Surface Oxidation of Al_2O_3/SiC Nanocomposite: Phase Transformation and Microstructure

The surface oxidation behavior of pressureless sintered Al2O3/SiC nanocomposite was studied from 1000 to 1400 ℃ for more than 10 h in air. Weight gain during the process of heat treatment was measured by TG analysis. Phase transformation and microstructure changes of these specimens due to oxidation were investigated with X-ray diffraction （XRD）, SEM and EDX technology. Thermogravimetric analysis show that the weight gain as a result of oxidation of SiC become significant above 1200 ℃. In the range of 1000 - 1300 ℃, the SiC grits are usually coated with a layer of amorphous silica after oxidation. Above 1300 ℃, the amorphous silica reacted with alumina matrix and formed mullite or crystallized into cristobalite. The rate of oxidation depends on the formation of dense cristobalite film. Large amount of needle-like mullite and alumina crystals are formed on the surface after oxidation at 1400℃.

Effect of inner-surface roughness of conical target on laser absorption and fast electron generation

The effect of inner-surface roughness of conical targets on the generation of fast electrons in the laser-cone interaction is investigated using particle-in-cell simulation. It is found that the surface roughness can reduce the fast-electron number （in the energy range E 〉 1 MeV） and energy, as compared to that from a cone with smooth inner wall. A scaling law for the laser reflectivity based on the vacuum-heating model is derived. Both theory and simulation indicate that laser reflection increases with the height-to-width ratio of the periodic inner surface structure and approaches that of a smooth cone as this ratio becomes zero.

Investigation into the surface active groups of coal

The oxidation heat of coal is the direct reason leading to coal spontaneous combustion. When coal is exposed in oxygen atmosphere, the physical adsorption and chemisorption happened, and then which resulting chemical reaction followed heat between coal and oxygen. Owing to the complexity and uncertain of molecular structure of coal,it was only reduced that bridge bonds, side chains and O 2 containing functional groups in coal may be prone to oxidation in last year, but not to deeply investigate into the structures and the type of the active radicals. In this paper, according to the last achievements in coal structure research, the hypomethylether bond, hypoalkyl bond of α carbon atom with hydroxyl and α carbon atom with hypomethy side chain and hypomethyl bonds linking up two aromatic hydrocarbon in bridge bonds, and methoxy,aldehyde and alkyls of α carbon atom with hydroxy in side bonds are inferred to be free radical easily to lead to oxidize coal under the ambient temperature and pressure. The order from strong to weak of oxide activation of the seven surface active groups is aldehyde side chains, hypomethylether bonds, hypoalkyl bonds of α carbon atom with hydroxyl, hypoalkyl bonds of α carbon atom with hypomethyl, hypomethyl bonds linking up two aromatic hydrocarbon,methoxy, alkyls side chains of α carbon atom with hydroxyl. Because of the two unsaturated molecular tracks of O 2, unpaired electron clouds of the part of surface active groups of coal enter molecular tracks of O 2 to lead to chemisorb on the conjugate effect and induced effect of surface active groups, and then chemical reaction followed heat happens in them. On the basis of change of bond energy, weighted average method is adopted to count the reaction heat value of each mol CO,CO 2 and H 2O. The property of coal spontaneous combustion is different for the different number and oxidability of the active structure in the coal resulting in the different oxidation heat.

Effect of Surface Modification on Corrosion Resistance of Pure Titanium.An in Vivo Observation

Objective: The aim of this experiment is to study the effect of three methods of surface modification on the corrosion resistance of commercial pure Titanium when used in oral environment for half a year.Method:48 specimens of pure titanium were made and divided into four groups randomly, one group was selected randomly as Group I (control group), the other three groups were treated by three methods of surface modification individually, GroupⅡ:heating oxidation in air(400℃,30min.), GroupⅢ:anodization (45 volts, 10 min.),GroupⅣ:TiN coating(firing temperature 200℃ , total coating time 62min.). Six edentulous volunteers with healthy oral mucosa participated in the in vivo study. One testing piece from each group was selected and fixed in the polished surface of upper complete dentures. Dynamic polarization curves were traced with electrochemical method after the specimens were placed either in oral cavity or in air for 6 months. Results: After all specimens were used, Ecorr altered in every group , Ecorr from high to low were in turn: TiN coating group>heating oxidation group> anodization group>control group, no obvious passive potential Ep and Ip was found in control group. Heating oxidation in air exhibited similar Ep to anodization, but Ip was remarkably lower than that of anodization; TiN coating showed obviously different polarization curves compared with heating-oxidation group and anodization group, Ecorr was positive, and no Ep and Ip was found. Conclusion: Under present experimental condition, all the three treatment methods could enhance corrosion resistance of pure titanium in oral environment, heating oxidation in air exhibited better resistance to corrode than anodization, TiN coating possessed the most excellent corrosion resistance, even after exposed in oral condition for 6 months, there was little change of corrosion resistance. Therefore TiN coating could be adopted to improve corrosion resistance of pure titanium in oral environment.

