稻壳基白炭黑的制备研究

以炭化稻壳为原料,Na2CO3为活化剂,采用沉淀法对稻壳基白炭黑的制备工艺进行了研究.结果表明沉淀法制备白炭黑的最佳工艺条件为:反应温度100℃,Na2CO3溶液浓度为13％(w/w),稻壳灰与Na2CO3溶液质量配比为1:40,反应时间4h,提取率可以达到93％以上.整个工艺流程中,Na2CO3溶液循环回用,有利于工业化放大,产品的相关质量检测均符合国家标准.     

Synthesis and characterization of high-purity silica nanosphere from rice husk

The work reports the synthesis, characterization, and the properties of high-purity silica nanospheres from low-cost rice husk. Primarily, the rice husk was washed with distilled water (DW) and subjected to acid leaching to remove the impurities. The treated rice husk was annealed at different temperatures (620 and 900 degrees C) for varied time periods to achive the desirable silica nanospheres. The annealing temperature and time considerably affected the properties of the synthesized silica nanospheres. The morphology studies confirmed that the size of nanospheres were of approximately 50-60 nm. The photoluminesence studies revealed that the synthesized silica nanospheres showed less structural defects and good optical properties. On the basis of the formation and the characterization of silica nanospheres a possible mechanism was suggested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis confirmed that the synthesized silica nanospheres contained approximately 99.93% purity.     

Coral-like hydroxy sodalite particles from rice husk ash as silica source

Coral-like hydroxy sodalite (HS) particles were prepared from rice husk ash as silica source in the presence of other aqueous-based precursor materials following a simple process under hydrothermal condition at 90 °C for 15 h. The particles obtained at 90 °C for different times (6, 10 and 15 h) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). The HS crystals along with a small amount of zeolite A particles were observed at 90 °C/6 h while phase pure HS particles were obtained at 90 °C for 10 and 15 h. The characteristic vibration bands of the HS particles were confirmed by FTIR spectroscopy. FESEM images showed that the HS particles obtained at 90 °C/15 h were coral-like morphology which were formed through the self-assembly of the smaller particles generated at the initial stage of reaction (6 and 10 h) under the same experimental conditions. A proposed mechanism for the formation of coral-like HS particles was also illustrated.     

Composition and structure of amorphous silica produced from rice husk and straw

We have studied amorphous silica samples prepared by a thermal method and precipitation from rice processing waste: straw and grain shells (husk and peelings). We have determined their true and bulk densities, silica content, and sorbed water vapor content. The porosity of the samples has been evaluated by different techniques: nitrogen desorption (Barrett-Joyner-Halenda method) and adsorption (BET analysis), water vapor adsorption, sorption of organic dyes (methylene blue and brilliant green), and positron annihilation spectroscopy. The effect of the nature of raw materials and processing procedure on the physicochemical properties of amorphous silica is examined.     

Short-period synthesis of high specific surface area silica from rice husk char

Porous silica with high specific surface areas is prepared from rice husk char within a short period by avoiding the commonly used hydrothermal treatment step and using polyethylene glycol (PEG, molecular weight = 20,000) as a template. The preparation process mainly involves sodium silicate production, precipitation with ortho-phosphoric acid, and calcination. The amount of used PEG significantly affects the silica textural properties like the specific surface area, total pore volume and mesopore volume. The reason should be attributed to the amount of PEG removed from the PEG-silica composites by calcination. By varying the PEG dosage from 100 to 176 mg, porous silica with specific surface areas ranging from 709 to 936 m²/g could be successfully prepared within 10 h.     

Preparation of an efficient humidity indicating silica gel from rice husk ash

An efficient humidity indicating silica gel was prepared using rice husk ash as a raw material via sodium silicate extraction and acid neutralization method. Cobalt chloride was impregnated into the silica gel as a colour indicating material. A low concentration of cobalt chloride solution (0·0005 mol dm^?3) was used for the impregnation. The effect of pH of the impregnating solution on the colour development behaviour of the gel was investigated. The specific surface area of the gel was determined by Brunauer-Emmett-Teller method. The gel has been characterized using X-ray diffraction, scanning electron microscopy and visible spectroscopy. The moisture adsorption and desorption kinetics of the desiccant were evaluated using simultaneous thermogravimetry and differential scanning calorimetry.     

High-purity nano silica powder from rice husk using a simple chemical method

A highly pure, small particle-sized and high surface area nano silica powder was prepared from rice husk using alkali extraction, followed by an acid precipitation method. The composition, phase, morphology, size and surface area of the as-synthesised nano silica powder was investigated by energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, particle size analyser and BET surface area analyser. High-purity nano silica powder was obtained by sodium hydroxide (NaOH) purification treatment (0.5, 1, 1.5, 2 and 2.5?N). The high purity of silica (～99.9%) was obtained at 2.5?N NaOH treatment. The pure nano silica powder that is obtained shows an average particle size of ～25?nm with a high-specific surface area (SSA) of 274?m²?g^?1, with an average pore diameter of 1.46?nm.     

