CN1363535A

CN1363535A - Process for preparing composition 'Sailong' from industrial waste dregs by in-situ synthesis

Info

Publication number: CN1363535A
Application number: CN01144655A
Authority: CN
Inventors: 徐利华; 董桂文; 钱扬保; 董桂强
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-12-24
Filing date: 2001-12-24
Publication date: 2002-08-14
Anticipated expiration: 2021-12-24
Also published as: CN1181013C

Abstract

A process for in-situ preparing high-performance Sialon composition from powdered coal ash, coal gangue, clay, white corundum, and carbon (or silicon) powder includes such steps as die pressing, drying at 110 deg.C and nitrifying sinter segmentally. Its advantages include high conversion rate, no carbon, high compactness, mechanical performance and refractory nature, excellent resistance to alkaline slag corrosion, and low cost.

Description

Preparation method for synthesizing sialon complex phase material in situ by using industrial waste residue

Technical Field

The present invention belongs to the low-cost preparation of reaction-sintered novel oxynitride materials.

Background

The Sialon material is Si₃N₄The solid solution is a high-performance engineering ceramic material developed in the last three decades. Compared with the traditional oxide structure material, the material has very excellent comprehensive properties, including mechanical properties (high strength, high hardness, high toughness, high wear resistance and the like), thermal properties (high temperature resistance, thermal shock resistance and the like), physical properties (small density, low expansion coefficient) and chemical properties (corrosion resistance, scouring resistance and the like). Because it is the essence ofthe current structural engineering material, it has a wide application prospect, and therefore it also occupies an important place in the large stage of international material research. Recently, corresponding reports are also reported on NATURE with the highest international journal grade, and the application prospect of the NATURE is extremely high.

The early preparation method of sialon powder is to synthesize Si₃N₄And AlN powder doped with SiO according to Si-Al-O-N phase diagram₂And Al₂O₃After being mixed in proportion, the mixture is produced by solid phase reaction at high temperature. The method has the basic characteristics of complex preparation process, extremely high raw material cost and difficult popularization and application. Then, the method develops the method that metal Si, Al and oxides thereof are used as starting materials,the reaction sintering is used for synthesizing the sialon, but a series of technical-economic problems caused by long reaction time and high synthesis temperature exist.

In order to reduce the production cost of sialon, countries such as the United states, Japan, England and the like respectively adopt cheap resources such as clay, rice hulls, carbon-containing mudstone and the like, and adopt the Carbothermic Reduction Nitridation (CRN) technology to synthesize sialon powder, and many researches are carried out, wherein the varieties are abundant, such as O' sialon, β sialon, calcium α sialon, yttrium α sialon and various allophane materials, such as MgAlON, vanadium AlON and the like.

For the synthesis of sialon powder, the traditional electric heating method is mainly adopted at present. However, in the sintering and nitriding process, the unit product has high energy consumption and limited production capacity, thereby basically restricting the mass production and the popularization and application of the technology. If the product loading is increased (the energy consumption per unit product can be reduced properly) by increasing the heating capacity of the furnace, the problems are also represented by the non-uniform distribution of the temperature field in the furnace (the rejection rate of the material is increased rapidly), and the phenomenon of insufficient nitridation reaction exists in some regions, which is caused by the partial large local resistance of the deposition, the non-uniform distribution of nitrogen gas, the low temperature and the like.

Secondly, the electric furnace nitriding technology has the problem of lack of effective electric heating rod materials, such as the common silicon carbide heating rod, the highest sintering temperature is only 1350 ℃, and the difference is still existed between the highest sintering temperature and the highest sintering temperature of the product which is completely reacted and sintered into sialon (1400-1600 ℃). Although the improved process can realize the low-temperature sintering of the sialon material, the long-time heat preservation inevitably leads to the increase of the energy consumption of unit products; heating with medium-high temperature heating rod-silicon-molybdenum rod (1650 deg.C or so), and heating with N in furnace body₂And reaction sintering stationThe released CO reacts with the high-temperature heating rod due to the leakage of oxygen in the air, so that the CO rapidly loses efficacy, and the service life of the CO is seriously influenced; if the graphite carbon rod with ultra-high temperature (up to more than 2000 ℃) is used as the heating element, the leakage of oxygen in the air is difficult because of the existence of the part with poor sealing in the furnace body with larger volumeAnd the resistance of the carbonaceous material to oxidizing gas is poor, the carbonaceous material is easy to oxidize (400 ℃ is oxidized by oxygen, 500 ℃ is acted with water vapor, 700 ℃ is acted with carbon dioxide), and the heating process is difficult to control due to the change of the resistance of the heating element along with the high-temperature oxidation reaction.

