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A model of nucleation in metasilicate melts, taking into account thermodynamic and kinetic factors of phase transformations, was developed on the basis of the notion of cybotaxic groups. The number of formed nuclei depends not only on the degree of supercooling of the melt but also on the temperature at which the melt is cast into a mold, in the course of which the kinetic factor is realized.

Sugarcane is a significant crop for production of sugar and ethanol in the world. In present perspective, drought is one of the frequently occurring abiotic stresses hampering the productivity of sugarcane causing heavy losses in sugar recovery. Post-harvest sugarcane deterioration attains more importance. Measures have been recommended in harvested canes to prevent these losses in general and under drought conditions but application of chemical formulation has not yet been tested over drought effected ones. Thus, we tried to investigate the efficacy of chemical formulation [Benzalkonium chloride (BKC) + Sodium metasilicate (SMS)] on sucrose losses occurring in harvested canes grown under drought and normal conditions. Results showed that application of chemical formulation had higher effect on drought canes in comparison to normal grown canes. Loss in cane weight was reduced to 8.25% and 11% in drought treated and normal treated grown canes, respectively, after 240 h of harvest in comparison to their respective control. In sucrose content and Commercial cane sugars %, drought treated canes showed an effect of BKC + SMS by reducing the losses to 1.26 units and 1.42 units, respectively, whereas in normal ones, reduction was of 0.38 units and 0.10 units, respectively. Biochemical analysis revealed that in reducing sugars, reduction in increase were of 44.51% and 25.50% in drought and normal grown canes, respectively, after 240 h of harvest. Dextran and soluble acid invertase estimations revealed that after application of BKC + SMS, reduction of dextran and invertase activity were of 49.74%, 66.84%, respectively, and 33.92%, 42.75%, respectively, in drought and normal grown canes, respectively. Total microbial load, showed effectiveness of 25.01% in drought grown canes while 14.41% in normal grown ones after 240 h of harvest. Our study was planned to use the anti-bacterial efficiency of both the chemicals over harvested canes so that the major sucrose losses occurring due to microbial deterioration could be inhibited. The use of this chemical formulation proves to be an effective one over post-harvest sucrose losses, particularly in drought grown canes. Keywords: Benzalkonium chloride + Sodium metasilicate, Dextran, Drought, Microbes, Sucrose, Sugarcane

In presented work Alginate-Neusilin US2 micro-composite beads (MCBs) were formulated and optimized for oral delivery of cilnidipine (CIL). Optimized formulation of CIL loaded MCB (BA-O) exhibits pa...

International audience; In this study, lead metasilicate glasses (PbSiO3) were densified at different maximum pressures in a diamond anvil cell (DAC) at room temperature. The densified glass samples were investigated ex-situ by Raman spectroscopy to probe their pressure-induced plastic deformation limit and permanent structural modifications on the Q(n) distribution. With a high Pb content, this glass exhibits a low elastic limit at similar to 4 GPa, which is linked to an initial compact structure. Spectral curve fitting of the high-frequency region of the Raman spectra, consisting of symmetric Si-O stretching modes, exhibit subtle Q(n) population modifications with maximum pressure. This reveals silica network depolymerization where the proportion of non-bridging oxygens (NBO) increases at the expense of bridging oxygens (BO). Possible densification mechanisms are discussed in contrast to those known in other silicate glasses.

Ab initio molecular dynamics simulations predict that CaSiO3 perovskite melts at 5600 K at 136 GPa, and 6400 K at 300 GPa, significantly higher than MgSiO3 perovskite. The entropy of melting (1.8 kB per atom) is much larger than that of many silicates at ambient pressure and of simple liquids and varies little with pressure. The volume of melting decreases rapidly with increasing pressure, to 3 % at 136 GPa, producing a melting slope that diminishes rapidly with pressure. We determine the melting temperature via the ZW method, combining the Z method, for which we clarify the theoretical basis, with a waiting time analysis. The ZW method results are internally confirmed by integrating the Clausius‐Clapeyron equation, which also yields our results for the entropy and volume of melting. We find the eutectic composition on the MgSiO3‐CaSiO3 join to be x Ca = 0.26 at 136 GPa and that metasilicate melt is denser than coexisting silicates., Key Points Calcium silicate perovskite melts at 5600 K at the core mantle boundaryMetasilicate liquids are denser than coexisting crystalline silicates at the core‐mantle boundaryThe Z method allows precise ab initio melting temperature determination

