Lamellar Pores Research Articles

Porous cellulose photonic film via controlled unidirectional interlayer freezing for rapid visual sensing

Structure color, arising from the interaction of light with regularly arranged sub-micrometer-sized structures, has spurred interest in sensor design. However, typical cellulose nanocrystal (CNC) photonic films derived from biomass, known for their sustainability and cost-effectiveness, often suffer from limited sensitivity and slow response times due to their dense structure. To address this challenge, we have utilized a unidirectional interlayer freezing-photopolymerization strategy to introduce porous structures into CNC photonic films without compromising their vibrant structural color. This method harnesses ice crystal-induced lamellar pores while preserving the periodic arrangement of CNCs. The underlying mechanism of ice kinetics and CNC assembly is established, highlighting the transition from non-iridescent aerogels to iridescent, porous photonic films. The resulting porous CNC photonic film exhibits apparent color response and rapid sensing capabilities in response to various solvent stimuli, outperforming its non-porous counterparts. We have validated the film as a portable vapor detector for rapid visualized alcohol detection. This approach provides promising developments in sustainable, highly responsive sensor technologies.

Porous Structure Enhances the Longitudinal Piezoelectric Coefficient and Electromechanical Coupling Coefficient of Lead-Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3.

The introduction of porosity into ferroelectric ceramics can decrease the effective permittivity, thereby enhancing the open circuit voltage and electrical energy generated by the direct piezoelectric effect. However, the decrease in the longitudinal piezoelectric coefficient (d33) with increasing porosity levels currently limiting the range of pore fractions that can be employed. By introducing aligned lamellar pores into (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3, this paper demonstrates an unusual 22-41% enhancement in the d33 compared to its dense counterpart. This unique combination of high d33 and a low permittivity leads to a significantly improved voltage coefficient (g33), energy harvesting figure of merit (FoM33) and electromechanical coupling coefficient ( ). The underlying mechanism for the improved properties is demonstrated to be a synergy between the low defect concentration and high internal polarizing field within the porous lamellar structure. This work provides insights into the design of porous ferroelectrics for applications related to sensors, energy harvesters, and actuators.

Fabrication and enhanced degradation behavior of sinterless porous apatite scaffolds with centrosymmetric structure

The primary component of natural bone minerals, hydroxyapatite (HA), has been the subject of research on materials for bone implants. Sintered HA scaffolds, on the other hand, degrade slowly after implantation and exhibit a high degree of crystallization at high temperatures, making it challenging to match the rate at which new bone grows. In this study, the benefit of self-curing calcium phosphate bone cement was employed to create porous apatite scaffolds without sintering. The lamellar pore structure was created by directional freeze-casting, and the enhanced specific surface area aided the in-situ hydration process. The crystallinity of sinterless porous apatite scaffolds diminishes when the TTCP and DCPD molar ratios drop. When the molar ratio is adjusted to 1:2.25, the crystallinity of the fabricated scaffold is reduced to 63.99 %, and 10.21 % can be degraded in 30 days. The degradation of porous scaffolds in simulated body fluids mainly depends on the rapid dissolution and transformation of solid phase powders in the early hydration reaction and the slow diffusion of the apatite in the later stage. The compressive strength of the porous scaffold is 5.3 MPa and its elastic modulus is 0.68 GPa. After 14 days of degradation, the compressive strength was 4.0 MPa and the elastic modulus was 0.64 GPa, which was still within the applicable range of cancellous bone repair. It has a promising application prospect as a substitute scaffold for absorbable cancellous bone.

Defects materials of Institut Lavoisier-125(Ti) materials enhanced photocatalytic activity for toluene and chlorobenzene mixtures degradation: Mechanism study