Thirdly, the leading product prepared by the electric furnace nitriding technology is sialon powder instead of sialon products (such as refractory bricks, ceramic plates and the like). The biggest reason is that a great deal of pores are formed in the sintered body due to the carbon as a reducing agent after the carbothermic reduction reaction and part of residual carbon is remained. In order to solve the problem of residual carbon, most measures are taken to prolong the nitriding time, but extra production cost is undoubtedly increased.

In summary, the conventional electrical heating CRN technology for producing sialon materials has several key problems as follows: (1) the production cost of the product is high (the energy consumption is high); (2) low throughput (limited heat receiving area); (3) poor product quality (non-uniform temperature field, residual carbon, etc.); (4) the process system is difficult to adjust (heating rod problem, etc.); (5) the product type is limited (restricted to powder materials). Therefore, the technology is difficult to popularize and apply in industrial production for more than twenty years after the invention. According to the results of the reports of research and study of Chinese patent, since 85 years, there are 7 reported patents which use sialon as a key word for search, and only 2 of them have been developed by carbothermic technology (application numbers 93102907, 00105941). However, the conventional electrical heating CRN method is still reported, the adopted raw materials are clay and natural silt minerals, and the research level is limited in the laboratory stage.

Disclosure of Invention

The invention designs and manufactures the intermediate-scale muffle type industrial kiln for the first time to replace the traditional electric heating method, and lays a foundation for industrially producing the sialon material with low cost and large capacity; secondly, a proper amount of sintering aid is added into the green body, and the sintering of the product is completed by a sectional control process system, so that the aim of one-step forming (namely in-situ sintering) is fulfilled; thirdly, the selected main raw materials are industrial solid waste residues (industrial fly ash and coal gangue produced from coal tailings), and the research level is deeper and more practical from the aspects of economic benefit, social environmental effect and innovation.

The invention provides a method for producing a high-performance Sialon (Sialon) complex phase material in situ by using industrial waste residues, which comprises the following steps: respectively adopting industrial fly ash and coal gangue as raw materials, crushing the raw materials, finely grinding, acid cleaning and filtering to form two types of batch mixtures, and placing the batch mixtures in an industrial muffle furnace for drying at 300 ℃, wherein the basic formulas (based on a sialon phase diagram) of the two types of batch mixtures are respectively as follows: I. 40-60% of fly ash; 20-30% of clay, and reducing agent: 10-15% of carbon powder and a correction material: 5-15% of white corundum; and a small amount of reducing assistant and sintering aid is added. II. 40-50% of coal gangue; 20-30% of clay, and reducing agent: 10-20% of carbon powder and a correction material: 10-20% of white corundum; a small amount of reducing auxiliary agent and sintering aid are added; the product molding process is machine pressing molding, the molding pressure is 30-50 MPa, and the product size is 45 multiplied by 220 multiplied by 110 mm; the sintering process is completed in the nitridation industry of a self-designed flame-isolation type rectangular down-draft kiln, and the specific process comprises the following steps: using liquefied petroleum gas as heat source, placing the product in a closed crucible, introducing nitrogen gas from the lower portion of the crucible, and making the waste gas (CO, SO) undergo the carbothermic reduction reaction (CRN)₂Etc.) is discharged from the top of the crucible; in order to ensure the yield of in-situ sintered products, the sintering process is optimized and designed in stages, namely the sintering rate at a low-temperature stage is 100 ℃/h, and the sintering rate at a high-temperature stage is 200 ℃/h; keeping the temperature at about 800 ℃ for 3 hours (mullite forming stage); 1500 ℃ heat preservation 20Hours (sialon phase reaction synthesis phase); and the temperature is kept for 4.5 hours at 1650 ℃ (sintering and compacting stage of the sialon complex phase material). And (4) after the firing is finished, stopping firing, cooling the product along with the furnace to 500 ℃, and then closing the nitrogen.