Aim to classify typical hot springs in Guizhou, China and their relevance to health. Assessing geochemical characters of typical hot springs of Guizhou and classifying through hierarchical cluster analysis, an epidemiologic study was conducted to analyze the correlation between hot spring types and health, which showed typical hot springs in Guizhou can be divided into two types, A and B. Type A is rich in fluorine, metasilicic acid, radon components and a large number of essential elements, such as Na, that the human body needs, with trace elements, such as Cr and V, that are essential or possibly essential. Type B is rich in fluorine, metasilicate, strontium components and a large number of essential elements, Ca, Mg, and S, with trace elements, Cu, Mn, Mo, Co, and Ni, that are essential or possibly essential. These hot springs' effects on the health of those bathing in them showed both types were associated with bone and joint diseases. Having bathed in hot springs during the past year was associated with skin symptoms and bone and joint symptoms, and having bathed within the past two weeks was linked to sleep quality and levels of appetite and energy. However, differences do exist between the correlation between the two types and some chronic diseases, with Type A hot springs significantly related to cardiovascular and cerebrovascular diseases and diabetes and Type B to hypertension. This classification of Guizhou's hot springs can guide the future development and use of hot spring physiotherapy.

International audience; Na-LTA zeolite crystals were synthesized via hydrothermal method using aluminum scraps and industrial sodium metasilicate. The obtained hydrogel with molar composition: 3.741 Na2O:Al2O3:1.450 SiO2:175.520 H2O, was aged at room temperature for 14 h and heated at 80 °C for 6 h. The use of aluminum scraps provides well-crystallized cubic Na-LTA zeolites with truncated edges and apexes. When H2O/Al2O3 molar ratio was decreased: 3.741 Na2O:Al2O3:1.450 SiO2:92.50 H2O, there is formation of an intergrowth of FAU/EMT phases contaminated with LTA zeolite after 6 h of crystallization. The prolongation of the crystallization time to 48 h leads to the formation of hydoxysodalite zeolite. On the other hand, with the increase in aging time to 96 h, the crystal sizes of zeolite decrease.

The sulfide capacities of CaO-MgO-Al2O3-SiO2-CrO x slags were measured by gas–slag equilibration method in the temperature range of 1823 K to 1898 K (1550 °C to 1625 °C) to reveal the effect of CrO x on the sulfide capacities of slags. Both higher basicity and temperature enhanced sulfide capacities. The CrO x additions in the range of 0 to 5 mass pct increased the sulfide capacity, but, further increase of CrO x contents to 7 pct was found to lower the sulfide capacity. Utilizing the relationship for estimating the ratio of Cr(II)/Cr(III) put forward by the present authors, the influence of Cr(II) on the sulfide capacities of the slags studied is discussed.

The rapid development of the concrete industry consumes many natural resources and has many negative impacts on the environment. Large numbers of research attempts are focused on finding alternatives to cement and sand for use in concrete mixes to improve the sustainability of concrete. Wollastonite microfibers comprise a calcium metasilicate minerals with a wide range of sources and can be used as cement substitutes in cementitious composites, which has attracted worldwide attention in recent years. This paper presents the state-of-the-art research on the properties of cementitious composites containing wollastonite microfibers as partial cement replacement from the following aspects: setting time, workability, mechanical properties, shrinkage, durability, microstructural properties, environmental and economic analysis, and future prospects. The literature review confirms the feasibility of using wollastonite microfiber as a partial substitute for cement in cementitious composites, but this research still needs to be further studied and discussed.

