铈含量对NiAl-28Cr-5.5Mo-0.5Hf共晶合金氧化性能的影响

研究了不同稀土元素Ce含量对NiAl-28Cr-5.5Mo-0.5Hf合金在1100℃空气中的氧化行为的影响.结果表明:适量稀土元素Ce的添加显著地提高了基体合金的抗高温氧化性能,而过量添加稀土元素则会恶化基体合金的高温氧化性能.X射线结构与SEM分析表明:基体合金表而氧化膜主要由α-Al2O3构成,并含有少量的Cr2O3和HfO2,而当稀土元素添加量达到0.5%(质量分数),氧化膜中出现富稀土Ce的氧化物.采用EDAX分析研究了合金表面氧化产物的微观组织及成分,并从合金相组成探讨了稀土元素Ce提高基体NiAl-28Cr-5.5Mo-0.5Hf合金的抗高温氧化性能的机制.     

NiAl-31Cr-3Mo合金高温氧化性能研究

研究了NiAl-31Cr-3Mo合金在1250～1500 K空气中的氧化行为.实验结果表明:在实验温度范围内,合金的氧化动力学曲线符合抛物线规律;氧化过程中合金表面生成了以а-Al2O3为主的氧化膜,并且含有Cr2O3.采用扫描电镜和能谱分析研究了氧化产物的微观组织及{连成,并从合金的相组成探讨了NiAl-31Cr-3Mo合金的氧化机制.     

机械合金化Fe-20Cr-2.5Al合金循环氧化行为

采用机械合金化及热压法制备Fe-20Cr-2.5Al、Fe-20Cr-2.5Al-0.8Y2O3和Fe-20Cr-2.5Al-3Y2O3合金,研究了不同Y2O3含量对MA Fe-Cr-Al合金在900℃空气中循环氧化行为的影响。结果表明,Fe-20Cr-2.5Al合金氧化增重最大,Fe-20Cr-2.5Al-3Y2O3合金氧化增重其次,Fe-20Cr-2.5Al-0.8Y2O3合金氧化增重最少,抗高温循环氧化性能最好。Fe-20Cr-2.5Al合金的氧化膜分为三层,外层主要为Fe2O3,与镍层连接界面有很薄一层不连续的Al2O3,中间层主要为Fe2O3和Cr2O3的复合氧化物,氧化膜内层主要为Fe Cr2O4;Fe-20Cr-2.5Al-0.8Y2O3合金的氧化膜没有明显分层现象,氧化膜主要为Cr2O3;Fe-20Cr-2.5Al-3Y2O3合金的氧化膜分为两层,外层主要由Al2O3和Cr2O3交替连接形成,内层主要由Cr2O3组成,有很薄的复合氧化物Fe Cr2O4。Y2O3的添加可有效提高Fe-20Cr-2.5Al合金的抗循环氧化能力,其中Fe-20Cr-2.5Al-0.8Y2O3合金好于Fe-20Cr-2.5Al-3Y2O3合金。     

TiAl合金表面阴极微弧制备的Al_2O_3膜结构与性能

以Al(NO3)3乙醇溶液为电解液,采用阴极微弧放电沉积方法,在TiAl合金表面制备连续的Al2O3薄膜,并对膜的结构与性能进行研究.利朋扫描电镜(SEM)观察到样品表面分布着熔融状颗粒,颗粒的平均直径约20μm,颗粒中间有小孔存在.X射线衍射(XRD)分析表明氧化膜的相成分主要为α-Al2O3和γ-Al2O3相,还有少量的ε-Al2O3相;氧化膜中α-Al2O3和γ-Al2O3的相对含量随着制备电压改变而变化.显微划痕实验测得膜与TiAl基体之间结合力大于20 N,表明制得的氧化膜与基体有良好的结合力.900℃的高温氧化实验表明氧化膜能够有效地提高基体的抗氧化性能.     

Y_2O_3对机械合金化Fe-20Cr-2.5Al合金热腐蚀行为的影响

为了研究稀土元素对高温热腐蚀行为的影响,采用机械合金化及热压法制备Fe-20Cr-2.5Al、Fe-20Cr-2.5Al-0.8Y2O3和Fe-20Cr-2.5Al-3Y2O3合金,并研究其在900℃,涂敷Na2SO4盐膜后的热腐蚀行为。结果表明,Fe-20Cr-2.5Al合金腐蚀增重最大,Fe-20Cr-2.5Al-3Y2O3合金腐蚀增重其次,Fe-20Cr-2.5Al-0.8Y2O3腐蚀增重最少,抗热腐蚀性能最好。Fe-20Cr-2.5Al合金的腐蚀膜主要为Fe2O3,在腐蚀膜与镀镍层界面处存在着少量的Al2O3。Fe-20Cr-2.5Al-0.8Y2O3合金的腐蚀膜主要为Cr2O3,在靠近基体一侧有少量的Al2O3。Fe-20Cr-2.5Al-3Y2O3合金的腐蚀膜分为2层,外层为Fe Cr2O4,内层为较致密的Cr2O3。三种合金均未发生内硫化现象。添加Y2O3的Fe-Cr-Al合金的抗热腐蚀性能明显好于对应未添加的合金,其中Fe-20Cr-2.5Al-0.8Y2O3合金好于Fe-20Cr-2.5Al-3Y2O3合金。     