In this paper, the effect of three monocarboxylic acids on MIL-125 synthesis was systematically investigated and the results were discussed in detail. X-ray diffractometry (XRD) and nitrogen adsorption–desorption curves indicated that small molecule acids (acetic acid, propionic acid and butyric acid) affected the morphology of MIL-125 and induced lamellar pores and structural defects in the crystals. Thermogravimetric measurements confirmed the presence of acid-regulated defective metal–organic frameworks (MOFs). Electrochemical tests and density function theory calculations indicated that acid modulation could change the forbidden bandwidth of the material. The acid modification strategy effectively promoted the transfer of photogenerated electrons and enhanced the adsorption and activation of O2 and H2O molecules, generating reactive radicals. The modified MOFs also showed excellent performance in the removal of mixed toluene and chlorobenzene. The degradation pathways of the mixture were analyzed by in situ infrared (IR) and gas chromatography-mass spectrometry (GC–MS). The mixture was converted to chlorophenolic intermediates in the presence of reactive oxygen species, further decomposed to form ethers and ethanol, and finally formed small molecules such as carbon dioxide and water. A feasible method was provided for the preparation of photocatalysts for the treatment of mixed VOCs.

Effects of heat-dry curing temperature on porous silicate cement membranes fabricated by the coupling process of freeze casting and heat-dry curing

Preparation of porous cement-based materials via freeze casting is a process with great potential. However, freeze-drying and steam curing complicate the preparation process and increase the preparation period. To simplify the process, heat-dry curing was used for replacing freeze-drying and steam curing during operation. The new preparation method combined freeze casting and heat-dry curing possesses characteristics of low-energy, simplicity, and time-saving. Compared with the traditional preparation method of porous cement-based materials, the novel preparation process can shorten preparation time by at least 16 % and retrench energy consumption by at least 18 %. As the improvement condition, temperature of heat-drying curing has great influence on the structure and performance of the samples. Therefore, it is of great significance to discuss the relationship between heat-dry temperatures and structural parameters by SEM, N2-adsorption/desorption, TG, and ATR-FTIR. Lamellar pores of membranes can be easier observed at low temperatures than that at 100 °C. The separation performance of oil-water is generally improved with the increase of temperature. Meanwhile, the molecular dynamics simulation was operated to illustrate the reaction mechanism of hydration with three temperatures. This study probably provides more theoretical basis for expanding the application of porous silicate cement membranes.

Increased Microporosity in Ceramic and Metal Foams: A Novel Processing Combination

Copper, aluminum, and alumina foams are prepared by a combination of reticulated foaming and freezing processing. This results in all of these foams in an additional strut porosity consisting of lamellar pores and material lamellae; the lamellar pores enable designed access to the inner volume of the struts. To increase the functionality in terms of enlarging the total surface area and increasing the adsorption activity, the foams are loaded with microporous materials by direct crystallization: the copper foams are combined with the metal organic framework HKUST‐1, the aluminum foams are combined with the zeolite SAPO‐34, and the alumina foams are combined with the zeolite silicalite‐1. All microporous materials are shown to access the inner strut pore surface area. Because of different crystal sizes of the different microporous materials, the load of the inner strut surface area varies significantly.

In-situ X-ray computed tomography tensile tests and analysis of damage mechanism and mechanical properties in laser powder bed fused Invar 36 alloy

Laser powder bed fusion (LPBF) is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry. Whereas it inevitably introduces specific microstructures and pore defects, which will further influence the mechanical properties. Hence, aiming at exploring the LPBF process-related microstructures and pore defects, and especially their influences on the damage mechanism and mechanical properties, Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds. The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density, while lower scanning speeds result in elongated columnar grains with lower dislocation density. The pore defects analyzed by X-ray computed tomography (XCT) suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion (LOF) pores, and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity. Moreover, the in-situ XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism. Specifically, high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scanning direction. Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces, while metallurgical and keyhole pores have little impact on damage evolution. Eventually, the process-structure-property correlation is established. The presence of high volume fraction of lamellar LOF pores, resulting from high scanning speed, leads to inferior yield strength and ductility. Besides, specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds, slightly reducing yield strength while slightly enhancing ductility. This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.

