The chemistry of ethyl silicate binders in refractory technology

The chemistry of the processes involved when an alkyl silicate such as ethyl silicate acts as a binder in refractory technology is described. The gel forming process involving catalysed hydrolysis and condensation of ethyl silicate and tetra-alkyl silicates has been studied using amine catalysts. Thermal studies of gels obtained from technical ethyl silicate and of gels obtained from technical ethyl silicate incorporated in refractory materials, together with infrared spectroscopy studies of gels obtained from technical ethyl silicate, suggest the nature of the degradation products, and the weight-loss patterns observed support the proposed mechanisms.     

Intumescent silicate-based materials: Mechanism of swelling in contact with fire

An intumescnt material has been developed, based on alkali silicates, which can be used in fire protection in the form of sheets or boards which can be joined to various materials, ranging from wood and wood products to metal. The swelling of the material on heating to over 100°C or on contact with a flame is due to and endothermic process and is associated with the emission of water vapour. The solid foam formed is rigid and consists of hydrated silica. The phenomena observed during the preparation of the boards and their behaviour on heating can be explained in terms of silicate chemistry.     

Green synthesis of calcium silicate bioceramic powders

Calcium silicates have proven to be potential candidates for biomedical applications because of their osteogenic properties. Sol–gel methods are typically used for the preparation of calcium silicate powders. However, in the sol–gel route, an acid or base and ethanol are used to catalyze the precursors. From the perspective of green chemistry, it is better to avoid the use of organic solvents. The objective of this study was to prepare calcium silicate powders using a green synthesis route (hydrothermal method) without organic solvents. The powders were also prepared via the sol–gel process using tetraethoxysilane (TEOS) and calcium nitrate as the raw materials for the purpose of comparison. The powders were sintered at temperatures ranging from 600 to 1000 °C after the application of both methods. To understand the feasibility of using the resulting materials in medical applications for bone repair, the powders were mixed with water to form cements. The results indicated that the powder composition was not significantly affected by the different techniques but was dependent on the Ca:Si ratio of the precursors and on the sintering temperature. The different techniques produced no differences in powder morphology. In addition, the setting times of the powder-derived cements were found to be independent of the sintering temperature and synthesis technique, but it was affected by the Ca:Si ratio of the precursors. The mechanical strength of the cements was similar. These encouraging results suggest that the hydrothermal method is a potentially beneficial alternative to the sol–gel route for the production of calcium silicate powders.     

Preparation and characterization of precipitated zinc silicates

The study aimed to obtain highly dispersed particles of zinc silicate, a potential filler of polymers or a paint pigment, by precipitation from solutions of sodium metasilicate and of zinc salts. The technique of silicate precipitation was worked out, and the conditions causing precipitation were optimized. The temperature, sodium metasilicate solution flow rate and concentration of zinc salts were selected so as to obtain silicates of the lowest possible bulk density, and which had low water‐absorbing capacity and high paraffin oil‐absorbing capacity. In the study, the effects of precipitation parameters were examined on the principal physicochemical properties of the silicates, the structure and uniform character of silicate particles, particle size distribution, and the surface morphology. Particular attention was devoted to the particle size distribution and the tendency to form primary agglomerates (aggregates) and secondary agglomerates, using dynamic light scattering (DLS). Studies were undertaken to develop a technique which could prevent formation of silicate particle agglomerates. With this aim, the silicates' surface was modified either during their precipitation or by the so‐called dry technique. For the modification, silane coupling agents were applied. The extent of silicate surface hydrophobicity was examined by estimation of the enthalpies of immersion of the modified silicate surface. The silicates obtained were tested as fillers of rubber mixtures (in butadiene–styrene rubber). © 2003 Society of Chemical Industry     

硅酸盐色谱分离中性氨基酸性能研究

将硅酸钠与硫酸铜或硫酸锌按等体积混合 ,制得新型无机离子交换剂硅酸铜、硅酸锌 ,分别用其作为色谱载体对中性氨基酸 (甘氨酸 ,丙氨酸 )进行分离 ,与强酸性阳离子交换树脂 0 0 1× 7的色谱行为作了比较。结果表明 ,合成的硅酸盐具有较好的分离性能。通过不同载体分离中性氨基酸 (甘氨酸 ,丙氨酸 )的流出体积的比较 ,硅酸铜的流出体积大于硅酸锌 ,硅酸锌的流出体积大于 0 0 1× 7。结果显示 ,硅酸铜比硅酸锌更适合于分离中性氨基酸 ,具有最好的分离特性     

