Magnesia-ammonium phosphate-bonded cordierite refractory castables: Phase evolution on heating and mechanical properties

A cordierite refractory castable was developed using the MgO-NH₄H₂PO₄ reaction. This castable was made with cordierite-mullite aggregates from scrap refractory material and a cement paste based on magnesia, calcined alumina, silica fume, and ammonium dihydrogen phosphate, which forms cordierite (2MgO·2Al₂O₃·5SiO₂) during heating at high temperature. The mix with water was cast into steel molds; the cold setting occurs within 30 min. The set castables were thermally treated and the evolution of the phases was observed. Struvite (NH₄·MgPO₄·6H₂O) was identified at room temperature; between 110 and 750 °C, the present phosphates were amorphous to X-ray diffraction (XRD). At 1100 °C, magnesium orthophosphate (Mg₃(PO₄)₂) and aluminum orthophosphate (AlPO₄) were present. At 1350 °C, the main crystalline phases were cordierite and mullite. Cold and hot flexural strength, thermal shock resistance, and physical properties were measured. The properties of magnesia-phosphate-bonded cordierite castables were compared with cordierite material obtained by conventional slip-casting method from aggregates, clay, talc, and calcined alumina.     

Rheology and gelation behavior of gel-cast cordierite-based glass suspensions

A cordierite-based glass suspension was shaped by gel-casting method. Effects of various parameters like pH, volume fraction of glass particles, gelling agents and dispersant on the rheology of the prepared slurries were investigated. The results demonstrated that using sodium tripolyphosphate (STPP) dispersant brings about a suspension of minimum viscosity. The bending strength of the dried gels was increased with the gelling agents. In addition, the utilization of cross linkers at a fixed concentration of monomer led to the gradual enhancement of the bending strength of the dried bodies. A bending strength of ∼11 MPa was obtained for the most promising dried gel cast bodies.     

Low permittivity cordierite-based microwave dielectric ceramics for 5G/6G telecommunications

5G and forthcoming 6G communication systems require dielectric ceramics with low relative permittivity (ε_r) and near-zero temperature coefficient of resonant frequency (τ_f) for the lower part of the microwave (MW) band and at sub-Terahertz. Mg₂Al₄Si₅O₁₈ (MAS) ceramics are promising candidates due to their low ε_r (~ 6) and high-quality factor (Q×f > 40,000 GHz) but have a large τ_f. In this study, 5.5 wt% TiO₂ (MAS-T_5.5) was used to adjust τ_f of MAS to ?2.8 ppm/℃ whilst retaining low ε_r (5.24) and good Q×f (33,400 GHz), properties consistent with those obtained by infrared reflectance. A demonstrator microstrip patch antenna with gain 4.92 dBi and 76.3% efficiency was fabricated from MAS-T_5.5.     

High-Qf value and temperature stable Zn2+-Mn4+ cooperated modified cordierite-based microwave and millimeter-wave dielectric ceramics

Cordierite-based dielectric ceramics with a lower dielectric constant would have significant application potential as dielectric resonator and filter materials for future ultra-low-latency 5G/6G millimeter-wave and terahertz communication. In this article, the phase structure, microstructure and microwave dielectric properties of Mg₂Al_4–2x(Mn_0.5Zn_0.5)_2xSi₅O₁₈ (0 ≤ x ≤ 0.3) ceramics are studied by crystal structure refinement, scanning electron microscope (SEM), the theory of complex chemical bonds and infrared reflectance spectrum. Meanwhile, complex double-ions coordinated substitution and two-phase complex methods were used to improve its Q×f value and adjust its temperature coefficient. The Q×f values of Mg₂Al_4–2x(Mn_0.5Zn_0.5)_2xSi₅O₁₈ single-phase ceramics are increased from 45,000 GHz@14.7 GHz (x = 0) to 150,500 GHz@14.5 GHz (x = 0.15) by replacing Al³⁺ with Zn²⁺-Mn⁴⁺. The positive frequency temperature coefficient additive TiO₂ is used to prepare the temperature stable Mg₂Al_3.7(Mn_0.5Zn_0.5)_0.3Si₅O₁₈-ywt%TiO₂ composite ceramic. The composite ceramic of Mg₂Al_3.7(Mn_0.5Zn_0.5)_0.3Si₅O₁₈-ywt%TiO₂ (8.7 wt% ≤ y ≤ 10.6 wt%) presents the near-zero frequency temperature coefficient at 1225 °C sintering temperature: ε_r = 5.68, Q×f = 58,040 GHz, τ_f = ?3.1 ppm/°C (y = 8.7 wt%) and ε_r = 5.82, Q×f = 47,020 GHz, τ_f = +2.4 ppm/°C (y = 10.6 wt%). These findings demonstrate promising application prospects for 5 G and future microwave and millimeter-wave wireless communication technologies.     