Oxidation Behavior of NiAl-30.75Cr-3Mo-0.25Ho Alloy at High Temperatures

The oxidation behavior of NiAl-30.75Cr-3Mo-0.25Ho alloy from 1300 to 1500 K in air atmosphere was investigated. The results reveal that oxidation resistance of the alloy is improved by the addition of Ho. At 1500 K, the oxidation kinetic curve obeys the parabolic law (n≈0.5), whereas the oxidation kinetic curve of the tested alloy follows the cubic relations (n≈0.3～0.4) from 1300 to 1450 K. An activation energy of about 261 kJ·mol-1 was determined for the tested alloy. It is found that a continuous and compact Al2O3 layer has formed on the surface of NiAl-30.75Cr-3Mo-0.25Ho alloy after oxidation 100 h at various tested temperatures. A rich-Ho solution formed on the boundaries of Cr(Mo) phase. Doped little amount of Ho in NiAl-31Cr-3Mo alloy promotes the transformation from θ-Al2O3 phase to α-Al2O3 phase, and decreases the size of Al2O3 and the crack forming in the oxidation scale prolongs the spalling time of the film at high temperature. The volatilizing oxides of Cr, Mo and the reactive element effects (REEs) make the mass gain lower than that of pure NiAl.     

Ni-Cr-Mo-W合金在900℃下的高温氧化行为研究

采用真空粉末冶金烧结法制备Ni-Cr-Mo-W高温合金,研究了Ni-Cr-Mo-W合金的表面氧化行为及氧化膜的组织形貌和物相组成。研究结果表明,Ni-Cr-Mo-W合金在900℃下氧化100h时,属于完全抗氧化级,表面氧化物层的主晶相为Cr2O3和具有尖晶石结构的NiCr2O4;添加一定量的难熔元素W,可提高Ni-Cr-Mo-W合金的抗高温氧化性。     

Ni-Cr-Al合金在1000℃空气中的氧化

研究了两种不同Cr含量的常规熔炼Ni-Cr-Al合金在1000℃空气中的氧化行为.合金氧化动力学遵循抛物线规律,Ni-20Cr-2.5Al合金在1000℃的氧化增重略小于Ni-15Cr-2.5Al合金,二者的氧化增重都明显小于Ni-20Cr合金.Ni-20Cr-2.5Al合金1000℃氧化后形成了外层的Cr2O3及内层极薄的Al2O3型氧化膜,在Ni-Cr合金中加入Al,由于Cr、Al的相互作用,降低了形成Cr2O3和Al2O3外氧化膜所需的Cr或Al的临界含量,促进了保护性Al2O3或Cr2O3膜的生成.     

00Cr25Ni22Mo2N奥氏体不锈钢的高温氧化行为

采用静态增重法研究了00Cr25Ni22Mo2N奥氏体不锈钢在不同温度下的循环氧化动力学曲线.结果表明,00Cr25Ni22Mo2N不锈钢在700℃时的氧化动力学曲线是一条平行于时间轴的直线,这说明其在该温度下氧化反应非常微弱;在800和900℃时的氧化动力学曲线遵循抛物线氧化规律,具有良好的抗氧化性能.利用扫描电镜、能谱分析和X射线衍射对氧化膜的表面形貌、截面形貌和相组成进行研究,发现该钢在3个温度下都生成了致密和黏附性好的保护性氧化膜,700℃生成的氧化膜主要由Cr2O3和Fe2O3组成,氧化膜很薄;800℃生成的氧化膜由Cr2O3、Fe2O3和少量的NiCr2O4、FeCr2O4组成,氧化膜厚度增加;900℃生成的氧化膜由Cr2O3、Fe2O3和NiCr2O4组成,氧化膜厚度进一步增加.认为氧化膜组成和结构是00Cr25Ni22Mo2N不锈钢具有良好抗高温氧化性能的重要原因.     

