Simulation of the neck growth of non-isometric biosphere during initial sintering

Because powders are mostly non-isometric during the sintering process, copper powders were chosen to study the effects of four material transport mechanisms, including surface diffusion, grain-boundary diffusion, volume diffusion, and multi-couplings. These material transport mechanisms were studied with respect to sintering neck growth of a non-isometric biosphere during initial sintering. The evolution of the neck growth in the four transport mechanisms was simulated by Visual C＋＋ as well based on the model of different particles. The results show that the increase of the sintering temperature, both the grain-boundary diffusion and volume diffusion play primary roles in neck growth, while surface diffusion gradually becomes the secondary mechanism. Both the sintered neck and the shrinkage of the two centers increase with increasing temperature by means of the coupling diffusion mechanism. The radius of the sintering neck decreased, and the shrinkage rate of the two centers increased with an increase of the diameter ratio of the two spheres.

Preparation and Microstructure of Green Ceramsite Made from Sewage Sludge

A pilot study was conducted to produce high performance green ceramsite by using sewage sludge, fly ash and silt. According to the theory of Riley, the proportions of raw materials were chosen to perform the sintering experiments. Thereby, the optimum proportion of sludge, fly ash and silt and sintering parameters were determined. The microstructure of the optimized mixture and the leaching of heavy metal elements were also analyzed. The lab testing results show that sintering parameters have significant impact on the performance of ceramsite. For solid waste ceramsite with high loss of ignition, inadequate pre-burning process lowers the strength and increases the water absorption. Low water absorption can be achieved by the enameled surface and closed pore structure. The high performance green ceramsite has the density grade of 700, water absorption of 6% and compressive strength of 6.6 MPa. The ceramsite is mainly composed of cristobalite and mullite. The leaching of heavy metal elements from the solid waste ceramsite are lower than the limits required by the national standard. This study shows that the utilization of solid waste ceramsite as the light Weight aggregate is feasible and safe.

Preparation and Physical Properties of Ceramsite Filter Media for Water Treatment Obtained from Municipal Solid Wastes

Sludge,solid waste of sewage treatment plants,poses a threat as a secondary pollution if it is not handled properly.In this study,artifical ceramsite filter material(ACFM)for water treatment,was obtained from sludge by high-temperature sintering process,and then it’s physical properties,leaching toxicity and sintering mechanisms were investigated.The results showed that the preferred conditions for the preparation of ACFM were that the mass ratio of sludge,river sediment and fly ash was 5∶4∶1,preheated at 400℃for 20 min and sintered at 1 150℃for 5 min.After the optimal sintering conditions treatment,the physical properties of the rate of breaking and wear,solubility in hydrochloric acid,silt carrying capacity,void fraction and Brunauer-Emmett-Teller(BET)specific surface area of ACFM were 0.2%,0.01%,0.2%,71.1%and 0.75×104cm2/g,respectively.The results confirmed that the ACFM’s physical properties were totally aligned to the requirements of China’s industry standard(CJ/T 299—2008).The leaching toxicity results indicated that the leaching contents of heavy metals,such as Cr,Zn and Cu,were much lower than the thresholds of China’s national standards(GB 5085.3—2007 and GB 8978—1996).

Investigation of Loss Weight and Densification of SiC-Al_2O_3-Y_2O_3 Ceramic Composite on Sintering

α-SiC, Al_2O_3 and Y_2O_3 powders were all used as raw materials. The SiC-Al_2O_3-Y_2O_3 ceramic composites were made by pressureless liquid phase sintering technology. The effects of sintering temperature, loss weight and coordination number on sintering densification were studied. The reason for producing loss weight on sintering was analysed. The results show that the primary reason for producing loss weight on sintering in SiC-Al_2O_3-Y_2O_3 ceramic composite was that chemical reactions between SiC and Al_2O_3 are happened during sintering, and given out volatile gases. If sintering temperature is excessively lower, grain size would be finer, and coordination number would be higher, well then material would be on no sintering densification. If sintering temperature is excessively higher, grains would grow up, though small coordination number would benefit to make pore eliminate and shrink, but coarse microstructure would also block gliding and resetting of grains, together affected by expansion stress from volatile gas, the material densification would instead go down. Only under the sintering process of 1850 ℃ for 30 min, material densification is better, and the mechanical property of ceramic composites is also improved.

