Rheological and casting properties of two Egyptian clays

Slips from Kalabsha and Malkatta clays, widely used in the Egyptian ceramics industry, were prepared with the aid of an appropriate deflocculant at a constant specific gravity of 1·80—which lies within the practical working range for the slip casting technique. The rheological and casting properties, including plasticity of clay pastes, apparent viscosity and thixotropy of the clay slips, as well as casting rate, water retention, porosity and mechanical strength of their casts, were studied.The two clays behave in a quite different manner, reflecting the marked variation in their nature. Kalabsha clay slip has the minimum apparent viscosity with moderate thixotropy in the presence of 0·8% deflocculant addition, while Malkatta clay slip needs twice as much deflocculant to attain maximum fluidity, which is accompanied by a little higher thixotropic structure. Kalabsha clay slip casts faster and leads to cast having lower water retention, shrinkage, modulus of rupture and bulk density and of higher apparent porosity than that of Malkatta slip. In formulating ceramic bodies processed by the slip casting method, a blend of the two clays must be utilized in order to get a mixture having the proper flow properties and the best casting qualities. For thin-walled articles, the content of Kalabsha clay should be kept lower than that of Malkatta clay; the reverse holds for heavy-section casts.     

有机阳离子聚合电解质对蒙脱石粘土(膨润土)泥浆稀释机理的研究

本文利用三种有机聚合电解质、三聚磷酸钠和六偏磷酸钠等添加剂对蒙脱石粘土(膨润土)泥浆进行了稀释试验,结果表明有机聚合电解质1#(NCMC)有很好的稀释效果.通过红外光谱、X-衍射和电子显微镜对有机聚合电解质、蒙脱石粘土泥浆以及加有聚合电解质的蒙脱石粘土泥浆进行分析,得出了NCMC的化学结构式,并确定它为有机阳离子聚合电解质.从而提出了这种阳离子聚合电解质对蒙脱石粘土泥浆的稀释机理和作用模型.     

A QUICK METHOD OF DETERMINING THE WATER CONTENT OF CLAYS1

The water content of clay is determined by taking a representative sample of the material, weighing out 2 kg. of it and adding 4 kg. of water. The sample is blunged quickly. A 250-cc. flask is filled with the resulting slip and weighed. The amount of dry clay is determined from the relation: D= (P−250)(G/G−1) where D= weight of dry clay P= weight of slip G= specific gravity of dry clay. From this the per cent water in the moist clay is readily computed.     

AN APPARATUS FOR THE DETERMINATION OF ADSORBED AIR1

Some possible ceramic applications of the Toepler mercury pump as employed in determination of gases in various materials are discussed. The procedure followed in measuring the gases given off by a clay slip at reduced pressures is described. It was found that 4.65% of gases by volume are removed from a sample of clay slip by reducing the pressure on the sample to boiling (25 mm.). An additional 0.18% of gases was cvolved between the boiling pressure and 1.8 mm. at which pressure the sample was dry.     

Zn in Athenian Black Gloss Ceramic Slips: A Trace Element Marker for Fabrication Technology

The black‐colored pottery slips produced in Athens from the 6th to 4th centuries B.C., had a consistent composition achieved through processing and refinement of raw clay. Little direct evidence has been established as to what were these refinement methods. To better understand how the slip material was prepared, the major and trace elemental compositions of 19 slips from different ceramic vessels and their corresponding bodies of Athenian red‐figure and black‐figure vases were determined using laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS). Notably higher Zn concentrations were found in the slips (271–1959 ppm) than in their corresponding body ceramics (<361 ppm). The Zn concentrations in the slips were also found to be above the natural background for typical clay (between 10 and 300 ppm) suggesting an unintentional anthropogenic enrichment of this metal. Based on the abnormally high Zn content of the slip, it is speculated that the clay was treated using vitriol (concentrated acid mine runoff which is rich in Zn), to induce flocculation and remove carbonate mineral phases from the raw material that, if present, would prevent the slip from vitrifying. This same signature of elevated levels of Zn with a corresponding Ce anomaly is also observed for black glosses produced in Corinthian and Etrurian (Italy) workshops indicating that these trace element signatures were imparted to the material by means of shared methods of manufacturing instead of being indicative of a single unique source for this material.     

Flow Properties of Majolica Slip with a Thinning Additive Based on Sodium Polyacrylate

The effect of a new thinning agent, namely 40% sodium polyacrylate (SPA), on flow properties of majolica slip and the effect of hardness of water on changes in suspension moisture are considered. The use of 40% SPA makes it possible to reduce its content in slip by nearly half, compared to sodium silicate solution, to improve the slip flow properties, and to insignificantly decrease its moisture. An optimum content of 40% SPA in thinning a polymineral clay slip from the Gzhel'skoe deposit and a majolica mixture is determined.     

