One pot fabircation of mixture of zero dimensional ß-silicon carbide and fe-si alloy nanoparticles from industrial wastes

Abstract

The present disclosure describe a method of one pot fabrication to produce mixture of nanomaterial ß-SiC and Fe-Si in an effort for sustainable reutilization of industrial solid waste into value added functional advance material. The solid wastes from two different industries i.e Fly ash from coal based power plant and bio char from agro industry was physically combined and exposed to carbothermal reduction reaction at 1400°C in an inert atmosphere. The pyrolysed sample was calcined to remove organics and unburnt carbon and the final product was composed of ß-SiC and Fe-Si along with unreacted silica and aluminosilicate and iron oxide.

Description

FIELD OF INVENTIONThe present disclosure generally relates to the development of mixture of β-silicon carbide (β-SiC) and Fe-Si alloy in zero dimensional state using industrial waste via physical mixing of the raw materials and applying carbo-thermal reduction method for the formation of the product.BACKGROUND OF INVENTIONSilicon carbide is a semiconductor made up of two elements i.e. silicon and carbon that combine to form many different polytypes, among these the most desired are α and β-SiC due to thermodynamically stable, high thermal conductivity of 120-270 W / mK, surface inertness, resistance to oxidation, high mechanical strength and tuneable surface properties. Among these two forms, β-SiC is the desirable form due to its porous structure and easy to synthesize at a temperature around 1200-1400°C. As a semiconductor, SiC has a tunable band gap (2.39-3.34 eV) with a high charge career mobility that allow this material to be suitable for photocatalytic activities.Among the most important utilities of this material is its application as reinforcement for carbon composites used for defence and strategic applications. Surface inertness and biocompatibility makes it useful for medical applications such as SiC based stents used for arteries responsible for blood flow to heart. Further, SiC is used as catalyst for Fischer Troph's process for syn gas production. Recently, SiC has been a material in demand in automotive sector as it optimizes EV (electric vehicle) fast charging process which is anticipated to increase the power density by 30% and reduce the loss of the overall system by 30%.The SiC in nanometre scale has found extraordinary properties and has better efficiency in material applications such as refractory material, its high hardness is being exploited for grinding application and is used in strengthening the alloys. With high thermal conductivity it is used in manufacturing of sealing valves, spray nozzle. Being photoactive, SiC nanomaterial is used for applications of high ultraviolet environment. Conventionally, SiC is produced two different methods as mentioned below:1. Lely's method : This method is based on crystal growth technology where SiC is sublimated at a very high temperature of 2500°C in the inert atmosphere in an induction furnace.2. Chemical vapour deposition method: In this method different gases are used in a vacuum environment combines to form the product on a substrate.3. Sol gel technique: For nanosize SiC, the researchers have used sol gel technology to produce nanosize glassy material known as polysiloxane which is mixed with carbon source. The raw hybrid is then exposed to carbothermal reduction at a temperature between 1200-1400°C in inert atmosphere. The product obtained is mainly β-SiC polymorh. Sol gel technique primarily produces one dimensional SiC nanomaterial such as nanofibers.The present invention is based on using waste materials rich in carbon and silica that could be successfully employed for developing zero dimensional β-SiC polymorh using carbothermal reduction.An alloy of iron and silica Fe-Si is a corrosion and high temperature resistant master alloy. It is having high specific gravity and magnetism and provide strength to the materials. The alloy is used for aircraft and automobile manufacturing and also used in steel and hydrogen production. Commercially Fe-Si is produced in a blast or electric arc furnace where sand and coke are reduced in the presence of iron. Nanocrystalline Fe-Si have been prepared using heat treating of melt spun amorphous alloy, ball milling of elemental powder for several days followed by heat treatment and gas phase reaction. SiC in combination with Fe and SiO2 has been widely researched for its catalytic efficiency especially for syn gas production.The SiC produced along with Fe-Si in a mixture SiO2 and aluminosilicate could act as an efficient catalytic combination for such process. SiC in combination with Fe and SiO2 has been widely researched for its catalytic efficiency especially for syn gas production. Tentatively, β-SiC in combination with Fe-Si is therefore expected to provide a unique material for strategic material applications for material and catalysis based industries especially if developed in nanometer scale range and in zero dimensional orientation of the structure.Hence we deployed Fly ash as precursor that is a rich resource of oxides of many metals where as the carbon content was obtained from biochar obtained from agricultural waste. The approach of developing this invention is aimed at utilizing resources from industrial waste leading