铝硅合金热法炼镁的理论分析

为了降低热炼镁的生产成本,提高生产效率,本文讨论了用电热法生产的粗铝合金作为不 炼镁的可行性。通过对用铝、硅还原镁的热力学计算,分析了降低还原温度的可能性,同时还进行了铝硅合金和硅铁还原剂的理论单耗计算分析。分析结果表明,用铝呈金为还原剂的热法炼镁是可行的。     

基于钙还原剂的金属镁生产新工艺

为了从根本上改进现行的硅热法炼镁工艺,本文从新的还原剂一液态钙着手,在研究了用液态钙为还原剂的金属镁还原新工艺的可行性后,设计了一种新型的镁还原装置.该装置简单、环保并能实现连续生产.     

皮江法炼镁新型真空系统的设计与选择

目前国内的皮江法炼镁的真空系统大都无预抽泵或使用油封机械泵做预抽泵,使得真空度在较长时间内达不到要求,致使还原剂和镁蒸汽被氧化、污染、生产周期长、产量低、动力消耗高。针对皮江法的特点,设计了新型真空系统,力求在短时间内使真空度达到要求,缩短还原周期,提高还原炉利用率,并使还原的动力消耗降低200～300kWh/t Mg。     

以菱镁矿为原料的铝热法炼镁试验研究

以菱镁矿为原料，以铝粉为还原剂的热还原法炼镁试验，取得了令人满意的结果。试验证明，以铝粉还原剂可降低还原温度。节约能源，延长还原罐的使用寿命，缩短还原周期，提高设备的生产率，随着设备生产率的提高，生产成本中管理费，设备折旧费，工人工资等多项均相应的下降；该法不产生废物，还原渣是生产高级耐火材料的理想原料，价格可观，由此可见，该方法有可能成为较有发展前途的生产方法。     

一种以菱镁石和白云石混合矿物为原料的真空热还原法炼镁技术

提出一种以白云石和菱镁石的混合矿物为原料、以铝粉为还原剂的真空热还原炼镁,然后利用镁还原后的残渣制取氢氧化铝的工艺和技术,并进行实验研究。结果表明:以煅烧后的白云石和菱镁石混合矿物为原料的真空金属热还原炼镁,在还原温度为1 200℃、还原时间为2 h、铝粉过量系数为5%的条件下,镁的还原率可达89%以上,还原渣主要物相为CaO.2Al2O3,还原渣中Al2O3的含量为67%左右;该炼镁还原渣经碳酸钠和氢氧化钠的混合碱液浸出后,Al2O3的浸出率达到85%,浸出Al2O3后渣的主要成分为CaCO3;浸出液中的Al2O3以可溶解的铝酸钠存在于浸出液中,后经碳分分解制得氢氧化铝,氢氧化铝的白度达到97%。     

以二次铝灰为还原剂还原炼镁-还原渣溶出氧化铝的实验研究

二次铝灰是铝电解和铝合金生产过程中产生的一种主要废弃物之一,截止目前,绝大部分的二次铝灰均未得到较好利用,主要采用填埋处理。本论文对以二次铝灰为还原剂真空热还原炼镁过程和还原渣中的氧化铝溶出过程进行了研究。实验结果表明:还原过程中氧化镁的还原率可达到85%以上,还原料镁比在8.5~9.0∶1,虽然由于还原料镁比的增加会导致还原能耗的增加和还原生产率的降低,但由于二次铝灰的成本较低,且还原渣中大部分的氧化铝和氮化铝可以被溶出生产高白的氢氧化铝,因此以二次铝灰还原炼镁仍有利可图。     

氟盐对炼镁还原渣中氧化铝浸出率的影响研究

以白云石和菱镁石为原料以铝粉为还原剂真空热还原炼镁过程中添加氟化钙可使镁还原率提高5%以上,还原温度降低50℃,还原后还原渣的主要物相为CaO.2Al2O3,加入的氟化钙在还原过程会参与反应生成氟铝酸钙。在实验室以氢氧化钠和碳酸钠的混合碱液对该含氟盐还原渣中氧化铝的浸出进行了研究,研究结果表明:经碱液浸出后还原渣中的CaO.2Al2O3全部被分解,还原渣中的氧化铝浸出率在70%以上,浸出渣的主要物相为CaCO3。含氟盐炼镁还原中氧化铝的浸出率比不含氟盐的氧化铝浸出率低10%以上,在还原过程中生成的氟铝酸钙和浸出过程中生成的水合铝酸钙是导致氧化铝损失增加的主要原因。     

