Diffusion and reaction mechanism of limestone and quartz in fluxed iron ore pellet roasting process

The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron ore powder and the mineralization mechanism of fluxed iron ore pellet in the roasting process were investigated through diffusion couple experiments.Scanning electron microscopy with energy dispersive spectroscopy was used to study the elements’diffusion and phase transformation during the roasting process.The results indicated that limestone decomposed into calcium oxide,and magnetite was oxidized to hematite at the early stage of preheating.With the increase in roasting temperature,the diffusion rate of Fe and Ca was obviously accelerated,while the diffusion rate of Si was relatively slow.The order of magnitude of interdiffusion coefficient of Fe_(2)O_(3)-CaO diffusion couple was 10^(−10) m^(2)·s^(−1) at a roasting temperature of 1200℃for 9 h.Ca_(2)Fe_(2)O_(5) was the initial product in the Fe_(2)O_(3)-CaO-SiO_(2) diffusion interface,and then Ca_(2)Fe_(2)O_(5) continued to react with Fe_(2)O_(3) to form CaFe_(2)O_(4).With the expansion of the diffusion region,the sillico-ferrite of calcium liquid phase was produced due to the melting of SiO_(2) into CaFe_(2)O_(4),which can strengthen the consolidation of fluxed pellets.Furthermore,andradite would be formed around a small part of quartz particles,which is also conducive to the consolidation of fluxed pellets.In addition,the principle diagram of limestone and quartz diffusion reaction in the process of fluxed pellet roasting was discussed.

A machine learning-based strategy for predicting the mechanical strength of coral reef limestone using X-ray computed tomography

Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL samples were utilized for training the support vector machine(SVM)-,random forest(RF)-,and back propagation neural network(BPNN)-based models,respectively.Simultaneously,the machine learning model was embedded into genetic algorithm(GA)for parameter optimization to effectively predict uniaxial compressive strength(UCS)of CRL.Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL.The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data.Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density,pore structure,and porosity of CRL are strongly correlated to UCS.However,the P-wave velocity is almost uncorrelated to the UCS,which is significantly distinct from the law for homogenous geomaterials.In addition,the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone(CFL)and coral boulder limestone(CBL),realizing the quantitative characterization of the heterogeneity and anisotropy of pore.The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.

The Influence of Limestone Powder and Metakaolin Co-Blending on the Hydration Process and Mechanical Properties of Q-Phase Cement

A ternary system comprising Ca_(20)Al_(26)Mg_(3)Si_(3)O_(68)(Q-phase),limestone,and metakaolin is proposed,and its hydration behavior,hydration product phases,microstructure,and mechanical properties are investigated and compared with pure Q-phase cement.The results indicate that the ternary system exhibits exceptional and sustained compressive strength even under a 40℃environment,significantly outperforming pure Q-phase.The mechanism lies in that metakaolin effectively inhibits the transformation of metastable phase.Meanwhile,the interactions among Q-phase,limestone,and metakaolin further enhance the cementitious performance.The ternary system effectively addresses potential issues of strength loss in Q-phase cement application,and as a low-carbon cementitious material system,it holds promising potential applications.

Graph theoretical analysis of limestone fracture network damage patterns based on uniaxial compression test

The topological attributes of fracture networks in limestone,subject to intense hydrodynamics and intricate geological discontinuities,substantially influence the mechanical and hydraulic characteristics of the rock mass.The dynamical evolution of fracture networks under stress is crucial for unveiling the interaction patterns among fractures.However,existing models are undirected graphs focused on stationary topology,which need optimization to depict fractures'dynamic development and rupture process.To compensate for the time and destruction terms,we propose the damage network model,which defines the physical interpretation of fractures through the ternary motif.We focus primarily on the evolution of node types,topological attributes,and motifs of the fracture network in limestone under uniaxial stress.Observations expose the varying behavior of the nodes'self-dynamics and neighbors'adjacent dynamics in the fracture network.This approach elucidates the impact of micro-crack behaviors on large brittle shear fractures from a topological perspective and further subdivides the progressive failure stage into four distinct phases(isolated crack growth phase,crack splay phase,damage coalescence phase,and mechanical failure phase)based on the significance profile of the motif.Regression analysis reveals a positive linear and negative power correlation between fracture network density and branch number to the rock damage resistance,respectively.The damage network model introduces a novel methodology for depicting the interaction of two-dimensional(2D)projected fractures,considering the dynamic spatiotemporal development characteristics and fracture geometric variation.It helps dynamically characterize properties such as connectivity,permeability,and damage factors while comprehensively assessing damage in rock mass fracture networks.