Design of carbonized unidirectional polyimide aerogel for CO2 capture: Effect of pore morphology/topology on CO2 capture

Design of efficient CO2 adsorbent is an effective way to capture CO2. Bamboo-derived activated carbon is a promising CO2 adsorbent. Inspired by this, carbonized unidirectional polyimide (CUPI) aerogels were newly designed by the ice templating method using directional freezing technology. The pore property of CUPI aerogel can be tuned by changing the solidification velocity, and a series of CUPI aerogels were designed to explore the CO2 capture performance in view of pore morphology/topology. As a result, the obtained CUPI-8 exhibits higher CO2 adsorption capacity compared to carbonized polyimide aerogels due to the synergistic effect of micropores and lamellar pores. Specially, the CO2 adsorption capacity over CUPI-8 can be up to 5.75 mmol/g at 20 bar and 298 K. Furthermore, the adsorption isotherm of CUPI-8 still shows an upward trend even nearly 20 bar. The isosteric adsorption heat (Qst) value of CUPI-8 is nearly in the ideal scope of 30–50 kJ mol−1. The efficient CO2 adsorption performance and good chemical stability of CUPI aerogel makes it a promising absorbent for practical application. This work provides a new opportunity for researching the effect of pore morphology/topology and the synergistic effect of hierarchical pores on CO2 capture.

Thermoelectric Freeze-Casting of Biopolymer Blends: Fabrication and Characterization of Large-Size Scaffolds for Nerve Tissue Engineering Applications.

Peripheral nerve injuries (PNIs) are detrimental to the quality of life of affected individuals. Patients are often left with life-long ailments that affect them physically and psychologically. Autologous nerve transplant is still the gold standard treatment for PNIs despite limited donor site and partial recovery of nerve functions. Nerve guidance conduits are used as a nerve graft substitute and are efficient for the repair of small nerve gaps but require further improvement for repairs exceeding 30 mm. Freeze-casting is an interesting fabrication method for the conception of scaffolds meant for nerve tissue engineering since the microstructure obtained comprises highly aligned micro-channels. The present work focuses on the fabrication and characterization of large scaffolds (35 mm length, 5 mm diameter) made of collagen/chitosan blends by freeze-casting via thermoelectric effect instead of traditional freezing solvents. As a freeze-casting microstructure reference, scaffolds made from pure collagen were used for comparison. Scaffolds were covalently crosslinked for better performance under load and laminins were further added to enhance cell interactions. Microstructural features of lamellar pores display an average aspect ratio of 0.67 ± 0.2 for all compositions. Longitudinally aligned micro-channels are reported as well as enhanced mechanical properties in traction under physiological-like conditions (37 °C, pH = 7.4) resulting from crosslinking treatment. Cell viability assays using a rat Schwann cell line derived from sciatic nerve (S16) indicate that scaffold cytocompatibility is similar between scaffolds made from collagen only and scaffolds made from collagen/chitosan blend with high collagen content. These results confirm that freeze-casting via thermoelectric effect is a reliable manufacturing strategy for the fabrication of biopolymer scaffolds for future peripheral nerve repair applications.

Densification behavior and attrition resistance of porous Al2O3beads prepared by dripping‐ice templating

AbstractPorous Al2O3ceramic beads with a small‐scale lamellar pore structure were prepared by the dripping‐ice templating method. The densification behavior of lamellar walls and the attrition resistance of porous Al2O3beads were investigated. For the two‐dimensional structural lamellar walls, the intrinsic pores shrunk, and the necking area grew during the sintering process, leading to the densification of lamellar walls and the shrinking of porous beads. In addition, the two‐dimensional lamellar walls and three‐dimensional Al2O3bulk are compared and possibilities of elaborating of the discrepancy in grain size and pore morphology are discussed. Attrition resistance was determined by a grinding test. The dominant attrition mechanism of porous Al2O3beads is abrasion. High sintering temperature led to a decrease in the attrition rate due to a wider necking area and denser pore walls.

