常见钠盐的高温挥发特性及热解机理

选取有机废液中常见的钠盐(氯化钠、碳酸钠、硫酸钠、甲酸钠、乙酸钠、草酸钠),通过热重分析仪,在25～1400℃考察其高温挥发特性。基于Gibbs自由能最小原理,对Na Cl、Na₂CO₃及Na₂SO₄的挥发特性进行热力学计算。结果表明,在N₂气氛中,Na Cl在达到熔点后以气态Na Cl及气态Na₂Cl₂的形式释放,Na₂SO₄升温至885℃分解生成Na₂O,同时Na₂O分解,并以Na单质形式释放。而有机羧酸钠盐在600℃之前均热解为Na₂CO₃,继续升高温度则分解为Na₂O,同样最后以气态Na单质的形式释放。在空气气氛中,由于O₂的存在,抑制了Na₂O的分解反应,致使Na₂CO₃分解速率小于N<...     

燃煤锅炉烟气中Na2SO4生成的化学动力学研究

准东煤燃烧过程中Na₂SO₄的形成会造成锅炉受热面沾污、尾部SCR催化剂失活等问题。烟气中Na₂SO₄形成及转化规律的研究对于预测和控制燃煤烟气中Na₂SO₄的形成有重要意义。发展了烟气中Na/Cl/S/O/H化学动力学模型,研究了烟气中Na₂SO₄的生成过程及转化机理,考察了含氧量、温度、SO₂浓度、H₂O浓度等因素对Na₂SO₄生成的影响。动力学计算结果表明,模型预测结果与实验数据吻合较好,验证了模型的准确性。烟气中的高氧气含量有利于Na₂SO₄的生成。高温加快化学反应的同时,抑制了Na₂SO₄的生成。SO₂和H₂O的影响效果受温度影响较大。反应路径分析表明,Na₂SO₄的生成路径有两个：一是依赖于SO₂直接氧化（NaCl→NaSO₃Cl→NaHSO₄→Na₂SO₄）,二是依赖于SO₂间接氧化（NaCl→NaO₂→NaSO₄→NaHSO₄→Na₂SO₄）。敏感性分析结果表明,Na₂SO₄的生成主要对系统中生成或消耗自由基的反应更为敏感。     

废液焚烧余热锅炉灰渣沉积机理分析

研究了取自某炼化公司废液焚烧余热锅炉不同部位换热面的多个沉积样品,分析了不同部位换热面沉积生长物的组分与沉积机理。利用X射线衍射分析仪（XRD）、扫描式电子显微镜（SEM）以及能量弥散X射线探测器（EDX）分别来鉴定样品的结晶物成分、形貌以及元素组成,各个样品的灰熔融特征温度在智能灰熔点测试仪上测定。结果表明,余热锅炉高温入口段主要沉积物为Na2SO4、NiO、Fe2.3Si0.7O4等,炉膛中低温区域主要出现Na2Ni(SO4)2?4H2O、Na3Fe(SO4)3及 Na6Fe(SO4)4等物质沉积。这主要是由于硫酸钠与受热面管壁氧化保护层（Fe2O3）发生高温腐蚀引起的。     

蛋白土与硫酸铵煅烧反应产物及过程动力学

蛋白土具有良好的应用前景,但是其自然白度较低制约了其开发应用。蛋白土硫酸铵煅烧法可去除其中的显色金属氧化物,提高蛋白土的白度,同时提取其中Al₂O₃。本文采用热重-差示扫描量热（TG-DSC）、同步热分析与红外质谱（TG-FTIR-MS）联用系统,结合X射线衍射对煅烧过程的固相及气相产物进行了表征分析,明析了其化学过程。结果表明,蛋白土中的Al₂O₃和Fe₂O₃在200~350℃时反应生成（NH₄）₃（Al,Fe）（SO₄）₃,同时逸出NH₃和H₂O;350~450℃时,进一步反应转化为NH₄（Al,Fe）（SO₄）₂,同时逸出NH₃、H₂O、SO₂和O₂;450~550℃时,NH₄（Al,Fe）（SO₄）₂分解生成（Al,Fe）₂（SO₄）₃,同时逸出NH₃、H₂O、SO₂和O₂;550~750℃时（Al,Fe）₂（SO₄）₃分解生成Al₂O₃和Fe₂O₃,同时逸出SO₂和O₂。采用Kissinger微分法与Ozawa积分法分别计算出4个阶段表观活化能后取二者平均值,分别为101.74kJ/mol、104.52kJ/mol、201.40kJ/mol、232.51kJ/mol,并获得对应4个热化学反应阶段的频率因子、反应级数和动力学方程。     