to waste management and sustainability.OBJECTIVE OF INVENTIONSustainability and waste management of the industrial waste is the prime objective of this invention. The waste management especially that of industries is high in demand in order to address the environmental safety and security. However, it becomes difficult for many companies to dispose of the waste generated in environmental friendly way. There is a need of innovation in this area to recover resources from these wastes and reutilized as valuable product.The next objective is to combine the waste from different industries especially the solid waste that is rich in silica and carbon that could be reutilized to form SiC nanomaterials using carbothemal reduction method.These objectives have been captured in the embodiment of the invention especially in the summary, description and drawings and other disclosures.SUMMARY OF INVENTIONGiven below is the summary of the invention for the use of industrial wastes to develop zero dimensional β-SiC polymorh in nanometer size.The present disclosure is not intended for the identification of the fundamental concept or scope. The disclosure specifically is meant to use the industrial waste material and reutilise it for the synthesis of SiC in combination with Fe-Si alloy thereby offering a platform for the readily available resources from the waste.1. SiC has two main components. The Si and C that combine together under ambient reaction conditions to for SiC.2. Fly ash is solid waste produced in abundance by coal based power industry. Fly Ash composition is made up of mainly silica [40 to 70%] depending on the type of coal used by the power plant. Besides silica, fly ash is also composed of a mixture of other oxides such as aluminium oxide, calcium oxide, magnesium oxide and many other metals. Fly ash is therefore a rich sources of Si that could be utilized as the inorganic component of SiC.3. To procure carbon part of SiC, the biochar is rich resources as one of the carbonaceous material which is obtained by pyrolysis of waste biomass that thermally decompose it to carbon rich material. The biochar has found many application areas such as soil amendment, stock fodder, water retention and source of carbon sink. Therefore, the it becomes an obvious choice to use biochar as source of carbon to develop SiC.The present disclosure offers to produce SiC in combination with Fe-Si alloy in a mixture of aluminosilicate, silica and iron oxide from the industrial waste materials which is synthesized and characterized as summarised below:I. Fly ash and bio-char was physically mixed in a ratio of % wt of [3:1] using pestle and mortar. For scale up mixing, any mixer would be employed.II. The mixture in a carbon boat was then carbo-thermally reduced in high temperature furnace up-to 1400°C using inert atmosphere in three step temperature program.III. At 1400°C, the reaction was kept at constant temperature for an hour and then cooled to room temperature.IV. The product was calcined up-to 800°C in a furnace in oxygen atmosphere for an hour to remove unburnt carbon and was then cooled to room temperature.BRIEF DESCIPTION OF ACCOMPANYING DRAWINGThe number of details suggested is not intended to limit the scope of this disclosure.Additional objects and advantages of the present invention will become more apparent from the following description when read in conjunction with the accompanying drawingsFigure 1 is the graphical abstract of the synthetic procedure using carbothermal reduction process for developing SiC.Figure 2 depicts the X-ray diffraction pattern of pyrolised and oxidised sample.Figure 3a provide the Fourier transform infra-red spectra of pyrolised sample SiC.Figure 3b provide Fourier transform infra-red spectra of oxidised pyrolosed sample of SiC.Figure 4a showcase the transmission electron of micrograph of pyrolised sample SiC at 500nm scale.Figure 4b showcase the transmission electron micrograph of oxidised pyrolosed sample of SiC at 500 nm scale.Figure 5 depicts the BET graph for oxidised sample of SiC.It is to bring to attention to those skilled in the art will appreciate, in view of the advantages of the present invention, that the examples shown in the Figures drawings are not necessarily drawn to scale. In order to facilitate better understanding of the disclosure, some of the features or components may be enlarged, reduced, or distorted. No specific material or orientation is implied or implied in the drawings unless the context clearly dictates otherwise.DETAILED DESCRIPTION OF INVENTIONDetailed description of the invention provide an elaborated version of the work done in the present embodiment of disclosure.The present disclosure is about industrial waste utilization to develop β-silicon carbide. Silicon carbide is made up from two elements silicon and carbon that are able to form bond at temperature range as high as 1200°C-1400°C in an Argon atmosphere. This process is termed as carbothermal reduction.In a present embodiment of the disclosure herein includes the following steps.(i) The raw materials used for the work were procured from local industries. Fly ash was obtained from coal based power industry where as the biochar was obtained from agrobased industry.