预渗处理对H13钢盐浴多元共渗行为的影响

以H13钢为基材,通过对比含预渗处理和不含预渗处理的稀土-N-C-S-V-Nb多元共渗复合表面强化工艺的处理结果,发现即使预渗温度和时间不同,也是经过预渗处理的渗层样品表层所含的碳、氮化物比未预渗的渗层样品多,其渗层厚度达100～120μm,组织致密且呈弥散分布,硬度比未预渗样品高,而且与基体的结合程度也得到很大改善。这表明预渗处理能有效增加H13钢多元共渗后的渗层厚度,改善渗层致密度,提高渗层与基体的结合程度。

预渗及稀土在膏剂渗碳中的作用

采用预渗和添加稀土的方法可以提高膏剂渗碳的速度。催渗的效果与预渗时间、稀土种类、稀土加入量有关。随渗碳时间的延长，稀土催渗率下降。本试验还对膏剂渗碳的渗剂进行了优选。不装箱膏剂渗碳适用于大件生产及工件的局部渗碳。

镶嵌铸铁圈预渗工艺及组织结构的对比研究

采用镀锌法、铝锌法、渗铝法三种预渗工艺来制备嵌入高镍奥氏体铸铁圈的大功率发动机的活塞,对比研究了该工艺条件下结合层的组织结构、强度等。结果表明,以上三种预渗处理对结合层的结合强度各有优势,且在实际生产中均可采用。

微量Mn、Cu、Ti对AlZnMg合金预渗氢试样应力腐蚀特点的影响

研究了微量添加元素Ｍｎ、Ｃｕ、Ｔｉ对ＡｌＺｎＭｇ合金阴极预渗氢试样的应力腐蚀寿命、截面缩减率和断口形貌的影响。结果表明，预渗氢使合金的应力腐蚀敏感性明显增加，微量添加元素均能改善合金的应力腐蚀性能，其中Ｔｉ的作用最大，Ｃｕ次之，Ｍｎ的作用最小。微量元素的影响可通过它们与合金中氢的交互作用来解释。

某尾矿坝反式预埋槽孔排渗管排渗效果有限元数值分析

针对某拟建尾矿坝采用反式预埋槽孔排渗管排渗系统可能出现的排渗问题,分别采用断面概化法、面积等效法建立了该尾矿坝的三维有限元精细模型,模拟了反式预埋排渗管的排渗效果,分析了其排渗影响范围,并计算确定了其合理布设间距。通过与传统褥垫式排渗方法的排渗效果进行对比分析,提出了排渗槽孔管的简化等效模拟方法并应用于三维模型中。结果表明,该方法简洁有效,适用于类似工程。

尾矿坝预埋排渗体合理位置分析

在尾矿坝体内合适的位置预埋具有透水功能的排渗体,利用这些排渗体在坝体内部形成足以控制浸润线高度的排渗系统,是目前工程设计中采用最多、最有效的方法。以某新建尾矿库工程为例,分析了预埋排渗体在坝体内的合理位置以及对坝体浸润线降深的影响。分析结果表明,预埋排渗体的合理位置应设置在尾矿坝的临界浸润线以下,这样既可避免因其埋设过浅而造成坝体的渗透破坏,又可避免因其埋设过深而造成工程投资的浪费,为尾矿坝的排渗设计提供依据。

预设排渗系统降低某尾矿库浸润线

浸润线作为尾矿库的生命线,对于衡量尾矿库坝体稳定性具有重要作用。结合某尾矿库降低浸润线的实际工程,分析浸润线升高原因,引入了预设排渗系统。实践表明:该系统能有效提高尾矿库垂直排渗能力、降低浸润线,节约了工程成本,确保尾矿库安全运行。

4320H行星齿轮轴渗碳淬火工艺优化

分析了齿根渗碳硬化层深的影响因素,通过采取增加预渗、延长淬火保温时间及改善淬火油的流速等工艺措施,使齿根硬化层深增加了约1.6倍,齿根硬化层深/齿面硬化层深比值约为75%,满足了AGMA 3级齿轮要求。