Synthesis of chemically bonded porous ceramics from MgO–C refractory bricks waste

Chemically bonded ceramics (CBCs) obtained from industrial waste have attracted great interest in recent years. In the present work, MgO raw material was substituted with refractory MgO–C bricks waste (MgW) for CBCs. Monopotassium phosphate (KDP) and MgW were used as binder systems with varied component ratios (KDP/MgW) of 0.17–0.33 (mass basis) and waste (MgO–C) particles with D50 = 20.5 μm. Bodies containing K-struvite phase (MgKPO₄·6H₂O), with compressive strength ranging from 1 to 1.4 MPa, were obtained. The total porosity ranged between 60 and 74%. Air permeability tests proved the presence of interconnected pores because the coefficients k₁ and k₂ increased with the increasing total porosity of the samples. The leaching test showed that the waste and the samples were nonreactive, nontoxic, and nonhazardous according to the Brazilian standard. The results showed that MgW-based chemically bonded porous ceramics can be produced from MgO–C refractory brick waste via synthesis processes for using as filters.     

转炉用快速烧结镁r质投补料

根据转炉大面耐火材料的使用条件 ,研究了影响沥青结合及树脂结合镁质投补料使用性能的主要因素。结果表明 ,控制配入合适溶剂的沥青或树脂的加入量 ,掺加少量外加剂 ,可获得性能良好的修补料。二者相比 ,沥青结合镁质投补料的烧结时间较长 ,容易出现凹坑 ;树脂结合投补料与砖体间的粘结性比沥青的稍差 ,容易出现翘曲。     

半干法烟气脱硫产物对水泥缓凝作用的研究

研究了以亚硫酸钙为主要成分的半干法烟气脱硫产物对水泥凝结时间和抗压强度的影响.试验表明,半千法烟气脱硫灰可以延长硅酸盐水泥的凝结时间,且缓凝效果比石膏明显,但水泥试样的抗压强度有所降低,且由于脱硫灰成分的波动较大,掺量需要及时调整.因此,用脱硫灰代替石膏作水泥缓凝荆,技术上可行,但市场应用不占优势.     

Cold sintering assisted CaF2 microwave dielectric ceramics for C-band antenna applications

A cold sintering process is adopted to pre-densify CaF₂ ceramics from 85.7% at 300 MPa to 91.7% at 750 MPa. Subsequent post-annealings at 1000–1150 °C lead to further improvements in densification, where great enhancements of grain size and crystallinity are also observed from the scanning and transmission electron micrographs. Significant advances in Qf values are achieved in the post-annealed CaF₂ ceramics. The optimum Qf value (80,522 GHz) is achieved after cold sintering at 750 MPa and post-annealing at 1000 °C, which is three times higher than the conventional sintered one at 1000 °C (26,448 GHz). Moreover, the obtained low-ε_r (5.9–6.5) of CaF₂ ceramics suggests broad application prospects in the high-band microwave communications. A microstrip patch antenna is fabricated using the CaF₂ ceramics as the substrate, which operates at 7.89 GHz in the C-band, with an S₁₁ of ?13.4 dB, simulated high gain and efficiency of 6.41 dBi and ?0.56 dB, respectively.     

Sintering characteristics of kaolin in the presence of phosphoric acid binder

The kaolin-phosphoric acid mixtures with various percentages of phosphoric acid (5 wt%; 10 wt% and 15 wt%) have been investigated at room temperature. During the maturation and the sintering processes, acid reacts with aluminium of kaolin to give a new phase of aluminophosphate. This new phase's appearance has been confirmed by the thermal analysis, infrared spectroscopy, X-ray diffraction and scanning electron microscopy measurements before and after the sintering processes at different temperatures (800 °C, 1100 °C and 1250 °C). The rupture strength of the body-shaped samples made with the kaolin-phosphoric acid mixtures is higher than that of those made with only kaolin. The porosity decreases with both the sintering temperature rise and the addition of phosphoric acid in the mixture. The addition of 10 wt% of phosphoric acid to the kaolin decreases its calcined temperature by 200 °C.     

