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1.
为解决黄河冲积平原地区粉土粘聚力低、水稳定性差等工程应用问题,采用烧结法赤泥和基质沥青为主材制备粉土固化剂(RAC)对粉土进行综合稳定。按5%水泥优选掺量并附加0,2,4,6,8% RAC成型稳定粉土试件,经过标准养护、浸水软化、循环加热、低温冻融、高温自愈等特定试验条件后,进行3d、7d和28d龄期的抗压强度与压缩模量试验,对比分析不同掺量RAC稳定粉土路用性能的变化规律。采用扫描电镜(SEM)分别观察粉土、水泥稳定粉土和RAC稳定粉土的微观结构形貌和孔隙特征,进而探讨固化稳定机理。结合实体工程的应用实践对RAC稳定粉土的路用性能进行测试分析与验证。结果表明:与单掺水泥相比,RAC稳定粉土具有良好的力学性能,2,4,6,8%RAC稳定粉土标准养护3d强度分别提高110%,146%,156%,161%,28d龄期浸水强度损失率均小于20%;当RAC掺量高于4%时,循环加热5次以上可使稳定粉土的强度增长超过140%,低温冻融强度损失率小于15%;试件加载至90%极限荷载,循环加热5次后,2,4,6,8%RAC稳定粉土强度变化率分别是-8.3%,-2.3%,+8.0%,+12.9%。SEM图像显示RAC稳定使粉土形成密实的胶结凝聚体和均匀分布的孔径小于1μm非连通微孔结构,有利于稳定粉土水稳定性和抗冻性的提高;高温条件下沥青组分发生湿润粘结包裹粉土颗粒及水化产物,同时加速扩散填充内部孔隙和微裂缝,实现土体的损伤修复和结构补强。实体工程中RAC稳定粉土结构层取芯测试抗压强度为1.7MPa,压缩模量为1360MPa,路面弯沉为18~23(0.01mm),未出现裂缝、坑槽、松散等损坏现象。  相似文献   
2.
Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y2O3-CeO2 solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce4+ to Ce3+ in Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions corresponds to less-negative Gibbs energy compared to ZrO2-CeO2 solid solutions.  相似文献   
3.
Alumina-based ceramic cores are used to manufacture the internal structures of hollow alloy blades, requiring both high precision and moderate properties. In this work, zirconia is regarded as a promoter to improve the mechanical properties of sintered ceramic. The effect of zirconia content and particle size on the microstructure and mechanical properties of ceramics was evaluated. The results indicate that the flexural strength of sintered ceramics reached the maximum of 14.5 ± 0.5 MPa when 20 wt% micron-sized (10 μm) zirconia (agglomerate size, consistent with the alumina particle size) was added, and 26.5±2.5 MPa when 15 wt% 0.3 μm zirconia was added. Zirconia with submicron-sized (0.3 μm) particles effectively filled the pores between alumina particles, thus leading to the maximum flexural strength with a relatively low content. The corresponding sintered ceramics had a bulk density of 2.0 g/cm3 and open porosity of 59.6%.  相似文献   
4.
研究了加压辅助闪烧烧结工艺参数(温度、电压、电流、压力)对钇稳氧化锆致密度、微观组织结构和成分组成的影响,该工艺在热压烧结基础上叠加闪烧效应,利用高电场强度使高温导电氧化锆瞬间发生密实化烧结。结果表明:钇稳氧化锆的闪烧临界温度为880℃,在相同的电场强度条件下,闪烧临界温度处烧结可获得最大的闪烧收缩量。氧化锆在临界烧结温度下瞬时放电快速烧结符合焦耳热效应和接触点局部热效应,临界闪烧温度的高峰值功率闪烧易导致样品的组织结构和成分变化,峰值功率应进行控制,即电流强度应低于3 A。  相似文献   
5.
戴文华  辛忠 《化工学报》2022,73(8):3586-3596
为了提高Cu/ZrO2催化剂在二氧化碳加氢制甲醇中的催化活性,制备了一系列不同Si/Zr的Si-ZrO2载体并负载5%(质量分数)Cu得到了Cu/Si-ZrO2催化剂。对所制备的催化剂进行了X射线衍射(XRD)、N2物理吸脱附(BET)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)、二氧化碳程序升温脱附(CO2-TPD)及高分辨透射电子显微镜 (HRTEM) 的表征。结果表明,Si的掺杂使得Cu/ZrO2体系获得了稳定的晶相,大的比表面积和更多的碱性位点,尤其是中强碱性位点,同时产生了更多的氧空位,促进了CO2的吸附和转化,因此得到了更高活性的催化剂。当Si与Zr的摩尔比为0.2时,在质量空速为6000 ml·g-1·h-1,温度为220℃、压力为3.0 MPa,V(H2)∶V(CO2)=3∶1(体积比)条件下,催化剂的CO2转化率为4.6%,CH3OH选择性为85%。  相似文献   
6.
