激光扫描对Ti（C,N）基金属陶瓷表面烧结结构的影响

采用真空烧结工艺制备了Ti(C,N)基金属陶瓷试样.利用5 kW横流CO2激光加工机,在激光功率为3.0 kW,光斑直径φ5 mm,扫描速度为5～30 mm/s,采用氩气保护条件下,对Ti(C,N)基金属陶瓷试样表面进行了处理.扫描电镜和电子探针的分析结果表明,激光扫描条件下,试样表面烧结结构中颗粒相的形态钝化,棱角变钝,多角形向椭球形转化,并发生了颗粒相的溶解烧损与分布状态的重排,颗粒相细化的同时,其分布变得均匀.在激光作用下,颗粒相之间及其与基体粘结相之间存在明显的交互作用,从结合强度上讲,使粘结相与硬质相能较好地结合,实现较大的结合强度.从力学性能分析,这对金属陶瓷韧性的提高非常有利,并增强了金属陶瓷表面层的抗颗粒相剥落性能,这些性能对刀具刃口使用性能的改善十分有益.(OE19)

稀释剂量对反应烧结Si_3N_4陶瓷结构和性能的影响

以工业Si粉为原料,α-Si3N4粉为稀释剂,聚乙烯醇为粘结剂,采用反应烧结工艺制备了Si3N4陶瓷。研究了稀释剂量对反应烧结Si3N4陶瓷的体积密度、开气孔率、相组成、微结构、弯曲强度和抗热震性的影响。结果表明,随稀释剂量的增加,Si3N4陶瓷的体积密度从2.27g/cm3降至2.04g/cm3,开气孔率从23%升至33.8%。Si3N4陶瓷由α-Si3N4、β-Si3N4和少量单质Si组成。Si3N4主要以针状晶形式存在,残留Si呈不规则块体。随着稀释剂量的增加,4组Si3N4陶瓷的三点抗弯强度分别为119MPa、112MPa、146MPa和113MPa;经50次800℃至室温空冷热震后,其强度保持率分别为81.5%、90.2%、87%和88.5%,表现出较好的抗热震性。

烧结多孔结构的渗透和流阻特性研究

为研究粉末冶金多孔结构的渗透性和流阻,以空气和氢气为介质进行了实验.实验显示微孔内流雷诺数低于1时,介质流量与穿过多孔结构的压降呈线性关系;当内流雷诺数高于1时,其流量与压降呈非线性特征.分析表明:传统的堆积床经验关系式将低估氢气和空气在烧结材料微孔中的流阻;相反,高估烧结多孔结构的渗透性能.并用粉末烧结结构的氢气和空气渗透实验数据拟合了多孔结构渗透率及摩擦阻力关联式.

精矿粉对烧结矿液相行为和结构的影响

粒级细小的精矿粉在烧结过程中对粘结液相的形成和行为具有重要影响。采用相图软件(FactSage^(T M)7.0)对Fe_2O_3-CaO-SiO_2渣系进行了计算,通过烧结试验对铁矿粉烧结液相行为受脉石的作用进行了研究。结果表明,SiO_2能明显提高烧结液相的量和流动行为,Al_2O_3也有一定的促进作用,MgO则会轻微抑制;同化性能好的铁矿粉形成的初始液相层较薄,有利于其扩散;烧结矿的粘结相和孔洞结构主要受液相行为和大颗粒矿粉自身致密度影响。

复杂中国矿形成的烧结矿结构

本文对来自中国六个厂家的本地铁矿石和烧结矿地评价分析。多数铁矿含有致密磁铁矿 失矿，而且复杂的铁矿含的矿物包括黄铁矿、磁黄铁矿、墨云母和菱铁矿，其中有一种特殊矿非常复杂，含有大量的氟。收到的烧结矿中有一种明显是磁铁矿为主要含铁料生产的烧结矿。硅酸盐玻璃及ＳＦＣＡ矿物是其主要胶接相，磁铁矿是其主要铁氧化物。用赤铁矿为主要含铁料厂家的烧结矿中ＳＦＣＡ含量相对较发育且含有较高的残余赤铁矿。

包钢铁精矿低硅烧结的实验研究

采用正交试验及微型烧结、矿相显微分析相结合的方法,研究了烧结温度、碱度、MgO含量、SiO2含量对于包钢特殊矿低硅烧结的强度及组成结构的影响规律.研究结果表明,在w(SiO2)=4.0%的条件下,包钢烧结矿也能具有较高的强度,各因素对烧结试样抗压强度的影响顺序是:烧结温度>碱度>MgO含量>SiO2含量.包钢特殊矿在1 320℃烧结时,烧结试样呈现极不均匀结构,铁酸钙由表及里逐渐减少,整体呈薄壁大气孔结构,烧结矿强度较差.当烧结温度在1 200℃时,主晶相赤铁矿增多,脉石含量增多,孔隙率增大,但孔隙分布均匀,矿相结构变均匀.

