喷雾对促进细颗粒物声波团聚的影响

以燃煤烟气为对象,实验研究了各参数对喷雾促进声波团聚的影响。结果表明,添加喷雾后,声波团聚效率提高了25%~40%。无论有无喷雾,声波团聚均存在相同的最佳频率,为1400 Hz左右。较低液气比时,团聚效率随液气比的增加而明显增大,但超过0.10后,团聚效率趋于稳定。添加喷雾时,团聚效率随停留时间的增加而提高,但达到4.2 s时基本达到最大值。分析了喷雾提高团聚效率的机理,在喷雾作用下,颗粒之间形成比范德华力更强的液桥力,增大了有效碰撞系数;同时,雾化液滴的加入为气溶胶团聚提供了种子颗粒,周围的细颗粒易与之发生碰撞团聚,使团聚效率提高。研究表明,喷雾方法可以大幅降低声波团聚工艺的操作能耗。     

Efficiency of mineral admixtures in mortars: Quantification of the physical and chemical effects of fine admixtures in relation with compressive strength

This work is the fourth part of an overall project the aim of which was the development of general mix design rules for concrete containing different kinds of mineral admixtures. The two first parts presented the separation and quantification, by means of an empirical model based on semi-adiabatic calorimetry measurements, of the different physical effects responsible for changes in cement hydration (short terms) when chemically inert quartz powders were used in mortars. Part three dealt with an intensive experimental program, presenting and commenting more than 2000 compressive strength measurements. This program concerned 1 day to 6 months old mortars containing up to 75% of inert and pozzolanic admixtures. All these compressive strength results are analyzed in this fourth part and the influence of three effects, namely dilution, heterogeneous nucleation and the pozzolanic effect, are discriminated and quantitatively evaluated. An efficiency concept is proposed in order to take into account the effect of mineral admixture in mortars from both the physical and chemical points of view. It uses an efficiency function ξ(p) that has notable properties: it is independent of time, independent of fineness and independent of the type of mineral admixture.     

电除尘器飞灰粒径表征及细颗粒降温团聚

基于50000m³/h实烧烟气中试系统,采用Mastersizer 2000E激光粒度分析仪和电子低压冲击仪（ELPI）,首次对电除尘器飞灰几何粒径和空气动力学粒径进行全面表征。结果表明,电除尘器入口及各电场的飞灰几何粒度分布均呈双峰分布特征,各电场峰值依次右移,但末级旋转电极电场≤ 1μm的颗粒占比略有升高,电除尘器入口及第1～5电场飞灰几何中位径分别为6.607μm、17.378μm、2.884μm、2.577μm、2.460μm、2.480μm;温度降低,电除尘器入口飞灰几何粒度分布的双峰均右移,颗粒团聚现象明显,80℃、90℃、110℃、130℃、150℃时电除尘器入口飞灰几何中位径分别为13.183μm、10.500μm、10.171μm、6.607μm、7.586μm,从130℃降至90℃,电除尘器入口几何粒径≤ 1μm、≤ 2.5μm、≤ 10μm的飞灰占比分别减少了19.8%、19.2%、12.6%;不同温度时,电除尘器对空气动力学粒径0.03～10μm段颗粒的个数浓度、质量浓度均有较高脱除效率,均在75%以上,最高可达99.9%;温度降低,电除尘器进出口空气动力学粒径不同粒径段颗粒个数浓度和质量浓度均有不同程度降低,从130℃降至90℃、80℃,对应电除尘器入口PM_2.5团聚效率分别为46.76%、60.08%,对应电除尘器出口PM₁₀减排分别为59.80%、91.08%,PM_2.5减排分别为45.94%、76.22%,PM1减排分别为40.40%、62.12%。     