(NH4)2S吸收净化冶炼烟气中SO2回收硫资源的方法

采用(NH₄)₂S溶液吸收净化高浓度SO₂烟气,得到(NH₄)₂S₂O₃和NH₄HSO₃的混合溶液并转移至高压反应釜中,控制反应条件,两种物质发生自氧化还原反应,生成硫磺和(NH₄)₂SO₄.实验考察了吸收SO₂过程和自氧化还原过程的影响条件,结果表明:在pH=3～7,SO₂气体流速300 ml·min^-1,(NH₄)₂S浓度为0.2～1.2 mol·L^-1,常温条件下,烟气中二氧化硫的吸收率达到99.8%以上,且无H₂S生成;在pH=2.5～3.0,温度为130℃条件下,反应进行1 h,硫磺收率达到95%以上,溶液经过蒸发结晶得到(NH₄)₂SO₄.用X射线衍射(XRD)和X射线荧光光谱(XRF)对硫磺和硫酸铵进行表征分析,结果表明:硫磺的纯度为99.14%,硫酸铵中氮元素含量为23.6%.     

硫酸铅在硼硅酸盐玻璃熔体中的溶解特性

针对高硫、高钠的高放废液玻璃固化过程中Na₂SO₄极易分解和分相的问题,本文提出在模拟高放废液中加入适量Pb(NO₃)₂溶液将Na₂SO₄转变成PbSO₄,再利用熔融法制备硼硅酸盐玻璃固化体。首次采用在钢铁材料中广泛应用的高温激光共聚焦显微镜原位观察PbSO₄在玻璃熔体中的溶解特性,并探究不同温度(800～1 150 ℃)下PbSO₄与硼硅酸盐玻璃混合熔制后的热稳定性以及玻璃体中的硫含量。结果表明:在硼硅酸盐玻璃中掺入6%(质量分数,以SO₃计)PbSO₄的样品在800 ℃和900 ℃为均匀的玻璃陶瓷,其中800 ℃时主要含SiO₂及少量BaSO₄、PbSO₄晶体,900 ℃时SiO₂晶体减少,BaSO₄晶体增多,PbSO₄消失并出现CaMgSi₂O₆晶体;样品在1 000 ℃时玻璃表面开始出现由PbO、BaSO₄、LiNaSO₄晶体组成的白色分相,在1 000～1 100 ℃时圆形PbO晶体逐渐长大,BaSO₄晶体由块状变为条状;样品在800～1 000 ℃时玻璃体中的硫含量基本保持不变,随着温度进一步升高硫含量迅速下降。     

6063铝合金碱性铈-钼化学转化工艺及膜层组织结构

以Ce(NO₃)₃和Na₂Mo O₄为成膜主盐,乙二胺四乙酸二钠(EDTA-2Na)为配位剂,在碱性条件下对6063铝合金进行化学转化处理。研究了转化液p H、温度和转化时间对Ce–Mo转化膜耐蚀性的影响,得到较优的工艺参数为:Ce(NO₃)₃·6H₂O 6 g/L,Na₂Mo O₄ 8 g/L,EDTA-2Na 4 g/L,尿素18 g/L,Na₂CO₃ 5 g/L,p H 8.5,温度80°C,时间20 min。所得Ce–Mo转化膜呈墨绿色,均匀、致密,主要由Al、Ce和Mo的氧化物组成,耐性硫酸铜点滴时间约为95 s。     

低温相变蓄热材料性能研究及在移动蓄热装置中应用

基于当前对KAl(SO₄)₂·12H₂O蓄热性能研究较少且很少有蓄热装置应用KAl(SO₄)₂·12H₂O作为相变蓄热材料的问题。对KAl(SO₄)₂·12H₂O的制备和蓄热性能进行了总结以及热力学性能分析,得出环境温度及初始温度对相变材料?效率影响较小,终止温度对?效率影响较大;当初始温度为328K,环境温度288K时,最佳终止温度为370K。同时,针对KAl(SO₄)₂·12H₂O应用于移动蓄热装置进行数值模拟,得到液相率、温度随时间的变化曲线。本文研究表明KAl(SO₄)₂·12H₂O是一种性能良好的低温蓄热材料。     