青海地区居住建筑外围护结构冬季传热过程研究

以青海地区居住建筑为研究对象,通过EnergyPlus模拟软件研究了不同传热系数和太阳辐射吸收系数下各朝向墙体内外表面温度的变化规律,并对其热流密度进行对比分析。结果表明:增大太阳辐射吸收系数能有效提高墙体外表面平均温度,减小传热系数能有效提高墙体内表面平均温度。太阳辐射吸收系数对南墙平均热流密度影响最大,其次为屋面,北墙最小;传热系数对北墙平均热流密度影响最大,其次为屋面,南墙最小。

铜表面-氧化石墨烯纳米涂层池沸腾换热特性实验

石墨烯材料因其优异的导热性能和化学惰性,在核反应堆先进换热设备领域有很大的应用前景。为探索石墨烯材料的强化换热性能,本文采用沸腾沉积法制备氧化石墨烯纳米涂层,开展了氧化石墨烯涂层-去离子水池沸腾换热特性实验。氧化石墨烯纳米流体工质浓度为0.001、0.003、0.005 mg/mL,加热时间控制为1 h和2 h,通过沸腾沉积在裸露铜表面制备6种氧化石墨烯涂层。以此为基础开展池沸腾实验,结果发现氧化石墨烯涂层对池沸腾换热系数的影响很小,但可显著增强池沸腾临界热流密度。从涂层表面润湿性、热导率及形貌结构变化等角度分析了氧化石墨烯涂层对池沸腾换热特性的影响机理。

Water sorption on coal:effects of oxygen-containing function groups and pore structure

Coal-water interactions have profound influences on gas extraction from coal and coal utilization.Experimental measurements on three coals using X-ray photoelectron spectroscopy(XPS),low-temperature nitrogen adsorption and dynamic water vapor sorption(DVS)were conducted.A mechanism-based isotherm model was proposed to estimate the water vapor uptake at various relative humidities,which is well validated with the DVS data.The validated isotherm model of sorption was further used to derive the isosteric heat of water vapor sorption.The specific surface area of coal pores is not the determining parameter that controls water vapor sorption at least during the primary adsorption stage.Oxidation degree dominates the primary adsorption,and which togethering with the cumulative pore volume determine the secondary adsorption.Higher temperature has limited effects on primary adsorption process.The isosteric heat of water adsorption decreases as water vapor uptake increases,which is found to be close to the latent heat of bulk water condensation at higher relative humidity.The results confirmed that the primary adsorption is controlled by the stronger bonding energy while the interaction energy between water molecules during secondary adsorption stage is relatively weak.However,the thermodynamics of coal-water interactions are complicated since the internal bonding interactions within the coal are disrupted at the same time as new bonding interactions take place within water molecules.Coal has a shrinkage/swelling colloidal structure with moisture loss/gain and it may exhibit collapse behavior with some collapses irreversible as a function of relative humidity,which further plays a significant role in determining moisture retention.

在加热阶段滚塑模具内表面传热系数的两种研究方法

提出了获得电加热滚塑模具内表面传热系数的两种研究方法,这两种方法适用于模内粉料开始熔融前的加热阶段。第一种方法是首先在4种情形下测量该滚塑模具的外表面温度和模内温度,然后根据能量守恒原理建立一个传热模型,并通过该模型将这些实测的温度值转换为在这4种情形下模具的内表面传热系数。第二种方法是将实际的滚塑模具等效地简化为一个二维圆筒,将模内空气当成主相流体,粉料当成第二相流体,通过FLUENT软件的多相流模块中的Mixture模型进行仿真计算以得到模具内表面的传热系数。结果表明,这两种方法所得的结果在其中的3种情形下都吻合得很好。随着模内粉料的体积百分比的增加,模具的内表面传热系数先是快速增大,然后增大的速率变慢,在达到最大值61.2 W/(m^(2)·K)后开始减小。当粉料的体积百分比不在58%~74%的范围内,由第二种方法仿真所得的模具内表面传热系数的相对误差不超过10%。