新钢烧结配料整体优化程序的开发

为发挥各品种铁料的互补优势,降低烧结配料结构成本,新钢铁前系统采用线性规划算法,使用C#2012编程语言和SQL SERVER 2012数据库技术,结合新钢铁前系统的工艺特点,自主开发了烧结配料整体优化程序。该程序具有原料参数导入功能、计算结果导出功能、计算烧结矿最低吨矿或吨铁成本等功能。

引流砂烧结机理研究现状

随着技术的进步,人们开始在钢包上使用滑动水口和引流砂。引流砂与钢液的烧结反应是钢包自开的决定性因素。引流砂与钢液烧结过度,导致钢包不自开则需氧枪手动开浇,不仅会影响连铸的顺行,对钢液的洁净度也会造成破坏,而且手动开浇对工人的安全存在隐患。为了提高钢包自开率,总结了引流砂的种类、性能、影响因素、烧结结构和烧结机理,为引流砂的烧结反应研究提供理论基础。

烧结机半干法烟气脱硫塔结垢的原因分析及改进

本文对烧结机半干法烟气脱硫塔结垢问题从设备结构和工艺操作上进行了分析,通过采取调整喷枪角度,优化喷枪布局,合理控制工艺操作参数,优化烧结原料结构等措施,降低了脱硫剂消耗,杜绝了脱硫塔结垢。

高效烧结板除尘器设计研究

为了能够实现除尘器具有捕集微尘效率高、体积小、维修保养方便、使用寿命长等特点,对高效烧结板除尘器的设计进行了研究,研究了塑烧过滤板的特点、高效烧结板除尘器构成、能源介质条件、烧结板结构、电气仪表及控制,并且分析了除尘器的工作原理、操作流程、使用过程中的注意事项以及除尘器保养要点。研究得出,高效烧结板除尘器实现了高效率的微粉捕集,注意事项以及除尘器保养要点的设定,降低了设备的故障率,有效地延长了除尘器的使用寿命。

细粒级铁矿粉对烧结液相和矿结构的影响

利用基础烧结设备检测了细粒级铁矿粉同化速度、流动能力,并通过微型烧结杯模拟料层下部单元点烧结过程的方法来研究配加15%细粒级矿粉的烧结矿结构变化,有效分析了3种细粒级矿粉在烧结时的液相行为及对烧结矿结构和性能的影响。通过比较生产用混匀矿与配加质量分数为15%的A、B、C粉的烧结矿结构表明:A粉有利于减少烧结矿内部孔洞的尺寸,减少核颗粒和液相间较大孔洞的数量,并能促进针铁矿发展;B粉会增加烧结矿内部大孔洞,增加柱状或片状铁酸钙的生成;C粉同化速度慢,液相流动能力差,粘结效果差,会使液相与核颗粒间孔洞尺寸和数量增加。烧结杯试验结果表明:在生产用混匀矿中使用质量分数为15%的A粉,烧结矿的转鼓指数提高2.94%,低温还原粉化指数(RDI)降低3.37%。

Effects of microwave sintering temperature and soaking time on microstructure of WC-8Co

WC-8Co cemented carbide samples were processed via microwave irradiation in a 2.45 GHz, high-power multi-mode microwave cavity. The densification of the compacts and the microstructures of the prepared alloys were studied. The results demonstrate that the liquid phase is formed around 1300 ℃ and nearly full densification is obtained at 1450 ℃ for 5 min via microwave irradiation. The microstructures of microwave sintered samples have finer and more uniform WC grains than those of vacuum sintered samples. Besides, the WC grain size and distribution are only decided by the sintering temperature. Holding time has negligible effects on them. No matter how holding time is, the mean grain size is 2.7 pan when the sintering temperature is kept at 1450 ℃.

Microstructure and mechanical properties of TiAl-based alloy prepared by double mechanical milling and spark plasma sintering

A fine-grained TiAl alloy with a composition of Ti-45Al-2Cr-2Nb-1B-0.5Ta-0.225Y （mole fraction, %） was prepared by double mechanical milling（DMM） and spark plasma sintering（SPS）. The relationship among sintering temperature, microstructure and mechanical properties was studied. The results show that the morphology of double mechanical milled powder is regular with size in the range of 20-40 μm and mainly composed of TiAl and Ti3Al phases. The main phase TiAl and few phases Ti3Al, Ti2Al and TiB2 were observed in the SPSed alloys. For samples sintered at 900 ℃ the equiaxed crystal grain microstructure is achieved with size in the range of 100-200 nm. With increasing the SPS temperature from 900 ℃to 1000 ℃ the size of equiaxed crystal grain obviously increases, the microhardness decreases from HV658 to HV616, and the bending strength decreases from 781 MPa to 652 MPa. In the meantime, the compression fracture strength also decreases from 2769 MPa to 2669 MPa, and the strain to fracture in compression increases from 11.69% to 17.76%. On the base of analysis of fractographies, it shows that the compression fracture transform of the SPSed alloys is intergranular rupture.