(ii) The fly ash was evaluated for elemental composition that revealed 72 wt% of SiO2 along with 22% of Al2O3. The balance of this was composed of CaO (2.02 wt%), TiO2 (0.43 wt%) and Fe2O3 (4.8 wt%). The amount provided is an approximate estimation using data obtained after sample analysis. The bio char was carbonized to evaluate the amount of carbon present which was found to be approximately 80 (wt%).(iii) The Fly ash and the biochar was used as such without any pretreatment in order to assess the applicability and efficiency to form silicon carbide. This was done with the aim of sustainability of utilizing the solid waste as such in order to reduce the chemical, water and energy usage for preconditioning and drying at an ambient temperature.(iv) In a typical pyrolysis experiment, a calculated amount of Fly Ash and Biochar in the ratio [3:1] wt% was physically mixed and pyrolysed in carbon boat placed in a high temperature furnace. The furnace was programmed with three step heating process in an argon atmosphere. The furnace was first purged with Argon gas and the temperature was increased from room temperature to 500°C at a rate of 10°C / min and thereafter 7°C / min until the temperature was 1000°C. The rate was reduced to 5°C / min from 1000°C to 1400°C and the sample was exposed to this temperature for 60 min. The furnace was cooled to room temperature hereafter without any program for about 24 hours.(v) The sample obtained after the pyrolysis was calcined again at 800°C at the heating rate of 5°C / min and was kept at this temperature for two hours in a high temperature furnace in silica boat in oxygen atmosphere to release unburnt carbon.(vi) The product obtained was blackish gray in colour and was analysed for elemental composition (X-ray diffraction pattern), functional group analysis (Fourier transform infra-red spectroscopy). These analysis confirmed the formation of β-SiC.(vii) Figure 1 is the graphical abstract of the synthetic procedure using a) Carbothermal reduction process [pyrolysis] for developing SiC and b) calcination set up. Briefly, for pyrolysis the raw sample [mixture of flyash and biochar] was kept in a carbon boat and loaded in a high temperature furnace. The furnace was attached with argon gas cylinder at one end and connected to fume hood at the other end. The furnace was purged with argon gas to create an inert atmosphere. The temperature cycle was programmed as mentioned above and started as soon as inert atmosphere was created inside the furnace. At the end of the three step temperature cycle, the furnace was switched off and it was allowed to cool down to room temperature which took almost 24 hours. The sample termed as pyrolysed SiC was taken out from the furnace and part of the sample was kept aside for the characterisation purpose. Further to emphasize that although the prime product β-SiC in combination with Fe-Si was formed in a mixture of SiO2, Fe2O3 and aluminium silicate (Al1.272 Si0.728 O4.864).b) Calcination [oxidation]: The method was adopted to oxidize the unburnt carbon that might have left during the previous step. The sample after the calcination was termed as oxidized sample and characterised for elemental composition, internal structure and porosity.(viii) Figure 2 depicts the X-ray crystallographic pattern of Fly ash, pyrolyzed β-SiC and oxidized β-SiC respectively. The pattern of Fly ash indicate the presence of SiO2, Fe2O3 and aluminium silicate (Al1.272 Si0.728 O4.864) as the main components. However, upon pyrolysis two new products i.e. β-SiC and Fe-Si were also formed. The calcination of pyrolyzed sample yielded the oxidized form and the X-ray diffraction pattern of the samples shows an increased intensity of the peaks referring to β-SiC and Fe-Si.(ix) Figure 3 a-b shows the FTIR spectra of pyrolyzed and oxidised samples. Fig 3 a indicate all the prominent peaks w.r.t to aluminosilicate, SiO2 and aromatic stretch. However, the β-SiC at 806 cm-1 appears as a very small peak. In case of oxidized sample as shown in Figure 3b, β-SiC peak is sharp and prominent peak along with the rest of the peaks. It is worth to mention that calcination was able to remove maximum carbon but there might be some carbon trapped inside the pores of the oxidized sample which perhaps would be responsible for the aromatic stretch even in this sample.(x) Figure 4 a-b, c-d depicts the transmission electron micrograph of the samples showcasing the internal structure. Figure 4 a and b are the TEM pictures of the pyrolysed sample taken at two different magnifications. Fig 4 a shows the formation of multiphase sample with dark spots indicating the carbon. The particles are round / circular shaped depicting the zero dimensional nanomaterial with the non-uniform particle size in the range of 10-50 nm. Fig 4 b shows a closer look of the particles in the multiphase sytem. Figure 4 c and d depicts the TEM micrographs of the oxidized sample with only difference in the amount of carbon trapped in the particles. Calcination could reduce the carbon on the surface, however, the trapped carbon could not be removed effectively. This could also be correlated with FTIR analysis where the C-H stretch / C=H stretch aromatic did not disappear form the spectra. The particle size, shape as well as multiphasic system remained the same as that of pyrolyzed sample.(xi) Figure 5 depicts the BET adsorption linear isotherm of the pyrolyzed sample. Table 1 showcase the average nanoparticle size, BET surface area, pore volume and pore size of the sample.Table 1