Synthesis and characterization of manganese oxide-doped dicalcium silicates obtained from rice hull ash

This work describes the synthesis and hydration behavior of dicalcium silicates doped with manganese. The syntheses were performed using silica obtained from rice hull ash. The solids (SiO₂, CaO and MnO) were weighed in stoichiometric proportions to prepare silicates having a ratio (Ca + Mn)/Si = 2. Insertion of manganese varied from 1 to 10% (mol). Solids were grounded and water was added rendering aqueous suspensions. The suspensions were sonicated for 60 min in an ultrasonic bath. After drying, the resulting solids were grounded and burned at 800 °C. The preparation of calcium silicates containing up to 10% of manganese oxide was observed.Hydration degree of a dicalcium silicate and calcium silicate containing 5% of manganese was determined by thermal analysis. Both materials present similar behavior. Hydration degree reaches approximately 70% after 60 days.     

适合压载舱涂层配套的船用车间底漆的研制

介绍了车间底漆的制备、性能的测试.讨论了硅酸乙酯在不同当量的酸性和碱性条件下的水解情况,碱性条件下反应剧烈,不易控制,且制得的水解液贮存期短;不同型号的硅酸乙酯经水解后,硅羟基的含量不同,导致交联密度也不同,使车间底漆涂层与钢材间的附着力产生较大的差异;分析了不同锌含量对车间底漆性能及与压载舱主涂层配套性的影响.     

Effect of calcium silicate sources on geopolymerisation

Seven different calcium silicate materials were used to investigate the role of calcium in geopolymerisation. At low alkalinity, the compressive strength of matrices prepared with predominantly amorphous calcium silicates (blast furnace slag) or containing crystalline phases specifically manufactured for reactivity (cement) is much higher than when the calcium is supplied as crystalline silicate minerals. The compressive strength of matrices containing natural (crystalline) calcium silicates improves with increasing alkalinity, however the opposite trend is observed in matrices synthesised with processed calcium silicate sources. The difference in compressive strength between matrices synthesised using different calcium silicate sources is significantly reduced at high alkalinity. An insufficient amount of calcium is dissolved from crystalline calcium silicates at relatively low alkalinity to enable formation of calcium silicate hydrate in coexistence with the aluminosilicate geopolymeric gel, and this leads to the poor mechanical properties of such matrices. At high alkalinity, calcium plays a lesser role in affecting the nature of the final binder, as it forms precipitates rather than hydrated gels. Thus, the different calcium silicate sources will not have a major impact on the mechanical properties of these matrices. The effects of different calcium silicates on geopolymerisation are therefore seen to depend most significantly on two factors: the crystallinity of the calcium silicate source, and the alkalinity of the activating solution used.     

Chloride-free biodegradable organic acid hydrolyzed zinc silicate coating

Partially hydrolyzed ethyl silicate has widely been used as a binder to formulate inorganic zinc silicate paint for anticorrosive coating applications. Hydrochloric acid is used most popularly to catalyze the hydrolysis of ethyl silicate. Although different acids have been tried as catalysts for ethyl silicate hydrolysis, no attempt has been made to make stable paints out of those hydrolyzed silicate binders. In this study, environment benign biodegradable organic acids such as oxalic acid, citric acid, lactic acid and acetic acid were used for the hydrolysis of ethyl silicate and compared with the hydrolysis using conventional hydrochloric acid. The hydrolyzed silicate sols were pigmented further with silica powder and evaluated for their stability. Of the various organic acids catalyst used, only oxalic acid catalyzed sol acted as a stable binder system. The pigmented binder was then mixed with metallic zinc to formulate anticorrosive inorganic zinc silicate paint. The resultant coatings were characterized for various physical, surface, mechanical and chemical resistance properties such as drying, hardness, adhesion (cross hatch) and solvent resistance. Corrosion resistance properties were analyzed by means of salt spray, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). The results revealed that the physical, mechanical, chemical and anticorrosive properties of the coating hydrolyzed with hydrochloric acid and oxalic acid are comparable. Thus, a chloride free biodegradable organic acid hydrolyzed inorganic zinc silicate primer is reported and due to its long term stability same also can be scaled up commercially.     

