Thermal interaction between limestone and silica

A thermodynamic analysis of the interaction between limestone and silica is carried out under normal pressure with the use of the TERRA program system. An equilibrium system is considered. The thermodynamic parameters are calculated with a step-by-step increase in temperature. The temperature of calcium silicate synthesis with respect to the initial mixture composition is found. At all possible ratios between limestone and silica, the products of the chemical reaction are determined. The reaction heat, synthesis temperature, enthalpy increment, and heat content are determined. It is shown that wollastonite isothermal synthesis proceeds at 550 K at a constant heat content, and rankinite isothermal synthesis proceeds at 750 K at a constant heat content as well. The reaction heat increases with rising limestone content until rankinite starts to form and then decreases to zero. The interaction between limestone and silica produces carbon dioxide gas, whose content grows simultaneously with the rising reaction heat. When the rankinite yield is maximal, the amount of carbon dioxide diminishes to zero, because free limestone forms and CO₂ is buried. On the basis of the results, the conclusion is drawn that the reaction proceeds with a latent exotherm due to latent limestone dissociation and formation of lime during the thermal interaction between limestone and silica.     

Investigation of reactions in high-alumina fly ash and lime pastes

By-product fly ash from coal combustion generally contains a high percentage of active silica and smaller amounts of alumina, although some coals can have higher alumina contents (30 to 40%). During our experimental tests on the utilization f fly ash in road and highway foundation sheets, we have found a fly ash poor in silica, having an exceptionally high alumina content. This material has shown a good reactivity towards lime paste, giving hardened mixtures with high mechanical properties.     

On determination of the toxity index in stabilized liquid combustion in a room

An analysis is performed of thermal gasdynamic conditions for experiments to determine toxity of combustion products with a fire in a room. Consideration is given to mathematical models of calculating heat and mass transfer parameters in characteristic small- and large-scale rooms. Results of numerical experiments on determining the density of carbon oxide formed in combustion of benzene and turbine oil in stabilized combustion are presented. It is shown that the coefficient of heat loss is a necessary criterion of the equality of toxity indices in a small-scale experimental setup and in an actual room.     

Thermal and catalytic degradation of polyethylene wastes in the presence of silica gel, 5A molecular sieve and activated carbon

A comparative study of thermal and catalytic degradation of polyethylene wastes has been carried out with the aim of obtaining chemical compounds with potential use in the chemical industry and the energy production. Polyethylene wastes were obtained from polyethylene bags used in supermarkets. Catalysts utilized in the study were silica gel, 5A molecular sieve and activated carbon. The pyrolysis was performed in a batch reactor at 450, 500 and 700 °C during 2h for each catalyst. The ratio catalyst/PE was 10% w/w and the solid and gaseous products were analyzed by gas chromatography and mass spectrometry. The optimum operation temperature and the influence of the three catalysts are discussed with regards to the products formed. The best temperature for degradation with silica gel and activated carbon as catalysts was 450 °C and with 5A molecular sieve was 700 °C. Degradation products of PE (solid fraction and gas fraction) are depending on temperature and catalyst used. External surface and structure of catalysts were visualized by Scanning Electron Microscopy (SEM) and the contribution on product distribution is commented. All products from different degradations could be used as feed stocks in chemical industry or in energy production based on the value of heat of combustion for solid fraction (45000 J/g), similar to the heat of combustion of commercial fuels.     

Microstructural investigation of a silica fume–cement–lime mortar

Several additions, minerals and organic, are used in mortars, such as pozzolanic materials, cementicious materials and polymers. Literature about the use of additions in masonry mortars (cement/lime/sand mixes) is scarce; usually, studies are about concrete mortars. The purpose of this work is to study the microstructural effects of the substitution of 10% of Portland cement by silica fume in a 1:1:6 (cement/lime/sand mix proportion by volume) masonry mortar. Scanning electron microscopy with energy dispersive X-rays analysis (SEM/EDX) shows that, with silica fume, the C–S–H formed is type III at early ages and that type III and type I coexist at later ages. Silica fume lowers the total porosity and increases compressive strength only at later age and, as expected, the pore structure of mortar with silica fume is found to be finer than of non-silica fume mortar.     