The comprehensive utilization of the resources and the research progress of the two types of bulk wastes to which the invention relates are illustrated next.

Along with the progress of world industrialization, the generation amount of industrial solid wastes in countries around the world is increasing. According to the statistics of Asian developing banks, the amount of waste generated by some major Asian countries in 1992-2010 will increase by 3 times, and the emission amount will rise sharply. At present, the amount of waste rocks, tailings and waste residues accumulated in coal, electric power and metallurgical chemical industry in China exceeds 12Gt, and the stockpiling of the waste residues occupies hundreds of thousands of acres of land. Moreover, the quantity of industrial waste residues to be discharged continuously is more than 6 hundred million tons every year, and thousands of acres of land are occupied every year, which is a striking number! Coal-fired power plants discharge a large amount of fly ash formed by coal ash annually, the production capacity of the fly ash accounts for 80-95% of the waste residue of the power plants, and the emission amount per year reaches more than 30Mt at present. Every year, more than one thousand tons of fly ash are discharged into rivers, lakes and seas, and a lot of industrial waste residues are directly discharged into lakes to block the channels, so that the area of the lakes is reduced by more than two thousand mu and ten thousand mu, the water quality is damaged, and the growth of aquatic organisms is seriously influenced. Regarding the comprehensive utilization of industrial fly ash resources, based on the fact that fly ash contains many useful chemical components, the current resource process measures are to extract carbon, iron, alumina, molecular sieve and white carbon black from the fly ash; meanwhile, the hollow glass beads are obtained by a physical flotation (dry method and wet method) method.

Meanwhile, China is a country with rich coal resources, along with the continuous increase of the coal mining usage amount, the discharged waste residues (mainly coal gangue) are increased, the discharge amount of the waste residues reaches 30% of the yield of raw coal, the coal gangue is stockpiled by billions of tons at present, the coal gangue discharged per year has 0.1-0.2Gt, a large amount of coal gangue is stockpiled like a mountain, the land is occupied, and the gangue with high sulfur content can be spontaneously combusted to become a secondary pollution source of atmosphere and water. According to statistics, the coal gangue used for producing building materials only reaches about 20% of the emission amount, so the problem of coal gangue waste residue accumulation is not completely solved at present. The resourceutilization of the coal gangue is generally used for producing cement admixture, brick firing, lime firing and road building and field building respectively according to different heat values contained in the coal gangue, and the coal gangue with high heat value is used for generating power.

From the results of the research of the Chinese patent from 85 years to the present (6 items in the declaration of coal gangue and 20 items in the declaration of fly ash), the coal gangue is utilized to respectively produce aluminum salt, silicate, smelted silicon-aluminum alloy, active blast furnace slag, waste heat roasting refined lime and chromium-containing titanium-nickel-vanadium waste residue coal gangue for detoxification and comprehensive utilization; the reported products of the comprehensive utilization of industrial fly ash resources are respectively used for producing light glazed tiles, microcrystalline glass (2 items), colored glass, cement concrete admixture (3 items), building material products (2 items), wall materials (2 items), sintered bricks (2 items), organic-inorganic composite materials, solid fuels and decorative materials (2 items); a method for treating wastewater and sewage by using fly ash (item 3).

In general, the two kinds of resource are low in degree of resource utilization, and the additional value of environment-friendly products is not high, and although people also strive to high-value transformation of the solid waste in recent years, high-grade products are not reported yet. The invention aims at the technical blank of the research field in international and domestic fields to realize the development of the low-cost and high-performance oxynitride environment-friendly product.