影响扩散的新因素

在进行工件渗硼试验中 ,发现了一种反常现象。渗碳后再进行渗硼 ,虽然工件表面含碳量大为增加 ,但渗硼速度不但不减 ,反而显著增大。此后又发现低温氮碳共渗亦能提高钢件的渗硼速度 ,更可贵的是氮碳共渗不仅能提高渗硼速度 。

Threshold pressure and infiltration behavior of liquid metal into fibrous preform

A dynamic measuring apparatus was developed to investigate the infiltration process of liquid metal into the fibrous preform. 10% （volume fraction） chopped carbon fiber preforms were infiltrated with magnesium alloy under different infiltration pressures. The threshold pressure and flow behavior of liquid metal infiltrating into the preforms were calculated and measured. The microstructure of obtained Ct4Mg composites was observed. The results indicate that the measured threshold pressure for infiltration was 0.048 MPa, which was larger than the calculated value. The infiltration rate increased with the increase of infiltration pressure, but the increase amplitude decreased gradually. The tiny pores in the composites could be eliminated by increasing the infiltration pressure. When the infiltration pressure rose to 0.6 MPa, high quality C1/Mg composite was obtained.

Bending properties and fracture mechanism of C/C composites with high density preform

C/C composites with banded structure pyrocarbon were fabricated by fast chemical vapor infiltration（CVI）,with C3H6 as carbon source,N2 as carrier gas,and three-dimensional（3D） 12K PAN-based carbon fabric with high density of 0.94 g/cm3 as preform.Experimental results indicated that the fracture characteristics of C/C composites were closely related to the frequency of high-temperature treatment（HTT） at the break of CVI process.According to the load？displacement curves,C/C composites showed a pseudoplastic fracture after twice of HTT.After three times of HTT,load？displacement curves tended to be stable with a decreasing bending strength at 177.5 MPa.Delamination failure and intrastratal fiber fracture were observed at the cross-section of C/C composites by scanning electronic microscope.Because the content of pyrocarbon and fibers has a different distribution in layers,the C/C composites show different fracture characteristics at various regions,which leads to good toughness and bending strength.

Laboratory study for effects of vacuum preloading on physical and mechanical properties of soft clayey soils

A new triaxial apparatus was designed and manufactured. It is able to applysurcharge and combined vacuum-surcharge pressures on soil samples, and allows for monitoring ofexcess pore-water pressure, axial strain or settlement, and volumetric strain during the process ofconsolidation. Tests were performed using the apparatus on undisturbed soft clayey soil samples,which were collected from Wenzhou, Zhejiang Province, China, at average natural water content 72. 5%. The consolidation behavior of theclay has no rigorous difference, whether it is consolidatedunder the vacuum, surcharge, or combined vacuum-surcharge preloading. The study shows that somephysical properties of the soft clayey soils are changed and mechanical properties are improved tosupport excessive loads transferred to the soil foundation due to construction.

Synthesis of high-purity ultrafine tungsten and tungsten carbide powders

High-purity ultrafine W or WC powder was prepared via a two-step process composed of the carbothermic pre-reduction of WO2.9 and the following deep reduction with H2 or carbonization with CH4+H2 mixed gases. The effects of C/WO2.9 molar ratio and temperature on phase composition, morphology, particle size, and impurity content of products were investigated. The results revealed that when the C/WO2.9ratio was in the range from 2.1:1 to 2.5:1, the carbothermic pre-reduction products consisted of W and a small amount of WO2. With changing C/WO2.9 ratio from 2.1:1 to 2.5:1, the particle sizes were gradually decreased. In order to prepare ultrafine W or WC powder, a relatively high C/WO2.9 ratio and a lower reaction temperature at this stage were preferred. After the second reaction, the final products of ultrafine W and WC powders with a high purity could be obtained, respectively.

