silica gel to be of mesoporous nature. BET surface area of silica gel-immobilized N. calcicola was 160 m² g^?1. The porous volume and average pore diameter were 0.40 cm³ g^?1 and ca. 100 Å, respectively, as calculated using the BJH model. Studies on silica-coated calcium alginate immobilized cells showed that these were superior to the uncoated CAG beads in terms of mechanical strength and metal accumulation. The silica matrices were found to be stable for repeated cycles of metal removal and with commonly used eluants for desorption processes. These matrices have potential applications in immobilization of industrially important biocatalysts.