Adaptation of the dynamic mechanical analysis to determine the gel point during the setting of liquid alkali silicates

The gel point is one of the relevant parameters for the characterization of materials that undergo a sol-to-gel-transition during their setting. A test method for its determination could be the Dynamic Mechanical Analysis, currently used in the field of polymer science. For the first time this measuring principle has been adapted to the group of liquid alkali silicates, thus verifying the possibility to describe their setting process. Three analytical methods for the determination of the gel point were studied with regard to their applicability and consistency for a compound alkali silicate system used as chemical hardener.     

1. Physicochemical aspects of the choice of silicon-bearing binders for production of refractories

The principles for selecting a silicon-bearing binder for refractory production are considered. The effect of the heat treatment temperature on the crystallization of SiO₂ gels with various prehistories is considered. It is shown that ethyl silicate binders have an advantage over other silicon-bearing binders that consists in that SiO₂ gel obtained from ethyl silicate éTS-32 can retain the amorphous state upon heating to over 1273 K. Translated from Ogneupory i Tekhnicheskaya Keramika, Nos. 1–2, pp. 8–11, January–February, 1999.     

原材料和制备工艺对硅酸锌陶瓷微波介电性能的影响

为了提高硅酸锌介质陶瓷的性能,研究了添加物、原材料和制备工艺对其微波介电性能的影响。采用固相法、并以去离子水代替乙醇作分散剂制备陶瓷粉料,闭腔法测量其无载Q值和频率温度系数。研究结果表明原材料的粒度、球磨工艺和烧结温度对Q.f值影响大,添加物TiO2不仅调节频率温度系数(τf),而且促进陶瓷烧结。当TiO2(wt%)12%,1240℃烧结时,获得优良的微波介电性能:介电常数(εr)为10.2,Q.f=91640GHz,τf=-5.78ppm/℃。并用该组成的材料制作了中心频率f0=5.4GHz,带宽Δf=96MHz,插损小于1.3dB的两级片式介质带通滤波器,可以用于通信系统。     

Experiences with the method of trimethylsilylation for the study of soluble silicates

It is possible to prepare organic derivatives of silicate groups in which each terminal oxygen is blocked by a trimethylsilyl group. This can provide a route for the preparation of new polymers. It can also provide information about the structure of the original silicate group, provided that this is faithfully reflected in the structure of the derivative. This will be true only if the silicate groups do not undergo any polymerisation, depolymerisation or rearrangement while the derivatives are being formed. The method has previously been successfully applied to a wide variety of silicates; this paper describes, in particular, attempts to apply it to the study of sodium silicates. An assessment is given of the difficulties involved and of the utility of the method for this type of study.     

Study on Industrial Scale Chromatographic Separation Methods of Galactose from Biomass Hydrolysates

Galactose is an aldohexose, which has commercial uses in the pharmaceutical and food industries. Since monomeric galactose is not a freely occurring compound, it must be produced from galactose‐containing hydrolysates. This paper reports the results of experimental studies of the chromatographic separation of galactose in aqueous solutions by ion exchange resins on an industrial scale. Until now, galactose has only been determined from various solutions by liquid chromatography (HPLC) on an analytical scale. Chromatographic separation of galactose from carbohydrate mixtures was studied with strong acid cation exchange resins in Na⁺, Ca²⁺ forms and strong base anion exchange resin in SO₄^2– form. The feed solutions were hydrolysates from three possible galactose sources: lactose, gum arabic and hemicellulose in spent sulfite liquor. The main monosaccharide impurities in these raw materials were glucose, arabinose, and xylose. It was demonstrated that large scale liquid chromatography can be used effectively for galactose separation from complex carbohydrate mixtures such as plant hydrolysates as well as lactose hydrolysate.     