The formation of metastable phases is a relevant, challenging and yet underexplored subject in glass crystallization. In this work, we examined the isothermal crystallization of PbO.SiO2 lead metasilicate glass by using in-situ Raman spectroscopy. We provide evidence for the evolution process from the glass to alamosite, the stable crystalline phase, which is intermediated by two distinct metastable phases at different temperatures. At 550 °C the crystallization pathway proceeded from the low PbSiO3 to alamosite, whereas at 600 °C the crystalline phase evolved from the hexagonal PbSiO3 to alamosite. We found no interconversion between these two metastable phases, indicating that both can precipitate prior to alamosite stabilization. These findings demystify the alleged complexity of the crystallization process of lead metasilicate glass, raised in the literature, whose data are critically analyzed and discussed herein.

Effect of TiO2 addition in Cs containing Sodium-borosilicate glasses is studied using Raman and infrared spectroscopic techniques. As revealed from infrared and Raman studies, TiO2 does not form segregated phase, but instead enters into the borosilicate network. It is further observed that TiO2 addition results in modifications of the borate and silicate structural units by transforming into tetraborates and metasilicate structural units. These structural modifications are responsible for Cs immobilization, leach rate and chemical durability of these glasses.

Nucleation of crystals in sodium-calcium-silicate glasses of the quasi-binary metasilicate section CaO · SiO2-Na2O · SiO2 has been investigated by the development method. The maximal stationary rate of crystal nucleation in the composition range Na2O · 2CaO · 3SiO2-Na2O · CaO · 2SiO2 increases substantially with the increase of the sodium oxide content. It was assumed that in this range, along with nucleation of crystals of solid solutions based on Na2O · 2CaO · 3SiO2, nucleation of crystals 2Na2O · CaO · 3SiO2 could occur as well. Nucleation of crystals of the above two phases in glass of the composition 28.4Na2O · 21.2CaO · 50.4SiO2 (mol %) from the middle of the range Na2O · CaO · 2SiO2-2Na2O · CaO · 3SiO2 has been studied.

Has been done a research about synthesis metasilicate gel from rice husk and its application as medium of growth single crystal. synthesis This research was carried out in several stage namely sample preparation, metasilicate gel synthesis, crystal CaTT synthesis, and metasilicate gel characterization. Rice husk ash that used content SiO2 of 98.45 %, it was potential to be a sodium silicate filtrate. Filtrate of sodium silicate was reacted with tartrat acid (C4H6O6) and produce metasilicate gel with pH 5,00; 5,25; 5,50; 5,75 and 6,00. The supernatant of calcium chloride (CaCl2) diffuse into the gel and formed the clear white crystal CaTT as much as 0,2659 g at the optimum pH 5,25. Analysis of functional groups of metasilicate gel by FTIR provides the specific absorption of –OH group at 3400.05 cm-1 and 920.05 cm-1, C=O group at 1622.13 cm-1 and C-O group at 1346.31 cm-1, and the Si-O-Si group at 1064.71 cm-1. Characterization of gel metasilicate by XRD indicated that metasilicate gel produced formed on Na2C4H4O6.2H2O, compound of SiO2 and C-Grafit. Based on the analysis of functional groups by FTIR and characterization by XRD, it was concluded that the rice husk was potentially to be a sources of metasilicate gel as medium to grow single crystal of CaTT.

The selective adsorption of metasilicate species by N-methyl D-glucamine functional groups in Amberlite IRA 743 resin was observed, which is clarified as the formation of sugar-metasilicate complexes and possible physical adsorptions. The existence of metasilicate matrices causes obvious discrepancies in the δ11B values of silicate materials. It opens the possibility for exploring relevant procedures for the separation/purification of silicon from geological samples.

The technology that silicic acid was pressurized under high temperature in order to dehydrate and transform was investigated in the paper. The effects, such as the ratio of liquid to solid, pressure, temperature, and reaction time on the dehydration rate and volume shrinkage rate, were researched. The experimental results show that the dehydration rate of silicic acid is up to 41.20 %, accompanying with the volume shrinkage rate of 40.37 % after silicic acid is pressurized under high temperature in the high-pressure kettle. The results of silicic acid tested by SEM indicate that the metasilicate acid molecules and water molecules are closely arranged, and there are almost no gaps before pressure reaction. There are many gaps accompanying with formatting lamellar structure after pressure reaction. The experimental results indicate the effect that silicic acid is dehydrated and transformation is obvious under high temperature and pressure.