球磨转速与球磨产品颗粒分布的关系

本文在实验室及工业生产的不同条件下，采用不同的固定转速及多种规律的变速球磨含瘠性料较多的釉面砖坯、釉料与含软质料较多的彩釉砖坯料，对其结果进行分析，研究，得出了固定转速从理论转速比１为界，≥１及＜１的球磨和不同规律的变速球磨等与球磨产品颗粒分布的关系及其特点，为寻求提高球磨产品颗粒分布质量的措施提供了依据。     

蒙脱石粘土（膨润土）及含蒙脱石瓷砂泥浆的稀释及稀释机理的研究

使用传统稀释剂和聚合物电解质对蒙脱石和含蒙脱石瓷砂泥浆进行稀释试验。结果表明,传统稀释剂对蒙脱石泥浆不能起稀释作用,但只对含蒙脱石的瓷砂泥浆有一定的稀释作用,其中六偏磷酸钠效果很好。而有机阳离子聚合电解质对二者都有很好的稀释作用。并通过ζ电位、红外光谱和透射电镜等测试,探讨了有机阳离子聚合电解质对蒙脱石的稀释机理。     

SEDIMENTATION AS A MEANS OF CLASSIFYING EXTREMELY FINE CLAY PARTICLES1

A method is described for determining the rate of sedimentation of clays by measuring the suspended weights of a glass plummet suspended in a clay slip at different intervals of time. The specific gravity of the slip remaining in suspension may be calculated as follows: S = P_d-P_s/P_d-P_w where S is specific gravity of slip, P_d is dry weight of a plummet in grams, P_w, is suspended weights of plummet in distilled water and P_s, is suspended weight of plummet in clay slip. The average weight of clay per cc. is calculated as follows: C_w= D(S-d)/D-d, where C_w, is average weight of clay per cc., D is the specific gravity of clip and D is the specific gravity of water. It is impractical to separate by elutriation, clay particles smaller than 0.003 mm. which constitute 50–100% of many clays. It is possible to classify particles as small as 0.0001 mm. by the plummet sedimentation method and the results are more uniform than those obtained by elutriation.     

THE CASTING OF CLAY WARE—A RÉSUMÉ*

Considerable difficulty has been encountered in developing methods suitable for determining the properties of a casting slip that in turn define the casting quality of the slip. A survey of the literature is made, especially that dealing with the colloidal phenomena of clay suspensions, which might be of assistance in solving some of the problems encountered in the use of the casting process. The term, casting quality of slip, is detined and the factors which influence this property are considered in detail. Control methods proposed by various investigators are discussed critically. A new method of slip control is suggested. The sources and remedies of some troubles encountered in the casting process are discussed.     

Use of mottled clay in the manufacture of grog refractories based on Vladimirovka kaolin

This paper sums up a study into the effect of mottled clay on the density of a grog—kaolin mix in pressing and firing. It is shown inadvisable to use coarse-ground mottled clay in the sintering of specimens. The clay was found to produce the best effect when added to the product batch as a fine co-ground mixture with grog or as a slip. The main process variables are given for the manufacture of critical grog refractories with mottled clay as the sintering agent.     

卫生陶瓷成型开裂缺陷的研究

介绍了卫生陶瓷在成型工序中开裂缺陷的特征，产生原因以及克服的方法．并指出保持泥浆的稳定性和规范的操作方法是克服开裂缺陷的关键。     

Ceramic Facing Tiles Based on Local Polymineral Clays

It is demonstrated that after polymineral clays from the Republic of Tatarstan are treated by various methods improving the quality of clay materials (diluting mixture with activated water, treating mixture in an electric classifier, introducing technological additives, such as mechanoactivated quartz-glauconite sand or phosphoric and high-melting clay) can be used in semidry molding combined with slip preparation of molding powder to produce tiles for interior and exterior facing satisfying standard requirements.     

粘土原料用于陶瓷注浆泥料的开发模式研究

以黑泥粘土原料的开发为依据,确定高岭石类粘土原料开发模式为:首先将待开发黑泥粘土原料的物理化学性质与苏州土的物理化学性质进行分析比较,确定其为高岭石类粘土原料后再用该粘土原料代替苏州土并进行陶瓷注浆泥料配方设计.     

SOME OBSERVATIONS ON THE AGING OF ENAMELS1

The tendency toward more rapid production of enameled ware has reduced to minimum the time allowed in most plants for aging of enamels. Aging of the enamel slip allows the clay to become thoroughly slaked, adsorb the larger enamel particles, and thus prepare it for its cohesion to the metal base. Aging or soaking of the clay before use is an excellent substitute for part of the time consumed in aging the enamel slip. Observations of results obtained in commercial application of enamels has lead to the following conclusions: (1) Enamels should be aged before use in order to gain the full benefit of the adsorption properties of the clay and enamel colloids. (2) If the proper time of aging of enamels cannot be allowed, at least the clay should be brought to fine state of subdivision by aging or soaking in water. (3) If aging is not allowed in some form, the enamel usually is not as easily applied with the ordinary handling encountered in average production. (4) If aging of the clay is allowed there is quicker turn over of the stock enamel in the mill room.     

