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Introduction Climate change links the technical work completed for the capstone project and the research work completed for the science, technology, and society (STS) research paper. The technical work described in this paper concerns development of a “carbon-negative” concrete building material. The material will sequester more carbon dioxide than it emits throughout the lifetime of its creation. It hopes to mitigate the effects of climate change by replacing traditional ordinary Portland cement (OPC) concrete, which emits one kilogram of carbon dioxide per one kilogram of concrete and is responsible for 8% of global carbon dioxide emissions. The STS portion of the project describes the effectiveness of carbon offsets, in an attempt to understand why they have become so popular and how they actually help reduce carbon emissions. In understanding more about how carbon offsets work, the paper hopes to understand how they can be used more effectively with other carbon emission-reducing strategies to reduce climate change effects. Technical Summary The capstone portion of the research focused on developing a life-cycle carbon-negative building material. The research was a continuation of previous work completed by the lab group that worked to understand how pseudowollastonite (PWOL) could be combined with granite aggregate, sodium hydroxide solution, and carbon dioxide (along with heat) to create calcium-silicate-hydrate gels which mimic the strength of traditional concretes. The PWOL was used as the binder, and the sodium hydroxide solution was substituted in lieu of water. The capstone project continued this research by utilizing waste materials from a metal processing plant that are high (> 50%) in PWOL. The use of waste materials significantly reduces the carbon footprint of the concrete. Many experiments were conducted over the course of the year. Much of the experiment design was spearheaded by either interest from the research group about how different materials and ratios affected the compressive strength or chemical composition of the concrete or by the industry partner who provided insight into the scalability and marketability of the product. The brunt of the research focused on the addition of small amounts of OPC to the waste slag. Different percentages of OPC were included in the mix to try to both increase the compressive strength as well as increase the viability of certain curing methods, such as curing the concrete while immersed in water (a traditional technique that does not work with PWOL-based materials). Since OPC releases a lot of carbon, however, a “golden” amount of OPC had to be found to maximize strength while maintaining carbon negativity. The project resulted in numerous data that will be published. This data hope to inform future and continued research into PWOL and waste-material-based concretes. STS Paper Summary The STS paper focuses on carbon offsets. It details how they came to be, what they are, how they work, and how they’ve evolved over the years. It then discusses, through the lens of a technological fix, the issues with carbon offsets and how they are currently used. These issues are societal, immense, and without an immediate, obvious solution (as is the case for technological fixes). The paper uses data from different carbon offset programs to illustrate the systematic and behavioral repercussions of carbon offsets. Large-scale systematic issues lead to exploitation of the system by its users for individual profit instead of using it for its intended purpose of reducing emissions. Individuals using carbon offsets may be induced, upon paying for the offset, to emit more overall due to the feeling of accomplishment that results from having helped the environment. Conclusion Working on both of these projects exposed me to a wealth of information about climate policy. The end product for our capstone will ultimately be more expensive to implement that sticking with current traditional methods, so we had to consider government subsidies that companies may receive. It was interesting in general to see how all these actors interact with each other and to see how the needs of Ash Grove cement conflicted with the needs and abilities of the research team. In the same vein, it was interesting to see how all the entities involved with carbon offsets interacted with each other—both projects involved such large complex systems that it was cool to see how they all worked together.