The removal of arsenic in micro-polluted water by enhanced coagulation with Poly Ferric Metasilicate (PFSS) was studied. The effects of dosage of PFSS , the dosage of oxidant and oxidize time on the removal efficiency of arsenic were discussed. Under the conditions of dosage of PFSS 0.065mmol/L, the residual concentration of arsenic in post-treated water was lower than 0.01 mg/L for raw water with initial concentration of arsenic 0.1 mg/L.

The potted chrysanthemum is one of the main flowers produced in protected cultivation. Silicon has promoted improvements both in quantitative and qualitative aspects when supplied to some ornamental species produced in these conditions. We evaluated the response of chrysanthemum cultivars grown in pots to the application of silicon. The experiment was conducted in a greenhouse of the Universidade Federal de Viçosa, Minas Gerais state, Brazil. Treatments were arranged in a 3x2 factorial scheme (three cultivars of chrysanthemum: Coral Charm, White Reagan and Indianapolis and two doses of silicon: 0 and 800 mg kg-1) with six replications, in an entirely randomized design. We evaluated the diameter of the flower buds and stems; length of the flower stems; height of the plants; dry matter production of roots, leaves, stems, inflorescence and shoots; total number of inflorescences; diameter of the most fully open inflorescences; Si content in the leaf tissue; and flowering cycle and shelf life. The White Reagan cultivar produced the greatest number of inflorescences (29.17) per pot and proved to be more precocious (85.83 days). There was no negative interaction between Si, Ca and K and no effect of silicon was shown on the production and shelf life of the chrysanthemum. There was an increase in the content of this element in the leaves with the application of potassium metasilicate.O crisântemo de vaso é uma das principais flores produzidas em ambiente protegido. O silício tem promovido melhorias tanto no aspecto quantitativo quanto no qualitativo quando fornecido a algumas espécies ornamentais produzidas nestas condições. Assim, o objetivo desse trabalho foi avaliar a resposta à aplicação de silício de três cultivares de crisântemo cultivadas em vaso. O experimento foi conduzido em casa de vegetação da Universidade Federal de Viçosa. Os tratamentos foram dispostos em esquema fatorial 3x2 (três cultivares de crisântemo: Coral Charm, White Reagan e Indianápolis e duas doses de silício aplicadas no substrato: 0 e 800 mg kg-1) com seis repetições, em delineamento inteiramente casualizado. Foram avaliados o diâmetro dos botões e das hastes florais; comprimento das hastes florais; altura da planta; produção de matéria seca de raízes, folhas, caule, inflorescências e parte aérea; número total de inflorescências; diâmetro da inflorescência mais aberta; teor de Si nos tecidos foliares; ciclo e longevidade floral. A cultivar White Reagan produziu o maior número de inflorescências (29,17) por vaso e mostrou ser mais precoce (85,83 dias). Não houve interação negativa entre Si, Ca e K e não foi constatado efeito do silício na produção e na longevidade das inflorescências de crisântemo. Houve aumento nos teores deste elemento nas folhas com a aplicação do metasilicato de potássio.

objects of the research are Kazakhstan’s Turgay clay, studied of method for alumina and potassium metasilicate obtaining from Turgay sub-standard aluminum raw materials. Concluded that optimal conditions for the process of Turgay clay: reaction temperature 100°C, original solution K2O concentration to 300 g/dm3, reaction time 120 min, liquid-solid ratio of 3:1; optimized the conditions of digestion alumina concentrate: original Na2O solution concentration of 400 g/dm3, temperature 280°C, molar ratio CaO : SiO2 = 1. Recovery is 99.6 % of alumina digestion under this condition; crystallized solid phase components as Na2O·Al2O3·6H2O sodium hydroaluminate crystals. Extracted of alumina from solution of sodium hydroaluminate

Crystals of a new polymorphic modification of monobasic sodium tartrate monohydrate NaHC4H4O6 · H2O have been grown in a metasilicate gel. Their atomic structure is solved by X-ray diffraction.