混凝土第二掺合料及水泥厂发展掺合料产业的思考

通过与单掺粉煤灰混凝土对比，分析了3种矿物掺合料即矿渣粉、L粉和B粉作为第二掺合料(与粉煤灰双掺)配制混凝土的技术经济可行性，并以此为引题提出了水泥厂以推广复合水泥的形式发展掺合料产业以提高掺合料质量稳定性、促进掺合料技术进步和简化混凝土生产工序的新思路。     

声波与喷雾对于飞灰颗粒团聚的影响

为了研究声波团聚的影响因素,以燃煤飞灰细颗粒作为声波团聚的实验对象,使用光学颗粒物粒径谱仪测量颗粒的粒径分布与浓度,主要研究了声波频率与喷雾对声波团聚的影响。结果表明：在声波的作用下,细颗粒浓度显著减少,且声波团聚效果对频率较为敏感;无论在高声压还是低声压级下,1400Hz的频率下能获得最佳的团聚效果;在加入喷雾后,颗粒物浓度显著减小,且随着喷雾量增大,颗粒物浓度越小;分析了喷雾增强团聚效果的机理：在加入喷雾后,细颗粒间的相对运动增强;同时喷雾颗粒增大了颗粒浓度,增大了细颗粒碰撞概率;此外,喷雾改变燃煤飞灰细颗粒的表面特性,使颗粒的表面黏性增大,有助于团聚体形成。     

Combined effects of mineral admixtures and curing conditions on the sorptivity coefficient of concrete

The effect of mineral admixture and curing condition on the sorptivity of concrete are investigated. In the present work, the maximum particle size and the grading of coarse aggregate, the cement content and water/cement ratio of the concrete are kept constant. Then, in the ordinary Portland cement (OPC) 42.5 concrete, a portion of the sand is replaced by a mineral admixture such as fly ash (FA), limestone filler, sandstone filler or silica fume (SF). This paper presents the results of both the sorptivity coefficient and the compressive strength of OPC 42.5 concretes with these mineral admixtures, and concretes with OPC 32.5, blended cement (BC) or trass cement (TC). The results obtained indicate that the sorptivity coefficient of concrete decreases as the compressive strength of concrete increases. It is also shown that the sorptivity coefficient of concrete is very sensitive to the curing condition. The effect of curing condition on the sorptivity coefficient of concrete seems to be higher in low-strength concretes.     

Effects of mineral and chemical admixtures on high-strength concrete in seawater

The effects of mineral and chemical admixtures namely fly ash, ground granulated blast furnace slag, silica fume and superplasticizers on the porosity, pore size distribution and compressive strength development of high-strength concrete in seawater curing condition exposed to tidal zone were investigated. In this study, three levels of cement replacement (0%, 30% and 70% by weight) were used. The total cementitious content used was 420 kg/m³. A water/binder ratio of 0.4 was used to produce concrete having a target compressive strength ranging between 54 and 63 MPa at the age of 28 days. At the age of 364 days, the compressive strength of the specimens produced ranged between 59 and 74 MPa. The pore size distribution of both high-strength concrete (MSS-0 and MSS-40) was significantly finer and the mean volume pore radii (MVPR) at the age of 6 months were reduced about three times compared to NPC concrete. Results of this study indicate that both concrete mixes (30% and 70%) exhibited better performance than the NPC concrete in seawater exposed to tidal zone. Hence, it is believed that both high-strength concrete produced would withstand severe seawater exposure without serious deterioration.     

Mineral admixtures in mortars effect of type, amount and fineness of fine constituents on compressive strength

This work is the third part of an overall project the aim of which is the development of general mix design rules for concrete containing different kinds of mineral admixtures (also named mineral additions or mineral constituents). It deals with the compressive strength of mortars made with up to 75% of crushed quartz, limestone filler or fly ash of different fineness. The paper presents all the experimental results as a sort of database and emphasizes the effects on strength of the nature, amount and fineness of mineral admixtures. For short hydration times (1 to 2 days), the nature of mineral admixture is not a significant parameter, as mortars containing the same amount of different kinds of admixtures having equivalent fineness present similar strengths. For long hydration times (up to 6 months), the excess strength due to fly ash pozzolanic activity is quantified by the difference between the strengths of mortars containing the same proportions of inert and pozzolanic admixtures with the same fineness. In the case of inert mineral admixtures, the increase in strength with the fineness of mineral admixtures cannot be explained by the filler effect, but can be attributed to the physical effect of heterogeneous nucleation. In the next part of this work, these results will be used for the elaboration of an empirical model leading to the quantification of both physical and chemical effects. This model presents strong similarities with the previous model based on calorimetric results.     

