Effects of CaCO3 additive on properties and microstructure of corundum- And mullite-based ceramic proppants

Corundum-mullite ceramic proppants have been successfully synthesized using raw materials of natural bauxite and solid waste coal gangue, CaCO₃, as additive. The influences of calcium carbonate additive on phase composition, microstructure, and mechanical performances were systematically investigated. The results indicate that the addition of CaCO₃ promotes the formation of liquid phase at lower temperature during sintering process, which is beneficial to the densification of the samples and the reduction of sintering temperature. Moreover, the mullite grains become finer and finer with the content of CaCO₃ additive increasing, which improves the toughness and strength of the samples via a grain refinement strengthening mechanism. The ceramic proppants exhibit optimal performances with additive of 5 wt.% at 1350°C, and the breakage ratio under 52 MPa closed pressure is the lowest. Additionally, the sintering temperature is dropped by 150°C compared with the samples without adding calcium carbonate.     

Sintering mechanism of high-intensity and low-density ceramic proppants prepared by recycling of waste ceramic sands

Waste ceramic sands were effectively used to prepare the high-intensity and low-density ceramic proppants, realising the recycling of the waste ceramic sands. The technology involved the pelletising in an intensive mixer, in which the waste ceramic sands and other starting materials were added, and followed by heat-treatment under different sintering conditions. The sintering temperature, holding time and heating rate were optimised by investigating the crystalline phase, microstructure, density and breakage ratio of the obtained proppants. The results showed that the proppants sintered at 1260°C for 2?h with a heating rate of 5°C?min^–1 under air atmosphere exhibited high crush resistance and low density, with the breakage ratio of 8.5% under 52?MPa closure pressure and bulk density of 1.65?g?cm^–3. The proppants prepared by bauxite, waste ceramic sands and sintering aids are promising candidates as high-intensity and low-density fracturing proppants in future applications.     

Effects of sintering temperature on microstructure,properties, and crushing behavior of ceramic proppants

Ceramic proppants with excellent performance were successfully prepared by second grade bauxite. The phase structure and the microstructure were investigated via X-Ray diffraction and scanning electron microscopy. The results suggested that bulk density and apparent density constantly increased, while the breakage ratio gradually decreased with the increasing in sintering temperature. When the sintering temperature reached to 1500°C, the breakage ratio obtained lowest value of 3.6% under 52 MPa closed pressure, which satisfied the requirement of Chinese Petroleum and Gas Industry standard. Furthermore, the mode of fracture for ceramic proppants was transformed from intergranular fracture into transgranular fracture and open pores had larger influence than closed pores for breakage ratio of ceramic proppants.     

Preparation and characterization of mullite whisker reinforced ceramics made from coal fly ash

Ceramics with mullite whiskers were prepared from coal fly ash and Al₂O₃ raw materials, with AlF₃ used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF₃ addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF₃, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm³ and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources.     

The composition,morphology, and mechanical properties of ethylene propylene diene monomer‐encapsulated coal gangue powder/polypropylene composites

The ternary composites of coal gangue powder encapsulated by ethylene propylene diene monomer (EPDM) filled polypropylene (PP) were prepared to reduce the cost and control the microstructure aiming at high performance cost ratio materials. The result showed that EPDM can not only enhance the interaction between coal gangue powder and the matrix but also promote the dispersion of coal gangue powder. With the addition of coal gangue encapsulated by EPDM, the impact strength of composition dropped greatly, but it still kept about 11 kJ/m² when the content of encapsulated coal gangue powder is more than 18 wt%. The tensile strength and fracture toughness (w_e) also dropped with the addition of encapsulated coal gangue powder, but only a small drop occurred when the content of encapsulated coal gangue powder is less than 18 wt% and great drop emerged when the content is larger than 18 wt%. Compared with coal gangue powder/PP binary composition, the ternary compositions involve higher content of coal gangue powder but present better properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Novel light-weight glass-ceramic proppants based on frits for hydraulic fracturing process