Water-induced physicochemical and pore changes in limestone for surrounding rock across pressure aquifers

Osmotic water alters the physicochemical properties and internal structures of limestone.This issue is particularly critical in tunnel construction across mountainous regions with aquifers,where pressurized groundwater can destabilize the limestone-based surrounding rock.Thus,systematic research into the physicochemical properties and pore structure changes in the limestone under pressurized water is essential.Additionally,it is essential to develop an interpretable mathematical model to accurately depict how pressurized osmotic water weakens limestone.In this research,a specialized device was designed to simulate the process of osmotic laminar flow within limestone.Then,four main tests were conducted:mass loss,acoustic emission(AE),mercury intrusion porosimetry(MIP),and fluorescence analysis.Experimental results gained from tests led to the development of a“Particle-pore throat-water film”model.Proposed model explains water-induced physicochemical and pore changes in limestone under osmotic pressure and reveals evolutionary mechanisms as pressure increases.Based on experimental results and model,we found that osmotic pressure not only alters limestone composition but also affects pore throats larger than 0.1μm.Furthermore,osmotic pressure expands pore throats,enhancing pore structure uniformity,interconnectivity,and permeability.These effects are observed at a threshold of 7.5 MPa,where cohesive forces within the mineral lattice are surpassed,leading to the breakdown of erosion-resistant layer and a significant increase in hydrochemical erosion.

Effect of diagenetic variation on the static and dynamic mechanical behavior of coral reef limestone

Coral reef limestone at different depositional depths and facies differ remarkably on the textural and mineralogical characteristics,owing to the complex sedimentary diagenesis.To explore the effects of pore structure and mineral composition associated with diagenetic variation on the mechanical behavior of reef limestone,a series of quasi-static and dynamic compression tests along with microscopic examinations were performed on the reef limestone at shallow and deep burial depths.It is revealed that the shallow reef limestone(SRL)is classified as a porous aragonite-type carbonate rock with high porosity(55.3±3.2)%and pore connectivity.In comparison,the deep reef limestone(DRL)is mainly composed of dense calcite-type calcium carbonate with low porosity(4.9±1.6)%and pore connectivity.The DRL strengthened and stiffened by the tight grain framework consistently displays much higher values of the dynamic compressive strength,elastic modulus,brittleness index,and specific energy absorption than those of the SRL.The gap between two types of limestone further increases with an increase in strain rate.It appears that the failure pattern of SRL is dominated by the inherent defects like weak bonding interfaces and growth lines,revealed by the intricate fracturing network and mixed failure.Likewise,although the preexisting megapores in DRL may affect the crack propagation on pore tips to a certain distance,it hardly alters the axial splitting failure of DRL under impacts.The stress wave propagation and attenuation in SRL is primarily controlled by the reflection and diffusion caused by plenty mesopores,as well as an energy dissipation in layer-wise pore collapse and adjacent grain crushing,while the stress wave in DRL is highly hinged on the insulation and diffraction induced by the isolated megapores.This process is accompanied by the energy dissipation behavior of inelastic deformation resulted from the pore-emanated microcracking.

Experimental Study on the Chloride Ion Concentration of Cement Pastes Prepared with Limestone Powder

To investigate the impact of limestone powder on the chloride ion concentration coefficient of cement pastes,various techniques such as scanning electron microscopy(SEM),X-ray diffraction(XRD),thermogravimetric analysis(TGA),and mercury-porosimetry(MIP)were employed in this paper.The findings demonstrate that the creation of Friedel's salt is inversely associated with the addition of limestone powder,that is,Friedel's salt production is lessened by adding more limestone powder,however,the coefficient of chloride ion concentration initially decreased and then increased again,as does the porosity,and most likely the pore size as well.The specific surface area of limestone powder has increased,and the content of Friedel’s salt increased first and then decreased.However,the shifting trend of Friedel's salt and chloride ion concentration coefficient is in direct opposition,and the pore structure was therefore significantly enhanced.The results of this study offer robust theoretical backing for the inclusion of limestone powder in concrete and provide a positive assessment of its potential applications.