The paper discusses various ways of activating phosphorus slags by introducing additives for the development of phosphorus slag binders (PSB), replacing cement. Considering that pseudowollastonite is the main mineral of phosphorus slags and without activating components does not possess the binding properties necessary for the production of building materials based on them, we used compositions of small amounts of sodium hydroxide with alkali metal salts, the anions of which form poorly soluble compounds with calcium. When choosing activating components, scarce alkaline additives were replaced by waste from chemical plants, which allows a passing solution of their practical use and environmental problems. The strength at a sodium hydroxide content of 1–4 % after curing of slag samples of various batches was in the range of 50.0–70.0 MPa. Samples of binders of normal hardening at the age of 28 days with a sodium hydroxide content of 0.5; 1.0, 2 and 4 % had the strength of 20.3; 35.4; 45.6; 55.8 MPa, respectively. The effect of the combined presence of alkali and salt is especially noticeable for small amounts of sodium hydroxide. Binders containing a composition of cement with salts under normal conditions and after curing showed a slightly lower strength than in an alkaline medium. With a constant cement content (4 %), the strength indicators increase with an increase in the proportion of the salt additive, reaching at 4 % its maximum value. The effect of the nature of activators on pH was determined. The data obtained indicate the advantages of using PSB and various industrial wastes with a low content of alkaline compounds in the production, В работе рассматриваются различные способы активации фосфорных шлаков путем введения добавок для разработки фосфорношлаковых вяжущих (ФШВ), заменяющих цемент. Учитывая, что псевдоволластонит является основным минералом фосфорных шлаков и без активирующих компонентов не обладает связующими свойствами, необходимыми для производства строительных материалов на их основе, мы использовали композиции из небольших количеств гидроксида натрия с солями щелочных металлов, анионы которых образуют плохо растворимые соединения с кальцием. При выборе активирующих компонентов ограниченные щелочные добавки были заменены отходами химических производств, что позволяет попутно решить проблемы их практического использования и защиты окружающей среды. Прочность при содержании гидроксида натрия 1–4 % после тепловлажностной обработки образцов шлака различных партий находилась в пределах 50,0–70,0 МПа. Образцы вяжущих нормального твердения в возрасте 28 суток с содержанием гидроксида натрия 0,5; 1,0, 2 и 4 % имели прочность 20,3; 35,4; 45,6; 55,8 МПа соответственно. Эффект совместного присутствия щелочи и соли особенно заметен для небольших количеств гидроксида натрия. Вяжущие, содержащие композицию цемента с солями, в нормальных условиях и после ТВО показали несколько меньшую прочность, чем в щелочной среде. При постоянном содержании цемента (4 %) показатели прочности увеличиваются с увеличением доли солевой добавки, достигая при 4 % своего максимального значения. Было определено влияние природы активаторов на рН. Полученные данные свидетельствуют о преимуществах использования ФШВ и различных промышленных отходов с низким содержанием щелочных соединений в производстве., У роботі розглядаються різні способи активації фосфорних шлаків шляхом введення добавок для розробки фосфорношлакових в'яжучих (ФШВ), що замінюють цемент. Враховуючи, що псевдоволластоніт є основним мінералом фосфорних шлаків і без активуючих компонентів не володіє в'яжучими властивостями, необхідними для виробництва будівельних матеріалів на їх основі, ми використовували композиції з невеликих кількостей гідроксиду натрію з солями лужних металів, аніони яких утворюють важкорозчинні сполуки з кальцієм. Під час вибору активуючих компонентів обмежені лужні добавки були замінені відходами хімічних виробництв, що дозволяє попутно вирішити проблеми їхнього практичного використання і захисту навколишнього середовища. Міцність при вмісті гідроксиду натрію 1–4 % після тепловологісної обробки зразків шлаку різних партій перебувала в межах 50,0–70,0 МПа. Зразки в'яжучих нормального твердіння у віці 28 діб з вмістом гідроксиду натрію 0,5; 1,0, 2 і 4 % мали міцність 20,3; 35,4; 45,6; 55,8 МПа відповідно. Ефект спільної присутності лугу і солі особливо помітний для невеликих кількостей гідроксиду натрію. В'яжучі, що містять композицію цементу з солями, в нормальних умовах і після ТВО показали дещо меншу міцність, ніж в лужному середовищі. При постійному вмісті цементу (4 %) показники міцності збільшуються зі збільшенням частки сольової добавки, досягаючи при 4 % свого максимального значення. Було визначено вплив природи активаторів на рН. Отримані дані свідчать про переваги використання ФШВ і різних промислових відходів з низьким вмістом лужних сполук у виробництві.

Environmental hazards due to alkali elution can be mitigated by investigating the dissolution kinetics of calcium silicate mineral phases in water. This study demonstrated the effect of the silicate skeleton structure on the dissolution kinetics of calcium silicate mineral phases in water. The time dependence of the Ca-Si relative release ratio during leaching indicated the preferential elution of Ca to Si in the initial stage of dissolution. The formation of a Ca-depleted layer on the surface of the leached sample was confirmed by X-ray photoelectron spectroscopy and time-of-flight secondary-ion mass spectrometry. The elution kinetics of Ca and Si were determined by the semi-infinite diffusion model and the detachment reaction of the intermediate phase that was formed on the surface of the mineral by hydration, respectively. Furthermore, the nanoscale intermediate phase was observed by transmission electron microscopy. The diffusion coefficient of Ca in the leached layer and the reaction-rate coefficient of Si were obtained from the elution kinetics of Ca and Si, respectively, and these decreased with the increase in the degree of polymerization of the silicate skeleton structure that varied in the following sequence: calcio-olivine (γ-Ca2SiO4) > rankinite (Ca3Si2O7) ≈ wollastonite (β-CaSiO3) > pseudowollastonite (α-CaSiO3).

Cement is the world’s most widely consumed man-made material and it contributes between 5% and 10% of the total annual anthropogenic CO2 emissions. Here, we report on a new method for producing cry...

Phase equilibria of the ternary CaO-ZnO-SiO2 system have been investigated at 1170 °C to 1691 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2 (up to two immiscible liquids), pseudowollastonite (CS) CaSiO3, rankinite (C3S2) Ca3Si2O7, dicalcium silicate (C2S) (Ca, Zn)2SiO4, tricalcium silicate (C3S) (Ca, Zn)3SiO5, lime (Ca, Zn)O, zincite (Zn, Ca)O, willemite Zn2SiO4 and hardystonite (melilite) Ca2ZnSi2O7, covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates followed by quenching and direct measurement of the Ca, Zn and Si concentrations in the phases with the electron probe X-ray microanalysis (EPMA) has been used to accurately characterize the system. Liquidus phase equilibrium data of the present authors for the CaO-ZnO-SiO2 system are essential to obtain a self-consistent set of parameters of thermodynamic models for all phases.