Preparation and thermal shock resistance of cordierite-spodumene composite ceramics for solar heat transmission pipeline

Cordierite-spodumene composite ceramics with 5, 10, 15 wt% spodumene used for solar heat transmission pipeline were in-situ prepared via pressureless sintering from kaolin, talc, γ-Al₂O₃ and spodumene. Effects of spodumene on densification, mechanical properties, thermal shock resistance, phase composition and microstructure of the composite ceramics were investigated. The results showed that spodumene used as flux material decreased the sintering temperature greatly by 40–80 °C, and improved densification and mechanical properties of the composite ceramics. Especially, sample A3 with 10 wt% spodumene additive sintered at 1380 °C exhibited the best bending strength and thermal shock resistance. The bending strengths of A3 before and after 30 thermal shock cycles (wind cooling from 1100 °C to room temperature) were 102.88 MPa and 96.29 MPa, respectively. XRD analysis indicated that the main phases of the samples before 30 thermal shock cycles were α-cordierite, α-quartz and MgAl₂O₄, and plenty of β-spodumene appeared after thermal shock. SEM micrographs illustrated that the submicron β-spodumene grains generated at the grain boundaries after thermal shock improved the thermal shock resistance. It is believed that the cordierite-spodumene composite ceramics can be a promising candidate material for heat transmission pipeline in the solar thermal power generation.     

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

Magnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium-free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite-ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron-size whisker network bond domination in their matrix. Such a whisker-network bond renders the material a successful eco-friendly alternative to magnesia–chrome refractory.     

Multi-phase hydration model for prediction of hydration-heat release of blended cements

Recently, the heat release during cement hydration and the so-caused temperature rise was exploited for (i) identification of material properties of early-age cement-based materials (stiffness, strength), and (ii) determination of the diameter and the cement content of jet-grouted structures. In this paper, the underlying hydration model for determination of the heat release and its rate is refined for Ordinary Portland Cements (OPC) and extended towards blended cements. Hereby, the overall degree of hydration with one kinetic law is replaced by a multi-phase hydration model, taking the hydration kinetics of the main clinker phases into account. As regards blended cements, which are commonly used in engineering practice, the effect of slag hydration is incorporated into the presented multi-phase model. The developed hydration model for both plain and blended cement is validated by means of differential-calorimetry (DC) experiments.     

水泥窑用耐碱浇注料的性能研究

本研究中以建筑陶瓷为主要原料制备耐碱浇注料,重点研究了铝酸钙水泥和硅微粉对耐碱浇注料性能的影响,并对试样的显微结构进行了分析。试验结果表明:铝酸钙水泥加入量的增加有助于110℃,24 h处理后常温强度的提高,而在10100℃,3 h处理条件下,铝酸钙水泥加入量的增加会提高基质中生成的液相,加入量在一定范围内使强度出现先增加后降低的趋势,同时也导致了线变化率的增加,在试验条件下铝酸钙水泥的合适加入量在7%~8%左右;耐碱浇注料中加入活性较高的硅微粉能够提高试样的强度和致密度,其加入量增加也会导致试样线变化率的增加,综合分析硅微粉的加入量以5%~6%为宜;经1100℃,3h处理后的试样中骨料和基质结合牢固,基质中存在莫来石化和低共熔物生成的双重反应。     

Cold sintering optimized SrF2 microwave dielectric ceramics for the development of dielectric resonator antenna at 5G millimeter-wave band

