The hydrolysis of aluminum-tri-(sec-butoxide), ASB, in ionic and nonionic media is shown to be a useful method for the synthesis of aluminum minerals. Infrared and X-ray analysis were used to identify the reaction products. Pseudoboehmite is formed at low water to aluminum ratios. At higher water content, transformation of pseudoboehmite occurs with bayerite as the final phase. Dawsonite-type minerals are produced when ASB is hydrolyzed in the presence of sodium, potassium, or ammonium bicarbonate. Infrared evidence suggests that the carbonate group is more perturbed than indicated by the proposed crystal structure. A compound with a structure like the pyoaurite-sjögrenite group was obtained when ASB reacted with a lithium carbonate solution. The infrared spectrum indicates the possible existence of bicarbonate and carbonate ions between the brucite-like layers.

Fibrous sepiolite crystals derive much of their commercial value from their molecular size channels and grooves. The crystals fold upon drying and these channels and grooves are lost. A model for the folding and unfolding of the crystals is presented. Extensive i.r., X-ray and thermogravimetric evidence shows that folding occurs when approximately half of the water of hydration, which is coordinated to the edge magnesium atoms inside of the channels, is removed. This occurs near 175°C under vacuum and near 300°C in air. When the crystals fold, all remaining water molecules enter a new environment, that of the hexagonal holes of the neighboring silica surface. A true anhydride is produced at about 500°C under vacuum when the final water is lost, but this final dehydration produces no important structural change. Rehydration of the anhydride to the normal hydrated sepiolite does not occur at room temperatures in 100% r.h. However, above, 60°C rehydration does occur.

Three sepiolite clays studied showed evidence for the presence of structural hydroxyl groups in three to five different environments depending on the composition of the clay. A 3720 cm−1 i.r. frequency is shown to be characteristic of SiOH at crystal edges which are very abundant in sepiolites. This band has not been seen by most workers because the Nujol, fluorolube or KBr used in sample preparation perturb it sufficiently to obscure it under other OH stretching bands. The 3680 cm−1 band is confirmed as being from the (Mg)3OH and evidence of a very small band near 3640 cm−1 is suggested to arise from limited trioctahedral substitution. The very crystalline Ampandrandava sepiolite shows only the above three bands. The intermediately crystalline Vallecas shows a 3620 cm−1 band in addition which is characteristic of dioctahedral systems and is due to either some vacancy sites or to the presence of attapulgite. This dioctahedral band is greater in the less crystalline Salinelles sepiolite; in addition, it has a smaller 3585 cm−1 band. Mg-Al-vacancy and Mg-Fe‴-vacancy are suggested as the source of the 3620 cm−1 and 3585 cm−1 bands.

Synthetic Al-hematites prepared from ferrihydrites, at low (∼ 100°C) and high (400° and 800°C) temperatures were studied for their morphological, crystallochemical, and infrared (IR) characteristics. Low-temperature Al-hematites had a platy morphology (the plate thickness was inversely related to amount of Al substitution), and the high temperature Al-hematites showed a poorly defined morphology due to interparticle sintering. In the low-temperature Al-hematites shifts in the IR mode frequencies were noted and could be partly explained by a shape factor that was deduced from particle morphology. The intrinsic effect of Al substitution, however, was to produce shifts of as much as 10–15 cm−1 for the highest Al substitution (∼ 16%). Similar shifts were observed for the high-temperature hematites in which morphology was not appreciably affected by Al substitution.