Efforts to develop safe and effective next-generation energy and carbon-storage technologies in the subsurface require novel means to control undesired fluid migration. Here we demonstrate that the carbonation of calcium silicates can produce reaction products that dramatically reduce the permeability of porous media and that are stable. Most calcium silicates react with CO2 to form solid carbonates but some polymorphs (here, pseudowollastonite, CaSiO3) can react to form a range of crystalline calcium silicate hydrates (CCSHs) at intermediate pH. High-pressure (1.1-15.5 MPa) column and batch experiments were conducted at a range of temperatures (75-150 °C) and reaction products were characterized using SEM-EDS and synchrotron μXRD and μXRF. Two characteristics of CCSH precipitation were observed, revealing unique properties for permeability control relative to carbonate precipitates. First, precipitation of CCSHs tends to occur on the surface of sand grains and into pore throats, indicating that small amounts of precipitation relative to the total pore volume can effectively block flow, compared to carbonates which precipitate uniformly throughout the pore space. Second, the precipitated CCSHs are more stable at low pH conditions, which may form more secure barriers to flow, compared to carbonates, which dissolve under acidic conditions.

The deposition of mineral phases on the heat transfer surfaces of brown coal power plants may have a negative effect on power plant boilers. The paragenesis of these deposits contains information about the actual temperature prevailed during the combustion of lignite, if the temperature-dependences of distinct mineral transformations or reactions are known. Here, we report results of a sintering study (to ~ 1100 °C) with samples containing anhydrite, quartz, and gehlenite, which are typical components of Rhenish lignite ashes. Thermal decompositions and solid-state reactions were analyzed (1) in situ and (2) both in situ and after quenching using confocal hyperspectral Raman imaging. This novel application of confocal Raman spectroscopy provides temperature- and time-resolved, 2-dimensional information about sintering processes with a micrometer-scale resolution. In the course of the sintering experiments with anhydrite and quartz with a weight ratio of 2:1 both polymorphs wollastonite and pseudowollastonite were identified in situ at about 920 and 1000 °C, respectively. The formation of pseudowollastonite was thus observed about 120 °C below the phase transition temperature, demonstrating that it can form metastably. In addition, $$\alpha_{L}^{\prime }$$ -Ca2SiO4 was identified at about 1100 °C. In samples containing equal weight fractions of anhydrite and quartz that were quenched after firing for 9 h at about 1100 °C, β-Ca2SiO4 (larnite) crystallized as rims around anhydrite grains and in direct contact to wollastonite. We furthermore observed that, depending on the ratio between quartz and anhydrite, wollastonite replaced quartz grains between 920 and 1100 °C., i.e., the higher the quartz content, the lower the formation temperature of wollastonite.

Phase equilibria of CaO-Al2O3-SiO2-Na2O slags were studied by thermal equilibration and quenching. The primary phases of the quenched slags were identified, and their equilibrium compositions determined by electron probe microanalysis. Liquidus temperatures of the slags were bracketed within an uncertainty of ± 10–20°C. Anorthite (CaO·Al2O3·2SiO2), gehlenite (2CaO·Al2O3·SiO2), pseudowollastonite (CaO·SiO2), and larnite (2CaO·SiO2) were observed as primary phases. Progressive doping by Na2O substantially changed the slag liquidus temperature, shifting the primary phase from anorthite to pseudowollastonite and larnite, and gehlenite to larnite. The liquidus temperature decreased significantly with increasing Na2O in slags with CaO/SiO2 (C/S) ratios of 0.3 and 0.6, while the liquidus temperature increased for slags with a C/S ratio of 1.0. The solid solubility of Na2O in the phases was quantified. Finally, the relevance of the phase equilibria study of the CaO-Al2O3-SiO2-Na2O system was discussed with regard to the optimum design of smelting with a focus on value recovery from e-waste.

The equations of state of different phases in the CaSiO3 system (wollastonite, pseudowollastonite, breyite (walstromite), larnite (Ca2SiO4), titanite-structured CaSi2O5 and CaSiO3-perovskite) are constructed using a thermodynamic model based on the Helmholtz free energy. We used known experimental measurements of heat capacity, enthalpy, and thermal expansion at zero pressure and high temperatures, and volume measurements at different pressures and temperatures for calculation of parameters of equations of state of studied Ca-silicates. The used thermodynamic model has allowed us to calculate a full set of thermodynamic properties (entropy, heat capacity, bulk moduli, thermal expansion, Gibbs energy, etc.) of Ca-silicates in a wide range of pressures and temperatures. The phase diagram of the CaSiO3 system is constructed at pressures up to 20 GPa and temperatures up to 2000 K and clarifies the phase boundaries of Ca-silicates under upper mantle conditions. The calculated wollastonite–breyite equilibrium line corresponds to equation P(GPa) = −4.7 × T(K) + 3.14. The calculated density and adiabatic bulk modulus of CaSiO3-perovskite is compared with the PREM model. The calcium content in the perovskite composition will increase the density of mineral and it good agree with the density according to the PREM model at the lower mantle region.

