Synthesis of Cr_2AlC from Elemental Powders with Modified Pressureless Spark Plasma Sintering

We introduced a modified pressureless sintering strategy by SPS with a new T-shape die and tapered punches, which helps the evaporation of melted Al and reduces the sample sticking with the inner wall of the die. Thus, the die breaking risk in the sintering process or the de-molding process is avoided at all. At a low temperature and short holding time, a high purity of Cr_2 AlC was obtained in this SPS process from the optimization of different molar ratios of raw materials. Simultaneously, the high porosity of the as-obtained sample was also a distinguishing feature worth noticing. The reaction mechanism for this process was also discussed in detail. This study presented a new venue for future development of high purity "MAX" materials and others related materials by a modified pressureless sintering strategy.     

Preliminary study of 0.14 THz water surface clutter reflectivity at near vertical incidence angle

As the development of radar systems developed for the terahertz and higher millimeter region continues to grow, the interest in the water surface and land clutter at terahertz and higher millimeter frequencies continues to increase. An empirical model of sea clutter reflectivity is described firstly, which is valid at near vertical incidence and has small average absolute deviation compared to other empirical models. Simulated results of 0.14 THz sea clutter at near vertical incidence with this model are shown. An indoor test-bed is constructed in order to measure 0.14 THz water surface clutter reflectivity and an experiment is carried out. Initial experimental results are presented and compared to the simulation results, which partially verifies that the empirical sea clutter model still works at 0.14 THz.     

聚合物燃烧过程中熔化特性研究

通过试验和模拟研究了大量聚合物包括热塑性和热固性聚合物在燃烧过程中的熔化特性。研究发现，在火灾情况下，有些热塑性聚合物如PP，LDPE，EVA-18和PA6等与PMMA相比熔化得较快，并且熔化物很快汽化，很少有熔化物遗留。相反，有些热固性树脂一般不熔化或者只是轻度熔化，如酚醛树脂和环氧树脂。在热塑性聚合物研究中，其熔化特性在温度燃烧阶段影响了质量损失速率。那些快速熔化的热塑性聚合物与PMMA相比，质量损失塑料较低，这跟单个聚合物高温分解机理有关。一般说来，热分解过程杂乱无序的聚合物更容易造成快速熔化。发生热聚作用的聚合物会导致快速挥发，因此熔化较少。开发了一个聚合物燃烧数学模型，能够模拟聚合物燃烧过程中的溶化特性。结果表明，考虑熔化特性的模型模拟结果与锥形量热仪测试结果的相符性比不考虑熔化特性的模型模拟结果的要好。     

世界各国的阻燃法规及相关管理规定

介绍了世界各国的阻燃法规及相关管理规定.采用阻燃制品防止人身伤害和恶性火灾事故的发生是世界各国经过多年的实践经验验证,并被证明行之有效的防火保护措施之一,美国、日本、加拿大等国家很早就制定了相关的阻燃法规.早期的阻燃法规是为了避免易燃织物给消费者带来伤害,后来逐步发展到限制火灾危险性大的塑料制品、地毯、展板、软垫座椅及床垫等家具产品.目前,我国正在制定相关的阻燃法规,学习和借鉴其他国家和地区的先进经验很有意义.     

提高超声波测距系统精度的研究

论述超声波测距系统的原理及在测量中影响测量精度的主要因素,并论述了温度变化和其他干扰信号对超声测距的影响,最后,对这些存在的问题提出了相应的解决方法.     

ON THE PRIMARY η-PHASE IN A HIGH-Ti Ni-Fe-Cr BASED SUPERALLOY

The precipitation and dissolution together with their control of the primary η-phase in ahigh-Ti Ni-Fe-Cr base superalloy have been investigated.The precipitation of primaryη-phase was found to be closely related to Ti or Al content and solidification rate of the alloy.The aggregation of blocky η-phase may remarkably reduce the tensile strength,ductility andrupture life of the alloy.The temperature-time relation of dissolution of the primary η-phaseobeys T=1370-86.1 lgt for as-cast superalloy.The formation of primary η-phase may beprevented by the reasonable control of Ti or Al content and smelting process.The adoption oftreatment under large hot deformation and homogenization may be the remedy forunfavorable influence of η-phase.     

THEORY OF DYNAMIC OPTIMIZATION FOR MATERIALS HEATING PROCESS——CRITERION RESTRAINING METHOD

A criterion restraining mehod adopted to the dynamic optimization for materials heat-ing process has been developed,by regarding it as controlled object of a regulator incontrol theory and combining the optimal criterion of it.The method may be availableto optimize fuel supply along furnace length and to provide a theoretical basis for theoptimization of fuel supply in time-varying.For soaking pit,the calculation shows thatin case of optimization by criterion restraining method,the thermal efficiency is 3.1higher than the modelling prediction result.In comparison with heat flux-decomposingmethod,the thermal efficiency increased from 43.1 to 43.8%,and the energy consumptionwas reduced by 7.28% relative to the practical production data.     

KINETICS OF REACTION BETWEEN Cu_2S AND Cu_2O

Reaction between Cu_2S and Cu_2O was investigated at 1150 to 1250℃.The reaction rate in-creases with the increase of surface area of Cu_2O grains and depends unobviously on temper-ature.At the suggestion of controlling step of reaction rate being oxygen diffusion through theliquid layer along reaction boundaries,two final kinetical equations would be made as follows:x=6.69×10~(-2)At for 0<α<0.74 and ln(l-α)=-A(9.83×10~(-2)t+1.76)for 0.74<α<1,whereα is SO_2 evolved in time t and A is surface area of Cu_2O particles.     

CONCENTRATION DISTRIBUTION OF ALLOYING ELEMENTS IN SURFACE LAYER OF Ti ALLOY MELTS

The concentration distribution of alloying elements such as Al,Sn,V,Si and Mo in surfacelayer of quenched Ti alloy melts(TC4,TA 7 and TC9)has been determined by EPMA.Ti al-loy samples were melted and evaporized by electron beam in water cooled copper curcible.Theactivity coefficient of alloy elements in Ti alloy melts are:γ_(Al)=0.009—0.018 and γ_(Sn)=0.066—0.123 at 1921—2106℃;γ_V=0.713 at 2021℃;γ_(Si)=0.020 and γ_(Mo)=0.913 at 1921℃.Therate controlling steps of the evaporation of alloying elements Al,Sn,V,Si and Mo from Ti al-loy melts have been discussed with the data of evaporation activation energies of such alloy el-ements.     

新型中空卤化银颗粒乳剂的制备和性能研究 Ⅱ.中子活化分析测定感光乳剂的元素组成

一般采用化学滴定法来定量分析卤化银乳剂中的银和卤素组份．其他仪器分析,如Ｘ射线能谱,Ｘ射线电子能谱,Ｘ光萤光等只能做到半定量或定性分析．而化学滴定法的实验操作步骤又十分繁琐,而且卤素的化学性质相近,需用差减法分别得到最后结果．本文采用中子活化分析法,样品不需预处理（即不需要去除明胶）,即可对卤化银乳剂同时进行元素测定．所测定的数值与化学滴定法的结果对照比较,两者十分相近．说明利用中子活化分析来测定卤化银乳剂的元素组份是可靠的方法