热法还原镁的研究及液相Si-X体系还原镁的热力学分析

我国是金属镁生产和出口第一大国,皮江法热还原炼镁在我国金属镁生产中占据着绝对优势,但是其能耗高、污染大且效率低,成为影响镁行业持续绿色发展的限制因素。鉴于此,国内外针对皮江法进行了不断改进,并开发出新型炼镁工艺。液-液还原和固-液还原炼镁因其效率较高、周期短、能耗小等优点,成为热还原炼镁的重要发展方向。本研究基于固-液还原反应提出一种炼镁工艺,并从热力学角度对多种Si-X合金还原过程进行了分析。为保证反应持续进行,低熔点组成的熔渣是其重要影响因素。     

Al-Mg-Sc中间合金的制备

在非真空条件下用氟化物熔盐体系镁 (铝 )热还原法制备了Al Mg Sc中间合金 ,讨论了金属还原剂的选择及还原温度、时间等工艺条件对钪收率的影响 ,并研究制定了氧化钪固相氟化制备氟化钪熔盐工艺。采用Al Mg合金熔体为还原剂经二次还原后钪收率 >80 %,制备的Al Mg Sc中间合金铸锭中钪含量 >1.9%,最佳的还原反应温度为 110 0K ,还原时间 40min .。氟化钪还原产生的初生态钪与铝作用形成稳定的Al3 Sc化合物 ,促进了还原的进行 ,使钪收率得到了大幅度提高。     

铝热法炼镁反应过程及其产物的研究

一、前言硅热法炼镁由于反应温度较高(1200℃),致使反应罐在高温、高真空条件下工作寿命较短。为了降低反应温度可用纯铝、含铝较高的铝硅合金代替硅铁作还原剂与煅烧白云石反应生产镁。但是,从文献报道看,对于纯铝或铝硅合金还原煅烧白云石的反应过程及其产物存在不同见解。目前国内流行的观点认为,铝还原煅烧白云石的反应为:     

压铸脱模剂喷涂新工艺--脉冲喷涂

提出了一种新型的脱模剂喷涂工艺——脉冲喷涂。利用有限元方法对脉冲喷涂和传统的连续喷涂进行了初步对比分析，并在压铸厂进行了一定模次的实效验证，结果表明脉冲喷涂使得模具内的温度梯度比传统连续喷涂时的温度梯度大幅降低，有利于减小热应力的产生，从而提高模具寿命，同时可减少脱模剂的使用量，改善铸件表面品质。     

低热应变镁合金研究综述

镁和镁基合金是重要的轻量化金属材料,广泛应用于汽车、通讯、航空等领域。由于镁合金热膨胀系数较高,当应用于精密器件时易导致组装精密度降低、力学性能下降等问题。因此需要研发低热应变镁基材料,以满足此类应用的要求。本文对降低镁合金热膨胀系数的原理及方法进行综述,归纳比较了合金化、复合材料和特殊加工工艺等调整镁合金热膨胀系数的主要方法的原理,总结出高熔点元素合金化、高硬度颗粒掺杂、低热膨胀系数纤维掺杂以及热处理结合挤压加工方法等降低镁合金热膨胀系数的有效方法,并对未来该领域的研究趋势进行了展望。     

Fabrication of SiC by carbothermal-reduction reactions of mountain leather asbestos

Fibrous magnesium silicate (Mg₆Si₄O₁₀(OH)₈: mountain leather asbestos) of Serbian origin was used as Si precursor for the synthesis of SiC by carbothermal-reduction process. As a reducing agent, carbon (from various precursors) was used. Formation of β-SiC was confirmed by XRD and SEM/EDS analyses. Porous SiC particles obtained at 1873 K possess longish plate-like morphology. The results show that reduction reaction is assisted by liquid phase formation, as well as vapor phase transport, and that mountain leather asbestos can be very effective mineral precursor for preparation of silicon carbide.     