Pretreatment of poly(acrylic acid) sodium by continuous diafiltration and time revolution of filtration potential

The pretreatment for the removal of small molecules from poly(acrylic acid) sodium (PAAS) solution by continuous diafiltration was investigated using ultrafiltration membrane. The effects of PAAS concentration, pH, trans-membrane pressure and pretreatment time on the permeate concentration and permeate flux were studied. The results show that the necessary pretreatment time (NPT) increases with PAAS concentration, decreases with TMP. The change trend of permeate flux with time is affected by pH. The permeate fluxes rapidly decrease from the start, and then increase gradually to stable values at pH 5.0, pH 7.0 and pH 9.3. However, it decreases gradually with time till a state value at pH 3.0 (iso-electric point, IEP). The removal of small molecules is easy at pH greater than iso-electric point (IEP). The change of filtration potential with time indicates the similar trend to that of permeation concentration, but the former is more convenient for indication of NPT.

Vacuum preloading combined electroosmotic strengthening of ultra-soft soil

To assess the effectiveness of vacuum preloading combined electroosmotic strengthening of ultra-soft soil and study the mechanism of the process, a comprehensive experimental investigation was performed. A laboratory test cell was designed and applied to evaluate the vacuum preloading combined electroosmosis. Several factors were taken into consideration, including the directions of the electroosmotic current and water induced by vacuum preloading and the replenishment of groundwater from the surrounding area. The results indicate that electroosmosis together with vacuum preloading improve the soil strength greatly, with an increase of approximately 60%, and reduce the water content of the soil on the basis of consolidation of vacuum preloading, howeve~ further settlement is not obvious with only 1.7 mm. The reinforcement effect of vacuum preloading combined electroosmosis is better than that of electroosmosis after vacuum preloading. Elemental analysis using X-ray fluorescence proves that the soil strengthening during electroosmotic period in this work is mainly caused by electroosmosis-induced electrochemical reactions, the concentrations of Al2O3 in the VPCEO region increase by 2.2%, 1.5%, and 0.9% at the anode, the midpoint between the electrodes, and the cathode, respectively.

Reduction and subsequent carburization of pre-oxidation magnetite pellets

Magnetite is a kind of iron ore that is difficult to carburize.In order to improve the carburizing performance of magnetite pellet,pre-oxidation treatment was carried out,and the oxidation,reduction and carburization behaviors of magnetite pellet were investigated in this study.The magnetite pellet was oxidized in the air and carburized in CO-CO_(2)-H_(2) gas mixtures,the oxidation,reduction and carburization behaviors were demonstrated by detecting phase change,microstructure,carburizing index via thermogravimetry,X-ray diffraction(XRD),infrared carbon-sulfur analyzer,and scanning electron microscope(SEM).The results show that the dense magnetite particles inside pellet are oxidized to porous hematite particles,and the Fe_(3)O_(4) transforms to Fe_(2)O_(3) with high lattice defect concentration during the pre-oxidation process.Then the porous hematite particles and newly formed Fe_(2)O_(3) significantly promote the reduction efficiency.Porous metallic iron particles are produced in the reduction process.Finally,both high reduction efficiency and the porous structure of metallic iron particles dramatically enhance the carburization efficiency of pellet.High preoxidation temperature favors to the carburization of magnetite pellet.However,the carburized index decreases due to the recrystallization of iron oxide when the temperature extends to 1000℃.The optimum pre-oxidation temperature for magnetite pellet carburization is 900℃.

Analytical solution of coal-bed methane migration with slippage effects in hypotonic reservoir

Using theoretical analysis, the single-phase gas seepage mathematical model influenced by slippage effects was established. The results show that the pressure of producing wells attenuates more violently than the wells without slippage effects. The decay rate of reservoir pressure is more violent as the Klinkenherg factor increases. The gas prediction output gradually increases as the Klinenberg factor increases when considering gas slippage effects. Through specific examples, analyzed the law of stope pore pressure and gas output forecast changing in a hypotonic reservoir with slippage effects. The results have great theoretical significance in the study of the law of coal-bed methane migration in hypotonic reservoirs and for the exploitation of coal-bed methane.