Dominance of rock exposure and soil depth in leaf trait networks outweighs soil quality in karst limestone and dolomite habitats

Leaf trait networks(LTNs)visualize the intricate linkages reflecting plant trait-functional coordination.Typical karst vegetation,developed from lithological dolomite and limestone,generally exhibits differential communities,possibly due to habitat rock exposure,soil depth,and soil physicochemical properties variations,leading to a shift from plant trait variation to functional linkages.However,how soil and habitat quality affect the differentiation of leaf trait networks remains unclear.LTNs were constructed for typical dolomite and limestone habitats by analyzing twenty-one woody plant leaf traits across fifty-six forest subplots in karst mountains.The differences between dolomite and limestone LTNs were compared using network parameters.The network association of soil and habitat quality was analyzed using redundancy analysis(RDA),Mantle's test,and a random forest model.The limestone LTN exhibited significantly higher edge density with lower diameter and average path length when compared to the dolomite LTN.It indicates LTN differentiation,with the limestone network displaying a more compact architecture and higher connectivity than the dolomite network.The specific leaf phosphorus and leaf nitrogen contents of dolomite LTN,as well as the leaf mass and leaf carbon contents of limestone LTN,significantly contributed to network degree and closeness,serving as crucial node traits regulating LTN connectedness.Additionally,both habitat LTNs significantly correlated with soil nitrogen and phosphorus,stoichiometric ratios,pH,and organic carbon,as well as soil depth and rock exposure rates,with soil depth and rock exposure showing greater relative importance.Soil depth and rock exposure dominate trait network differentiation,with the limestone habitat exhibiting a more compact network architecture than the dolomite habitat.

对大规模PKI中CRL分发机制的分析和比较

CRL是PKI中处理证书撤销的最常用方法。通过分析X.509v1CRL存在的问题，提出了在大规模PKI中评价CRL分发机制的5个准则。一种好的分发机制应该尽可能减小信任方所需下载的CRL大小，降低CRL库的峰值负荷和/或平均负荷，减轻CRL的时间碎片问题，同时可以根据信任方的不同需求提供不同的服务，可以动态更新CRL的分割策略。如果还可以不对原客户端程序做很大改动，甚至不需要改动，那就更好了。另外利用这些评价准则，对当前主要的几种CRL分发机制的改进方法，包括CRL分发点、Delta－CRL、重叠发布CRL、最新撤销信息指针和重定向指针，详细地进行了分析和比较。

人工合成CRL(褶皱假丝酵母脂肪酶)基因

通过序列设计、合成策略设计等方法 ,由CRL中最重要的同工酶LIP1的成熟多肽序列 ,生成适合在毕赤酵母中表达的基因序列sculipⅠ。通过链延伸反应及PCR反应将DNA单链人工合成为一段长为 16 35bp的DNA双链 ;并将其克隆入质粒pBluescriptⅡSK ( +)。PCR鉴定及测序结果表明sculipⅠ得到了正确的合成与克隆。还就若干长片段基因人工合成应该注意的问题进行讨论。

CRL分段-过量发布综合模型研究

提出了一种应用证书撤消列表CRL(CertificaterevocationList)发布公钥基础设施PKI(Publickeyinfrastruc ture)证书状态信息新模型 :分段 过量发布综合模型 ,该模型采用先将CRL分段 ,然后各段独立过量发布的方式来实现 .通过分析表明 ,该方式既可以减少CRL的长度 ,使存储库以更快的速度提供请求服务 ,又可以降低峰值请求率、峰值带宽和平均负荷 ,减少时间碎片 ,满足大规模PKI对证书撤消的要求 .

基于CRL的证书状态信息发布机制的研究

随着数字证书不断的被接受和使用,人们从中获得了更大的动力寻找各种方法来撤销已停止使用的数字证书,并及时通知终端用户,避免他们使用已被撤销的证书。证书撤销的问题在广域网的PKI产品开发中愈加显得关键。文中阐述了证书撤销的需求与重要性,分析了目前被采用的各种基于CRL的证书状态信息发布机制,并着重讨论了MYPKI中DeltaCRL的实现。

CRL增量-过量发布综合模型研究

针对当前PKI应用规模的变化,提出了一种新模型:增量-过量发布综合模型。该模型采用将Delta-CRLs的Base CRL过量发布来实现。通过比较表明,该方式既可以减小信任方下载的CRL大小,改善了响应时间,减少时间碎片;又可以降低对Base CRL峰值请求率,从而降低对存储库的峰值带宽和平均负荷。文中同时指出,增量-过量发布综合模型优于传统模型和增量模型,但其发布性能依赖于PKI系统的证书有效期、证书吊销率、Delta CRL的颁发周期和时间跨度。Delta CRL的颁发周期越长,时间跨度越大,证书吊销率越高,证书有效期越短,过量发布Base CRL所带来的性能优化就越小。因此,增量-过量模型适合于在Delta CRL的颁发周期和时间跨度较短、证书吊销率不高、证书有效期较长的大型PKI系统中。

