Compositional changes in lime-based mortars exposed to different environments

Specimens of aerial and hydraulic lime-based mortars to be used in restoration works were prepared, hardened and subjected to different environments to study their compositional changes during setting, hardening and exposure to environment. Outside exposure, weathering cycles in a climatic chamber, SO₂-rich environment and indoor exposure (as control group) were selected to expose the mortars. XRD, FT-IR and TG-DTA analyses were performed at 7, 14, 21 and 28 days to determine the chemical and mineralogical composition, as well as the formation of the degradation products. Outside and SO₂-chamber exposures and increasing the relative humidity allowed faster carbonation (enhancing CO_2(g) dissolution) and hydration of hydraulic compounds. In SO₂-chamber, sulfate attack appears as a surface phenomenon, giving: gypsum in aerial specimens and gypsum and syngenite in hydraulic specimens.     

In situ neutron powder diffraction investigation of the hydration of tricalcium aluminate in the presence of gypsum

The hydration of a 1:3 molar ratio of tricalcium aluminate, Ca₃Al₂O₆, to gypsum, CaSO₄·2D₂O, was investigated at temperatures of 25, 50, and 80 °C using time-of-flight powder neutron diffraction combined with multiphase Rietveld structural refinement. It was shown that ettringite, Ca₆[Al(OD)₆]₂(SO₄)₃·∼26D₂O, was the first and only hydration product of the system, in contrast to a prior investigation which suggested the occurrence of a precursor phase prior to the formation of ettringite. Kinetics data showed that the hydration reaction is very sensitive to temperature: hydration at 25 °C was characterized by a single kinetic regime while hydration at higher temperatures consisted of two distinct kinetic regimes. The presence of two kinetic regimes was attributed to a change in either the dimensionality of the growth process or a change in the rate controlling mechanism in the hydration reaction.     

Modelling of calcium sulphate solubility in concentrated multi-component sulphate solutions

The chemistry of several calcium sulphate systems was successfully modelled in multi-component acid-containing sulphate solutions using the mixed solvent electrolyte (MSE) model for calculating the mean activity coefficients of the electrolyte species. The modelling involved the fitting of binary mean activity, heat capacity and solubility data, as well as ternary solubility data. The developed model was shown to accurately predict the solubility of calcium sulphate from 25 to 95 °C in simulated zinc sulphate processing solutions containing MgSO₄, MnSO₄, Fe₂(SO₄)₃, Na₂SO₄, (NH₄)₂SO₄ and H₂SO₄. The addition of H₂SO₄ results in a significant increase in the calcium sulphate solubility compared to that in water. By increasing the acid concentration, gypsum, which is a metastable phase above 40 °C, dehydrates to anhydrite, and the conversion results in a decrease in the solubility of calcium sulphate. In ZnSO₄–H₂SO₄ solutions, it was found that increasing MgSO₄, Na₂SO₄, Fe₂(SO₄)₃ and (NH₄)₂SO₄ concentrations do not have a pronounced effect on the solubility of calcium sulphate. From a practical perspective, the model is valuable tool for assessing calcium sulphate solubilities over abroad temperature range and for dilute to concentrated multi-component solutions.     

聚羧酸类超塑化剂分子结构对石膏分散性能的影响

研究了甲基丙烯酸-甲氧基聚乙二醇甲基丙烯酸酯(MAA-MPEGMA)、甲基丙烯酸-烯丙基聚乙二醇醚(MAA-APEG)、丙烯酸-烯丙基聚乙二醇醚(AA-APEG)三类梳形聚羧酸类接枝共聚物以及丙烯酸均聚物(PAA)对石膏粉体分散性能和凝结时间的影响.聚合物侧链长度越短、分子量越小、电荷密度越高对石膏的分散性能越好,同时...     