SrF₂ is a promising low-ε_r fluoride with outstanding microwave dielectric properties, while densification of SrF₂ ceramics is challenging via traditional thermal sintering (TTS). In this work, dense SrF₂ ceramics with 93.4%–97.2% relative density have been obtained via cold sintering (300 MPa–900 MPa, 150 °C, 1 h) and subsequent post-annealing at 950 °C/3 h. The pretreated cold sintering process is beneficial for microstructure optimization, where the maximum Qf value (62,037 GHz) is obtained at 750 MPa, nearly three times higher than the TTS sample (21,080 GHz). An ultra-low dielectric constant (ε_r) of 5.94 is simultaneously obtained, together with a temperature coefficient of resonant frequency τ_f = ?78.26 ppm/°C. Good chemical compatibility between SrF₂ ceramics and silver is verified, indicating great promise for their use in LTCC technology. Moreover, the low-ε_r and high Qf values of the cold sintering optimized SrF₂ ceramics suggest great potential in the 5G millimeter-wave antenna systems. A SrF₂-based dielectric resonator antenna is designed and fabricated, which resonates at the desired 24.5 GHz and exhibits an outstanding S₁₁ of ?43.95 dB and a broad bandwidth of 4.51 GHz.     

高技术混凝土

高效能混凝土与化学结合陶瓷最近受到较多重视,被称作高技术混凝土,它们既是在近代科技成就的基础上发展起来,又将在高新工程技术领域中开发应用。本文综述高效能混凝土,无宏观缺陷水泥（ＭＤＦ）水泥,超细粒紧密水泥（ＤＳＰ）和碱激发矿渣水泥;为了使这些材料能够在工程中及早推广应用,作者首次提出镶嵌部件的建议。     

硫铝酸盐水泥基防渗堵漏材料凝结时间调控机制的研究

通过硫酸铝对硫铝酸盐水泥基防渗堵漏材料凝结时间影响的试验研究,在硫铝酸盐熟料中加入适量的硫酸铝能改变硫铝酸盐水泥熟料的早期水化进程,从而缩短水泥浆体的凝结时间。运用水化理论、双电层理论等分析了凝结时间变化的原因,得出了通过改变熟料颗粒水化环境和颗粒的双电层结构可以调控硫铝酸盐水泥基防渗堵漏材料凝结时间机制的结论。     

聚合物改性碱式硫酸镁水泥用于路面裂缝修补的工作性能研究

为了研究聚合物改性碱式硫酸镁水泥用于路面裂缝修补的工作性能,对不同配合比的改性碱式硫酸镁水泥的粘度、可灌性、凝结时间进行了测试,讨论了不同聚合物掺量对碱式硫酸镁水泥工作性能的影响.结果表明,碱式硫酸镁水泥的粘度随着聚合物掺量的增加而减小,表现为更好的流动性和可灌性,聚合物掺量为20％时,改性碱式硫酸镁水泥对应30 min时的粘度为17 s,与未掺加聚合物的碱式硫酸镁水泥30 min时的粘度相比缩小了50％;碱式硫酸镁水泥的凝结时间随着聚合物掺量的增加先增大后减小,与未改性碱式硫酸镁水泥凝结时间相比,聚合物掺量为10％和20％时凝结时间分别延缓3 h和缩短50 min.     

电解锰渣替代石膏生产水泥的试验研究

电解锰渣为含CaSO4·2H2O较高的工业废料,如果加以利用,将获得较好的经济效益与社会效益。实验将锰渣分别进行105℃低温烘干和300℃高温锻烧处理,然后替代石膏配制水泥试验并按国家标准检测方法进行相关水泥性能试验。结果表明,电解锰渣的缓凝作用虽差于天然石膏,但可完全替代天然石膏生产水泥;且高温锻烧处理的电解锰渣的缓凝和增强作用,均好于低温烘干料。     

微集料对超速凝超早强水泥凝结硬化的作用

本实验研制的超速凝结早强水泥中的微集料掺加量高达１３％。实验表明，在该掺量下微集料有助于凝结时间的缩短，但使强度略有降低，本文讨论了其作用。微集料的细度是影响水泥性能的关键。     

用磷石膏烧成硫铝酸盐水泥的研究

讨论了在还原气氛下,用磷石膏烧成硫铝酸盐水泥的可行性。结果表明,在弱还原气氛下,可以烧成强度较高（３ｄ抗压强度６４.７ＭＰａ）、凝结时间正常的熟料（初凝时间３７ｍｉｎ）;在还原气氛较浓的情况下,含杂质较高的磷石膏大量分解,熟料偏离正常矿物组成,生成Ｃ１２Ａ７和还原性矿物ＣａＳ,急凝低强。