Preparation and Properties of High-strength Ceramsite in Low Water Absorption

Fly ash used as the main raw materials,incorporated with sintering expansion additive and fluxing additive in different ratio,was sintered high-strength lightweight aggregates of fly ash (ceramsite) in the laboratory-controlled electric furnace.The results show that the optimal sintering system is the sintering temperature range of 1250 ℃ to 1280 ℃ and retaining time of 5 min-10 min.The bulk density,the apparent density and 24 h water absorption of ceramsites decrease with the increase of sintering additive and the decrease of the amount of fly ash.The addition of fluxing additive can significantly enhance the compressive strength of ceramsite pellets,reduce its water absorption at 24 h and improve pore-shape ofinner structure.The firing coefficient (Pk) changed within 7.8-8.1 of raw materials can prepare high strength and low water absorption ceramsites.Pk kept a good linear relationship with porosity and strength of ceramsite particles.

In situ observation of grain evolution in ceramic sintering by SR-CT technique

Grain evolution of boron carbide ceramic powder during isothermal sintering process was in situ investigated by synchrotron radiation X-ray computed tomography (SR-CT) technique. The process of grain growth and material migration during three sintering stages was clearly distinguished from the 2-D and 3-D reconstructed images. The results show that from room temperature to 1 200 ℃ (0-270 min), grains gradually approach each other and form the sintering neck but grain growth does not start, which is indicated as the initial sintering stage. While the sintering time is between 270-390 min (temperature is 1 200 ℃), material migration between grains starts, while grains and sintering neck grow up, which is defined as the middle sintering stage. As the sintering time exceeds 390 min (temperature is 1 200 ℃), pores become isolated and spheroidized, which shows the final sintering stage. The double logarithm curve of mean grain radius and time logarithm during middle stage of isothermal sintering process is obtained from reconstructed images and the grain growth exponent is 0.364 03, falling in the predicted range of the traditional sintering theory. The experiment results are in accordance with those of the traditional sintering theory and provide effective experimental data for further analysis of the sintering process and the mechanical characteristics of ceramics.

Fabrication of Fe-6.5wt%Si Bulk by Spark Plasma Sintering

Fe-6.5wt%Si composite compact was fabricated by spark plasma sintering(SPS).Mec hanical alloying(MA)was used to prepare Fe-Si composite powders.The composite p owders were sintered by SPS at elevsated temperature from 500℃ to 700℃.The exp erimental results indicate that the non-equilibrium state of composite Fe-Si i s preserved in the compact.The density of the bulk rises with the increasing tem perature and there is no diffusion of silicon and iron in the interface.

煤气化炉渣免烧陶粒的制备及其在反硝化滤池中的应用

煤气化炉渣是煤气化过程中产生的固体废弃物。大量的炉渣堆积不仅造成了资源的浪费,而且增加了企业的运营成本,对当地环境造成危害。以内蒙古地区的煤气化炉渣为主要原料,加入水泥、生石灰、CaSO_(4)等,通过免烧结的方式制备陶粒。在制气炉渣、水泥、生石灰、CaSO4质量比为70∶30∶2.5∶5的条件下制得的陶粒性能最优越,比表面积可达51.7 m^(2)/g,堆积密度为809 kg/m^(3),颗粒破碎强度为6.61 MPa。将该陶粒用作反硝化生物滤池填料,相比于普通市售陶粒挂膜速度更快;在水力停留时间(HRT)为12 h时,化学需氧量(COD)由300 mg/L下降至60 mg/L以下,COD去除率在80%以上;硝态氮(NO_(3)^(-)-N)由60 mg/L下降至2 mg/L以下,NO_(3)^(-)-N去除率在95%以上。利用煤气化炉渣制备免烧结陶粒实现了煤气化炉渣的资源化利用,同时为污水反硝化处理提供了一种新的填料。

以非氧化物为烧结助剂制备高导热氮化硅陶瓷的研究进展

功率半导体器件高电压、大电流、高功率密度的发展趋势,对器件中陶瓷基板的散热能力和可靠性提出了更高的要求,兼具高热导率和优异力学性能的氮化硅陶瓷作为功率半导体器件的首选散热基板材料受到了广泛关注。目前氮化硅陶瓷热导率的实验值与理论值存在较大差距,高温、长时间保温的制备条件不仅会使晶粒过分长大,削弱其力学性能,而且会造成成本高企,限制了其规模化应用。晶格氧缺陷是影响氮化硅陶瓷热导率的主要因素,通过筛选非氧化物烧结助剂降低体系中的氧含量,调节液相的组成和性质并构建“富氮-缺氧”的液相,调控液相中的溶解析出过程,促进氮化硅陶瓷晶格氧的移除及双峰形貌的充分发育,从而实现氮化硅陶瓷热导率-力学性能的协同优化是目前研究的热点。本文基于元素分类综述了当前国内外开发的非氧化物烧结助剂体系,着重从液相调节和微观形貌调控的角度介绍了非氧化物烧结助剂改善氮化硅陶瓷热导率的作用机理,分析了晶粒发育、形貌演变规律和晶格氧移除机制,并展望了高导热氮化硅陶瓷的未来发展前景。