Made available in DSpace on 2021-07-14T10:26:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-10-30. Added 1 bitstream(s) on 2021-07-14T11:30:02Z : No. of bitstreams: 1 S0366-69132020000400413.pdf: 1427762 bytes, checksum: 101c416ef2eff63ec6e1bcc4c1cc8722 (MD5) A reciclagem tem sido apontada como alternativa ao descarte de resíduos em aterros industriais. No presente trabalho é mostrada a transformação de resíduos (areia descartada de fundição - ADF, grits e lama de cal) em materiais vitrocerâmicos. Os vidros foram obtidos pelo método de fusão/resfriamento. Os materiais precursores, compostos vítreos e vitrocerâmicos foram caracterizados pelas técnicas de difração de raios X (DRX), fluorescência de raios X (FRX) e calorimetria exploratória diferencial/análise termogravimétrica (CED/ATG). Os materiais vítreos foram moídos, pastilhados e tratados termicamente nas temperaturas de cristalização obtidas por CED para preparar os materiais vitrocerâmicos (885, 961 e 1090 ºC). As fases obtidas foram cristobalita, α-wolastonita (parawolastonita) e β-wolastonita (pseudowolastonita). As vitrocerâmicas apresentaram baixa absorção de água e porosidade aparente (0,26 até 0,88 wt% e 0,66 até 1,77 vol%, respectivamente). Os resultados confirmaram que os resíduos estudados podem ser utilizados como matéria-prima na fabricação de materiais vítreos e vitrocerâmicos. Recycling has been pointed out as an alternative to the disposal of waste materials in industrial landfills. In the present study, the transformation of residues (discarded foundry sand - DFS, grits, and lime mud) in glass-ceramic materials is shown. The glasses were obtained by the melting/cooling method. The precursor materials, glasses, and glass-ceramics were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), and differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA). The glassy materials were milled, pelleted, and thermally treated at the crystallization temperatures given by DSC data to obtain the glass-ceramics (885, 961, and 1090 ºC). The main formed phases were cristobalite, α-wollastonite (parawollastonite), and β-wollastonite (pseudowollastonite). The glass-ceramics showed very low water absorption and apparent porosity (0.26 to 0.88 wt% and 0.66 to 1.77 vol%, respectively). The results confirmed that the studied residues can be used as raw materials for the manufacture of vitreous and glass-ceramic materials. Universidade Estadual Paulista, Faculdade de Ciências e Tecnologia Universidade do Oeste Paulista, Faculdade de Engenharia e Arquitetura Universidade Estadual Paulista, Faculdade de Ciências e Tecnologia

Phase equilibria of the binary PbO-CaO and ternary PbO-CaO-SiO2 systems have been investigated at 870-1655 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2, pseudowollastonite CaSiO3, dicalcium silicate (Ca,Pb)2SiO4, tricalcium silicate (Ca1−xPbx)3SiO5 (x

Bioactive composites consist of pseudowollastonite and mullite synthesized from natural resources was developed for bone implant applications. To realize such applications, a mechanical test of these composites and in vitro bioactivity in SBF solution were studied. The present paper reports pseudowollastonite synthesized from the rice husk ash and limestone reinforced with 10, 20 and 30 wt. % of mullite. Influence of sintering temperature, phase composition, morphology towards mechanical properties of various pseudowollastonite-mullite (PSW-M) composites was examined prior to the bioactivity test. It was found that pseudowollastonite with the addition of 20 wt. % of mullite sintered at 1150°C gave the best result for diametral tensile strength (DTS) and hardness with the value of 8.8 ± 0.15 MPa and 3.79 ± 0.13 GPa, respectively. The obvious increment in the mechanical strength was due to the formation of liquid phase CaAl2O3 during sintering at 1150°C. In addition, the formation of fibrous apatite (HA) layer of amorphous calcium phosphate (ACP) with Ca/P ratio 1.8 on PSW20M sample confirmed the good bioactivity of the composite.

The reaction of CO2(aq) with calcium silicates creates precipitates that can impact fluid flow in subsurface applications such as geologic CO2 storage and geothermal energy. These reactions nominally produce calcium carbonate (CaCO3) and amorphous silica (SiOx). Here we report evidence that the crystal structure of the parent silicate determines the way in which it reacts with CO2 and the resulting structures of the reaction products. Batch experiments were performed using two polymorphs of a model calcium silicate (CaSiO3), wollastonite (chain-structured) and pseudowollastonite (ring-structured), at elevated temperatures (150 °C) and partial pressures of CO2 (0–11 MPa). Reaction of CO2(aq) with wollastonite produced CaCO3 and SiOx, whereas reaction of CO2(aq) with pseudowollastonite produced platelike crystalline calcium silicate phases, along with CaCO3 and SiOx. A reaction mechanism that explains the observations in relation to dissolution of the parent silicate, the pH of the solution, and the presenc...