High strength proppants were always in demand for hydraulic fracturing techniques used in unconventional reservoirs for oil and gas extraction processes. To support this concept, relatively low-alumina content glass-ceramic proppants based on the system Fe₂O₃–TiO₂–MgO–CaO–SiO₂–Al₂O₃ have been prepared by using frit, kaolin, and bentonite in a glaze formulation. By deposition of glaze drops on porous ceramic tile, a semi-dry proppant beads were obtained. Different frit compositions of aluminum oxide replacing calcium oxide were used to obtain highly sintered proppants with a robust glassy matrix at 1100 °C in a fast firing cycle. The microstructure by scanning electron microscopy (SEM) and the phase structure by X-ray diffraction (XRD) were investigated. The results revealed the formation of two main phases; cristobalite and calcium aluminum silicate in addition to the other two phases of mullite and Diopside ferrian in some samples. By evaluating the employed fabricated ceramic compositions as high conductivity and high strength proppants for hydraulic fracturing process it was found that all samples exhibited competitive properties according to American Petroleum Institute standards (API RP 19C Standard) for proppants criteria. Crushing loss under 7500 psi closed pressure was (from 1.5% to 6.7%), the weight loss by acids attack was (from 0.001% to 0.07%), sphericity and roundness were (0.9) in addition, the apparent and bulk densities were (from 2.51 to 2.58 g/cm³) and (from 1.46 to 1.50 g/cm³), respectively.     

Preparation of SiC from acid‐leached coal gangue by carbothermal reduction

For the comprehensive utilization of coal gangue, acid‐leached coal gangue was used as silicon source and part of carbon source, low ash anthracite and degreasing cotton were added respectively as supplementary carbon source, SiC and SiC fiber were prepared by carbothermal reduction method accordingly. The results show that the main components in leached coal gangue are amorphous SiO₂ and carbon, which are suitable for the synthesis of SiC as raw materials. The synthesis temperature and holding time have important influence on the synthesis of SiC, and the optimum synthesis parameters for SiC are at 1550°C for 4 hours; under this condition, the yield of SiC is 78.27%, and the specific surface area is 6750 cm²/g. The results show that the resulting products are essentially composed of β‐SiC with a minor amount of α‐SiC. Besides, based on the carbon fiber transformation method, SiC fiber was prepared by using leached coal gangue and degreasing cotton as raw materials. Therefore, it can be concluded that leached coal gangue is a very effective and inexpensive source for preparing SiC, and more importantly, this work has important economic and social significance to realize waste recycling and control pollution.     

铝钒土含量对低膨胀高远红外瓷质卫生陶瓷性能的影响

采用煤矸石废料、劣质原料黑滑石和铝钒土为主要原料,通过原位生长法制备了堇青石质低膨胀高远红外瓷质卫生陶瓷。利用XRD、SEM和性能测试研究铝钒土含量对堇青石卫生陶瓷性能的影响。实验结果表明:铝钒土含量对吸水率、抗折强度和膨胀系数具有较明显的影响,而对远红外辐射率并未带来不利的影响,所有样品的远红外率均保持在0.93以上。当铝钒土含量为27%,煤矸石33wt.%,黑滑石37%时,陶瓷性能达到最优:吸水率为0.04%,热膨胀系数为2.74×10-6/℃,抗折强度为87.4 MPa。这主要是由于样品的主晶相堇青石含量最高,并且烧结致密化程度高,其中气孔分布更加均匀所致。相关研究结果对环境保护和工业废物的资源化利用有着积极意义。     

不同造孔剂对煤矸石合成多孔莫来石性能影响的研究

以煤矸石为主要原料,高铝矾土熟料为调配成分,选取不同种类的造孔剂,通过模压成型的工艺,在1200℃下烧结制备多孔莫来石材料。通过TG-DTA、阿基米德法、XRD和SEM等检测手段,对制品的显气孔率、体积密度、力学性能和微观结构等进行研究。结果表明:在1200℃合成主晶相为莫来石的多孔莫来石材料;造孔剂的种类和粒径不同,造孔效果不同;随着造孔剂含量的增加,显气孔率增大,体积密度和抗折强度呈下降趋势。     

Effect of in situ synthesized and additives on the thermal performance of mullite thermal storage ceramics

High-performance thermal storage ceramics can enable utilization of solar thermal power generation plants. In this work, in situ synthesis was used to prepare mullite thermal storage ceramics. Calcined bauxite, talc, and kaolin were used as raw materials. The effects of additives (e.g., SiC, Si₃N₄, TiC, and ZrB₂) on the density, mechanical durability, phase components, microstructure, and thermal performance of the mullite ceramics were studied. The results showed that the thermal expansion coefficient, thermal conductivity, and heat storage density of the mullite ceramics were affected by their phase components. SiC and Si₃N₄ did not decompose during the in situ syntheses, but TiC and ZrB₂ decomposed. With the addition of 10 wt% SiC, the thermal conductivity improved to 2.72 W (m K)^?1 (298 K). The heat storage density of this material was 688 kJ kg^?1 (273–1073 K). Consequently, the in situ synthesized mullite thermal storage ceramic with added SiC could be a promising candidate material for a compound latent-sensible heat storage system.     