Preparation and characterization of hollow silica nanocomposite functionalized with UV absorbable molybdenum cluster

The nanoparticle-based material technology has recently opened a new heat shielding material generation for window applications such as aerogel, vacuum insulation panel or nanospace materials. Aiming to prepare a nanospace-based heat insulation material functionalized with an ultraviolet (UV) absorbent, the Mo₆ cluster-deposited hollow silica nanoparticles (HSNs) were prepared by the vacuum impregnation process (VIP). The pore channels of the hollow silica wall filled with the Cs₂[Mo₆Iⁱ₈(OCOC₂F₅)^a₆] octahedral cluster (CMIF) were confirmed by an HR-TEM coupled EDX device, ICP-OES and BET analysis. The retention of the octahedral structure or the typical optical property of the Mo₆ cluster in the pores of the HSNs was demonstrated by ultraviolet (UV) light absorption and photoluminescence spectroscopes even though the powders were heated to 200 °C. The multi-functional CMIF@HSNs nanocomposite could adsorb the UV rays under 400 nm and scatter the NIR light through the pores of the silica wall in order to reduce the heat passing a window. For this purpose, the film preparation based on the CMIF@HSNs nanocomposite was performed by dip coating in the commercially available top coat suspension (TCS) on soda lime glass. Excellent mechanical and optical properties of the CMIF@HSNs-based thin film were visibly obtained with a relative transmittance. This study suggests a potential insulation material prepared by a high efficiency and simple method for reducing the air temperature in buildings.     

Mathematical modeling of the heat treatment and combustion of a coal particle. I. Heating stage

Mathematical modeling of the heat treatment and subsequent combustion of a coal particle as a multistage process has been carried out. The basic parameters of the following sequential stages of this process have been calculated by approximate-analytic dependences: heating of particles; their drying; yield of volatiles, their ignition and combustion; and burning out of the coke residues. A detailed parametric analysis of the influence of the physical and regime characteristics of the process on the burning mechanism of a coal particle (with the example of coal from the Shivee-Ovoo deposit in Mongolia) has been performed. The conditions for effective burning of a single coal particle as the main element of the whole process in the furnace have been determined.     

Chemical thermodynamics of the vapor-oxygen gasification of graphite

A thermodynamic analysis of the vapor-oxygen gasification and combustion of graphite with a variation of the oxidizer excess α has been performed. Chemical reactions proceeding in the process of gasification and combustion, as well as components of flammable gases, which are the combustion products, have been determined. The channels of the distributing of the energy of exothermal and endothermal processes have been revealed. The energy of exothermal reactions compensates the endothermal effect of the reaction and increases the physical heat of the system. Expenditures on the endothermal reaction where flammable gases are produced are not irretrievable and transverse to the calorific power of the flammable gases. The effect of the oxidizer concentration on the adiabatic temperature at partial combustion of graphite has been analyzed. The thermal efficiency has been found as the ratio of the total thermal energy in the combustion of flammable gases and their physical heat to the spent energy, which is determined by the calorific power of graphite. The thermal efficiency is about 100%.     

生物质燃料的燃烧过程及其焚烧灰特性研究

采用热重-差热分析法分析了秸秆、木屑生物质燃料的直接燃烧过程,研究了其焚烧灰的化学成分、晶相结构及其形貌等特性。结果表明,秸秆、木屑生物质燃料的挥发分含量高、灰分低、着火温度低、易燃烧、放热量高,其燃烧过程可分为水分蒸发、挥发分析出燃烧和固定碳燃烧3个阶段;秸秆焚烧灰中钾、钙、硫及氯含量高,木屑焚烧灰中碱金属含量低,硅、钙含量高;生物质燃料焚烧灰中的碱金属氧化物含量高导致其熔点较低、易熔融、结渣。     

Experimental Investigation on the Specific Heat of Carbonized Phenolic Resin-Based Ablative Materials