Retardation calculation for achromatic and apochromatic quarter and half wave plates of gypsum based birefringent crystal

This paper presents retardation calculations for achromatic and apochromatic half and quarter wave retarders of gypsum based birefringent crystal. The calculations indicate that an achromatic wave plates can be obtained by combining gypsum crystal with KDP, ADP, MgF₂, sapphire and calcite birefringent crystals. The residual variation percentages of retardations as a function of wavelength for gypsum/KDP, gypsum/ADP, gypsum/MgF₂, gypsum/sapphire and gypsum/calcite were found to be ± 1.7%, ± 3%, ± 12.2%, ± 12.0% and ± 7.2%, respectively. To reduce the spectral variation of retardations, a third layer (apochromatic) of birefringet material is added to the aforementioned achromatic wave plates. The proposed apochromatic wave plates are gypsum/KDP/quartz, gypsum/ADP/quartz, MgF₂/ADP/gypsum, MgF₂/KDP/gypsum and gypsum/sapphire/MgF₂. The addition of a third layer has reduced spectral residual variation percentages of retardations of the aforementioned apochromatic designs to ± 0.27, ± 0.33, ± 0.3, ± 0.17 and ± 0.45, respectively.     

Sulphur and oxygen isotopic characters of dissolved sulphate in groundwater from the Pleistocene aquifer in the southern Jordan Valley (Jericho area,Palestine)

Sulphate and chloride concentrations in the shallow Pleistocene aquifer systems in the lower Jordan valley area indicate a general trend of increasing salinity eastward and southward. This study was conducted in one of the important sub-basins feeding the Pleo–Pleistocene aquifer in the Jericho area in the southern part of the valley using S and O isotopes of dissolved sulphate. The results show that sulphate has mainly two contributions to the groundwater. One is the surface seepage, which is present as a salty leachate form with the positive δ³⁴S_sulphate values of primary gypsum in Lisan and Samara formations, and the second is the upwelling saline water which was in contact with a deep secondary gypsum, aragonites and salty rocks and rose up under heavy abstraction with depleted ³⁴S in sulphate and relatively high sulphate and chloride content. The latest was clearly shown in the Arab Project wells to the east that is undergoing a continuous heavy abstraction. The isotopic signatures of S and O in these wells to the east show that this depleted ³⁴S and highly concentrated sulphate might also indicate a dissolved sulphate originating from pyrite oxidation that results from the interaction with a pyrite-rich aquifer, which can well up with salty water under heavy abstraction and is oxidised in the upper aerobic shallow aquifer.     

偏硼酸锂-四硼酸锂熔融-电感耦合等离子体原子发射光谱(ICP-AES)法测定石膏中多组分含量

石膏在我国储量丰富,应用广泛,快速准确分析其成分含量对石膏资源的综合利用具有重要意义。针对酸溶法无法测定SiO2,碱熔法无法测定K2O、Na2O的问题,本文建立一种偏硼酸锂-四硼酸锂熔融-电感耦合等离子体发射光谱法同时测定石膏中CaO、SO3、Al2O3、Fe2O3、MgO、TiO2、K2O、Na2O、SiO2含量。实验优化了熔剂用量、熔融温度,结果表明采用试样与偏硼酸锂-四硼酸锂混合熔剂质量比例1：5,在铂金坩埚中1000 ℃熔融10 min,在超声条件下,于50 mL 10 %盐酸中浸取熔融物,能够有效分解试样而浸取待测组分。向标准溶液系列中加入偏硼酸锂-四硼酸锂-盐酸基体溶液以消除基体对测试结果的影响。各待测组分的校准曲线的相关性系数均大于0.9990,方法检出限在3~292 μg/g范围内;采用实验方法分别对国家一级标准物质GBW03109a、GBW03110和实际样品进行测定,标准物质的5次平行测试的相对标准偏差在0.14 %~8.86 %之间,测定结果的相对误差在0.03~8.75 %之间,测试结果与标准值无显著性差异;实际样品中各成分测定值的RSD（n=5）为0.24~8.80 %。该方法操作简单、准确度高、精密度好、检出限低,可以同时测定石膏中的多组分含量,能够为石膏资源综合利用调查评价提供一定的技术支撑 。     