纳米氧化镧的制备

以氯化镧水溶液为原料，通过水解和热处理制备出纳米氧化镧粉体。研究了反应温度、反应物浓度、分散剂和煅烧温度对纳米氧化镧原始粒径、比表面积和团聚现象的影响。利用BET、TEM和XRD等技术对纳米氧化镧粉体进行表征。XRD、DSC和TG表明，氢氧化镧在。750℃下煅烧2小时，完全转化为纳米氧化镧；BET结果说明，当热处理温度超过800℃时，纳米氧化镧粒子快速增大，比表面积急剧下降。TEM显示，反应温度和反应浓度是影响纳米氧化镧的原始粒径的重要因素，反应温度升高，平均原始粒径逐渐增大：反应浓度增加，平均原始粒径下降，团聚现象加剧。通过加入聚乙二醇可有效减轻纳米氧化镧的团聚现象。     

Analysis of the spectral reflectance and color of mineral pigments affected by their particle size

The color of mineral pigments changes obviously with their particle size. However, how the particle size of these mineral pigments affects the color of the mineral pigment color block remains unclear. Based on optical principles and the physical properties of mineral pigment particles, our analysis found that changes in the particle size not only nonlinearly affect the behavior of light at the first surface of the mineral pigment color block, but also affect the interaction of light with the particles within the body of the mineral pigment color block, ultimately changing the spectral reflectance and color of the mineral pigment color block. Finally, we derived a nonlinear monotonically decreasing relationship between the particle size and the spectral reflectance. The experiment conducted in this article selected six kinds of mineral pigments as color block samples and observed the changes in the spectral reflectance and color value with the particle size. These studies are beneficial for color researchers conducting scientific research related to mineral pigments.     

A study on the effect of fine mineral powders with distinct vitreous contents on the fluidity and rheological properties of concrete

This paper presents an investigation on the effects of fine mineral powders on the fluidity and rheological properties of concrete. It was observed that the fluidity of concrete increased noticeably, and the plastic viscosity decreased, when vitreous powders were substituted partially for cement. It was found that vitreous powders have a strong dispersion effect on the fluidity and rheological properties of concrete, and this effect can be correlated with the vitreous content of the powders incorporated.     

NOVA1000e型比表面积和孔径分析仪测定高纯纳米氧化铝比表面积

主要讲述了使用NOVA1000e型比表面积和孔径分析仪测定高纯纳米氧化铝的比表面积,仪器操作方法和测试过程中样品处理条件.把NOVA1000e型比表面积和孔径分析仪与ST-03型比表面积分析仪进行性能对比.     

浅谈粉末涂料中的粒度理论及粒度仪的选择

介绍了粒度测量基础理论、基本概念以及常用的粒度仪,提出了涂料企业如何选择粒度仪的建议,并说明了粉末涂料粒度控制的重要性。     

A TEM-based method as an alternative to the BET method for measuring off-line the specific surface area of nanoaerosols