A layered double hydroxide with a chemical composition [Al2Li(OH)6]+X− · nH2O, where X− is an interlayer anion, has been synthesized hydrothermally at 130°C from aluminum-tri-(sec-butoxide) and lithium carbonate. Electron micrographs showed the product to have a platy morphology with distinct hexagonal symmetry, which has been corroborated by selected area electron diffraction patterns corresponding to a projection of the structure on its (001) plane. Evidence for a superlattice with a = 5.32 Å was obtained, indicating cation ordering among octahedral sites. X-ray powder diffraction data also can be interpreted by reference to a hexagonal supercell with dimensions a = 5.32 Å and c = 15.24 Å. The arrangement of the octahedral sites appears to be that of gibbsite, but with the vacancies filled with lithium cations. Anions must be present between the sheets to balance the charge. A complete assignment of the observed infrared lattice vibrations can be made for the anion [Al2LiO6] with the ideal D3d symmetry for motions within one octahedral sheet. The results show that [Al2Li(OH)6]+X− · nH2O is a hydrotalcite-like compound with the octahedral cations largely ordered. The general formula for hydrotalcite-like compounds, [M2+1−xM3+x(OH)2]x+Xm−x/m · nH2O, should be extended to include the monovalent lithium cation.

The rheological behavior of concentrated lateritic suspensions from Cuba is affected by mineral composition and particle size. Electrophoretic mobility and yield stress were considered. The lateritic samples were found to be mostly composed of mixtures of serepentine and goethite in varying proportions. The flow properties of the lateritic suspensions are strongly affected by the mineral composition and particle size. This result was determined by comparison of flow properties of the bulk sample and the colloidal fraction. The electrokinetic curves suggest that heterocoagulation is present in all samples, with a zeta potential minimum at the isoelectric point (IEP), which varies with the serpentine to goethite ratio. A relationship between yield stress (τ0) and the sample volume fraction (ϕ) and particle size (d) was obtained at the IEP from the expression τ0 = kϕ3/d0.5, with the constant k dependent on the sample serpentine to goethite ratio.

The crystallochemical features of Co in Co-substituted goethite solid-solutions prepared by two different procedures have been studied using infrared, X-ray photoelectron and electron energy loss spectroscopies. It was found that the path followed for the synthesis of Co-substituted goethite determines the oxidation state of Co in the goethite structure. Thus, in the solid-solution prepared by precipitation with Na2CO3 of an Fe(II) aqueous solution containing Co(II) cations, followed by the aerial oxidation of the precipitate, the Co cations were found to be divalent, whereas trivalent Co was incorporated into the goethite obtained by ageing a solution containing Fe(III) and Co(II) cations precipitated by the addition of KOH. This different behavior is explained by the higher pH of goethite formation in the latter case, which favors the oxidation of the Co(II) cations.

Soil formation usually results in an increase in magnetic susceptibility. The magnetic properties of the products of transformation of ferrihydrite, a typical precursor of other soil Fe oxides, were examined in the present work. Synthetic 2-line ferrihydrite was aged at two temperatures (25 and 50°C) and two different relative humidities (80 and 100%) in the presence of silicate, phosphate, citrate, and tartrate as adsorbed ligands (molar anion/Fe ratio = 1–3%). The ligands delayed or prevented the transformation of ferrihydrite to hematite. The magnetic susceptibility of the ferrihydrite transformation products increased with aging, the rate of increase depending on the type of ligand added and its concentration. The largest increase in magnetic susceptibility, sixfold, was obtained with ferrihydrite in a citrate/Fe ratio of 1%, after 1500 days. The resulting magnetic products exihibited superparamagnetic behavior at room temperature and high coercivity at 5 K. The formation of an intermediate ferrimagnetic phase in the ferrihydrite-to-hematite transformation might explain the magnetic enhancement observed in many aerobic soils lacking other sources of magnetic minerals.

The influence of dissolved species and particle morphology on the electrokinetic behavior and the initial yield stress values of Cuban lateritic aqueous suspensions was studied. The lateritic samples were mixtures of serpentine and goethite in different relative proportions. The addition of silicate and Mg ionic species, which are normally found in natural waters used in industrial processes, affected the electrokinetic and flow behavior of the lateritic suspensions. Specific adsorption of these species on particle surfaces was shown by a shift of the isoelectric point and the maximum of the initial yield stress to more acidic pH (Si ionic species adsorption) and more basic pH (Mg ionic species adsorption), when compared to suspensions containing only non-adsorbing electrolytes. The initial yield-stress values determined in samples consisting entirely of goethite varied from sample to sample. A detailed crystallochemical characterization revealed that these changes were associated with the axial ratio (i.e. ratio of particle length to width) of the mineral particles. Goethite samples with larger particle size (smaller number of particles for a given solid concentration) and greater axial ratios presented initial yield-stress values greater than those goethites with smaller particle size and lower axial ratio.