《Ceramics International》2022,48(12):17185-17195
This study introduces micro-nano bubbles (MNBs) in the process of polishing zirconia ceramics through sodium borohydride hydrolysis to assist in polishing yttria-stabilized zirconia (YSZ). Compared with conventional silica sol, the material removal rate using this MNB-assisted technology is increased by 261.4%, and a lower surface roughness of 1.28 nm can be obtained. Raman, X-ray diffraction, and X-ray photoelectron spectroscopy are used to study the structural changes and phase stability of the YSZ during different polishing periods. The results show that MNBs are the key factor promoting the transformation from the tetragonal phase to the monoclinic phase on the surface of the YSZ during polishing. The H2O molecules (or OH? ions) on the surface of the YSZ are driven by the thermal kinetic energy of the micro-jets formed by the collapse of micro-bubbles, and they permeate to occupy more oxygen vacancies in the crystal lattice. Atomic force microscopy and nano-indentation tests show that the micro-protrusions on the surface of the YSZ preferentially undergo phase transformation, and their hardness decreases. This promotes abrasives to preferentially remove rough spots on the surface and achieve more efficient polishing. We believe this work adds valuable insights regarding low-temperature degradation and ultra-precise machining of YSZ ceramic materials.  相似文献   
7.
Heat transfer within ceramic feedstock powders is still unclear, which impedes optimization of the thermal and mechanical properties of the thermal sprayed coatings. The microspheres (yttria-stabilized zirconia YSZ and lanthanum zirconate LZO) were prepared via the electro-spraying assisted phase inversion method (ESP). The thermal properties of the two ESP microspheres and a commercial hollow spherical powder (HOSP) were investigated by using theoretical, experimental, and simulation methods. Thermal conductivity of the single microsphere was estimated via a novel nest model that was derived from the Maxwell-Eucken 1 and the EMT model. Thermal conductivity of a single YSZ/LZO-ESP microsphere prepared at 1100–1200 °C was within 0.36–0.75 W/m K, which was ~ 20 % lower than that of a single YSZ-HOSP microsphere with a similar porosity. Heat flux simulation showed that high tortuosity around the multi-scaled voids of the ESP microsphere led to a more efficient decrease in thermal conductivity compared with total porosity.  相似文献   
8.
Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics with outstanding mechanical properties and aesthetic origins are expected to be used in dental implant applications. However, tetragonal zirconia ceramics are not bioactive, which affect the osseointegration and reliability as dental implant materials. Herein, in this study, Y-TZP ceramics were modified by grain-boundary activation via coating a bioactive glass (BG) sol with different content on the crystal surfaces of zirconia powder and followed by being gelled, dried, granulated, low-temperature treated, molded and sintered at 1450°C for 3 h in air. The effects of BG content on the morphology, phase compositions, mechanical properties, in vitro mineralization ability and cell biological properties of the bioactivity modified Y-TZP ceramics were evaluated. The BG additive did not affect the tetragonal–monoclinic phase transformation of ZrO2. However, the addition of BG decreased the flexural strength of the modified Y-TZP ceramics compared to that of Y-TZP. The in vitro mineralization results showed that a homogeneous apatite layer was produced on the surface of the Y-TZP ceramics when they were immersed in the simulated body fluid for 21 days. The cell response results indicated that the bioactive surface modification of Y-TZP ceramics could promote cell adhesion, propagation and osteogenic differentiation performance. Thus, our research results suggest that the highly bioactive Y-TZP ceramics could be a potential candidate for dental implant material.  相似文献   
9.
Gadolinium zirconate (GZ) is an attractive material for thermal barrier coatings (TBCs). However, a single layer GZ coating has poor thermal cycling life compared to Yttria Stabilized Zirconia (YSZ). In this study, Solution Precursor High Velocity Oxy-Fuel (SP-HVOF) thermal spray was used to produce a double layer GZ/YSZ TBC and compared the thermal cycling performance with the single layer YSZ TBC. The temperature behaviour of the solution precursor GZ was studied, and single splat tests were carried out to obtain an optimised spray parameter. In thermal cycling tests, the single-layer YSZ reached 20 % failure at 85 ± 5 cycles, whereas the double-layer GZ/YSZ was at 70 ± 15 cycles. The single-layer failed at the topcoat/TGO interface, whereas the double-layer failed at GZ/YSZ interface and topcoat/TGO interface. Moreover, Gd diffusion occurred near the GZ/YSZ interface, resulting in porosities in the GZ layer.  相似文献   
10.
The synthesis of polyoxymethylene dimethyl ethers as an ideal diesel fuel additive is the current hot topic of modern petrochemical industry for their expedient properties in mitigating air pollutants emission during combustion. In this work, a series of spherical sulfated zirconia catalysts were prepared by a one-pot hydrothermal method assisted with surfactant cetyltrimethylammonium bromide (CTAB). The prepared sulfated zirconia catalysts were used to catalyze PODEn synthesis from methanol and formaldehyde solution. Various characterization (XRD, BET, SEM, TGA, NH3-TPD, FTIR, and Py-IR) were employed to elaborate the structure–activity relationship of the studied catalytic system. The results demonstrated that S/Zr molar ratio in precursor solution played an effective role on catalyst morphology and acidic properties, where the weak Brønsted acid sites and strong Lewis acid sites were favorable to the conversion of methanol and formation of long-chain PODEn, respectively. The reaction parameters such as catalyst amount, molar ratio of FA/MeOH, reaction time, temperature and pressure were optimized. The speculated reaction pathway for PODEn synthesis was proposed based on the synergy of Brønsted and Lewis acid sites, which suggested that Brønsted and Lewis acid sites might be advantageous to the activation of polyoxymethylene hemiformals [CH3(OCH2)nOH] and methylene glycol (HOCH2OH), respectively.  相似文献   
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