基于流固耦合的燃气冲刷烧蚀内膛特性分析

火炮发射时,火药燃气与身管间发生剧烈的传热传质作用是导致身管烧蚀的重要因素。为了研究某155 mm火炮中高温高压高速的燃气流对身管的烧蚀特性,采用CFD流固耦合方法,建立了发射过程中的身管非稳态流动传热模型,并根据炮钢在不同温度下的烧蚀特点,将烧蚀过程分为热化学烧蚀和熔化烧蚀,建立了分段烧蚀模型。计算结果表明,身管内壁温度随时间的增加先迅速增大,随后逐渐降低。整体上,内壁温度随身管轴向距离的增大而逐渐降低。身管膛线起始区域的壁面温度最高,其烧蚀是熔化和热化学烧蚀共同导致的,而线膛部的大部分区域仅发生了热化学烧蚀。总烧蚀量随着身管轴向距离的增大而逐渐降低,膛线起始部的烧蚀最为严重,单发总烧蚀量(常温)为5.06μm。同时分析了不同工况对身管烧蚀特性的影响,发现最大烧蚀量与初始壁面温度呈现很强的正相关性,温度的升高会加剧身管的烧蚀。

电缆-整流罩组件内表面的涂覆工艺与性能

电缆-整流罩组件是飞行器的重要组成部分,承受着高速飞行过程中大量的气动载荷和热载荷,其内部电缆作为各个系统之间信息传输的重要通道,是保障信号输入输出的重要部件。讨论了一种电缆-整流罩组件内表面涂覆工艺,该工艺采用喷涂内隔热层、电缆固定、电缆灌封等工艺流程,为产品的可靠性提供了工艺保障。电缆整流罩组件涂覆成型后的性能测试结果显示,内表面隔热涂层剪切强度、灌封体力学性能、电缆电性能均满足设计指标要求。

低碳钢表面氧化效应对加热面朝下CHF的影响

先进压水堆压力容器下封头采用材料为低碳钢SA508,其表面容易氧化,可能对堆内熔融物滞留(IVR,in-vessel retention)策略临界热流密度(CHF,critical heat flux)产生显著影响,从而影响该策略安全余量。针对这一问题,本文首先研究了低碳钢SA508不同程度表面氧化对加热面朝下CHF的影响,其次研究了在低碳钢表面氧化情况下纳米流体强化CHF效果。结果发现,低碳钢SA508表面氧化对加热面朝下池式沸腾CHF具有显著影响,随着氧化程度的加深,CHF快速增长并最终达到稳定,表面完全氧化情况下CHF稳定值是表面轻微氧化情况下的2倍左右;将完全氧化低碳钢表面放入纳米流体中进行沸腾实验,发现纳米流体可以继续提高完全氧化表面CHF但效果大幅减弱,CHF增强原因在于表面纳米颗粒沉积层具有很强的吸水性。

新技术在锅炉高温受热面氧化皮检测中的应用

目前,一些大容量机组的奥氏体高级钢不断应用于锅炉的高温受热面。受热面管内壁在高温下不可避免地被蒸汽氧化,从而形成一定厚度的氧化皮。由于氧化皮和管壁的膨胀系数不同出现氧化皮不断剥离,导致管道受热面壁不断变薄。此外由于氧化皮脱落堵塞管子后,蒸汽通流面积减少,易造成受热面金属温度持续升高,可能出现爆管不安全事故,从而影响锅炉机组的安全、稳定、经济运行。针对高温受热面氧化皮剥离的问题,文中首先分析了氧化皮的产生原因和脱落影响,然后提出了新技术在氧化皮检测中的应用。应用后可以及时发现氧化皮易脱落的部位进行提前预防,使氧化皮的的生产得到缓解,锅炉运行的安全稳定性大大提高。

煤氧复合热效应的影响因素分析

煤的氧化放热是引起煤自燃的主要原因。煤氧复合热效应与耗氧速率和表面反应热有关。通过分析得出 ,q(z,n,CO2 ,T,d5 0 ) =h(Z) .g(n) .f (CO2 ) .I(T) .Ψ (d5 0 )。其中主要影响因素为煤结构、温度、氧浓度及粒度。根据威斯化学结构模型、本田化学结构模型及煤分子中包含的 7种表面活性结构 ,推出煤自燃表面分子结构模型 ,并分析其表面活性结构的种类、数量、活泼性 ,它们随煤体不同而千差万别 ;表面活性结构随温度变化的氧化活泼性及反应过程不同 ,造成煤表面氧化反应热 H不同。外在主要影响因素—煤的温度、氧浓度、粒度不同造成了耗氧速率 VO2 不同 ,使煤的放热强度不同。对此 ,通过 XK型煤自然发火实验台及