As typical phenolic resin-based ablative materials, the high silica/phenolic and carbon/phenolic composites are widely used in aerospace field. The specific heat of the carbonized ablators after ablation is an important thermophysical parameter in the process of heat transfer, but it is rarely reported. In this investigation, the carbonized samples of the high silica/phenolic and carbon/phenolic were obtained through carbonization experiments, and the specific heat of the carbonized samples was determined by a 3D DSC from 150 \(^{\circ }\hbox {C}\) to 970 \(^{\circ }\hbox {C}\). Structural and compositional characterizations were performed to determine the mass fractions of the fiber and the carbonized product of phenolic which are the two constituents of the carbonized samples, while the specific heat of each constituent was also measured by 3D DSC. The masses of the carbonized samples were reduced when heated to a high temperature in the specific heat measurements, due to the thermal degradation of the carbonized product of phenolic resin in the carbonized samples. The raw experimental specific heat of the two carbonized samples and the carbonized product of phenolic resin was modified according to the quality changes of the carbonized samples presented by TGA results. Based on the mass fraction and the specific heat of each constituent, a weighted average method was adopted to obtain the calculated results of the carbonized samples. Due to the unconsolidated property of the fiber samples which impacts the reliability of the DSC measurement, there is a certain deviation between the experimental and calculated results of the carbonized samples. Considering the similarity of composition and structure, the data of quartz glass and graphite were used to substitute the specific heat of the high silica fiber and carbon fiber, respectively, resulting in better agreements with the experimental ones. Furthermore, the accurate specific heat of the high silica fiber and carbon fiber bundles was obtained by inversion, enabling the prediction of the specific heat of the carbonized ablators with different constituent mass fractions by means of the weighted average method in engineering.     

Mathematical simulation of the front processes of combustion of condensed systems in view of the velocity of propagation of heat

It is suggested to use the hyperbolic heat equation for mathematical simulation of the front processes of combustion of energy-intensive condensed systems (CS). The correlation between the velocity of propagation of thermal wave with the velocity of front motion, the thermal effect of the reaction of thermal decomposition, and the value of heat flux delivered to the surface is analytically determined. Numerical solutions of hyperbolic heat equation are obtained for unsteady-state mode of ignition of energy-intensive materials. The agreement between calculated dependences and experimental data on the combustion of energy-intensive compounds is considered.     

基于响应面法的石灰-矿渣/生土复合材料热湿综合性能

采用石灰和矿渣作为改性材料制备石灰-矿渣/生土复合材料,利用响应面法研究石灰掺量、矿渣掺量和含水率对石灰-矿渣/生土复合材料热湿综合性能的影响,对石灰-矿渣/生土复合材料的制备工艺进行优化。结果表明,石灰掺量、矿渣掺量和含水率均对热湿综合性能产生影响;通过回归分析得到石灰-矿渣/生土复合材料的制备优化方案是石灰掺量(石灰与复合材料的质量比)为10.19%、矿渣掺量(矿渣与复合材料的质量比)为4.02%、含水率(水量与复合材料的质量比)为9.00%,且优化石灰-矿渣/生土复合材料平均平衡含湿量为12.725%,导热系数为0.798 W/(m·K),具有良好的热湿综合性能;通过结构分析可知,在碱性激发和微集料作用下,优化石灰-矿渣/生土复合材料内部呈现出完整、密实的结构体系特点,兼顾材料的力学、耐久性和热湿性能。     

Coloration and structure behavior after silver and copper nanoparticles formation in soda lime glass

In this work, an ion exchange non‐conventional process commonly called ancient painting process without using molten salts is used as a method for glass coloring. In this process of coloration, a mixture of metallic particles with kaolin and arabic adhesive is applied on the soda lime glass surface. Afterwards, the painted glass is submitted to the heat treatment to obtain the color. A comparative study is carried out in order to investigate the diffusion of metallic nanoparticles (silver and copper) in soda lime glasses depending on several parameters as the concentration and composition of stain spread on glass, and the heat treatment temperature. Characterization of the composition and structure of the painted glasses is performed by UV‐visible spectroscopy. In addition, nanoindentation and scanning electron microscopy (SEM) with energy dispersive X‐ray analysis (EDS) techniques are used to determine the penetration of metallic nanoparticles into glass. The obtained result shows that the coloration of painted glass differs and depends on the concentration and the kind of the mixture of the paw. Moreover, it was found that the effect of the heat treatment temperature is primordial on the formation and diffusion of metallic nanoparticles.     