Porous silicate cement membranes generated by the novel method combining freeze casting and heat-dry curing

Porous silicate cement membranes (PSCMs) fabricated by the freeze casting method show great potential to be utilized in seawater pretreatment, fermentation broth separation, and industrial wastewater treatment due to its merit of high-temperature resistance, low-cost, and hierarchically ordered porous structures, while the freeze casting method is complex and time-consuming. In this work, a combination of freeze casting and heat-dry curing was initially applied to generate PSCMs. The preparation periods of PSCMs could be shortened by simplifying preparation processes and reducing curing time. The resulting membranes presented double-layer structures, containing a nucleation zone (N-zone) with dense structures and a stability zone (S-zone) with lamellar pore structures. The X-ray diffraction pattern of membranes displayed the mixed hexagonal and rhombohedral structures. This novel method could save more than half of energy consumption compared with the traditional preparation technology of silicate cement samples. The membranes with a mesopore size of 3.794 nm showed high permeation performance with pure water flux reaching 207.23 L m−2 h−1 under 0.15 MPa and room temperature. The separation efficiency of oil-water was 78.05% under operating pressure of 0.05 MPa. Molecular dynamics simulation was applied to narrate the microscopic process of transformation during heat-dry curing, and obtained a good similarity of consequences between the computational method simulation and experimental operation.

Controlling the cell and surface architecture of cellulose nanofiber/PVA/Ti3C2TX MXene hybrid cryogels for optimized permittivity and EMI shielding performance

Anisotropic, nanoporous structures are promising materials for manipulating the propagation of electromagnetic waves at millimeter and sub-THz frequencies as well as for electromagnetic interference (EMI) shielding with rapidly evolving green electronics. In this work, cell and surface architecture of sustainable hybrid cryogels of cellulose nanofibers, polyvinyl alcohol (PVA) and Ti3C2TX MXene was controlled to adjust their GHz and THz dielectric permittivity and EMI shielding performance. Temperature gradient freeze-drying was used to obtain aligned honeycomb and lamellar pore structures with specific surface layer designs. The millimeter wave permittivity varied relative to thickness direction as the side of cryogels that was directly exposed to cold gradient had systematically a higher permittivity. This anisotropy was caused by a thin, smooth outermost surface layer covering the open core structure. The surface designs of all cryogels dominated signal permittivity, and the effects of higher MXene dosages could be offset by the surface layer. Cryogels with dense surface layer containing 70 and 50 wt % of MXene displayed very high average attenuation levels of 52.1 and 37.2 dB, respectively. Overall, the results show that the structural design of porous hybrid material can be used to adjust their EMI shielding performance at GHz and THz frequencies.

Maximizing sound absorption, thermal insulation, and mechanical strength of anisotropic pectin cryogels

Effective use of sound absorption materials is the main way to reduce noise pollution, which constitutes a major environmental and health problem. However, the currently used porous sound absorption materials cause not only environmental pollution but their usage is also a potential health risk. Here, we demonstrate a facile strategy to create environmental-friendly and non-toxic lightweight pectin-based cryogels with hierarchically porous anisotropic structure, which integrates small pores on the walls of lamellar pores, via freeze-casting method. The fabricated pectin cryogels have better sound absorption performance (average sound absorption coefficient up to 0.76 in 500–6000 Hz), higher compression modulus (300 to 700 times higher than commercial glass wool), and comparable thermal conductivity comparing to other reported bio-based porous materials. Moreover, the sound absorption performance could be enhanced and optimized by tuning the pore wall density of lamellar pores and the size of small pores to the level of viscous and thermal layers via increasing of freeze-casting temperature and adding NaCl in pectin solution prior to the freeze-casting process. The outstanding sound absorption is linked to the unique hierarchically porous morphology of these cryogels. This strategy paves the way for the design of bio-based porous anisotropic materials for highly efficient noise absorption.

Freeze-Casted Keratin Matrix as an Organic Binder to Integrate Hydroxyapatite and BMP2 for Enhanced Cranial Bone Regeneration.

An ideal bone regenerative scaffold is expected to possess architectural characteristics that mimic the bone tissue, osteoconductive properties, and osteoinductive functionality. Key challenges to creating a scaffold with these ideal characteristics simultaneously are the selection of appropriate processing methods and biocompatible materials. Herein, human hair keratin is proposed as an organic binder for the simultaneous incorporation of bone's major inorganic component, hydroxyapatite and bone's growth factor, recombinant human bone morphogenetic protein 2 (rhBMP2) to enable both osteoconductive and osteoinductive characteristics in the creation of bone scaffolds. Furthermore, a freeze-casting method is selected to fabricate this rhBMP2-incorporated keratin/hydroxyapatite (KHA) scaffold with aligned lamellar pores to guide and promote bone regeneration. The aligned KHA scaffolds display better mechanical properties, sustained rhBMP2 release, good cell compliance, and 3D cellular infiltration. Implantation of KHA scaffolds in vivo reveals that scaffolds with aligned pores effectively accelerate the healing process of bone defects compared to scaffolds with random pores. This work indicates the distinctive potential of freeze-casted rhBMP-2 incorporated KHA scaffolds for bone regeneration.