Brief description of the drawingsfigure 1 is a schematic view of a small rectangular muffle-type nitriding furnace with a closedcrucible for a silicon nitride product, the firing profile of the material of fig. 2FIG. 3 XRD of β -sialon complex phase material synthesized by coal gangue-clay series raw material through carbothermic process FIG. 4 XRD of β -sialon complex phase material synthesized by coal ash-clay series raw material through carbothermic process (β sialon-Si)₃Al₃O₃N₅(ii) a x sialon- -Si₆Al₁₀O₂₁N₄)

Detailed Description

The present invention will be described in detail below. 1. Chemical composition and basic formula design of starting raw materials

The solid waste residue-coal gangue prepared by the method has the following chemical components:

the coal gangue comprises the following chemical components: SiO 2₂：60.28；Al₂O₃：28.37；Fe₂O₃：4.94；CaO：0.92；MgO：1.26；

Industrial analysis of coal gangue: ash content: 83.24, respectively; volatile components: 9.20; fixing carbon: 7.56

The chemical components of the fly ash are as follows: SiO 2₂：51.52；Al₂O₃：33.43；Fe₂O₃: 8.86 of the total weight of the mixture; CaO: 4.9; specific surface area 3108cm²/g

The adopted clay (Shandong Zibo) comprises the following chemical components:

SiO₂：67.04；Al₂O₃：16.19；Fe₂O₃：5.39；CaO：1.45；MgO：1.40；K₂O+Na₂o: 2.01; vector burning: 6.55

In order to further reduce the iron content in the solid waste residue, the finely ground raw material is subjected to acid washing treatment by 0.1M HCl, filtered, dried in an industrial muffle furnace at 300 ℃, and then treated according to β sialon (Si)₃Al₃O₃N₅) The synthesis requirement is as follows:

(1)

in order to improve the plasticity in the forming process, 20-30% of clay is added into the batch; maintenance of Al in base formulation₂O₃∶SiO₂The molar ratio of (A) to (B) is 1: 2; in order to satisfy the above-mentioned metering ratio, an addition partThe recipe was calibrated by dividing the alumina.

Meanwhile, in order to overcome the defects of excessive residual carbon caused by excessive carbon powder added in the traditional formula and high porosity of a ceramic body, the invention is doped with a small amount of Si powder (30 percent of carbon powder) and sintering aid (Y)₂O₃，TiO₂) The amount of carbon powder is controlled to 10-20%. 2. Forming and sintering process

And pressing the mixture into a green body by adopting a machine pressing forming process, wherein the forming pressure is 30-50 MPa, and the product size is 45 multiplied by 220 multiplied by 110 mm. And (4) removing water from the green body at about 110 ℃ to obtain a dry body.

The sintering process is to carry out nitridation sintering in a muffle type rectangular down-draft kiln (see figure 1). The rectangular down-draft kiln has an inner bore size of 1200 (height) 1000 (length) 900 (width) mm, a silicon nitride crucible with a size of phi 600X 700mm (wall thickness delta: 5mm) is arranged in the rectangular down-draft kiln, liquefied petroleum gas is used as a heat source, a dry blank is arranged in the crucible through stacking bricks, the opening of the crucible is covered by a corundum plate, then alumina cement is used for sealing, nitrogen is directly introduced to the bottom of the crucible through an alumina tube, and waste gas (CO, SO) after carbothermic reduction reaction₂Etc.) from the top side of the crucible throughAnd discharging the alumina pipe after the alumina pipe is discharged out of the furnace body. 3. Optimized process design and principle

In order to achieve the purpose of in-situ sintering (one-step material formation), a sintering process system is designed in a heat preservation mode in a sectional mode (as shown in an attached figure 2), namely the sintering rate of 100-800 ℃ in a medium-low temperature stage is controlled at 100 ℃/h, and sufficient time is kept for water evaporation and organic matter decomposition in a blank body; keeping the temperature at 800 ℃ for 3 hours, which is a mullite forming stage; the sintering rate of the section of 800-1500 ℃ is controlled at 200 ℃/h, and the temperature is kept at 1500 ℃ for 20 h, so as to ensure that the solid-phase reaction synthesis of the product is smoothly carried out; then, the temperature is continuously increased to 1650 ℃, and the temperature is kept for 4.5 hours, so as to ensure that the sialon product achieves sintering compactness under the action of the sintering aid. And (4) after the firing is finished, stopping firing, cooling the product along with the furnace to 500 ℃, and then closing the nitrogen.