Objectives. Cage design and material properties play a crucial role in the long-term results, since interbody fusions using intervertebral cages have become one of the basic procedures in spinal surgery. Our aim is to design a novel Apatite-Wollastonite interbody fusion cage and evaluate its biomechanical behavior in silico in a segmental spinal model. Materials and Methods. Mechanical properties for the Apatite-Wollastonite bioceramic cages were obtained by fitting finite element results to the experimental compression behavior of a cage prototype. The prototype was made from hydroxyapatite, pseudowollastonite, and frit by sintering. The elastic modulus of the material was found to be 32 GPa. Three intact lumbar vertebral segments were modelled with the ANSYS 12.0.1 software and this model was modified to simulate a Posterior Lumbar Interbody Fusion. Four cage designs in different geometries were analyzed in silico under axial loading, flexion, extension, and lateral bending. Results. The K2 design had the best overall biomechanical performance for the loads considered. Maximum cage stress recorded was 36.7 MPa in compression after a flexion load, which was within the biomechanical limits of the cage. Conclusion. Biomechanical analyses suggest that K2 bioceramic cage is an optimal design and reveals essential material properties for a stable interbody fusion.

In this paper we report on X-ray studies on amorphization of pseudowollastonite following 30 min mechanical activation using a centrifugal planetary mill AGO-2 in atmospheric air. In addition, milling resulted in chemical reaction which led to the formation of calcium carbonate and silica. In general, the chemical composition of the sample corresponded to the formula CaSi0.997C0.014O3.02. Theoretically calculated scattering intensity for a model of mechanical mixture corresponded to the following ratio: 0.75 scattering intensity of the cluster consisting of four unit cells of pseudowollastonite disordered in a molecular dynamic experiment; 0.25 scattering intensity of the cluster consisting of one unit cell of CaCO3; 0.25 scattering intensity of the cluster consisting of one unit cell of α-SiO2. The R-factor for scattering intensity I(s) was 5.5%. The curve of s-weighted interference function H(s) calculated for the model coincided with the experimental curve. Characteristics of tetrahedra arrangement in the initial pseudowollastonite cluster and in the same cluster after molecular dynamic were calculated by the method based on the searching for a coordination polyhedra in the clusters and the constructing of graphs.

At temperatures less than ~1500 K, previously published C P data demonstrate that the heat capacities of orthoenstatite, proto-enstatite, diopside, and pseudowollastonite include primarily Debye type vibrational and anharmonic contributions, whereas the alkali chain, sheet, and ring silicates, Na 2 SiO 3 , Li 2 SiO 3 , K 2 SiO 3 , and Na 2 Si 2 O 5 include a third contribution. The third contribution to C P arises from defect formation due to the mobility Na, K, Li, and O 2 − . The contribution becomes apparent at temperatures above 700–800 K for Na and K silicates, and above 900–1000 K for Li metasilicate. With strong thermal agitation, alkali-non-bridging oxygen (NBO) bonds are ruptured with the cations exiting their structural sites to occupy interstitial sites, thereby producing intrinsic Frenkel defects, which contribute to the C P of the alkali silicates. The magnitudes of the C P defect contributions correlate inversely with cation-oxygen bond strengths, as measured by bond dissociation energies. K-O and Na-O bond strengths are weak (239 and 257 kJ/mol) and defect contributions are large for these alkali chain, ring, and sheet silicates. The greater bond strength of Li-O (341 kJ/mol) correlates with a weaker defect contribution to the C P of Li 2 SiO 3 . Mg-O and Ca-O bonds are stronger still (394 and 464 kJ/mol) and no C P defect contributions are observed for the pyroxenes and pseudowollastonite up to ~1500 K. Above ~800 K a polymerization reaction occurs in Na 2 SiO 3 , which produces some Q 3 species and free oxygen (O 2 − or oxide ion). The polymerization reaction annihilates an oxygen structural site so that the O 2 − produced must reside on non-structural sites thus producing intrinsic anionic defects. The same reactions likely occur in Na 2 Si 2 O 5 and K 2 SiO 3 . Raman spectra of Na 2 SiO 3 indicate >10% of Na + and ~1.7% of O 2 − on interstitial sites at 1348 K. Ca- and Mg-bearing mantle minerals subjected to temperature greater than ~1500 K experience the destabilizing effects of disordering (Frenkel defect formation). The minerals may respond either by changing their composition or by changing phase. An abundance of Ca and Na defects in pyroxenes, for example, likely promotes production of new components (e.g., CaAl 2 SiO 6 , NaAlSi 2 O 6 ) in pyroxenes. By their production, Ca and Na defect concentrations are reduced thereby stabilizing the phases. Mg-O bond dissociation and production of intrinsic Mg 2+ and O 2 − point defects within olivine likely destabilize it and promote the phase transition to wadsleyite at the base of the upper mantle.