Utilizing partial least square and support vector machine for TBM penetration rate prediction in hard rock conditions

Rate of penetration(ROP) of a tunnel boring machine(TBM) in a rock environment is generally a key parameter for the successful accomplishment of a tunneling project. The objectives of this work are to compare the accuracy of prediction models employing partial least squares(PLS) regression and support vector machine(SVM) regression technique for modeling the penetration rate of TBM. To develop the proposed models, the database that is composed of intact rock properties including uniaxial compressive strength(UCS), Brazilian tensile strength(BTS), and peak slope index(PSI), and also rock mass properties including distance between planes of weakness(DPW) and the alpha angle(α) are input as dependent variables and the measured ROP is chosen as an independent variable. Two hundred sets of data are collected from Queens Water Tunnel and Karaj-Tehran water transfer tunnel TBM project. The accuracy of the prediction models is measured by the coefficient of determination(R2) and root mean squares error(RMSE) between predicted and observed yield employing 10-fold cross-validation schemes. The R2 and RMSE of prediction are 0.8183 and 0.1807 for SVMR method, and 0.9999 and 0.0011 for PLS method, respectively. Comparison between the values of statistical parameters reveals the superiority of the PLSR model over SVMR one.

Effects of Chemical Osmotic Pretreatment on Drying Characteristics and Quality of Blueberry under Hot Air Drying

In order to study the effects of chemical osmotic pretreatment on the characteristics and quality of blueberry under hot air drying,fresh blueberries were pretreated with 2.5 g/100 mL K2CO3+0.6 g/100 mL olive oil,and 5.0 g/100 mL K2CO3+0.6 g/100 mL olive oil at(45±0.5)℃,respectively.The changes of water content,rehydration,hardness,microstructure,color difference,active ingredient anthocyanin,total phenol and DPPH radical scavenging capacity of dried blueberries in different treatment groups under hot air drying were compared and analyzed.The results showed that the dehydration rates of blueberries vary greatly according to the type of pretreatments when the samples were dried to the same water content with hot air.Specifically,the dehydration rate of dried blueberries pretreated by 5.0%K2CO3 solution was the highest,followed by 2.5%K2CO3 osmotic pretreatment and lastly the control group;the corresponding dehydration time was 10,14 and 20h,respectively.The physical qualities of dried blueberries,involving the browning degree,color difference,rehydration and microstructure,were significantly different between the chemical osmotic pretreatment group and the control group(P<0.05).The chemical osmotic pretreatment of K2CO3 solution increased the dehydration rate of the samples,shortened the drying time and maintained the quality of blueberries dried with hot air.There was no significant difference between the physical quality of dried blueberries pretreated by 2.5%and 5.0%K2CO3 solution(P>0.05),whereas there was significant difference in drying time and nutrient quality which is characterized by total phenols,anthocyanins,DPPH radical scavenging rate,soluble total sugar(P<0.05).Conclusion:5.0%K2CO3 osmotic pretreatment combining with hot air drying can improve the dehydration rate,shorten the drying time and maintain the physical and nutritional quality.

Pretreatment of Isopropanol Solution from Pharmaceutical Industry and Pervaporation Dehydration by NaA Zeolite Membranes

NaA zeolite membranes with 80 cm in length and 12.8 mm in outer diameter were prepared by our research group cooperating with Nanjing Jiusi Hi-Tech Co., China. The influence of dissolved inorganic salts and pH value in the feed of isopropanol （IPA） solution on NaA zeolite membranes was investigated. It was found that both factors exhibited strong influence on the stability of NaA zeolite membranes. A set of pretreatment steps such as pH adjustment and distillation of the IPA solution were proposed to improve stability for pervaporation dehydration. An industrial-scale pervaporation facility with 52 m2 membrane area was built to dehydrate IPA solution from industrial cephalosporin production. The facility was continuously operated at 368-378 K to dehydrate IPA solution from water mass content of 15%-20% to less than 2% with a feed flow rate of 400-500 L·h^-1 and an average water flux of 1-1.5 kg·m^-2·h-1. The successful application of this facility suggested a promising application of NaA zeolite mem-brane for IPA recovery from pharmaceutical production.