The optimized sintering process formulated by the invention is based on the knowledge principle of thermodynamics, kinetics and phase diagram of synthetic materials and the sintering theory: the temperature (thermodynamic reaction requirement) and time (reaction process kinetic requirement) required for the high-temperature physicochemical complete reaction of the sialon material;

according to the carbothermal reduction nitridation process of slag-clay minerals, firstly, at a low temperature stage (100 ℃ C.) the water evaporation and the organic matter decomposition are carried out, and secondly, at about 550 ℃ C. and 600 ℃ C, the decomposition of kaolin in clay is carried out, and the reaction equation is as follows:

thus, a smaller warming rate is controlled to ensure the product is intact.

The reason for the 3 hour incubation at 800 ℃ is that metakaolin decomposes to mullite at this stage:

the reason for the long-term incubation at 1500 ℃ (20 hours) is: firstly, a series of physical and chemical reactions occur in the temperature range, and secondly, the CO gas generated by the reaction sintering has enough time to be removed.

Mullite and SiO exist in the system₂C, and other intermediates. When the temperature reaches 1400 ℃ and 1500 DEG C：

(carbon excess)

Taking SiO as an intermediate product, and continuing the reaction (about 1450 ℃):

Al₂O₃by solid solution of Si₂N₂O, which in turn forms O' -Sialon, X-Sialon up to β -Sialon (1450-.

From the silicon-aluminum-oxygen-nitrogenphase diagram of sialon and the analysis of the state of thermodynamic parameters, it can be seen that when there is a sufficiently high partial pressure of nitrogen (P) around the material_N2Greater than 0.8), with a suitable amount of reducing agent (e.g. carbon) inside the mass, the above synthesis reaction can proceed. Meanwhile, the uniform distribution of the nitrogen flow around the materials is also very critical.

After the reaction sintering is finished (marked by no gas discharge in the gas outlet pipe), the temperature is increased to 1650 ℃ (keeping the temperature for 4.5 hours) to ensure that the sialon realizes low-temperature densification sintering under the action of the sintering aid. And then the product is cooled with the furnace. 4. Phase analysis and performance analysis of sialon complex phase material

After the material is sintered by reaction, the components of the coal gangue system are transformed into ternary composite phase (as shown in figure 3) β -Sialon (Si) by XRD phase detection₃Al₃O₃N₅)(45％)，X-Sialon(x--Si₆Al₁₀O₂₁N₄) (34%), SiC (21%), the appearance of SiC phase is related to excessive reducing agent C, the fly ash system component is transformed into binary composite phase (figure 4): β -Sialon (Si)₃Al₃O₃N₅)(72％)，X-Sialon(x--Si₆Al₁₀O₂₁N₄)(28％)。

By adopting the raw material formula and the process control of the invention, the initial oxide components in the raw materials are all converted into the non-oxide sialon composite phase, wherein the sialon phase conversion rate (β and X phase) is 79-100 percent, and the level of synthesizing the sialon by the electric heating carbothermic process is reached.

The physical and chemical properties of the sialon product prepared by the method exceed those of a clay product (equivalent to the raw material of the invention is sintered in an oxidizing atmosphere), and the sialon is synthesized by a domestic electric heating carbothermic reduction process. TABLE 1 preparation of two kinds of sialon products of the invention and clayey products and domestic reaction sintering sialon products

Comparison of product Properties

Property of (2) Can be used for	Preparation of the invention Sialon (coal gangue) Series)	The invention prepares the match Long (fly ash series)	Clayey system Article (A)	Reaction burning Node sialon
Property of (2) Can be used for	Preparation of the invention Sialon (coal gangue) Series)	The invention prepares the match Long (fly ash series)	Clayey system Article (A)	Reaction burning Node sialon	Conversion rate of sialon ％	79	100	-	＞50
Residual carbon	Is free of	Is free of	-	Small amount of	Conversion rate of sialon ％	79	100	-	＞50
Residual carbon	Is free of	Is free of	-	Small amount of	Density g/cm³	2.56	2.80	2.4	1.79
Porosity%	18	15	10-20	35	Density g/cm³	2.56	2.80	2.4	1.79
Porosity%	18	15	10-20	35	Compressive strength MPa	145	187	90	32
Refractoriness degree C	＞1790	＞1790	1610	＞1700	Compressive strength MPa	145	187	90	32
Refractoriness degree C	＞1790	＞1790	1610	＞1700	Softening under load (200KPa)， ℃	1640	1695	1300-141 0	1598
Resistance to slag and alkali erosion Evaluation of	The paint is smooth and has no cracks, superior food	The paint is smooth and has no cracks, superior food	Surface thinning Loose and poor appetite	Slightly powdered Hua, good	Softening under load (200KPa)， ℃	1640	1695	1300-141 0	1598