Effect of Heat Transfer on the First and Second Law Efficiency Analysis and Optimization of an Air-standard Atkinson Cycle

In this paper, the first and second-law analysis for the thermodynamic air-standard Atkinson cycle with an account for heat transfer is performed using finite-time thermodynamics. In order to have more accurate evaluations, the effects of thermodynamic and design key parameters on the performance characteristics of Atkinson cycle are shown. Further, artificial neural network and imperialist competition algorithm are employed to predict and optimize the net work output value versus the minimum cycle temperature and also the compression ratio. The results obtained show that the heat loss is an effective factor of the performance of the cycle and it should be considered in the analysis and comparison of practical internal combustion engines.     

CCB-based encapsulation of pyrite for remediation of acid mine drainage

Acid mine drainage (AMD) from abandoned coal mines continues to be one of the most significant environmental problems. Remediation of AMD requires an addition of lime source to decrease the acidity, and grouting the entire mine and encapsulating the pyrite by calcium-rich additives is often employed. Utilization of alkaline coal combustion by-products (CCBs) has gained acceptance in such remediation applications because of their cost-effectiveness. A study was conducted to investigate the effectiveness of CCBs to abate acid mine drainage by encapsulation of pyrite. Geomechanical, hydraulic, and environmental tests were performed on grouts prepared with various ratios of CCBs as well as an alternative free lime source, lime kiln dust (LKD). The results indicated that the mechanical properties of grouts were dependent on their free lime contents. Hydraulic conductivities of pyrite-grout columns were relatively high due to the coating of the pyrite rock with the grout rather than the filling of all of the void spaces, as commonly experienced in field applications. The leaching tests indicated that the presence of high amounts of lime in a grout is not solely sufficient to improve the quality of AMD, since the rate of dissolution of a high lime content grout may be slow due to its rapid hardening. Therefore, it is recommended that grouts be selected with consideration of their hardening capacities, as well as the percentage of lime content present in the mixture.     

Alkali activation of reactive silicas in cements: in situ 29Si MAS NMR studies of the kinetics of silicate polymerization

In the highly alkaline environment of the cement paste of a concrete, a source of silica can potentially react in two ways. In the pozzolanic reaction, it can combine with free lime to generate additional calcium silicate hydrate binding phase. Alternatively, reaction with alkali to form a gel can occur; this gel may swell and degrade the concrete. ²⁹Si magic angle spinning (MAS) and cross-polarization (CP) MAS nuclear magnetic resonance (NMR) studies have been performed to determine the silicate connectivity in some model cement systems; ²⁹Si enrichment was utilized to enable a series of spectra to be acquired in situ from a single sample.The hydrate from pozzolanic reaction of lime with silica was similar to the hydrate formed around silica in blended pozzolanic cements, with a relatively high crystallinity and long silicate chains. In the absence of lime, silica reacted with an alkaline solution to produce a gel having a high degree of cross linking, and a range of silicate mobilities. Tricalcium silicate hydration was found to be accelerated significantly by high levels of alkali (KOH) in solution; the hydrate formed had shorter silicate chains and was more crystalline than that produced by reaction in pure water. Hydration in alkali solution of a model blended cement, comprising a mixture of tricalcium silicate and silica, gave rise to two products, a long chain calcium silicate hydrate (C-S-H) and an alkali silicate of low rigidity. The alkali silicate phase gradually polymerized; at later ages it underwent a phase change, although no crystalline phase appeared to be formed. Silicate exchange took place between the C-S-H and the alkali silicate phase at a slow rate.     