基于增量CRL证书撤销机制的改进

文章提出了改进的增量CRL机制,在Delta-CRL的发布周期内,CA发布Base-CRL和Delta-CRL,用户除初始化外,其他时刻只下载Delta-CRL即可,可在客户端重构完整的CRL。与传统增量CRL相比,能够有效减少CRL的下载尺寸,降低通信载荷,提供更为及时的证书撤销信息,而不会增加平均请求率。

Study on the Characteristics of Main Vegetation Communities in the Limestone Region of Taihang Mountain

[Objective] The aim was to study the characteristics of main vegetation communities in the limestone region of Taihang Mountain,so as to lay foundation for the further improvement of site conditions and the scientific breeding of vegetation used to restore the mountain field in limestone region.[Method] Based on the investigation of various vegetation communities in controlled test area,forbidden region and barren hillsides in Daqing Mountain basin,Beishui Valley,Mancheng County,Hebei Province,the difference among controlled region,forbidden region and barren hillsides could be found through data analysis and composite score,and the modes of vegetation communities in controlled region and forbidden region were compared to select predominant species of arbor,shrub and grass in limestone region.[Result] Under the similar site conditions,nutrient content and physical properties of soil in controlled region and forbidden region were superior to those of barren hillsides,and persimmon had high nutrient content and better physical properties compared with oriental arborvitae in controlled region;soil water maintenance and litter characters in controlled region and forbidden region improved more obviously than that of barren hillsides,and shrubbery in forbidden region was the most excellent,arborvitae and persimmon in controlled region the second;the biomass and the coverage rate of vegetation communities in controlled region and forbidden region were higher than those of barren hillsides,and those of shrubbery in forbidden region were better than tussock in closing hill,while persimmon was better than arborvitae in controlled region.The predominant species of arbor,shrub and herbage were obtained through composite score.[Conclusion] From the aspects of soil nutrient,physical properties,soil water maintenance,litter characters,vegetation biomass,canopy density and coverage,controlled region and forbidden region were superior to barren hillsides,and the selection of predominant species of arbor,shrub and herbage considered both ecological and economic benefits.

一种在线CRL发布策略的研究

本文首先对传统CRL发布机制进行分析,提出了CRL分散发布策略,实现了对CRL数据库的均衡访问;通过分析OC-SP协议,指出了它的优势和不足;结合OCSP的优势和CRL分散发布策略,提出了在线CRL发布策略。在线CRL发布策略既可以实时地查询指定证书的状态,又可以实时地下载CRL,提高了PKI的运行效率。这为建立科学合理的CRL提供了重要的依据和方法。

认证废除清单(CRL)的分发

目前电子商务日益成为商业活动的主流 ,而安全作为电子商务的基础 ,也日益成为人们关注和研究的重点。本文论述电子商务中涉及的安全问题及已有的解决方案 ,指出认证过程的重要性 。

基于Over-Issued增量CRL发布机制的研究

目前关于公钥基础设施(public key infrastructure)中证书撤销问题的主要解决方案是使用X.509证书撤销列表(CRL)来定期发布证书状态信息;现有的发布机制主要针对提高处理时间,而对存储库性能的优化仍然存在一些问题———CRL存储库峰值负荷过大;通过对增量CRL和Over-Issued CRL模型的分析,给出了一种基于Over-Issued增量CRL机制的证书状态信息发布方法;它结合了上述两种模型的优点,通过改变Over-Issued CRL发布的时间间隔和增量CRL发布窗口大小,有效降低了存储库峰值负荷。

随机CRL证书撤销机制研究

提出了一种随机CRL(corit certificate revocation list)证书撤销机制,能够在PKI环境下有效降低系统的CRL峰值请求率,均衡系统负载,而不会增加系统的平均请求率.

基于Over-Issued CRL机制证书状态信息分发方法研究

商用 CA或 PKI系统中主要使用定期颁布证书撤消列表 (CRL )来分发证书状态信息 ,但现有方法主要侧重于对 CRL的时间和空间特性改进 ,而对存储库性能的优化 ,尤其是如何有效降低存储库峰值负荷方面仍有一些未解决的问题 .本文通过对现有方法在存储库性能改进不力的分析 ,提出一个新的基于 Over- Issued CRL机制的证书状态信息分发方法 .它通过改变 Over- Issue发放的时间间隔 ,使得 CRL请求率大幅降低并迅速达到稳态 。