Effect of Microstructure on Deformation of Polycrystalline MgO

Six types of polycrystalline MgO, one nominally fully dense and the others having porosities of ∼1 to 2%, were tested in compression up to 1400°C. At 1200°C and above, all materials deformed plastically; two of the materials, both porous, also exhibited plastic flow at temperatures down to 800°C, and a third at 1000°C. A qualitative analysis of the microstructures of these materials indicated that the differences in behavior arose primarily because of variations in the size and distribution of pores and in the concentration of impurities at the grain boundaries. It is suggested that the following factors aid plasticity below ∼1200°C: (1) Strong grain boundaries, in the absence of excessive impurities, permit buildup of stress concentrations with consequent nucleation of slip on the {100} system and the extension of slip across the boundaries and (2) clusters of very fine pores within the grains allow some mass accommodation.     

脉冲激光重熔对YSZ涂层微观结构的影响

本文采用电子束物理气相沉积技术在Ni基单晶基体表面制备双层结构的热障涂层后,采用脉冲Nd∶YAG(钇铝石榴石晶体)激光对其进行表面改性处理,分别研究了脉冲宽度和脉冲频率对重熔钇稳定氧化锆涂层(yttria-stabilised-zirconia,YSZ)微观结构及孔隙率的影响。结果发现:激光重熔的YSZ陶瓷层会在快速冷却过程中形成裂纹等缺陷,激光束的脉冲宽度和频率会显著地影响到涂层微观结构,脉冲宽度的增加会使重熔陶瓷层表面紧密、孔隙减少,脉冲频率的增加会使重熔陶瓷层表面的孔隙率先减小后增大。     

杀白蚁剂对水泥基材料强度与微观结构的影响

采用扫描电镜、X射线衍射技术研究了三种杀白蚁剂对水泥基材料的水化产物及其微观结构的影响,并结合掺杀白蚁剂水泥基材料的强度,探究两者之间的内在联系.结果 表明:杀白蚁剂的掺入会降低水泥基材料的强度,且随着杀白蚁剂浓度的提高,强度会逐渐降低.各试验组的主要水化产物均为Ca(OH)2和CaCO3,掺入杀白蚁剂并不会产生新的水化产物.与此同时,掺入较高浓度杀白蚁剂时,有利于促进水泥基材料的早期水化.相比于联苯菊酯和毒死蜱杀白蚁剂,吡虫啉杀白蚁剂对水泥基材料的影响更为严重.     

Microstructure and Grain-Boundary Effect on Electrical Properties of Gadolinium-Doped Ceria

The microstructural evolution and grain-boundary influence on electrical properties of Ce_0.90Gd_0.10O_1.95 were studied. The nanoscale powders synthesized from a semibatch reactor exhibited 50% green density and 92% sintering density at 1200°C (∼200°C lower than previous studies). Impedance spectra as a function of temperature and grain size were analyzed. The Ce_0.90Gd_0.10O_1.95 with finest grain size possessed highest overall grain-boundary resistance; this contribution was eliminated at temperatures >600°C, regardless of grain size. The grain conductivity was independent of grain size and was dependent on temperature with two distinct regimes, indicative of the presence of Gd'_Ce− V _o^∘∘ complexes that dissociated at a critical temperature of ∼580°C. The activation energy for complex dissociation was ∼0.1 eV; the value for the grain-boundary was ∼1.2eV, which was size independent.     

MgO对连铸保护渣的结构和结晶矿相微观形貌的影响

研究了MgO的含量对保护渣的结构和析晶行为的影响,并分析了晶相的种类、含量和形貌对热导率的影响.利用DSC测量了保护渣的析晶温度,表明析晶温度随MgO含量的增加而降低,在841℃位置的析晶峰强度随MgO的含量增加而降低.通过FT-IR和Raman光谱分析发现保护渣网络聚合程度随MgO的增加而降低.XRD结果表明保护渣在不同温度下析出的主晶相为镁黄长石,其含量随MgO含量的增加而降低,次晶相主要为镁橄榄石且其含量随MgO的增加而增加.同时也发现随热处理温度的提高镁橄榄石的含量也在不断增加,但是镁黄长石的含量随热处理温度提高而降低.此外,还有氟晶云母相和钾霞石相也存在于保护渣中.FE-SEM图说明黄长石主要为层状的晶体结构,晶体的排列致密程度、晶体的尺寸、界面以及其分布情况都会对热导率产生很大影响.当MgO含量小于12％时,保护渣在热处理以后的热导率随MgO含量的增加而增加,当MgO含量超过12％时,其热导率随MgO含量增加而迅速降低,但是在1100℃热处理的保护渣的热导率随MgO的含量增加而不断增加.     