The invention has the characteristics that: 1, the solid waste residue and cheap clay are used as raw materials, so that the manufacturing cost of the sialon can be greatly reduced. 2, a muffle type nitriding industrial kiln is adopted to replace an electric heating process, so that the production energy consumption is further reduced, and the large-scale production of the sialon material is realized. 3 in the preparation process, the reasonable design of the components (sintering aid Y) is adopted₂O₃，TiO₂) And the staged sintering process is optimally designed (the complete reaction and low-temperature sintering are ensured), and the in-situ sintering of the sialon complex-phase product is realized for the first time.4, the product in the traditional carbothermic reduction process is improved by doping part of 30 percent of silicon powder in a main reducing agent (carbon powder) in a basic formulaThe problem of high porosity (reduced from 35% to 15-18%); simultaneously reasonably controlling the nitriding reaction time, completely solving the problem of residual carbon in the product and having high sialon phase conversion rate. 5 the material has higher volume density and better mechanical property, and can be used as an advanced structural material in various industrial fields. 6 since the said material has transformation characteristics (transformation from oxide system to non-oxide system), its fire-resistant performance (including refractoriness and refractoriness under load) is far superior to that of the original (clay system), indicating that the grade of the product has been increased from that of ordinary refractory to that of high-grade refractory. Compared with common clay materials and domestic reaction sintering sialon materials, the two types of in-situ sintering products of the invention have excellent slag and alkali erosion resistance and can be used as refractory candidate materials for the lower section of the furnace body of the metallurgical blast furnace (the materials and the technology will lead the industrial production of the blast furnace ceramic cup in China). 8, the preparation technology of the invention provides an effective measure for the resource comprehensive utilization of bulk fly ash and coal gangue, greatly improves the added value of environment-friendly products and improves social environment effect.

Claims

1. The method for producing the high-performance Sialon (Sialon) complex phase material in situ by utilizing the industrial waste residue comprises the following steps: respectively adopting industrial fly ash and coal gangue as raw materials, crushing the raw materials, finely grinding, acid cleaning and filtering to form two types of batch mixtures, and placing the batch mixtures in an industrial muffle furnace for drying at 300 ℃, wherein the basic formulas (based on a sialon phase diagram) of the two types of batch mixtures are respectively as follows: I. 40-60% of fly ash; 20-30% of clay, and reducing agent: 10-15% of carbon powder and a correction material: 5-15% of white corundum; a small amount of reducing auxiliary agent and sintering aid are added; II. 40-50% of coal gangue; 20-30% of clay, andreducing agent: 10-20% of carbon powder and a correction material: 10-20% of white corundum; a small amount of reducing auxiliary agent and sintering aid are added; the product molding process is machine pressing molding, the molding pressure is 30-50 MPa, and the product size is 45 multiplied by 220 multiplied by 110 mm; the sintering process is completed in the nitriding industry of a self-designed flame-isolated rectangular down-draft kiln, preferably petroleum liquefied gas is used as a heat source,placing the product in a closed crucible, introducing nitrogen gas from the lower part of the crucible, and performing Carbothermic Reduction (CRN) to obtain waste gas (CO, SO)₂Etc.) is discharged from the top of the crucible; in order to ensure the yield of in-situ sintered products, the sintering process is optimized and designed in stages, namely the sintering rate at a low-temperature stage is 100 ℃/h, and the sintering rate at a high-temperature stage is 200 ℃/h; keeping the temperature at about 800 ℃ for 3 hours (mullite forming stage); keeping the temperature at 1500 ℃ for 20 hours (sialon phase reaction synthesis phase); and the temperature is kept at 1650 ℃ for 4.5 hours (sintering and compacting stage of the sialon complex phase material), the product is cooled along with the furnace after the sintering is finished and the nitrogen is closed after the product is cooled to 500 ℃.