The source of metasilicate in mineral water of Jingyu County. located in Changbai Mountains of northeastern China, was analysed through two groups of water-rock interaction experiments. One is a hydrolysis immersion experiment using basalt and the other is an immersion experiment utilizing a mixture of soil, scoria, and clastic basalt under the same conditions. Results indicate that the metasilicate in mineral water is mainly derived from the hydrolysis of silicates and silica in the basalt, scoria, and soil. In the first immersion experiment, the release of metasilicate is linear, with dissolved metasilicate increasing continuously through time at a stable release rate of about 0.01 mg/(kg·day). The second experiment indicates that the contribution of soil and scoria to metasilicate in mineral water is higher than that of clastic basalt under the same conditions.

These days, most celebrities--young and old--have their hair highlighted. That is why it is not surprising that even the youth have their hair highlighted as they emulate their favorite actors, unaware of the harmful consequences of this unsafe procedure. Hair highlighting involves decolorizing melanin pigments of select hair strands through an oxidation reaction under alkaline conditions by the active ingredients of the highlighting mixture--hydrogen peroxide, persulfates, and metasilicate. Hydrogen peroxide and the persulfates are flammable, necessitating that regulatory bodies (namely, the U.S. Food and Drug Administration [FDA] and the Cosmetic Ingredient Review [CIR] Expert Panel, the European Union's (EU), European Economic Community [EEC] directives, the Australian government's National Industrial Chemicals Notification and Assessment Scheme [NICNAS], and the Association of Southeast Asian Nations [ASEAN]) to regulate the permissible amounts of these chemicals in hair highlighting products.To review published case reports of resulting in severe acute irritant dermatitis ("burns") of the scalp caused by hair highlighting, to explain why these scalp burns happen, to identify preventive measures to avoid such occurrences, and to discuss the implications for society.We searched medical and scientific search engines and used keywords such as hair highlights, scalp burn, and other related terms..Six articles were obtained, yielding 8 reported cases (2 of the 6 articles had 2 cases each) of hair highlighting resulting in scalp burns; these 8 cases were reviewed and analyzed. Five of the 8 patients belonged to the pediatric age group.The causes of scalp burn were classified into 2 categories: chemical (caustic nature of the highlighting mixture, spillage of the hot mixture, toxic reaction to the dyes) and thermal (by contact of the scalp with overheated aluminum foil and by the blow dryer). The 5 pediatric patients in the group unnecessarily suffered pain and embarrassment caused by this procedure, as well as the risk of developing malignancy in the future.Hairstylists play a large role in the occurrence of scalp burns. Thus, they need to be careful and knowledgeable of the caustic nature of the highlighting mixture and the potential harm these chemicals may cause. The authors strongly propose that the relevant regulatory bodies review the permissible levels of the caustic chemicals, and that this unsafe procedure should be performed only on adults.

Na-LTA, Na-X and HS zeolites have been prepared from Tunisian sand and aluminum scraps. The alkaline attack of the sand leads to the metasilicate sol used as a source of silica. The aluminum source was prepared by dissolving aluminum in NaOH solution. The influence of several physicochemical parameters such as temperature, crystallization time and the alkalinity of the reaction mixture on the nature and the purity of the obtained products have been investigated.

Silication of potato starch was performed by microwave irradiation and convectional heating of starch with sodium metasilicate. The study has shown that microwaves offered more selective silication than convectional heating. Depending on the dose of metasilicate products of either monoesterification or crosslinking esterification were formed. Increase in the amount of the silicating agent favoured crosslinking of starch. In the case of microwave irradiation, the C–O–SiO 2 Na moieties were formed, whereas the convectional heating generated the C–O–Si–O–Si–O–C crosslinks.