Permeation of solvents through disk type rice husk silica membrane modified with alkyl silylation reagents

Rice husk silica (RHS) which was obtained with thermal treatment of rice husk has the size of approximately 10 micrometer with 4-5 nm pore. RHS can be mold to a disk type membrane. The membrane may have submicron pore originated from the space among the particles, and the nano pores of the rice husk silica (RHS pore). Even it is difficult to adjust the size of the pores, we can suggest that the membrane shows different permeability for the organic/inorganic solvents if the affinity between the surface of the pores and the permeating molecule is changed. In this study, we investigated the permeation of the typical solvents such as water, ethanol and toluene to the RHS membranes sintered at 1100 degrees C, 1150 degrees C and 1200 degrees C and modified with triethoxymethyl silane (CH3)Si(C2H5O)3, diethoxydiemethyl silane (CH3)2Si(C2H5O)2 and ethoxytriemethyl silane (CH3)3Si (C2H5O). The result showed that permeability of original membranes for water (e.g., 1100 degrees C, 2.87 x 10(-3) mol/m2 s Pa) was larger than ethanol (1100 degrees C, 5.51 x 10(-4) mol/m2 s Pa) and toluene (1100 degrees C, 3.09 x 10(-4) mol/m2 s Pa) at the sintering temperatures. For the silane modified membranes, the permeability for water decreased drastically while those for ethanol and toluene increased.     

A sustainable route for the preparation of activated carbon and silica from rice husk ash

An environmentally friendly and economically effective process to produce silica and activated carbon form rice husk ask simultaneously has been developed in this study. An extraction yield of silica of 72-98% was obtained and the particle size was 40-50 nm. The microstructures of the as-obtained silica powders were characterized by X-ray diffraction (XRD) and infrared spectra (IR). The surface area, iodine number and capacitance value of activated carbon could achieve 570 m(2)/g, 1708 mg/g, 180 F/g, respectively. In the whole synthetic procedure, the wastewater and the carbon dioxide were collected and reutilized. The recovery rate of sodium carbonate was achieved 92.25%. The process is inexpensive, sustainable, environmentally friendly and suitable for large-scale production.     

Morphology of the cross section of silica layer in rice husk

The physical adsorption of nitrogen and gas flow experiments on the silica layer in rice husk indicated that an existence of nano meter sized through holes. In this study, the external shape of the holes on the cross section of the layer was investigated with a scanning electron microscope equipped with an energy dispersive spectrometer, an atomic force microscope and scanning tunneling microscope. In the energy dispersive mapping image, 2-5 micron thick silica layer under outer cellulose layer, silica nano particles in the middle cellulose layer and sub micron silica layer in inner cellulose layer were observed. The cross section of the layer showed 20 nm building units with approximately 100 nm convexities. The atomic force microscopic image also showed the approximately 100 nm convexities as well as a roughness of approximately 20 nm. When osmium was coated on the silica layer, the wells with 2 approximately 5 nm horizontal and approximately 2 nm vertical lengths were observed on the plate surface in scanning tunneling microscopic image. From the results, it was suggested that the holes in the rice husk silica layer are almost straight and not zigzag spaces originated from the simple packing of nano particles.     

Review Processing, properties and applications of reactive silica from rice husk—an overview

Rice husk is an abundantly available waste material in all rice producing countries. In certain regions, it is sometimes used as a fuel for parboiling paddy in the rice mills. The partially burnt rice husk in turn contributes to more environmental pollution. There have been efforts not only to overcome this but also to find value addition to these wastes using them as secondary source of materials. Rice husk contains nearly 20% silica, which is present in hydrated amorphous form. On thermal treatment, the silica converts to crystobalite, which is a crystalline form of silica. However, under controlled burning conditions, amorphous silica with high reactivity, ultra fine size and large surface area is produced. This micro silica can be a source for preparing advanced materials like SiC, Si₃N₄, elemental Si and Mg₂Si. Due to the high pozzolanic activity, this rice husk silica also finds application in high strength concrete as a substitute for silica fume. Possibility of using this silica as filler in polymers is also studied. The present paper is an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on the processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.     

Nature and reactivity of silica available in rice husk and its ashes

Scanning electron microscopy, reactivity and surface area measurements of rice husk and its ashes reveal the gradual formation of amorphous silica during ashing. The reactivity of the silica thus formed is found to be at its maximum for ashing temperatures between 400 and 600°C and hold-time from 6 to 12 h. The reactivity of the ash is found to decrease with increasing temperature (⩾ 600°C) and hold-time. IICT Communication No. 2375.     

Effect of organic acid treatment on the properties of rice husk silica

Rice husk, an agro waste material, contains about 20% ash which can be retrieved as amorphous, chemically reactive silica. This silica finds wide applications as filler, catalyst/catalyst support, adsorbent and a source for synthesizing high performance silicon and its compounds. Various metal ions and unburned carbon influence the purity and color of the ash. Controlled burning of the husk after removing these ions can produce white silica of high purity. The present paper deals with the investigation carried out on two rice husk samples of different origin, one from the state of Andhra Pradesh (APRH) in the central part of India and the other from Kerala (KRH) the southern most part of the country. Leaching the husk with acetic and oxalic acids was attempted for the first time and the improvement in properties of the ash was studied. The husk samples were also treated with hydrochloric and nitric acids of different concentrations for comparison. The ashes produced by controlled burning of these samples before and after acid treatment, were characterized for the optical properties in addition to the chemical and physical nature. The APRH ash was found to be inferior to the KRH ash in all properties. Pretreatment of the husks with the organic acids improved the properties of ashes and the effect was comparable to that achieved by mineral acid leaching. Amorphous, reactive and high purity silica with high surface area and pore volume and good optical properties could be prepared from both the husks under specific conditions.     