Enhanced compressive strengths of lamellar porous titanium scaffolds with in-situ generated carbide fiber-bridged structure

Directional lamellar porous titanium scaffolds have an anisotropic pore structure, which has a high compressive strength in a single direction due to the buckling deformation of the lamellar pore walls. However, the weak bond between the pore walls easily leads to splitting, resulting in the insufficient mechanical stability of porous titanium scaffolds. Porous titanium scaffolds with a directional straight-through structure were fabricated in this study by directional freeze casting combined with TiH 2 in-situ reduction reaction, and short carbon fibers were introduced to form a fiber-bridge structure between the lamellar pore walls. TiC/Ti fibers were formed by diffusion and the in-situ reaction of carbon and titanium atoms. The fiber bridging density increased with the short carbon fiber contents. Interlayer splitting due to compressive stress can be prevented, and the compressive strength can be improved by constraining the buckling deformation of pore walls. The maximum compressive strength of fiber-bridged porous titanium scaffolds was 161.66 MPa, which is 36 % higher than that of pure porous titanium scaffolds. Fabricated scaffolds can be applied in the field of bone implant materials due to their low biotoxicity and biocompatibility. • Porous titanium scaffolds with carbide fiber-bridged structure were fabricated. • Interlayer splitting due to compressive stress can be prevented. • The compressive strength was improved by constraining the buckling deformation. • The enhanced mechanism of fiber-bridged structure was discussed.

Utilization of Waste Amine-Oxime (WAO) Resin to Generate Carbon by Microwave and Its Removal of Pb(II) in Water.

Utilising waste amine-oxime (WAO) resin through microwave semi-carbonization, a carbon adsorbent (CA) was obtained to remove Pb(II). After microwave treatment, the pore size of the skeleton structure, three-dimensional porous network, and lamellar pore structure of WAO was improved. The distribution coefficient (Kd) of Pb(II) onto CA is 620 mL/g, and the maximum adsorption capacity of Pb(II) is 82.67 mg/g after 20 min of WAO microwave treatment. The adsorption kinetics and adsorption isotherms conform to the quasi-second-order kinetic equation and Langmuir adsorption isotherm model, respectively. The surface of MT-WAO is negatively charged and the adsorption mechanism is mainly electrostatic interaction. Pb(II) elution in hydrochloric acid solution is more than 98%, and its recovery is high at 318 K and for 1 h.

3D printed zirconia dental implants with integrated directional surface pores combine mechanical strength with favorable osteoblast response

Dental implants need to combine mechanical strength with promoted osseointegration. Currently used subtractive manufacturing techniques require a multi-step process to obtain a rough surface topography that stimulates osseointegration. Advantageously, additive manufacturing (AM) enables direct implant shaping with unique geometries and surface topographies. In this study, zirconia implants with integrated lamellar surface topography were additively manufactured by nano-particle ink-jetting. The ISO-14801 fracture load of as-sintered implants (516±39 N) resisted fatigue in 5–55 °C water thermo-cycling (631±134 N). Remarkably, simultaneous mechanical fatigue and hydrothermal aging at 90 °C significantly increased the implant strength to 909±280 N due to compressive stress generated at the seamless transition of the 30–40 µm thick, rough and porous surface layer to the dense implant core. This unique surface structure induced an elongated osteoblast morphology with uniform cell orientation and allowed for osteoblast proliferation, long-term attachment and matrix mineralization. In conclusion, the developed AM zirconia implants not only provided high long-term mechanical resistance thanks to the dense core along with compressive stress induced at the transition zone, but also generated a favorable osteoblast response owing to the integrated directional surface pores. Statement of significanceZirconia ceramics are becoming the material of choice for metal-free dental implants, however significant efforts are required to obtain a rough/porous surface for enhanced osseointegration, along with the risk of surface delamination and/or microstructure variation. In this study, we addressed the challenge by additively manufacturing implants that seamlessly combine dense core with a porous surface layer. For the first time, a unique surface with a directional lamellar pore morphology was additively obtained. This AM implant also provided strength as strong as conventionally manufactured zirconia implants before and after long-term fatigue. Favorable osteoblast response was proved by in-vitro cell investigation. This work demonstrated the opportunity to AM fabricate novel ceramic implants that can simultaneously meet the mechanical and biological functionality requirements.