A sol–gel modified method for obtention of gray and pink ceramic pigments in zircon matrix is discussed in this work. The chromophoric powders were firstly well dispersed in the solution containing zirconium and metasilicate ions before gelation and the product ceramic pigments obtained by calcining the xerogel with mineralizers. The zircon was well crystallized at 1,050 °C with the yield about 97%. The mineralization mechanism of the zircon formation was also discussed.

The cordierite was synthesized by two unconventional methods: 1) the method which uses hydrosilicate precursors and 2) the method which uses organic precursors. Comparison of these synthesis methods with the classical one is the main subject of the presented paper. The influence of Li2O on the cordierite phase formation was investigated too. The results have suggested that the method which uses hydrosilicate precursors provides the SiO2 linkage as magnesium metasilicate, but is not adequate for the cordierite synthesis. Only in the presence of Li2O considerably amount of the ?-cordierite modification was formed, confirming the mineralizing effect of this oxide. In addition, the results have clearly demonstrated that the method which uses organic precursors is suitable for the cordierite synthesis. Thus, even without mineralizer it can be used for the preparation of the almost pure ?-cordierite at 1200?C. Because of that this method was used to obtain pigments with cordierite structure, in which Al3+ was partially substituted with Cr3+ (pink pale colour), and Mg2+ was partially substituted with Co2+ (blue colour).

The specific features of the dynamics of oxygen ions in Ме2O · SiO2 (Ме = Li, Na, K, Cs) and Na2O·ZnO·P2O5 melts at а temperature of 2000 K were investigated bу the molecular dynamics method. It is demonstrated that, as in the systems studied earlier, the formation of defect complexes is а necessary condition fог an oxygen diffusion event to bе successful. The scenarios of generating defect соmplexes аrе described, and the lifetimes of these complexes are calculated. The structure of the defect complexes is determined. It is shown that two-membered rings, free and threefold-coordinated oxygen ions сап also bе involved in the formation of defect complexes.

aB s T rac T In the present study, we summarize indications for the existence of kinked post-perovskite structures in the MAS system. X-ray diffraction data and Raman spectra of aluminous magnesium metasilicate post-perovskite are inconsistent with the CaIrO3 structure. Instead the observations are consistent with structures intermediate between the perovskite and the CaIrO3 structure. Ab initio calculations show that the enthalpies of the kinked structures are slightly higher than the CaIrO3 structure at 0 K. Finite temperature, minor element chemistry, kinetics of phase transformation, and actual stress regime are plausible reasons for the observed differences between the present and the previously reported postperovskite phases.

The coordination environment around Ti4+ in the photoluminescent compound BaTiSi2O7 and in BaTiSi4O11 was investigated with X-ray absorption near-edge structure spectroscopy and micro-Raman spectroscopy. The presence of VTi in TiO5 pyramidal units with one short Ti–O bond involving the apical oxygen was detected in both compounds. Interpretation of the vibrational signal from the silicate framework suggested that BaTiSi4O11 is a metasilicate containing building units of SiO4 tetrahedra, which are larger than in other barium titanosilicates. These results confirmed the same structural environment of Ti4+ as recently disclosed by structure refinement of BaTiSi2O7 and provided new insights into the unknown structure of BaTiSi4O11 in the light of the study of its physical properties as potential functional material.

In this work, drilling fluids with 135 400 mg kg−1 of total petroleum hydrocarbons (TPH) were washed with six different surfactants (the non-ionic Emulgin 600, Emulgin 1000, Brij 35 and Tween 80, ionic SDS, and zwitterionic Polafix CAPB) and their mixtures. Due to the high Ca content in the samples, three different approaches were employed when washing with SDS, because of its ionic character: a) using mixtures of surfactants, b) addition of NaCl, and c) addition of a Ca sequestrant, i. e., sodium metasilicate. Drilling fluids were washed; TPH, electric conductivity (EC, as an indirect measurement of salinity), and pH values were measured before and after the washing process. Surface tension of the clean and spent washing solutions (surfactant or surfactants mixture, with or without salts) was measured. TPH removals as high as 75% were achieved using SDS + sodium metasilicate. EC values diminished 75% with the washing process, but for the experiments in which salts were added, increments in electric conductivity of up to 367% were observed. Regarding the pH changes, initial sample pH value was 7.77, and in most cases this value was reduced, except for some of the cases where salt was added. Surfactant solution's surface tension changes (before and after the washing process) correlated fairly with TPH removals.