Ce和Re对CoNiCrAlY合金1000℃氧化行为的影响

在热障涂层粘结层用CoNiCrAl Y合金中添加适量活性元素Ce和合金元素Re,1000℃空气气氛下进行恒温氧化,测试合金氧化动力学,采用X射线衍射(XRD)、扫描电镜/能谱(SEM/EDS)等手段观测氧化产物的物相组成和转变、氧化膜结构,进而比较添加适量活性元素Ce和合金元素Re对合金氧化行为的影响。结果表明,当前氧化条件下,合金氧化动力学可以划分为两个阶段:氧化初期,氧化速率较快;稳定氧化阶段,氧化产物由亚稳态θ-Al2O3转化成稳态α-Al2O3,氧化速率明显降低。CoNiCrAl Y合金表面形成了单一Al2O3膜,而CoNiCrAl YRe合金生成了富Cr氧化物外层+Al_2O_3内层双层氧化膜,并且在贫铝区形成了少量内氮化物。0.1%Ce(质量分数)的加入促进了Al的选择性氧化,加快了Al2O3的相转变,从而促进保护性α-Al2O3氧化膜的更快形成,使得CoNiCrAl Y合金稳定氧化阶段氧化速率常数由3.3×10~(-13)g~2·cm~(-4)·s~(-1)降低为1.5×10~(-13)g~2·cm~(-4)·s~(-1)。而且,Ce和Re元素共同存在时对合金抗氧化性能的改善效果更显著,CoNiCrAl YRe Ce合金表面形成了单一、连续、致密的Al_2O_3保护膜,Ce的加入使得含Re合金CoNiCrAl YRe的稳定氧化阶段氧化速率常数由2.8×10~(-13)g~2·cm~(-4)·s~(-1)降低为7.5×10~(-14)g~2·cm~(-4)·s~(-1)。     

Summary of penile cancer: relation of extent of nodal metastasis to survival (by Sri V. Srinivas, MD, M.J. Morse, MD, H.W. Herr, MD, P.C. Sogani, MD, and W.F. Whitmore, Jr, MD). 1987

BACKGROUND: Two major flaws have been previously identified in the resource-based relative value scale (RBRVS): (1) inaccurate estimation of physician work effort; and (2) RBRVS compression, which results in undervaluation of major surgical procedures. The impact of RBRVS for physicians treating patients with ruptured abdominal aortic aneurysms (RAAAs) has not been previously reported and is important owing to the severity of the illness, the potential to quantitate actual work effort, and the high percentage of these patients covered by Medicare. PATIENTS AND METHODS: All patients were studied who underwent surgery for RAAAs during a 5-year period encompassing the implementation of RBRVS. Analysis included all physician services including vascular surgeons, anesthesiologists, and all other medical specialists. Total work effort was quantitated for each specialty in minutes/patient. The financial data were obtained by reviewing all professional bills and reimbursements. Cost of service was calculated to include physician compensation, practice overhead costs, and malpractice expenses. RESULTS: In all, 84 patients underwent repair of a RAAA with a mortality rate of 42%. Medicare was the primary insurance for 87% of patients. The cost of service exceeded the reimbursement by 50% for vascular surgeons, resulting in an average loss of $1,593/patient. Actual operative time represented only 24% of total surgical work effort. Early death and a length of stay (LOS) < or = 1 day for 24 patients resulted in a reimbursement rate of $5.98/minute for surgeons. This gain was significantly offset by 30 patients with a LOS > or = 14 days, resulting in a reimbursement rate of $1.94/minute for vascular surgeons. Over the 5-year period there was a trend of decreasing reimbursement for vascular surgeons (P <0.005) but not other physicians. Vascular surgeons incurred a 28% decrease in reimbursement over the study period. CONCLUSIONS: Physician reimbursement under RBRVS for the treatment of patients with RAAAs is inadequate to cover the costs of providing this care. Reimbursement trends and potential changes to the practice component of the RBRVS will further aggravate the losses involved in caring for these very ill patients. Vascular surgeons must continue to provide input to the Health Care Financing Administration to help correct inequities built into RBRVS.     

Rats, Man . . .

Comments on the article by Richter entitled "Rats, Man, and the Welfare State" (see record 1960-02810-001). The commenter notes that in his article Richter did not indicate how hereditary and environmental factors were controlled. In comparing the hereditary survival characteristics of wild versus domesticated rats, it would be essential that the environmental influences on the survival characteristics of the wild rats should be ruled out. Another factor to be considered is that the wild state may offer a diet and other environmental influences, which in the life of a single individual would produce organic changes, accounting for some of the differences between wild and domestic rats. It would seem that the most effective way to determine the hereditary differences between wild and domestic rats would be to create a wild group, composed solely of the offspring of wild rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)