Materials based on highly concentrated ceramic binding suspensions (HCBS). Corundum and corundum-mullite ceramic castables based on plasticized hcbs of bauxite

HCBS of roasted Chinese bauxite, plasticized with additives of refractory clay, and corundum or bauxite filler are used for the production of pressed ceramic castables of corundum and mullite-corundum compositions with 93–95% and 80–85% A1₂,O₃, respectively. The optimum clay additive does not exceed 1–2%. The ceramic castables have a porosity of 15–18% and an ultimate compressive strength of 100–200 MPa after treatment at 1200–1300°C. As compared to traditional corundum refractories they are characterized by a finer capillary structure and a higher mechanical strength attained at a diminished (by a factor of 2–3) pressing pressure and a lower (by 400- 500°C) firing temperature.     

污泥用于水泥混合材的探讨试验

以城市污泥作辅材,煤矸石等其它材料为主要原料,开发制备低碳节能水泥用混合材料。通过对城市污泥与其它原材料共同混合制备水泥用混合材料的性能试验,优化不同种类原材料配比并选择适合的配比试验分析其理化性能、火山灰性评定。结果表明,利用污泥替代部分石灰石、煤矸石,其中污泥占其质量比10%~15%,石灰石、煤矸石分别占物料总质量比20%-60%,制备的水泥混合材料具有人工火山灰质材料特性,可实现以废治废及废弃物有效利用。     

Al2O3/GdAlO3 reaction sintered composites produced from milled powders: Microstructure,neutron-capture cross section,and mechanical properties

The incorporation of high thermal neutron capture elements in ceramic materials is relevant for the design of traceable proppants for obtaining information in petrology, such as the location and height of fractures in unconventional gas and oil wells. Among these, GdAlO₃ has attracted interest because of its good thermo-mechanical properties. In this work, four Al₂O₃/GdAlO₃ reaction sintered composites were prepared using Gd₂O₃ and Al₂O₃ powders as raw materials and high-energy ball milling followed by sintering at 1600 °C. This combination of ball milling and reaction sintering is considered as a mechanism to produce large bulk ceramics with different Al₂O₃/GdAlO₃ compositions. The composite formulations range from pure alumina to eutectic ceramic. The obtained materials were characterized using X-ray diffraction for identifying the crystalline phases, Archimedes method for the textural properties, scanning electron microscopy for the microstructure, and Vickers indenter and three-point bending tests for the mechanical properties. In addition, the macroscopic capture cross-section Σ for thermal neutrons was estimated considering each composite formulation. It was found that the processing route is very suitable for producing low-porosity Al₂O₃/GdAlO₃ composites, which present similar mechanical properties to those of alumina. Both the material density and Σ increase with increasing the starting amount of Gd₂O₃, in a way that for the eutectic composite the density is 50% higher than that of pure alumina, and Σ is about 550000 c.u. The effect of the material porosity on Σ was also considered. The obtained results indicate that the proposed processing route is very attractive for producing these ceramic composites for technological applications.     

Ba0.6Sr0.4TiO3–MgO ceramics from ceramic powders prepared by improved aqueous gelcasting-assisted solid-state method

Based on aqueous gelcasting-assisted solid-state method (AGASSM), improved aqueous gelcasting-assisted solid-state method (IAGASSM) was proposed to prepare the 45 wt% Ba_0.6Sr_0.4TiO₃–55 wt% MgO (BSTM) ceramic powders. It is found that the BSTM ceramic powders prepared by IAGASSM are the most uniform with the smallest particles (D_av = 0.83 μm) than those prepared by solid-state method (SSM) and AGASSM. The phase compositions of the BSTM ceramic powders and ceramics from the prepared ceramic powders are the same whatever ceramic powder preparation method is adopted. Compared with SSM and AGASSM, the BSTM green samples and ceramics from ceramic powders prepared by IAGASSM are the most uniform. Furthermore, it is found that adopting IAGASSM to prepare ceramic powders could not only improve the dielectric properties of the BSTM ceramics considerably, but also decrease their sintering temperature.     