烧成制度对铝质高强瓷显微组织结构的影响

本文利用X-ray衍射与SEM等分析测试手段,探讨了烧成制度对微观结构与相组成的影响,从而为获得高性能的瓷坯探索出合理的烧成工艺制度,并提出了必要的依据。     

火灾高温对混凝土残余强度和微观结构的影响

为了研究混凝土力学性能和微结构的耐火性特征,对混凝土试件进行不同高温的加热作用,然后开展相应的三轴压缩试验和CT扫描试验.结果表明,随着加热温度增加,混凝土试样的三轴试验峰值强度逐渐减小;在相同温度下,试件的残余峰值强度随固结围压增大呈线性上升趋势;根据CT扫描试验获得的混凝土二维/三维图像发现混凝土的孔隙度和平均孔隙半径随着温度增大而逐渐上升;混凝土的残余强度随温度升高存在明显劣化效应,其原因是作用于混凝土试件的温度越高,混凝土内部高温裂解效应越明显,导致孔隙体积增加,从而使得热裂解后的残余强度相对降低.本试验研究结果为深入认识粉煤灰混凝土耐火性的特征提供了参考.     

氟硫掺杂对MgO固溶及高镁熟料结构与性能的影响

利用化学分析、力学性能测试、岩相分析和XRD Rieitveld精修,研究了氟硫掺杂对高镁熟料中MgO固溶量、熟料强度、熟料显微结构和萃取阿利特的指纹区XRD特征峰及晶胞.结果显示:掺加一定量的SO3、CaF2能有效促进熟料中MgO的固溶.当掺加的CaF2掺量≤0.25％时,MgO固溶量随SO3含量增加而增加.随着熟料中CaF2掺量的增加,SO3含量的变化对MgO的固溶影响越来越弱.在SO3掺量≤1.2％,CaF2掺量的增加更利于熟料中MgO的固溶.单掺SO3时,熟料28 d强度随着SO3掺量增大而降低.而在同时掺有0.50％ CaF2的熟料中,随着SO3掺量的增大,熟料的3d、28 d强度均呈先增加后减少的趋势.在掺杂适量的CaF2的前提下,掺加一定量的SO3有助于提高熟料的强度,但存在一个最佳掺量.且在一定范围内熟料中CaF2的含量越高,水泥熟料的后期强度也越高.在熟料中同时含有SO3和MgO时,室温下能稳定M2-M3型的的阿利特.且在掺杂一定量的SO3时,随着熟料中CaF2含量的提高,阿利特的对称性也会逐步提高.与仅掺加MgO的样品相比,SO3、CaF2的掺杂使得alite的a轴稍有变小、b轴和c轴稍有变大,晶轴角则基本不变.     

Effect of Thermal Treatment on Microstructure and Fracture Strength of SiC Coatings

SiC coatings in tri‐structural isotropic‐coated (TRISO) particles were thermally treated at 2000°C for 1 h in argon atmosphere. The fracture strength of the SiC decreased while change in the Weibull modulus of the failure strength is more complex after the thermal treatment. The variation in both fracture strength and Weibull modulus can be explained by the formation of the pores in SiC due to thermal treatments, as annihilation of the stacking faults and diffusion of intrinsic defects lead to the pore formation.     

脉冲频率对纳米晶镍镀层结构及性能的影响

采用脉冲电沉积方法在黄铜基体上制备纳米晶镍镀层。研究了脉冲频率对镀镍层的微观结构、硬度及耐蚀性的影响。结果表明:直流电沉积制备的镀镍层表现为(111)晶面和(200)晶面的双择优取向,而脉冲电沉积制备的镀镍层仅在(111)晶面表现出择优取向;脉冲电沉积制备的镀镍层的硬度和耐蚀性均高于直流电沉积制备的镀镍层的;不同脉冲频率下制备的镀镍层的硬度没有显著差别,约为5 500 MPa;但不同脉冲频率下制备的镀镍层的耐蚀性存在差别,脉冲频率为0.1kHz时制备的镀镍层在3.5%的NaCl溶液中的耐蚀性最好。     