THE MEASUREMENT OF THE PLASTICITY OF CLAY SLIPS12

• 1 The paper emphasizes the great need of a quantitative measure of the physical properties commonly included in the term “plasticity” of clays and clay slips. Various indirect methods previously suggested are likely to lead to erroneous conclusions, while measurement of the flow or apparent viscosity of clay slips made up with a constant amount of water is shown to give misleading results.
• 2 The work described in this paper is preliminary in nature and has been confined to a study of the properties of clay-water mixtures in the casting rather than in the molding range. In the light of these results it is recommended that, instead of the vague term plasticity, the properties of a given clay, at least for casting purposes, be expressed in terms of (a) the water content required to give proper working consistency, and (b) the resistance of the resulting slip to small deforming forces (such as gravity). Specifically, use is made of a modified Bingham plastometer, and the figures reported are (a) the amount of water required to give a slip of a specified mobility, and (b) the yield value of the slip thus obtained.
• 3 The method is shown to be capable of giving quantitative figures for the yield values at constant mobility which correspond well with the customary qualitative ideas as to the plasticity of clays. The amount of water required to give constant mobility varies to a surprising extent, and does not appear to bear any definite relationship to the usual classifications of more or less plastic clays. It probably does parallel fairly well the shrinkage on drying.
• 4 Small amounts of acid or alkali are shown to have a negligible effect on the mobility of a clay slip, but a very large effect on the yield value, the variations being greater than the difference between a non-plastic kaolin and a highly plastic ball clay. This brings out the necessity, and indeed the potential value, of carefully controlling the hydrogen-ion content of the water used in making the slips.
• 5 Some preliminary data are given on the effect of additions of flint and similar non-plastic materials to clay slips.
• 6 It is recommended that an attempt be made to agree upon standard dimensions for the capillary and the desirable mobility for various purposes, and that the plastometer then be used as a standard method of test in the ceramic industry.

     

STUDY OF FACTORS INVOLVED IN GLAZE-SLIP CONTROL,I–IV* I,GLAZE-SLIP SPECIFICATIONS

Experiments were conducted to find a simple, adequate means of specifying glaze consistency. Tests showed that the amount of slip clinging to a glass plate after it is withdrawn from a reservoir of slip (known as its coherence value) was directly influenced by such factors as amount of water, clay content, and age. These factors are commonly thought of as governing the working quality of the slip. Surface tension has little apparent relation to the working qualities of the slip. Examination of the fired glazes revealed that a distinct coherence value separated good glazes from poor types. A total of 110 pieces was fired; of these samples, fifty-two were glazed with slips having coherence values above 0.04 gm. per sq. cm. Only three of the fifty-two samples were satisfactory; the remaining fifty-eight were coated with slips with a coherence value of less than 0.04 gm. per sq. cm. Only nine of these were defective in any respect and most of them were in the region of 0.04 gm. per sq. cm. coherence value.     

Performance of mixers at the Chasov Yar Refractories Combine

Conclusions During the blending of bodies, containing a mixture of chamotte and clay ground in combination in tube mills, on mixers of four types used at the Chasov Yar Combine, the best pressed specimens were obtained when the bodies were worked on the centrifugal runnermills 115 M with normal rollers. Therefore, we do not recommend the removal from these mixers of factory-made rollers, although the mixers require improvement.The dispersed feeding of slip into the mixer reduces the quantity of coarse granules in the prepared bodies. In this case it is necessary to use replaceable tubes for periodic cleansing of the apertures or to ensure forced delivery of the slip with spattering across the surface of the body being mixed.Translated from Ogneupory, No. 8, pp. 17–21, August, 1970.     

Humidity Drying of Plastic Clay

The humidity drying cycle gives rise to surface and body cracks in plastic clay. The cracks appear in the initial stages when the clay is being heated in a saturated atmosphere. Various factors affecting cracking in this initial heating stage were studied using a purified kaolin in the plastic state, and appropriate experimental models were used to isolate certain aspects for study. It is shown that the condensation of moisture on the clay surface is the major factor influencing the cracking of the plastic clay. The effect of thermal diffusion is insignificant and the loss of mechanical strength is of secondary importance. The balance af evidence from the literature and from this study indicates that capillarity plays a major part in the movement of moisture and the production of stresses during drying. When air spaces are present in the body, thermal capillarity may become important. Stresses caused by thermal expansion oppose those caused by drying shrinkage, while the thermal expansion of capillaries will have a negligible effect.     

基于F-K滑移流模型的柱面微槽气浮密封浮升能力分析

由于气浮密封薄膜引发的滑移流现象频发,本文针对一种新型柱面螺旋槽气浮密封,基于线性化Boltzmann方程（F-K 模型）,引入流量因子,建立稀薄气体润滑的F-K滑移流模型。采用高精度八点差分法和Newton-Raphson迭代法求解气膜压力,解决了表面槽-台阶跃、径向偏心与极薄气膜三者耦合下对求解发散和计算精度的影响。将计算结果与现有研究对比,并考察了气体滑移流效应与运行参数的内在关联,研究结果验证了新型柱面螺旋槽气浮密封在高速、低压、小膜厚和大偏心下具有较为明显的滑移流效应;此外,虽然槽深、槽数和槽长的增加提高了气膜浮力,但是增强了槽内滑移流动的响应。研究结果为拓宽动压密封应用范围提供理论了基础。