Claims

1. The solid industrial wastes i.e Fly ash [obtained from coal based power plant] and biochar [converted from agro waste] were used as a raw material for developing silicon carbide along with Fe-Si in a cocktail mixture of SiO2 and aluminosilicate. This was carried out in following simple steps. (i) The elemental composition of raw materials were done prior to the main experiment to assess the amount of carbon (in biochar) and SiO2 (in Fly ash) available for the carbothermal reduction. Based on the values obtained the ratio of Fly ash to Biochar was calculated as [3:1] to obtain β-SiC. (ii) The Flyash and the biochar was physically mixed with no pretreatment. (iii) The mixed raw product was loaded onto the carbon boat and placed in a high temperature furnace which was purged with Argon gas to create an inert atmosphere for the carbothermal reduction reaction. (iv) The furnace was heated upto 1400°C in a three step temperature program and was maintained for an hour. After this, the furnace was cooled to room temperature. The product obtained was termed as pyrolyzed product. (v) The pyrolyzed sample was then placed in cermanic / silica boat and kept in a furnace to be calcined at 800°C in air atmosphere. The temperature of furnace was maintained at 800°C for an hour before cooling down to room temperature again. The product obtained was termed as oxidised sample. (vi) The pyrolyzed sample was black in colour whereas oxidized sample was blackish gray in colour. (vii) The pyrolyzed and oxidized samples were analysed for elemental composition, functional group analysis as well as internal structure study.

2. We claim the formation of β-SiC and Fe-Si as confirmed from X-ray and FTIR analysis in a mixture of unreacted silica as well as aluminosilicate.