Effect of the Cell Count on Geometrical, Mechanical, and Thermal Properties of Hierarchical‐Porous Reticulated Copper Foams from a Combination of Sponge Replication and Freeze‐Drying Techniques

Effect of the Cell Count on Geometrical, Mechanical, and Thermal Properties of Hierarchical‐Porous Reticulated Copper Foams from a Combination of Sponge Replication and Freeze‐Drying Techniques

Compound surfactant-based emulsion method for the preparation of high-porosity alumina microspheres

Porous alumina microspheres have attracted significant attention owing to their high mechanical strength and excellent chemical and thermal stability. The emulsion method is considered as a simple and controllable method for the preparation of inorganic microspheres. However, preparing alumina microspheres with the emulsion method is challenging because the emulsification of the precursor is inhibited by the rapid hydrolysis of aluminum alkoxide. Herein, we report a new emulsion method for the preparation of high-porosity alumina microspheres using a combination of ionic and non-ionic surfactants; in this method, the compound surfactants act as a template agent to guide aluminum alkoxide to form a lamellar structure through self-assembly. The decomposition of the templating agent and transformation of the alumina crystal at a high temperature result in structural collapse and formation of lamellar pores. Compound surfactants increased the spheroidization rate of the emulsion from 47% to 63% after hydrolysis, whereas the particle size was decreased by almost half. Additionally, the morphology and porosity of the alumina microspheres were changed. With increasing anionic surfactant content, the porosity increased initially and then decreased. The porosity of the alumina microspheres reached a maximum value of 76% at the 1:1 mass ratio of the non-ionic to anionic surfactants. Heat treatment was found to change the size of lamellar pores, with the pore diameter reaching maximum value at 1300 °C. The compound surfactants also increased the compressive stress and specific surface area of the porous alumina microspheres.

Identification and quantitative evaluation of pores and throats of a tight sandstone reservoir (Upper Triassic Xujiahe Formation, Sichuan Basin, China)

Pores and throats are the key parameters for determining the pore structure and fluid flow behavior in tight sandstone reservoirs. In this paper, pores and throats of the tight sandstone reservoir of the Upper Triassic Xujiahe Formation in the northern Sichuan Basin were investigated using classical petrography, scanning electron microscopy, and confocal laser scanning microscopy. In addition, a method of pore as well as throat identification and quantitatification using high-pressure mercury injection (HPMI) measurements was worked out. The results show that clay mineral-related pores are well developed in lithic sandstone and feldspathic lithic sandstone in addition to pores produced by dissolution of calcite cement and clastic grains. Intergranular pores are connected by lamellar, curved lamellar, and narrow pore throats. The pores and throats associated with intragranular dissolution and clay minerals are mostly tube shaped. The rapid-increasing and slow-increasing profiles of the mercury injection curves represent the dominance of pores and throats, respectively, allowing to differentiate pores and throats. Calculations show, in addition to fractured lithic sandstone, that has micron-sized pore–throat systems, the other lithic sandstones possess dominatly nano-sized pore–throat systems. In case of feldspathic lithic sandstones, micron-sized and nano-sized pore throat systems are equally important. In micron-sized pore throat dominated reservoirs, the pore volume is slightly larger than the throat volume, whereas for the nano-sized pore throat system, the pore volume is considerably larger than the throat volume. The key factors that are favorable for the formation of lithic sandstone pore throat systems are early calcite dissolution, lithic fragments dissolution, and early chlorite cementation. In contrast the key factors that are favorable for the formation of feldspathic lithic sandstone pore throat systems are dissolution of feldspars and lithic fragments.