北京地区冬季气溶胶分级化学成分及来源分析

在北京城区进行冬季大气气溶胶采样,样品采用PIXE方法进行分析,得到大气气溶胶中20种元素的质量浓度。结果表明:元素Mg、Fe、Si这3种元素均呈粗粒模态单峰型分布,且峰值出现在2～4μm,表明它们来自土壤尘;S、Cl、K等3种元素谱分布呈细粒单峰型分布,峰值都出现在0.25～0.5μm范围内,表明这3种元素主要来自燃煤;Cu、Zn、As、Br、Pb等5种元素谱分布呈双峰型谱分布;Ni、Cu、Zn、As、Se、Br、Pb等元素的粗、细模态的富集因子都较大,尤其是细粒模态,表明这些元素更容易在细粒模态上富集,进一步说明这些元素主要来自人为污染源。因子分析结果表明:土壤尘、煤烟尘、工业源和汽车尾气排放源对北京冬季气溶胶有主要贡献。     

合肥地区气溶胶光学特性的地基观测研究

利用自主研制的DTF-5型太阳辐射计观测合肥地区2008年10月—2010年5月的太阳直接辐射消光,反演合肥地区气溶胶光学厚度、Angstrom参数和沙尘天气过程中的粒子谱分布,并对结果进行分析。结果表明:合肥地区气溶胶光学厚度季节变化除气候因素外,受人为因素影响明显,季节变化规律复杂。总体上秋季较小,冬春季节持续增大,夏季较平稳。而Angstrom参数与气溶胶光学厚度大致呈反相关,秋冬上升,春季骤降,夏季平稳值较大。气溶胶光学厚度日变化大致可分为4种类型:日变化相对稳定;整体呈上升趋势;整体呈下降趋势;一日内出现一到多个峰值。其中第四种类型出现几率最大。沙尘天气过程中,气溶胶光学厚度和Angstrom参数分别呈现出"谷-峰-谷"、"峰-谷-峰"的变化规律,其中Angstrom参数在沙尘影响严重时甚至出现负值。半径为0.2~1.0μm的大粒子和大于1.0μm的巨粒子浓度在沙尘天气过程中大幅增加。     

气溶胶在岩体裂隙中迁移特性的实验研究

为得到实际岩体裂隙中气溶胶的穿透行为特性,为山体中存储间的选址及洞室工程防护措施的制定提供精确的数据支持,利用电子低压碰撞器对气溶胶在岩体裂隙中的穿透率进行实验测量,得到气流速度、粒径大小、裂隙长度、裂隙高度等参数对穿透率的影响。结果表明,在较低的流速下,小粒径粒子的穿透率随流速的增大稍微增大,大粒径粒子趋势不明显;随着气溶胶粒径的增大,穿透率先增大后减小,峰值在0.3～1.0μm之间;随着裂隙长度的增加,穿透率呈指数减小,且不同长度裂隙、不同粒径气溶胶粒径的穿透率减小趋势基本一致;裂隙高度的增加使气溶胶的穿透率显著增大,高为1.0 mm的裂隙中,气溶胶的穿透率更大,更接近理论结果;在常温常压下,高为0.1 mm的裂隙中,流速为5.6 m/s时,粒径为0.3μm的气溶胶在0.1 mm宽岩体裂隙中的迁移距离非常有限。粒子除了受重力沉积和扩散沉积作用,还受到碰撞效应等作用。     

衡水湖地区气溶胶分布特征的航测研究

利用飞机机载粒子测量系统(PMS)对河北省衡水湖自然保护区上空的大气气溶胶粒子进行观测研究。观测结果表明:下垫面、天气条件、逆温等对气溶胶的分布存在较大的影响;衡水湖上空不同高度的气溶胶平均谱分布均呈现出单峰分布;细粒子谱分布在0.28μm左右处出现峰值;多阶Γ函数对气溶胶粒子谱有较好的拟合效果。     