粉煤灰陶粒的制备技术及研究进展

粉煤灰是中国最大的固废污染源,对其进行高值化应用不仅能变废为宝,而且是中国经济建设中一项重要的技术经济政策,是解决中国电力生产环境污染和资源缺乏之间矛盾的重要手段。粉煤灰陶粒的制备对于粉煤灰资源化利用具有重要意义。综述了粉煤灰陶粒的制备方法及国内外研究进展,分别对焙烧法和免烧法制备粉煤灰陶粒的工艺及机理进行了详细的分析,介绍了粉煤灰陶粒目前的市场应用领域及采用的标准,同时提出了在综合利用过程中存在的问题和解决办法,并对未来的发展趋势进行了展望。

赤泥-钢渣基免烧陶粒的制备及除磷特性研究

针对传统烧结陶粒制备过程中成本高、能耗大的缺点,以赤泥和钢渣为主要原料,通过免烧工艺制备出了具有磷吸附性能的陶粒。以解体率为其力学性能指标,通过正交实验确定了陶粒的最佳质量配比(赤泥、钢渣质量比4:3、稻壳灰添加量10%、石膏添加量4%、水泥添加量10%),最佳制备工况下的陶粒解体率为3.90%;所制作陶粒无重金属浸出风险,属于环境友好型材料。陶粒对水中磷的吸附特性实验结果表明,陶粒在酸性溶液中具有最佳的除磷效果;对于初始磷浓度为20 mg/L的溶液,设置30 g/L的陶粒投加量,除磷率可达96.40%;陶粒吸附过程遵循准二级动力学模型和Langmuir等温吸附模型,最大理论吸附量为0.99 mg/g;磷与陶粒表面的CO_(3)^(2-)、Ca^(2+)、Fe^(3+)、Al^(3+)发生离子交换和磷酸盐共沉淀反应,是水中的磷去除的机理,沉淀物质主要由Ca_(3)(PO_(4))_(2)、FePO_(4)、AlPO_(4)组成。

单掺和双掺不同长径比钢纤维对全轻混凝土力学性能的影响

为研究单掺和双掺不同长径比钢纤维对免烧结粉煤灰陶粒全轻混凝土力学性能影响,选用体积掺量为1%的剪切钢纤维作为增强材料,以钢纤维长径比(18.75,25和31.25)和掺入方式(单掺、双掺)为试验参数,对LC30全轻混凝土进行立方体抗压强度、轴心抗压强度、抗折强度、劈裂抗拉强度和弹性模量试验。试验结果表明:钢纤维能明显改善全轻混凝土的力学性能;不同的长径比和掺入方式对全轻混凝土的抗折度和劈裂抗拉强度影响较大,对立方体抗压强度和轴心抗压强度影响较小,对弹性模量几乎没有影响。

铁尾矿基陶粒的制备及应用研究进展

铁尾矿是我国堆存量最大的尾矿,其长期大量排放造成了严重的环境污染和安全隐患,提高其资源化利用水平迫在眉睫。陶粒是一种新型人造轻骨料,因具有轻质高强、保温隔热、抗冻耐久等优异性能而被广泛应用于建筑、园林、化工等领域。本文根据铁尾矿的分布状况及基本性质,分析了利用铁尾矿取代天然原料生产陶粒的可行性,以提升铁尾矿的利用价值。详细论述了铁尾矿制备陶粒常用的烧胀和免烧两种生产工艺,着重阐述了铁尾矿烧胀陶粒在改善黏聚成球性、轻质高强性和保温隔热性等方面采取的措施。提出了在未来的研究中需要解决的问题和重要的发展方向。

Fe基类Fenton催化剂非均相处理造纸废水

针对传统均相Fenton法深度处理造纸废水中铁泥量大、成本较高等问题,将Fe_(2)O_(3)、Al_(2)O_(3)、SiO_(2)、石墨粉采用高温烧结的方式,制备Fe基类Fenton催化剂,并用于非均相Fenton处理造纸废水,可达到节省FeSO_4用量的效果。结果表明,经高温烧结制备的Fe基类Fenton催化剂具有丰富的孔隙结构,在pH值为3、催化剂投加量15 g/L、COD_(Cr)和H_(2)O_(2)质量比1∶0.75、反应时间90 min的条件下,造纸废水COD_(Cr)去除率为74.8%,且经过10次循环实验仍达70%以上,BOD_5去除率可达67%以上。