阳离子树脂交换分离-电感耦合等离子体质谱(ICP-MS)法测定地质石膏样品中硼

硼石膏近些年在水泥、沥青混合材料等领域应用广泛,其主要成分为CaSO4·2H2O和B2O3以及其他杂质,因此准确、快速测定石膏样品中的硼元素对石膏的应用、资源综合利用等方面具有重要意义。而国家标准GB/T 5484-2012《石膏分析方法》中并没有硼元素的化学分析方法,且相关文献报道也很少。目前测定硼元素主要采用电感耦合等离子体质谱法（ICP-MS）,样品前处理多采用酸溶法,而碱熔法应用不多,主要原因是碱熔后溶液中产生大量盐分影响等离子体焰的稳定性,而732型阳离子交换树脂能吸附大量的钠离子,同时吸附了钙、镍、铁及稀土等阳离子,减少盐分干扰。基于此原理,本文采用氢氧化钠碱熔-732型阳离子交换树脂交换分离,在线加入铑内标的方式,建立了ICP-MS法测定石膏中硼的方法,同时由于石膏国家标准物质不包含硼元素的含量,采用高纯硫酸钙分别与岩石标准物质、水系沉积物国家标准物质和土壤国家标准物质混合配置成人工标准物质,并讨论了熔矿体系、阳离子加入量与吸附时间、清洗液、同位素的选择等实验条件。本方法的检出限为0.76μg/g,精密度（RSD,n=7）为0.9%~1.7%,相对误差为1.56%~3.96%,加标回收率在97.5%~102%,该方法快速、准确,记忆效应小,适合石膏中硼元素的测定。     

南京石膏矿特大突水灾害机理研究

发生于2006年9月11日的南京石膏矿特大突水灾害不仅改变了矿区及外围的地下水流场, 并引发了矿区地面沉降变形, 对地表附属物产生了一定的破坏作用, 造成了包括矿山关闭在内的巨大财产损失。南京石膏矿涉及典型的深部矿山地质工程问题, 影响地下开采稳定、矿山灾害和环境问题的主要因素是矿体及围岩的岩性结构及岩体结构构造, 特别是断裂构造及其影响带裂隙发育情况、富水性、导水率。围岩的岩溶强烈富水带的存在是矿坑突水的直接水源; 矿体的软岩特性、矿山开采扰动使采场周围的应力场重新分布、开采对断裂构造及裂隙带等结构体的活化作用都加剧了突水灾害的发生。     

Hydration of calcium sulfate hemihydrate (CaSO4· H2O) into gypsum (CaSO4·2H2O). The influence of the sodium poly(acrylate)/surface interaction and molecular weight

The retarding influence of sodium poly(acrylate) (PANa) on the hydration of calcium sulfate hemihydrate (CaSO₄· H₂O) was investigated. This study reports the influence of sodium poly(acrylate) on hemihydrate dissolution, on homogenous and heterogeneous gypsum (CaSO₄·2H₂O) nucleation as well as on gypsum growth. It is shown that adsorption of PANa does not hinder the dissolution of hemihydrate in the present experimental conditions. The specific interaction of PANa with gypsum can explain the oriented growth of gypsum crystal. The gypsum growth is slowed down but cannot be blocked by the adsorption of PANa. On the other hand, PANa can block the heterogeneous and homogenous gypsum nucleation. As soon as a critical surface density of PANa onto the hemihydrate surface is reached, the heterogeneous gypsum nucleation is prevented and hemihydrate hydration is indefinitely blocked. The interaction between PANa and the hemihydrate surface is of prime importance to control hydration. Also, the influence of the molecular weight of PANa on homogenous nucleation has been investigated. The precipitation of calcium polyacrylate can explain the differences between the two molecular weights used (2100 and 20 000). This work leads to the conclusion that heterogeneous nucleation is the key process that controls hydration of a system in which hemihydrate dissolution, gypsum nucleation and growth are all occurring at the same time in a continuous manner.