Sintering reactions of clay bodies have previously been studied by numerous experiments that involve quenching of the sintered ceramic bodies to room temperature and analyzing the reaction product by different analytical techniques. In this study, green bodies containing quartz, alkali feldspar, kaolinite, and calcite, were progressively fired in air at various temperatures from room temperature to about 1060°C. For the first time, mineral reactions and textural relationships were studied in situ as a function of temperature and time with a spatial resolution of a few micrometers by confocal hyperspectral Raman imaging. Gehlenite, wollastonite, and pseudowollastonite could unambiguously be identified as newly formed phases during sintering, and their textural evolution could be followed with temperature and time. From 800°C onwards wollastonite formed at the direct contact to gehlenite, whereby at temperatures higher than 990°C wollastonite seems to be gradually replacing gehlenite. The crystallization of pseudowollastonite was observed already ~290°C below the accepted critical temperature (~1125°C) for the wollastonite-to-pseudowollastonite transformation, suggesting that pseudowollastonite can form metastably. The results of this study demonstrate that hyperspectral Raman imaging is a powerful method to study in situ phase transitions and recrystallization processes at grain boundaries during high-temperature sintering of ceramic materials. This article is protected by copyright. All rights reserved.

Two new barium-bearing minerals: gurimite, Ba3(VO4)2 (IMA2013-032) and hexacelsian, BaAl2Si2O8 (IMA2015-045) were discovered in veins of paralava cutting gehlenite-flamite hornfels located in the Gurim Anticline in the Negev Desert, Israel. Gurimite and hexacelsian occur in oval polymineralic inclusions in paralava and are associated with gehlenite, pseudowollastonite or wollastonite, rankinite, flamite, larnite, schorlomite, andradite, fluorapatite, fluorellestadite, kalsilite, cuspidine, aradite, zadovite and khesinite. Gurimite and hexacelsian form elongate crystals –3 for gurimite and 3.305 g cm–3 for hexacelsian. Mean refractive indexes, 1.945 and 1.561, respectively, were also calculated using the empirical formulas and the Gladstone-Dale relationship. The minerals are uniaxial and nonpleochroic. The following empirical crystal chemical formulae were assigned to holotype gurimite: (Ba2.794K0.092Ca0.084Na0.033Sr0.017)∑3.020(V1.8275+S0.0916+P0.0515+Al0.040Si0.005Fe0.0053+)∑2.017O8,and holotype hexacelsian: (Ba0.911K0.059Ca0.042Na0.010)∑1.022Al1.891Fe0.0723+Si2.034O8. The Raman spectrum of hexacelsian is similar to the one of the synthetic disordered β-BaAl2Si2O8. The Raman spectrum of gurimite is identical to that of synthetic Ba3(VO4)2. The electron back-scattered diffraction (EBSD) pattern of gurimite was fitted to the structure of its synthetic analogue with the cell parameters of R3m, a = 5.784(1),c = 21.132(1) Å, V = 612.2(2) Å3, Z = 3, giving a mean angular deviation = 0.43° (good fit). The Raman spectra of hexacelsian and its EBSD pattern suggest that natural hexacelsian corresponds to disordered synthetic β-hexacelsian P63/mcm, a = 5.2920(4) Å, c = 15.557(2) Å, α = β = 90°, γ = 120°. We suggest that after relatively fast crystallization of the main constituents of the paralava, gurimite, hexacelsian and also other Ba-bearing phases crystallized from residual melt enriched in incompatible elements that filled interstices between crystals of the main constituents.

Khesinite, Ca 4 Mg 2 Fe 3+ 10 O 4 (Fe 3+ 10 Si 2 )O 36 , is a new member of the rhonite group of the sapphirine supergroup. Khesinite was discovered in thin veins of paralavas within fine-grained gehlenite rocks (hornfels) of the Hatrurim Complex in the Negev Desert, Israel. Paralavas are composed of rankinite, pseudowollastonite (rarely wollastonite), flamite, kalsilite, cuspidine and members of the solid-solution series: schorlomite–andradite, gehlenite–ackermanite–“Fe 3+ -gehlenite”, magnesioferrite–spinel and fluorapatite–fluorellestadite. Accessory and rare minerals are represented by baryte, walstromite, fresnoite, vorlanite, barioferrite, hematite, perovskite, gurimite, zadovite, aradite and hexacelsian. Electron-microprobe analysis of the holotype khesinite gives the following empirical formula for 40 oxygens and 28 cations: Ca 4 (Fe 3+ 8.528 Mg 1.635 Ca 0.898 Ti 4+ 0.336 Ni 2+ 0.217 Mn 2+ 0.155 Cr 3+ 0.132 Fe 2+ 0.098 ) Σ12 [(Fe 3+ 6.827 Al 2.506 Si 2.667 ) Σ12 O 40 ]. Khesinite is black to dark brown. It has semi-metallic lustre and does not show fluorescence. Cleavage and parting are not observed, fracture is irregular. Khesinite has a Mohs9 hardness of 6; microhardness VHN 50 is 943 kg mm −2 . The calculated density is 4.097 g cm −3 . In reflected light khesinite is grey with weak internal brown reflections. Reflectance data for the COM (Commission of Ore Mineralogy, IMA) wavelengths vary from ~13.4% (470 nm) to ~11.8% (700 nm). The crystal structure of khesinite [ P 1 ¯ a = 10 . 5363 ( 1 ) , b = 10.9242(2), c = 9.0612(1) A, α = 106.340(1)°, β = 95.765(1)°, γ = 124.373(1)°, V = 780.54(2) A 3 ] was refined from X-ray single-crystal data to R 1 = 0.046. The khesinite structure is close to that of the synthetic compounds SFCA and SFCAM. Khesinite crystallized in paralava from melt, sometimes forming isolated crystals, but more commonly reaction rims on magnesioferrite in association with pseudowollastonite and flamite at temperature not lower than 1200 °C.