Influence of Surface Condition on the Strength of Polycrystalline MgO

The mechanical behavior of high-purity (greater than 99.9%) polycrystalline MgO, with relative density exceeding 9875, is described. By fracto-graphic techniques, it was determined that inter-granular cracks initiate fracture. These cracks originate from the extension of surface flaws into the MgO and are particularly severe in areas of high, localized, intergranular porosity. Ceramic machining techniques, such as diamond sawing and lapping with coarse abrasives, induce these surface flaws and limit the strength of MgO. The effectiveness of lapping, thermal conditioning, and chemical polishing techniques in removing these flaws and producing a substantial increase in mechanical strength is shown to be dependent on grain size and porosity.     

预氧化处理对反应烧结碳化硅微观结构和弯曲强度的影响

本文提出了一种简单有效的预氧化处理方法,用来强化反应烧结碳化硅(RBSC),研究了800~1 300 ℃预氧化处理对其微观结构和力学性能的影响,探究了含不同尺寸压痕裂纹的材料在氧化前后残余弯曲强度的变化规律。结果表明,随着氧化温度的升高,RBSC的室温强度和Weibull模数均存在先下降后上升,然后再下降的趋势,主要原因是不同温度氧化后的RBSC表面形貌不同。在1 200 ℃下预氧化2 h,RBSC的弯曲强度和Weibull模数都明显变大,强度提升了19.9%,Weibull模数由7.3提升到11.8。然而,800 ℃低温氧化不完全和1 300 ℃高温氧化反应过于强烈均会导致弯曲强度和Weibull模数下降。在最优氧化条件(1 200 ℃氧化2 h)下,含压痕裂纹(载荷20 N)的RBSC试样的残余弯曲强度在氧化后由201.1 MPa提高到324.2 MPa,强化机理是高温氧化生成的SiO₂能够消除材料表面缺陷和微裂纹。     

养护温度对矿粉水泥石强度及细观结构影响研究

为研究不同养护温度下矿粉水泥石早期（28 d）强度及细观孔结构分布特征,设定水泥石的水灰比为0．24,以掺入不等量的矿粉为掺合料,分别将水泥试块在－3℃和20℃条件下养护28 d,测定水泥石的抗压强度,用孔结构分析仪对细观孔结构进行分析,并通过水泥石的孔隙结构计算水泥石的实际抗压强度,对比分析其规律。结果表明：矿粉掺量相同时,－3℃养护下水泥石较20℃养护下水泥石早期抗压强度明显降低,水泥石硬化后含气量变小,孔间距系数和气孔平均弦长增大,孔径粗化严重;随着矿粉掺量的增多,水泥石早期抗压强度呈下降趋势,水泥石硬化后含气量增大,孔间距系数和气孔平均弦长增大,其中－3℃养护下的水泥石孔间距系数、气孔平均弦长和早期抗压强度变化趋势较20℃养护下变化明显。     

Creep-Sintering and Microstructure Development of Heterogeneous MgO Compacts

Simultaneous creep and densification and the microstructure development of magnesium oxide powder compacts were studied at 125°C and for applied stresses of up to 0.25 MPa. Die-pressing the powder into compacts with a relative green density of ∼0.40 led to an approximately bimodal distribution of pores, with one fraction having sizes of the order of 10 times the (initial) particle size and the other fraction having pore sizes of the order of the particle size. The presence of the large pores in turn gave rise to rather unusual sintering effects. After first decreasing with relative density (ρ), the densification rate (dρ/dt) and the creep rate (dɛ/dt) then increased dramatically for 0.6 < ρ < 0.75. This range of ρ corresponded to the stage of microstructure development when grain growth and coalescence of the smaller pores have created a more uniform pore distribution. Above ρ∼ 0.75, both dρ/dt and dɛ/dt again decreased with ρ. These trends in the densification behavior are discussed in terms of material parameters such as the equilibrium dihedral angle and the pore coordination number.     