我国硅热法炼镁发展中值得重视的几个问题

硅热法炼镁在我国发展速度是较快的，2004年前我国硅热法炼镁的产能已接近50万t／a，实际产量已达到35.4万t／a，目前国内某些地区根据其资源与经济实力，拟较大规模的兴建硅热法炼镁厂。本文提出在兴建硅热法炼镁厂时，必须重视对炼镁原料（白云石、硅铁）；燃料与动力（煤炭与电力）；建厂规模及生产设备组合；产品种类；原材料的加工（硅铁、熔剂、还原罐）及残渣的综合利用以及环境保护等问题的考虑。以使新建的镁厂具有最先进的生产技术，最低的生产成本。最优的产品质量，最大的经济效益，良好的绿色环境。     

Effect of a chromium-containing fuel additive on hot corrosion

Four cast superalloys (one cobalt-base and three nickel-base) were tested at 900°C for 100 h in Mach 0.3 combustion gases. 5 ppm of synthetic sea salt were added to the gases in the combustion chamber. Several types of thermal cycle and washing procedures were employed. Similar tests were made with the addition of 300 ppm of a chromium-containing fuel additive. In both sets of tests the extent of hot corrosion was evaluated by specific weight change and metal recession. In general, the chromium additive in the fuel reduced the extent of hot (salt) corrosion but did not eliminate it. The percentage reduction of hot corrosion attack was similar for all four alloys. As great a reduction of hot corrosion was achieved by reducing the number of thermal cycles during the test from 100 to 5 of 6. The effect of washing the alloys every ten cycles as opposed to the end of the test was erratic; some alloys were attacked slightly more, others somewhat less. A NiCrAlY coating was found to be more effective in reducing hot corrosion than either the fuel additive or the washing schedule.     

A new concept for producing Ti sponge: Calciothermic reduction

This article presents a new cell concept for the calciothermic reduction of titanium dioxide and an ongoing test program for its experimental verification. The thermochemical background of this concept is focused and a new cell design is described. This system consists of a single cell, where both the reduction reaction and the electrolytic reaction for recovery of reducing agent coexist in the same molten calcium-chloride bath. The theoretical electric energy requirement for this cell is about half of that for the magnesium electrolytic cell in the Kroll process.     

主盐及还原剂对AZ31镁合金化学镀镍-磷合金的影响

以硫酸镍为主盐,次亚磷酸钠为还原剂的镀液体系在AZ31镁合金基体表面化学沉积镍-磷镀层,并通过扫描电子显微镜(SEM)、能谱分析(EDS)、金相分析和极化曲线等分析手段探讨了化学镀液中主盐和还原剂的摩尔浓度比(CNi2+/CH2PO-2)对镁合金表面Ni-P镀层的形貌、成分、沉积速度和耐蚀性能的影响。结果表明:CNi2+/CH2PO-2对Ni-P镀层形貌的影响较小,但与膜层中的镍、磷元素的含量呈明显的线性关系;当CNi2+/CH2PO-2在0.4~0.6之间时,镀层沉积速度最快;CNi2+/CH2PO-2为0.3和0.4时,所得镀层的耐蚀性能较好。综上,在仅考虑主盐和还原剂对镀层性能影响的前提下,CNi2+/CH2PO-2=0.4时所得镀层的综合性能最好。     

Low Thermal Conductivity Yttria-Stabilized Zirconia Thermal Barrier Coatings Using the Solution Precursor Plasma Spray Process

The primary function of thermal barrier coatings (TBCs) is to insulate the underlying metal from high temperature gases in gas turbine engines. As a consequence, low thermal conductivity and high durability are the primary properties of interest. In this work, the solution precursor plasma spray (SPPS) process was used to create layered porosity, called inter-pass boundaries, in yttria-stabilized zirconia (YSZ) TBCs. IPBs have been shown to be effective in reducing thermal conductivity. Optimization of the IPB microstructure by the SPPS process produced YSZ TBCs with a thermal conductivity of 0.6 W/mK, an approximately 50% reduction compared to standard air plasma sprayed (APS) coatings. In preliminary tests, SPPS YSZ with IPBs exhibited equal or greater furnace thermal cycles and erosion resistance compared to regular SPPS and commercially made APS YSZ TBCs.     

Influence of alloying additions on microstructure and thermal properties in compact graphite irons

Abstract

Nineteen compacted graphite cast irons were investigated to determine how alloying additions affect the thermal transport properties and microstructure. All melts were based on one chemical composition and alloying elements were added to obtain melts with variation in magnesium, silicon, carbon, copper, tin, chromium and molybdenum. Increasing amounts of magnesium resulted in a further compaction of the graphite particles, reducing the thermal conductivity. Large amounts of silicon resulted in a fully ferritic metal matrix. Silicon also formed solid solution with iron which had a deteriorating effect on the thermal conductivity, i.e. the larger amount of silicon the lower the thermal conductivity. Copper and tin promoted formation of pearlite that had worse thermal properties compared to ferrite. Increasing amount of ferrite generally had a positive influence of the thermal conductivity. Chromium and molybdenum were carbide forming elements and carbides had a negative influence on the thermal conductivity.