硫修饰的多孔Co3O4活化过一硫酸盐降解亚甲基蓝

以Na₂S₂O₃为硫源，采用改进的草酸盐-热解法制备了一系列硫修饰的Co₃O₄多孔催化剂[S_x@Co₃O₄,x=0.25、0.50、0.75、1,x为硫的修饰量，以Co(NO₃)₂·6H₂O的物质的量为基准，下同]。以亚甲基蓝(MB)为降解模型，考察了不同催化剂活化过一硫酸盐(PMS)的性能。探讨了催化剂用量、PMS浓度、反应温度、常见阴离子种类在S_x@Co₃O₄-PMS体系下对MB降解率的影响，并评价了催化剂的循环稳定性。结果表明，随着硫修饰量的增加，Co₃O₄的催化性能逐渐升高，S₁@Co₃O₄表现出最佳的催化性能。硫元素以SO₄^2–     

低成本大比表面积γ-Al2O3的制备

以廉价无机铝盐硫酸铝为原料,氨水为沉淀剂,十二烷基硫酸钠为添加剂,采用简单沉淀法制备得到较大比表面积γ-Al₂O₃。通过N₂低温物理吸附-脱附、X射线衍射、红外光谱、热重、元素分析、扫描及透射电镜等,研究制备过程中沉淀温度、溶液pH值和添加剂用量对产物γ-Al₂O₃及其前驱体的晶相结构、形貌织构等性质的影响。结果表明,在沉淀温度75 ℃、硫酸铝浓度0.25 mol·L^-1、溶液pH=9.0、老化时间12 h和n(十二烷基硫酸钠)∶n[Al₂(SO₄)₃]=0.375∶1条件下,所得前驱体(拟薄水铝石)经600 ℃焙烧后,可获得大比表面积(416.65 m²·g^-1)γ-Al₂O₃,并且样品中因十二烷基硫酸钠添加,引入的S及Na等杂质含量极少。     

Corrosion studies with a new laboratory-scale system simulating large-scale diesel engines operating with residual fuels: Part II. Particle and deposit characteristics

Particle and deposit characteristics were studied with a new laboratory-scale deposition–corrosion apparatus designed to simulate the particle formation and deposition in large-scale diesel engines. Synthetic ash particles containing V, Ni, and Na are generated with an ultrasonic nebuliser. Total particle mass concentrations varied from 463 to 1739 mg/N m³ and highest concentrations were reached with SO₂(g) feed and cold dilution. Mass size distributions at the size range of 0.01–15 μm (aerodynamic size) were unimodal at 1.4 μm. Particle morphology changed dramatically from 1 to 5 μm sized solid particles without SO₂(g) feed into flat wet “pools” with SO₂(g) feed. It seemed that condensing sulphuric acid had dissolved the particles. Small 70–90 nm spherical particles were also observed with SO₂(g) feed. On the other hand, hardly any S was found in the deposits, which indicated that S as SO₂(g)/SO₃(g) was transported through the deposit pile into the base material.     

Acidic and basic binders for magnesite based aggregate in plaster of tundish

Binders are generally inorganic, organic or organomineral and have an important influence on the performance and corrosion resistance of slag line and deskulling. Since silicate and phosphate binders have some side effects, in this work sulphate binders such as sulphamic acid, H₂NSO₃H; aluminum sulphate, Al₂(SO₄)₃; ammonium sulphate, (NH₄)₂SO₄; magnesium sulphate, MgSO₄; calcium sulphate, CaSO₄; sodium sulphate, Na₂SO₄; and potassium sulphate, K₂SO₄, are investigated. Cold crushing strength at different heat treatments of room temperature, 110 °C, 1100 °C, 1400 °C is measured. Apparent porosity of samples without pulp and bulk density together with pH of the binder solution is evaluated and XRD and SEM studies are performed. Among these sulphate binders MgSO₄ was found to be the best. It is acidic in nature and develops strong bonds to the basic aggregate, MgO, at low temperatures. At high temperatures it dissociates from MgO(s) and SO₃(g) and the remained portion of MgO is the same as host oxide, with no corrosion and easy deskulling. Basic binders such as calcium sulphate, sodium sulphate and potassium sulphate could not strongly bond the MgO aggregates.     