Solid-phase sintering process and forced convective heat transfer performance of porous-structured micro-channels

A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.

烧结丝网结构蒸发器内传热特性实验研究

本研究开展了不同工质、不同运行压力、不同丝网厚度及目数对烧结丝网结构蒸发器内传热特性影响的实验研究。实验中采用工质分别为R141b、R113、R649;运行压力范围为0.86×10~5~2.0×10~5 Pa;烧结丝网结构的厚度分别为0.6mm、0.8 mm、1.0 mm;丝网目数分别为60目和140目。实验结果表明:运行压力、丝网厚度和丝网目数对丝网结构换热表面的换热特性有重要的影响;汽化核心随着热流密度的增加而增加;单个气泡生长过程与池沸腾气泡的生长过程明显不同。

Bimodal-grained Ti fabricated by high-energy ball milling and spark plasma sintering

Bimodal-grained Ti containing coarse and fine grains was fabricated by high-energy ball milling and spark plasma sintering (SPS). The microstructure and mechanical properties of the compacts sintered by Ti powders ball-milled for different time were studied. Experimental results indicated that when the ball-milling time increased, the microstructure of sintered Ti was firstly changed from coarse-grained to bimodal-grained structure, subsequently transformed to a homogeneous fine-grained structure. Compared with coarse-grained Ti and fine-grained Ti, bimodal-grained Ti exhibited balanced strength and ductility. The sample sintered from Ti powders ball-milled for 10 h consisting of 65.3% (volume fraction) fine-grained region (average grain size 1 μm) and 34.7% coarse-grained region (grain size > 5 μm) exhibited a compress strength of 1028 MPa as well as a plastic strain to failure of 22%.

Formation mechanism and crystal simulation of Na_2O-doped calcium aluminate compounds

Calcium aluminate clinkers doped with Na2O were synthesized using analytically pure reagents CaCO3, Al2O3, SiO2 and Na2CO3. The effects of Na2O-doping on the formation mechanism of calcium aluminate compounds and the crystal property of 12CaO·7Al2O3 (C12A7) cell were studied. The results show that the minerals containing Na2O mainly include 2Na2O·3CaO·5Al2O3 and Na2O·Al2O3, when the Na2O content in clinkers is less than 4.26% (mass fraction). The rest of Na2O is mainly doped in 12CaO·7Al2O3, which results in the decrease of the crystallinity of 12CaO·7Al2O3. The crystallinity of 2Na2O·3CaO·5Al2O3 is also inversely proportional to the Na2O content in clinkers. The formation processes of 2Na2O·3CaO·5Al2O3 and 12CaO·7Al2O3 can be divided into two ways, which are the direct reactions of raw materials and the transformation of CaO·Al2O3, respectively. The simulation shows that the covalency of O-Na bond in Na2O-doped 12CaO·7Al2O3 cell is weaker than those of O-Ca and O-Al bonds. The free energy of the unit cell increases because of Na2O doping, which results in the improvement of chemical activity of 12CaO·7Al2O3. The leaching efficiency of Al2O3 in clinker is improved from 34.81% to 88.17% when the Na2O content in clinkers increases from 0 to 4.26%.

Experimental investigation of performance properties and agglomeration behavior of fly ash from gasification of corncobs

The gasification industries make use of biomass residue as feedstock to produce synthesis gas,but the gasification of this waste biomass generates tons of ash everyday.Performance properties and agglomeration behavior of corncob ash(CCA) collected from the gasification of corncobs in a pilot-scale gasification station were investigated by using some experimental methods.Based on the chemical composition results,the agglomeration tendency of CCA from combustion and gasification process was also analyzed.Chemical analysis shows that the fly ash is mainly composed of inorganic matters formed by K,Mg,Ca,Na,Fe,Al,S,etc.The agglomeration characteristics indicate that the slagging degree increases with the increase of ashing temperature,and the slagging tendency of these CCA samples from gasification or combustion is different with various slagging indices.All CCA samples from combustion or gasification can cause slagging/fouling problems in thermal conversion systems.The applications of CCA are closely related to its performances,and CCA has the potential to be used in various fields,for example,as a material for ceramic products and activated carbon,as an adsorbent,as a crude fertilizer,and as a structural material.

Sintering and microstructure of silicon carbide ceramic with Y_3Al_5O_(12) added by sol-gel method

Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’.

Microstructure and properties of alumina-silicon carbide nanocomposites fabricated by pressureless sintering and post hot-isostatic pressing

A1203/5%SIC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed （HIP）, which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of A1203 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, A12OJSiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed A1203/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the A1203/5%SIC nanocomposites by pressureless sintering and post HIP process.