辐射供暖房间耗热量分析

比较了辐射供暖与散热器供暖方式下房间外围护结构内表面温度的差异 ,指出辐射供暖房间在某些条件下由于耗热量较大 ,将会影响供暖的节能性。通过对辐射供暖方式节能率的分析 ,认为外围护结构内表面辐射吸收因数是影响节能效果的关键因素 ,给出了其取值范围。

加热工艺对含铜钢表面氧化的影响

研究了加热工艺对含铜钢表面氧化的影响。结果表明，加热温度和加热时间对含铜钢表面氧化程度影响显著。含铜钢液态铜相出现在1100～1200℃的加热温度范围，而在1000℃和1300℃加热时，基体与氧化层界面处不出现液态铜相。加热温度为1100℃时，液态铜相沿奥氏体晶界向基体的渗透能力比1200℃时更强。高温加热时，随加热时间延长，含铜钢的氧化程度加重，同时也增强了液态铜相向基体的渗透。加镍可有效防止含铜钢在高温过程中形成液态铜相，避免铜发生热脆。

炭分子筛的制备及表面结构

以大庆石油焦为原料,采用KOH活化法,考察了碱炭比、活化温度、活化时间对吸附性能的影响,确定最佳工艺条件,碱炭比4∶1、活化温度800℃、活化时间2h。并制得比表面积大于3000m2 g的超级活性炭。通过热处理得到孔径均一(中孔率>85%),比表面积大于1500m2 g的炭分子筛;再用表面氧化方法,得到表面酸度适宜(150℃～240℃之间为弱酸,240℃～340℃为中强酸,340℃～450℃为强酸分布)的催化剂载体。炭分子筛与传统氧化铝比较具有酸度分布广泛等特点,因较好的酸强度分布,可以增强载体与金属离子之间的作用力,增加负载量。因此,经氧化后的炭分子筛更适于作催化剂载体。

夏热冬暖地区复合墙体内表面温度响应特性

根据建筑复合型外墙在室外气象参数周期性变化的边界条件,建立了复合墙体内表面温度在一维非稳态导热控制方程作用下的计算模型,结合夏热冬暖地区复合墙体的结构特点及该地区的夏季气象参数,分析了不同朝向复合墙体随室外气象参数变化的内表面温度响应特性及变化规律,为复合型墙体在隔热和室内舒适性方面的研究提供了理论指导.

停机过程中锅炉高温受热面蒸汽侧氧化膜的应力分析

电站锅炉高温受热面蒸汽侧氧化膜在机组停机降负荷时可能发生脱落,对安全性构成严重威胁。通过建立有限元分析模型,对锅炉停机过程中受热面蒸汽侧氧化膜内的应力进行了计算和分析。对铁素体合金和奥氏体合金进行了研究,其中铁素体合金以T91为代表,奥氏体合金以TP347H为代表。通过对各应力分量以及von Mises等效应力进行分析,揭示机组降负荷过程中两种合金管蒸汽侧氧化膜内应力的变化规律,阐明两种合金管蒸汽侧氧化膜可能的失效模式,同时得出了铁素体合金管和奥氏体合金管蒸汽侧氧化膜分别在负荷降低后期和初期容易发生脱落的结论。

石油焦系超级活性炭的孔结构控制(英文)

采用KOH活化法从大庆石油焦制得超级活性炭,而后对其进行微孔和中孔的调控。中孔调控采用热处理法,所得超级活性炭的中孔率在85%以上,比表面积大于1 500m2/g。同时对热处理后的超级活性炭进行表面硝酸氧化,引入部分含氧官能团。60m in酸处理效果明显,羧基的增加量是20m in酸处理的9倍。处理后的超级活性炭更适合作催化剂载体。微孔的控制采用化学气相炭沉积法(以苯为碳源),所得超级活性炭的微孔率从51%增加到87%。对CO2和CH4的分离能力从30mg/g提升到47mg/g,具有良好的筛分效果。

内蒙古中西部地面感热通量影响沙尘暴的观测分析

利用内蒙古中西部不同地表类型的16个测站2005—2006年3—5月逐小时地面观测资料和逐日沙尘暴资料,计算了地面感热通量、地面位温并分析它们与沙尘暴的关系,结果发现:在内蒙古中西部春季地面感热通量表现为净加热,且沙尘暴发生次数多的年份净地面感热加热强度反而较小。在沙尘暴发生前,沙漠区和高平原区地面感热通量达到最大,而丘陵和平原地区反而开始降低。对于沙尘暴发生前12h累积的地面感热加热强度及导致的地面位温上升幅度,高平原和丘陵平原区要强于沙漠区。但相对而言,沙漠和高平原地区地面感热加热影响沙尘暴的"效率"更高。