We determined the structural changes in CaSiO 3 and CaMgSi 2 O 6 glasses recovered from high pressure and temperature conditions (up to 7.5 GPa and 500 °C) using X-ray diffraction, Raman, infrared and X-ray emission spectroscopy. Densities of the metasilicate glasses increase with applied pressure at high temperature; CaMgSi 2 O 6 glass is more compressed than CaSiO 3 glass when recovered from 7.5 GPa and 500 °C. We propose a mechanism for densification of these glasses, that is mainly due to the compaction in medium-range scale (i.e. decrease in cluster size of SiO 4 anionic units with Ca, Mg polyhedra). Reduction of Si–O–Si bond angle is very small in the recovered CaSiO 3 and CaMgSi 2 O 6 glasses, as previously suggested.

The steatite ceramics are mostly used in electrotechnics. Although distinguished by their mechanical and electrical properties they are unstable. The desirable, high temperature protoenstatite phase inverses into magnesium metasilicate low-temperature form—clinoenstatite, even upon standing. In this work the steatite polymorphism was studied in relation with steatite mechanical properties and microstructure. It was find out that the stabilization of protoenstatite in steatite body is achievable by the development of small crystals, yet it is still not resistant to action of water what put in question its potential application as dental material.

The enthalpy of formation of the metasilicate hydrate Na 2 SiO 3 .5H 2 O referred to the anhydrous silicate and water was determined by solution calorimetry at 298.2 K : −59.3 ± 3.0 kJ / mol . Some considerations on the thermochemistry of hydrates are proposed.

The β → α phase transition, melting, crystallization, and vitrification of calcium metasilicate were studied by high-temperature Raman scattering spectroscopy. The results demonstrate that, in the course of melting, the [Si3O9] metasilicate rings, which form the structural basis of the α phase, transform mainly into [SiO3]∞ anions. The structural similarity or dissimilarity of the CaO · SiO2 melt to crystalline phases is shown to have a crucial effect on its crystallization/vitrification behavior.

A coupled coagulation and photo-Fenton treatment has been applied to an industrial wastewater coming from the use of an alkaline cleaning solution. The real wastewater contained anionic and nonionic surfactants, tripolyphosphate, soda ash, metasilicate and oil residuals. After the proposed treatment, the wastewater fulfilled Argentine regulations for sewage discharge (10 mg/L total phosphorus, 0.7 g/L COD). First, phosphorous was eliminated by coagulation with FeSO4 and then COD was removed by a photo-Fenton treatment. The dark Fenton treatment was also effective to remove COD but it did not allow achieving the discharge regulations, and the application of light was needed. The photo-Fenton treatment showed to be very effective to treat this particular wastewater in 2 h and with a high efficiency of H2O2 consumption. The experiments performed at bench scale allowed to propose a scheme for the in situ treatment of the alkaline cleaning solution wastewater, which could be extended to other similar wastewaters. Fil: Senn, Alejandro Marcelo. Comisión Nacional de Energía Atómica; Argentina. Comisión Nacional de Energía Atómica; Argentina Fil: Russo, Yamila M.. Universidad Tecnológica Nacional; Argentina Fil: Litter, Marta Irene. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental; Argentina

Silicas were obtained using a precipitation technique from metasilicate solution with an acidic agent. The precipitation process includes formation of silica particles and their aggregation. Alcohol solutions were used in the production process of the highly dispersed silicas, resulting in a partial blocking of the silica surface silanol groups and, thus, in a decreased hydrophilicity of silica. The precipitated silicas were subjected to physicochemical, structural, and microscopic evaluation, and their surface properties were examined. The effect of alcohols on the silica particle size distributions and on hydrophobicity of silica surface was tested.