雾化水性聚氨酯模拟气溶胶凝并实验研究

通过比较室内不同粒径范围的颗粒物在自然沉降、水雾化及水性聚氨酯雾化3种状态下气溶胶浓度减半所需的半值时间,计算相应的凝并系数,研究室内水性聚氨酯雾化后对模拟气溶胶粉尘颗粒物的凝并及去除效果。结果表明,与自然凝并和水雾化相比,在0.6⁴0.0μm粒径范围内,水性聚氨酯溶液雾化后模拟气溶胶颗粒的半值时间分别缩短35.3%、40.6%;在2.040.0μm粒径范围内,水性聚氨酯溶液雾化后模拟气溶胶颗粒的半值时间分别缩短35.3%、40.6%;在2.0¹05.0μm范围内,半值时间分别缩短10.3%、26.2%。     

大豆蛋白液喷雾场粒度分布变化

目的研究大豆蛋白液喷雾场粒度分布的变化规律,为选择一个合适的蔬菜纸喷涂面提供实验数据,以期得到质量好的蔬菜复合纸覆膜。方法将大豆蛋白喷涂雾化场网格化,使用粒度仪分别测量各个区域的粒径和粒度占比分布。结果雾化场轴向距离从H=10 cm处的95μm左右,到H=15 cm处的85μm左右,到H=20 cm处的65μm左右,再到H=30 cm处的45μm左右,最大粒径占比范围逐渐降低;雾化场径向距离从L=4 cm处的40~50μm,到L=8 cm处的35~40μm,到L=12 cm处的35~40μm,再到L=16 cm处的30~35μm,最大粒径占比范围也逐渐降低;在相同的喷涂气压、喷涂液压下,随着轴向距离的增加,大豆蛋白液液滴粒径分布范围的减小,大粒径大豆蛋白液液滴的比例逐渐减少,粒径分布朝着小粒径方向靠拢,大豆蛋白液液滴粒径分布曲线越来越陡峭;在喷涂气压、喷涂液压不变的情况下,仅仅改变大豆蛋白液的粘度,在相同的喷雾场位置随着大豆蛋白液粘度的减小,粒度分布朝小粒径方向靠拢,小粒径大豆蛋白液液滴比例逐渐减小。结论喷涂气压越大、大豆蛋白液粘度越小,雾化效果越好,而喷涂液压对雾化效果影响不大;大豆蛋白液喷雾场液滴的粒径分布随着喷雾贯穿距离的增加,小粒径液滴所占比例逐渐增加,粒径分布曲线朝小粒径方向发展,同时随着垂直与喷雾轴心线径向距离的增加,小粒径液滴所占百分比也增加,粒径分布曲线朝着小粒径方向发展。     

气旋式生物气溶胶采样器采集物理效率评价方法研究

为了评价气旋式生物气溶胶采样器的采集效率,搭建了颗粒物浓度均匀、稳定的静态箱法评价装置,对国内2款气旋式生物气溶胶采样器的采集物理效率进行了测量,最终拟合得到采集效率曲线。测量结果表明：在品牌一采样器的固定采样流量下,其采集物理效率曲线的D_a50(采集效率为50%时的空气动力学直径)为0.91μm;品牌二采样器具有5种可调的采样流量,在不同流量下D_a50分别为1.60μm、1.36μm、1.19μm、1.06μm和1.05μm。对比了使用初始容量分别为15 mL和7.5 mL的采样液得到的品牌二采样器的采集物理效率,发现采样液初始容量较少时,采集物理效率偏低。为气旋式生物气溶胶采样器性能的评价方法提供了参考。     