Development of a modeling approach to predict ash formation during co-firing of coal and biomass

The scope of this paper includes the development of a modelling approach to predict the ash release behaviour and chemical composition of inorganics during co-firing of coal and biomass. In the present work, an advanced analytical method was developed and introduced to determine the speciation of biomass using pH extraction analysis. Biomass samples considered for the study include wood chips, wood bark and straw. The speciation data was used as an input to the chemical speciation model to predict the behaviour and release of ash. It was found that the main gaseous species formed during the combustion of biomass are KCl, NaCl, K₂SO₄ and Na₂SO₄. Calculations of gas-to-particle formation were also carried out to determine the chemical composition of coal and biomass during cooling which takes place in the boiler. It was found that the heterogeneous condensation occurring on heat exchange surfaces of boilers is much more than homogeneous condensation. Preliminary studies of interaction between coal and biomass during ash formation process showed that Al, Si and S elements in coal may have a ‘buffering’ effect on biomass alkali metals, thus reducing the release of alkali–gases which act as precursors to ash deposition and corrosion during co-firing. The results obtained in this work are considered to be valuable and form the basis for accurately determining the ash deposition during co-firing.     

Ash deposition characteristics of Moolarben coal and its blends during coal combustion

We report a systematic and comprehensive laboratory investigation of the ash deposition behavior of Moolarben (MO) coal, which has recently begun to be imported into Korea. Ash deposition experiments were conducted in a drop tube reactor, and a water-cooled ash deposit probe was inserted into the reactor to affix the ash. The tests were conducted using five types of single coals (two bituminous and three sub-bituminous, including MO coal) and blended coals (bituminous coal blended with sub-bituminous coal). Two indices represent ash deposition behavior: capture efficiency and energy-based growth rate. A thermomechanical analysis evaluated the melting behavior of the resulting ash deposits. The MO coal had the least ash deposition of the single coals due to its high melting temperature, indicated by high ash silica content. Indonesian sub-bituminous coals formed larger ash deposits and were sticky at low temperatures due to relatively high alkali content. However, blends with MO coal had greater ash deposition than blends with other bituminous coals. This non-additive behavior of MO coal blends is likely due to interactions between ash particles. Coals with higher silica content more effectively retain alkali species, resulting in lower melting temperatures and larger ash deposits. Therefore, we recommend that when blending in a boiler, silica-rich coals (SiO₂>80%, SiO₂/Al₂O₃> 5) should be blended with relatively low-alkali coals (Na₂O+K₂O<3%), and the blending ratio of the silica-rich coals indicates less than 10%, which can safely operate the boiler.     

Effect of pH and current density on the electrodeposition of Zn–Ni–Fe alloys from a sulfate bath

An investigation was done on the influences of current density and pH on the electrodeposition behavior of Zn?CNi?CFe alloys using a sulfate bath. The bath consisted of 0.1?M ZnSO₄, 0.1?M NiSO₄, 0.1?M FeSO₄, 0.2?M Na₂SO₄, 0.2?M H₃BO_3, and 0.01?M H₂SO₄. The results of Zn?CNi?CFe alloys?? codeposition revealed that the significant inhibition of Ni and Fe deposition takes place because of the presence of Zn²⁺ in the plating bath. A transition current density was noticed above wherein a transition from normal to anomalous deposition took place. Bright and uniform surface appearance deposits of Zn?CNi?CFe were the results obtained at pH range 2?C5, and the deposits showed high corrosion resistance. During the investigation, the usage of cyclic voltammetry and galvanostatic techniques for electrodeposition were utilized, while linear polarization resistance and anodic linear sweeping voltammetry techniques were used for the corrosion study. Characterization of morphology and the chemical composition of the deposits were performed by means of scanning electron microscopy and atomic absorption spectroscopy.     