The irruption of additive manufacturing techniques opens the possibility to develop three-dimensional structures with complex geometries and high precision. In the current investigation a newly designed composite combining silicon (30, 40 and 50 wt%) with a bioactive glass and printed into scaffolds was obtained, using a direct selective laser melting (SLM) approach for the first time. Samples were computer-aided designed (CAD) to have cylindrical pores of 400 μm in diameter in order to be used as biomaterials for bone replacement. X – Ray diffraction was used to characterize the appearance of a new phase of pseudowollastonite precipitated by the partial devitrification of the glassy phase after the incidence of laser radiation. The mechanical behaviour of each composition was studied trough stress-strain curves, obtaining higher values of compressive strength as the silicon content increases. Scanning electron microscopy coupled to energy dispersive X – Ray spectroscopy (SEM-EDS) and Raman spectroscopy were used to study the bioactivity of each composite after soaking in the simulated body fluid (SBF) for 7 days, confirming this behaviour., The authors would like to acknowledge Dora Plus program no 3–14/2030/3 “Scholarship for short term visit”offered by the TalTech University of Tallinn (TTÜ, Estonia), thefinancial support in the frame of projects CSIC-201760E022, CSIC-201860E127 and the personalgrant with contract number 2018 186-11 to participate on the January2020 ACerS Winter Workshopfinanced by JECS Trust Board. This workwas also supported by the Estonian Research Council grant PRG643 (I.Hussainova).

In the present work, Ca-containing silicon oxycarbides (SiCaOC) with varying Ca content have been synthesized via sol-gel processing and thermal treatment in inert gas atmosphere (pyrolysis). It has been shown that the as-prepared SiCaOC materials with low Ca loadings (Ca/Si molar ratios = 0.05 or 0.12) were X-ray amorphous, their glassy network contains Q3 sites, indicating the presence of Ca2+ at non-bridging-oxygen sites. SiCaOC with high Ca content (i.e., Ca/Si molar ratio = 0.50) exhibits the presence of crystalline calcium silicate (mainly pseudowollastonite). Furthermore, it has been shown that the incorporation of Ca into the SiOC glassy network has a significant effect on its porosity and specific surface area. Thus, the as-prepared Ca-free SiOC material is shown to be non-porous and having a specific surface area (SSA) of 22.5 m2/g, whereas SiCaOC with Ca/Si molar ratio of 0.05 exhibits mesoporosity and a SSA value of 123.4 m2/g. The further increase of Ca content leads to a decrease of the SSA and the generation of macroporosity in SiCaOC, thus, SiCaOC with Ca/Si molar ratio of 0.12 is macroporous and exhibits a SSA value of 39.5 m2/g. Bioactivity assessment in simulated body fluid (SBF) confirms the hydroxyapatite formation on all SiCaOC samples after seven days soaking, unlike the relatively inert ternary silicon oxycarbide reference. In particular, SiCaOC with a Ca/Si molar ratio of 0.05 shows an increased apatite forming ability compared to that of SiCaOC with Ca/Si molar ratio of 0.12, this difference is considered to be a direct consequence of the significantly higher SSA of the sample with the Ca/Si ratio of 0.05. The present work indicates two effects of Ca incorporation into the silicon oxycarbide glassy network on its bioactivity: Firstly, Ca2+ is shown to contribute to the slight depolymerization of the network, which clearly triggers the hydroxyapatite formation (compare the bioactive behavior of SiOC to that of SiCaOC with Ca/Si molar ratio 0.12 upon SBF exposure), secondly, the Ca2+ incorporation seems to strongly affect the porosity and SSA in the prepared SiCaOC materials. There is an optimum of Ca loading into the silicon oxycarbide glassy network (at a Ca/Si molar ration of 0.05), which provides mesoporosity and reaches maximum SSA, both highly beneficial for the bioactive behavior of the materials. An increase of the Ca loading leads, in addition to the crystallization of calcium silicates, to a coarsening of the pores (i.e., macroporosity) and a significant decrease of the SSA, both negatively affecting the bioactivity.