粉体气溶胶旋流生成效率的试验研究

针对一种3级旋流-粉体气溶胶发生装置,测试分析旋流生成气溶胶的粒谱分布特征,由此定义气溶胶旋流生成效率;研究气流压力、脉冲时间、粉体装填量、旋流喷嘴结构等参数对生成效率的影响。结果表明,旋流装置对粒径为1~10μm的超细粉体能达到很高的气动分散效率;在较小的气流压力下,旋流装置仍能获得很高的气溶胶生成效率;适当减小粉体装填量,可改善气溶胶的生成效果;进气角度、出口锥角分别为15、45°时,气溶胶生成效率最高。     

球磨时间对BC干粉灭火剂形态特征的影响

为了探究球磨时间对BC干粉灭火剂形态特征的影响机理,以常用的BC干粉灭火剂为原料,硬脂酸镁为表面改性剂,采用机械粉磨法对其进行粉磨,并测定其形态特征。结果表明,当球磨时间为0.5~4 h时,粉体表观中位粒径呈现先减小后增大的趋势,粉体形貌由较为松散的团聚体变为较密实的球形团聚体,转折点为球磨时间2 h,球磨工艺的最优表观中位粒径为3.82μm,最佳球磨时间为2 h,极限粒径约为0.9~1.2μm。     

废玻璃粉的火山灰活性

研究中位粒径为15.63、14.93、9.54μm的3种废玻璃粉,分别以相同的质量分数取代10%、20%、30%的水泥制成的胶砂试件7、14、21、28、35、120 d的抗压强度比(活性指数),测定不同龄期废玻璃粉石灰溶液与粉煤灰石灰溶液pH。结果表明:取代率越大,废玻璃粉的活性指数越小;35 d以前的龄期,中位粒径为15.63、14.93μm的废玻璃粉组活性指数最大,35~120 d的后期,中位粒径为9.54μm的废玻璃粉组活性指数最大;废玻璃粉组活性指数前期随着龄期的延长呈减小趋势,后期增大,120 d时达90%以上,比粉煤灰组活性指数约小15%;废玻璃粉石灰溶液与粉煤灰石灰溶液前期pH均呈减小趋势,后期增大;废玻璃粉和粉煤灰的石灰溶液均生成大量CaO-SiO2-H2O凝胶,粉煤灰石灰溶液中还有钙矾石生成,说明废玻璃粉后期有很强的火山灰活性。     

Calibration of the cloud and aerosol spectrometer for coal dust composition and morphology

The cloud and aerosol spectrometer (CAS) was calibrated to enable CAS sizing of coal dust for studies on flammable dust control. Coal dust sizes were determined by light-scattering theories for irregular particles that account for particle composition and morphology in computing coal dust diameters. Coal dust size computations were compared with test dust that was generated by cyclone separation and air-jet sieving and characterized by aerodynamic particle sizer (APS) and computer-controlled scanning electron microscopy (CCSEM) measurements. For test dust in the range of 0.5–32 μm, coal dust size distributions were consistent with cyclone-separated and sieve-segregated sizes. For the 3–20 μm size range, the coal dust size distribution had a mass median diameter that was 14% larger than that of the APS. This difference was reasonable considering that the basic calibration for glass spheres had 13% uncertainty. For the 20–32 μm and 32–45 μm test dusts, mass median diameters differed from CCSEM measurements by only 4% and 5%, respectively. Overall, the results suggest agreement between test dust sizes and computations for coal dust. Alternatively, using conventional Mie theory computations for spheres, coal dust mass median diameters were 35% and 40% larger than APS and CCSEM measurements, respectively.     