利用煤矸石制备微晶泡沫玻璃的研究

研究了以废玻璃和煤矸石为主要原料,采用烧结法制备新型微晶泡沫玻璃。该材料以透辉石CaMg(Si2O6)和硅灰石CaSiO3为主晶相,密度是0.93 g.cm-3,抗压强度为6.7 MPa。本研究为煤矸石的综合利用开辟了一个新的途径,具有明显的环境效益、经济效益和社会效益。     

Porous ceramics derived from steel slag/coal gangue mixtures using cigarette butts as the pore-forming agent

Fabrication of ceramic materials with interconnected pores is necessary to improve thermal energy storage efficiency in high-temperature infiltration technology. In the present study, industrial wastes such as coal gangue, steel slag, etc., were selected as the raw materials to prepare ceramics with interconnected pores. By adopting 50% cigarette butts as the pore-forming agent, steel slag–coal gangue mixtures with a mass ratio of steel slag to coal gangue of 1:9 were sintered at 1100°C, and ceramics with interconnected elongated pores were prepared successfully. The highest apparent porosity and lowest volume density of the as-prepared ceramics were ca. 73% and .74 g/cm³, respectively. Further measurements of the thermophysical properties indicated that no obvious mass loss was observed in the temperature range from ambient temperature to 800°C. The maximum values of specific heat and thermal conductivity were 1.38 J/(g K) and 1.661 W/(m K), respectively, and meanwhile the minimum compressive strength could exceed 3.5 MPa. These research results implied that the as-prepared steel slag–coal gangue ceramics can provide long-term service and offer excellent thermal stability over a wide temperature range. Therefore, they should have potential applications in high-temperature infiltration technology.     

Application of modified iron-containing catalysts and preliminary ozonization of coal from the Shubarkol deposit to the hydrogenation of this coal

The results of the hydrogenation processing of coal from the Shubarkol deposit in the presence of natural bauxites from the Turgai deposit in the Republic of Kazakhstan are reported. With the use of a sample of bauxite containing 23.7% Fe₂O₃ as a catalyst, a higher yield of liquid products (54.2%) was obtained, as compared with those on other bauxite samples (49.5–53.8%). It was established that the modification of catalysts containing iron with elemental sulfur additives (0.75–1.25%) makes it possible to increase the yield of liquid products to 62.3–67.3%. A positive role of the preliminary ozonization of coal, which makes it possible to increase the yield of total liquid products upon hydrogenation by 13.3% in comparison with the yield of liquid products obtained with the use of coal not treated with ozone, was demonstrated.     

ZnO和CuO烧结助剂对KNN压电陶瓷性能的影响

以微波水热法制备的KNN粉体为原料,添加1mol%ZnO、1mol%CuO烧结助剂,采用传统电子陶瓷制备方法,研究了烧结助剂对KNN陶瓷的陶瓷体积密度、显微结构和电性能的影响,结果表明:添加烧结助剂ZnO和CuO可以降低KNN陶瓷的烧结温度,提高KNN陶瓷的体积密度;与此同时,ZnO和CuO添加后降低了KNN无铅压电陶瓷的压电常数d33、介电常数ε33T/ε0,但机械品质因数Qm得到很大的提高,介电损耗tanδ明显降低。其中CuO烧结助剂可以使KNN陶瓷的d33由142 pC/N降低至118 pC/N,Qm值由82提高至427,tanδ由2.46%降低至0.64%。     

Production and service of high-alumina ceramic castables. 1. Ramming mixtures based on modified bauxite HCBS

The prospects of using bauxite-base HCBS in the production of high-quality ramming mixtures for lining blast furnace spouts are considered. A system of Chinese bauxite (filler) and bauxite HCBS (binder) is shown to give a ramming mixture with a porosity of 18 – 22% and σ_c of 120 MPa. The effect of some process factors on the properties of the new refractory material is considered. The life of the mixture in the main hearth spout is shown to be 70 – 90 thousand tons cast iron before the first repair at a consumption of 0.53 – 0.63 kg mixture per one ton cast iron. The processes that occur in the interaction between the material and blast furnace slags of various chemical compositions is considered. The characteristics of the developed mixture are compared with those of the standard ones. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 37–41, March, 2000.     

超低密压裂支撑剂的制备及性能研究

以二级铝矾土(65wt％Al2O3)和钾长石为原料,在添加不同含量的白云石的基础上制备了超低密高强的压裂支撑剂,并研究了白云石的添加量对烧成温度和石油压裂支撑剂性能的影响.结果表明:在原料中加入适量的钾长石,不仅可以降低烧结温度,同时还能降低压裂支撑剂的密度;添加白云石能有效降低支撑剂的烧结温度和破碎率,同时白云石和钾长石共同作用,促进了烧结致密化的进行,有利于棒状莫来石的生长发育,从而提高了支撑剂的强度.当白云石的添加量为2wt％,烧结温度为1330 ℃时,所制备的压裂支撑剂性能最优,其体密仅为1.30 g/cm3,52 MPa下的破碎率为4.51wt％.