酶法水解和筛选蛋黄蛋白质中的药物前驱型降血压肽

为了筛选鸡蛋蛋黄蛋白质的酶解产物中的药物前驱型降血压肽,将鸡蛋蛋黄蛋白质经超临界CO2-乙醇萃取脱脂和NaOH溶液脱磷处理,用12种蛋白酶在各自适宜的条件下进行酶解,采用HPLC分析各酶解产物对血管紧张素酶(ACE)的抑制活性(IC50),并对IC50较小的6种水解产物进行保温实验,筛选药物前驱型降血压肽。结果显示,12种酶解产物对ACE的IC50值在0.69 mg.mL-1~4.06 mg.mL-1;保温实验显示仅有酶L的酶解产物IC50值明显减小,即由1.19 mg.mL-1降至0.59 mg.mL-1,其他5种酶解产物的IC50值则保持不变或升高,表明酶L的酶解产物中含药物前驱型降血压肽。     

Influence of Silicate Depolymerisation on the Polycondensation Reaction with Hydroxoaluminate in Alkaline Aqueous Solution

The polycondensation reaction between silicate and hydroxoaluminate in alkaline aqueous solution has been experimentally studied. The time required for the solution to transform to a gel was measured to determine the reaction rate. The addition of alkali hydroxide to the silicate solution was found to strongly accelerate the subsequent reaction of silicate with hydroxoaluminate. The results indicate that the acceleration was caused by depolymerisation of the oligosilicates contained in the water glass, which was used as the source of soluble silicates. The course of oligosilicate depolymerisation in aqueous alkaline solution was experimentally observed by measuring the electrical conductivity of the solution.     

Alkaline treatment of clay minerals from the Alhambra Formation: Implications for the conservation of earthen architecture

Clay–water interactions result in damage and loss of earthen architecture. Natural and artificial additives were traditionally added to earth in order to increase its water resistance and mechanical strength. More recently, portland cement, ethyl silicates and synthetic resins have been applied to consolidate earthen structures, however often with limited success. Here, in an effort to design a more effective procedure for the in situ consolidation of earthen architectural remains, the alkaline reaction of clay-rich earth used in the construction of the Alhambra (Spain) was studied. Alhambra Formation clays were treated with diluted Ca(OH)₂, NaOH and KOH solutions. The most sensitive smectite fraction was rapidly destroyed after alkaline treatment. Furthermore, NaOH and KOH treatments resulted in the formation of interstratified illite–smectite, the partial destruction of both expandable and non-expandable clays, and their transformation into poorly-crystalline alkali aluminosilicates and calcium silicate hydrates, the latter two exhibiting cementing properties. These preliminary results suggest that alkaline activation might be efficient in stabilizing earthen architecture, as well as other clay-rich building and ornamental materials by reducing the intracrystalline swelling capacity of smectites, limiting osmotic swelling of both expandable and non-expandable clays, and producing gel-like silicate cements. However, further research and field tests will be necessary to study the effectiveness of the treatment in situ.     

Ionomer cements

The chemistry and properties of the ionomer cements are reviewed. These cements are defined by the acid-base interaction between metal oxides or silicates with aqueous solutions of organic polymeric acids. the cements formed both from ion-leachable aluminosilicates and from zinc oxide are of practical importance and characterised by their ability to bond to active substrates under moist conditions. The polymer solutions used in these formulations tend to gel slowly over a period of several months. This phenomenon can be avoided by partial methylation of the polymer or by the use of a suitable copolymer. The role of the anoins present in the system and those, such as tartrate, added to improve rheological properties, is discussed. The nature of the bonding in these cement gels is considered in terms of ion-binding of polyanions of polyvalent cations. The function of water in the cement and hydrolysis of cations is discused. In the final section the long-term development of surface hardness and compressive strenght is reported. The modulus of elasticity and stress relaxation properties of these cements are compared to those of the brittle dental silicate cement.     

Application of ultrafiltration to the preparation of defined hydrolysates of bovine haemoglobin

Many uses of protein hydrolysates have been developed and applied to areas such as nutritional therapy, culture media, and the isolation of biologically active peptides. All these applications need carefully controlled and characterized hydrolysates. In order to produce such a type of hydrolysate, it is possible to use haemoglobin which is a very well defined and constant protein source. Enzymic hydrolysis of haemoglobin by pepsin was carried out at pilot-plant scale in an ultrafiltration reactor with mineral membranes. The object was to obtain a reproducible, decolorized, salt-free enzymic hydrolysate. Two types of membranes were tested having 10000 dalton (M5 type) and 20000 dalton (M4 type) cut-offs. Little significant difference was observed in the final products when both types of membranes were used. Reproducibility of hydrolysates was verified by amino acid analysis and gel filtration chromatography. The haemoglobin hydrolysates produced contained more than 90% protein and are especially suitable for fine applications.