三七超微粉体与细粉、不同目数范围粉体的粒度分布和显微形貌特征的比较

通过比较三七超微粉体、细粉(三七常规饮片)以及不同目数范围粉体(三七细粉经多次筛分得到的粉体)在粒度分布、显微形貌特征方面的差异,探讨了超微粉碎技术应用于中药三七加工的优势。应用激光粒度分析仪对三七超微粉体与细粉、不同目数范围粉体的粒度及其分布进行表征,观察其显微形貌特征。粒度分布测试和显微形貌观察的结果表明,超微粉粒度分布在0.30～24μm,大部分粉体达到了10μm以下,呈对称的单峰分布,引起团聚的作用力为各种表面力,说明超微粉体均匀度高质量易控。三七细粉及不同目数范围的粉体粒度分布范围在2～190μm,分布不对称,引起团聚的作用力为重力的等质量力,说明其均匀度差,质量难以控制。     

Particle size measurement of reference particle candidates and uncertainty region of count and mass based cumulative distribution

In order to confirm reliable particle size measurement technique and to prepare standard reference particles for calibrating particle size measurement devices, uncertainty region of count and mass based size distribution have been theoretically examined. The uncertainty region of count base cumulative size distribution is smaller than that of the mass base cumulative distribution.The uncertainty region of count base cumulative size distribution is nearly constant over wide range of particle diameter and the region is nearly constant for sample size greater than about 20,000.On the other hand, the uncertainty region of mass base cumulative distribution increases with the increase of particle diameter.The reliability of theoretical uncertainty region is confirmed by the experimental data of particle size measurement.     

Characterizing organic monolithic columns using capillary flow porometry and scanning electron microscopy

Polyethylene glycol diacrylate monoliths prepared using different amounts of monomer, porogen ratio, and capillary dimensions were characterized using capillary flow porometry (CFP) and scanning electron microscopy (SEM). Our results reveal good agreement between SEM and CFP measurements for through-pore size distribution. The CFP measurements for monoliths prepared by the same procedure in capillaries with different diameters (i.e., 75, 150, and 250 μm) clearly confirmed a change in through-pore size distribution with capillary diameter, thus, certifying the need for in-column measurement techniques over bulk measurements (e.g., mercury intrusion porosimetry). The mean through-pore size varied from 3.52 to 1.50 μm with a change in capillary diameter from 75 to 250 μm. Consistent mean through-pore size distribution for capillary columns with the same internal diameter but with different lengths (1.5, 2, and 3 cm) confirms the high interconnectivity of the pores and independence of CFP measurements with respect to capillary length. CFP and SEM measurements not only allow pore structure analysis but also prediction of relative column performance. Monoliths with narrow through-pore size distribution (0.8-1.2 μm), small mean through-pore size, and thin skeletal size (0.55 μm) gave the best performance in terms of efficiency for polyethylene glycol diacrylate monoliths.     

Effect of particle size distribution on flowability of granulated lactose

The flowability of powders used in tableting significantly affects tablet weight and content uniformity of active pharmaceutical ingredients. Use of granulated materials instead of powdered materials can improve flowability. In this study, the effect of particle size distribution on flowability of granulated lactose was quantitatively analyzed. Three types of granulated lactose were classified into progressively narrower size fractions, and nine samples were systematically prepared. The mass median diameters were nearly constant (i.e., 130.5 ± 13.5 μm) and the geometric standard deviations ranged from 1.29 to 2.04. Two flow properties (angle of repose and compressibility) were measured. The correlations between flow properties and the particle size distributions were analyzed, and the coefficients of determination were obtained for different particle diameters and cumulative mass fractions. The optimal conditions to maximize the coefficients of determination were defined. Furthermore, static and dynamic friction properties were evaluated, and their correlations with particle size distribution were calculated.     