At the present time, no stabilised method exists allowing an estimation of the specific surface area for airborne nanostructured particles (nanoaerosols). Recent toxicological studies have, however, revealed biological effects linked to the surface area of these particles. Only the BET method, which can determine the specific mass surface area of a powder, constitutes a reference both in toxicology and in the materials domain. However, this technique is not applicable to nanostructured aerosols given the mass quantities of particles required (between approximately some mg to hundreds of mg taking into account the limit of quantification of existing BET instruments).To characterise the specific surface area of airborne nanostructured particles, a method based on analysing transmission electron microscopy (TEM) images is proposed. This has recourse in particular to previous work carried out in the area of nanoparticles originating from combustion (soot), and takes into account structural parameters of nanostructured particles including the number distribution of primary particles, their overlap coefficient and the fractal dimension of agglomerates and aggregates.The approach proposed in this work was applied to five commercially-available nanostructured powders of differing natures (SiO₂, ZrO₂, Al₂O₃, Fe₂O₃ and Fe₃O₄). This first involved their prior analysis by the BET method and then being placed in suspension in aerosol form using a vortex-type shaker system. The procedure to calculate the specific surface area using image analysis was then applied to the sampled aerosols and compared to the BET measurements. The experimental results obtained on the five nanostructured powders cover a range of specific surface areas from 20 to 200 m²/g, the primary particles having mean diameters varying from 7 to 47 nm. Close agreement was observed between the two approaches which, taking into account measurement uncertainties, are statistically equivalent at significance level α = 0.05.     

Porosity and specific surface area of Roman cement pastes

Mercury porosimetry, water vapour and nitrogen adsorption were used to follow the hydration of Roman cements — belite cements calcined at low temperature. Generally, unimodal distribution of pore sizes was observed, with the threshold pore width decreasing considerably with increasing curing time. An open porous structure with the threshold pore diameter between 0.2 and 0.8 μm and the specific surface area not exceeding 20 m²/g was produced at early ages when quick growth of the C–A–H phases is observed. The surface area reached up to 120 m²/g and the threshold pore width shifted to around 0.02 μm when the subsequent formation of C–S–H gel filled the larger pores. Both mercury porosimetry and water vapour adsorption were found to be capable of following the progress of hydration of the Roman cements with high reliability at least for a comparative evaluation of historic Roman cement mortars and repair materials used in restoration projects.     

电凝并技术脱除PM2.5的研究现状及发展方向

针对传统除尘器无法有效捕集PM2.5的问题,笔者论述了同极荷电颗粒在交变电场中的凝并、异极性荷电粉尘的库伦凝并、异极荷电颗粒在交变电场中的凝并、异极荷电颗粒在直流电场中的凝并、四级凝并5种电凝并技术的研究现状,并提出了电凝并技术的发展方向。5种电凝并技术中,异极荷电颗粒在交变电场中的凝并效果较好;两区式异极荷电颗粒在交变电场中的凝并效果优于三区式。低温等离子体-电凝并技术将低温等离子体-电凝并设备直接置于管道中,对粉尘预荷电;基于原有布袋除尘器开发出双踪电笼布袋除尘装置,联合脱除PM2.5。利用低温等离子体-电凝并技术开发的复合反应器结构紧凑,占地面积小,对细微粒子的除尘效率高达99%,可实现脱硫脱硝脱汞的协同脱除,是电凝并技术的发展方向。     

A study on the process for formation of spherical cement through an examination of the changes of powder properties and electrical charges of the cement and its constituent materials during surface modification

In the initial stage of surface modification treatment to form cement particles into a spherical shape, the fine cement particles below 3 μm increased and the specific surface area also increased. However, in the final stage of treatment, both the fine particles and the specific surface area decreased when compared to raw cement. These results seem to endorse a process for formation of spherical cement, namely grinding of the particles in the initial stage and then adhering and fixing the fine particles to the surfaces of larger core particles in the next stage. Clinker powder had a positive charge, whereas gypsum powder had a negative charge. The difference observed in the electrical charge proved that the attachment of gypsum particles to clinker particles was caused by the attraction of opposite charges in addition to the van der Waals interaction. Therefore, gypsum played an important role as an adhesive agent. The fluidity of clinker powder after it was treated with finely ground gypsum improved. This was because the fine gypsum particles quickly attached to the surfaces of the larger particles of clinker, and consequently, the final process for formation was accelerated.     