A systematic investigation of the influence of pseudowollastonite on the performance of a new family of low calcium hydraulic binders is described. Samples of the new low calcium binder were produced by an innovative process consisting of heating and homogenizing the mix of raw materials (limestone, sand, and fuel cracking catalyst) at a constant temperature followed by the rapid cooling of the mixture itself. Different maximum temperatures, close to the melting temperature of the mix, were tested, and materials with CaO/SiO2 (C/S) ratios of 0.9, 1.1, and 1.25 were produced into the form of the amorphous phase with small percentages of pseudowollastonite. Compressive strength results were determined at 7, 28, and 90 days of hydration, and the hydrated phases were analyzed using isothermal calorimetry, X-ray diffraction (XRD) analysis, thermogravimetry analysis (TGA), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The present work is focused on the influence of the percentage of the pseudowollastonite phase on the binder compressive strength performance.

Silicate weathering is important in many natural and engineered contexts including in the performance of cement. Cement is the most common man-made material in the world and is responsible for over 5% of annual CO2 emissions. Here, the reaction of a model calcium silicate, pseudowollastonite (CaSiO3) with aqueous solutions containing CO2 was evaluated in depth to understand how this class of reactions might be deployed in two contexts. The first application is subsurface engineering activity where permeability control is desirable for sustainable deployment of geologic carbon storage, geothermal energy, or energy storage. The second application is in the synthesis of pre-cast concrete that is low carbon and high performance. The reaction of CaSiO3 with CO2(aq) nominally produces calcium carbonate (CaCO3) and amorphous silica (SiO2) but here, experiments suggest that the crystal structure of the parent silicate and the solution pH determine the way in which the silicate reacts with CO2 and the resulting structures of the reaction products. Batch experiments were carried out using two polymorphs of CaSiO3, wollastonite (chain-structured) and pseudowollastonite (ring-structured), at elevated temperatures and CO2(aq) concentrations. Reaction of CO2(aq) with wollastonite produced CaCO3 and SiO2, whereas reaction of CO2(aq) with pseudowollastonite produced numerous plate-like crystalline calcium silicate hydrate (CCSH) phases, along with CaCO3 and SiO2. Analyses of the resulting CCSH phases suggest that they are similar to those responsible for providing the strength and durability of Roman cements in terms of morphology and composition. The first application of CCSH-based cement is presented in the context of controlling fluid transport in the subsurface, which is relevant to geologic carbon sequestration, oil and gas well closure, and enhanced geothermal energy production. The CCSH phases, in porous media, were compared to calcium carbonate precipitates, which are typically thought to form in the naturally carbon-rich environments in the subsurface. A suite of analytical methods including electron microscopy, synchrotron-based X-ray diffraction and fluorescence, and permeability measurements, among others, show that the CCSH phases, which formed in the presence of dissolved CO2(aq) and NaOH at pH 6.65, decreased permeability in sand columns by 2.83 orders of magnitude in 495 hours of reaction. Under the same conditions with no NaOH (pH 3.94), calcium carbonate was the predominant precipitate and led to a decrease in permeability of only 1.16 orders of magnitude. Acetic acid injected into the columns revealed that the CCSH phases were more resistant to dissolution at low pH than calcium carbonate, which could result in longer-lasting seals for undesirable fluid migration in the subsurface. The second application addresses CCSH performance in the context of precast cement and compares characteristics of strength, durability, resistance to acid-dissolution, and environmental impact to those of Portland and carbonate-based cements. Precast mortar specimens were prepared via a novel curing technique that involved first allowing the specimens to harden in a CO2 atmosphere and then submerging them in a heated carbonate-rich solution buffered with NaOH in order for CCSH phases to precipitate. A Taguchi design of experiments was implemented to optimize the curing conditions, which yielded mortar with comparable strength as the alternatives (13.9 MPa at 7 days of curing), while possessing lower diffusivity to dissolved ions, and more resistance to acid-attack. Relative to Portland cement, a lifecycle analysis shows that CCSH cement could be produced with 85% lower CO2 emissions.

Fully dense biphasic calcium silicates with improved biomechanical behavior were fabricated via mechanothermal method followed by the conventional sintering process. The effects of dopant concentration on the phase composition, structural evolution, and mechanical properties of palladium-doped calcium silicates (PCSs) were investigated. The results showed that the coalescence of nanoparticles, coarsening of particles, and the formation of large agglomerates occurred during the mechanothermal reactions. Attenuated total reflection (ATR) spectroscopy spectra of the PCSs represented the characteristic bands of the calcium silicates, including the bending mode of Si–O–Si and O–Si–O, the stretching vibration of O–Si–O group, the stretching mode of Si–O–Ca, as well as the symmetrical stretching mode of Si–O–Si group. The results of the Rietveld refinement indicated that the phase compositions and structural features noticeably affected by the dopant concentration so that the phase fraction (PF) of Wollastonite-1A and Pseudowollastonite was 0.318 ± 0.035 and 0.526 ± 0.025 in the case of undoped calcium silicate (PCS0), which respectively reached 0.411 ± 0.021 and 0.589 ± 0.021 for the Pd-doped calcium silicate (PCS20). Comparing with the PCS0, the Vickers hardness of the consolidated PCS20 increased by ~79%. From the biomineralization analysis, the surface of the consolidated sample was covered by the bone-like apatite after soaking in a simulated body fluid (SBF) for 2 weeks.