烧结颈分布对3D打印覆膜Al2O3零件强度的影响

从烧结颈的尺寸及分布入手,研究覆膜Al2O3粉末的粒径分布对零件强度的影响。使用UV激光对覆膜粉末进行原位加热,在影像测量仪下测量并获得烧结颈束腰直径与颗粒直径之间的关系。建立颗粒堆积模型,将烧结颈分布与颗粒配位点对应,计算得出某一截面上被断开的烧结颈的投影面积比例。结果表明:对于2%(质量分数)树脂含量的覆膜Al2O3粉末,随着颗粒直径从75μm增长至375μm,烧结颈的束腰直径从40μm增长至100μm。而堆积模拟结果显示,随着颗粒直径从75~107μm区间增加至300~375μm区间,烧结颈的投影面积比例从0.2557降低至0.0823,与实验测量的覆膜Al2O3粉末的抗拉强度的趋势一致。将70/100,100/140目的颗粒按照质量比0∶10,1∶9,2∶8,3∶7,4∶6,5∶5,6∶4,7∶3,8∶2,9∶1,10∶0混合后计算,发现投影面积比例从0.1772降低至0.1264,孔隙率从0.4511升高至0.4633。综合考虑抗拉强度及透气性,得出优化结果为两者比例为7∶3时,投影面积比为0.1481,堆积孔隙率为0.4596。     

粒径对Ni/硅橡胶复合材料压敏性及介电性质的影响

采用不同粒径的Ni粉与硅橡胶(110型)按质量比2.4∶1.0制成Ni/硅橡胶复合材料, 分别测量了其压敏导电性及介电性质, 并结合扫描电镜照片对其微观导电机制进行了分析。结果表明随着填料Ni粉粒径的减小, Ni/硅橡胶复合材料的直流电阻率对外加压强更加敏感: 在低压强下, 粒径为74、48和18 μm的样品的电阻率随压强的变化率分别为1.73×104、2.59×104和3.71×10 4 Ω·m/kPa。样品直流电阻率陡降的区域随粒径的减小向压强较小的方向移动, 显示出复合材料的渗流阈值与填充粒子的粒径有关: 粒径越小, 渗流阈值也越小。Ni/硅橡胶复合材料的交流电导率、介电常数、介电损耗均随填料Ni粉粒径的减小而变大: Ni粉粒径为18 μm的Ni/硅橡胶复合材料的电导率约为10-2 S·m-1, 比74 μm粒径样品的电导率(约10-7 S·m-1)提高了5个数量级; 对应的介电常数由约102提高到约103。改变填料Ni粉粒径可以有效地调节复合材料的弹性和压敏、电输运特性。      

Comparative study of ground and sonicated vermiculite

The aim of this work is to compare the effects of grinding and ultrasonic treatment on vermiculite. Sonication produces a drastic change in particle size (mass median particle diameter 2.4 μm, layer thickness 38 nm), while the resulting material is crystalline as assayed by X-ray diffraction patterns. The TEM study shows that the sonicated vermiculite consists of nanometric flakes. On the other hand, grinding produces particles with medium diameter in the range of about 9 μm and very broad particle size distribution. X-ray and TEM studies of ground sample show an important alteration with grinding time. Prolonged grinding of vermiculite produces the loss of long-range order and eventually an amorphous product is obtained. The results show that grinding treatment produces a decrease of particle size, amorphization and agglomeration of the particles, whereas the ultrasound treatment only produces a decrease of particle size.     

粒径对煤粉云最低着火温度特性的影响

为了研究粒径对煤粉云最低着火温度特性的影响,采用粉尘云最低着火温度测试装置测试了不同粒径下煤粉云的最低着火温度,并结合ReaxFF分子动力学对其反应机理进行了微观层面的探讨。结果表明:当煤粉中位径在34 μm时,煤粉云的最佳着火质量浓度为750 g/m³,最低着火温度为550 ℃;随着煤粉粒径的增加,煤粉云最低着火温度逐渐增大,当煤粉中位径达到124 μm,煤粉云最低着火温度上升至650 ℃。通过ReaxFF分子动力学对煤粉热解过程的计算结果表明:随着反应的进行,大分子煤结构逐步分解,芳香环、C—C键、C—O键和C—H键等断裂,产生更小的分子结构,其中,H₂、H₂O、CO₂和CH₂O等小分子产生的数量逐渐增多;H·自由基和OH·自由基在反应初期有明显的数量变化,且其含量对于最终稳定产物有重要影响。