Dependence of SiO2> Gel Structure on Gelation Conditions and Sol Reaction Temperature as Followed by FTIR and Nitrogen Adsorption Measurements

The acid catalyzed hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in the absence of alcohol was studied using cylindrical internal reflectance Fourier transform infrared (CIR-FTIR) spectroscopy at four temperatures. Special attention was given to the low-frequency band around 940 cm^-1 and its evolution corresponding to the changing silicic acid concentration. This method compared well with other published methods for studying condensation kinetics.Three different conditions for gelation were used to determine temperature and humidity effects on resultant gels. In addition, effect of reaction temperature on gel porosity and surface area was studied. Sols that were gelled at high humidity (84–96% R.H.) and room temperature, 22–24°C, had a much higher surface area and porosity than those gelled at low humidity (5–50% R.H.) and room temperature, 22–24°C, whereas sols gelled at high humidity (79–98% R.H.) and low temperature, 7–8°C, had an intermediate surface area and porosity. Temperature of hydrolysis and condensation reactions did not have a significant effect on surface area. It is proposed that differences in surface area and porosity are mainly caused by the rate of solvent evaporation. Rapid evaporation of solvent and quick gelation of the low humidity samples results in a close-packed microporous xerogel. This is in contrast to the slow gelation and increased available time for condensation in the higher humidity samples, resulting in a more open structure.     

The effects of particle size distribution and surface area upon cement strength development

Particle size distribution, uniformity of the distribution and specific surface area (SSA) have a great influence on service properties of cement, particularly on strength. In this paper the effects of these physical parameters on strength development were studied using PC 42.5 R.In order to understand the significance of different particle size ranges in a distribution, samples having size distributions such as − 10 µm, − 20 µm, − 30 µm, − 45 µm, − 32 + 3 µm and − 20 + 5 µm were prepared from PC 42.5 R by using a laboratory scale 3rd generation separator. Additionally − 32 + 3 µm and − 20 + 5 µm fractions were added to the original PC 42.5 R in varying amounts to study SSA and uniformity effects. Same strength values were obtained for samples with a narrower size distribution but smaller SSA. Fineness is very important for strength development, particularly in the early stages of hydration.     

Effect of methyltrimethoxysilane as a synthesis component on the hydrophobicity and some physical properties of silica aerogels

The effects of adding methyltrimethoxysilane (MTMS) to the synthesis formulation on the hydrophobicity and physical properties of silica aerogels are reported. The molar ratio of the methanol (MeOH) solvent, water (H₂O), and the ammonia (NH₄OH) catalyst to tetramethoxysilane (TMOS) precursor was fixed at 1TMOS:12MeOH:4H₂O:3.6×10⁻³NH₄OH throughout the experiment and the MTMS/TMOS molar ratio M was varied from 0 to 1.55. After gelation, the alcogels were dried supercritically by high-temperature solvent extraction. The hydrophobicity of the resulting aerogels was tested by measuring the water uptake by the aerogel as a function of time, after putting them directly on the surface of water. It was found that for M<0.26 the aerogels were less hydrophobic but more transparent (>90% in the visible range), whereas for M>1.03 the aerogels were more hydrophobic but semi-transparent to opaque. Aerogels that possessed good hydrophobicity and transparency (85% in the visible range) were obtained with an M≈0.70. An increase in the MTMS content in the gels shifted the pore size distribution towards larger pore radii with a broad distribution. In order to determine the thermal stability of the hydrophobic nature of the aerogels, they were heat-treated in air in the temperature range between 25 and 350°C. It was found that below 280°C the aerogel samples showed hydrophobic properties, whereas above 280°C the hydrophobicity vanished. This is due to the disappearance of the CH₃ groups in the aerogels. The aerogels were characterized by optical transmittance, pore size distribution, BET surface area and infrared spectroscopy measurements.