高温碳化养护对干硬性水泥净浆强度及微观性能的影响

碳化养护可在加快水泥制品早期强度发展的同时固定二氧化碳,因此已引起国内外学者的广泛关注,然而,高温对碳化养护进程的影响却未见报道。本文选用5个温度(20 ℃、100 ℃、120 ℃、140 ℃、160 ℃)对干硬性水泥净浆进行碳化养护,探究了抗压强度随碳化温度的变化规律,并结合热重分析、X-射线衍射、红外光谱及扫描电镜等方法对碳化养护后样品的微观性能进行表征。结果表明:抗压强度及碳化程度随温度的升高表现出先增加后趋于平缓的趋势,碳化温度为140 ℃的试件相比碳化温度为20 ℃的试件抗压强度增长近4倍,表明高温碳化是加速养护的有效措施,适当的高温可以蒸发部分自由水,有利于碳化反应进行。此外,高温碳化养护生成了高聚合程度的无定形硅胶和三种不同晶型的碳酸钙(CaCO₃),其中文石和球霰石所占比例相比于常温碳化有所上升。     

Effect of Copper Additive on the Microstructure and Electrical Properties of Polycrystalline Zinc Oxide

Nonohmic behavior is obtained for polycrystalline ZnO with copper as the only additive in the range 0.3 x 1 wt%. The effect of copper on the microstructure and electrical behavior of ZnO:Cu ceramics is investigated. The leakage current decreases and the breakdown electric field increases as the copper concentration increases. The large apparent dielectric constant of ZnO:Cu ceramic ( k > > k _ZnO, k _ZnO is the dielectric constant of pure ZnO) is attributed to the grain boundary barrier layer effect. A Schottky barrier height of 0.27–0.46 eV is obtained for various copper-added samples, depending on sintering temperatures.     

硅灰对碳纤维混凝土强度及电阻率影响研究

通过在碳纤维混凝土中加入硅灰,研究了硅灰对碳纤维混凝土抗压强度、抗折强度和劈裂强度的影响规律,同时研究了硅灰对碳纤维混凝土电阻率的影响作用。结果表明:碳纤维混凝土相对素混凝土,抗压强度降低了5.9%,抗折强度提高了25.8%,劈裂强度增加了了21.1%;加入硅灰后,碳纤维混凝土抗压强度、抗折强度和劈裂强度都有所增加;10%硅灰掺量时,抗压强度增加了39%,抗折强度提高了40.6%,劈裂强度提高了34.3%。加入硅灰后碳纤维混凝土电阻率也明显降低,3 d时两者电阻率降低了8.6Ω,随着时间的推移,差值越来越小。说明硅灰对碳纤维混凝土的电阻率也有明显作用,进一步证明了加入硅灰可以有效提高碳纤维在混凝土中的分散性。     

Effect of Hot Extrusion, Other Constituents, and Temperature on the Strength and Fracture of Polycrystalline MgO

Improved agreement was confirmed between the Petch intercept and single-crystal yield stresses at 22°C. Hot-extruded MgO crystal specimens (recrystallized with no obvious grain boundary phases or residual porosity), stressed parallel with the resultant (100) axial texture (1) gave the highest and least-scattered strength–grain size results at 22°C, (2) showed direct fractographic evidence of microplastic initiated fracture at 22°C and showed macroscopic yield at 1315° and especially 1540°C, and (3) fractured entirely via transgranular cleavage, except for intergranular failure initiation from one or a few grain boundary surfaces exposed on the subsequent fracture surface, mainly at 1540°C. Hot-extruded, hot-pressed MgO billets gave comparable strength when fracture initiated transgranularly, but lower strength when fracture initiated from one or especially a few grain boundary surfaces exposed on the fracture (with residual pores). The extent and frequency of such boundary fracture increased with test temperature. While oxide additions of ≤5% or impurities in hot-pressed or hot-extruded MgO can make limited strength increases at larger grain sizes, those having limited solubility can limit strength at finer grain sizes, as can coarser surface finish (the latter especially at 22°C). Overall, MgO strength is seen as a balance between flaw and microplastic controlled failure, with several parameters shifting the balance.     

半水磷石膏粒径对砌块显微组织和强度的影响

采用机械破碎结合震动筛分方法获得了几种粒径分布半水磷石膏粉体。在养护温度及水膏比相同的条件下,用不同粒径半水磷石膏粉制备出了相应的砌块。研究表明,随着半水磷石膏粒径的减小,胶凝后的砌块强度先升高后降低。当半水磷石膏粒径约为45~75μm时,获得的砌块抗折和抗压强度均达到最大值,分别为4.06MPa和16.93MPa。粒度变化影响最终砌块微结构是导致强度变化的根本原因。