Na2SO4 deposit-induced hot corrosion of SiC fibers relevant for SiC CMCs

Hi Nicalon, Hi Nicalon S, Sylramic, and Sylramic iBN SiC fibers were exposed to ~60 μg/cm² of Na₂SO₄ in a 0.1% SO₂/O₂ gaseous environment for times between 0.75 and 24 h at 1000°C. After exposure, the corrosion products were characterized using SEM, EDS, ICP-OES, TEM, and EFTEM to determine their high-temperature resistance to Na₂SO₄ and key reaction mechanisms. All SiC fiber types tested in this work exhibited little resistance to Na₂SO₄ deposit-induced attack relative to their behavior in dry O₂ environments. It was found that Hi-Nicalon displayed the least resistance to Na₂SO₄ deposit-induced attack due to excess carbon content resulting in the formation of a highly porous crystalline oxide and promotion of basic corrosion conditions. All fiber types formed a crystalline SiO₂ reaction product, either cristobalite or tridymite. Sylramic and Sylramic iBN formed a crystalline SiO₂ reaction layer containing TiO₂ needles due oxidation of TiB₂ particles. Additionally, Na₂SO₄ deposits resulted in pitting of all fiber surfaces.     

High velocity oxygen fuel sprayed Cr3C2-NiCr coatings against Na2SO4 hot corrosion at different temperatures

Cr₃C₂-NiCr/NiCrAlY coating was prepared by high velocity oxygen fuel (HVOF) spraying. The microstructure and the Na₂SO₄ hot corrosion behavior at different temperatures of the coating were investigated. The Na₂SO₄ hot corrosion mechanism of Cr₃C₂-NiCr coating was also discussed. The results showed that HVOF Cr₃C₂-NiCr coating was relatively dense and mainly composed of Cr₃C₂, NiCr and a small amount of Cr₇C₃ three phases. The dense Cr₂O₃ layer was formed on the surface of Cr₃C₂-NiCr coating after Na₂SO₄ corrosion at 750 °C to further prevent corrosion. The coating had produced the obvious longitudinal crack with the increase of hot corrosion temperature up to 900 °C. The corrosion mechanism of Cr₃C₂-NiCr coating against the Na₂SO₄ salt at high-temperature was as follows: firstly, the protective oxidizing film was formed at 750 °C, then the protective oxide film dissolved at the interface between the coating and Na₂SO₄ salt with the hot corrosion temperature increasing up to 900 °C, and subsequently the dissolved anions and cations could migrate to the interface between molten salt and air and the loose and unprotected oxides were regenerated, thereby exacerbating the failure of the coating.     

Hot corrosion behavior of Ti3SiC2 in the mixture of Na2SO4–NaCl melts

The corrosion behavior of polycrystalline Ti₃SiC₂ was studied in the mixture of Na₂SO₄–NaCl melts with various mass ratios at 850 °C. The results demonstrated that Ti₃SiC₂ suffered from serious hot corrosion attack in the mixture of Na₂SO₄–NaCl melts when the concentration of Na₂SO₄ was higher than 35 wt.%. A large amount of corrosion products spalled from specimens during the tests and obvious mass loss was observed. Hot corrosion of Ti₃SiC₂ would become severe because NaCl had lower melting-point and caused Na₂SO₄–NaCl mixture melted below 850 °C. However, when the concentration of Na₂SO₄ was lower than 25 wt.% in the mixture, a protective oxide layer (SiO₂ + TiO₂) formed on the substrate, the corrosion rate of Ti₃SiC₂ became quite slow and slight mass gain was observed, the corrosion products did not spall from substrate at 850 °C. The microstructure and phase composition of the corroded samples were investigated by SEM/EDS and XRD.     

Hot corrosion phenomena of Nb-Ti-Si based alloy and its silicide coating induced by different corrosive environments at 900 °C

This study aims to elucidate the hot corrosion behavior of Nb-Ti-Si based alloy and its silicide coating in different molten salts at 900?°C. The results show that both K₂SO₄ and Na₂SO₄ had detrimental effect on the corrosion performance of the alloy, but almost no effect on the coating. However, NaCl accelerated the corrosion process for both the alloy and coating, showing highest scale thickness and mass gain. The main corrosion products consist mainly of Na or K containing oxides, TiO₂ and amorphous silicate. The reactivity of the alloy and the coating in different corrosive environments is discussed.