We present the general analytical solution of the Riemann problem (decay of a jump discontinuity) for non-convex relativistic hydrodynamics. In convex dynamics, an elementary nonlinear wave, i.e. a rarefaction or a shock, originates at the discontinuity and travels towards one of the initial states. Between the left and right waves, an equilibrium state appears represented by a contact discontinuity. The exact solution to the Riemann problem in convex relativistic hydrodynamics was first addressed by Martí & Müller (J. Fluid Mech., vol. 258, 1994, pp. 317–333). In non-convex dynamics, two sequences of elementary nonlinear waves move towards the left and right initial states. Solving the Riemann problem involves determining the types of wave developing and the equilibrium state where they coincide. The procedure consists of constructing the wave curves associated with the nonlinear waves in the pressure–velocity phase space, where the intersection of the wave curves indicates the equilibrium state. We describe the relation between the wave curves, the explicit formulas for their calculation, and the outline of the process for a correct derivation and representation of the waves in the spatial domain. We present examples of the exact solution of a Riemann problem that illustrate the complex phenomena of non-convex dynamics by using the phenomenological non-convex equation of state proposed by Ibáñez et al. (Mon. Not. R. Astron. Soc., vol. 476, 2017, pp. 1100–1110).

Family functioning may serve as protective or risk factors in the development of youth psychopathology. However, few studies have examined the potentially reciprocal relation between child psychopathology and family functioning. To fill this gap in the literature, this study tested for time-ordered associations between measures of family functioning (e.g., cohesion, conflict, and emotional expressiveness) and child psychopathology (e.g., total behavior problems, externalizing, and internalizing problems) using data from the Longitudinal Studies of Child Abuse and Neglect (LONGSCAN; N = 1143, 52.3% female, Nwaves = 5). We used a random-intercept cross-lagged panel model to identify whether child psychopathology preceded and predicted family functioning, the reverse, or both processes occurred simultaneously. At the between-person level, families who tended to have more cohesion, who lacked conflict, and who expressed their emotions had lower levels of child psychopathology. At the within-person level in childhood, we found minimal evidence for time-ordered associations. In adolescence, however, a clear pattern whereby early psychopathology consistently predicted subsequent family functioning emerged, and the reverse direction was rarely found. Results indicate a complex dynamic relation between the family unit and child that have important implications for developmental models that contextualize risk and resilience within the family unit.

From the moment it launched its armed insurgency in 1980 until the death of its former leader in September 2021, Peru’s Shining Path mesmerized observers. The Maoist group had a well-established reputation as a personality cult whose members were fanatically devoted to Abimael Guzmán, the messianic leader they revered as “Presidente Gonzalo.” According to this narrative, referred to here as the “Gonzalo mystique,” Shining Path zealots were prepared to submit to Guzmán’s authority and will—no matter how violent or suicidal—because they viewed him as a messiah-prophet who would usher in a new era of communist utopia. Drawing on newly available sources, including the minutes of Shining Path’s 1988–1989 congress, this article complicates the Gonzalo mystique narrative, tracing the unrelenting efforts by middle- and high-ranking militants to challenge, undermine, disobey, and even unseat Guzmán throughout the insurgency. Far from seeing their leader as the undisputed cosmocrat of the popular imagination, these militants recognized Guzmán for who he was: a deeply flawed man with errant ideas, including a dubious interpretation of Maoism, problematic military strategy, and a revolutionary path that was anything but shining.