晶界扩散Mg对钕铁硼磁体磁性能及微观组织的影响

烧结Nd-Fe-B磁体在风力发电、电动汽车等环保节能新能源产业中扮演着重要角色,因此研究制备高矫顽力及高磁能积的钕铁硼永磁材料是目前迫切需要解决的重要问题。本研究基于磁控溅射沉积非稀土元素Mg薄膜,再经过热处理使其扩散进入磁体内部,通过设定不同的扩散温度和时间,得到最佳扩散工艺参数,磁体矫顽力最大值达到17.12 kOe,增幅达到3.86 kOe,综合磁性能较为良好。通过对比分析实验前后磁体的磁性能和微观组织,Mg元素扩散过程中,低熔合金与富Nd相结合形成低熔液相,润湿性良好的低熔液相促进富Nd相流动,形成连续平滑的细晶界。这种方法可提高材料性能,适用于制备、表面改性和界面工程等领域。

锂云母渣免烧陶粒滤料制备及耐酸改性研究

为制备具有耐酸性的锂云母渣免烧陶粒滤料,采用蒸汽蒸压工艺对原料进行活化以提高陶粒滤料力学强度,并采用化学改性剂提高其表面耐酸性能。结果表明,随着锂云母渣掺量的增加,陶粒滤料强度密度比逐渐降低,锂云母渣取代河砂比例为5%时,制备的陶粒滤料堆积密度为985 kg/m^(3),筒压强度为5.9 MPa。盐酸浸泡后陶粒滤料的盐酸可溶率达到12.7%,样品中方解石含量从15.0%降至6.4%。耐酸剂NSJ改性的陶粒滤料经盐酸浸泡后,方解石含量仍有13.8%,与未浸泡陶粒滤料样品方解石含量相当,盐酸可溶率指标从12.7%降至1.5%,陶粒滤料抗酸侵蚀能力显著提升。

铁尾矿基超强陶粒的制备及性能研究

随着建筑用石的价格逐年升高,采用尾矿、污泥、粉煤灰、建筑垃圾等固体废弃物制备高强陶粒替代石子成为研究热点。本试验采用铁尾矿为主要原料制备超强陶粒,研究原料配比、烧成制度对陶粒性能的影响。最终制得抗压碎强度为56.5 MPa(约为石子抗压碎强度的4倍),表观密度为2.56 g/cm^(3),吸水率为0.06%的超强陶粒,为铁尾矿资源化利用提供了可行途径。

Thermodynamic Properties of Non-Oxide Composite Refractories

For initiative application of non-oxides in refractories, it is essential to study thermodynamic properties of non-oxides. The stability and stable order of non-ox- ides under oxidized atmosphere are analyzed firstly and then a new process, “converse reaction sintering”, is proposed. The results of study on oxidation mechanism of silicon and aluminum nitrides indicate that the gaseous suboxides can be produced observably when the oxygen partial pressure is lower than “conversion oxygen partial pressure”. The suboxides can be deposited near the surface of composite to become a compact layer. This causes the material possessing a performance of “self-impedient oxidation”. Metal Si and Al are the better additives for increasing the density and width of compact layer and increasing the ability of anti-oxidation and anti-corrosion. The study on Si3 N4-Al2O3, Si3N4-MgO, Si3 N4-SiC systems is also enumerated as examples in the paper. The experimental results show that the converse reaction sintering is able to make high performance composites and metal Si and Al not only can promote the sintering but also increase the density and width of compact layer.

赤泥煤矸石吸音降噪陶粒的研制

吸音降噪陶粒广泛应用于建筑、交通等领域的声屏障和吸音板,现有陶粒主要原料是黏土、页岩等不可再生资源。为制备绿色环保的高性能吸音降噪陶粒,解决我国赤泥、煤矸石和废弃石粉存量大、利用难的问题。利用拜耳法赤泥、煤矸石和废弃石粉,经圆盘成球和烧结工艺制备陶粒,通过观察宏观形貌和测试物理性能探究陶粒最佳烧结温度,并测定陶粒的放射性,由驻波管法和流阻试验测定陶粒混凝土标准试件的最佳吸声系数。结果表明,烧结温度为1120℃陶粒性能最佳,筒压强度为7.0 MPa,堆积密度为947 kg/m^(3),内照射性指数为0.6,外照射性指数为1.0;当水灰比为0.2,流阻率在2535~3429 Pa·s/m^(2)时,陶粒混凝土标准试件的平均吸声系数最佳,为0.50。吸音降噪陶粒的物理性能达到GB/T 17431.1-2010《轻集料及其试验方法第1部分:轻集料》对高强人造轻集料的要求,放射性满足GB 6566-2010《建筑材料放射性核素限量》对建筑主体材料的要求。