ゲル内結晶成長法を用いて多種類の形態の亜硫酸ストロンチウム結晶を合成し, 結晶成長過程の観察から, 多種類の形態は結晶の成長過程における形態変化によって得られることを明らかにした. 結晶成長開始の初期段階では, すべての条件で針状結晶の集合体である球晶の亜硫酸ストロンチウムが生成したが, 球晶が成長するに伴い, 球晶の双晶を経て板状結晶のだ円球状集合体に変化する過程と, 双晶の中央部から紡錘状の単結晶に変化する過程の二系統の形態変化が起こることを確認した. さらに, 結晶形態変化が起こる条件をゲル内のイオソ積 ( [Sr2+] [SO32-] )から解明した. すなわち, [Sr2+] [SO32-] =70.5×10-6-8.06×10-6mol2dm-6の条件では球晶のままであったが, [Sr2+] [SO32-] =5.72×10-6-0.87×10-6mol2dm-6では球晶が双晶を経てだ円球状集合体に変化した. [Sr2+] [SO32-] =0.63×10-6-0.32×10-6mol2dm-6の条件下では紡錘状単結晶に形態変化することが確かめられ, ゲル内のイオン積が結晶形態変化の要因であることを明らかにした.

Anomalous birefringent glasses were obtained by thermomechanical treatment of quenched or pre-nucleated Li2O · 2SiO2 (LS2) and Na2O · 2CaO · 3SiO2 (NC2S3) glasses. Cylindrical glass samples were compressed in the viscoelastic temperature range above Tg under various loads and cooled under these loads slowly enough to avoid thermal stresses. In contrast to this, normal stress optical behavior of these glasses is observed at room temperature. The frozen-in anomalous birefringence may be correlated to a distribution birefringence, indicating order phenomena in the stoichiometric LS2 and NC2S3 glass melts. Results are compared with multicomponent di- and metasilicate glasses which show normal frozen-in birefringence. Microstructural heterogeneities are discussed to affect volume nucleation in the LS2 and NC2S3 glass melts.

Glass fibers of alkali disilicate composition were prepared under defined and systematically varied nozzle drawing conditions. Optical birefringence, ‘frozen-in’ apparent stress optical constant, density changes relative to the bulk glass and the expansion and shrinking behaviour during heating and annealing were examined. The optical properties indicate a marked cross-linking of the chain structure. The shrinking behaviour of the fibers shows an anomaly which seems to be typical of alkali disilicate glass fibers. Results add to earlier investigations on silicate glass fibers between the metasilicate range and silica glass fibers along the series xSiO2(1 − x)R2O. The structural alterations due to the variation of the ratio network former/network modifier are discussed over the large range of the nearly ideal three-dimensionally connected network structure of the silica glass fibers and of the nearly ideal one-dimensionally connected chain-ring-like structure of the meta-silicate glass fibers.

The Na2O-Cs2O-SiO2 system has been investigated by means of a new differential thermal analysis apparatus. Two compounds have been observed for the first time in the metasilicate and disilicate joins. The CsNaSi2O5 disilicate melts congruently at 1217 K and the peritectic fusion of the CsNaSiO3 metasilicate occurs at 1120 K.

Single crystals of Sr2(VO)2Si4O12 could be obtained by high-pressure high-temperature reaction of a SrSiO3/SiO2/V2O5 mixture in a modified Belt-type apparatus. The green crystals are orthorhombic, space group Cmcm, with a = 5.3139(3), b = 14.6281(7), c = 7.0329(4) Å and Z = 2. The structure comprises vierer single chains of SiO4 tetrahedra, the resulting Si4O12 units being connected by VO5 square pyramids. There is one short distance (V - O = 1.61 (1) Å) within the square pyramid, giving definite evidence to a (VO)2+ group with a V = O double bond. The crystal structure of microcrystalline Sr2(TiO)2Si4O12, obtained by high-pressure hightemperature reaction of a SrSiO3/SiO2/TiO2 mixture, was refined by the Rietveld technique. The compound (Cmcm, a = 5.3530(2), b = 14.4864(7), c = 7.0817(3) Å, Z = 2) is isostructural with the vanadium compound.