Preparation and characterization of nano-porous silica aerogel from rice husk ash by drying at atmospheric pressure

Silica aerogel, a mesoporous material, was prepared from rice husk ash by sol–gel method and dried under atmospheric pressure. In this method, rice husk ash, which is rich in silica, was extracted with sodium hydroxide solution to produce a sodium silicate solution. This solution was neutralized with acid to form a silica hydrosol, and a small amount of tetraethyl silicate (TEOS) to form a gel. The aged gel was washed carefully by distilled water and ethanol and finally dried under atmospheric air. The prepared silica aerogels were characterized by XRF, FT-IR, TG, DTA, DTG, XRD, BET and SEM measurements. The synthesized TEOS-doped silica aerogel was a light solid with specific surface area of 315 m²/g, pore volume 0.78 cm³/g, average pore size 9.8 nm, bulk density 0.32 g/cm³ and porosity 85%.     

Silicon carbide materials obtained from rice husk

Thermal processing of a rice husk sol in air at T≥750°C leads to the phase transformation of amorphous silicon dioxide (SiO₂) into crystobalite (type B samples). Thermal treatment of the same sol at T≈ 1400 °C in a closed graphite crucible leads to the formation of a mixture comprising hexagonal SiC phases and graphite (type A samples). Unannealed type A samples showed high refractory properties, being stable up to 1650°C. Using kaolin binder in silicon carbide articles leads to a decrease in the material refractoriness.     

Crystalline rice husk silica reinforced AA7075 aluminium chips by cold compaction method

Aluminium matrix composite is highly demanded in various industries due to its low density and good mechanical properties as most commonly studied for metal matrix composite. The properties of the composite be improved with the addition of reinforcement significantly such as silicon carbide, aluminium oxide, and boron carbide that can be mixed easily to metal matrix composite. The study of crystalline rice husk silica reinforced AA7075 aluminium chips on mechanical properties were investigated. The rice husk ash was burned at 1200 °C and it was characterized in the crystalline phase by conducting x-ray diffraction test. The mechanical properties of aluminium matrix composite were obtained by microhardness and compression tests. Results of mechanical properties for the addition of rice husk silica up to 7.5 wt.% composition of crystalline rice husk silica showed increase value of microhardness and compression strength which are the highest value of 75.94 HV 0.1 and 443 MPa, respectively compared to another aluminium matrix composite. Hence, based on investigation to crystalline rice husk silica reinforced aluminium, it has good potential to improve the mechanical properties of aluminium matrix composite which were dependent to the composition of crystalline rice husk silica reinforcement in aluminium matrix composite.     

Synthesis of mixed-phase uniformly infiltrated SBA-3-like in SBA-15 bimodal mesoporous silica from rice husk ash

The mixed-phase bimodal mesoporous silicas (BMS) were simply synthesized via sol-gel technique using rice husk ash-derived sodium silicate as a silica source, and Pluronic P123 and cetyltrimethyl ammonium bromide (CTAB) as the pore structure-directing agents. The gel solution composition in the synthesis process was based on SiO₂:Pluronic P123:CTAB:HCl:H₂O molar ratio of 1:0.088:0.088:4:200. The effect of mixing sequences of starting materials on BMS structures was investigated. The phase separation among SBA-15, SBA-3-like porous silica and xerogel was found when the gel solutions of SBA-15 and SBA-3-like were prepared separately in the primary stage, whereas the mixed-phase uniformly infiltrated SBA-3-like in SBA-15 bimodal porous silica was successfully synthesized when CTAB was added into the SBA-15 gel solution and the secondary micelle structure was formed inside the primary SBA-15 framework.     

Electrical evaluation of ceramic obtained from white rice husk ash and soda lime silica glass for electronic applications

In this work, Polarization–Electric field (P–E) hysteresis loop was evaluated and dielectric studies of the ceramic obtained from white rice husk ash (WRHA) and soda lime silica (SLS) glass was reported for electronic applications. Dielectric properties and hysteresis loop of the specimens were measured using a LCR meter and Sawyer–Tower circuit, respectively. The dielectric analysis clearly shows that the different amount of SLS glass content gives the different value of dielectric constant and loss to the ceramic. Sample with 2.5 wt% SLS glass content includes the lowest dielectric constant (11.13) among others, at 100 kHz, when sintered at 1,200 °C. The results show dielectric constant and loss of the specimens decrease with increasing applied frequency. P–E loop measurement indicates that the WRHA ceramic, generally, had capacitor capability and became more “resistor-like” than “capacitor-like”, with addition of SLS glass content.