Gamma-ray shielding properties of zinc oxide soda lime silica glasses

In the present work, the gamma ray shielding properties of zinc oxide soda lime silica, (ZnO)_x(SLS)_1?x glasses with 0 ≥ x ≥ 50 wt% have been investigated. By using WinXCom computer software, the mass attenuation coefficient (µ/ρ) and half value layer (HVL) for total photon interaction in the energy range of 1 keV–100 GeV were calculated. Furthermore and by Geometric Progression method exposure buildup factor values were calculated for incident photon energy 0.015–15 MeV up to penetration depths of 40 mfp (mean free path). The addition of zinc oxide (ZnO) into soda lime silica (SLS) glass resulted in an increase the mass attenuation coefficient and decreases both the half value layer and exposure buildup factor. The obtained results of the selected glass series have been compared, in terms of mass attenuation coefficient, half value layer and exposure buildup factor with some common shielding materials. The shielding effectiveness of the selected glasses is found comparable to that of common ones; which indicates that the SLS glasses with suitable ZnO content may be developed as gamma ray shielding materials.     

高活性铝钆合金的制备及热氧化特性研究

为降低纯铝粉燃料的点火温度,提升体积燃烧热,改善热氧化特性,采用真空感应熔炼法制备了铝钆合金Al-10Gd和Al-2Gd,并破碎成粉制得样品。SEM、EDS图像显示:样品呈片状,元素分布均匀。结合微机全自动量热仪与真密度测试仪对样品的燃烧热进行测量与计算。结果表明:铝钆合金的质量燃烧热与纯铝粉相当,体积燃烧热要高于纯铝粉,在装药体积有限的情况下可以释放更多的能量。采用同步热分析仪研究了样品的热氧化特性。结果表明:铝钆合金的熔点和初始氧化温度均低于纯铝粉,反应放热至少持续到1 550.0 ℃以上,增重约60.42%。金属钆会促进铝粉的热氧化,从而降低燃料的着火点,使燃料迅速升温放热。     

Determination of CaCO<Subscript>3</Subscript> and SiO<Subscript>2</Subscript> content in the binders of historic lime mortars

The binders of historic mortars composed of small grain sized silica (SiO₂) and carbonated lime (CaCO₃) are considered as the main part that give hydraulic character and high strength to the mortar. In this study, FTIR, SEM–EDS, LIBS and XRD spectroscopy were used to find out the weight ratios of CaCO₃ to SiO₂ in the binders of historic lime mortars. For this purpose, a series of pure calcium carbonate and silica mixture were prepared in ten combinations in varying ratios from 0.5 to 5. Calibration curve was prepared for each analysis by plotting the peak area or intensity ratios of CaCO₃ to SiO₂ versus the weight ratios of CaCO₃ to SiO₂. A good linear correlation coefficient was obtained for each analysis respectively. The analyses were then tested on the binder of the Roman mortar samples. The results indicated that FTIR, SEM–EDS and LIBS spectroscopy are convenient tools to determine the weight ratios of CaCO₃ to SiO₂ in the binders of mortars. But XRD spectroscopy is not convenient for quantitative analysis of binders due to the presence of varied amounts of amorphous or poor crystalline silica in their compositions.     

内燃机燃烧测试分析系统的设计与开发

开发一套基于PC机的内燃机燃烧测试分析系统,并对气缸压力的采集,数据的匀化、光顺处理,动态上止点位置的确定等做介绍。利用测量的气缸压力曲线和能量守恒原理,在LabVIEW软件平台上编写出内燃机燃烧放热率计算程序,研究主要经验参数对放热率及缸内平均温度的影响。结果表明:采用Woschni传热公式计算的放热率曲线值高于采用Eichelberg传热公式和Sitkei传热公式计算的放热率曲线值。扫气系数φs的变化对气缸内平均温度有显著影响,φs=0.99时的缸内平均温度明显高于φs=0.95时的缸内平均温度,两者最高温度相差81.4 K。